Description
Title of Invention: ELECTRODE MATERIAL, METHOD FOR
MANUFACTURING ELECTRODE MATERIAL, AND
SECONDARY BATTERY
Technical Field
[0001] The present disclosure relates to an electrode material, a method for manufacturing
the electrode material, and a secondary battery.
Background Art
[0002] A lithium-sulfur secondary battery has been developed, where a sulfur simple
substance is used as a positive electrode active material and lithium (Li) is used as a
negative electrode active material. The theoretical capacity densities of lithium and
sulfur are about 3862 mAh/g and about 1672 mAh/g, respectively, and it is believed
that a secondary battery having a very high energy density can be obtained. However,
the facts that
(1) the utilization factor of sulfur as a positive electrode active material is low and
(2) the charge-discharge cycle characteristics are poor can be mentioned as the
reasons for which the lithium-sulfur secondary battery has not been commercialized at
the present stage. A very large theoretical capacity density, which is a characteristic of
the lithium- sulfur secondary battery, has not been utilized to the full.
[0003] As for the causes of the above-described item (1), the following reasons are
considered. That is, in discharge, a lithium ion reacts with S sulfur in a positive
electrode, so as to generate sulfide Li2Sx. As this reaction proceeds, the value of x
changes from 8 to 4, 2, and 1. When the value of x is 8, 4, and 2, a portion which
dissolves into an electrolytic solution is generated in Li2Sx. Then, the reaction proceeds
and when the dissolved sulfide becomes Li2S (that is, x = 1), this sulfide is insoluble
into the electrolytic solution and is precipitated, so as to damage an electrode.
Therefore, at the present, the sulfide can be subjected to discharge until x = 2
(theoretical capacity density: 836 mAh/g) is approached.
[0004] As for the above-described item (2), causes are believed to be that sulfur (for
example, S sulfur) is an insulating material having an electric resistance value of 10
ohm/cm and polysulfide is eluted into an electrolytic solution. In addition, there is also
a problem in that, in charge, a cut-off voltage is not reached and a state of overcharge
is induced because of a redox shuttle reaction in which polysulfide eluted into the elec
trolytic solution is reduced on the negative electrode to generate polysulfide having a
shorter sulfur chain and the resulting polysulfide is moved to the positive electrode so
as to be oxidized again.
Citation List
Patent Literature
[0005] PTL 1: Japanese Unexamined Patent Application Publication No. 2010-257689
Non Patent Literature
[0006] NPL 1: L. Nazar et al., Nature Materials, 8, 500, 2009
NPL 2: M. Watanabe et al., Chem. Commun., 47, 8157-8159 (2011)
Summary of Invention
Technical Problem
[0007] As for a method to solve the above-described problems, a method can be mentioned,
in which sulfur is inserted into a porous carbon material. Consequently, an electrically
conductive substance is allowed to present in the vicinity of a sulfur component, and
electrons can move easily. Meanwhile, sulfur can be held in gaps of the porous carbon
material and, in addition, sulfur and lithium ions react in the gaps, so that outflow of
the generated sulfide from the gaps to the outside can be prevented. In general, Ketjenblack
which is a nano-carbon material having a hollow structure including a
graphene layer, carbon black, and acetylene black are used as the porous carbon
material (refer to PTL 1, for example). As for other porous materials, a system in
which sulfur is held in gaps of rod-shaped nano-carbons (refer to NPL 1) and a system
in which sulfur is held in inverse opal carbon (refer to NPL 2) are mentioned in the
related art. However, proposals of porous carbon materials having electrical con
ductivity and optimum gaps (size and volume) in combination are few in number, and
only a little discussion has been made on an optimum gap.
[0008] It is desirable to provide an electrode material which can improve a utilization factor
of active material and which is for obtaining a secondary battery having excellent char
acteristics, a method for manufacturing the electrode material, and a secondary battery
by using such an electrode material.
Solution to Problem
[0009] An electrode material for a secondary battery according to a first embodiment of the
present disclosure is made from a porous carbon material exhibiting a half-width of
diffraction intensity peak of the (100) face or (101) face of 4 degrees or less with
reference to a diffraction angle 2 theta on the basis of an X-ray diffraction method. In
an embodiment, the diffraction intensity peaks of the (100) face and the (101) face are
overlapped and it is different to separate. Therefore, the diffraction intensity peak of
the (100) face and the diffraction intensity peak of the (101) face are collectively
expressed as described above. The same goes for the following explanations.
[0010] An electrode material for a secondary battery according to a second embodiment of
the present disclosure is made from a porous carbon material, wherein an absolute
value of a differential value of mass, that is obtained when a mixture of the porous
carbon material and S sulfur mixed at a mass ratio of 1:2 is subjected to thermal
analysis, where temperature is employed as a parameter, (absolute value of -dW/dt)
takes on a value of more than 0 at 450 degrees centigrade and a value of 1.9 or more at
400 degrees centigrade.
[001 1] A secondary battery according to the first embodiment of the present disclosure
includes an electrode made from a porous carbon material exhibiting a half- width of
diffraction intensity peak of the (100) face or (101) face of 4 degrees or less with
reference to a diffraction angle 2 theta on the basis of an X-ray diffraction method.
[0012] A secondary battery according to the second embodiment of the present disclosure
includes an electrode made from a porous carbon material, wherein an absolute value
of a differential value of mass, that is obtained when a mixture of the porous carbon
material and S sulfur mixed at a mass ratio of 1:2 is subjected to thermal analysis,
where temperature is employed as a parameter, (absolute value of -dW/dt) takes on a
value of more than 0 at 450 degrees centigrade and a value of 1.9 or more at 400
degrees centigrade.
[0013] A method for manufacturing an electrode material for a secondary battery according
to the first embodiment of the present disclosure is a method for manufacturing an
electrode material for a secondary battery made from a porous carbon material ex
hibiting a half- width of diffraction intensity peak of the (100) face or (101) face of 4
degrees or less with reference to a diffraction angle 2 theta on the basis of an X-ray
diffraction method and includes carbonizing a plant-derived material at 400 degrees
centigrade to 1400 degrees centigrade, performing an acid or alkali treatment, and
performing a heat treatment at a temperature higher than the carbonization tem
perature. In addition, a method for manufacturing an electrode material for a secondary
battery according to the second embodiment of the present disclosure is a method for
manufacturing an electrode material for a secondary battery which is made from a
porous carbon material and which exhibits an absolute value of a differential value of
mass, that is obtained when a mixture of the porous carbon material and S sulfur
mixed at a mass ratio of 1:2 is subjected to thermal analysis, where temperature is
employed as a parameter, taking on a value of more than 0 at 450 degrees centigrade
and a value of 1.9 or more at 400 degrees centigrade, and includes carbonizing a plantderived
material at 400 degrees centigrade to 1400 degrees centigrade, performing an
acid or alkali treatment, and performing a heat treatment at a temperature higher than
the carbonization temperature. In another embodiment, a method of manufacturing an
electrode material includes carbonizing a plant-derived material at a first temperature;
performing an acid treatment or an alkali treatment on the carbonized plant-derived
material to form a porous carbon material; and subjecting the porous carbon material to
a heat treatment at a second temperature, wherein the second temperature is higher
than the first temperature.
Advantageous Effects of Invention
[0014] In the electrode material for a secondary battery and the method for manufacturing
the electrode material according to the first embodiment of the present disclosure and
the secondary battery according to the first embodiment of the present disclosure, the
value of half-width of diffraction intensity peak of the (100) face or (101) face of the
porous carbon material on the basis of an X-ray diffraction method is specified. That
is, the porous carbon material has high crystallinity. Therefore, this porous carbon
material has excellent electrical conductivity. The secondary battery in which this
porous carbon material is used as an electrode can improve the utilization factor of an
active material and, in addition, has excellent charge-discharge cycle characteristics.
[0015] In the electrode material for a secondary battery and the method for manufacturing
the electrode material according to the second embodiment of the present disclosure
and the secondary battery according to the second embodiment of the present
disclosure, thermal behavior of a mixture of the porous carbon material and S sulfur is
specified. That is, even when heat is applied, sulfur does not leave the mixed system of
the porous carbon material and S sulfur easily. As a result, this porous carbon material
is allowed to hold an active material in the pores thereof reliably and outflow of
reaction products, which have been generated in gaps, of the active material from the
pores to the outside can be prevented. Consequently, the utilization factor of the active
material can be improved and, in addition, excellent charge-discharge cycle charac
teristics are exhibited.
[0016] In the method for manufacturing an electrode material according to the first em
bodiment or the second embodiment of the present disclosure, the heat treatment is
performed at a temperature higher than the carbonization temperature, and a kind of
densification of the porous carbon material occurs. As a result, a porous carbon
material having gaps (size and volume) more suitable for the electrode material can be
provided.
Brief Description of Drawings
[0017] [fig.l]Fig. 1 is a graph showing measurement results of the X-ray diffraction intensity
of porous carbon material in Example 1.
[fig.2]Fig. 2 is a graph illustrating a method for determining the half-width of
diffraction intensity peak of the (100) face or (101) face on the basis of the mea
surement result of the X-ray diffraction intensity of porous carbon material.
[fig.3]Fig. 3 is a graph showing the TG measurement results of a mixture of a porous
carbon material and S sulfur and the like.
[fig.4]Fig. 4 is a graph showing absolute values of a differential value of mass, where
temperature is employed as a parameter, (absolute value of -dW/dt) determined on the
basis of the TG measurement results of a mixture of a porous carbon material and S
sulfur and the like.
[fig.5]Fig. 5A is a graph showing the result of determination of the charge-discharge
capacity densities in discharge after production of a lithium- sulfur secondary battery,
in which a porous carbon material in Example IB was used as an electrode material,
and the following charge, and, Fig. 5B is a graph showing the result of determination
of the charge-discharge capacity densities in discharge after production of a lithiumsulfur
secondary battery, in which a porous carbon material intermediate was used as
an electrode material, and the following charge.
[fig.6]Fig. 6A is a graph showing the result of impedance measurement after
production of a lithium- sulfur secondary battery, in which a porous carbon material in
Example IB was used as an electrode material, the result of impedance measurement
after discharge, and the result of impedance measurement after the following charge,
and, Fig. 6B is a graph showing the result of impedance measurement after production
of a lithium- sulfur secondary battery, in which a porous carbon material intermediate
was used as an electrode material, the result of impedance measurement after
discharge, and the result of impedance measurement after the following charge.
Description of Embodiments
[0018] The present disclosure will be described below on the basis of the example with
reference to the drawings. However, the present disclosure is not limited to the
example, and various numerical values and materials in the example are exempli
fications. The explanations will be made in the following order.
1. Explanations of the electrode materials, the methods for manufacturing the
electrode materials, and the secondary batteries according to the first embodiment and
the second embodiment of the present disclosure on the whole
2. Example 1 (the electrode materials, the methods for manufacturing the electrode
materials, and the secondary batteries according to the first embodiment and the
second embodiment of the present disclosure) and others
(Explanations of the electrode materials, the methods for manufacturing the electrode
materials, and the secondary batteries according to the first embodiment and the
second embodiment of the present disclosure on the whole)
[0019] The electrode material according to the first embodiment of the present disclosure,
the secondary battery according to the first embodiment of the present disclosure, and
the method for manufacturing an electrode material for a secondary battery according
to the first embodiment of the present disclosure may be collectively referred to as "the
first embodiment according to the present disclosure" simply. The electrode material
according to the second embodiment of the present disclosure, the secondary battery
according to the second embodiment of the present disclosure, and the method for
manufacturing an electrode material for a secondary battery according to the second
embodiment of the present disclosure may be collectively referred to as "the second
embodiment according to the present disclosure" simply. The first embodiment
according to the present disclosure and the second embodiment according to the
present disclosure may be collectively referred to as "the present disclosure" simply.
[0020] In the second embodiment according to the present disclosure, it is preferable that the
half-width of diffraction intensity peak of the (100) face or (101) face of the porous
carbon material be 4 degrees or less with reference to a diffraction angle 2 theta on the
basis of an X-ray diffraction method.
[0021] In the present disclosure including the above-described preferred configurations, it is
preferable that the porous carbon material have a value of specific surface area of 10 m
2/g or more on the basis of a nitrogen BET method and a pore volume of 0.1 cm g or
more on the basis of a BJH method and a MP method. In this case, it is preferable that
the raw material for the porous carbon material be a plant-derived material having a
silicon (Si) content of 5 percent by mass or more, although not limited thereto. It is
desirable that the silicon (Si) content of the porous carbon material be less than 5
percent by mass, preferably 3 percent by mass or less, and more preferably 1 percent
by mass or less.
[0022] In the method for manufacturing an electrode material for a secondary battery
according to the first embodiment or the second embodiment of the present disclosure
including the above-described preferred configurations, it is preferable that a silicon
component in the plant-derived material after carbonization be removed by an acid or
alkali treatment. Meanwhile, an activation treatment may be performed after the acid
or alkali treatment, or the activation treatment may be performed before the acid or
alkali treatment.
[0023] In the secondary battery according to the first embodiment or the second embodiment
of the present disclosure including the above-described preferred configurations, a
positive electrode may be formed from an electrode. Furthermore, the secondary
battery may be made from a lithium-sulfur secondary battery, and the electrode may
carry sulfur or a sulfur compound. The configuration and the structure of the secondary
battery in itself may be the configuration and the structure in the related art. Sulfur may
be S sulfur and the sulfur compound may be insoluble sulfur, colloidal sulfur, and
organic sulfur compounds (disulfide compounds, trisulfide compounds, and the like).
Examples of methods for producing a positive electrode may include a method in
which sulfur or a sulfur compound, a porous carbon material, and other materials are
made into a slurry and the resulting slurry is applied to a base member constituting the
positive electrode, a liquid infiltration method, a solution infiltration method, a PVD
method, and a CVD method.
[0024] In the X-ray diffraction method, the Cu-K alpha line (wavelength: 0.15045 nm) is
used as an X-ray source, the applied voltage is specified to be 50 kV, the scanning rate
is specified to be 5 degrees/min, and the measurement is performed at the diffraction
angle 2 theta of 10 degrees to 60 degrees. Fig. 2 shows an example of the measurement
result of diffraction intensity. The point "A" at which the diffraction intensity exhibits
a local minimum value between the diffraction angle 2 theta of 35 degrees centigrade
and 40 degrees centigrade is determined. A straight line which is started from A and
which is tangent to the diffraction intensity between the diffraction angle 2 theta of 50
degrees centigrade and 55 degrees centigrade is determined as a base line AB. The
diffraction intensity (peak height) from the base line AB to the top of the diffraction
intensity peak of the (100) face or (101) face is specified to be "100". Points "a" and
"b", at which a straight line passing through a point C corresponding to the diffraction
intensity of "50" and being parallel to the base line intersects with the diffraction
intensity peak of the (100) face or (101) face, are determined. The diffraction angles 2
theta and 2 thetab corresponding to the points "a" and "b", respectively, are determined
and, in addition, (2 thetaa - 2 thetab) is determined. The value of this (2 thetaa - 2 thetab)
is the half-width of the diffraction intensity peak of the (100) face or (101) face.
[0025] In the second embodiment according to the present disclosure, the mixture of the
porous carbon material and S sulfur mixed at a mass ratio of 1:2 is subjected to
thermal analysis. Here, S sulfur (manufacture's code 194-05712) produced by Wako
Pure Chemical Industries, Ltd., is used. Then, 0.3000 g of porous carbon material and
0.6000 g of S sulfur are pulverized and mixed in an agate mortar for 30 minutes and,
thereafter, heating is performed at 155 degrees centigrade for 3 hours. Cooling to room
temperature is performed, and a thermogravimetric analysis measurement (TG mea
surement) is performed by using, for example, "Thermo Plus" produced by Rigaku
Corporation. Specifically, the TG measurement is performed from room temperature to
550 degrees centigrade at a temperature raising rate of 5 degrees centigrade/min in a
nitrogen atmosphere.
[0026] Various elements can be analyzed by using, for example, an energy dispersive X-ray
analyzer (for example, JED-2200F produced by JEOL LTD.) on the basis of an energy
dispersive spectroscopy (EDS). As for the measurement condition, for example, the
scanning voltage may be specified to be 15 kV, and the illumination current may be
specified to be 10 microampares.
[0027] In the present disclosure, as described above, a material obtained by carbonizing a
plant-derived material at 400 degrees centigrade to 1400 degrees centigrade and,
thereafter, performing an acid or alkali treatment may be referred to as a "porous
carbon material intermediate" for the sake of convenience. Hereafter a method for
manufacturing such a porous carbon material intermediate may be referred to as a
"method for manufacturing a porous carbon material intermediate". An electrode
material for a secondary battery or a porous carbon material can be obtained by
subjecting the porous carbon material intermediate to a heat treatment at a temperature
higher than the carbonization temperature. A material which has been obtained by c ar
bonizing a plant-derived material at 400 degrees centigrade to 1400 degrees centigrade
and which is before subjected to the acid or alkali treatment is referred to as a "porous
carbon material precursor" or "carbonaceous substance".
In the method for manufacturing the electrode material according to the first em
bodiment or the second embodiment of the present disclosure (hereafter these methods
may be generically simply called "method for manufacturing the electrode material
according to the embodiments of the present disclosure"), as described above, the ac
tivation treatment may be performed after the acid or alkali treatment or the acid or
alkali treatment may be performed after the activation treatment is performed. In the
method for manufacturing the electrode material according to the embodiments of the
present disclosure including the above-described preferred configuration, before the
plant-derived material is carbonized, the plant-derived material may be subjected to a
heat treatment (pre-carbonization treatment) at a temperature (for example, 400
degrees centigrade to 700 degrees centigrade) lower than the carbonization temperature
under the state in which oxygen is cut off, although depending on the plant-derived
material employed. According to this, a tar component which may be generated during
carbonization can be extracted and, as a result, the tar component which may be
generated during carbonization can be reduced or removed during carbonization. In
this regard, the state in which oxygen is cut off can be achieved by, for example, e s
tablishing an atmosphere of inert gas, e.g., a nitrogen gas or an argon gas, establishing
a vacuum atmosphere, or bringing the plant-derived material into a kind of state of
being baked in a casserole. In the method for manufacturing the electrode material
according to the embodiments of the present disclosure, in order to reduce a mineral
component and water contained in the plant-derived material or prevent an occurrence
of off-flavor during carbonization, the plant-derived material may be immersed in
alcohol (for example, methyl alcohol, ethyl alcohol, or isopropyl alcohol), although
depending on the plant-derived material employed. In the method for manufacturing
the electrode material according to the embodiments of the present disclosure, a precarbonization
treatment may be performed thereafter. Preferable examples of materials
to be subjected to a heat treatment in an inert gas atmosphere may include plants which
generate large amounts of pyroligneous acid (tar and light oil). Preferable examples of
materials to be subjected to a pretreatment with alcohol may include seaweed
containing iodine and various minerals to a great extent.
[0029] In the method for manufacturing the porous carbon material intermediate, the plantderived
material is carbonized at 400 degrees centigrade to 1400 degrees centigrade.
The carbonization refers to conversion of an organic substance (in the present
disclosure, plant-derived material) to a carbonaceous substance by a heat treatment
(refer to, for example, JIS M0104-1984). As for the atmosphere for the carbonization,
an atmosphere in which oxygen is cut off can be mentioned. Specifically, a vacuum at
mosphere, an atmosphere of inert gas, e.g., a nitrogen gas or an argon gas, and an at
mosphere in which the plant-derived material is brought into a kind of state of being
baked in a casserole can be mentioned. The temperature raising rate to reach the car
bonization temperature is not specifically limited, but 1 degree centigrade/min or more,
preferably 3 degrees centigrade/min or more, and more preferably 5 degrees
centigrade/min or more in the above-described atmosphere can be mentioned. The
upper limit of the carbonization time may be 10 hours, preferably 7 hours, and more
preferably 5 hours, although not limited to them. The lower limit of the carbonization
time may be the duration in which the plant-derived material is carbonized reliably.
The plant-derived material may be pulverized, as necessary, to have a predetermined
particle size, or be classified. The plant-derived material may be washed in advance.
Alternatively, the resulting porous carbon material precursor, porous carbon material
intermediate, or porous carbon material may be pulverized, as necessary, to have a pre
determined particle size, or be classified. Alternatively, the porous carbon material in
termediate or porous carbon material after being subjected to the activation treatment
may be pulverized, as necessary, to have a predetermined particle size, or be classified.
The form, the configuration, and the structure of a furnace used for carbonization are
not specifically limited, a continuous furnace may be employed, or a batch furnace
may be employed.
[0030] As for the atmosphere for the heat treatment, an atmosphere in which oxygen is cut
off can be mentioned. Specifically, a vacuum atmosphere, an atmosphere of inert gas,
e.g., a nitrogen gas or an argon gas, and an atmosphere in which the plant-derived
material is brought into a kind of state of being baked in a casserole can be mentioned.
The temperature raising rate to reach the heat treatment temperature is not specifically
limited, but 1 degree centigrade/min or more, preferably 3 degrees centigrade/min or
more, and more preferably 5 degrees centigrade/minor more in the above-described a t
mosphere can be mentioned. The difference between the carbonization temperature
and the heat treatment temperature may be determined appropriately by performing
various tests. The upper limit of the heat treatment time may be 10 hours, preferably 7
hours, and more preferably 5 hours, although not limited to them. The lower limit of
the heat treatment time may be the duration in which predetermined characteristics can
be given to the porous carbon material. The form, the configuration, and the structure
of a furnace used for heat treatment are not specifically limited, a continuous furnace
may be employed, or a batch furnace may be employed.
[0031] In the method for manufacturing the electrode material according to the embodiments
of the present disclosure, as described above, micropores (described later) having a
pore diameter of smaller than 2 nm can be increased by performing the activation
treatment. As for the activation treatment method, a gas activation method and a
chemical activation method may be mentioned. The gas activation method refers to a
method in which oxygen, steam, carbon dioxide, air, or the like is used as an activator,
and the porous carbon material intermediate is heated in this gas atmosphere at 700
degrees centigrade to 1400 degrees centigrade, preferably, 700 degrees centigrade to
1000 degrees centigrade, and more preferably 800 degrees centigrade to 1000 degrees
centigrade for several ten minutes to several hours, so as to develop a fine structure by
volatile components and carbon molecules in the porous carbon material intermediate.
More specifically, the heating temperature in the activation treatment may be selected
appropriately on the basis of the type of the plant-derived material, and the type, the
concentration, and the like of the gas. The chemical activation method refers to a
method in which activation is performed by using zinc chloride, iron chloride, calcium
phosphate, calcium hydroxide, magnesium carbonate, potassium carbonate, sulfuric
acid, or the like in place of oxygen or steam used in the chemical activation method,
washing is performed with hydrochloric acid, the pH is adjusted with an alkaline
solution, and drying is performed.
[0032] In the method for manufacturing the electrode material according to the embodiments
of the present disclosure, a silicon component in the plant-derived material after car
bonization is removed by the acid or alkali treatment. As for the silicon component,
silicon oxides, e.g., silicon dioxide, silicon monoxide, and silicon oxide salts, may be
mentioned. A porous carbon material having a high specific surface area can be
obtained by removing a silicon component in the plant-derived material after car
bonization, as described above. In some cases, a silicon component in the plant-derived
material after carbonization may be removed on the basis of a dry etching method.
That is, in a preferred configuration of the porous carbon material, plant-derived
material containing silicon (Si) is used as a raw material. In the conversion to the
porous carbon material precursor or the carbonaceous substance, the plant-derived
material is carbonized at a high temperature (for example, 400 degrees centigrade to
1400 degrees centigrade), so that silicon contained in the plant-derived material is not
converted to silicon carbide (SiC), but is converted to silicon components (silicon
oxides), e.g., silicon dioxide (Si0 2), silicon monoxide, and silicon oxide salts. In this
regard, silicon components (silicon oxides) contained in the plant-derived material
before carbonization are not substantially changed even when carbonization is
performed at a high temperature (for example, 400 degrees centigrade to 1400 degrees
centigrade). Therefore, the silicon components (silicon oxides), e.g., silicon dioxide,
silicon monoxide, and silicon oxide salts, are removed in the following step by the acid
or alkali (base) treatment and as a result, a large specific surface area value on the basis
of the nitrogen BET method can be obtained. In addition, the preferred configuration
of the porous carbon material is a natural product-derived environment-compatible
material, and the fine structure thereof is obtained by removing silicon components
(silicon oxides) contained in advance in the raw material, which is a plant-derived
material, through the acid or alkali treatment. Consequently, the arrangement of pores
maintains the biological regularity in the plant.
[0033] As described above, the raw material of the porous carbon material can be a plantderived
material. As for the plant-derived material, hulls and straws of rice (paddy),
barley, wheat, rye, barnyard grass, and millet, coffee beans, tea-leaves (for example,
leaves of green tea, black tea, and the like), sugar canes (more specifically, bagasses of
sugar canes), corn (more specifically, cobs of corn), fruit peels (for example, citrus
peels, such as, orange peel, grapefruit peel, and mandarin orange peel, banana peel,
and the like), reed, and wakame stem can be mentioned, although not limited to them.
In addition, for example, terrestrial vascular plants, pteridophyte, bryophyte, algae, and
sea grass can be mentioned. Further, the raw material for the porous carbon can include
peat, a coconut husk-derived material, a sawdust-derived material and an alkaline
treated plant-derived material, where the coconut husk-derived material and the
sawdust-derived material are typically known as a medicinal carbon. These materials
may be used alone as a raw material, or some types of them may be used in com
bination. The shape and the form of the plant-derived material are not specifically
limited. For example, hulls and straws may be as-is used, or dehydrated products may
be used. Furthermore, materials subjected to various treatments, e.g., a fermentation
treatment, a roasting treatment, and a extraction treatment, in food and drink
processing of beer, Western liquor, and the like may also be used. In particular, from
the viewpoint of resource recovery of industrial waste, it is preferable that straws and
hulls after processing, e.g., threshing, be used. These straws and hulls after processing
are available from, for example, agricultural cooperative associations, alcoholic drink
manufacturers, food-products companies, and food processing companies in large
quantity easily.
[0034] The porous carbon material has many pores. Pores include "mesopore" having a pore
diameter of 2 nm to 50 nm, "micropore" having a pore diameter of less than 2 nm, and
"macropore" having a pore diameter of more than 50 nm. Specifically, mesopores
include a high proportion of pores having a pore diameter of 20 nm or less, and p ar
ticularly include a high proportion of pores having a pore diameter of 10 nm or less.
Micropores include, for example, a high proportion of pores having a pore diameter of
about 1.9 nm, pores having a pore diameter of about 1.5 nm, and pores having a pore
diameter of about 0.8 nm to 1 nm. In the porous carbon material, the pore volume is
preferably 0.4 cm3/g or more on the basis of the BJH method, and further preferably
0.5 cm3/g or more.
[0035] In the porous carbon material, in order to obtain further excellent functionality, it is
desirable that the value of specific surface area on the basis of the nitrogen BET
method (hereafter may be referred to as "value of specific surface area" simply) be
preferably 50 m2/g or more, more preferably 100 m2/g or more, and further preferably
400 m2/g or more.
[0036] The nitrogen BET method refers to a method in which an adsorption isotherm is
measured by allowing an adsorbent (here, porous carbon material) to adsorb and
desorb nitrogen serving as an adsorbate molecule, the resulting data are analyzed on
the basis of the BET equation represented by Formula (1). The specific surface area,
the pore volume, and the like can be calculated on the basis of this method.
Specifically, in the case where the value of specific surface area is calculated by the
nitrogen BET method, initially, an adsorption isotherm is determined by allowing the
porous carbon material to adsorb and desorb nitrogen serving as an adsorbate
molecule. Subsequently, [p/{V (p0 - p)}] is calculated from the resulting adsorption
isotherm on the basis of Formula (1) or Formula (G) transformed from Formula (1),
and is plotted with respect to the equilibrium relative pressure (p/po). This plot is
assumed to be a straight line, and the slope s (= [(C - l)/(CV m)]) and the intercept i (=
[l/(CV m)]) are calculated on the basis of the least squares method. Then, Vm and C are
calculated from the resulting slope s and intersect i on the basis of Formula (2-1) and
Formula (2-2). In addition, the specific surface area calculated from Vm on the
basis of Formula (3) (refer to Manual of BELSORP-mini and BELSORP analysis
software produced by BEL Japan, Inc., pages 62 to 66). This nitrogen BET method is a
measuring method in conformity with JIS R 1626-1996 "Measuring method for the
specific surface area of fine ceramic powders by gas adsorption using the BET
method".
(Math. 1)
V = (Vmx C x p)/[(po - p){ 1 + (C - l)(p/p 0)}] (1)
[p/{V (p0 - p)}] = [(C - 1)/(C x Vm)](p/p 0) + [1/(C x Vm)] (G)
Vm = l/(s + i) (2-1)
C = (s/i) + 1 (2-2)
asBET = (Vm x L x s)/22414 (3)
[0037] Where symbols are defined as described below.
V : amount of adsorption
Vm: amount of adsorption of monomolecular layer
p : equilibrium pressure of nitrogen
p0: saturated vapor pressure of nitrogen
L: Avogadro's number
sigma: adsorption cross-sectional area of nitrogen
[0038] In the case where the pore volume Vp is calculated by the nitrogen BET method, for
example, the adsorption data of the determined adsorption isotherm are subjected to
linear interpolation, and the amount of adsorption V is determined at a relative pressure
set with the pore volume calculation relative pressure. The pore volume Vp can be
calculated from the resulting amount of adsorption V on the basis of Formula (4) (refer
to Manual of BELSORP-mini and BELSORP analysis software produced by BEL
Japan, Inc., pages 62 to 65). In this regard, the pore volume on the basis of the nitrogen
BET method may be hereafter referred to as "pore volume" simply.
(Math. 2)
V = (V/22414) x (M /[rho] ) (4)
[0039] Where symbols are defined as described below.
V: amount of adsorption at relative pressure
Mg: molecular weight of nitrogen
[rho] g: density of nitrogen
[0040] The pore diameter of the mesopore can be calculated as the distribution of pores from
the rate of change in pore volume with respect to the pore diameter on the basis of, for
example, the BJH method. The BJH method is a method widely used as a pore dis
tribution analysis method. In the case where the pore distribution is analyzed on the
basis of the BJH method, initially, a desorption isotherm is determined by allowing the
porous carbon material to adsorb and desorb nitrogen serving as an adsorbate
molecule. Subsequently, the thicknesses of adsorption layers when the adsorbate
molecules are desorbed stepwise from the state in which pores are filed with the
adsorbate molecules (for example, nitrogen) and the inside diameter (twice as much as
the core radius) of the hole generated at that time are determined on the basis of the
resulting desorption isotherm, the pore radius rp is calculated on the basis of Formula
(5), and the pore volume is calculated on the basis of Formula (6). Then, the rate of
change in pore volume (dVp/drp) with respect to the pore diameter (2rp) is plotted on
the basis of the pore radius and the pore volume and, thereby, a pore distribution curve
is obtained (refer to Manual of BELSORP-mini and BELSORP analysis software
produced by BEL Japan, Inc., pages 85 to 88).
(Math. 3)
r = t + r (5)
V = R x dV - R x dt x c x SA (6)
[0041] Where symbols are defined as described below.
rp: pore radius
rk: core radius (inside diameter/2) in the case where an adsorption layer having a
thickness of t is adsorbed to the inside wall of a pore having a pore radius rp at that
pressure
Vp : pore volume when the nth desorption of nitrogen has occurred
dV : amount of change at that time
d amount of change in thickness of adsorption layer when the nth desorption of
nitrogen has occurred
r : core radius at that time
c : fixed value
rp : pore radius when the nth desorption of nitrogen has occurred
Meanwhile,
(Math. 4)
SApj
represents an integrated value of the area of the wall surface of the pore of j = 1 to j =
n - 1.
[0042] The pore diameter of the micropore can be calculated as the distribution of pores
from the rate of change in pore volume with respect to the pore diameter on the basis
of the MP method. In the case where the pore distribution is analyzed on the basis of
the MP method, initially, an absorption isotherm is determined by allowing the porous
carbon material to adsorb nitrogen. Subsequently, the resulting adsorption isotherm is
converted to the pore volume with respect to the thickness t of the adsorption layer
(plotted with respect to t). Then, a pore distribution curve can be obtained on the basis
of the curvature of the resulting plot (the amount of change in pore volume with
respect to the amount of change in thickness t of the adsorption layer) (refer to Manual
of BELSORP-mini and BELSORP analysis software produced by BEL Japan, Inc.,
pages 72, 73, and 82).
[0043] The porous carbon material precursor is treated with an acid or alkali. Specific
examples of the treatment method may include a method in which the porous carbon
material precursor is immersed in an acid or alkali aqueous solution and a method in
which the porous carbon material precursor is reacted with an acid or alkali in a vapor
phase. More specifically, in the case where an acid treatment is performed, examples
of acids may include fluorine compounds exhibiting acidity, e.g., hydrogen fluoride,
hydrofluoric acid, ammonium fluoride, calcium fluoride, and sodium fluoride. In the
case where a fluorine compound is used, it is enough that the amount of fluorine
element is four times the amount of silicon element in the silicon component contained
in the porous carbon material precursor, and it is preferable that the concentration of
the fluorine compound aqueous solution be 10 percent by mass or more. In the case
where the silicon component (for example, silicon dioxide) contained in the porous
carbon material precursor is removed by hydrofluoric acid, silicon dioxide is reacted
with hydrofluoric acid as shown in Chemical formula (A) or Chemical formula (B) and
is removed as hexafluorosilicic acid (H2SiF ) or silicon tetrafluoride (SiF4), so that the
porous carbon material intermediate can be obtained. Thereafter, washing and drying
may be performed.
(Chem. 1)
[0044] In the case where an alkali (base) treatment is performed, examples of alkali may
include sodium hydroxide. In the case where an alkali aqueous solution is used, it is
enough that the pH of the aqueous solution is 11 or more. In the case where the silicon
component (for example, silicon dioxide) contained in the porous carbon material
precursor is removed by sodium hydroxide aqueous solution, the sodium hydroxide
aqueous solution is heated and, thereby, silicon dioxide is reacted as shown in
Chemical formula (C) and is removed as sodium silicate (Na2Si0 3), so that the porous
carbon material intermediate can be obtained. Meanwhile, in the case where the
treatment is performed by reacting sodium hydroxide in a vapor phase, solid sodium
hydroxide is heated and, thereby, silicon dioxide is reacted as shown in Chemical
formula (C) and is removed as sodium silicate (Na2Si0 3), so that the porous carbon
material intermediate can be obtained. Thereafter, washing and drying may be
performed.
(Chem. 2)
Example 1
[0045] Example 1 relates to the electrode materials, the methods for manufacturing the
electrode materials, and the secondary batteries according to the first embodiment and
the second embodiment of the present disclosure.
[0046] An electrode material for a secondary battery in Example 1 was made from a porous
carbon material exhibiting a half-width of diffraction intensity peak of the (100) face
or (101) face of 4 degrees or less with reference to a diffraction angle 2 theta on the
basis of an X-ray diffraction method. Alternatively, an electrode material for a
secondary battery in Example 1 was made from a porous carbon material, wherein an
absolute value of a differential value of mass, that was obtained when a mixture of the
porous carbon material and S sulfur mixed at a mass ratio of 1:2 was subjected to
thermal analysis, where temperature was employed as a parameter, (absolute value of -
dW/dt) took on a value of more than 0 at 450 degrees centigrade and a value of 1.9 or
more (preferably 2.0 or more) at 400 degrees centigrade.
[0047] A secondary battery in Example 1 included an electrode made from a porous carbon
material exhibiting a half-width of diffraction intensity peak of the (100) face or (101)
face of 4 degrees or less with reference to a diffraction angle 2 theta on the basis of an
X-ray diffraction method. Alternatively, a secondary battery in Example 1 was a
secondary battery including an electrode made from a porous carbon material, wherein
an absolute value of a differential value of mass, that was obtained when a mixture of
the porous carbon material and S sulfur mixed at a mass ratio of 1:2 was subjected to
thermal analysis, where temperature was employed as a parameter, (absolute value of -
dW/dt) took on a value of more than 0 at 450 degrees centigrade and a value of 1.9 or
more (preferably 2.0 or more) at 400 degrees centigrade.
[0048] In a method for manufacturing an electrode material for a secondary battery in
Example 1, the above-described electrode material for a secondary battery in Example
1 was obtained by carbonizing a plant-derived material at 400 degrees centigrade to
1400 degrees centigrade, performing an acid or alkali treatment, and performing a heat
treatment at a temperature higher than the carbonization temperature.
[0049] Specifically, hulls which were plant-derived materials having a silicon (Si) content of
5 percent by mass or more were used as the raw material, and carbonization (firing)
was performed at 800 degrees centigrade in a nitrogen atmosphere, so that a porous
carbon material precursor was obtained. The resulting porous carbon material
precursor was immersed in a 48-percent by volume hydrofluoric acid aqueous solution
for a night so as to perform an acid treatment and, thereby, a silicon component in the
plant-derived material after carbonization was removed. Thereafter, washing was
performed by using water and ethyl alcohol until the pH reached 7. Then, drying was
performed, so that a porous carbon material intermediate was obtained. Subsequently,
the temperature was raised to 900 degrees centigrade in a nitrogen atmosphere, and ac
tivation treatment with steam was performed. The temperature of the porous carbon
material intermediate subjected to the activation treatment was raised to a prede
termined temperature, at which a heat treatment was performed, at a temperature
raising rate of 5 degrees centigrade/min. After the predetermined temperature was
reached, the predetermined temperature was maintained for 1 hour, so that a porous
carbon material was obtained. The silicon (Si) content of the resulting porous carbon
material was 1 percent by mass or less. The porous carbon material had a value of
specific surface area of 10 m2/g or more on the basis of the nitrogen BET method and a
pore volume of 0.1 cm3/g or more on the basis of the BJH method and the MP method.
[0050] The predetermined temperature were specified to be 900 degrees centigrade
(Reference example 1A), 1000 degrees centigrade (Reference example IB), 1200
degrees centigrade (Reference example 1C), 1300 degrees centigrade (Example 1A),
1400 degrees centigrade (Example IB), and 1500 degrees centigrade (Example 1C).
Each of the resulting porous carbon materials at predetermined temperatures was
subjected to the XRD measurement by using an X-ray diffractometer (RINT-TTRII)
produced by Rigaku Corporation. The measurement results of half-width of diffraction
intensity peak of the (100) face or (101) face on the basis of the X-ray diffraction
method are shown in Table 1 described below. The measurement results of the
diffraction intensity are indicated in a graph shown in Fig. 1. In this regard, the value
of half-width of diffraction intensity peak of the (100) face or (101) face of the porous
carbon material intermediate on the basis of the X-ray diffraction method was
equivalent to the value of Reference example 1A.
[0051] (Table 1)
[0052] The measurement result of TG of the mixture of the porous carbon material at each
of the predetermined temperatures and S sulfur was shown in Fig. 3, and the mea
surement results of TG of S sulfur and Ketjenblack (KB) are also shown in Fig. 3. In
addition, absolute value of differential value of mass, where temperature was
employed as a parameter, (absolute value of -dW/dt) are shown in Fig. 4. As shown in
Table 2 described below, the absolute value of -dW/dt of each porous carbon material
in Example 1 was more than 0 at 450 degrees centigrade and was 1.9 or more at 400
degrees centigrade. In this regard, the absolute values of -dW/dt of the porous carbon
material intermediate at 400 degrees centigrade and 450 degrees centigrade were
equivalent to the values of Reference example 1A.
[0053] (Table 2)
[0054] The measurement results of pores and the like of each porous carbon material are
shown in Table 3 described below. In Table 3, the terms "nitrogen BET method", "MP
method", and "BJH method" refers to the value of specific surface area (unit: m2/g) on
the basis of the nitrogen BET method, the value of pore volume (unit: cm3/g) on the
basis of the MP method, and the value of pore volume (unit: cm3/g) on the basis of the
BJH method, respectively. The unit of the total pore volume is "cm3/g".
[0055] (Table 3)
[0056] An electrode was produced by using the porous carbon material and the like, and a
lithium-sulfur secondary battery was prototyped. A positive electrode is formed from
the electrode, and sulfur was carried by the electrode.
[0057] A positive electrode of a lithium-sulfur secondary battery was prototyped by using S
sulfur, the porous carbon material in Example 1, and other materials. Specifically, a
slurry having the composition shown in Table 4 described below was prepared. In this
regard, the term "KS6" refers to a carbon material produced by TIMCAL Graphite &
Carbon, the term "VGCF" refers to a vapor-grown carbon fiber produced by SHOWA
DENKO K.K., and the term "PVDF" is the abbreviated name for polyvinylidene
fluoride which functions as a binder.
[0058] (Table 4)
[0059] More specifically, in a mortar, 5 percent by mass of polyvinyl alcohol (PVA) which
functions as a binder was added to the above-described composition (positive electrode
material), N-methyl pyrrolidone (NMP) serving as a solvent was further added, and
kneading was performed, so that a slurry state was brought about. The kneaded
material was applied to aluminum foil, and hot air drying was performed at 120
degrees centigrade for 3 hours. Hot pressing was performed by using a hot press
machine under the condition of a temperature of 80 degrees centigrade and a pressure
of 580 kgf/cm2, so as to increase the density of the positive electrode material, prevent
an occurrence of damage due to contact with an electrolytic solution, and reduce the
resistance value. Subsequently, punching was performed in such a way that the
diameter became 15 mm, and vacuum drying was performed at 60 degrees centigrade
for 3 hours to remove water and the solvent. The thickness of the thus obtained
positive electrode portion excluding the aluminum foil (positive electrode material
layer) was 80 micrometers to 100 micrometers, the mass was 8 mg to 12 mg, and the
density was about 0.6 g/cm3. The thus obtained positive electrode was used and a
lithium-sulfur secondary battery made from a 2016 coin battery was assembled.
Specifically, the lithium-sulfur secondary battery made from the 2016 coin battery was
assembled by stacking the positive electrode including the aluminum foil and the
positive electrode material layer, the electrolytic solution, lithium foil having a
thickness of 0.8 mm, and a nickel mesh. As for the electrolytic solution, a solution in
which 0.5 mol LiTFSI/0.4 mol LiN0 3 was dissolved in a mixed solvent of dimethyl
ether and 1,3-dioxane (volume ratio 1/1) was used.
[0060] The charge-discharge test condition of the lithium-sulfur secondary battery was as
shown in Table 5 described below.
[0061] (Table 5)
The porous carbon material in Example IB and the porous carbon material in
termediate were used as electrode materials, and a lithium-sulfur secondary battery for
evaluation was prototyped. After production, discharge was performed to determine
the discharge capacity density, and charge was performed to determine the charge
capacity density. The results thereof are shown in Fig. 5A (porous carbon material in
Example IB was used) and Fig. 5B (porous carbon material intermediate was used).
The measurement results of impedance after production, the measurement results of
impedance after discharge, and the measurement results of impedance after charge
thereafter are shown in Fig. 6A (porous carbon material in Example IB was used) and
Fig. 6B (porous carbon material intermediate was used) as Nyquist plots. The terms
"before discharge", "after discharge", and "after charge" shown in Fig. 6A and Fig. 6B
indicate the battery internal resistance value on the basis of an impedance measurement
after the lithium- sulfur secondary battery for evaluation was prototyped, the battery
internal resistance value on the basis of an impedance measurement after discharge
was performed, and the battery internal resistance value after charge was performed
following the discharge, respectively. In this regard, the resistance component of the
negative electrode and the electrolytic solution (including the interface resistance) is
about 5 ohms and, therefore, most of the resistance components derived from arcs
shown in Fig. 6A and Fig. 6B are the resistance of the positive electrode.
[0063] As is clear from Fig. 5A and Fig. 5B, the example secondary battery including the
porous carbon material in Example IB has a high charge-discharge capacity density as
compared with the comparative example secondary battery including the porous
carbon material intermediate. Meanwhile, as is clear from Fig. 6A and Fig. 6B, the
example secondary battery including the porous carbon material in Example IB has a
low positive electrode resistance value as compared with that of the comparative
example secondary battery including the porous carbon material intermediate. In this
regard, five lithium- sulfur secondary batteries for evaluation were prototyped so as to
be subjected to the test, and the same results were obtained with respect to all the
lithium-sulfur secondary batteries for evaluation. The example secondary batteries
including the porous carbon material in Example IB were able to be subjected to 50
times or more of charge and discharge, whereas no comparative example secondary
batteries including the porous carbon material intermediate exhibited the number of
times of charge and discharge of more than 10 times.
[0064] The characteristics of the example secondary batteries including the porous carbon
materials in Example 1A and Example 1C were substantially equivalent to the charac
teristics of the example secondary battery including the porous carbon material in
Example IB. On the other hand, the characteristics of the example secondary batteries
including the porous carbon materials in Reference example 1A, Reference example
IB, and Reference example 1C were substantially equivalent to the characteristics of
the comparative example secondary battery including the porous carbon material in
termediate.
[0065] As described above, in the electrode material for a secondary battery and the manu
facturing method therefor in Example 1 and the secondary battery in Example 1, the
value of half-width of diffraction intensity peak of the (100) face or (101) face of the
porous carbon material on the basis of an X-ray diffraction method is specified. That
is, the porous carbon material has high crystallinity. Therefore, the porous carbon
material in Example 1 has excellent electrical conductivity. The secondary battery in
which this porous carbon material is used as an electrode can improve the utilization
factor of an active material and, in addition, has excellent charge-discharge cycle char
acteristics. Also, in the electrode material for a secondary battery and the manu
facturing method therefor in Example 1 and the secondary battery in Example 1,
thermal behavior of a mixture of the porous carbon material and S sulfur is specified.
That is, even when heat is applied, sulfur does not leave the mixed system of the
porous carbon material and S sulfur easily. As a result, this porous carbon material can
hold an active material in the pores thereof reliably and outflow of reaction products,
which are generated in gaps, of the active material from the pores to the outside can be
prevented. Consequently, the utilization factor of the active material can be improved
and, in addition, excellent charge-discharge cycle characteristics are exhibited.
[0066] Up to this point, the present disclosure has been explained with reference to the
favorable examples. However, the present disclosure is not limited to these examples
and can be variously modified. In the examples, the case where hulls are used as the
raw material of the porous carbon material has been explained, although other plants
may be used as the raw material. Examples of other plants may include straw, reed,
wakame stem, terrestrial vascular plants, pteridophyte, bryophyte, algae, and sea grass.
These plants may be used alone, or some types of them may be used in combination.
Specifically, for example, the plant-derived material, which is the raw material for the
porous carbon material, is specified to be rice straw (for example, isehikari of
Kagoshima origin), and the porous carbon material can be obtained by carbonizing the
straw serving as the raw material to convert to a carbonaceous substance (porous
carbon material precursor) and performing an acid treatment. Alternatively, the plantderived
material, which is the raw material for the porous carbon material, is specified
to be gramineous reed, and the porous carbon material can be obtained by carbonizing
the reed serving as the raw material to convert to a carbonaceous substance (porous
carbon material precursor) and performing an acid treatment. The same result was
obtained in the case of a porous carbon material obtained by treating with alkali (base),
e.g., a sodium hydroxide aqueous solution, in place of the hydrofluoric acid aqueous
solution. The method for manufacturing the porous carbon material may be the same as
that in Example 1.
[0067] Alternatively, the plant-derived material, which is the raw material for the porous
carbon material, is specified to be wakame stem (Sanriku in Iwate prefecture origin),
and the porous carbon material can be obtained by carbonizing the wakame stem
serving as the raw material to convert to a carbonaceous substance (porous carbon
material precursor) and performing an acid treatment. Specifically, for example,
wakame stem is heated at a temperature of about 500 degrees centigrade so as to be
carbonized. For example, the wakame stem serving as the raw material may be treated
with alcohol before heating. As for a specific treating method, a method in which
immersion in ethyl alcohol or the like is performed is mentioned and, thereby, water
contained in the raw material can be reduced and, in addition, elements other than
carbon and mineral components contained in the finally obtained porous carbon
material can be eluted. Furthermore, generation of gases during carbonization can be
suppressed by this treatment with alcohol. More specifically, the wakame stem is
immersed in ethyl alcohol for 48 hours. It is preferable that an ultrasonic treatment be
performed in ethyl alcohol. Subsequently, the resulting wakame stem is carbonized by
heating in a nitrogen stream at 500 degrees centigrade for 5 hours, so as to obtain a
carbonized material. A tar component, which may be generated in the following car
bonization, can be reduced or removed by performing such a treatment
(pre-carbonization treatment). Thereafter, 10 g of the resulting carbonized material is
put into an alumina crucible, and temperature is raised to 1000 degrees centigrade in a
nitrogen stream (10 1/min) at a temperature raising rate of 5 degrees centigrade/min.
Carbonization is performed at 1000 degrees centigrade for 5 hours to induce
conversion to a carbonaceous substance (porous carbon material precursor), and
cooling to room temperature is performed. The nitrogen gas is continuously passed
during carbonization and cooling. An acid treatment is performed by immersing the
resulting porous carbon material precursor in a 46-percent by volume hydrofluoric acid
aqueous solution for a night, and washing is performed by using water and ethyl
alcohol until the pH 7 is reached. Finally, drying is performed, so that a porous carbon
material can be obtained.
The present disclosure can also have the following configurations.
[1] [Electrode material: first embodiment]
An electrode material for a secondary battery made from a porous carbon material
exhibiting a half- width of diffraction intensity peak of the (100) face or (101) face of 4
degrees or less with reference to a diffraction angle 2 theta on the basis of an X-ray
diffraction method.
[2] [Electrode material: second embodiment]
An electrode material for a secondary battery made from a porous carbon material,
wherein an absolute value of a differential value of mass, that is obtained when a
mixture of the porous carbon material and S sulfur mixed at a mass ratio of 1:2 is
subjected to thermal analysis, where temperature is employed as a parameter, takes on
a value of more than 0 at 450 degrees centigrade and a value of 1.9 or more at 400
degrees centigrade.
[3] The electrode material for a secondary battery according to the item [2], wherein
the half- width of diffraction intensity peak of the (100) face or (101) face of the porous
carbon material is 4 degrees or less with reference to a diffraction angle 2 theta on the
basis of an X-ray diffraction method.
[4] The electrode material for a secondary battery according to any one of the items [1]
to [3], wherein the porous carbon material has a value of specific surface area of 10 m2
/g or more on the basis of a nitrogen BET method and a pore volume of 0.1 cm3/g or
more on the basis of a BJH method and a MP method.
[5] The electrode material for a secondary battery according to the item [4], wherein
the raw material for the porous carbon material is a plant-derived material having a
silicon content of 5 percent by mass or more.
[6] [Secondary battery: first embodiment]
A secondary battery including an electrode made from a porous carbon material ex
hibiting a half-width of diffraction intensity peak of the (100) face or (101) face of 4
degrees or less with reference to a diffraction angle 2 theta on the basis of an X-ray
diffraction method.
[7] [Secondary battery: second embodiment]
A secondary battery including an electrode made from a porous carbon material,
wherein an absolute value of a differential value of mass, that is obtained when a
mixture of the porous carbon material and S sulfur mixed at a mass ratio of 1:2 is
subjected to thermal analysis, where temperature is employed as a parameter, takes on
a value of more than 0 at 450 degrees centigrade and a value of 1.9 or more at 400
degrees centigrade.
[8] The secondary battery according to the item [7], wherein the half-width of
diffraction intensity peak of the (100) face or (101) face of the porous carbon material
is 4 degrees or less with reference to a diffraction angle 2 theta on the basis of an X-ray
diffraction method.
[9] The secondary battery according to any one of the items [6] to [8], wherein the
porous carbon material has a value of specific surface area of 10 m2/g or more on the
basis of a nitrogen BET method and a pore volume of 0.1 cm3/g or more on the basis of
a BJH method and a MP method.
[10] The secondary battery according to the item [9], wherein the raw material for the
porous carbon material is a plant-derived material having a silicon content of 5 percent
by mass or more.
[11] The secondary battery according to any one of the items [6] to [10], wherein a
positive electrode is formed from the electrode.
[12] The secondary battery according to any one of the items [6] to [11], wherein the
secondary battery is made from a lithium-sulfur secondary battery, and the electrode
carries sulfur or a sulfur compound.
[13] [Method for manufacturing electrode material: first embodiment]
A method for manufacturing an electrode material for a secondary battery made from a
porous carbon material exhibiting a half-width of diffraction intensity peak of the (100)
face or (101) face of 4 degrees or less with reference to a diffraction angle 2 theta on
the basis of an X-ray diffraction method, the manufacturing method including car
bonizing a plant-derived material at 400 degrees centigrade to 1400 degrees centigrade,
performing an acid or alkali treatment, and performing a heat treatment at a tem
perature higher than the carbonization temperature.
[14] [Method for manufacturing electrode material: second embodiment]
A method for manufacturing an electrode material for a secondary battery which is
made from a porous carbon material and which exhibits an absolute value of a dif
ferential value of mass, that is obtained when a mixture of the porous carbon material
and S sulfur mixed at a mass ratio of 1:2 is subjected to thermal analysis, where tem
perature is employed as a parameter, taking on a value of more than 0 at 450 degrees
centigrade and a value of 1.9 or more at 400 degrees centigrade, the manufacturing
method including carbonizing a plant-derived material at 400 degrees centigrade to
1400 degrees centigrade, performing an acid or alkali treatment, and performing a heat
treatment at a temperature higher than the carbonization temperature.
[15] The method for manufacturing an electrode material for a secondary battery,
according to the item [14], wherein the half- width of diffraction intensity peak of the
(100) face or (101) face of the porous carbon material is 4 degrees or less with
reference to a diffraction angle 2 theta on the basis of an X-ray diffraction method.
[16] The method for manufacturing an electrode material for a secondary battery,
according to any one of the items [13] to [15], wherein the porous carbon material has
a value of specific surface area of 10 m2/g or more on the basis of a nitrogen BET
method and a pore volume of 0.1 cm3/g or more on the basis of a BJH method and a
MP method.
[17] The method for manufacturing an electrode material for a secondary battery,
according to the item [16], wherein the raw material for the porous carbon material is a
plant-derived material having a silicon content of 5 percent by mass or more.
[18] The method for manufacturing an electrode material for a secondary battery,
according to any one of the items [13] to [17], wherein a silicon component in the
plant-derived material after carbonization is removed by the acid or alkali treatment.
[19]An electrode material comprising: a porous carbon material, wherein the porous
carbon material has a half- width of diffraction intensity peak of a (100) face or a (101)
face of 4 degrees or less with reference to a diffraction angel 2 theta on a basis of an Xray
diffraction method.
[20]The electrode material according to [19], wherein a sulfur material is carried in
pores of the porous carbon material.
[21]The electrode material according to [20], wherein the sulfur material is selected
from the group consisting of: S sulfur, insoluble sulfur, colloidal sulfur and an organic
sulfur compound.
[22]The electrode material according to [19], wherein the porous carbon material has a
specific surface area of 10m2/g or more on a basis of a nitrogen BET method.
[23] The electrode material according to [19], wherein the porous carbon material has a
pore volume of 0.1 cm3/g or more on a basis of a BJH method and a MP method.
[24] The electrode material according to [19], wherein a raw material for the porous
carbon material is a plant-derived material having a silicon content of 5 percent by
mass or more.
[25] The electrode material according to [19], wherein a raw material for the porous
carbon material is selected from the group consisting of: peat, a coconut husk-derived
material, a sawdust-derived material and an alkaline treated plant-derived material.
[26] The electrode material according to claim [19], wherein a silicon content of the
porous carbon material is less than 5 percent by mass.
[27] A battery comprising: a positive electrode; and a negative electrode, wherein the
positive electrode includes an electrode material comprising a porous carbon material,
and wherein the porous carbon material has a half-width of diffraction intensity peak
of a (100) face or a (101) face of 4 degrees or less with reference to a diffraction angel
2 theta on a basis of an X-ray diffraction method.
[28] An electrode material comprising: a porous carbon material, wherein an absolute
value of a differential value of mass obtained when a mixture of the porous carbon
material and S sulfur mixed at a mass ratio of 1:2 is subjected to thermal analysis,
where temperature is employed as a parameter, has a value of more than 0 at 450
degrees centigrade and a value of 1.9 or more at 400 degrees centigrade.
[29] A battery comprising: a positive electrode; and a negative electrode, wherein the
positive electrode includes an electrode material comprising a porous carbon material,
and wherein an absolute value of a differential value of mass obtained when a mixture
of the porous carbon material and S sulfur mixed at a mass ratio of 1:2 was subjected
to thermal analysis, where temperature is employed as a parameter, has a value of more
than 0 at 450 degrees centigrade and a value of 1.9 or more at 400 degrees centigrade.
[30] A method of manufacturing an electrode material comprising: carbonizing a plantderived
material at a first temperature; performing an acid treatment or an alkali
treatment on the carbonized plant-derived material to form a porous carbon material;
and subjecting the porous carbon material to a heat treatment at a second temperature,
wherein the second temperature is higher than the first temperature.
[31] The method of manufacturing an electrode material according to [30], wherein the
first temperature ranges from 400 degrees centigrade to 1400 degrees centigrade.
[32] The method of manufacturing an electrode material according to[30], wherein the
plant-derived material has a silicon content greater than 5 percent by mass.
[33] The method of manufacturing according to [30], wherein a raw material for the
porous carbon material is selected from the group consisting of: peat, a coconut huskderived
material, a sawdust-derived material and an alkaline treated plant-derived
material.
[34] The method of manufacturing an electrode material according to [30], further
comprising performing an activation treatment on the plant-derived material.
[35] The method of manufacturing an electrode material according to [30], further
comprising performing a pre-carbonization treatment on the plant-derived material
before the carbonizing step, wherein the pre-carbonization treatment is performed at a
temperature lower than the first temperature under a state in which oxygen is cut off.
[36] The method of manufacturing an electrode material according to [30], further
comprising immersing the plant-derived material in an alcohol before the carbonizing
step.
[0069] The present disclosure contains subject matter related to that disclosed in Japanese
Priority Patent Application JP 2012-1771 14 filed in the Japan Patent Office on August
09, 2012, the entire contents of which are hereby incorporated by reference.
[0070] It should be understood by those skilled in the art that various modifications, com
binations, sub-combinations and alterations may occur depending on design re
quirements and other factors insofar as they are within the scope of the appended
claims or the equivalents thereof.
PCT/JP2013/004415
Claims
An electrode material comprising: a porous carbon material, wherein
the porous carbon material has a half-width of diffraction intensity peak
of a (100) face or a (101) face of 4 degrees or less with reference to a
diffraction angel 2 theta on a basis of an X-ray diffraction method.
The electrode material according to claim 1, wherein a sulfur material
is carried in pores of the porous carbon material.
The electrode material according to claim 2, wherein the sulfur material
is selected from the group consisting of: S sulfur, insoluble sulfur,
colloidal sulfur and an organic sulfur compound.
The electrode material according to claim 1, wherein the porous carbon
material has a specific surface area of 10m2/g or more on a basis of a
nitrogen BET method.
The electrode material according to claim 1, wherein the porous carbon
material has a pore volume of 0.1 cm3/g or more on a basis of a BJH
method and a MP method.
The electrode material according to claim 1, wherein a raw material for
the porous carbon material is a plant-derived material having a silicon
content of 5 percent by mass or more.
The electrode material according to claim 1, wherein a raw material for
the porous carbon material is selected from the group consisting of:
peat, a coconut husk-derived material, a sawdust-derived material and
an alkaline treated plant-derived material.
The electrode material according to claim 1, wherein a silicon content
of the porous carbon material is less than 5 percent by mass.
A battery comprising: a positive electrode; and a negative electrode,
wherein the positive electrode includes an electrode material
comprising a porous carbon material, and wherein the porous carbon
material has a half-width of diffraction intensity peak of a (100) face or
a (101) face of 4 degrees or less with reference to a diffraction angel 2
theta on a basis of an X-ray diffraction method.
An electrode material comprising: a porous carbon material, wherein an
absolute value of a differential value of mass obtained when a mixture
of the porous carbon material and S sulfur mixed at a mass ratio of 1:2
is subjected to thermal analysis, where temperature is employed as a
parameter, has a value of more than 0 at 450 degrees centigrade and a
value of 1.9 or more at 400 degrees centigrade.
PCT/JP2013/004415
A battery comprising: a positive electrode; and a negative electrode,
wherein the positive electrode includes an electrode material
comprising a porous carbon material, and wherein an absolute value of
a differential value of mass obtained when a mixture of the porous
carbon material and S sulfur mixed at a mass ratio of 1:2 was subjected
to thermal analysis, where temperature is employed as a parameter, has
a value of more than 0 at 450 degrees centigrade and a value of 1.9 or
more at 400 degrees centigrade.
A method of manufacturing an electrode material comprising: car
bonizing a plant-derived material at a first temperature; performing an
acid treatment or an alkali treatment on the carbonized plant-derived
material to form a porous carbon material; and subjecting the porous
carbon material to a heat treatment at a second temperature, wherein
the second temperature is higher than the first temperature.
The method of manufacturing an electrode material according to claim
12, wherein the first temperature ranges from 400 degrees centigrade to
1400 degrees centigrade.
The method of manufacturing an electrode material according to claim
12, wherein the plant-derived material has a silicon content greater than
5 percent by mass.
The method of manufacturing according to claim 12, wherein a raw
material for the porous carbon material is selected from the group
consisting of: peat, a coconut husk-derived material, a sawdust-derived
material and an alkaline treated plant-derived material.
The method of manufacturing an electrode material according to claim
12, further comprising performing an activation treatment on the plantderived
material.
The method of manufacturing an electrode material according to claim
12, further comprising performing a pre-carbonization treatment on the
plant-derived material before the carbonizing step, wherein the precarbonization
treatment is performed at a temperature lower than the
first temperature under a state in which oxygen is cut off.
The method of manufacturing an electrode material according to claim
12, further comprising immersing the plant-derived material in an
alcohol before the carbonizing step.