【Technical Field】
The present invention relates to a sacrificial positive electrode material which is doped
with a metal (M) such as Zn, Ge, Mg, or Si and having a metal (M) defect formation energy
controlled to a specific level, and a lithium secondary battery including the same.
The present application claims the benefit of priority based on Korean Patent
10 Application No. 10-2021-0024259 dated February 23, 2021, and all contents published in the
literature of the Korean patent application are incorporated as a part of this specification.
【Background Art】
In recent years, the demand for secondary batteries as an energy source is rapidly
increasing. Among these secondary batteries, a lithium secondary battery having high energy
15 density and voltage, a long cycle life, and a low self-discharge rate has been commercialized and
widely used.
Although graphite is mainly used as a negative electrode material of a lithium secondary
battery, since graphite has a small capacity per unit mass of 372 mAh/g, it is difficult to increase
the capacity of a lithium secondary battery. Accordingly, in order to increase the capacity of a
20 lithium secondary battery, as a non-carbon-based negative electrode material having a higher
3
energy density than graphite, a negative electrode material that forms an intermetallic compound
with lithium, such as silicon, tin, and oxides thereof, has been developed and used. However,
in the case of such a non-carbon-based negative electrode material, although the capacity is
large, the initial efficiency is low, there is a problem that the lithium consumption during the
initial charging/discharging is large, and the irreversible 5 capacity loss is large.
In this regard, there has been proposed a method for overcoming the irreversible
capacity loss of the negative electrode by using a material that can provide a lithium ion source
or reservoir for the positive electrode material and that is electrochemically active after an initial
cycle so as not to degrade the overall performance of the battery. Specifically, as a sacrificial
10 positive electrode material or an irreversible additive (or an overdischarging inhibitor), for
example, a method of applying an oxide including an excess of lithium, such as Li6CoO4, to the
positive electrode is known.
However, the sacrificial positive electrode material or the irreversible additive has an
unstable structure, and may cause oxidation during the activation stage of the battery as well as
15 the subsequent charging/discharging process to generate oxygen gas inside the battery. Oxygen
gas thus generated may cause volume expansion and the like, and may be one of the main factors
leading to deterioration of battery performance.
Therefore, the development of a sacrificial positive electrode material exhibiting a high
charging/discharging capacity is required.
20 [Related art literature]
Republic of Korea Patent Publication No. 10-2019-0059115
4
【Disclosure】
【Technical Problem】
Accordingly, an object of the present disclosure is to provide a sacrificial positive
electrode material realizing a high initial charging/discharging efficiency while improving the
irreversible capacity loss generated in the negative electrode during initial 5 charging/discharging,
and reducing the amount of gas additionally generated during charging/discharging thereafter,
and a positive electrode and a lithium secondary battery including the same.
【Technical Solution】
In order to solve the above-mentioned problem, in one embodiment, the present
10 disclosure provides a sacrificial positive electrode material including:
a lithium cobalt oxide represented by the following Chemical Formula 1, and
the sacrificial positive electrode material has a defect formation energy of metal (M),
calculated using density functional theory (DFT), of -4.0 to -8.5 eV:
[Chemical Formula 1]
15 LixCo(1-y)MyO4
wherein,
M is at least one selected from the group consisting of Al, Fe, Zn, Ti, W, Mg, Ge, Mn
and Si,
x and y are 5≤x≤7 and 0.05≤y≤0.6.
20 In this case, in the Chemical Formula 1, M may be at least one selected from the group
5
consisting of Mg, Ge, and Si, and y may be 0.2≤y≤0.4.
In addition, the defect formation energy of the metal M according to the density
functional theory (DFT) of the sacrificial positive electrode material may be -4.9 to -6.4 eV.
In addition, the sacrificial positive electrode material may have a tetragonal structure
with a space 5 group of P42/nmc.
In addition, the sacrificial positive electrode material may have a powder electrical
conductivity of 5 x 10-4 S/cm to 1 x 10-2 S/cm.
In one embodiment, the present disclosure provides a positive electrode including:
a positive electrode current collector; and
10 a positive electrode mixture layer containing a positive electrode active material, a
conductive material, an organic binder polymer, and a sacrificial positive electrode material on
the positive electrode current collector;
the sacrificial positive electrode material includes lithium cobalt oxide represented by
the following Chemical Formula 1, and the sacrificial positive electrode material has a defect
15 formation energy of the metal (M), calculated using density functional theory (DFT), of -4.0 to -
8.5 eV:
[Chemical Formula 1]
LixCo(1-y)MyO4
wherein,
20 M is at least one selected from the group consisting of Al, Fe, Zn, Ti, W, Mg, Ge, Mn
and Si,
6
x and y are 5≤x≤7 and 0.05≤y≤0.6.
Here, the content of the sacrificial positive electrode material may be 0.001 to 5.0 parts
by weight based on 100 parts by weight of the positive electrode active material.
In addition, the content of the conductive material may be 0.5 to 10 parts by weight
based on 100 parts by weight of the total positive electrode 5 mixture layer.
In addition, the conductive material may include at least one carbon-based material
selected from the group consisting of natural graphite, artificial graphite, carbon black, acetylene
black, Ketjen black, and carbon fiber.
In addition, the positive electrode active material may include two or more elements
10 selected from the group consisting of nickel (Ni), cobalt (Co), manganese (Mn), aluminum (Al),
zinc (Zn), titanium (Ti), magnesium (Mg), chromium (Cr) and zirconium (Zr).
In addition, the average thickness of the positive electrode mixture layer may be 100 μm
to 200 μm.
In addition, the positive electrode may have a change rate of resistance value of 10% or
15 less after 30 times of charging/discharging compared to the resistance value during initial
charging/discharging.
Also, in one embodiment, the present disclosure provides an electrode assembly
including the above-described positive electrode.
Furthermore, in one embodiment, the present disclosure provides a lithium secondary
20 battery including the electrode assembly.
【Advantageous Effects】
7
The sacrificial positive electrode material according to the present disclosure is doped
with a specific metal, and a defect formation energy of the metal according to the density
functional theory (DFT) is controlled within a specific range, so that it is possible to realize a
high initial charging/discharging efficiency during initial charging/discharging and to reduce the
amount of gas additionally generated at the later time of charging/discharging, 5 and thus there is
an advantage that the effect of improving the stability and the charging/discharging performance
of a battery including the positive electrode are excellent.
【Brief Description of the Drawings】
The Figure is a graph showing the initial charging capacity for each type of metal doped
10 into lithium cobalt oxide (LixCoO4, 5≤x≤7).
【Detailed Description of the Preferred Embodiments】
Since the present disclosure can have various changes and can have various
embodiments, specific embodiments will be described in detail in the detailed description.
However, this is not intended to limit the present disclosure to specific embodiments,
15 and it should be understood to include all modifications, equivalents and substitutes included in
the spirit and scope of the present disclosure.
In the present disclosure, it is to be understood that the terms “include(s)” or “have(has)”
and the like are intended to specify the presence of stated features, numbers, steps, operations,
components, components or combinations thereof, but do not preclude the presence or addition
20 of one or more other features or numbers, steps, operations, components and combinations
8
thereof.
Further, in the present disclosure, when a portion of a layer, film, region, plate, etc. is
described as being “on” another portion, it includes not only the case where the other portion is
“directly on” but also the case where there is another portion therebetween. Conversely, where
a portion of a layer, film, region, plate, etc. is described as being “under” 5 another portion, this
includes the case where there is another portion therebetween as well as “directly under” the
other portion. Also, herein, what is referred to as being disposed “on” may include being
disposed not only an upper part but also on a lower part.
10 Hereinafter, the present disclosure will be described in more detail.
Sacrificial Positive Electrode Material
In one embodiment, the present disclosure provides a sacrificial positive electrode
material including the following:
15 lithium cobalt oxide represented by the following Chemical Formula 1, and
the sacrificial positive electrode material has a defect formation energy of metal (M),
calculated using density functional theory (DFT), of -4.0 to -8.5 eV:
[Chemical Formula 1]
LixCo(1-y)MyO4
20 wherein,
M is at least one selected from the group consisting of Al, Fe, Zn, Ti, W, Mg, Ge, Mn
9
and Si,
x and y are 5≤x≤7 and 0.05≤y≤0.6.
The sacrificial positive electrode material according to the present disclosure includes
lithium cobalt metal oxide represented by Chemical Formula 1 as a main component. Here, the
“main component” may mean 80 wt% or more, 90 wt% or more, 95 wt% or 5 more, or 97.5 wt%
or more, based on the total weight of the sacrificial positive electrode material, and in some
cases, when the sacrificial positive electrode material entirely consists of lithium cobalt metal
oxide represented by Chemical Formula 1, that is, it may mean 100% by weight.
The lithium cobalt metal oxide represented by Chemical Formula 1 have a structure
10 doped with one or more metals selected from the group consisting of Al, Fe, Zn, Ti, W, Mg, Ge,
Mn and Si at the cobalt position of the lithium cobalt oxide (LixCoO4, 5≤x≤7) emitting a large
amount of lithium ions, and specifically, may have a structure doped with one or more metals
selected from the group consisting of Mg, Ge, and Si.
At this time, the amount of doping the metal may be a 5 to 60 mole fraction (i.e.,
15 0.05≤y≤0.6), specifically, a 10 to 50 mole fraction (0.1≤y≤0.5); a 15 to 50 mole fraction
(0.15≤y≤0.5); a 15 to 45 mole fraction (0.15≤y≤0.45); a 20 to 40 mole fraction (0.2≤y≤0.4); or a
25 to 35 mole fraction (0.25≤y≤0.35). In the present disclosure, structural distortion of lithium
cobalt oxide can be alleviated by controlling the doping amount of the metal to be within the
above molar fraction range, and thus structural stability can be further improved.
20 In addition, the lithium cobalt metal oxide represented by Chemical Formula 1 may have
a tetragonal crystal structure, and among it, may have a space group of P42/nmc. In general,
10
lithium cobalt metal oxide having a tetragonal crystal structure has a structurally unstable
structure due to the distortion of the tetrahedral structure formed by the cobalt element and the
oxygen element, and this structural instability causes a problem that gas containing oxygen gas is
generated even during charging after activation of the battery. However, in the sacrificial
positive electrode material of the present disclosure, at least one metal selected 5 from the group
consisting of Al, Fe, Zn, Ti, W, Mg, Ge, Mn and Si is doped at the cobalt position of lithium
cobalt oxide (LixCoO4, 5≤x≤7) to have a doped structure, and thus an effect of reducing the
amount of gas generated can be exhibited even if the lithium cobalt metal oxide represented by
Formula 1 having a tetragonal crystal form is contained.
10 In addition, in the sacrificial positive electrode material, the defect formation energy of
metal (M) according to density functional theory (DFT) may be controlled to satisfy a specific
range. Specifically, the defect formation energy of the metal (M) according to the density
functional theory (DFT) of the sacrificial positive electrode material may be -4.0 to -8.5 eV,
more specifically -4.0 to -7.0 eV; -4.0 to -6.5 eV; -4.5 to -7.0 eV; -4.9 to -6.4 eV; -5.0 to -6.0 eV;
15 -4.5 to -5.6 eV; -5.0 to -5.5 eV; -5.5 to -5.9 eV; or -6.0 to -6.5 eV. The defect formation energy
of the metal (M) refers to the energy required to generate a crystallographic defect due to the
metal (M) doped in lithium cobalt oxide (LixCoO4, 5≤x≤7), and in the present disclosure, by
controlling the defect formation energy of (M) within the above range, the structural stability of
the sacrificial positive electrode material can be improved, and both the amount of gas generated
20 during initial charging/discharging and the amount of cumulative gas generated afterward can be
reduced.
11
In addition, in the sacrificial positive electrode material, the lithium cobalt metal oxide
represented by Chemical Formula 1 may have a powder electrical conductivity of 5 × 10-4 S/cm
to 1 × 10-2 S/cm, specifically 5 × 10-4 S/cm to 1 × 10-3 S/cm; 5 × 10-4 S/cm to 1 × 10-2 S/cm; 5 ×
10-4 S/cm to 5 × 10-3 S/cm; 8 × 10-4 S/cm to 9 × 10-3 S/cm; 1 × 10-3 S/cm to 8 × 10-3 S/cm; 6.0 ×
10-3 S/cm to 7.5 × 10-3 S/cm; or 3.5 × 10-3 S/cm to 6.5 × 10-3 S/cm. The 5 powder electrical
conductivity of the sacrificial positive electrode material can be adjusted according to the amount
of metal (M) doped at the cobalt position of lithium cobalt oxide (LixCoO4, 5≤x≤7) having a
remarkably low powder electric conductivity of 10−7 S/cm or less, the production conditions of
the sacrificial positive electrode material, and the like, and by adjusting the powder electric
10 conductivity within the above range, it is possible to further improve charging/discharging
capacity while reducing the amount of gas generated during charging of the battery.
As described above, the sacrificial positive electrode material according to the present
disclosure includes lithium cobalt metal oxide represented by Chemical Formula 1 doped with a
specific metal, so that it is possible to realize a high initial charging/discharging efficiency at the
15 time of initial charging/discharging and to reduce the amount of gas additionally generated at the
later time of charging/discharging, and thus there is an advantage that the effect of improving the
stability and the charging/discharging performance of a battery including the positive electrode
are excellent.
20 Positive Electrode
In one embodiment, the present disclosure provides a positive electrode including:
12
a positive electrode current collector; and
a positive electrode mixture layer containing a positive electrode active material, a
conductive material, an organic binder polymer, and a sacrificial positive electrode material on
the positive electrode current collector, and
the sacrificial positive electrode material includes lithium cobalt oxide 5 represented by
the following Chemical Formula 1, wherein the sacrificial positive electrode material has a
defect formation energy of the metal (M), calculated using density functional theory (DFT), of -
4.0 to -8.5 eV:
[Chemical Formula 1]
10 LixCo(1-y)MyO4
wherein,
M is at least one selected from the group consisting of Al, Fe, Zn, Ti, W, Mg, Ge, Mn
and Si,
x and y are 5≤x≤7 and 0.05≤y≤0.6.
15 The positive electrode according to the present disclosure has a structure in which a
positive electrode mixture layer is formed on a positive electrode current collector, wherein the
positive electrode mixture layer includes the sacrificial positive electrode material of the present
disclosure described above together with a positive electrode active material; conductive
material; and an organic binder polymer, and the positive electrode has a high
20 charging/discharging capacity, and has an excellent effect of reducing gas, particularly oxygen
(O2) gas, generated during charging/discharging of the battery.
13
Here, the positive electrode active material may be a lithium composite transition metal
oxide containing two or more elements selected from the group consisting of nickel (Ni), cobalt
(Co), manganese (Mn), aluminum (Al), zinc (Zn), titanium (Ti), magnesium (Mg), chromium
(Cr) and zirconium (Zr). For example, the positive electrode active material may include a
layered compound such as lithium cobalt oxide (LiCoO2) and lithium nickel 5 oxide (LiNiO2), or a
layered compound substituted with one or more transition metals; lithium manganese oxides of
the formula Li1+xMn2-xO4 (wherein x is 0 to 0.33), LiMnO3, LiMn2O3, LiMnO2, etc.; lithium
copper oxides such as Li2CuO2; vanadium oxides such as LiV3O8, Li3VO4, V2O5, Cu2V2O7; Ni
site-type lithium nickel oxide represented by the formula LiNi1-xMxO2 (wherein M = Co, Mn, Al,
10 Cu, Fe, Mg, B or Ga, and x = 0.01 to 0.3); lithium manganese composite oxide represented by
the formula LiMn2-xMxO2 (where M = Co, Ni, Fe, Cr, Zn or Ta, and x = 0.01 to 0.1) or
Li2Mn3MO8 (where M = Fe, Co, Ni, Cu or Zn); lithium manganese composite oxide having a
spinel structure represented by LiNixMn2-xO4; LiMn2O4 in which a part of Li in the formula is
substituted with an alkaline earth metal ion; disulfide compounds; Fe2(MoO4)3 etc.
15 In addition, the sacrificial positive electrode material may be included in an amount of
0.001 to 5.0 parts by weight based on 100 parts by weight of the positive electrode active
material. More specifically, the sacrificial positive electrode material may be included in an
amount of 0.001 to 4.0 parts by weight; 0.001 to 3.0 parts by weight; 0.001 to 2.0 parts by
weight; 0.001 to 1.0 parts by weight; 0.01 to 2.0 parts by weight; 0.05 to 2.0 parts by weight; 0.1
20 to 2.0 parts by weight; or 0.1 to 1.5 parts by weight, based on 100 parts by weight of the positive
electrode active material.
14
In addition, the conductive material may be included in an amount of 1 to 20 parts by
weight, specifically, 1 to 10 parts by weight; 1 to 5 parts by weight; 3 to 8 parts by weight; or 2
to 5 parts by weight, based on 100 parts by weight of the positive electrode active material.
In addition, the conductive material is not particularly limited as long as it has
conductivity without causing a chemical change in the battery. For example, 5 graphite such as
natural graphite or artificial graphite; carbon black such as acetylene black, Ketjen black,
channel black, furnace black, lamp black, and thermal black; conductive fibers such as carbon
fibers and metal fibers; carbon fluoride; metal powders such as aluminum, and nickel powder;
conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as
10 titanium oxide; and conductive materials such as polyphenylene derivatives may be used.
In addition, the organic binder polymer is a component that assists in bonding of the
active material and the conductive material and bonding to the current collector, and it may be
included in an amount of 1 to 20 parts by weight, specifically, 1 to 10 parts by weight; 1 to 5
parts by weight; 3 to 8 parts by weight; or 2 to 5 parts by weight, based on 100 parts by weight of
15 the positive electrode active material.
In addition, examples of the organic binder polymer include polyvinylidene fluoride
(PVdF), polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose,
regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene,
polypropylene, an ethylene-propylene-diether polymer (EPDM), a sulfonated EPDM, styrene20
butyrene rubber, fluororubber, various copolymers, etc.
In addition, the positive electrode may further include a filler for suppressing the
15
expansion of the positive electrode in addition to the positive electrode active material, the
conductive material, and the organic binder polymer in the positive electrode mixture layer, and
the filler is not particularly limited when it is a fibrous material that does not cause a chemical
change in the battery. Specifically, as the filler, an olefin-based polymer such as polyethylene
or polypropylene; a fibrous material such as glass fiber or carbon 5 fiber may be used.
As one example, the positive electrode mixture layer may include 1 part by weight of a
sacrificial positive electrode material (Li6Co0.7Zn0.3O4) based on 100 parts by weight of lithium
nickel cobalt manganese oxide (LiNi0.8Co0.1Mn0.1O2); 5 parts by weight of acetylene black as a
conductive material; and 10 parts by weight of a binder (PVdF).
10 In addition, the average thickness of the positive electrode mixture layer may be 100 μm
to 200 μm, specifically, 120 μm to 180 μm; 140 μm to 170 μm; or 150 μm to 200 μm.
In addition, the positive electrode mixture layer may be a single layer or may have a
multi-layer structure of two or more layers, and in the case of a multi-layer structure of two or
more layers, the content of the sacrificial positive electrode material included in the positive
15 electrode mixture layer may be different; the type and/or content of the positive electrode active
material, the conductive material, and the binder may be the same or different.
As an example, the positive electrode mixture layer may have a two-layer structure in
which a first mixture layer and a second mixture layer are sequentially stacked on a positive
electrode current collector, and the first mixture layer may include 1 part by weight of a
20 sacrificial positive electrode material (Li6Co0.7Zn0.3O4) based on 100 parts by weight of lithium
nickel cobalt manganese oxide (LiNi0.8Co0.1Mn0.1O2); 5 parts by weight of acetylene black as a
16
conductive material; and 10 parts by weight of a binder (PVdF) and the second mixture layer
may include 2 parts by weight of a sacrificial positive electrode material (Li6Co0.7Zn0.3O4) based
on 100 parts by weight of lithium nickel cobalt manganese oxide (LiNi0.6Co0.2Mn0.2O2); 5 parts
by weight of acetylene black as a conductive material; and 9 parts by weight of a binder (PVdF).
Furthermore, when the positive electrode mixture layer has a 5 two-layer structure in
which a first mixture layer and a second mixture layer are sequentially stacked on a positive
electrode current collector, each layer may satisfy Equation 1 below:
[Equation 1]
0.05 ≤ SCM1st/SCM2nd ≤ 0.9
10 wherein,
SCM1st represents the content of the positive electrode additive contained in the first
positive electrode mixture layer,
SCM2nd represents the content of the positive electrode additive contained in the second
positive electrode mixture layer.
15 Equation 1 shows the ratio of the positive electrode additive contained in each of the
first positive electrode mixture layer and the second positive electrode mixture layer, and the
content of the positive electrode additive contained in the second positive electrode mixture
layer, that is, the content of lithium cobalt oxide represented by Chemical Formula 1, and means
that the content of the positive electrode additive contained in the first positive electrode mixture
20 layer is less than that of the positive electrode additive contained in the second positive electrode
mixture layer. The positive electrode mixture layer according to the present disclosure may
17
satisfy Equation 1 above with 0.05 to 0.9 (for example, 0.05≤SCM1st/SCM2nd≤0.9), specifically
0.1 to 0.9 (for example, 0.1≤SCM1st/SCM2nd≤0.9), 0.2 to 0.8 (for example,
0.2≤SCM1st/SCM2nd≤0.8), 0.3 to 0.7 (for example, 0.3≤SCM1st/SCM2nd≤0.7), or 0.4 to 0.8 (for
example, 0.4≤SCM1st/SCM2nd≤0.8). The positive electrode mixture layer according to the
present disclosure can further improve the irreversible reaction efficiency 5 of the positive
electrode additive during initial charging by satisfying the condition of Equation 1, thereby
reducing gas generation through charging/discharging after the initial charging/discharging.
In addition, the positive electrode current collector is not particularly limited as long as it
has high conductivity without causing a chemical change in the battery, and for example,
10 stainless steel, aluminum, nickel, titanium, calcined carbon, etc. may be used, and in the case of
aluminum or stainless steel, a surface treated with carbon, nickel, titanium, silver, etc. may be
used. In addition, fine irregularities may be formed on the surface of the positive electrode
current collector to increase the adhesion of the positive electrode active material, and various
forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a nonwoven body are
15 possible. In addition, the average thickness of the positive electrode current collector may be
appropriately applied in a range of 3 to 500 μm in consideration of the conductivity and total
thickness of the positive electrode to be prepared.
In addition, the positive electrode according to the present disclosure may have excellent
electrical performance by including the above configuration. Specifically, the positive
20 electrode may have low electrode resistance at room temperature (23±2 °C), and even after
repeated charging/discharging of the battery, the change in resistance of the electrode may be
18
low to improve the lifespan of the battery.
As an example, the positive electrode may have a resistance value change rate of 10% or
less after 30 times of charging/discharging compared to the electrode resistance value during
initial charging/discharging (for example, activation step). For example, the positive electrode
may have an electrode resistance value change rate of 8% or less; 6% or less; 5 4% or less; or 3%
or less after initial charging/discharging and 30 times of charging/discharging.
Electrode Assembly
Also, in one embodiment, the present disclosure provides an electrode assembly
including the above-described positive electrode.
10 The electrode assembly according to the present disclosure may have a structure
including the above-described positive electrode, a negative electrode, and a separation
membrane interposed between the positive electrode and the negative electrode, and in some
cases, the separation membrane may be excluded.
Here, the negative electrode is manufactured by coating, drying and pressing the
15 negative electrode active material on the negative electrode current collector, and if necessary,
the conductive material, organic binder polymer, filler, etc. as described above may be optionally
further included.
In addition, as the negative electrode active material, for example, graphite having a
completely layered crystal structure such as natural graphite, and soft carbon having a low
20 crystallinity layered crystal structure (graphene structure; a structure in which hexagonal
honeycomb planes of carbon are arranged in layers) and graphite materials such as hard carbon,
19
artificial graphite, expanded graphite, carbon fiber, non-graphitizable carbon, carbon black,
carbon nanotubes, fullerenes, activated carbon, etc. in which carbon and these structures are
mixed with amorphous parts; metal complex oxides such as LixFe2O3(0≤x≤1), LixWO2(0≤x≤1),
SnxMe1-xMe'yOz (Me: Mn, Fe, Pb, Ge; Me', Al, B, P, Si, Group 1 of the periodic table, metal
complex oxides such as Group 2 and Group 3 elements and halogens; 0 < x ≤ 5 1; 1 ≤ y ≤ 3; 1 ≤ z
≤ 8); lithium metal; lithium alloys; silicon-based alloys; tin-based alloys; metal oxides such as
SnO, SnO2, PbO, PbO2, Pb2O3, Pb3O4, Sb2O3, Sb2O4, Sb2O5, GeO, GeO2, Bi2O3, Bi2O4 and
Bi2O5; conductive polymers such as polyacetylene; Li-Co-Ni-based materials; titanium oxide;
Lithium titanium oxide and the like, may be used.
10 In addition, the negative electrode current collector is not particularly limited as long as
it has high conductivity without causing a chemical change in the battery, and for example,
copper, stainless steel, nickel, titanium, calcined carbon, etc. may be used, and in the case of
copper or stainless steel, a surface treated with carbon, nickel, titanium, silver, etc. may be used.
In addition, like the positive electrode current collector, fine irregularities may be formed on the
15 surface of the negative electrode current collector to strengthen the adhesion with the negative
electrode active material, and various forms such as films, sheets, foils, nets, porous materials,
foams, non-woven materials, etc. are possible. In addition, the average thickness of the
negative electrode current collector may be appropriately applied in a range of 3 to 500 μm in
consideration of the conductivity and total thickness of the negative electrode to be
20 manufactured.
In addition, the separation membrane is interposed between the negative electrode and
20
the positive electrode, and an insulating thin film having high ion permeability and mechanical
strength is used. The separation membrane is not particularly limited as long as it is
conventionally used in the art, but specifically, a sheet or nonwoven fabric made of chemical
resistant and hydrophobic polypropylene, glass fiber, polyethylene or the like may be used, and
in some cases, a composite separation membrane in which inorganic particles/o 5 rganic particles
are coated with an organic binder polymer on a porous polymer substrate such as a sheet or
nonwoven fabric may be used. When a solid electrolyte such as a polymer is used as the
electrolyte, the solid electrolyte may also serve as a separation membrane. In addition, the
separation membrane may have an average pore diameter of 0.01 to 10 μm, and an average
10 thickness of 5 to 300 μm.
Meanwhile, the electrode assembly may be wound in the form of a jelly roll and stored
in a cylindrical battery, a prismatic battery, or a pouch-type battery, or may be stored in a pouchtype
battery in a folding or stack-and-folding form, but is not limited thereto.
Lithium Secondary Battery
15 Furthermore, in one embodiment, the present disclosure provides a lithium secondary
battery including the above-mentioned electrode assembly.
The lithium secondary battery according to the present disclosure may have a structure
in which the electrode assembly is impregnated with a lithium salt-containing electrolyte.
In this case, the lithium salt-containing electrolyte may consist of an electrolyte and a
20 lithium salt, and as the electrolyte, a non-aqueous organic solvent, an organic solid electrolyte,
an inorganic solid electrolyte, and the like may be used.
21
As the non-aqueous organic solvent, for example, an aprotic organic solvent such as Nmethyl-
2-pyrrolidinone, ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl
carbonate, diethyl carbonate, gamma-butyrolactone, 1,2-dimethoxyethane, tetrahydroxy franc, 2-
methyl tetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide,
dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphoric 5 acid triester,
trimethoxymethane, dioxolane derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-
imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ether, propionic
methyl or propionic ethyl, may be used.
As the organic solid electrolyte, for example, polyethylene derivatives, polyethylene
10 oxide derivatives, polypropylene oxide derivatives, phosphoric acid ester polymers, poly alginate
lysine, polyester sulfide, polyvinyl alcohol, polyvinylidene fluoride, a polymeric material
including an ionic dissociating group and the like may be used.
As the inorganic solid electrolyte, nitrides, halides, sulfates, etc. of Li, such as Li3N, LiI,
Li5Ni2, Li3N-LiI-LiOH, LiSiO4, LiSiO4-LiI-LiOH, Li2SiS3, Li4SiO4, Li4SiO4-LiI-LiOH, Li3PO4-
15 Li2S-SiS2, may be used.
The lithium salt is a material easily soluble in the non-aqueous electrolyte, and for
example, LiCl, LiBr, LiI, LiClO4, LiBF4, LiB10Cl10, LiPF6, LiCF3SO3, LiCF3CO2, LiAsF6,
LiSbF6, LiAlCl4, CH3SO3Li, (CF3SO2)2NLi, chloroborane lithium, lithium lower aliphatic
carboxylates, lithium 4-phenylboronate, lithium imide and the like may be used.
20 In addition, for the purpose of improving charging/discharging characteristics, flame
retardancy, etc., for example, pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylene
22
diamine, n-glyme, hexamethylphosphate triamide, nitrobenzene derivatives, sulfur, quinone
imine dyes, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl
ether, ammonium salts, pyrrole, 2-methoxyethanol, aluminum trichloride and the like may be
added to the electrolyte. In some cases, in order to impart incombustibility, a halogencontaining
solvent such as carbon tetrachloride and ethylene trifluoride may 5 be further included,
and carbon dioxide gas may be further included to improve high temperature storage
characteristics, and fluoro-ethylene carbonate (FEC), propene sultone (PRS), etc. may be further
included.
Further, in one embodiment, the present disclosure provides a battery module including
10 the above-described secondary battery as a unit cell, and provides a battery pack including the
battery module.
The battery pack may be used as a power source for a medium or large device that
requires high temperature stability, long cycle characteristics, and high rate characteristics, and
specific examples of the medium or large device include a power tool that is powered by an
15 electric motor; electric vehicles including electric vehicles (EVs), hybrid electric vehicles
(HEVs), plug-in hybrid electric vehicles (PHEVs), and the like; electric two-wheeled vehicles
including electric bicycles (E-bikes) and electric scooters (E-scooter); electric golf carts; and a
system for storing power, and more specifically, a hybrid electric vehicle (HEV), but is not
limited thereto.
20
Hereinafter, the present disclosure will be described in detail by way of Examples.
23
However, the following Examples and Experimental Examples are merely illustrative of
the present disclosure, and the content of the present disclosure is not limited to the following
Examples and Experimental Examples.
Examples 1 to 11: Preparation of Sacrificial Positive 5 Electrode Material
Lithium oxide (Li2O) and cobalt oxide (CoO) and the metal oxide (MO) shown in Table
1 below were input into a reactor, and uniformly dry-mixed for about 30 minutes using a mixer.
Then, the prepared raw material mixture was put into an electric furnace and calcined for 10
hours at about 700±10° C under argon gas (Ar) conditions to obtain lithium cobalt oxide (Li6Co1-
10 yMyO4), a sacrificial positive electrode material.
At this time, the molar ratio of lithium oxide and cobalt oxide input into the reactor was
1:3.0 to 3.03, i) the type of metal oxide (MO) and ii) the molar ratio of cobalt oxide to the metal
oxide (MO) are shown in Table 1 below, and for each of the prepared sacrificial materials, ①
the defect formation energy of the doped metal (M) and ② the powder electrical conductivity
15 were analyzed.
Specifically, in the case of ① metal (M) defect formation energy, it was calculated
using density functional theory (DFT), and the calculation of the density functional theory (DFT)
was carried out using the Vienna Ab initio Simulation Package (VASP) as a projectoraugmented
wave (PAW) method to calculate the structure and energy of atoms and electrons; the
20 electron exchange-correlation function was calculated using the Perdew, Burke, and Ernzerhof
(PBE) model method based on generalized gradient approximation (GGA); Kinetic energy cutoff
24
was set to 500 eV; for each metal (M) surface, the 2Х2Х3 Monkhorst-Pack method was used.
In addition, ② in order to measure the powder electrical conductivity of the sacrificial
positive electrode material, each prepared sacrificial positive electrode material was compressed
to prepare a powder. Then, the sheet resistance according to the volume and pressure change of
each sacrificial positive electrode material was measured using a powder resistance 5 characteristic
measuring instrument for the prepared powder by a 4-point probe method, and the powder
electrical conductivity of the sacrificial positive electrode material was calculated using the
measured volume and input mass. The measured results are shown in Table 1 below.
[Table 1]
Metal oxide (MO) Defect
formation
energy of metal
(M)
Powder
electrical
conductivity
Type CoO:MO
Example 1 GeO2 7:3 (y=0.3) -5.1±0.1 eV 6.2×10-3 S/cm
Example 2 MgO 7:3 (y=0.3) -5.8±0.1 eV 7.1×10-3 S/cm
Example 3 SiO2 7:3 (y=0.3) -6.2±0.1 eV 6.5×10-3 S/cm
Example 4 Al2O3 7:3 (y=0.3) -6.3±0.1 eV 5.3×10-3 S/cm
Example 5 Fe2O3 7:3 (y=0.3) -4.2±0.1 eV 7.8×10-3 S/cm
Example 6 ZnO 7:3 (y=0.3) -4.2±0.1 eV 6.0×10-3 S/cm
Example 7 TiO2 7:3 (y=0.3) -5.6±0.1 eV 4.9×10-3 S/cm
Example 8 WO3 7:3 (y=0.3) -8.3±0.1 eV 4.5×10-3 S/cm
Example 9 MnO2 7:3 (y=0.3) -4.4±0.1 eV 6.7×10-3 S/cm
Example 10 GeO2 9:1 (y=0.1) -5.1±0.1 eV 5.3×10-3 S/cm
Example 11 GeO2 5:5 (y=0.5) -5.1±0.1 eV 5.6×10-3 S/cm
10
Comparative Examples 1 to 3: Preparation of Sacrificial Positive Electrode Material
It was carried out in the same manner as in Example 1, except that i) the type of metal
oxide (MO) mixed with lithium oxide (Li2O) and cobalt oxide (CoO) and ii) the molar ratio of
cobalt oxide and the metal oxide were adjusted as shown in Table 2 below to obtain lithium
25
cobalt oxide (Li6Co1-yMyO4), a sacrificial positive electrode material.
At this time, ① the defect formation energy of the doped metal (M) and ② powder
electrical conductivity of the prepared sacrificial positive electrode material were analyzed in the
same manner as in Examples, and the results are shown in Table 2 below.
5 [Table 2]
Metal oxide (MO) Defect
formation
energy of
metal (M)
Powder
electrical
conductivity
Type CoO:MO
Comparative
Example 1
- 10:0 (y=0) - 4.3×10-4 S/cm
Comparative
Example 2
GeO2 9.9:0.1 (y=0.01) -5.1±0.1 eV 9.1×10-4 S/cm
Comparative
Example 3
GeO2 3:7 (y=0.7) -5.1±0.1 eV 3.7×10-3 S/cm
Experimental Example
In order to evaluate the performance of the sacrificial positive electrode material
prepared in the present disclosure, the following experiment was performed.
10
A) Initial charging/discharging capacity and efficiency evaluation
An N-methylpyrrolidone solvent was introduced into a homo mixer, and each of the
sacrificial positive electrode materials prepared in Examples 1 to 11 and Comparative Examples
1 to 3, an acetylene black conductive material, a modified silanol binder, and a dispersant was
15 added in a weight ratio of 95:3:1.7:0.3 and then mixed at 3,000 rpm for 60 minutes to prepare a
pre-dispersion.
The prepared pre-dispersion was mixed with the positive electrode active material so
26
that the content of the sacrificial positive electrode material was 2 parts by weight based on 100
parts by weight of the positive electrode active material (LiNi0.6Co0.2Mn0.2O2), and the positive
electrode active material mixed in an N-methylpyrrolidone solvent, PVdF as a binder and carbon
black as a conductive material were put into a homo mixer so as to have a weight ratio of 96:1:3,
and then dispersed at 3,000 rpm for 80 minutes to prepare a slurry for a positive 5 electrode. The
prepared positive electrode slurry was applied to one surface of an aluminum current collector,
dried at 100° C, and rolled to manufacture a positive electrode.
A 2032 type coin cell was manufactured using the positive electrode and a lithium metal
counter electrode. A separator (thickness: about 16 μm) made of a porous polyethylene (PE)
10 film was interposed between the positive electrode and the lithium metal counter electrode, and
an electrolyte was injected to manufacture a half-cell type coin cell.
In this case, E2DVC was used as the electrolyte. Here, "E2DVC" is a kind of
carbonate-based electrolyte, and means a solution obtained by mixing lithium
hexafluorophosphate (LiPF6, 1.0M) and vinyl carbonate (VC, 2% by weight) in a mixed solution
15 of ethylene carbonate (EC):dimethyl carbonate (DMC):diethyl carbonate (DEC)=1:1:1 (volume
ratio).
For the manufactured coin cell, initial charging/discharging capacity were measured by
performing initial charging/discharging (formation) at 25 °C with a reference capacity condition
of 200 mAh/200 mAh, and the efficiency was calculated from the measured initial
20 charging/discharging capacity, and thus, the results are shown in Table 3 below.
[Table 3]
27
Initial charging
capacity
[mAh/g]
Initial discharging
capacity
[mAh/g]
Initial
charging/dischargi
ng efficiency
[%]
Example 1 690.2 56.8 8.2
Example 2 734.4 39.9 5.4
Example 3 513.8 25.6 5.0
Example 4 305.9 4.6 1.5
Example 5 717.4 28.6 4.0
Example 6 717.4 28.6 4.0
Example 7 654.8 13.5 2.1
Example 8 313.0 1.83 0.6
Example 9 718.0 27.9 3.9
Example 10 721.7 42.1 5.8
Example 11 675.3 61.8 9.2
Comparative
Example 1
815.7 31.1 3.8
Comparative
Example 2
807.9 32.3 4.0
Comparative
Example 3
630.1 62.4 9.9
As shown in Table 3, it can be seen that the sacrificial positive electrode material
according to the present disclosure has a high initial charging capacity during initial
charging/discharging and exhibits high initial charging/discharging efficiency.
5
B) Evaluation of gas generation after initial charging/discharging
The previously used coin cell was repeatedly charged and discharged 50 times under
0.3C/0.3C conditions at 45 °C, and the amount of gas generated during each
charging/discharging was measured to calculate the amount of cumulative gas generated after the
10 initial charging/discharging. The results are shown in Table 4 below.
[Table 4]
28
Cumulative gas generation
[mL/g]
Example 1 4.5
Example 2 5.3
Example 3 6.1
Example 4 5.7
Example 5 7.1
Example 6 6.6
Example 7 5.8
Example 8 5.1
Example 9 4.9
Example 10 4.4
Example 11 4.1
Comparative
Example 1
13.0
Comparative
Example 2
9.7
Comparative
Example 3
7.8
It can be seen that in the case of the sacrificial positive electrode material according to
the present disclosure, the amount of gas generated due to charging/discharging after initial
charging/discharging is reduced.
Specifically, it can be seen that the sacrificial positive electrode 5 materials of Examples
had a low cumulative gas generation amount of 7.5 mL/g or less due to charging/discharging
29
after the initial charging/discharging, but the sacrificial positive electrode materials of
Comparative Examples had a high cumulative gas generation amount of 7.5 mL/g or more.
From these results, it can be seen that when the sacrificial positive electrode material
according to the present disclosure is doped with a specific metal, and the defect formation
energy of the metal according to the density functional theory (DFT) 5 is controlled within a
specific range, it is possible to realize a high initial charging/discharging efficiency at the time of
initial charging/discharging and to reduce the amount of gas additionally generated at the later
time of charging/discharging, there is an advantage that the effect of improving the stability and
the charging/discharging performance of a battery including the positive electrode are excellent.
10 While the foregoing has been described with reference to preferred embodiments of the
present disclosure, it should be understood by those skilled in the art or by those of ordinary skill
in the art that various changes and modifications can be made therein without departing from the
spirit and scope of the disclosure as set forth in the claims that follow.
Accordingly, the technical scope of the present disclosure should not be limited to the
15 content described in the detailed description of the specification, but should be defined by the
claims.

【Claims】
【Claim 1】
A sacrificial positive electrode material, comprising:
a lithium cobalt oxide represented by the following Chemical Formula 1, wherein the sacrificial
positive electrode material has a defect formation energy of metal (M) 5 of -4.0 to -8.5 eV,
calculated using density functional theory (DFT):
[Chemical Formula 1]
LixCo(1-y)MyO4
wherein,
10 M is at least one selected from the group consisting of Al, Fe, Zn, Ti, W, Mg, Ge, Mn
and Si,
x and y are 5≤x≤7 and 0.05≤y≤0.6.
【Claim 2】
15 The sacrificial positive electrode material of claim 1, wherein M is one or more selected
from the group consisting of Mg, Ge, and Si.
【Claim 3】
The sacrificial positive electrode material of claim 1, wherein y in Formula 1 is
20 0.2≤y≤0.4.
31
【Claim 4】
The sacrificial positive electrode material of claim 1, wherein the defect formation
energy of the metal (M) is -4.9 to -6.4 eV.
5
【Claim 5】
The sacrificial positive electrode material of claim 1, wherein the sacrificial positive
electrode active material having a tetragonal structure with a space group of P42/nmc.
10 【Claim 6】
The sacrificial positive electrode material of claim 1, the sacrificial positive electrode
active material having a powder electrical conductivity of 5 x 10-4 S/cm to 1 x 10-2 S/cm.
【Claim 7】
15 A positive electrode comprising:
a positive electrode current collector; and
a positive electrode mixture layer containing a positive electrode active material, a
conductive material, an organic binder polymer, and a sacrificial positive electrode material on
the positive electrode current collector;
20 the sacrificial positive electrode material comprises lithium cobalt oxide represented by
32
the following Chemical Formula 1, and having a defect formation energy of the metal (M) of -
4.0 to -8.5 eV , calculated using density functional theory (DFT):
[Chemical Formula 1]
LixCo(1-y)MyO4
5 wherein,
M is one or more selected from the group consisting of Al, Fe, Zn, Ti, W, Mg, Ge, Mn
and Si, and
x and y are 5≤x≤7 and 0.05≤y≤0.6.
10 【Claim 8】
The positive electrode of claim 7, wherein the content of the sacrificial positive
electrode material is 0.001 to 5.0 parts by weight based on 100 parts by weight of the positive
electrode active material.
15 【Claim 9】
The positive electrode of claim 7, wherein the content of the conductive material is 0.5
to 10 parts by weight based on 100 parts by weight of the total positive electrode mixture layer.
【Claim 10】
20 The positive electrode of claim 7, wherein the conductive material comprises one or
33
more carbon-based materials selected from the group consisting of natural graphite, artificial
graphite, carbon black, acetylene black, Ketjen black, and carbon fiber.
【Claim 11】
The positive electrode of claim 7, wherein the positive electrode 5 active material is a
lithium composite transition metal oxide containing two or more elements selected from the
group consisting of nickel (Ni), cobalt (Co), manganese (Mn), aluminum (Al), zinc (Zn),
titanium (Ti), magnesium (Mg), chromium (Cr) and zirconium (Zr).
10 【Claim 12】
The positive electrode of claim 7, wherein the average thickness of the positive electrode
mixture layer is 100 μm to 200 μm.
【Claim 13】
15 An electrode assembly comprising the positive electrode of claim 7.
【Claim 14】
A lithium secondary battery comprising the electrode assembly of claim 13.