U.S. patent application number 14/603204 was filed with the patent office on 2015-05-14 for electrode materials with high surface conductivity.
The applicant listed for this patent is Michel Armand, Simon Besner, Jean-Francois Magnan, Nathalie Ravet, Martin Simoneau, Alain Vallee, Karim Zaghib. Invention is credited to Michel Armand, Simon Besner, Jean-Francois Magnan, Nathalie Ravet, Martin Simoneau, Alain Vallee, Karim Zaghib.
Application Number | 20150132660 14/603204 |
Document ID | / |
Family ID | 4163509 |
Filed Date | 2015-05-14 |
United States Patent
Application |
20150132660 |
Kind Code |
A1 |
Ravet; Nathalie ; et
al. |
May 14, 2015 |
ELECTRODE MATERIALS WITH HIGH SURFACE CONDUCTIVITY
Abstract
The present invention concerns electrode materials capable of
redox reactions by electron and alkali-ion exchange with an
electrolyte. The applications are in the field of primary
(batteries) or secondary electrochemical generators,
supercapacitors and light modulating systems of the electrochromic
type.
Inventors: |
Ravet; Nathalie; (Montreal,
CA) ; Besner; Simon; (Coteau-du-Lac, CA) ;
Simoneau; Martin; (St. Bruno de Montarville, CA) ;
Vallee; Alain; (Varennes, CA) ; Armand; Michel;
(Montreal, CA) ; Magnan; Jean-Francois; (Neuville,
CA) ; Zaghib; Karim; (Longueuil, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Ravet; Nathalie
Besner; Simon
Simoneau; Martin
Vallee; Alain
Armand; Michel
Magnan; Jean-Francois
Zaghib; Karim |
Montreal
Coteau-du-Lac
St. Bruno de Montarville
Varennes
Montreal
Neuville
Longueuil |
|
CA
CA
CA
CA
CA
CA
CA |
|
|
Family ID: |
4163509 |
Appl. No.: |
14/603204 |
Filed: |
January 22, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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13945713 |
Jul 18, 2013 |
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14603204 |
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13449135 |
May 4, 2012 |
8506851 |
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13945713 |
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12951335 |
Nov 22, 2010 |
8173049 |
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13449135 |
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12033636 |
Feb 19, 2008 |
7815819 |
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12951335 |
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11266339 |
Nov 4, 2005 |
7344659 |
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12033636 |
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10740449 |
Dec 22, 2003 |
6962666 |
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11266339 |
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10175794 |
Jun 21, 2002 |
6855273 |
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10740449 |
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09560572 |
Apr 28, 2000 |
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10175794 |
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Current U.S.
Class: |
429/306 ;
252/504; 252/506; 252/507; 429/231.1 |
Current CPC
Class: |
H01M 2300/0082 20130101;
H01G 9/155 20130101; H01M 4/5825 20130101; Y02E 60/13 20130101;
H01B 1/24 20130101; H01M 4/485 20130101; H01M 4/58 20130101; H01M
4/52 20130101; H01M 4/625 20130101; H01M 4/50 20130101; Y02E 60/10
20130101; H01M 4/136 20130101; H01M 4/622 20130101; H01M 4/364
20130101; H01M 4/583 20130101; H01M 10/052 20130101; H01M 10/0565
20130101; H01M 4/48 20130101; H01G 9/042 20130101 |
Class at
Publication: |
429/306 ;
252/506; 252/507; 252/504; 429/231.1 |
International
Class: |
H01M 4/136 20060101
H01M004/136; H01M 10/0565 20060101 H01M010/0565; H01M 4/62 20060101
H01M004/62; H01M 4/58 20060101 H01M004/58; H01M 4/485 20060101
H01M004/485 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 30, 1999 |
CA |
2270771 |
Claims
1-38. (canceled)
39. An electrode material comprising: a particle of electroactive
material comprising: at least one complex oxide of the formula
A.sub.aM.sub.mZ.sub.zO.sub.oN.sub.nF.sub.f, wherein: A comprises at
least one alkali metal; M comprises at least one transition metal;
Z comprises at least one non-metal; O is oxygen; N is nitrogen; F
is fluorine; wherein the coefficients a, m and z>0; wherein at
least one of o, n and f>0; and a solid polymer comprising
between 60 molar % and 100 molar % carbon (C) and having an
electronic conductivity of at least 10.sup.-6 S/cm, wherein the
solid polymer is coated on the surface of the electroactive
material, wherein the particle retains at least approximately 85%
of its theoretical capacity after at least five cycles in an
electrochemical cell cycled at 20 mV/h.
40. The electrode material of claim 39, wherein the solid polymer
has an electronic conductivity of at least 10.sup.-4 S/cm.
41. The electrode material of claim 39, wherein the solid polymer
further comprises hydrogen (H), oxygen (O), or nitrogen (N).
42. The electrode material of claim 39, wherein M is selected from
the group consisting of Fe.sup.2+, Mn.sup.2+, V.sup.2+, V.sup.3+,
Ti.sup.2+, Ti.sup.3+, Mo.sup.3+, Mo.sup.4+, Nb.sup.3+, Nb.sup.4+,
and W.sup.4+.
43. The electrode material of claim 39, wherein the electrode
material particle comprises between 10% to 70% solid polymer by
electrode material particle volume.
44. The electrode material of claim 43, wherein the alkali metal
comprises Li, Na, or K.
45. The electrode material of claim 39, wherein the electrode
material further comprises an additional conductive carbon material
in the form of a fine power or fiber.
46. The electrode material of claim 45, wherein the additional
conductive carbon material comprises carbon black or carbon
fibers.
47. The electrode material of claim 45, wherein the electrode
material is in the form of an electrode material particle
comprising between 0.5% to 10% conductive carbon material by
electrode material particle volume.
48. The electrode material of claim 39, wherein the particle
retains at least approximately 70% of its theoretical capacity
after at least one thousand cycles in an electrochemical cell
cycled at 20 mV/h.
49. A secondary battery comprising an electrode material
comprising: a particle of electroactive material comprising: at
least one complex oxide of the formula
A.sub.aM.sub.mZ.sub.zO.sub.oN.sub.nF.sub.f, wherein: A comprises at
least one alkali metal; M comprises at least one transition metal;
Z comprises at least one non-metal; O is oxygen; N is nitrogen; F
is fluorine; wherein the coefficients a, m and z>0; wherein at
least one of o, n and f>0; and a solid polymer comprising
between 60 molar % and 100 molar % carbon (C) and having an
electronic conductivity of at least 10.sup.-6 S/cm, wherein the
solid polymer is coated on the surface of the electroactive
material, wherein the particle retains at least approximately 85%
of its theoretical capacity after at least five cycles in an
electrochemical cell cycled at 20 mV/h.
50. The secondary battery of claim 49, wherein the solid polymer
has an electronic conductivity of at least 10.sup.-4 S/cm.
51. The secondary battery of claim 49, wherein the solid polymer
further comprises hydrogen (H), oxygen (O), or nitrogen (N).
52. The secondary battery of claim 49, wherein M is selected from
the group consisting of Fe.sup.2+, Mn.sup.2+, V.sup.2+, V.sup.3+,
Ti.sup.2+, Ti.sup.3+, Mo.sup.3+, Mo.sup.4+, Nb.sup.3+, Nb.sup.4+,
and W.sup.4+.
53. The secondary battery of claim 49, wherein the electrode
material particle comprises between 10% to 70% solid polymer by
electrode material particle volume.
54. The secondary battery of claim 53, wherein the alkali metal
comprises Li, Na, or K.
55. The secondary battery of claim 49, wherein the electrode
material further comprises an additional conductive carbon material
in the form of a fine power or fiber.
56. The secondary battery of claim 55, wherein the additional
conductive carbon material comprises carbon black or carbon
fibers.
57. The secondary battery of claim 55, wherein the electrode
material is in the form of an electrode material particle
comprising between 0.5% to 10% conductive carbon material by
electrode material particle volume.
58. The secondary battery of claim 49, further comprising the
electrode material deposited on and aluminum (Al) a current
collector.
59. The secondary battery of claim 49, further comprising a polymer
electrolyte.
60. The secondary battery of claim 49, wherein the particle retains
at least approximately 70% of its theoretical capacity after at
least one thousand cycles of the secondary battery at 20 mV/h.
Description
[0001] The present application is a continuation of U.S. patent
application Ser. No. 12/951,335, filed Nov. 22, 2010, which is a
continuation of U.S. patent application Ser. No. 12/033,636, filed
Feb. 19, 2008 (now U.S. Pat. No. 7,815,819), which is a divisional
of U.S. patent application Ser. No. 11/266,339, filed Nov. 4, 2005
(now U.S. Pat. No. 7,344,659), which is a continuation of U.S.
application Ser. No. 10/740,449 filed Dec. 22, 2003, (now U.S. Pat.
No. 6,962,666), which is a divisional of U.S. application Ser. No.
10/175,794, filed Jun. 21, 2002 (now U.S. Pat. No. 6,855,273),
which is a continuation of U.S. application Ser. No. 09/560,572,
filed Apr. 28, 2000, now abandoned, which claims the benefit of CA
2,270,771, filed Apr. 30, 1999. The entire contents of which are
hereby incorporated herein by reference.
FIELD OF INVENTION
[0002] The present invention concerns electrode materials capable
of redox reactions by electron and alkali-ion exchange with an
electrolyte. The applications are in the field of primary
(batteries) or secondary electrochemical generators,
supercapacitors and light modulating systems of the electrochromic
type.
BACKGROUND OF THE INVENTION
[0003] Insertion compounds (hereinafter also referred to as
electroactive materials or redox materials) are well known, and
their operation is based on the exchange of alkali ions, in
particular lithium ions, and valence electrons of at least one
transition element, in order to keep the neutrality of the solid
matrix. The partial or complete maintenance of the structural
integrity of the material allows the reversibility of the reaction.
Redox reactions resulting in the formation of several phases are
usually not reversible, or only partially. It is also possible to
perform the reactions in the solid phase through the reversible
scission of the sulphur-sulphur bonds or the redox reactions
involved in the transformation of the aromatic organic structures
in quinonoid form, including in conjugated polymers.
[0004] The insertion materials are the electrochemical reactions
active components used, in particular, in electrochemical
generators, supercapacitors or light transmission modulating
systems (electrochromic devices).
[0005] The progression of the ions-electrons exchange reaction
requires the existence within the insertion material of a double
conductivity, simultaneous with the electrons and the ions, in
particular lithium ions, either one of these conductivities which
may be too weak to ensure the necessary kinetic exchanges for the
use of the material, in particular for electrochemical generators
or supercapacitors. This problem is partly solved by using
so-called "composite" electrodes, wherein the electrode material is
dispersed in a matrix containing the electrolyte and a polymer
binder. When the electrolyte is a polymer electrolyte or a polymer
gel working in the presence of a solvent, the mechanical binding
role is carried out directly by the macromolecule. Gel means a
polymer matrix, solvating or not, and retaining a polar liquid and
a salt, to confer to the mixture the mechanical properties of a
solid while retaining at least a part of the conductivity of the
polar liquid. A liquid electrolyte and the electrode material can
also be maintained in contact with a small fraction of an inert
polymer binder, i.e., not interacting with the solvent. With any of
these means, each electrode material particle is thus surrounded by
an electrolyte capable of bringing the ions in direct contact with
almost the totality of the electrode material surface. To
facilitate electronic exchanges, it is customary, according to the
prior art, to add particles of a conductive material to one of the
mixtures of the electrode material and electrolyte mentioned above.
Such particles are in a very divided state. Generally, carbon-based
materials are selected, and especially carbon blacks (Shawinigan or
Ketjenblack.RTM.). However, the volume fractions used must be kept
low because such material strongly modifies the rheology of their
suspension, especially in polymers, thereby leading to an excessive
porosity and loss of operating efficiency of the composite
electrode, in terms of the fraction of the usable capacity as well
as the kinetics, i.e., the power available. At these low
concentrations used, the carbon particles structure themselves in
chains, and the contact points with the electrode materials are
extremely reduced. Consequently, such configuration results in a
poor distribution of the electrical potential within the
electroactive material. In particular, over-concentrations or
depletion can appear at the triple junction points:
##STR00001##
[0006] These excessive variations of the mobile ions local
concentrations and the gradients within the electroactive materials
are extremely prejudicial to the reversibility of the electrode
operation over a high number of cycles. These chemical and
mechanical constraints or stresses result, at the microscopic
level, in the disintegration (particulation) of the electroactive
material particles, a part of which become susceptible to losing
contact with the carbon particles and thus becoming
electrochemically inactive. The material structure can also be
destroyed, with the appearance of new phases and possible release
of transition metal derivatives, or other fragments in the
electrolyte. These harmful phenomenons appear even more easily the
larger the current density or the power requested at the electrode
is.
IN THE DRAWINGS
[0007] FIG. 1 illustrates the difference between a classic
electrode according to the prior art (A) and an electrode according
to the invention wherein the electroactive material particles are
coated with a carbonaceous coating (B).
[0008] FIGS. 2 and 3 illustrate a comparison between a sample of
LiFePO.sub.4 coated with a carbonaceous deposit, and an uncoated
sample. The results were obtained by cyclic voltammetry of
LiFePO.sub.4/POE.sub.20LiTFSI/Li batteries cycled at 20 mVh.sup.-1
between 3 and 3.7 V at 80.degree. C. The first cycle is shown in
FIG. 2, and the fifth in FIG. 3.
[0009] FIG. 4 illustrates the evolution of capacity during cycling
for batteries containing carbonaceous and non-carbonaceous
LiFePO.sub.4 samples.
[0010] FIG. 5 illustrates the performances of a battery containing
carbonaceous LiFePO.sub.4 and cycled under an intentiostatic mode
between 3 and 3.8 V at 80.degree. C. with a charge and discharge
speed corresponding to C/1.
[0011] FIG. 6 illustrates the evolution of the current vs. time of
a LiFePO.sub.4/gamma-butyrolactone LiTFSI/Li containing a
carbonaceous sample and cycled at 20 mVh.sup.-1 between 3 and 3.7 V
at room temperature.
[0012] FIG. 7 illustrates the evolution of the current vs. time of
a LiFePO.sub.4/POE.sub.20LiTFSI/Li containing a carbonaceous
sample.
[0013] FIGS. 8 and 9 illustrate a comparison between carbonaceous
and non-carbonaceous LiFePO.sub.4 samples, cycled. The results have
been obtained by cyclic voltammetry of
LiFePO.sub.4/POE.sub.20LiTFSI/Li batteries cycled at 20 mVh.sup.-1
between 3 and 3.7 V at 80.degree. C. The first cycle is shown in
FIG. 8, and the fifth in FIG. 9.
[0014] FIG. 10 illustrates the evolution of the capacity during
cycling of batteries prepared with carbonaceous and
non-carbonaceous LiFePO.sub.4 samples.
SUMMARY OF THE INVENTION
[0015] In accordance with the present invention, there is provided
an electrode material comprising a complex oxide corresponding to
the general formula A.sub.aM.sub.mZ.sub.zO.sub.oN.sub.nF.sub.f
wherein:
[0016] A comprises an alkali metal;
[0017] M comprises at least one transition metal, and optionally at
least one non-transition metal such as magnesium or aluminum; and
mixtures thereof;
[0018] Z comprises at least one non-metal;
[0019] O is oxygen, N is nitrogen and F is fluorine; and
[0020] the coefficients a, m, z, o, n, f.gtoreq.0 and are selected
to ensure electroneutrality, wherein a conductive carbonaceous
material is deposited homogeneously on a surface of the material to
obtain a substantially regular electric field distribution on the
surface of material particles. The similarity in ionic radii
between oxygen, fluorine and nitrogen allows mutual replacement of
these elements as long as electroneutrality is maintained. For
simplicity, and considering that oxygen is the most frequently used
element, these materials are hereinafter referred to as complex
oxides. Preferred transition metals comprise iron, manganese,
vanadium, titanium, molybdenum, niobium, tungsten, zinc and
mixtures thereof. Preferred non-transition metals comprise
magnesium and aluminum, and preferred non-metals comprise sulfur,
selenium, phosphorous, arsenic, silicon, germanium, boron, and
mixtures thereof
[0021] In a preferred embodiment, the final mass concentration of
the carbonaceous material varies between 0.1 and 55%, and more
preferably between 0.2 and 15%.
[0022] In a further preferred embodiment, the complex oxide
comprises sulfates, phosphates, silicates, oxysulfates,
oxyphosphates, and oxysilicates of a transition metal and lithium,
and mixtures thereof. It may also be of interest, for structural
stability purposes, to partially replace the transition metal with
an element having the same ionic radius, but not involved in the
redox process. For example, magnesium and aluminum, in
concentrations preferably varying between 1 and 25%, may be
used.
[0023] The present invention also concerns electrochemical cells
wherein at least one electrode is made of an electrode material
according to the present invention. The cell can operate as a
primary or secondary battery, a supercapacitor, or a light
modulating system, the primary or a secondary battery being the
preferred mode of operation.
DETAILED DESCRIPTION OF THE INVENTION
[0024] The present invention allows the fabrication of electrode
materials of extremely varied compositions with its surface, or
most of it, coated with a uniform coating of a conductive
carbonaceous material deposited chemically. The presence in the
electrode materials of the invention of a uniform coating, when
compared to contact points obtained with carbon powders or other
prior art conductive additives, allows a regular distribution of
the electrical field at the surface of the electroactive material
particles. Further, the ion concentration gradients are
considerably diminished. Such improved distribution of the
electrochemical reaction at the surface of the particles allows, on
one side, the maintenance of the structural integrity of the
material, and on the other side, improves the kinetics in terms of
the current density and power availability at the electrode,
because of the greater surface accessibility.
[0025] In the present application, carbonaceous material means a
solid polymer comprising mainly carbon, i.e., from 60 to 100%
molar, and having an electronic conductivity higher than 10.sup.-6
S/cm at room temperature, preferably higher than 10.sup.-4 S/cm.
Other elements that can be present are hydrogen, oxygen, and
nitrogen, as long as they do not interfere with the chemical
inertia of the carbon during the electrochemical operation. The
carbonaceous material can be obtained through thermal decomposition
or dehydrogenation, e.g., by partial oxidation, of various organic
materials. In general, any material leading, through a reaction or
a sequence of reactions, to the solid carbonaceous material with
the desired property without affecting the stability of the complex
oxide is a suitable precursor. Preferred precursors include, but
are not limited to: hydrocarbons and their derivatives, especially
those comprising polycyclic aromatic moieties, like pitch and tar
derivatives; perylene and its derivatives; polyhydric compounds
like sugars and carbon hydrates and their derivatives; and
polymers. Preferred examples of such polymers include polyolefins,
polybutadienes, polyvinylic alcohol, phenol condensation products,
including those from a reaction with an aldehyde, polymers derived
from furfurylic alcohol, polymer derivatives of styrene,
divinylbenzene, naphthalene, perylene, acrylonitrile, vinyl
acetate, cellulose, starch and their esters and ethers, and
mixtures thereof
[0026] The improvement of the conductivity at the surface of the
particles obtained with the carbonaceous material coating according
to the present invention allows the satisfactory operation of
electrodes containing electroactive materials having an
insufficient electronic conductivity to obtain acceptable
performances. Complex oxides with redox couples in a useful voltage
range and/or using inexpensive or nontoxic elements but whose
conductivity otherwise would be too low for practical use, now
become useful as electrode materials when the conductive coating is
present. The choice of the structures or phase mixtures possessing
redox properties but having an electronic conductivity that is too
low, is thus much wider than that of compounds of the prior art. It
is possible to include within the redox structures, at least one
element selected from non-metals (metalloids) such as sulphur,
selenium, phosphorus, arsenic, silicon or germanium, wherein the
greater electronegativity allows the modulation of the redox
potential of the transition elements, but at the expense of the
electronic conductivity. A similar effect is obtained with the
partial or complete substitution of the oxygen atoms with fluorine
or nitrogen.
[0027] The redox materials are described by the general formula
A.sub.aM.sub.mZ.sub.zO.sub.oN.sub.nF.sub.f wherein:
[0028] A comprises an alkali metal such as Li, Na, or K;
[0029] M comprises at least one transition metal, and optionally at
least one non-transition metal such as magnesium or aluminum; or
mixtures thereof;
[0030] Z comprises at least one non-metal such as S, Se, P, As, Si,
Ge, B;
[0031] O is oxygen;
[0032] N is nitrogen and F is fluorine, wherein the latter elements
can replace oxygen in the complex oxide because the ionic radii
values for F.sup.-, O.sup.2- and N.sup.3- are similar; and
[0033] each coefficient a, m, z, o, n and f.gtoreq.0 independently,
to ensure electroneutrality of the material.
[0034] Preferred complex oxides according to the invention comprise
those of formula Li.sub.1+xMP.sub.1-xSi.sub.xO.sub.4;
Li.sub.1+x-yMP.sub.1-xSi.sub.xO.sub.4-yF.sub.y;
Li.sub.3-x+zM.sub.2(P.sub.1-x-zS.sub.xSi.sub.zO.sub.4).sub.3;
Li.sub.3+u-x+zV.sub.2-z-wFe.sub.uTi.sub.w(P.sub.1-x-z
S.sub.xSi.sub.zO.sub.4).sub.3, or Li.sub.4+xTi.sub.5O.sub.12,
Li.sub.4+x-2yMg.sub.yTi.sub.5O.sub.12, wherein w.ltoreq.2;
0.ltoreq.x, y.ltoreq.1; z.ltoreq.1 and M comprises Fe or Mn.
[0035] The carbonaceous coating can be deposited through various
techniques that are an integral part of the invention. A preferred
method comprises the pyrolysis of organic matter, preferably
carbon-rich, in the presence of the redox material. Particularly
advantageous are mesomolecules and polymers capable of easily
forming, either mechanically or by impregnation from a solution or
through in situ polymerization, a uniform layer at the surface of
the redox material particles. A subsequent pyrolysis or
dehydrogenation step thereof provides a fine and uniform layer of
the carbonaceous material at the surface of the particles of the
redox material. To ensure that the pyrolysis or dehydrogenation
reaction will not affect the latter, it is preferred to select
compositions wherein the oxygen pressure liberated from the
material is sufficiently low to prevent oxidation of the carbon
formed by the pyrolysis. The activity of the oxygen of compounds
A.sub.aM.sub.mZ.sub.zO.sub.oN.sub.nF.sub.f can be controlled by the
concentration of alkali metal, which itself determines the
oxidation state of the transition element or elements contained in
the material and being a part of the invention. Of particular
interest are the compositions wherein the coefficient "a" of the
alkali metal concentration allows the maintenance of the following
oxidation states: Fe.sup.2+, Mn.sup.2+, V.sup.2+, V.sup.3+,
Ti.sup.2+, Ti.sup.3+, Mo.sup.3+, Mo.sup.4+, Nb.sup.3+, Nb.sup.4+,
W.sup.4+. Generally, oxygen pressures on the order of 10.sup.-20
bars at 0.degree. C. and of 10.sup.-10 bars at 900.degree. C. are
sufficiently low to allow the deposition of carbon by pyrolysis,
the kinetics of carbon formation in the presence of
hydrocarbonaceous residues resulting from the pyrolysis being
quicker and less activated than oxygen formation from the redox
materials. It is also possible and advantageous to select materials
having an oxygen pressure in equilibrium with the materials that
are inferior to that of the equilibrium:
C+O.sub.2CO.sub.2
[0036] In this instance, the carbonaceous material can be
thermodynamically stable vis-a-vis the complex oxide. The
corresponding pressures are obtained according to the following
equation:
ln P ( O 2 ) = ln P ( CO 2 ) = 94050 R ( 273.2 + .theta. )
##EQU00001##
wherein R is the perfect gas constant (1.987
calmole.sup.-1K.sup.-1); and .theta. is the temperature in .degree.
C.
[0037] Table 1 provides oxygen pressures at several
temperatures:
TABLE-US-00001 P(O.sub.2) P(O.sub.2) .theta. (.degree. C.)
P(CO.sub.2) = 1 atm P(CO.sub.2) = 10.sup.-5 atm 200 3.5 .times.
10.sup.-44 3.5 .times. 10.sup.-49 300 1.4 .times. 10.sup.-36 1.4
.times. 10.sup.-41 400 2.9 .times. 10.sup.-31 2.9 .times.
10.sup.-36 500 2.5 .times. 10.sup.-27 2.5 .times. 10.sup.-32 600
2.9 .times. 10.sup.-24 2.5 .times. 10.sup.-29 700 7.5 .times.
10.sup.-22 7.5 .times. 10.sup.-27 800 7.0 .times. 10.sup.-20 7.0
.times. 10.sup.-25 900 3.0 .times. 10.sup.-18 3.0 .times.
10.sup.-23
[0038] It is also possible to perform the carbon deposition through
the disproportionation of carbon oxide at temperatures lower than
800.degree. C. according to the equation:
2COC+CO.sub.2
[0039] This reaction is exothermic but slow. The complex oxide
particles can be contacted with carbon monoxide, pure or diluted in
an inert gas, at temperatures varying from 100 to 750.degree. C.,
preferably between 300 and 650.degree. C. Advantageously, the
reaction is carried out in a fluidized bed, in order to have a
large exchange surface between the gaseous phase and the solid
phase. Elements and cations of transition metals present in the
complex oxide are catalysts of the disproportionation reaction. It
can be advantageous to add small amounts of transition metal salts,
preferably iron, nickel, or cobalt, at the surface of the
particles, these elements being particularly active as catalysts of
the disproportionation reaction. In addition to carbon monoxide
disproportionation, hydrocarbons in gaseous form can be decomposed
at moderate to high temperatures to yield carbon deposits. Of
special interest for the operation are the hydrocarbons with a low
energy of formation, like alkenes, alkynes or aromatic rings.
[0040] In a variation, the deposition of the carbonaceous material
can be performed simultaneously with a variation of the composition
of alkali metal A. To do so, an organic acid or polyacid salt is
mixed with the complex oxide. Another possibility comprises the in
situ polymerization of a monomer or monomer mixtures. Through
pyrolysis, the compound deposits a carbonaceous material film at
the surface and the alkali metal A is incorporated according to the
equation:
A.sub.a'M.sub.mZ.sub.zO.sub.oN.sub.nF.sub.f+A.sub.a-a'C.sub.cO.sub.oR'A.-
sub.aM.sub.mZ.sub.zO.sub.oN.sub.nF.sub.f
R' being an organic radical, which may be part of a polymeric
chain.
[0041] Compounds capable of permitting this reaction may include,
but are not limited to, salts of carboxylic acids such as oxalic,
malonic, succinic, citric, polyacrylic, polymethacrylic, benzoic,
phtalic, propiolic, acetylene dicarboxylic, naphthalene di- or
tetracarboxylic, perylene tetracarboxylic and diphenic acids.
[0042] Obviously, the pyrolysis of an organic material deprived of
an alkali element in combination with an alkali element salt can
also lead to the desired stoichiometry of the complex oxide.
[0043] It is also possible to obtain a carbonaceous material
deposit, especially at low or mid-range temperatures, lower than
400.degree. C., by reduction of carbon-halogen bonds according to
the equation:
CY--CY+2e.sup.--C.dbd.C-+2Y.sup.-
wherein Y represents a halogen or a pseudo-halogen. The term
pseudo-halogen means an organic or inorganic radical capable of
existing in the form of an ion Y.sup.- and forming a corresponding
protonated compound HY. Examples of halogen and pseudo-halogen
include F, Cl, Br, I, CN, SCN, CNO, OH, N.sub.3, RCO.sub.2,
RSO.sub.3, wherein R is H or an organic radical. The formation by
reduction of CY bonds is preferably performed in the presence of
reducing elements such as hydrogen, zinc, magnesium, Ti.sup.3+
ions, Ti.sup.2+ ions, Sm.sup.2+ ions, Cr.sup.2+ ions, V.sup.2+
ions, tetrakis(dialkylamino ethylene) or phosphines. These reagents
can optionally be obtained or regenerated electrochemically.
Further, it can also be advantageous to use catalysts to increase
the reduction kinetics. Palladium or nickel derivatives are
particularly efficient, particularly in the form of complexes with
phosphorous or nitrogen compounds like 2,2'-bipyridine. Similarly,
these compounds can be generated chemically in an active form in
the presence of reducing agents, such as those mentioned above, or
electrochemically. Compounds capable of generating carbon by
reduction include perhalocarbons, particularly in the form of
polymers, hexachlorobutadiene and hexachlorocyclopentadiene.
[0044] Another way to release carbon from a low temperature process
comprises the elimination of the hydrogenated compound HY, Y being
as defined above, according to the equation:
--CH--CY-+B--C.dbd.C-+BHY
[0045] Compounds capable of generating carbon from reduction
include organic compounds comprising an even number of hydrogen
atoms and Y groups, such as hydrohalocarbons, in particular in the
form of polymers, such as vinylidene polyfluoride, polychloride or
polybromide, or carbon hydrates. The dehydro (pseudo) halogenation
can be obtained at low temperatures, including room temperature, by
reacting a base with the HY compound to form a salt. Examples of
suitable bases include tertiary bases, amines, amidines,
guanidines, imidazoles, inorganic bases such as alkali hydroxides,
organometallic compounds behaving like strong bases, such as
A(N(Si(CH.sub.3).sub.3).sub.2, LiN[CH(CH.sub.3).sub.2].sub.2, and
butyl-lithium.
[0046] In the last two methods, it can be advantageous to anneal
the material after the carbon deposition. Such treatment improves
the structure or the crystallinity of the carbonaceous deposit. The
treatment can be performed at a temperature varying between 100 and
1000.degree. C., preferably between 100 and 700.degree. C., to
prevent the potential reduction of the complex oxide by the
carbonaceous material.
[0047] Generally, it is possible to obtain uniform carbonaceous
material coatings, ensuring a sufficient electronic conductivity,
i.e., at least on the same order as the ionic conductivity of the
oxide particle. The thick coatings provide a conductivity
sufficient so that the binary mixture of complex oxide particles
coated with the carbonaceous material, and the liquid or polymeric
electrolyte or the inert macromolecular binder to be wetted with
the electrolyte, is conductive by a simple contact between the
particles. Generally, such behavior can be observed at volumic
fractions comprised between 10 and 70%.
[0048] It can also be advantageous to select deposits of
carbonaceous materials sufficiently thin to prevent obstruction of
the passage of ions, while ensuring the distribution of the
electrochemical potential at the surface of the particles. In this
instance, the binary mixtures possibly do not possess an electronic
conductivity sufficient to ensure the electronic exchanges with the
electrode substrate (current collector). The addition of a third
electronic conductive component, in the form of a fine powder or
fibers, provides satisfactory macroscopic conductivity and improves
the electronic exchanges with the electrode substrate. Carbon
blacks or carbon fibers are particularly advantageous for this
purpose and give satisfactory results at volumic concentrations
that have little or no effect on the rheology during the use of the
electrode because of the existence of electronic conductivity at
the surface of the electrode material particles. Volumic fractions
of 0.5 to 10% are particularly preferred. Carbon black such as
Shawinigan.RTM. or Ketjenblack.RTM. are preferred. Among carbon
fibers, those obtained by pyrolysis of polymers, such as tar,
pitch, polyacrylonitrile as well as those obtained by cracking of
hydrocarbons, are preferred.
[0049] Interestingly, because of its light weight and malleability,
aluminium is used as the current collector constituent. This metal
is nonetheless coated with an insulating oxide layer. This layer,
which protects the metal from corrosion, can in certain conditions
increase the thickness, leading to an increased resistance of the
interface, prejudicial to the good operation of the electrochemical
cell. This phenomenon can be particularly detrimental and fast when
the electronic conductivity is only ensured, as in the prior art,
by the carbon particles having a limited number of contact points.
The use, in combination with aluminium, of electrode materials
coated with a conductive carbonaceous material layer increases the
exchange surface aluminium-electrode. The aluminium corrosion
effects are therefore cancelled or at least significantly
minimized. It is possible to use either aluminium collectors in the
form of a sheet or possibly in the form of expanded or perforated
metal or fibers, which allow a weight gain. Because of the
properties of the materials of the invention, even in the case of
expanded or perforated metal, electronic exchanges at the collector
level take place without a noticeable increase of the
resistance.
[0050] Whenever the current collectors are thermally stable, it is
also possible to perform the pyrolysis or dehydrogenation directly
on the collector so as to obtain, after carbon deposition, a
continuous porous film that can be infiltrated with an ionic
conductive liquid, or with a monomer or a mixture of monomers
generating a polymer electrolyte after in situ polymerization. The
formation of porous films in which the carbonaceous coating forms a
chain is easily obtained according to the invention through
pyrolysis of a complex oxide-polymer composite deposited in the
form of a film on a metallic substrate.
[0051] In using the electrode material according to the invention
in an electrochemical cell, preferably a primary or secondary
battery, the electrolyte is preferably a polymer, solvating or not,
optionally plasticized or gelled by a polar liquid in which one or
more metallic salts, preferably at least a lithium salt, are
dissolved. In such instance, the polymer is preferably formed from
units of oxyethylene, oxypropylene, acrylonitrile, vinylidene
fluoride, acrylic acid or methacrylic acid esters, or itaconic acid
esters with alkyls or oxaalkyl groups. The electrolyte can also be
a polar liquid immobilized in a microporous separator, such as a
polyolefin, a polyester, nanoparticles of silica, alumina or
lithium aluminate (LiAlO.sub.2). Examples of polar liquids include
cyclic or linear carbonates, alkyl formiates, oligoethylene
glycols, .alpha.-.omega. alkylethers, N-methylpyrrolidinone,
.gamma.-butyrolactone, tetraalakylsulfamides and mixtures
thereof.
[0052] The following examples are provided to illustrate preferred
embodiments of the invention, and shall not be construed as
limiting its scope.
Example 1
[0053] This example illustrates the synthesis of a material of the
present invention leading directly to an insertion material coated
with a carbonaceous deposit.
[0054] The material LiFePO.sub.4 coated with a carbonaceous deposit
is prepared from vivianite (Fe.sub.3(PO.sub.4).sub.2.8H.sub.2O) and
lithium orthophosphate (Li.sub.3PO.sub.4) in stoichiometric amounts
according to the reaction:
Fe.sub.3(PO.sub.4).sub.2.8H.sub.2O+Li.sub.3PO.sub.43LiFePO.sub.4
[0055] Polypropylene powder in an amount corresponding to 3% by
weight of vivianite is added. The three components are intimately
mixed together and ground in a zirconia ball mill. The mixture is
then heated under an inert atmosphere of argon, first at
350.degree. C. for 3 hours to dehydrate the vivianite.
Subsequently, the temperature is gradually increased up to
700.degree. C. to crystallize the material and carbonize the
polypropylene. The temperature is maintained at 700.degree. C. for
7 hours. The structure of the material obtained, as verified by
X-rays, corresponds to that published for triphyllite. The amount
of carbon present in the sample has been determined by elemental
analysis, and gave a concentration of 0.56%. For comparison
purposes, a similar sample has been prepared in similar conditions,
but without the addition of polypropylene powder. This latter
sample also shows a pure crystalline structure of the type
LiFePO.sub.4.
Electrochemical Properties
[0056] The materials prepared were tested in button batteries of
the CR2032 type at room temperature and 80.degree. C.
Tests at 80.degree. C. (Polymer Electrolyte)
[0057] The materials obtained above have been tested in button
batteries of the CR2032 type. The cathode was obtained by mixing
together the active material powder with carbon black
(Ketjenblack.RTM.) to ensure the electronic exchange with the
current collector, and polyethylene oxide with a molecular weight
of 400,000 is added as both a binder and an ionic conductor. The
proportions, by weight, are 35:9:56. Acetonitrile is added to the
mixture to dissolve the ethylene polyoxide. The mixture is
homogenized and poured on a stainless steel disc of 1.7 cm.sup.2.
The cathode is dried under vacuum, and transferred in a Vacuum
Atmospheres glove box, under helium atmosphere (<1 vpm H.sub.2O,
O.sub.2). A sheet of lithium (27 .mu.m) laminated on a nickel
substrate is used as the anode. The polymer electrolyte comprises
polyethylene oxide of weight 5,000,000 and LiTFSI (lithium
bis-trifluoromethanesulfonimide) in proportions of oxygen of
oxyethylene units/lithium of 20:1.
[0058] The electrochemical experiments were carried out at
80.degree. C., the temperature at which the ionic conductivity of
the electrolyte is sufficient (2.times.10.sup.-3 Scm.sup.-1). The
electrochemical studies are performed by slow voltammetry (20
mVh.sup.-1) controlled by a battery cycler of the Macpile.RTM.
type. The batteries were charged and discharged between 3.7 and 3
V.
[0059] FIG. 2 illustrates the first cycle obtained for carbonaceous
and noncarbonaceous materials prepared above. For the
non-carbonaceous sample, the oxidation and reduction phenomenons
extend over a wide potential range. For the carbonaceous sample,
the peaks are much better defined on a narrow potential domain. The
evolution of both materials during the first 5 cycles is very
different (FIG. 3). For the carbon-coated sample, the oxidation and
reduction kinetics become faster and faster, thus leading to better
defined peaks (larger peak currents and narrower peak widths).
However, for the non-carbonaceous sample, the kinetics become
slower and slower. The evolution of the capacity of both samples is
illustrated in FIG. 4. For the carbonaceous sample, the capacity
exchanged is stable. It represents from 94 to 100% of the
theoretical capacity (170 mAhg.sup.-1) depending on the sample. The
initial capacity of the non-carbonaceous material is around 145
mAhg.sup.-1, i.e., about 85% of the theoretical capacity. For this
sample, the capacity exchanged quickly decreases. After 5 cycles,
the battery has lost 20% of its initial capacity.
[0060] The carbonaceous sample is cycled under an intentiostatic
mode between 3.8 and 3 V with fast charging and discharging rates.
The imposed currents correspond to a C/1 rate, which means that all
the capacity is exchanged in 1 hour. These cycling results are
shown in FIG. 5. The first 5 cycles are performed under a
voltamperometric mode to activate the cathode and determine its
capacity. In this instance, 100% of the theoretical capacity is
exchanged during the first voltammetric cycles and 96% during the
first 80 intentiostatic cycles. Subsequently, the capacity slowly
decreases, and after 1000 cycles, 70% of the capacity (120
mAhg.sup.-1) is still exchanged at this rate. The cycling in the
potentiodynamic mode performed after 950 cycles shows that in
reality, 89% of the initial capacity is still available at slower
discharge rates. The loss of power is associated with the increase
of the resistance at the lithium/polymer electrolyte interface. The
parameter (capacity passed during charging)/(capacity passed during
discharging) becomes erratic in appearance. This parameter C/D,
shown on FIG. 5 at the end of cycling, leads to the presumption
that dendrites are formed.
Tests at Room Temperature (Liquid Electrolyte)
[0061] The LiFePO.sub.4 coated with a carbonaceous deposit was also
tested at room temperature. In this instance, the composite cathode
is prepared by mixing the active material with carbon black and
EPDM (preferably dissolved in cyclohexane) in a ratio of 85:5:10.
The mixture is spread onto a stainless steel current collector in
the form of a disc of 1.7 cm.sup.2, dried under vacuum, and kept in
a glove box under helium atmosphere. As above, lithium is used as
the anode. Both electrodes are separated by a Celgard.TM. porous
membrane. The electrolyte used is a LiTFSI 0.8 molal solution in
gamma-butyrolactone. The voltamperograms illustrated in FIG. 6 were
obtained at room temperature under slow voltammetry (20 mVh.sup.-1)
between 3 and 3.8 V. With such configuration, the oxidation and
reduction kinetics appear to be much slower than at 80.degree. C.
Further, the power of the battery decreases slowly during cycling.
On the other hand, the entire theoretical capacity is accessible
(97.5% cycle 1, 99.4% cycle 5), i.e., reversibly exchanged without
loss during cycling (5 cycles). It is not excluded that the low
power of this battery may come from a poor permeation of the
electrode by the electrolyte, the latter being a poor wetting agent
for the binding polymer.
[0062] The example illustrates that the improvement of the material
studied, because of the presence of the carbonaceous deposit at the
surface of the particles, is reflected on the kinetics, the
capacity and the cyclability. Further, its role is independent from
that of the type of carbon black added during the preparation of
composite cathodes.
Example 2
[0063] This example shows the formation of a conductive
carbonaceous deposit from a hydrocarbon gas. The synthesis
described in Example 1 for the preparation of lithium iron
phosphate is repeated without adding polypropylene powder, and by
replacing the thermal treatment inert atmosphere with a mixture of
1% propene in nitrogen. During the thermal treatment, propene
decomposes to form a carbon deposit on the material being
synthesized. The resulting sample obtained contains 2.5% of carbon,
as determined by chemical analysis. Cyclic voltammetry is performed
on this sample under the conditions described in Example 1, and
shows the important activation phenomenon during the first cycles
(see FIG. 6). The improvement in redox kinetics is accompanied in
this instance by an increase of the capacity reversibly exchanged.
As measured during the discharge step, the initial capacity of the
LiFePO.sub.4 sample prepared represents 77% of the theoretical
capacity, taking into account the 2.5% electrochemically inactive
carbon. After 5 cycles, the capacity reaches 91.4%. The activation
phenomenon observed is linked to the thickness of the carbon layer,
which may be porous, coating the particles and capable of slowing
the diffusion of the cations.
[0064] The following examples 3-5 illustrate the treatment of the
complex oxide, namely the lithium iron phosphate (LiFePO.sub.4),
prepared thermally and independently in order to obtain a
conductive carbonaceous coating.
Example 3
[0065] The tryphilite sample LiFePO.sub.4 prepared above is
analyzed. Its mass composition is: Fe: 34.6%, Li: 4.2%, P: 19.2%,
which represents a 5% difference with respect to the
stoichiometry.
[0066] The powder to be treated is impregnated with an aqueous
solution of commercial sucrose and dried. The amount of solution is
selected to correspond to 10% of the weight of sucrose with respect
to the weight of the material to be treated. Water is completely
evaporated under agitation to obtain a homogeneous distribution.
The use of sugar represents a preferred embodiment because it melts
before being carbonized, thereby providing a good coating of the
particles. Its relatively low carbon yield after pyrolysis is
compensated by its low cost.
[0067] The thermal treatments are performed at 700.degree. C. under
argon atmosphere. The temperature is maintained for 3 hours.
Elemental analysis shows that this product contains 1.3% by weight
of carbon. Such thermal treatment leads to a black powder giving an
electronic conductivity measurable with a simple commercial
ohm-meter. Its electroactivity, as measured on the 1.sup.st (FIG.
8) and 5.sup.th (FIG. 9) charge-discharge cycle, is 155.9
mAhg.sup.-1 and 149.8 mAhg.sup.-1 respectively, which is 91.7% and
88.1% of the theoretical value. These values are to be compared
with that of the product not coated with the carbon deposit, that
has only 64% electroactivity. After 5 cycles, this value fades to
37.9% (FIG. 10).
Example 4
[0068] Cellulose acetate is added to the phosphate LiFePO.sub.4 of
Example 3 as a precursor of the carbon coating. This polymer is
known to decompose with high carbonization yields, on the order of
24%. It decomposes between 200 and 400.degree. C. Above this
temperature, the amorphous carbon rearranges to give a
graphite-type structure that favors coherent and highly conductive
carbon deposits.
[0069] Cellulose acetate is dissolved in acetone in a ratio
corresponding to 5% by weight of the material to be treated, and
dried before proceeding as above. The carbon concentration of the
final product is 1.5%. The thermal treatment leads, in a similar
manner, to a black powder having surface electronic conductivity.
Its electroactivity, as measured on the 1.sup.st (FIG. 8) and
5.sup.th (FIG. 9) charge-discharge cycles, is 152.6 mAhg.sup.-1 and
150.2 mAhg.sup.-1 respectively, which is 89.8% and 88.3% of the
theoretical value. This value is to be compared with that of the
product not coated with the carbon deposit, that has only 64%
electroactivity. After 5 cycles, this value fades to 37.9% (FIG.
10).
Example 5
[0070] Perylene and its derivatives are known to lead, after
pyrolysis, to graphitic-type carbons because of the existence of
condensed cycles in the starting molecule. In particular, the
perylene-tetracarboxylic acid anhydride decomposes above
560.degree. C. and provides a thin carbon layer sufficient to cover
the particle surface. However, this product shows a poor
solubility, and their intimate mixture with the complex oxide, here
also LiFePO.sub.4 of Example 3, is difficult to embody. To solve
this problem, a polymer containing perylene groups separated with
an ethylene polyoxide chain has been prepared in a first step. The
oxyethylene segments are selected to be sufficiently long to act as
solubilizing agents for the aromatic groups in the usual organic
solvents. Therefore, commercial 3,4,9,10-perylenetetracarboxylic
acid anhydride (Aldrich) is reacted with Jeffamine 600 (Hunstmann)
at high temperatures, according to the following reaction:
##STR00002##
wherein
R=--[CH(CH.sub.3)CH.sub.2O--].sub.p(CH.sub.2CH.sub.2O--).sub.q[CH-
.sub.2--CH(CH).sub.3O].sub.p-1CH.sub.2--CH(CH).sub.3--
1.ltoreq.p.ltoreq.2; 10.ltoreq.n.ltoreq.14. The synthesis is
completed within 48 hours in dimethylacetamide under reflux
(166.degree. C.). The polymer formed is precipitated in water, and
a solid-liquid separation is carried out. It is purified by
dissolution in acetone, followed by re-precipitation in ether. The
process allows the removal of unreacted starting materials, as well
as low mass products. The powder is finally dried.
[0071] Carbonization yield of this product is on the order of 20%.
The polymer is dissolved in dichloromethane in a ratio
corresponding to 5% of the weight of the material to be treated
before proceeding as described above in Examples 3 and 4. The
carbon content of the final product is 1%. The thermal treatment
leads, as described above, to a black conductive powder. Its
electroactivity, as measured on the 1.sup.st (FIG. 8) and 5.sup.th
(FIG. 9) charge-discharge cycles, is 148.6 mAhg.sup.-1 and 146.9
mAhg.sup.-1 respectively, which is 87.4% and 86.4% of the
theoretical value. This value is to be compared with that of the
product not coated with the carbon deposit, that has only 64%
electroactivity. After 5 cycles, this value fades to 37.9% (FIG.
10).
Example 6
[0072] This example illustrates the use of an elimination reaction
from a polymer to form a carbonaceous deposit according to the
invention.
[0073] Ferric iron sulfate (Fe.sub.2(SO.sub.4).sub.3) with a
"Nasicon" orthorhombic structure was obtained from commercial
hydrated iron (III) sulfate (Aldrich) by dehydration at 450.degree.
C. under vacuum. With cooling, and under stirring, the powder
suspended in hexane was lithiated with stoichiometric 2M butyl
lithium to reach the composition
Li.sub.1.5Fe.sub.2(SO.sub.4).sub.3. 20 g of the resulting white
powder were slurried in 100 mL acetone and 2.2 g of poly(vinylidene
bromide) (--CH.sub.2CBr.sub.2).sub.n-- were added and the mixture
was treated for 12 hours in a ball mill with alumina balls. The
suspension thus obtained was dried in a rotary evaporator and
crushed as coarse powder in a mortar. The solid was treated with 3
g of diazabicyclo[5.4.0]unde-7-cene (DBU) in acetonitrile under
reflux for three hours. The black powder thus obtained was filtered
to eliminate the resulting amine bromide and excess reagent, rinsed
with acetonitrile and dried under vacuum at 60.degree. C. Further
annealing of the carbonaceous deposit was performed under
oxygen-free argon (<1 ppm) at 400.degree. C. for three
hours.
[0074] The material coated with the carbonaceous material was
tested for electrochemical activity in a lithium cell with a
lithium metal electrode, 1 molar lithium
bis-(trifluoromethanesulfonimide) in 50:50 ethylene
carbonate-dimethoxymethane mixture as electrolyte immobilized in a
25 .mu.m microporous polypropylene separator. The cathode was
obtained from the prepared redox material mixed with
Ketjenblack.RTM. and slurried in a solution of
ethylene-propylene-diene polymer (Aldrich), the ratio of solids
content being 85:10:5. The cathode mix was spread on an expanded
aluminium metal grid and pressed at 1 ton cm.sup.-2 to a resulting
thickness of 230 .mu.m. The button cell assembly was charged (the
tested material being the anode) at 1 mAcm.sup.-2 between the
cut-off potentials of 2.8 and 3.9 V. The material capacity is 120
mAhg.sup.-1, corresponding to 89% of theoretical value. The average
potential was obtained at 3.6 V vs. Li.sup.+:Li.sup.o.
Example 7
[0075] This example illustrates the use of a nitrogen-containing
compound as an electrode material.
[0076] Powdered manganous oxide (MnO) and lithium nitride, both
commercial (Aldrich), were mixed in a dry box under helium in a 1:1
molar ratio. The reactants were put in a glassy carbon crucible and
treated under oxygen-free nitrogen (<1 vpm) at 800.degree. C. 12
g of the resulting oxynitride with an antifluorite structure
Li.sub.3MnNO were added to 0.7 g of micrometer size polyethylene
powder and ball milled under helium in a polyethylene jar with dry
heptane as the dispersing agent and 20 mg of Brij.TM. 35 (ICI) as
the surfactant. The filtered mix was then treated under a flow of
oxygen-free nitrogen in a furnace at 750.degree. C. to ensure
decomposition of the polyethylene into carbon.
[0077] The carbon-coated electrode material appears as a black
powder rapidly hydrolyzed in moist air. All subsequent handling was
carried out in a dry box wherein a cell similar to that of Example
6 was constructed and tested for electrochemical activity of the
prepared material. The electrolyte in this case is a mixture of
commercial tetraethylsulfamide (Fluka) and dioxolane in a 40:60
volume ratio. Both solvents were purified by distillation over
sodium hydride (under 10 torrs reduced pressure for the sulfamide).
Lithium bis-(trifluoromethanesulfonimide) (LiTFSI) is added to the
solvent mixture to form a 0.85 molar solution. Similar to the
set-up of Example 6, the cell comprises a lithium metal electrode,
the electrolyte immobilized in a 25 .mu.m porous polypropylene
separator and the material processed in a way similar to that of
Example 6.
[0078] The cathode is obtained from the prepared redox material
mixed with Ketjenblack.RTM. and slurried in a solution of
ethylene-propylene-diene polymer, the ratio of solids content being
90:5:5. The cathode mix is pressed on an expanded copper metal grid
at 1 ton cm.sup.-2 with a resulting thickness of 125 .mu.m. The
button cell assembly is charged at 0.5 mAcm.sup.-2 (the oxynitride
being the anode) between the cut-off potentials of 0.9 and 1.8 V.
The material's capacity was 370 mAhg.sup.-1, i.e., 70% of the
theoretical value for two electrons per formula unit. The average
potential is found at 1.1 V vs. Li.sup.+:Li.sup.o. The material is
suited for use as a negative electrode material in lithium-ion type
batteries. An experimental cell of this type has been constructed
with the electrode material on a copper metal grid similar to that
tested previously and a positive electrode material obtained by
chemical delithiation of the lithium iron phosphate of Example 1 by
bromine in acetonitrile. The iron (III) phosphate obtained was
pressed onto an aluminium grid to form the positive electrode and
the 0.85 M LiTFSI tetraethylsulfamide/dioxolane solution used as an
electrolyte. The average voltage of such cell is 2.1 V and its
energy density, based on the weight of the active materials, is 240
Wh/Kg.
Example 8
[0079] Lithium vanadium (III) phosphosilicate
(Li.sub.3.5V.sub.2(PO.sub.4).sub.2.5(SiO.sub.4).sub.0.5), having a
"Nasicon" structure was prepared in the following manner:
[0080] Lithium carbonate (13.85 g), lithium silicate
Li.sub.2SiO.sub.3, (6.74 g), dihydrogen ammonium phosphate (43.2 g)
and ammonium vanadate (35.1 g) were mixed with 250 mL of
ethylmethylketone and treated in a ball mill with alumina balls in
a thick-walled polyethylene jar for 3 days. The resulting slurry
was filtered, dried and treated in a tubular furnace under a 10%
hydrogen in nitrogen gas flow at 600.degree. C. for 12 hours. After
cooling, 10 g of the resulting powder were introduced in a
planetary ball mill with tungsten carbide balls. The resulting
powder was added to a solution of the polyaromatic polymer prepared
in Example 5 (polyoxyethylene-co-perylenetetracarboxylicdimide 0.8
g in 5 mL acetone), well homogenized, and the solvent was
evaporated.
[0081] The red-brown powder was thermolyzed in a stream of
oxygen-free argon at 700.degree. C. for 2 hours, leaving after
cooling a black powder with a measurable surface conductivity. The
material coated with the carbonaceous material was tested for
electrochemical activity in a lithium-ion cell with a natural
graphite electrode (NG7) coated on a copper current collector and
corresponding to 24 mg/cm.sup.2, 1 molar lithium
hexafluorophosphate in 50:50 ethylene carbonate dimethylcarbonate
mixture as electrolyte immobilized in a 25 .mu.m microporous
polypropylene separator. The cathode was obtained from the lithium
vanadium phosphosilicate mixed with Ketjenblack.RTM. and slurried
in a solution of vinylidenefluoride-hexafluoropropene copolymer in
acetone, the ratio of solids content being 85:10:5. The cathode mix
was spread on an expanded aluminium metal grid and pressed at 1 ton
cm.sup.-2 to a resulting thickness of 190 .mu.m corresponding to an
active material loading of 35 mg/cm.sup.2. The button cell assembly
was charged (the tested material being the anode) at 1 mAcm.sup.-2
between the cut-off potentials of 0 and 4.1 V. The capacity of the
carbon coated material was 184 mAhg.sup.-1, corresponding to 78% of
the theoretical value (3.5 lithium per unit formula), slowly fading
with cycling. In a comparative test, a similar cell constructed
using the uncoated material, as obtained after milling the heat
treated inorganic precursor but omitting the addition of the
perylene polymer, shows a capacity of 105 mAhg.sup.-1, rapidly
fading with cycling.
Example 9
[0082] This example illustrates the formation of a carbonaceous
coating simultaneous to a variation of the alkali metal content of
the redox material.
[0083] 13.54 g of commercial iron (III) fluoride (Aldrich), 1.8 g
of the lithium salt of hexa-2,4-dyine dicarboxylic acid are ball
milled in a thick-walled polyethylene jar with alumina balls, in
the presence of 100 mL of acetonitrile. After 12 hours, the
resulting slurry was filtered and the dried powder was treated
under a stream of dry, oxygen-free nitrogen in a tubular furnace at
700.degree. C. for three hours. The resulting black powder
contained from elemental analysis: Fe: 47%, F: 46%, Li: 1.18%, C:
3.5%, corresponding to the formula Li.sub.0.2FeF.sub.3C.sub.0.35.
The electrode material was tested for its capacity in a cell
similar to that of Example 6 with the difference being that the
cell is first tested on discharge (the electrode material as
cathode), and then recharged. The cut-off voltages were chosen
between 2.8 and 3.7 V. The experimental capacity on the first cycle
was 190 mAhg.sup.-1, corresponding to 83% of the theoretical value.
For comparison, a cell with FeF.sub.3 as the electrode material and
no carbonaceous coating has a theoretical capacity of 246
mAhg.sup.-1. In practice, the first discharge cycle obtained in
similar conditions to the material of the invention is 137
mAhg.sup.-1.
Example 10
[0084] This example also illustrates the formation of a
carbonaceous coating simultaneous to a variation of the alkali
metal content of the redox material.
[0085] Commercial polyacrylic acid of molecular weight 15,000 was
dissolved as 10% solution in water/methanol mixture and titrated
with lithium hydroxide to a pH of 7. 4 .mu.L of this solution were
dried in the crucible of a thermogravimetry air at 80.degree. C. to
evaporate the water/methanol. The heating was then continued to
500.degree. C., showing a residue of 0.1895 mg of calcination
residue as lithium carbonate.
[0086] 18.68 g of commercial iron (III) phosphate dihydrate,
(Aldrich), 8.15 g lithium oxalate (Aldrich), 39 mL of the lithium
polyacrylate solution, 80 mL of acetone and 40 mL of 2,2-dimethoxy
acetone as water scavenger were ball milled in a thick-walled
polyethylene jar with alumina balls. After 24 hours, the resulting
slurry was filtered and dried. The resulting powder was treated
under a stream of dry, oxygen-free nitrogen in a tubular furnace at
700.degree. C. for three hours, resulting in a blackish powder. The
resulting product had the following elemental analysis: Fe: 34%, P:
18.8%, Li: 4.4%, C: 3.2%. The X-ray analysis confirmed the
existence of pure triphilite LiFePO.sub.4 as the sole crystalline
component. The electrode material was tested for its capacity in a
cell similar to that of Example 1 with a PEO electrolyte, and then
recharged. The cut-off voltages were chosen between 2.8 and 3.7 V.
The experimental capacity on the first cycle was 135 mAhg.sup.-1,
corresponding to 77% of the theoretical value, increasing to 156
mAhg.sup.-1 (89%) while the peak definition improved with further
cycling. 80% of this capacity is accessible in the potential range
3.3-3.6 V vs. Li.sup.+:Li.sup.o.
Example 11
[0087] The compound LiCo.sub.0.75Mn.sub.0.25PO.sub.4 was prepared
from intimately ground cobalt oxalate dihydrate, manganese oxalate
dihydrate and dihydrogen ammonium phosphate by firing in air at
850.degree. C. for 10 hours. The resulting mauve powder was ball
milled in a planetary mill with tungsten carbide balls to an
average grain size of 4 .mu.m. 10 g of this complex phosphate were
triturated in a mortar with 10 mL of 6% solution of the perylene
polymer of Example 5 in methyl formate. The solvent rapidly
evaporated. The resulting powder was treated under a stream of dry,
oxygen-free argon in a tubular furnace at 740.degree. C. for three
hours, resulting in a black powder. The electrochemical activity of
the cell was tested in a lithium-ion cell similar to that of
Example 6. The electrolyte was, in this case, lithium
bis-fluoromethanesulfonimide (Li[FSO.sub.2].sub.2N) dissolved at a
concentration of 1M in the oxidation-resistant solvent
dimethylamino-trifluoroethyl sulfamate
(CF.sub.3CH.sub.2OSO.sub.2N(CH.sub.3).sub.2). When initially
charged, the cell showed a capacity of 145 mAhg.sup.-1 in the
voltage window 4.2-4.95 V vs. Li.sup.+:Li.sup.o. The battery could
be cycled for 50 deep charge-discharge cycles with less than 10%
decline in capacity, showing the resistance of the electrolyte to
high potentials.
Example 12
[0088] The compound Li.sub.2MnSiO.sub.4 was prepared by calcining
the gel resulting from the action of a stoichiometric mixture of
lithium acetate dihydrate, manganese acetate tetrahydrate and
tetraethoxysilane in a 80:20 ethanol water mixture. The gel was
dried in an oven at 80.degree. C. for 48 hours, powdered and
calcined under air at 800.degree. C. 3.28 g of the resulting
silicate and 12.62 g of lithium iron phosphate from Example 3 were
ball milled in a planetary mill similar to that of Example 11, and
the powder was treated at 800.degree. C. under a stream of dry,
oxygen-free argon in a tubular furnace at 740.degree. C. for 6
hours. The complex oxide obtained after cooling has the formula
Li.sub.1.2Fe.sub.0.8Mn.sub.0.2P.sub.0.8Si.sub.0.2O.sub.4. The
powder was moistened with 3 mL of a 2% solution of cobalt acetate,
then dried. The powder was treated in the same tubular furnace at
500.degree. C. under a flow of 1 mL/s of 10% carbon monoxide in
nitrogen for two hours. After cooling, the resulting black powder
was tested for electrochemical activity in conditions similar to
those of Example 1. With a PEO electrolyte at 80.degree. C., the
capacity was measured from the cyclic voltamogram curve at 185
mAhg.sup.-1 (88% of theory) between the cut-off voltages of 2.8 and
3.9 V vs. Li.sup.+:Li.sup.o. The uncoated material, tested in
similar conditions, has a specific capacity of 105 mAhg.sup.-1.
Example 13
[0089] Under argon, 3 g of lithium iron phosphate from Example 3
was suspended in 50 mL acetonitrile to which was added 0.5 g of
hexachlorocyclopentadiene and 10 mg of
tetrakis(triphenylphosphine)nickel (0). Under vigorous stirring,
1.4 mL of tetrakis(dimethylamino)ethylene was added dropwise at
room temperature. The solution turned blue, and after more reducing
agent was added, black. The reaction was left under stirring for 24
hours after completion of the addition. The resulting black
precipitate was filtered, washed with ethanol and dried under
vacuum. Annealing of the carbon deposit was performed at
400.degree. C. under a flow of oxygen-free gas for 3 hours. The
resulting black powder was tested for electrochemical activity in
conditions similar to those of Example 1. The measured capacity
between the cut-off voltages of 2.9 and 3.7 V vs. Li.sup.+:Li.sup.o
was found experimentally at 160 mAhg.sup.-1 (91% of theory). The
uncoated material has a specific capacity of 112 mAhg.sup.-1 in the
same experimental conditions.
Example 14
[0090] The spinel compound Li.sub.3.5Mg.sub.0.5Ti.sub.4O.sub.12 was
prepared by sol-gel technique using titanium tetra(isopropoxide)
(28.42 g), lithium acetate dihydrate (35.7 g) and magnesium acetate
tetrahydrate (10.7 g) in 300 mL 80:20 isopropanol-water. The
resulting white gel was dried in an oven at 80.degree. C. and
calcined at 800.degree. C. in air for 3 hours, then under 10%
hydrogen in argon at 850.degree. C. for 5 hours. 10 g of the
resulting blue powder were mixed with 12 mL of a 13 wt % solution
of the cellulose acetate in acetone. The paste was dried and the
polymer carbonized in the conditions of Example 4 under inert
atmosphere at 700.degree. C.
[0091] The positive electrode of an electrochemical super capacitor
was built in the following manner. 5 g of carbon-coated
LiFePO.sub.4 from Example 3, 5 g of Norit.RTM. activated carbon, 4
g of graphite powder (2 .mu.m diameter), 3 g of chopped aluminium
fibers (20 .mu.m long and 5 mm diameter), 9 g of anthracene powder
(10 .mu.m) as a pore former and 6 g of polyacrylonitrile were mixed
in dimethylformamide wherein the polymer dissolved. The slurry was
homogenized and coated onto aluminium foil (25 .mu.m) and the
solvent was evaporated. The coating was then slowly brought to
380.degree. C. under nitrogen atmosphere. The anthracene evaporated
to leave a homogeneous porosity in the material and the
acrylonitrile underwent thermal cyclization to a conductive polymer
consisting of fused pyridine rings. The thickness of the resulting
layer is 75 .mu.m.
[0092] A similar coating is done for the negative electrode with a
slurry where LiFePO.sub.4 is replaced with the coated spinel as
prepared above. The super capacitor assembly is obtained by placing
the two prepared electrodes face to face, separated by a 10
.mu.m-thick polypropylene separator soaked in 1 molar LiTFSI in
acetonitrile/dimethoxyethane mixture (50:50). The device can be
charged at 30 mAcm.sup.-2 and 2.5 V and delivers a specific power
of 3 kW/L.sup.-1 at 1.8 V.
Example 15
[0093] A light modulating device (electrochromic window) was
constructed in the following manner.
[0094] LiFePO.sub.4 from Example 3 was ball milled in a high energy
mill to particles of an average size of 120 nm. 2 g of the powder
were mixed with 1 mL of a 2 wt % solution of the
perylene-co-polyoxyethylene polymer of Example 5 in methyl formate.
The paste was triturated to ensure uniform distribution of the
polymer at the surface of the particles, and the solvent was
evaporated. The dry powder was treated under a stream of dry,
oxygen-free nitrogen in a tubular furnace at 700.degree. C. for
three hours to yield a light gray powder.
[0095] 1 g of the carbon-coated powder was slurried in a solution
of 1.2 g polyethyleneoxide-co-(2-methylene)propane-1,3-diyl
prepared according to J. Electrochem. Soc., 1994, 141(7), 1915 with
ethylene oxide segments of molecular weight 1000, 280 mg of LiTFSI
and 15 mg of diphenylbenzyl dimethyl acetal as photoinitiator in 10
mL of acetonitrile. The solution was coated using the doctor blade
process onto an indium-tin oxide (ITO) covered glass (20
S.sup.-1.quadrature.) to a thickness of 8 .mu.m. After evaporation
of the solvent, the polymer was cured with a 254 nm UV light (200
mWcm.sup.-2) for 3 minutes.
[0096] Tungsten trioxide was deposited by thermal evaporation onto
another ITO covered glass to a thickness of 340 nm. The device
assembly was done by applying a layer of a polyethylene oxide (120
.mu.m) electrolyte with LiTFSI in an oxygen (polymer) to salt ratio
of 12, previously coated on a polypropylene foil and applied to the
WO.sub.3-coated electrode using the adhesive transfer technology.
The two glass electrodes were pressed together to form the
electrochemical chain:
[0097] glass/ITO/WO.sub.3/PEO-LiTFSI/LiFePO.sub.4 composite
electrode/ITO/glass
[0098] The device turned blue in 30 seconds upon application of a
voltage (1.5 V, LiFePO.sub.4 side being the anode) and bleached on
reversal of the voltage. The light transmission is modulated from
85% (bleached state) to 20% (colored state).
[0099] While the invention has been described in connection with
specific embodiments thereof, it will be understood that it is
capable of further modifications, and this application is intended
to cover any variations, uses or adaptations of the invention
following, in general, the principles of the invention, and
including such departures from the present description as come
within known or customary practice within the art to which the
invention pertains, and as may be applied to the essential features
hereinbefore set forth, and as follows in the scope of the appended
claims.
* * * * *