The present disclosure generally relates to electrode compositions. In
specific embodiments, the present disclosure relates to a method of making and using
compositions for cathode materials. The disclosure also includes energy storage
devices that utilize such cathode materials.
Metal halide (Mx) batteries are useful for a number of energy storage
applications. These batteries include both a negative electrode (anode) and a positive
electrode (cathode) that serve to move electrons during the battery's operation.
Nickel is a common component of the positive electrode. The current sodium metal
halide batteries, for instance, use a considerable amount of nickel that is not required
for operation of the cell but is required to maintain packing density. In these instances,
the nickel is being used to create structure and conductivity but the entire amount
typically used is not required for operation of the battery.
There continues to be a growing need in the art for high performance metal
halide batteries with lower fabrication costs. Prior attempts for achieving this have
utilized reticulated carbon foams and meshes. However, these materials frequently do
not allow for even distribution across the cathode. Additionally, they are often more
expensive than the nickel they are trying to replace. The methods of introducing these
materials to the cathode can be quite arduous and difficult to put into commercial
large scale operation.
Thus, it may be desirable to have an electrode material that maintains the
performance of the battery, but allows for a reduction in costs over those materials
currently available.
BRIEF DESCRIPTION
The present disclosure provides, in a first aspect, a cathode composition.
The cathode composition comprises granules of at least one electroactive metal, at
least one alkali metal halide, and carbon black. An energy storage device that
comprises such a cathode composition constitutes another embodiment of the
invention. An article that comprises such a cathode composition constitutes another
embodiment of the invention. This article may be an energy storage device or an
unintermptable power supply (UPS) device.
The present disclosure provides, in a second aspect, a method of forming a
cathode material. The method comprises the steps of:
a) providing a powder comprising at least one electroactive metal and at
least one alkali metal halide;
b) blending carbon black into the powder such that the carbon black
becomes interspersed within the powder to form a non-agglomerated
mixture; and
c) forming granules from the mixture.
The present disclosure provides, in a third aspect, an energy storage device.
The device comprises:
a) a first negative compartment comprising an alkali metal;
b) a negative electrode current collector
c) a second compartment comprising a positive electrode composition
that itself comprises granules comprised of at least one electroactive metal, at least
one alkali metal halide and carbon black;
d) a positive electrode current collector; and
e) a solid separator capable of transporting alkali metal ions between
the first and the second compartments.
This device may be rechargeable over a plurality of cycles. An energy storage battery
that comprises a plurality of such rechargeable energy storage devices constitutes
another embodiment of the invention.
The present disclosure provides, in a fourth aspect, a method for the
preparation of an energy storage device. This method comprises:
a) providing a positive electrode and a negative electrode, ionically
connected to each other by a separator, and capable of reacting
galvanically upon connection;
b) providing an electrically-conductive electrolyte to at least the positive
electrode; and
c) providing positive and negative current collectors for attachment to the
positive and negative electrodes, respectively, to direct current resulting
from the galvanic reaction to a desired location.
The positive electrode of this embodiment comprises granules of at least one
electroactive metal, at least one alkali metal halide and carbon black.
These and other objects, features and advantages of this disclosure will
become apparent from the following detailed description of the various aspects of the
disclosure taken in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 depicts a schematic, cross-sectional view of an electrochemical cell
for embodiments of this disclosure.
FIG. 2 depicts a graph comparing recharging time of a control cell with an
embodiment of the disclosure.
DETAILED DESCRIPTION
Each embodiment presented below facilitates the explanation of certain
aspects of the disclosure, and should not be interpreted as limiting the scope of the
disclosure. Moreover, approximating language, as used herein throughout the
specification and claims, may be applied to modify any quantitative representation
that could permissibly vary without resulting in a change in the basic function to
which it is related. Accordingly, a value modified by a term or terms, such as
"about," is not limited to the precise value specified. In some instances, the
approximating language may correspond to the precision of an instrument for
measuring the value.
In the following specification and claims, the singular forms "a", "an" and
"the" include plural referents unless the context clearly dictates otherwise. As used
herein, the terms "may" and "may be" indicate a possibility of an occurrence within a
set of circumstances; a possession of a specified property, characteristic or function;
andlor qualifL another verb by expressing one or more of an ability, capability, or
possibility associated with the qualified verb. Accordingly, usage of "may" and "may
be" indicates that a modified term is apparently appropriate, capable, or suitable for
an indicated capacity, function, or usage, while taking into account that in some
circumstances, the modified term may sometimes not be appropriate, capable, or
suitable.
As discussed in detail below, some of the embodiments of the present
disclosure provide a cathode composition comprised of granules of at least one
electroactive metal, at least one alkali metal halide, and carbon black. The disclosure
works by formulating a cathode to include levels of carbon black, a conductive,
relatively inexpensive material, instead of the entire initial amount of electroactive
metal. This addition of carbon black allows for maintaining the interfacial area of the
cathodelbase while reducing the amount of electroactive metal required. These
embodiments allow for operation of a cell that utilizes the cathode more costeffectively
by using a much less expensive material to achieve the same goal.
As used herein, "cathode material" (or "cathode composition", "positive
electrode material" or "positive electrode composition", which may all be used
interchangeably) is the material that supplies electrons during charging, and is present
as part of a redox reaction. The "anode material" (or "negative electrode") accepts
electrons during charging and is present as part of the redox reaction.
For most end use applications, the cathode composition comprises at least
one electroactive metal selected from the group consisting of titanium, vanadium,
niobium, molybdenum, nickel, cobalt, chromium, copper, manganese, silver,
antimony, cadmium, tin, lead, iron, and zinc. Combinations of any of these metals are
also possible. In some specific embodiments, the electroactive metal is nickel, iron,
copper, zinc, cobalt, chromium, or some combination thereof. Very often, nickel is
the most preferred electroactive metal, in view of various attributes, including cost,
availability, the relatively high reduction potential ("redox potential") of nickel,
relative to sodium; and the relatively low solubility of the nickel cation in the
reaction-catholyte. Usually, the metals are obtained as powders from various
commercial sources.
Typically, the cathode composition also comprises at least one alkali metal
halide to promote the desired electrochemical reaction for the device of interest. In
some embodiments, halides of sodium, potassium, or lithium are used. In some
embodiments, the composition comprises at least sodium chloride. In other
embodiments, the composition comprises sodium chloride and at least one of sodium
iodide and sodium fluoride. Some specific positive electrode compositions are
described in copending Application 131034184 (D. Bogdan et al; filed February 24,
201 1 for the Assignee of this case; and incorporated herein by reference). In some
specific embodiments, sodium iodide, when present, is at a level of about 0.1 weight
percent to about 0.9 weight percent, based on the weight of the metal halides present
in the positive electrode.
In embodiments of the disclosure, carbon black is used to replace a volume
of the electroactive metal of the granules. The carbon black used in embodiments of
the disclosure has certain characteristics. In some embodiments, the carbon black has
a surface area in the range of about 50 m2/gram and about 1000 m2/gram. In other
embodiments, the carbon black has a surface area between about 50 m2/gram and
about 600 m2/gram. Non-limiting examples of carbon black that may be used include
Cabot XC72 and Cabot LBX101.
In some embodiments of the disclosure, it may be beneficial to treat the
surface of the carbon. Commercially available carbon black, for instance, often
includes side groups such as oxygen complexes. The carbon black can be treated
thermally to remove some of these side groups. For instance, in one condition the
carbon black was heated in an inert atmosphere at -550°C for an hour under argon. a The carbon black may also be chemically treated to replace the protons of
the side groups. This may be accomplished by making the carbon acidic, then
neutralizing with a base. In one example, the carbon was exposed to concentrated
nitric acid at 60°C for two hours. The solution was then exposed to aqueous 45%
NaOH solution and heated at 70°C for six hours, then filtered and washed with
deionized water repeatedly until the wash solution was neutral after filtering. Finally,
the carbons were dried in an oven at 250°C. In this instance, the protons of the side
groups were replaced with sodium.
Up to about 70% of the mass of the electroactive metal that would be
utilized in a comparably-sized cathode (i.e., a control) may be replaced with carbon
black. To illustrate, 15% of the mass of the electroactive metal present in a control
cathode has a specific volume. This volume of electroactive metal may be replaced
by an equivalent volume of carbon black. In most cases, the mass of the carbon black
will not be the same as the mass of the removed electroactive metal. In some
embodiments of the disclosure, the volume-to-volume ratio of the carbon black to the
electroactive metal is between about 5:95 and about 70:30, inclusive. In other
embodiments, the ratio is between 10:90 and 40:60, inclusive. In still other
embodiments, the ratio is between 10:90 and 25:75, inclusive. In some embodiments,
the ratio is about 15:85. The efficiency of the cathode must be balanced by the cost of
the granules: replacing a large portion of the granules' electroactive metal with carbon
black would cost less, but could result in a lower efficiency of the resulting energy
storage device.
In many cases, the positive electrode composition is prepared by combining
powders of the various constituents, e.g., powders of electroactive metals and of alkali
metal halides, and blending it with carbon black.It has also been found that, in some
embodiments, the method of adding the carbon black is essential. A traditional
tumbling and mixing operation tends to cause failure in mixing because of the relative
hardness of the electroactive metal powder, as compared to the softness of carbon
black. Thus, the carbon black must be mixed into the powder in such a way that the
hardness of the electroactive metal does not prevent adequate dispersion of the carbon
due to, for instance, agglomeration of the carbon or the deposition of the carbon on
the surface of the mixing vessel. For instance, the use of a traditional roller may not
be ideal, in that the hardness of the electroactive metal pushes the carbon toward the
walls of the roller, and the comparative softness of the carbon causes it to stick to the
inside surface of the mixing vessel. A gentle rotation or shaking, however, allows for
good premixing without causing agglomeration. Other methods of blending the
electroactive metal powder with the carbon may also be used, provided they prevent
agglomeration of the carbon in the resulting mixture. This allows for a substantially
uniform distribution of the carbon throughout the volume of the finished granule.
The mixture of the electroactive metal and alkali metal halide powders and
the carbon black is often flattened into a "pancake", which is then broken up into
millimeter-size granules. It is important to note that this compacted form need not be
completely flat. For instance, the edges may be rolled andor the thickness of the
flake may not be completely uniform. The granules can then be sized by various
techniques, if desired, so as to segregate materials of a preferred size, prior to being
loaded into a cathode chamber with the electrolyte.
For the purpose of this description, the size of the granule is measured along
its largest dimension. A convenient way to express the size is by way of the granule's
effective diameter "D,", which can be expressed as
wherein V, is the volume of the granule. In general, the effective diameter of the
granules is usually in the range of about 0.1 millimeter to about 5 millimeters. In
some specific embodiments, the range is between about 0.25 millimeter and about 3
millimeters. In other embodiments, the range is between 1 millimeter and 3
millimeters. Methods for determining the size of granules and other types of particles
are known in the art, e.g., the use of commercial particle size analyzers, as described
in U.S. Patent 7,247,407.
In some embodiments, the granule comprises nickel and iron. The granule
may also contain sodium chloride. In some embodiments, the granule may
additionally contain a metal iodide.
These granules are then included in a cathode chamber. The cathode may
then be included in an article that comprises a positive electrode, such as an energy
storage device, an unintermptable power supply device or an energy storage battery.
In some instances, the cathode chamber may contain about 50% granules
(e.g., containing perhaps equal amounts of metals and salts); and about 50% of molten
electrolyte material, by volume. In addition to the electrolyte salt discussed below,
the positive electrode composition may include a number of other constituents. As an
example, aluminum may be included, i.e., in a form other than its form in the
electrolyte salt, and other than as an aluminum halide. In other words, the aluminum
would usually be in elemental form, e.g., aluminum metal flakes or particles. The
aluminum may assist in improving the porosity of the cathode granules described
below. In some embodiments, the amount of elemental aluminum present in the
positive electrode composition is in a range from about 0.2 volume percent to about
0.5 volume percent, based on the volume of the positive electrode composition. In
another embodiment, the amount of aluminum present in the positive electrode
composition is in a range from about 0.25 volume percent to about 0.45 volume
percent.
In one embodiment, the positive electrode composition may further
comprise sulfur, in the form of molecular sulfur or a sulfur-containing compound. If
present, the level of sulfur is usually in the range from about 0.1 weight percent to
about 3 weight percent, based on the total weight of the positive electrode
composition. However, as described in Application 131034 184, it is sometimes
preferred that the positive electrode be substantially free of sulfur, i.e., containing, at
most, impurity levels.
The positive electrode composition may include other additives that
beneficially affect the performance of an energy storage device. Such performance
additives may increase ionic conductivity, increase or decrease solubility of the
charged cathodic species, improve wetting of a solid electrolyte, i.e., the separator, by
the molten electrolyte; or prevent ripening of the positive electrode micro-domains, to
name several utilities. Usually, though not always, the performance additive is
present in an amount that is less than about 1 weight percent, based on the total
weight of the positive electrode composition. Examples of such additives include one
or two additional metal halides, e.g., sodium fluoride or sodium bromide.
Another embodiment of this invention is directed to an article that includes a
positive electrode composition, as described herein. As one example, the article may
be in the form of an energy storage device. The device usually comprises (a) a first
compartment comprising an alkali metal; (b) a second compartment including a
positive electrode composition, as described herein; and (c) a solid separator capable
of transporting alkali metal ions between the first and the second compartments.
The device also includes a housing that usually has an interior surface
defining a volume. A separator is disposed in the volume. The separator has a first
surface that defines at least a portion of a first compartment, and a second surface that
defines a second compartment. The first compartment is in ionic communication with
the second compartment through the separator. As used herein, the phrase "ionic
communication" refers to the traversal of ions between the first compartment and the
second compartment, through the separator.
Referring to FIG. 1, an electrochemical cell 100 is provided. More
particularly, a front cross-sectional view 1 10 of the cell is depicted. The
electrochemical cell 100 includes a housing 1 12. The housing 1 12 usually has an
interior'surface 1 14, defining a volume. A separator 1 16 is disposed inside the
housing 112. The separator 1 16 has a first surface 1 18 that defines a first
compartment 120, e.g., usually an anode compartment. The separator has a second
surface 122 that defines a positive electrode compartment 124. An anode current
collector 126 (which may function as a shim, as well) is connected to the anode
compartment 120. A positive electrode current collector 128 is usually connected to
the positive electrode compartment 124. A positive electrode composition 130,
described herein but detailed in other figures, is disposed inside the positive electrode
compartment 124, as also described above. The working temperature of the
electrochemical cell 100, when it is a sodium-nickel chloride cell, is usually about
250-350 degrees Celsius. The person of skill will realize that the electrochemical cell
described above could also be modified such that the anode and cathode positions are
reversed. In these instances, the cathode structures are contained in the outside
compartment and the anode structures are on the inside.
The housing of the electrochemical cell can be sized and shaped to have a
cross-sectional profile that is square, polygonal, or circular, for example. Typically,
the aspect ratio of the housing is determined by the aspect ratio of the separator. In
many cases, the walls of the separator should be relatively slender, to reduce the
average ionic diffusion path length. In one embodiment, the height to effective
diameter ratio (2 x (square root of (cross-sectional areatpi)) of the housing is greater
than about 5. In some other embodiments, the ratio is greater than about 7. The
housing can be formed from a material that is a metal, ceramic, or a composite; or
some combination thereof. The metal can be selected from nickel or steel, as
examples; and the ceramic is often a metal oxide.
Typically, the anode compartment is empty in the ground state (uncharged
state) of the electrochemical cell. The anode is then filled with metal from reduced
metal ions that move from the positive electrode compartment to the anode
compartment through the separator, during operation of the cell. The anodic material,
(e.g., sodium) is molten during use. The first compartment (usually the anode
compartment) may receive and store a reservoir of anodic material.
Additives suitable for use in the anodic material may include a metallic
oxygen scavenger. Suitable metal oxygen scavengers may include one or more of
manganese, vanadium, zirconium, aluminum, or titanium. Other useful additives may
include materials that increase wetting of the separator surface 1 16 defining the anode
compartment, by the molten anodic material. Additionally, some additives or
coatings may enhance the contact or wetting between the separator and the current
collector, to ensure substantially uniform current flow throughout the separator.
The separator is usually an alkali metal ion conductor solid electrolyte that
conducts alkali metal ions during use between the first compartment and the second
compartment. Suitable materials for the separators may include an alkali-metal-betaalumina,
alkali-metal-beta"-alumina, alkali-metal-beta'-gallate, or alkali-metal-betangallate.
In various embodiments, the solid separator may include a beta-alumina, a
beta9'-alumina, a gamma alumina, or a micromolecular sieve such as, for example, a
tectosilicate, such as a feldspar, or a feldspathoid. Other exemplary separator
materials include zeolites, for example a synthetic zeolite such as zeolite 3A, 4A,
13X, ZSM-5; rare-earth silicophosphates; silicon nitride; or a silicophosphate; a beta'-
alumina; a betaw-alumina; a gamma alumina; a micromolecular sieve; or a
silicophosphate (NASICON: Na3Zr~Si2P012).
In some preferred embodiments, the separator includes a beta alumina. In
one embodiment, a portion of the separator is alpha alumina, and another portion of
the separator is beta alumina. The alpha alumina, a non-ionic-conductor, may help
with sealing and/or fabrication of the energy storage device.
The separator can be sized and shaped to have a cross-sectional profile that
is square, polygonal, circular, or clover leaf, to provide a maximum surface area for
alkali metal ion transport. The separator can have a width to length ratio that is
greater than about 1: 10, along a vertical axis 132. In one embodiment, the length to
width ratio of the separator is in a range of from about 1: 10 to about 15, although
other relative dimensions are possible, as described in S.N. 131034,184. The ionic
material transported across the separator between the anode compartment and the
positive electrode compartment can be an alkali metal. Suitable ionic materials may
include cationic forms of one or more of sodium, lithium and potassium.
The separator may be stabilized by the addition of small amounts of a
dopant. The dopant may include one or more oxides selected from lithia, magnesia,
zinc oxide, and yttria. These stabilizers may be used alone or in combination with
themselves, or with other materials. In one embodiment, the separator comprises a
beta alumina separator electrolyte (BASE), and may include one or more dopants.
As noted above, the separator is disposed within the volume of the housing
1 12. The separator may have a cross-sectional profile normal to a vertical axis 132 of
the housing 112. Examples of profileslshapes include a circle, a triangle, a square, a
cross, a clover leaf, or a star. Alternatively, the cross-sectional profile of the separator
can be planar about the vertical axis 132. A planar configuration (or one with a slight
dome) may be useful in a prismatic or button-type battery configuration, where the
separator is domed or dimpled. Similarly, the separator can be flat or undulated.
In one embodiment, the solid separator may include a shape which may be
flat, undulated, domed or dimpled, or comprises a shape with a cross-sectional profile
that may be an ellipse, triangle, cross, star, circle, cloverleaf, rectangular, square, or
multi-lobal. The separator can be a tubular container in one embodiment, having at
least one wall. The wall can have a selected thickness; and an ionic conductivity.
The resistance across the wall may depend inpart on that thickness. In some cases,
the thickness of the wall can be less than about 5 millimeters. A cation facilitator
material can be disposed on at least one surface of the separator, in one embodiment.
The cation facilitator material may include, for example, selenium, as discussed in
published U.S. Patent Application No. 2010/0086834, incorporated herein by
reference.
In some embodiments, one or more shim structures can be disposed within
the volume of the housing. The shim structures support the separator within the
volume of the housing. The shim structures can protect the separator from vibrations
caused by the motion of the cell during use, and thus reduce or eliminate movement of
the separator relative to the housing. In one embodiment, a shim structure functions
as a current collector.
In most embodiments, the energy storage device described herein may have
a plurality of current collectors, including negative (e.g., anode) current collectors,
and positive electrode current collectors. The anode current collector is in electrical
communication with the anode chamber, and the positive electrode current collector is
in electrical communication with the contents of the positive electrode chamber.
Suitable materials for the anode current collector include iron, aluminum, tungsten,
titanium, nickel, copper, molybdenum, and combinations of two or more of the
foregoing metals. Other suitable materials for the anode current collector may include
carbon. The positive electrode current collector may be in various forms, e.g., rod, a
sheet, wire, paddle may or mesh, formed fkom platinum, palladium, gold, nickel,
copper, carbon, or titanium. The current collector may be plated or clad. In one
embodiment, the current collector is free of iron.
As described for some embodiments in U.S. Application S.N. 131034,184,
referenced above, at least one of the alkali metals in the positive electrode may be
sodium, and the separator may be beta-alumina. In another embodiment, the alkali
metal may be potassium or lithium, with the separator then being selected to be
compatible therewith. For example, in embodiments where the ions include
potassium, silver, strontium, and barium cations, the separator material may include
beta alumina. In certain other embodiments, where lithium cations are used, a
lithiated borophosphate BP04-Li20, may be employed as the separator material.
A plurality of the electrochemical cells (each of which may be considered a
rechargeable energy storage device) can be organized into an energy storage system,
e.g., a battery. Multiple cells can be connected in series or parallel, or in a
combination of series and parallel. For convenience, a group of coupled cells may be
referred to as a module or pack. The ratings for the power and energy of the module
may depend on such factors as the number of cells, and the connection topology in the
module. Other factors may be based on end-use application specific criteria.
In some particular embodiments, the energy storage device is in the form of
a battery backup system for a telecommunications ("telecom") device, sometimes
referred to as a telecommunication battery backup system (TBS). The device could
be used in place of (or can complement) the well-known, valve-regulated lead-acid
batteries (VRLA) that are often used in a telecommunications network environment as
a backup power source. Specifications and other system and component details
regarding TBS systems are provided from many sources, such as OnLine Power's
"Telecommunication Battery Backup Systems (TBS)"; TBS-TBS6507A-81312004 (8
pp); and "Battery Backup for Telecom: How to Integrate Design, Selection, and
Maintenance" ; J. Vanderhaegen; 0-7803-8458-X/04,02004 IEEE (pp. 345-349).
Both of these references are incorporated herein by reference.
In other embodiments, the energy storage device is in the form of an
unintermptable power supply device (UPS). The primary role of most UPS devices is
to provide short-term power when the input power source fails. However, most UPS
units are also capable in varying degrees of correcting common utility power
problems, such as those described in Patent Application S.N. 131034,184. The
general categories of modem UPS systems are on-line,line-interactive,orstandby. An
on-line UPS uses a "double conversion" method of accepting AC input,rectifyingto
DC for passing through therechargeable battery, then inverting back to 120Vl230V
AC for powering the protected equipment. A line-interactive UPS maintains the
inverter in line and redirects the battery's DC current path from the normal charging
mode to supplying current when power is lost. In a standby system, the load is
powered directly by the input power; and the backup power circuitry is only invoked
when the utility power fails. UPS systems including batteries having electrode
compositions as described above may be ideal in those situations where high energy
density within the battery is a requirement.
Another embodiment of this invention is directed to a method for the
preparation of an energy storage device, as mentioned previously. In some specific
embodiments, the method comprises providing a housing having an interior surface
defining a volume; disposing a separator inside the housing, wherein the separator has
a first surface that defines at least a portion of a first compartment, and a second
surface that defines a second compartment. The first compartment is in ionic
communication with the second compartment through the separator. The method
includes the step of preparing a positive electrode composition (as described
previously), comprising granules which themselves comprise at least one electroactive
metal, at least one alkali metal halide and carbon black; and disposing this material in
the second compartment. Other steps to fully fabricate the device can then be
undertaken, e.g., filling the cathode compartment with electrolyte, compartmentsealing
steps, electrical connection steps, and the like. The method may include
taking the battery or other type of energy storage device through a plurality of
chargeldischarge cycles, to activate or condition the positive electrode composition
material.
The energy storage devices illustrated herein may be rechargeable over a
plurality of charge-discharge cycles. In another embodiment, the energy storage
device may be employed in a variety of applications; and the plurality of cycles for
recharge is dependent on factors such as charge and discharge current, depth of
discharge, cell voltage limits, and the like.
The energy storage system described herein can usually store an amount of
energy that is in a range of from about 0.1 kilowatt hour (kWh) to about 100 kWh.
An illustration can be provided for the case of a sodium-nickel chloride energy
storage system (i.e., a battery) with a molten sodium anode and a beta-alumina solid
electrolyte, operating within the temperature range noted above. In that instance, the
energy storage system has an energy-by-weight ratio of greater than about 100 Watt-
Hours per kilogram, andlor an energy-by-volume ratio ofgreater than about 200 Watt-
Hours per liter. Another embodiment of the energy storage system has a specific
power rating of greater than about 200 Watts per kilogram; andlor an energy-byvolume
ratio ofgreater than about 500 Watt-Hours per liter. The power-to-energy
ratio is usually in the range of about 1 : 1 hour-' to about 2: 1 hour-'. (It should be
noted that the energy term here is defined as the product of the discharge capacity
multiplied by the thermodynamic potential. The power term is defined as the power
available on a constant basis, for 15 minutes of discharge, without passing through a
voltage threshold sufficiently low to reduce the catholyte).
Other features associated with the energy storage system may constitute
embodiments of this invention; and some are described in the referenced Application
S.N. 131034,184. As an example, the system can include a heat management device,
to maintain the temperature within specified parameters. The heat management
device can warm the energy storage system if too cold, and can cool the energy
storage system if too hot, to prevent an accelerated cell degradation. The
heatmanagement system includes a thaw profile that can maintain a minimal heat
level in the anode and positive electrode chambers, to avoid freezing of cell reagents.
Some other embodiments are directed to an energy management system that
includes a second energy storage device that differs from the first energy storage
device. This dual energy storage device system can address the ratio of power to
energy, in that a first energy storage device can be optimized for efficient energy
storage, and the second energy storage device can be optimized for power delivery.
The control system can draw from either energy storage device as needed, and charge
back either energy storage device that needs such a charge.
Some of the suitable second energy storage devices, for the power platform,
include a primary battery, a secondary battery, a fuel cell, and/or an ultracapacitor. A
suitable secondary battery may be a lithium battery, lithium ion battery, lithium
polymer battery, or a nickel metal hydride battery.
EXAMPLES
The examples presented below are intended to be merely illustrative and
should not be construed to be any sort of limitation on the scope of the claimed
invention. Unless specified otherwise, all of the components are commercially
available from common chemical suppliers.
A nickeVsodium chloride based energy cell was assembled, using the
following materials:
Table 1
Two electrochemical cells were constructed and tested to compare the
recharging time of a control cell with a cell containing a cathode composition of the
disclosure. These examples had substantially similar components, except for the
replacement of a portion of the electroactive metal (nickel) with the corresponding
volume of carbon black in the experimental cell. In one instance, the control cell does
not contain carbon, while the experimental cell has had 15% of the nickel mass of the
control cell replaced by an equivalent volume of carbon black.
The cells were then tested in the following manner. The cells are tested at
300°C. Cells are discharged at 9.5W for 4 hours and then recharged to 2.67V. Every
twenty cycles there is an additional deeper discharge (data not shown).FIG. 2 shows
Properties
97.9 percent pure, 0.6 square meters per
gram surface area, 2.2 to 2.8
micrometers particle size)
99.99 percent pure
-99 percent pure
-100+325 mesh particle size, 99.97
percent pure
less than 10 micrometers particle size,
99.9 percent pure
-99 percent pure
99.9 percent pure
Ash content <100ppm
Material
Nickel 255 (metal
nickel powder,
Ni)
Sodium Chloride
(NaCl)
Sodium Fluoride
(NaF)
Aluminum
powder (Al)
Iron (metal iron
powder) (Fe)
Sodium iodide
(NaI)
Iron sulfide (FeS)
Carbon
Source
Inco Special
products
Custom Powders
Ltd, UK
Sigma Aldrich
Alfa Aesar Item
#429 19
Alfa Aesar Item
#00 170,
Sigma Aldrich
Alfa Aesar Item
# 14024
Cabot XC17
Cabot LITXSO
the length of time it takes to recharge the cell after a discharge. The data shown is an
average of three cells for both the control (squares) and experimental (circles). As
shown in FIG. 2, the required recharging time for the experimental cell is shorter than
that required for the control cell over the measured period of approximately three
months. Further, the slope of the curve is indicative of the amount of cell degradation,
that is, the shallower the slope, the slower the degradation rate of the cell. As FIG. 2
shows, the experimental cell has a shallower slope than does the control cell,
indicating that less degradation is occumng in the experimental cell over this time
period.
While several aspects of the present disclosure have been described and
depicted herein, alternative aspects may be effected by those skilled in the art to
accomplish the same objectives. Accordingly, it is intended by the appended claims
to cover all such alternative aspects as fall within the true spirit and scope of the
disclosure.
The present invention has been described in terms of some specific
embodiments. They are intended for illustration only, and should not be construed as
being limiting in any way. Thus, it should be understood that modifications can be
made thereto, which are within the scope of the invention and the appended claims.
Furthermore, all of the patents, patent applications, articles, and texts which are
mentioned above are incorporated herein by reference.

WE CLAIM:
1. A cathode composition, comprising granules which themselves
comprise at least one electroactive metal, at least one alkali metal halide, and carbon
black.
2. The composition of claim 1, wherein said carbon black has a surface
area between about 50 m2/gram and about 1000 m2/gram.
3. The composition of claim 2, wherein said carbon black has a surface
area between about 50 m21gram and about 600 m2/gram.
4. The composition of claim 1, wherein the electroactive metal is selected
from the group consisting of titanium, vanadium, niobium, molybdenum, nickel,
cobalt, chromium, copper, manganese, silver, antimony, cadmium, tin, lead, iron,
zinc, and combinations thereof.
5. The composition of claim 1, wherein the alkali metal halide comprises
at least one halide of sodium, potassium, or lithium.
6. The composition of claim 1, wherein the volume-to-volume ratio of the
carbon black to the electroactive metal is between about 5:95 and about 70:30,
inclusive.
7. The composition of claim 6, wherein said ratio is between 10:90 and
25:75, inclusive.
8. The composition of claim 1, wherein said carbon is deposited
throughout the volume of the granule in a substantially uniform distribution.
9. The composition of claim 1, wherein said carbon black is thermally
treated carbon black.
10. The composition of claim 1, wherein said carbon black is chemically
treated carbon black.
1 1. The composition of claim 1, wherein said granule comprises nickel and
iron.
12. The composition of claim 1, wherein said granule comprises nickel,
iron and sodium chloride.
13. The composition of claim 1, wherein said granule comprises nickel,
iron, sodium chloride and a metal iodide.
14. The composition of claim 8, wherein said granule comprises nickel,
iron, sodium chloride and a metal iodide.
15. A method of forming a cathode material, comprising:
providing a powder comprising at least one electroactive metal and at least
one alkali metal halide;
blending carbon black into said powder, wherein said carbon black becomes
interspersed within said powder to form a non-agglomerated mixture; and
forming granules from said mixture.
16. The method of claim 15, wherein said carbon is deposited throughout
the volume of the granule in a substantially uniform distribution.
17. The method of claim 15, wherein said method further comprises:
compacting said mixture into a flattened form; and
fragmenting said flattened form into granules.
18. An article, comprising a positive electrode, which itself comprises
granules comprised of at least one electroactive metal, at least one alkali metal halide
and carbon black.
19. The article of claim 18, in the form of an energy storage device which
itself comprises a cathode material, wherein said cathode material comprises granules
comprising at least one electroactive metal, at least one alkali metal halide, and
carbon black.
20. The article of claim 19, characterized as being rechargeable over a
plurality of cycles.