 |
Description  |
|
|
BACKGROUND OF THE INVENTION
(1) Field of the Invention
This invention relates to a process for adding filler materials to a
conjugated polymer matrix. More particularly, this invention relates to
such a process in which the integrity and cohesiveness of the resulting
composite is retained throughout extreme and/or repetitive shape changes
of the filler and/or polymer.
(2) Prior Art
Conjugated backbone polymers, e.g., polyacetylene, polyphenylene,
polyacenes, polythiophene, poly(phenylene vinylene), polyazulene,
poly(phenylene sulfide), polyphenyleneazomethine poly(phenylene oxide),
polythianthrene, poly(N-methylcarbazole) poly(phenylquinoline),
polyaniline, and polypyrrole, have been suggested for use in a variety of
applications based upon their characteristic of becoming conductive when
oxidized or reduced either chemically or electrochemically. The secondary
battery application described by, e.g. MacDiarmid et al. in U.S. Pat. No.
4,321,114, (1981); J. de Physique, Colloque C3, Vol. 44 (1983), articles
beginning on page 579, page 615 and page 537; and K. Kaneto et al.,
Japanese J. of Applied Physics, Vol. 22, pp. L567-L568 (September 1983)
and pp. L412-L414 (July 1983), employs one or more electrodes having
conjugated backbone polymers as the electroactive material. Such
electrodes can, for example, be reversibly complexed with alkali metal or
tetraalkylammonium cations during battery cycling, most commonly with
insertion of cations into a polymer anode (the negative battery electrode)
occurring during charging. The more such cations are inserted, the more
conductive the electrode becomes and the more cathodic the potential of
the anode becomes.
U.S. Pat. No. 4,002,492 discloses electrochemical cells having an anode
consisting essentially of lithium aluminum alloys that contain lithium in
amounts between about 63% and 92% and the balance essentially aluminum.
Anodes composed of lithium and aluminum are also disclosed in Rao, et al.,
J. Electrochem. Soc. 124, 1490 (1977), and Besenhard, J. Electroanal.
Chem., 94, 77 (1978).
European Patent No. 0070107 Al; Murphy et al., J. Electrochem. Soc., 126,
349 (1979) and Murphy et al., Mat. Res. Bull., 13, 1395 (1978) disclose
batteries based on lithium intercalation in layered transition metal
dichalcogenides.
Composite structures of a conjugated backbone polymer and a
non-electroactive material have been described in U.S. Pat. No. 4,394,304
and in the above J. de Physique issue, articles beginning on page 137 and
on page 151. Representative other components that have been blended with
polyacetylene or onto which polyacetylene or polypyrrole has been
deposited include polyethylene, polystyrene, graphite, carbon black, NESA
glass and silicon. In selected instances, such composite structures have
been suggested for use in batteries, (see Showa Denko K.K, European
Published Patent Application 76,119 (1982)).
SUMMARY OF THE INVENTION
In accordance with this invention there is provided a process for
fabricating a composite comprising a substrate and a polymer selected from
the group consisting of a conjugated backbone polymer or a polymer which
can be converted into a conjugated backbone polymer, which polymer adheres
to the surface of said substrate. The process comprising contacting
monomers or other precursors of the polymer with a substrate whose surface
possesses catalytic activity for the polymerization of said monomers or
precursors thereby forming a conjugated backbone polymer or a polymer
which can be converted into a conjugated backbone polymer on the surface
of the substrate. In the embodiments of this invention in which the
substrate material is not itself catalytic for the polymerization of
monomers or precursors of the polymer, the process comprises the steps of:
(a) derivatizing the surface of said substrate with an active
polymerization catalyst; and
(b) contacting said derivatized substrate with said monomers or other
presursors of said polymer and polymerizing said monomers or precursores
in the presence of said derivatized substrate thereby forming said polymer
on the derivatized surface of said substrate. In the embodiments of the
invention in which the polymer substrate composite forms an article having
a continuous polymer phase, the process includes an additional step (c) in
which the polymer-coated substrate is combined with additional polymer,
either by blending or by further polymerization of monomers or precursors
in the presence of the polymer-coated substrate. In those embodiments of
the invention in which the polymer is of the type which can be converted
into a conjugated backbone polymer, the process includes an additional
step (d), in which the conversion is carried out through use of some
suitable conversion means such as thermal, chemical, electrochemical or
photochemical treatment.
The process of this invention provides superior adhesion between the
substrate and the polymer, thereby providing for enhanced electrical
contact between the substrate and the conjugated backbone polymers in the
doped form, and improved mechanical stability of the polymer/substrate
composite.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The shape and size of the substrate is not critical and can vary widely.
The substrate can be in the form of powders, flakes, sheets, fibers,
ribbons and the like. The substrate can be composed of any material
provided that the substrate includes a surface layer which is suitable for
anchoring a polymerization catalyst; or a surface layer which is capable
of bonding tightly to a coating which is suitable for anchoring a
polymerization catalyst; or a surface layer which is active as a
polymerization catalyst. For example, such substrate can be metals or
highly conducting materials such as alumimun, titanium, nickel, steel,
stainless steel, graphite and like fillers where the resulting, filled
polymer is used for EMI shielding purposes. The substrate can be a
semi-conductor material such as silicon, selenium, germanium, gallium
arsenide, cadium sulfide, and the like where the polymer coating is used
to protect the semiconductor when it is used in photoelectric and
photo-electrochemical cells. The substrate can also be a material which is
subject to corrosion, in which event, the process is used to apply the
polymer as a corrosion preventing or resistant coating. In addition, the
substrate can consist of a metal grid such as a steel, stainless steel or
nickel grid when the polymer coated substrate is intended for use as a
current collector in a battery. Similarly, the substrate can consist of
finely divided filler material, when the polymer coated substrate is
intended for use as a precursor material in the manufacture of electrodes
for secondary batteries. Illustrative of materials useful in the
manufacture of battery anodes are alkali metal alloying materials, as for
example, antimony, silicon, magnesium, lead, tin, aluminum, bismuth, Al-Si
alloys, Al-Mg alloys, Al-Si-Sn alloys, Bi-Pb-Sn-Cd alloys, Li-Al alloys,
or tin/lead alloys; transition metal chalcogenides capable of inserting
alkali metal cations at an electrochemical potential of less than about
1.5V with respect to that of the Li/Li.sup.+ couple such as Li.sub.x
TiS.sub.2 (1.ltoreq.x.ltoreq.2, ), MoO.sub.2, WO.sub.2 and Li.sub.x
VS.sub.2 (1.ltoreq.x.ltoreq.2); and the like. Illustrative of materials
useful in the manufacture of battery cathodes are materials which are
capable of inserting cations or anions at an electrochemical potential
greater than about 1.5V versus Li/Li.sup.+, as for example, transition
metal chalcogenides such as CoO.sub.2, TiS.sub.2, MoS.sub.2, V.sub.6
O.sub.13, NiPS.sub.2, MoO.sub.3, Cr.sub.1-x V.sub.x S.sub.2, Cr.sub.3
O.sub.8 V.sub.2 O.sub.5 and graphite; the alkali-metal inserted forms of
such metal chalcogenides such as Li.sub.x CoO.sub.2, Na.sub.x CoO.sub.2,
and Li.sub.x V.sub.6 O.sub.13 ; and the like. The type of substrates
mentioned above are for illustrative purposes only and should not be
construed as exhaustive of types of useful substrates.
For substrates having a surface suitable for anchoring polymerization
catalysts, the first step of the process is the derivatization of the
substrate surface by a component of a catalyst system that is active in
polymerization reactions forming conjugated backbone polymers or polymers
which can be converted to conjugated backbone polymers. The derivatization
is performed by contacting a catalyst component with a substrate whose
surface contains reactive functionalities such as oxides, hydroxides,
sulfides, hydrogen sulfides and the like. For example, when the substrate
consists of a metal, often the surface of the metal possess an oxide
hydroxide layer which may react with a suitable catalyst component such as
AlCl.sub.3, Ti(O-nBu).sub.4, MoOCl.sub.4, MoCl.sub.5 or WCl.sub.6, to
yield a metal substrate bonded at the surface via its oxide layer to a
modified catalyst component according to the equation:
Metal--OH+AX.sub.m .fwdarw.Metal--O.sub.n -AX.sub.m-n +HX
where, A represents for example a transition metal and X represents for
example a halide or an alkoxide. Prior to contacting the derivatized
substrate with monomers, the remaining catalyst components are added as
neccessary to the derivatized substrate to make a complete catalyst bonded
to the substrate.
For those substrates that do not possess a surface layer which reacts with
suitable catalyst components and that are not polymerization catalysts
themselves, the process requires a pretreatment of the substrate, as for
example pretreatment with nitric acid, chromic acid and sodium hydroxide,
to introduce surface functional groups such oxides, hydroxides, sulfides,
carboxylic acids and the like. Derivatization of the treated surface can
then proceed as above.
For the substrate whose surface is catalytic for polymerization,
derivatization is not required and the substrate and the monomers or
precursors are merely contacted in a suitable medium. For example,
Na.sub.x CoO.sub.2, Li.sub.x CoO.sub.2, V.sub.2 O.sub.5, or other high
potential transition metal chalcogenides can be contacted with a solution
of reactive monomers such as pyrrole or thiophene in the presence of an
electrolyte salt to form oxidized polypyrrole or polythiophene on the
substrate surface.
In the preferred embodiments of the invention in which the process is used
to prepare an anode containing a finely divided electroactive material
dispersed in a conjugated backbone polymeric matrix, the substrate is a
finely divided metal, alloy or other electroactive material. Preferred
metals and alloys include aluminum, lithium-aluminum alloys, lead, tin,
tin/lead alloys and other metal and alloys which can alloy with alkali
metals. Other useful and preferred electroactive materials which can be
used in the manufacture of anodes are the transition metal chalcogenides.
Such chalcogenides for use in the practice of this invention can vary
widely and include WO.sub.2, MoO.sub.2, Li.sub.x TiS.sub.2, Li.sub.x
VSe.sub.2, and Li.sub.x VS.sub.2 where 1<x<2.
In these preferred embodiments of the invention, the powdered metal, alloy
or other electroactive material generally has an average particle diameter
of from about 100 .mu.m to about 0.05 .mu.m. In the preferred embodiments
of the invention, average particle diameter is from about 20 .mu.m to
about 0.1 .mu.m, and in the particularly preferred embodiments is from
about 0.1 .mu.m to about 10 .mu.m. Amongst these particularly preferred
embodiments most preferred are those embodiments in which average particle
diameter is from about 0.1 .mu.m to about 5 .mu.m.
In the polymerization step of the process of this the invention, the
substrate having a catalytic surface and in a suitable form, as for
example, in the form of a finely divided particulate material or large
solid substrate is contacted with a gas, suspension or solution of the
monomer, monomers or other precursors of the desired conjugated backbone
polymer, or other polymer which can be converted into a conjugated
backbone polymer after polymerization, if necessary in the presence of a
co-catalyst, such as triethylaluminum, tetramethyl tin, tetraphenyl tin
and the like. Thereafter the monomer, monomers or precursors are
polymerized, forming the polymer on the surface of the substrate anchored
thereto through the bonded catalyst.
The polymer-coated substrate may be combined with additional conjugated
backbone polymers or polymers which can be converted to a conjugated
backbone polymer by blending the polymer-coated substrate with the
preformed polymer or by the further polymerization of monomers of the
additional polymer by unmodified catalyst in the presence of the
polymer-coated substrate. This combination yields a desired ratio of
substrate to polymer, and is useful is the fabrication of articles having
a continuous conjugated backbone polymer phase containing dispersed
substrate. In the preferred embodiments of this invention, the
polymerization of monomers or precursors is performed in a mixture of
substrates having a catalytic surface and unmodified polymerization
catalyst. This combination of steps (b) and (c) yields a composite with
good adhesion between substrate and the additional polymer via the polymer
coating, as well as the desired weight ratio of substrate to polymer.
The types of monomers or precursors employed will vary widely depending on
the desired conjugated backbone polymer. Useful monomer are those which
are precursors in the production of conjugated backbone polymers known to
those of skill in the art or monomers which form other types of polymers
which can be converted into the desired conjugated backbone polymer.
Illustrative of monomers used in the formation of polymers which are
convertible into conjugated backbone polymers is
7,8-bis(trifluorometyl)tricyclo[4,2,20]deca-3,7,9-triene whose metathesis
polymerization product can be converted to polyacetylene, and monomers
which can be polymerized to form
poly(5,6-diacetoxycyclohex-2-ene-1,4-diyl) which can be converted to
poly(paraphenylene). Mixtures of monomers can be used. For example,
various combinations of monomers can be employed to form conjugated
backbone copolymers, or blends of one or more conjugated backbone
homopolymers or copolymers with one or more conjugated backbone or
non-conjugated backbone homopolymers or copolymers. As is apparent from
the foregoing, monomers useful in the practice of this invention can vary
widely and may include monomers which can be polymerized into
unsubstituted and substituted polyacetylene, poly paraphenylene),
poly(phenylquinoline), poly(phenylene vinylene) and the like. Other useful
monomers include those which can be polymerized into conjugated backbone
polymers claimed by others as useful in batteries such as monomers which
form polythiophene, polyazulene, poly(phenylquinoline), polypyrrole,
polyacenes, polyaniline, polyacenediyls, polynaphthalene, substituted
derivatives, polymeric blends thereof and the like.
Preferred for use in the practice of this invention are monomers which can
be directly polymerized to form conjugated backbone polymers useful as
battery electrodes, or to form other polymers which can be converted into
these conjugated backbone polmers. Conjugated backbone polymers useful as
negative electrodes are conductive in their reduced form, and capable of
reversibly inserting cations. Conjugated backbone polymers useful as
positive electrodes are conductive in their oxidized or reduced form, and
are capable of reversibly inserting anions or cations. Amongst these
illustrative conjugated backbone polymers, polyacetylene, poly(phenylene
vinylene) and poly(p-phenylene) are preferred for use in negative
electrodes, and polyacetylene and poly(p-phenylene) are particularly
preferred for such use. Polyacetylene, polypyrrole, polyaniline,
polythiophene and substituted derivatives thereof are preferred for use in
positive electrodes and polyaniline and polypyrrole are particularly
preferred for this use. Accordingly, monomers and other precursors which
result in the formation of these polymers are preferred and particularly
preferred for use in the practice of this invention, respectively. Most
preferred for use in the practice of this invention is polyacetylene and
accordingly, acetylene is the most preferred monomer.
Polymerization reaction conditions for the polymers and precusor polymers
described above as well known in the art. For example, useful conditions
are described in detail in H. Shirakawa, et al., Polym. J., 2, 231 (1971);
J.C.W. Chien, et al., Macromolecules, 14, 497, (1981), (W.J. Feast et al.,
European Pat. publication No. 0080 329), Kovacic, J. Am. Chem. Soc.
85:454-458 (1963), and U.S. Pat. No. 3,404,132. The monomer or other
precursors undergo coordination polymerization to yield a conjugated
backbone polymer or a polymer which can be converted into a conjugated
backbone polymer which adheres to the surface of the substrate. Insoluble
polymers form particles and/or gels or films nucleated about the substrate
having a catalytic surface, as for example particles of derivatized metal,
alloy or other electroactive material, and are attached to the surface of
the substrates. Soluble polymers form mixtures of a solution of the
polymer and the insoluble polymer-coated substrate which may be suspended
in the solution if it is finely divided. If the polymer in solution is the
same as or is compatible with the polymers bound onto the surface of the
substrate, the articles which are cast from the solution suspenion will
contain polymer tightly bound to the substrate via the polymer coating.
The composite of polymer and substrate can be recovered from the
polymerization mixture using standard procedures. Composites of soluble
polymers nucleated about substrates can be filtered to recover the
insoluble derivatized fraction. Composites which are powders, gels, or
films of insoluble polymers nucleated about derivatized substrates can be
extracted with a solvent which is unreactive with the polymer and the
substrate. For example, in those embodiments of this invention in which
the product is a continuous film of polymer having finely divided
electroactive material therein or coated onto a grid of some material,
such as nickel, steel, stainless steel, graphite, and the like, the film
composite, is removed from the polymerization mixture, extracted with an
inert solvent, and thereafter used in battery construction as an electrode
in accordance with conventional procedures. Illustrative of such
procedures are those described in Kaner and MacDiarmid, J. Chem. Soc.
Faraday Trans, 1, 80, 2109 (1984) and Nagatomo et al., J. Electrochem.
Soc., 132, 1380 (1985), which are hereby incorporated by reference.
In the preferred embodiments of this invention in which the substrate is a
finely divided metal, alloy or other electroactive material, the coated
substrate is fabricated into a cohesive solid such as for use in the
construction of an electrode of a battery. Useful fabrication procedures
include compressing or rolling powdered or gel composites into a film or
other solid object or removing the solvent component of a suspended
polymer composite to form a film. Such fabrication techniques as are
applied to the construction of battery electrodes are known to those of
skill in the art, as for example, those described in U.S. Pat. No.
4,496,640 and European Patent Application EP 0 076 119 A2, all of which
are incorporated herein by reference.
The following specific examples are presented to more particularly
illustrate the invention and are not to be construed as limitations
thereon.
EXAMPLE I
A. An aluminum-polyacetylene composite film was formed by the
polymerization of acetylene gas in a vigorously stirred slurry of aluminum
powder derivatized by TiCl.sub.4 in 6 .mu. Ti(O-nBu).sub.4 /AlEt.sub.3
(1:7) in toluene at -78.degree. C., using a modification of the procedure
described in by J. Hocker (Bayer) U.S. Pat. No. 4,408,207. Aluminum
spheres ca. 20 .mu.m in diameter were heated to 465.degree. C. in vacuo
for 16 hours, stirred in 10% TiCl.sub.4 in cyclohexane at 18.degree. C.
for 16 hours, washed three times in fresh cyclohexane and vacuum dried.
When combined with alkyl aluminum compounds, TiCl.sub.4 has been shown to
be a polymerization catalyst. See Kambara, Katano & Hosoe, J. Chem. Soc.
Japan, Inc. Chem., 65, 720 (1962). The TiCl.sub.4 reacted with the oxide
layer of the aluminum spheres to produce tetravalent titanium chloride
bonded to the aluminum surface via aluminum-oxygen-titanium bonds. A 500
mL 3-necked reactor equipped with a mechanical stirrer was charged with 2g
of derivatized Al powder, 50 mL toluene, 0.34 mL AlEt.sub.3, and 0.1 mL
Ti(O-nBu).sub.4 under a constant flow of dry nitrogen. The reactor was
cooled to -78.degree. C. and vigorous stirring was established before
acetylene gas was added to the N.sub.2 flow to make a 1:1 mixture of
gases. Polymer particles, which were in part nucleated about the
derivatized Al powder, were formed immediately. After 10 min., the
stirring caused these particles to aggregate on the reactor wall forming a
smooth film. Scanning electron micrographs indicate a uniform distribution
of aluminum particles through the film thickness as well as intimate
contact between Al metal and polymers fibrils.
B. A 1.5-cm.sup.2 film weighing 30 mg and having a gross composition of
(CHAl.sub.1.5).sub.x prepared as in Step A was electrochemically reduced
and reoxidized in an electrolyte of lM LiBBu.sub.4 /THF versus a lithium
metal counter electrode. During the constant current cycle at 0.33
mA/cm.sup.2, the composition of the electrode varied from CHAl.sub.1.5 to
Li.sub.0.6 CHAl.sub.1.5 and back to Li.sub.0.07 CHAl.sub.1.5 corresponding
to a utilization of about 6 mAh/cm.sup.2 or 380 mAh/g. The initial stage
of reduction to Li.sub.0.12 CHAl.sub.1.5, exhibited a sloping voltage vs.
charge associated with the n-doping of polyacetylene to 12 mole percent or
Li.sub.0.12 CH. The remainder of the reduction process took place at a
nearly constant voltage of .28V and is attributed to the alloying of Li
with Al to yield a Li distribution of Li.sub.0.12 CH(Li.sub.0.32
Al).sub.1.5. The reoxidation proceeded at ca. 0.48V until the composition
was again Li.sub.0.12 CHAl.sub.1.5 at which point the voltage began to
increase as lithium was removed from the polyacetylene. A second reduction
was allowed to proceed until a lower voltage limit of 0.2V was reached, at
which point, the electrode composition was consistent with 100% Li
alloying of the aluminum and 14 % doping of the polyacetylene or
Li.sub.0.14 CH (Li.sub.1.0 Al).sub.1.5, a utilization equivalent to about
675 mAH/g.
EXAMPLE II
A. An aluminum-polyacetylene composite was formed by the polymerization of
acetylene gas in a stirred slurry of powdered LiAl alloy in a dilute
solution of Ti(O-nBu).sub.4 /AlEt.sub.3 (1:4) in toluene at -78.degree. C.
Metallurgically prepared Li.sub.1.0 Al alloy was pulverized in a ball mill
for 16 hours. A 150 mL reactor was charged with 1 g of the powdered alloy,
50 mL of toluene, 0.17 mL of AlEt.sub.3 and finally 0.10 mL of
Ti(O-nBu).sub.4 causing the powder to darken. After chilling to
-78.degree. C. and degassing the mixture, ca. 0.5 atm. of acetylene was
introduced. Since the stirring was slow and insufficient to cause powder
formation, a polymer film formed at the top of the catalyst pool and
incorporated some of the powdered alloy. After 14 hours, the film was
washed in THF and dried. The resulting copper-colored film had a room
temperature conductivity of 80 Scm.sup.-1 and an open circuit voltage vs.
Li of 0.76 V, consistent with polyacetylene n-doped to ca. 7% with
Li.sup.+ as the counterion.
B. A 1.0-cm.sup.2 film weighing 16.5 mg and having an initial composition
of Li.sub.0.07 CHAl.sub.0.07 prepared as in Step A. Step A was
electrochemically reduced and reoxidized in an electrolyte of 1M
LiBBu.sub.4 /THF versus a Li metal counter electrode. After first
stripping away the original Li content, the first cycle at 0.5 mA/Cm.sup.2
between voltage limits of 2.5 and 0.2V, resulted in a composition change
from CHAl.sub.0.07 to Li.sub.0.19 CHAL.sub.0.07 and back to CHAl.sub.0.07.
The initial stage of reduction to Li.sub.0.12 CHAl.sub.0.07 exhibited the
sloping voltage vs. charge associated with n-doping polyacetylene to 12%
or Li.sub.0.12 CH. The remainder of the reduction process took place at a
nearly constant voltage of 0.3V attributed to the alloying of Li with Al
to yield a Li distribution of Li.sub.0.12 CH(LiAl).sub.0.07. The
reoxidation proceeded to 0.45V until the composition was again Li.sub.0.12
CHAl.sub.0.07 at which point, the lithium content of the alloy was
exhausted and the polyacetylene began to undope. An additional 29 cycles
between 0.2 and 1.5V exhibited the same voltage characteristics and 100%
coulombic efficiency throughout. The utilization ranged from 4.4
mAh/cm.sup.2 on the fifth cycle to 4.1 mAh/cm.sup.2 on the fifteenth cycle
to 3.8 mAh/cm.sup.2 on the thirtieth cycle. The amount of Li cycled on the
last cycle between the voltage limits of 0.2 and 1.5V was 83% of that
observed on the first cycle within the same voltage range.
EXAMPLE III
A. An aluminum-polyacetylene composite was prepared by the polymerization
of acetylene in a rapidly spinning cylindrical reactor (100 mm
I.D..times.120 mm) containing 20g Al powder derivatized by TiCl.sub.4
(50-1000 .mu.m), 35 mL of toluene, 3.5 mL triethyl aluminum, 2.0 mL of
titanium tetrabutoxide, and a derivatized cylinder of expanded nickel
screen (314 mm.times.120 mm) previously derivatized by reaction with
TiCl.sub.4 fitted closely to the inside wall of the reactor. After
chilling to -79.degree. C. and degassing the catalyst mixture, the reactor
was rotated about its axis such that the aluminum/catalyst slurry was
uniformly distributed on the reactor wall completely immersing the nickel
screen. Both the Al powder and the nickel screen had been dried in vacuo
at 450.degree. C. and reacted with TiCl.sub.4 as in Example I. A pressure
of 500 torr (66.5 kPa) of C.sub.2 H.sub.2 was maintained for 3 hours which
allowed the polymer to form throughout the volume of the catalyst-Al
slurry, thereby encasing both the Al powder and the nickel screen. After
repeated THF washes, two 3.5 cm.sup.2 samples each weighing ca. 0.22g
(0.025g (CH).sub.x, 0.055g Ni, 0.140g Al) were reduced by reaction with a
0.1M solution of sodium naphthalide in THF, washed again in THF, and
exposed to 400 torr (53.2 kPa) of ethylene oxide for 1/2 hour to produce
poly(ethylene oxide) at the polyacetylene surfaces (U.S. Pat. No.
4,472,487). Following a final THF wash to remove unbonded poly(ethylene
oxide), the samples were employed as anodes in the battery cell described
in Section B, below.
B. A battery cell having an anode comprised of aluminum
powder-polyacetylene (CHAl.sub.n).sub.x composite prepared as in Step A
which had been surface modified with polyethylene oxide, lithium cobalt
dioxide cathode, and an electrolyte of lithium perchlorate in propylene
carbonate was charged and deeply discharged 36 times at 2.8 mA/cm.sup.2 in
the voltage range of 3.0V to 4.1V prior to cycling the cell, consisting of
two 3.5 cm.sup.2 plates of (CHAl.sub.n).sub.x and three plates of
LiCoO.sub.2 and having a volume of 1.6 cm.sup.3, delivered 36 mA at 3.6V
and 120 ma at 2.8V. The amount of charge released per cycle could be held
at ca. 50 mAh but not without gradually increasing the upper voltage limit
from 3.9 to 4.1V. The onset of the 20mA discharge was at ca. 3.85V and
sloped gradually to 3.5V before turning down to the cut-off voltage; the
average value of the discharge voltage was ca. 3.7V. The coulomb
efficiency remained between 98 and 100% throughout the 36 cycles. The
composition of the composite ranged from an initial valued of
(CHAl.sub.2).sub.x to ca. Li.sub.0.14 CH(Li.sub.0.15 Al).sub.2, when the
cell was charged, and back to ca. Li.sub.0.07 CHAl.sub.2 with each cycle.
Raising the upper voltage limit was necessary to access more of the Li
stored in the LiCoO.sub.2 cathodes because it was not being restored fully
from the composite anodes during recharge. This was presumably due to
shedding of the large (45-2000 Mm) Al particles occurring during the
alloying process and the consequent isolation of some of the Li-loaded
fragments.
EXAMPLE IV
In a three neck round bottom flask, 0.356g of aluminum powder and 6.0g of
molybdenum (VI) tetrachloride oxide were combined under argon. Using a
syringe, 10g of benzene were added and the mixture was stirred under argon
for 120 hours at room temperature.
The resulting poly(p-phenylene) Al composite was washed repeatedly with
benzene, acetonitrile, water, and acetone and dried under vacuum. Infrared
spectra showed absorption bands characteristic of poly(p-phenylene).
An electrode was fashioned by pressing a mixture of 77% poly(p-phenylene)
Al composite, 13% carbon black, and 10% binder onto a nickel grid at
1000hg/cm.sup.2 in a rectangular press. The electrode was then removed and
heat set at 160.degree. C.
After low molecular weight oligomers were extracted, this electrode was
incorporated into a half cell consisting of a lithium reference and
counter electrode and 0.5M LiBBu.sub.4 in THF as the electrolyte. The cell
was cycled between 1.1V and 0.1V with respect to the lithium reference.
The capacity was 575C per gram of composite of which 345C were due to Li
insertion into the alumunim and 230C were due to Li insertion into the
poly(p-phenylene). The average coulombic efficiency over twelve cycles was
98% and there was no loss in capacity with cycling.
* * * * *
|
|
 |
|
 |
Description |
|
