U.S. patent application number 09/162428 was filed with the patent office on 2002-11-28 for high energy density boride batteries.
Invention is credited to AMENDOLA, STEVEN.
Application Number | 20020177042 09/162428 |
Document ID | / |
Family ID | 26858752 |
Filed Date | 2002-11-28 |
United States Patent
Application |
20020177042 |
Kind Code |
A1 |
AMENDOLA, STEVEN |
November 28, 2002 |
HIGH ENERGY DENSITY BORIDE BATTERIES
Abstract
Borides generally can produce a cell with a high energy density.
High power densities are also achievable using borides that are
reasonably good conductors of electricity. High density is
important to achieve high energy density. Another important factor
is lower molecular weight per available electron. The borides
generally provide a favorable balance of these factors compared to
a number of other materials, such as lithium or zinc. Individual
borides have other important characteristics. Titanium diboride is
safe. The inclusion of a halide, particularly fluoride, in the
anodic storage medium signficantly improvers performance.
Inventors: |
AMENDOLA, STEVEN; (OCEAN,
NJ) |
Correspondence
Address: |
JOHN W FREEMAN
FISH & RICHARDSON
225 FRANKLIN STREET
BOSTON
MA
021102804
|
Family ID: |
26858752 |
Appl. No.: |
09/162428 |
Filed: |
September 28, 1998 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09162428 |
Sep 28, 1998 |
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08829497 |
Mar 27, 1997 |
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5948558 |
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Current U.S.
Class: |
429/218.1 ;
429/101; 429/50 |
Current CPC
Class: |
H01M 4/582 20130101;
H01M 4/00 20130101; H01M 4/38 20130101; H01M 6/04 20130101; H01M
4/388 20130101; H01M 12/04 20130101 |
Class at
Publication: |
429/218.1 ;
429/50; 429/101 |
International
Class: |
H01M 004/58 |
Claims
What is claimed is:
1. A battery comprising an anode and a cathode in electrical
communication, the anode including an anodic electrochemical
storage medium comprising as a reduced species: a) boron; b) at
least one reduced boron-containing compound; or c) both; the
reduced species being oxidizable to an oxidized boron-containing
compound in a reaction which yields an electric current, the
oxidized boron-containing compound being soluble in said
electrochemical storage medium as said battery is discharged.
2. The storage medium of claim 1 in which the storage medium is in
an aqueous system.
3. The battery of claim 2 in which the reduced boron-containing
compound is a boride.
4. The battery of claim 3 in which the anodic medium comprises at
least one halide.
5. The battery of claim 4 in which the halide is fluoride.
6. The battery of claim 5 in which the anodic storage medium
comprises sodium fluoride.
7. The battery of claim 4 in which the halide is chloride.
8. The battery of claim 7 in which the halide is sodium or
potassium chloride.
9. The battery of claim 5 or claim 6 in which the anodic medium
further comprises chloride.
10. The battery of claim 3 in which the boride is conductive.
11. The battery of claim 3 in which the boride is a transition
metal boride.
12. The battery of any one of claims 3, 4, 5, or 7 in which the
reduced boron-containing compound is titanium diboride.
13. The battery of any one of claims 3, 4, 5, or 7 in which the
reduced boron-containing compound is vanadium diboride.
14. A battery according to any one of claims 3, 4, 5, or 7 in which
the cathode comprises a structure that is exposed to oxygen.
15. The battery of claim 14 in which the cathode structure is
exposured to air.
16. The battery of claim 14 in which cathode is exposed to an
aqueous electrolyte, and oxygen is reduced to --OH.sup.-.
17. The battery of any one of claims 3, 4, 5, or 7 in which in
which the cathode comprises a structure that is exposed to oxygen,
and the reduced boron containing compound is titanium diboride,
vanadium diboride, or both.
18. The battery of claim 1 or claim 3 in which the anodic medium
further comprises a borohydride in addition to said boron or said
reduced boron-containing compound.
19. The battery of claim 1 or claim 3 in which the anodic medium
further comprises a metallic boride.
20. The battery of claim 19 in which the metallic boride is FeB or
NiB.sub.2.
21. The battery of claim 1 or claim 3 in which the anodic storage
medium further comprises a conductivity enhancer which itself is
oxidized to provide addition current during oxidation of said
reduced boron-containing compound.
22. The battery of claim 1 in which the anodic storage medium
further comprises graphite.
23. The battery of claim 1 in which the anodic storage medium
further comprises an inert conductivity enhancer.
24. The battery of claim 3 in which the anodic medium comprises a
combination of borides.
25. The battery of claim 5 in which the oxidized boron-containing
compound is a boron halide or a boron oxyhalide.
26. The battery of claim 1 in which the oxidized boron-containing
compound is a borate or polyborate.
27. The battery of claim 2 in which the oxidized boron-containing
compound is conductive.
28. The battery of claim 3 in the reduced boron-containing compound
is an aluminum boride.
29. The battery of claim 3 in which the boride is a boride selected
from the list in table 1.
30. The battery of any one of claims 4, 5, or 7 in which the anodic
electrochemical storage medium further comprises EDTA, in addition
to said boron or reduced boron-containing compound.
31. The battery of claim 3 in which the oxidized boron-containing
compound includes a metal oxide and a borate.
32. The battery of claim 3 in which the oxidized boron-containing
compound contains a combination of corresponding metal oxides,
halides and oxyhalides.
33. The battery of claim 3 in which the anodic storage medium has a
pH above 8.5.
34. The battery of claim 33 in which the anodic storage medium has
a pH above 11.0.
35. A battery according to any one of claims 3, 4, 5, or 7 in which
the cathode comprises an oxygen-containing oxidizing compound.
36. A battery according to claim 35 in which the oxidizing compound
is selected from ferrates, MnO.sub.2, CrO.sub.3, KMnO.sub.4,
LiCoO.sub.2, NIOOH, peroxides, perhalates, perchlorate, chlorates,
bromates, perbromates, iodates, periodates, hypochlorites
chlorites.
37. A battery according to claim 1 in which the cathode comprises a
non-oxygen containing oxidizing compound.
38. A battery according to claim 37 in which the non-oxygen
compound comprises a high valency metal.
39. A battery according to claim 37 in which the non-oxygen
compound is an interhalogen.
40. A battery according to claim 37 in which the non-oxygen
compound is a metal-halide in which the metal can be reduced to a
lower valence.
41. A method of generating a current by contacting a load to the
battery of claim 1.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is a continuation in part of my co-pending
application USSN 08/829,497, filed Mar. 27, 1997, which is hereby
incorporated by reference.
FIELD OF THE INVENTION
[0002] This invention is in the general field of electrochemical
conversion using cells, particularly high energy density
batteries.
BACKGROUND OF THE INVENTION
[0003] Many devices that require electricity from a battery are
limited in usefulness by the battery's lifetime. Both weight and
size (in other words, energy density) can be limiting factors on
battery life, particularly for small devices. In particular hearing
aids and many other devices would be enhanced by increasing the
battery's energy density. For example, many devices could be
further miniaturized if a smaller battery that gave reasonable
energy density were available.
[0004] Accordingly, there is a general need to generate as much
electrical energy as possible from a battery having a limited
volume.
SUMMARY OF THE INVENTION
[0005] I have discovered that the use of certain borides can
produce a high energy density cell. High power densities are also
achievable, for example, by using borides that are reasonably good
conductors of electricity. I have further discovered that the
performance of borides such as titanium boride is significantly
improved by adding a halide, such as a fluoride, in the electrolyte
system. Without wishing to bind myself to a specific theory, I
conclude that even though the borides or the resulting borates in
question may have desirable properties,--e.g., high energy density
and high conductivity and aqueous compatibility, if the resulting
borate (e.g., titanium borate) is very insoluble, it can coat the
boride and thereby degrade battery performance. In particular, such
coating reduces the available power and it causes the battery to
fail prematurely, before substantially all of the material is
oxidized. Batteries having a halide- (particularly fluoride-)
containing electrolyte will perform substantially better. Again,
without binding myself to a particular theory, if fluoride ion is
present in this system, the highly soluble complex anions of
titanium hexafluoride and boron tetrafluoride are formed. These
soluble ions now diffuse away from the boride particle and allow
further reaction until the boride is more effectively consumed.
[0006] Accoringly, one aspect of the invention generally features a
battery comprising an anode and a cathode in electrical
communication; the anodic electrochemical storage medium comprises
as a reduced species: a) boron; b) at least one reduced
boron-containing compound; or c) both. The reduced species is
oxidizable to an oxidized boron-containing compound in a reaction
which yields an electric current, and the oxidized boron-containing
compound is soluble in the electrochemical storage medium as the
battery is discharged.
[0007] The battery is particularly adapted to the use of aqueous
systems for the storage medium. Particularly preferred reduced
boron-containing compounds are borides. As noted, it is
particularly useful to include a halide (e.g. a fluoride such as
may be provided by sodium fluoride) in the the anodic medium.
Alternatively, or in combination with the fluoride, the halide may
be chloride (e.g., sodium or potassium chloride).
[0008] Preferred borides are conductive to enhance the overall
conductivity and therefore the deliverable current. Transition
metal borides are particularly preferred. Titanium diboride and
vanadium diboride are preferred.
[0009] Preferred cathodes comprise a structure that is exposed to
oxygen (e.g. to air), such as those in which cathode is also
exposed to an aqueous electrolyte, and oxygen is reduced to
--OH.sup.-.
[0010] The anodic medium may further comprise a borohydride in
addition to boron or the reduced boron-containing compound. It may
also comprise a metallic boride such as FeB or NiB.sub.2. The
anodic storage medium may also further comprise a conductivity
enhancer such as graphite. The enhancer may itself be oxidized to
provide addition current during oxidation of the reduced
boron-containing compound, or it may be inert. The anodic medium
may comprises a combination of borides. For example, mixtures of
the borides are contemplated to achieve desired combinations of
energy density and conductivity, depending on the application. For
example, a low conductivity boride may be mixed with a higher
conductivity boride to achieve a desired energy density and
conductivity.
[0011] The oxidized boron-containing compound may be a boron halide
or a boron oxyhalide, a borate or polyborate. Preferably, the the
oxidized boron-containing compound is conductive.
[0012] Other borides that may serve as the reduced boron-containing
compound include aluminum borides. See also, table 1.
[0013] The anodice stoarage medium may further comprise EDTA, in
addition to the boron or reduced boron-containing compound. The
oxidized boron-containing compound may include a metal oxide and a
borate. The oxidized boron-containing compound may contains a
combination of corresponding metal oxides, halides and
oxyhalides.
[0014] Typically the storage medium is an aqueous, but the
invention may also be used in non aqueous systems. Another way to
enhance conductivity and thereby increase current is to use a
conductive electrolyte. Conductivity enhancers, such as
borohydrides or metallic borides, may also be added to the medium
to both enhance conductivity and to contribute, to some extent, to
electrical output. Alternatively, inert conductivity enhancers,
such as graphite or other conductive carbon formulations may be
used.
[0015] The electrochemical reaction is improved by alkaline pH, so
the storage medium preferably has a pH above 8.5, and most
preferably it has a pH above 11.0. Typically, an alkali metal
hydroxide is added to the storage medium to provide conductivity as
well as to control pH.
[0016] As an alternative to the so-called air or breathing cathode,
the cathode may include an oxygen-containing oxidizing compound
such as compounds is selected from ferrates, MnO.sub.2, CrO.sub.3,
KMnO.sub.4, LiCoO.sub.2, NiOOH, peroxides, perhalates, perchlorate,
chlorates, bromates, perbromates, iodates, periodates,
hypochlorites chlorites.
[0017] Alternatively, the cathode may comprise a non-oxygen
containing oxidizing compound, such as a high valency metal or an
interhalogen or a metal-halide in which the metal can be reduced to
a lower valence.
[0018] The invention also features methods of generating a current
by contacting a load to any of the above described batteries.
[0019] Without binding myself to a specific mechanism of action or
limiting myself to one specific advantage of the invention, high
(mass) density is important to achieve high energy density. Another
important factor is lower weight per available mole of electrons.
The borides generally provide a favorable balance of these factors
compared to a number of other materials, such as lithium or
zinc.
[0020] Moreover, individual borides have other important
characteristics. Titanium diboride is safe and environmentally
acceptable--the final products of titanium boride discharge in a
basic medium are essentially borax and titanium dioxide, both of
which have a relatively low environmental impact. Even the staring
materials, the borides themselves, are somewhat refractory and also
relatively benign environmentally. Other borides, such as vanadium
boride with a high density of 5.1 g/cc, may be used.
BRIEF DESCRIPTION OF THE DRAWING
[0021] FIG. 1 is a diagrammatic view, in section, of a single use
battery according to the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0022] Boride-containing anode materials provide high energy. When
combined in a battery, e.g., with an air breathing electrode as the
cathode, high energy density can be achieved. Other suitable
oxidizers may also be utilized as a cathode in a battery that has a
boride-containing cathode.
[0023] Using titanium diboride as an example, the half reactions
taking place in the battery are as follows:
2TiB.sub.2+20OH--+20e--=2TiO.sub.2+2B.sub.2O.sub.3+10H.sub.2O
(anode) (1)
5O.sub.2+10H.sub.2O=20OH--+20e-- (cathode) (2)
[0024] These two reactions result in the net reaction of:
2TiB.sub.2+5O.sub.2=2TiO.sub.2+2B.sub.2O.sub.3 (net) (3)
[0025] While not predicting 100% efficiency, it should be noted
that the amount of energy (known as .DELTA.G) theoretically
available from reaction (3)--over 4,000 kJ per 2 moles of titanium
diboride (about 139.4 grams)--is very high, more than 28 Megajoules
per kilogram and more than 140 megajoules per liter.
[0026] The chemistry of the boride compounds is complex. There are
many non-stoichiometric compounds of boron with the elements. For
example, while equations (1) and (3) use TiB.sub.2, the boride can
be any boride or mixture of borides, including elemental boron. The
anode may also include other compounds which would enhance any of
the performance parameters of the battery, as desired.
[0027] Examples of other borides that are suitable for use in the
battery generally fall into the following classes of compounds:
[0028] A. Alkali metal borides: Group Ia (group 1) borides;
[0029] B. Alkaline metal borides: Group IIa (group 2) borides;
[0030] C. Group IIIa (Group 11) borides;
[0031] D. Group IVa (Group 12) borides;
[0032] E. Transition metal borides including groups 1b to 8b
(groups 3 to 10);
[0033] F. Lanthanide and actinide group borides
[0034] More specifically the compounds include those listed
below.
1TABLE 1 Borides Lithium borides; Beryllium boride; Boron; Boron
carbides; Boron nitrides; Sodium borides; Magnesium borides;
Aluminum borides; Silicon borides; Phosphorus borides; Potassium
borides; Calcium borides; Scandium borides; Titanium borides;
Vanadium borides; Chromium borides; Manganese borides; Iron
borides; Cobalt borides; Nickel borides; Copper borides; Gallium
borides; Arsenic Borides; Rubidium borides; Strontium borides;
yttrium borides; zirconium borides; niobium borides; molybdenum
borides; technetium borides; ruthenium borides; rhodium borides;
palladium borides; silver borides; cesium borides; barium borides;
lanthanum borides; cerium borides; praseodymium borides; neodymium
borides; promethium borides; samarium borides; europium borides;
gadolinium borides; terbium borides; dysprosium borides; holmium
borides; erbium borides; thulium borides; ytterbium borides;
lutetium borides; hafnium borides; tantalum borides; tungsten
borides; rhenium borides; osmium borides; iridium borides; platinum
borides; thorium borides; uranium borides; plutonium borides.
[0035] The existence of useful non stoichiometric boron compounds
means that the ratio of the elements represented as E.sub.xB.sub.y
will vary considerably without deviating from the teachings of this
patent. Elemental boron as well as the other element (E) may be
added as a components of the anode.
[0036] For borides that react with water, the system used is
non-aqueous system or it is stored in a mode which prevents
activation until the electrolyte is allowed to come into contact
with the boride. Additionally, as a general rule for applying the
above list, the energy density will tend to decrease going down and
to the right-hand side of the periodic chart. Reactivity with water
generally tends to occur only with the first two columns on the
left of the chart. Higher electrically conductivities tend to be
found in the center of the chart, with many of the transition metal
borides exhibiting high or even metallic conductivities. It is the
very wide range of properties of these compounds that gives the
wide range of diversity of the finished batteries.
[0037] A wide array of electrolytes and oxidizers may be
incorporated in the battery to complement the boride compounds that
can be used. Examples are: water/sodium hydroxide systems; alkali
metal hydroxides such as lithium hydroxide; sodium hydroxide;
potassium hydroxide; rubidium hydroxide; cesium hydroxide;
tetraorganoammonium hydroxides of the general formula
R.sub.4NOH--where the R groups can be the same or different on the
same molecule--such as tetramethylammonium hydroxide; and
glycerin/water/boric acid or borates.
[0038] The above described anode materials or combination of
materials may be used in a battery whose cathode is a suitable
oxidizing agent. Among the suitable cathode materials are: cathodes
which use molecular oxygen (O.sub.2) such as direct air breathing
electrodes; cathodes which include a oxidizing agent, e.g., any
material that provides oxygen such as ferrates MnO2, CrO3, KMnO4,
NiOOH, peroxides, perhalates, perchlorate, chlorates, bromates,
perbromates, iodates, periodates, hypochlorites chlorites, high
valence metal halides, etc. In general one can use the halates of
the formula HAL.sub.xOy.sub.n where the oxidation state of the
halogen (HAL) is from +1 to +7 and the number of oxygen atoms is
such that the charge of the anion is usually -1 so the value of n
is usually 1. Other materials may be based on halogens such as
fluorine or high valency metal fluorides or chlorides materials
such as NiF.sub.3 or interhalogens such as IF.sub.5 or ClF.sub.3,
etc. Non aqueous systems may be used for halogen-based materials
that are water sensitive. For example, such systems may use organic
solvents that are conductive (or can be made conductive by the
addition of enhancers).
[0039] An important feature of this chemistry is its ability to
operate at ambient or moderate temperatures, avoiding the use of
molten salts and allowing the batteries to be used in many
applications such as consumer products. By establishing a desired
reaction rate, one can make the current output suitable for the
given application. This rate is determined by the combination of
factors previously mentioned, the key ones being electrolyte
composition, conductivity of the entire cell, the anode and cathode
materials.
[0040] For example, highly alkaline aqueous systems (pH over 9.0
and preferably over 11.0) will provide a more rapid reaction, and,
all other things being equal, if ionic species in the electrolyte
are a factor limiting conductivity, higher pH will also increase
conductivity and current. Those skilled in the art will also
understand that a variety of current enhancers can be used as
desired in a given application. For example, inert
(non-participatory) materials such as graphite or more ionic
electrolytes may be used. In some applications, it may be desirable
to use a current enhancer that itself participates in oxidation,
thus contributing, at least to some extent, to the current density
as well as conductivity. In those cases, e.g., metallic borides
(e.g., NiB.sub.2, FeB, or other borides) may be added.
[0041] Those skilled in the art will understand, therefore, that
the invention may be adapted to many different battery applications
with differing volume limitations and current requirements.
[0042] One preferred way to provide the boride compound in a
battery is to make a hydroxide (NaOH, LiOH) slurry (paste) that
contacts the anode. The cathode may be an air breathing electrode.
For example, the cathode may be a air-permeable plastic in contact
with felt comprising a metal powder, such as nickel, platinum, or
silver. Air oxidizes the metal powder, in a reaction that can be
coupled with the boride-containing anode storage medium (e.g., the
slurry described above). Electrosynthesis Corp. of Lancaster, N.Y.
sells air breathing cathodes that are suitable for some
applications.
[0043] In FIG. 1, a button battery 10 is the type of battery which
is used in a hearing aid or other electronic device. Battery 10
includes a metal cap providing the negative terminal, which covers
a TiB.sub.2/KOH paste 14 contained in a metal cup 16. The bottom of
cup 16 includes very small air breathing holes which allow air to
reach air breathing cathode 20. Cathode 20 includes an air
permeable plastic base 22 covered by a felt layer 24. Felt layer 24
is impregnated with a metal powder (e.g., Ag, Ni, Pt, etc.) that
reacts with O.sub.2 in the air. A metal (e.g. Ni) mesh 26 is also
included in the felt layer to improve conductivity.
[0044] Alternative cathodes include electrodes based on MnO.sub.2
as a redox material.
[0045] Selection of boride and the use of halides
[0046] The choice of boride types may be limited by the electrolyte
system. As the boride is oxidized during discharge an oxidized
borate is formed. If this borate is not soluble the boride
particles will become coated with an insulating layer of this
borate and the reaction will shut down before all the boride is
oxidized. As a result, the battery may `die` well before all the
energy has been extracted, thus undermining one of the important
benefits of using borides, i.e., high energy. The use of fluorides
or other halides in the electrolyte system will prevent by forming
soluble complexes with a wider variety of borates and metals.
[0047] The invention effectively oxidizes most or all of the
borides in a one way reaction that yields greater energy in a
system that is not rechargeable, and it allows for the use of an
aqueous system and still with several oxidizing agents for
cathodes.
[0048] A battery that uses a metal boride as an anode will
ultimately convert this material to either a combination of the
metal oxide and boron oxide; and/or the metal borate. For materials
where the metal oxides or borates are soluble the discharge
reaction is not hindered by the active particles becoming coated
with a nonconductor and therefore not further useful in the
discharge. One of the best candidate borides for this system is
titanium diboride, which does indeed for non-conductive insoluble
reaction products. Therefore to prevent this problem an electrolyte
system using fluoride to complex the initial oxidation products
results in a cell that produces both superior energy and power
density verses a simple hydroxide electrolyte.
[0049] While the battery is discharging the reaction of the anode
is (for TiB2) as an example,
TiB.sub.2+2O.sub.2=TiO.sub.2+B.sub.2O.sub.3 (1)
[0050] and
2TiB.sub.2+5O.sub.2=Ti(BO.sub.2).sub.4+TiO.sub.2 (2)
[0051] The titanium dioxide and titanium borate are both insoluble
and will therefore hinder the completion of this reaction. However,
if ions are available in the electrolyte that allows the formation
of soluble complexes they will form. For example with fluoride
below
TiB.sub.2+O.sub.2+14F.sup.-+5H.sub.2O=[TiF.sub.6].sup.2-+2BF.sup.4-+10OH.s-
up.- (3)
[0052] Notice that all the species are ionic and therefore soluble
and capable of carrying charge.
[0053] It is a further teaching that even though equation 3
stipulates 14 fluorides that the fluorides can be used several
times since over time the fluoro complexes in the presence of base
eventually turn into the products of equation 1 so that the net
consumables are still those of equation 1. The hydrolysis reactions
are as follows.
[TiF.sub.6]+4OH.sup.-=TiO.sub.2+2H.sub.2O+6F.sup.- (4)
2BF.sup.4-++6OH.sup.-=B.sub.2O.sub.3+3H.sub.2O+8F.sup.- (5)
[0054] As can be seen the addition of equations 3, 4 and 5 yield
equation 1.
Examples of halide-containing storage media
Example 1
[0055] A standard coin cell (2325) 23 mm diameter 2.5 mm thickness
is fitted with an Johnson Matthey GDE 1 0 1 gas diffusion electrode
used as an standard Pt catalyzed air electrode is placed in the
cathode can with two 0.0625" dia holes for air passage. Over this
is placed a Nafion 117 membrane disk. A mixture containing 85% by
TiB2 and 15% of a solution of 40% NAOH is prepared. 1.5 gms of this
mixture was scaled into the anode compartment of the cell. A cyclic
voltammagram (using an EG&G Model 273A Potentiostat) was run on
the cell. The Open circuit voltage was 1.19 volts. The short
circuit current was 35 milliamps. Then a constant voltage of 1.0
was maintained--The initial current was 12 milliamps. This held for
12 minutes the current started to drop over the next 41 minutes to
a level of 2.1 milliamps which was sustained for the next three
hours with a final current of 1.9 milliamps at which point the test
was terminated.
Example 2
[0056] An identical air breathing coin cell as used in example 1
above was assembled. However 0.2 grams of NaF was added to the
anode mixture and the cell sealed as before. A cyclic voltammagram
was = as before. The open circuit voltage was 1.30 volts and the
short circuit current now jumped to 364 milliamps. At the constant
voltage of 1.0 the current was now 77 milliamps. Further no
"shoulder" occurred as before but a gentle decrease in the current
to 69 milliamps was observed over the four hour test at which time
the test was ended.
[0057] As is readily apparent the addition of the fluoride made a
substantial difference in the performance of the battery. This
difference is very important in the applications that the battery
will be suitable for. Since borides are a very high-energy source
it is very important that this high-energy source be utilized in as
many applications as possible. Since borides are high density
TIB.sub.2 for instance has a theoretical energy density of over
40,000-watt hours per liter. This is over 4x higher than the
theoretical for lithium and is higher than any non-nuclear battery
available.
[0058] Using the above information it will be obvious to those
skilled in the art what additional ions would be suitable to form
complexes with the corresponding metal boride. For example chloride
will also work in place of fluoride in the above example. However,
chloride has a slightly less aff@ty to complex with Ti or B and
therefore would not produce quite as good an improvement as shown
in Example 2. Nevertheless the improvement may well be enough for
many applications. Additionally, chloride are more economical than
fluorides. The other halogens (Br.sup.- and I.sup.-) are also
suitable.
[0059] Of course beside the sodium cation as used in sodium
fluoride above any soluble form of fluoride that provides fluoride
ions is suitable, such as Li.sup.+, K.sup.+, NH.sup.4+, Cs.sup.+,
Ag.sup.+, and also quaternary ammonium salts
(RN.sub.4.sup.+F.sup.-) etc. Of course materials that bind or
precipitate fluoride (Other than the boride itself) ions such as
calcium are to be avoided. Of course if chloride is used then
calcium is an acceptable component. Other suitable complexing
agents are other anions such as sulfide S.sup.-2, cyanide CN.sup.-,
thiocyanide SCN.sup.-, cyanto OCN.sup.-, etc. which enhance the
solubility of either the metal or the boride moiety of the metal
boride will also be apparent based on a simple example of the
solubility's of the corresponding compounds. Further general
chelating agents such as EDTA that would complex with several of
the transition metal elements that the borides may be made from.
This is important since mixtures of borides may also be used in the
anode to achieve certain effects. For example nickel boride added
to titanium boride could increase the conductivity of the cell. As
the nickel boride is oxidized the nickel could be chelated by the
EDTA or other similar chelating type agents thereby preventing
interference from insoluble nickel oxides or borates.
* * * * *