U.S. patent number RE41,578 [Application Number 11/866,722] was granted by the patent office on 2010-08-24 for micro electrochemical energy storage cells.
This patent grant is currently assigned to Ramot At Tel-Aviv University Ltd.. Invention is credited to Dan Haronian, Menachem Nathan, Emanuel Peled.
United States Patent |
RE41,578 |
Nathan , et al. |
August 24, 2010 |
Micro electrochemical energy storage cells
Abstract
Thin-film micro-electrochemical energy storage cells (MEESC)
such as microbatteries and double-layer capacitors (DLC) are
provided. The MEESC comprises two thin layer electrodes, an
intermediate thin layer of a solid electrolyte and optionally, a
fourth thin current collector layer; said layers being deposited in
sequence on a surface of a substrate. The MEESC is characterized in
that the substrate is provided with a plurality of through cavities
of arbitrary shape, with high aspect ratio. By using the substrate
volume, an increase in the total electrode area per volume is
accomplished.
Inventors: |
Nathan; Menachem (Tel Aviv,
IL), Peled; Emanuel (Even Yehuda, IL),
Haronian; Dan (Efat, IL) |
Assignee: |
Ramot At Tel-Aviv University
Ltd. (Tel-Aviv, IL)
|
Family
ID: |
22643891 |
Appl.
No.: |
11/866,722 |
Filed: |
October 3, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
Reissue of: |
09176321 |
Oct 22, 1998 |
06197450 |
Mar 6, 2001 |
|
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Current U.S.
Class: |
429/236; 429/304;
429/231.1; 29/623.1 |
Current CPC
Class: |
H01G
11/56 (20130101); H01M 6/40 (20130101); H01M
10/0585 (20130101); H05K 1/16 (20130101); H01G
11/06 (20130101); H01G 9/155 (20130101); H01G
11/26 (20130101); H01G 11/22 (20130101); H01G
11/70 (20130101); H01G 11/74 (20130101); H01M
10/052 (20130101); H01M 6/18 (20130101); H01L
2924/0002 (20130101); Y10T 29/49108 (20150115); H01M
50/209 (20210101); H01M 2010/0495 (20130101); Y02E
60/13 (20130101); H05K 2201/10037 (20130101); Y02E
60/10 (20130101); H01L 2924/0002 (20130101); H01L
2924/00 (20130101) |
Current International
Class: |
H01M
6/42 (20060101); H01M 4/76 (20060101); H01M
4/40 (20060101); H01M 6/18 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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0 331 342 |
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3313342 |
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2 550 015 |
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FR |
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2550015 |
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Feb 1985 |
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2 606 207 |
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May 1988 |
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FR |
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2606207 |
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FR |
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2621174 |
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FR |
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2 621 174 |
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FR |
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2 621 179 |
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2161988 |
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Jan 1986 |
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GB |
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2 161 988 |
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Jan 1986 |
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GB |
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2168560 |
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Jun 1990 |
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JP |
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Other References
Lehman et al., Thin Solid Films, vol. 276, Issue 1-2, pp. 138-142,
Apr. 1996. cited by examiner .
Patent Abstracts Of Japan, Publication No. 091186461, Publication
Date Jul. 15, 1997. cited by examiner .
Lehmann et al., Thin Solid Films, vol. 276, Issue 1-2, Apr. 1996,
138-142. cited by examiner .
Owen, "Ionically conducting glasses", Solid State Batteries,
Sequiera and Hooper, Nato Science Series E, Springer, Oct. 1985.
cited by other.
|
Primary Examiner: Walker; Keith
Attorney, Agent or Firm: Browdy and Neimark, PLLC
Claims
What is claimed is:
.[.1. A thin-film micro-electrochemical energy storage cell (MEESC)
in the form of a microbattery, said microbattery comprising: a
substrate having two surfaces, a thin layer anode consisting of
alkali metal (M), alkali metal alloy or in the charged state
consisting of lithiated carbon or graphite, a thin layer cathode
consisting of LiCoO.sub.2, LiNiO.sub.2, LiMn.sub.2O.sub.4,
TiS.sub.2, V.sub.2O.sub.5, V.sub.3O.sub.8 or lithiated forms of the
vanadium oxides, a solid electrolyte intermediate to said anode and
cathode layers, consisting of a tin layer of an ionically
conducting or electronically non-conducting material selected from
glass, poly(ethylene oxide) based polymer electrolyte or
polycrystalline material, and optionally, a fourth current
collector layer; said anode or cathode layer being deposited in
sequence on both surfaces of said substrate, said microbattery
being characterized in that the substrate is provided with a
plurality of through cavities of arbitrary shape, with an aspect
ratio greater than 1, the diameter of said cavities being from
about 15.mu. to about 150.mu.; said anode, cathode, solid
electrolyte layers and optional current collector layer being also
deposited throughout the inner surface of said cavities..].
.[.2. The microbattery of claim 1, wherein the substrate is made of
a single crystal or amorphous material..].
.[.3. The microbattery of claim 2, wherein the substrate material
is selected from the group consisting of glass, alumina,
semiconductor materials for use in microelectronics and ceramic
materials..].
.[.4. The microbattery of claim 3, wherein the substrate material
is made of silicon..].
.[.5. The microbattery of claim 1, wherein the alkali metal (M)
which forms the anode is lithium..].
.[.6. A lithium ion type microbattery according to claim 1, being
fabricated in the discharge state where the cathode is fully
lithiated and the alloy, carbon or graphite anode is not charged
with lithium..].
.[.7. The microbattery of claim 1, wherein the through cavities of
the substrate are formed by Inductive Coupled Plasma
etching..].
.[.8. The microbattery of claim 1, wherein the through cavities of
the substrate have an aspect ratio of between about 2 to about
50..].
.[.9. The microbattery of claim 1, wherein said cavities have a
cylindrical geometry..].
.[.10. The microbattery of claim 1, wherein the solid electrolyte
is a polymer electrolyte based on poly(ethylene oxide) and
CF.sub.3SO.sub.3Li, (CF.sub.3SO.sub.2).sub.2NLi, or mixtures
thereof..].
.[.11. The microbattery of claim 1, wherein the solid electrolyte
is selected from Li.sub.XPO.sub.YN.sub.Z where 2<x<3, 2y=3z
and 0.18<z<0.43, or LiS-SiS.sub.2 glasses doped with up to 5%
LiSO.sub.4 or 30% LiI..].
.[.12. The microbattery of claim 1, wherein the solid electrolyte
is a polymer electrolyte and it comprises between about 2 to about
15% (V/V) high surface area of inorganic, nanosize particles of
ceramic powder which consists of Al.sub.2O.sub.3, SiO.sub.2, MgO,
TiO.sub.2 or mixtures thereof..].
.[.13. The microbattery of claim 1, wherein the solid electrolyte
comprises Li.sub.2CO.sub.3 doped with up to about 10% (% atomic
weight relative to Li) of Ca, Mg, Ba, Sr, Al or B..].
.[.14. A self-powered semiconductor component comprising a
microbattery according to claim 2..].
.Iadd.15. A thin-film micro-electrochemical energy storage cell
(MEESC) in the form of a microbattery, said microbattery
comprising: a substrate having two surfaces and including a
plurality of through cavities of arbitrary shape, said cavities
characterized by having an aspect ratio greater than 1 and
extending between said two surfaces; a thin layer anode; a thin
layer cathode; and an electrolyte intermediate to said anode and
cathode layers; wherein said anode layer, said cathode layer, and
said electrolyte intermediate to said anode and cathode layers, are
deposited over said two surfaces and throughout the inner surface
of said cavities..Iaddend.
.Iadd.16. A thin-film micro-electrochemical energy storage cell
(MEESC) in the form of a microbattery according to claim 15 and
wherein said substrate comprises a single crystal
substrate..Iaddend.
.Iadd.17. A thin-film micro-electrochemical energy storage cell
(MEESC) in the form of a microbattery according to claim 16 and
wherein said single crystal substrate comprises a silicon
substrate..Iaddend.
.Iadd.18. A thin-film micro-electrochemical energy storage cell
(MEESC) in the form of a microbattery according to claim 15 and
wherein said substrate comprises a single amorphous
material..Iaddend.
.Iadd.19. A thin-film micro-electrochemical energy storage cell
(MEESC) in the form of a microbattery according to claim 15 and
wherein said substrate comprises at least one material selected
from the group consisting of glass, alumina, semiconductors and
ceramic materials..Iaddend.
.Iadd.20. A thin-film micro-electrochemical energy storage cell
(MEESC) in the form of a microbattery according to claim 15 and
wherein said anode comprises at least one material selected from
the group consisting of an alkali metal, an alkali metal alloy,
carbon and graphite..Iaddend.
.Iadd.21. A thin-film micro-electrochemical energy storage cell
(MEESC) in the form of a microbattery according to claim 20 and
wherein said alkali metal comprises lithium..Iaddend.
.Iadd.22. A thin-film micro-electrochemical energy storage cell
(MEESC) in the form of a microbattery according to claim 20 being
fabricated in the discharge state wherein said cathode layer is
fully lithiated..Iaddend.
.Iadd.23. A thin-film micro-electrochemical energy storage cell
(MEESC) in the form of a microbattery according to claim 22 and
wherein said metal alloy is not charged with lithium..Iaddend.
.Iadd.24. A thin-film micro-electrochemical energy storage cell
(MEESC) in the form of a microbattery according to claim 22 and
wherein said carbon and said graphite are not charged with
lithium..Iaddend.
.Iadd.25. A thin-film micro-electrochemical energy storage cell
(MEESC) in the form of a microbattery according to claim 15 and
wherein said cavities have an aspect ratio greater than 1 and up to
about 50..Iaddend.
.Iadd.26. A thin-film micro-electrochemical energy storage cell
(MEESC) in the form of a microbattery according to claim 15 and
wherein said electrolyte comprises a polymer
electrolyte..Iaddend.
.Iadd.27. A thin-film micro-electrochemical energy storage cell
(MEESC) in the form of a microbattery according to claim 68 and
wherein said polymer electrolyte comprises at least one material
selected from the group consisting of glass, a polyethylene oxide
based polymer, a polycrystalline material, ethylene carbonate (EC),
diethylcarbonate (DEC), dimethylcarbonate (DMC), ethyl methyl
carbonate (EMC), butyl carbonate, propylene carbonate, vinyl
carbonate, dialkylsulfites, LiPF.sub.6, LiBF.sub.4, LiAsF.sub.6,
LiCF.sub.3, LiN(CF.sub.3SO.sub.2).sub.2, LiI and LiBr..Iaddend.
.Iadd.28. A thin-film micro-electrochemical energy storage cell
(MEESC) in the form of a microbattery according to claim 15 and
wherein said electrolyte is selected from Li.sub.xPO.sub.yN.sub.z
where 2<x<3, 2y=3z and 0.18<z<0.43, or LiS--SiS.sub.2
glasses doped with up to 5% LiSO.sub.4 or 30% LiI..Iaddend.
.Iadd.29. A thin-film micro-electrochemical energy storage cell
(MEESC) in the form of a microbattery according to claim 15 and
wherein the electrolyte comprises Li.sub.2CO.sub.3 doped with up to
about 10%, of atomic weight relative to Li, of Al..Iaddend.
.Iadd.30. A thin-film micro-electrochemical energy storage cell
(MEESC) in the form of a microbattery according to claim 15 and
wherein said anode layer comprises lithium metal foil..Iaddend.
.Iadd.31. A thin-film micro-electrochemical energy storage cell
(MEESC) in the form of a microbattery according to claim 15 and
wherein said cathode layer comprises at least one material selected
from the group consisting of LiCoO.sub.2, LiNiO.sub.2,
LiMn.sub.2O.sub.4, TiS.sub.2, V.sub.2O.sub.5, V.sub.3O.sub.13, the
lithiated form of V.sub.2O.sub.5 and the lithiated form of
V.sub.3O.sub.13..Iaddend.
.Iadd.32. A thin-film micro-electrochemical energy storage cell
(MEESC) in the form of a microbattery according to claim 15 and
also comprising at least one PVDF-graphite layer deposited on said
cathode layer..Iaddend.
.Iadd.33. A thin-film micro-electrochemical energy storage cell
(MEESC) in the form of a microbattery according to claim 15 and
wherein said anode layer and said cathode layer comprise
carbon..Iaddend.
.Iadd.34. A thin-film micro-electrochemical energy storage cell
(MEESC) in the form of a microbattery according to claim 33 and
wherein said electrolyte comprises a polymer
electrolyte..Iaddend.
.Iadd.35. A thin-film micro-electrochemical energy storage cell
(MEESC) in the form of a microbattery according to claim 15 and
also comprising a current collector layer..Iaddend.
.Iadd.36. A thin-film micro-electrochemical energy storage cell
(MEESC) in the form of a microbattery according to claim 35 and
wherein said current collector layer is deposited over said anode
layer, said electrolyte, and said cathode layer..Iaddend.
Description
.Iadd.NOTICE OF MULTIPLE REISSUE APPLICATIONS.Iaddend.
.Iadd.More than one reissue application has been filed with respect
to the present Pat. No. 6,197,450, the first being application Ser.
No. 10/382,466, filed Mar. 6, 2003, and the second, which is a
continuation of the first, being application Ser. No. 11/866,722,
filed Oct. 3, 2007..Iaddend.
FIELD OF THE INVENTION
This invention relates to thin film micro-electrochemical energy
storage cells (MEESC), such as microbatteries and double-layer
capacitors (DLC).
BACKGROUND OF THE INVENTION
Advances in electronics have given us pocket calculators, digital
watches, heart pacemakers, computers for industry, commerce and
scientific research, automatically controlled production processes
and a host of other applications.
These have become possible largely because we have learned how to
build complete circuits, containing millions of electronic devices,
on a tiny wafer of silicon no larger than 25-40 mm square and
0.4-0.5 mm thick. Microelectronics is concerned with these
miniaturized integrated circuits (ICs), or "chips" as they are
called. In a circuit, electrical energy is supplied from, for
example, a microbattery or a double-layer capacitor (DLC) and is
changed into other forms of energy by appliances in the circuit,
which have resistance.
Recently, with the tendency of miniaturizing of small-sized
electronic devices, there have been developed thin-film
microbatteries, which have several advantages over conventional
batteries, since battery cell components can be prepared as thin
(1-20 .mu.m) sheets built up as layers. Usually, such thin layers
of the cathode, electrolyte and anode are deposited using
direct-current and radiofrequency magnetron sputtering or thermal
evaporation.
The area and thickness of the sheets determine battery capacity and
there is a need to increase the total electrode area in a given
volume. Thin films result in higher current densities and cell
efficiencies because the transport of ions is easier and faster
through thin-film layers than through thick layers.
U.S. Pat. Nos. 5,338,625 and 5,567,210 describe thin-film lithium
cells, especially thin-film microbatteries having application as
backup or primary integrated power sources for electronic devices
and method for making such. The batteries described in these
references are assembled from solid state materials, and can be
fabricated directly onto a semiconductor chip, the chip package or
the chip carrier. These batteries have low energy and power. They
have an open circuit voltage at full charge of 3.7-4.5 V and can
deliver currents of up to 100 .mu.A/cm.sup.2. The capacity of a 1
square cm microbattery is about 130 .mu.A/hr. These low values make
these batteries useful only for very low power requirements in some
microelectronic circuits.
A double-layer capacitor (DLC), as opposed to a classic capacitor,
is made of an ion conductive layer between two electrodes. In order
to make an electric double-layer capacitor smaller and lighter
without any change in its capacitance, it is necessary to increase
the energy. This may be accomplished, for example, as described in
U.S. Pat. No. 5,754,393, by increasing the working voltage by use
of an electrolyte having a high decomposition voltage.
Advanced etching technologies, such as reactive-ion etching (RIE),
electron-cyclotron-resonance (ECR) etching and inductively coupled
plasma (ICP) etching have been developed to etch semiconductor
devices having extremely small features sizes. By using the ICP
technique it is possible to etch small diameter through-cavities
such as through-holes with a very high aspect ratio and smooth
surfaces in a substrate such as a silicon wafer.
The present invention is based on a novel approach, according to
which a thin-film micro-electrochemical energy storage cell (MEESC)
such as a DLC or a microbattery is created on a macroporous
substrate, thus presenting increased capacity and performance. By
using the substrate volume, an increase in the total electrode area
per volume is accomplished. The cavities within a substrate are
formed by deep wet or dry etching of the substrate. For example,
holes may be formed by an Inductive Coupling Plasma (ICP) etching
using the Bosch process described in U.S. Pat. No. 5,501,893.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a
micro-electrochemical energy storage cell (MEESC) such as a DLC or
a microbattery exhibiting superior performance as compared to such
cells known in the art. A more particular object of the invention
is to provide a DLC or a microbattery with up to two orders of
magnitude increase in capacity.
The above objects are achieved by the present invention, wherein a
thin-film MEESC is formed on a substrate having etched structures.
The use of such a substrate increases the available area for thin
film deposition, thus leading to an increase in volume, i.e.
capacity of the cell.
Thus, the present invention provides a thin-film
micro-electrochemical energy storage cell (MEESC) comprising two
thin layer electrodes and intermediate to these electrodes, a thin
layer of a solid electrolyte consisting of an ionically conducting
or electronically non-conducting material such as glass, polymer
electrolyte or polycrystalline material, and optionally a fourth
thin current collector layer, all these layers being deposited in
sequence on a surface of a substrate, wherein the MEESC is
characterized in that the substrate is provided with a plurality of
cavities with high aspect ratio; said electrodes, solid electrolyte
and current collector layers being deposited also throughout the
inner surface of said cavities and on both surfaces.
In a preferred embodiment the MEESC of the present invention is a
thin film microbattery which comprises:
a thin layer anode consisting of alkali metal (M), alkali metal
alloy, for example alkali metal alloy based on Zn, Al, Mg, or Sn or
in the charged state consisting of lithiated carbon or
graphite,
a thin layer cathode consisting of LiCoO.sub.2, LiNiO.sub.2,
LiMn.sub.2O.sub.4, TiS.sub.2, V.sub.2O.sub.5, V.sub.3O.sub.8 or
lithiated forms of the vanadium oxides,
a solid electrolyte intermediate to the anode and cathode layers,
which consists of a thin layer of an ionically conducting or
electronically non-conducting material such as glass, polymer
electrolyte or polycrystalline material, and
optionally, a current collector layer; the anode or cathode layer
being deposited on a surface of a substrate, the microbattery being
characterized in that the substrate is provided with a plurality of
cavities with high aspect ratio; said anode, cathode and solid
electrolyte layers being deposited also throughout the inner
surface of said holes.
In cases wherein the microbattery is a lithium ion type, such a
battery is fabricated in the discharge state where the cathode is
fully lithiated and the alloy, the carbon or the graphite anode is
not charged with lithium.
According to another preferred embodiment, the MEESC of the present
invention is a double-layer capacitor (DLC), which comprises two
electrodes made of high surface area carbon powder and intermediate
to these electrodes a solid electrolyte layer, preferably a polymer
electrolyte.
BRIEF DESCRIPTION OF THE DRAWINGS
In order to understand the invention and to see how it may be
carried out in practice, a preferred embodiment will now be
described, by way of non-limiting example only, with reference to
the accompanying drawings, in which:
FIG. 1 is a schematic diagram of a thin-film microbattery coating a
silicon wafer with through-holes.
FIG. 2 is a schematic view of a test cell.
DETAILED DESCRIPTION OF THE INVENTION
Thin-film rechargeable power sources can be applied for computer
memory back-up and many other uses, such as autonomous micro
electro-mechanical systems (MEMS). Lithium batteries have been
brought recently to an extreme stage of miniaturization. Sequential
gas phase deposition techniques of anode, electrolyte and cathode
layers make it possible to incorporate such lithium batteries on a
silicon substrate. In a chemical vapor deposition process gases
and/or vapors react to form a solid compound. This reaction usually
takes place after adsorption and partial decomposition of the
precursors on the substrate surface, though reaction in the gas
phase is possible.
The thin-film MEESC of the present invention consists of a sandwich
of multiple layers, coating the inside of a through-cavity of
arbitrary shape, formed in a substrate, for example by means of
Inductive Coupled Plasma (ICP) etching when the substrate is made
of silicon. Generally, the substrate material is made of a single
crystal or amorphous material and is selected from glass, alumina,
semiconductor materials for use in microelectronics, or ceramic
materials. The substrate material is preferably silicon.
The through-cavities etched have very high aspect ratio and smooth
surfaces, both features being essential for achieving uniform
coating and an increase in the area available for thin-film
deposition. The thin-film layers of the electrodes and electrolyte
are deposited by either Chemical Vapor Deposition (CVD), casting or
plating techniques. In CVD, gases providing the required materials
will pass the cavity, undergo a chemical reaction induced by heat,
plasma or a combination of the two, and deposit the material
uniformly on the inside wall and between the cavities.
According to the present invention, for microbattery applications
the polymer electrolyte is designed so as to contain at least one
material that can be reduced to form an insoluble solid electrolyte
interphase (SEI) on the anode surface. Aprotic solvents such as
ethylene carbonate (EC), diethylcarbonate (DEC), dimethylcarbonate
(DMC), ethyl methyl carbonate (EMC), butyl carbonate, propylene
carbonate, vinyl carbonate, dialkylsulfites and any mixtures of
these, and metal salts such as LiPF.sub.6, LiBF.sub.4, LiAsF.sub.6,
LiCF.sub.3, and LiN(CF.sub.3SO.sub.2).sub.2 are considered to be
good SEI precursors, as well as other salts such as LiI and LiBr.
The polymer electrolyte further contains a polymer, preferably
polyethylene oxide, adapted to form a complex with the metal salt
and optionally a nanosize ceramic powder to form a composite
polymer electrolyte (CPE).
While lithium metal foil is typically used for the negative
electrode, the negative electrode is not specifically restricted as
long as it comprises an electrically conductive film that provides
alkali metal in a form effective for the electrode reaction. The
preferred microbattery used in the present invention is a lithium
ion type battery fabricated in the discharge state wherein the
anode is made of Al, Sn, Zn, Mg based alloys, carbon or graphite.
Lithium-ion cells made according to the present invention are air
stable in the discharged state and are charged only after the
assembly of the cell, thus being more favorable in terms of ease of
production.
Similarly, the active substance of the positive electrode is not
specifically restricted as long as it is of a type in which the
metal ions, e.g. lithium ions are intercalated or inserted during
discharge and taken out during charge of the battery. Inorganic
compounds are typically employed, for example LiCoO.sub.2,
LiNiO.sub.2, LiMn.sub.2O.sub.4, and lithiated vandium oxides for
the lithium ion microbattery, while FeS.sub.2 and TiS.sub.2 can be
used for the lithium metal anode microbattery. Fine powders of
these compounds are cast together with the polymer electrolyte. In
addition, it was found that where a composite polymer electrolyte
and/or a cathode contain up to 15% (V/V) of inorganic nanosize
powder such as Al.sub.2O.sub.3, SiO.sub.2, MgO, TiO.sub.2 or
mixtures thereof, the cell demonstrates improved charge-discharge
performance.
For the DLC application additional salts can be used such as
amonium and alkyl amonium salts. The DLC is made in a similar way
as the microbattery: the electrodes are made in a same manner as
the cathode layer in microbatteries, but the cathode powder is
replaced by a high surface area (over 50 m.sup.2/g) carbon.
FIG. 1 shows a possible cylindrical geometry implemented in a
substrate, for example silicon, of a microbattery. The anode is
made, in the charged state, of an alkali metal (M), alkali metal
alloy or lithiated carbon. The preferred alkali metal is lithium
and the preferred alloys are Al, Mg, Sn and Zn based alloys. The
solid electrolyte is made of an ionically conducting glass,
preferably Li.sub.XPO.sub.YN.sub.Z where 2<x<3, 2y=3z and
0.18<z<0.43, or Li.sub.2S-SiS.sub.2 glasses doped with up to
5% LiSO.sub.4 or 30% LiI, or a poly(ethylene oxide) based polymer
electrolyte, preferably cross-linked poly (ethylene oxide) with
CF.sub.3SO.sub.3Li or LiN(CF.sub.3SO.sub.2).sub.2. The cathode is
made of LiCoO.sub.2, LiNiO.sub.2, LiMn.sub.2O.sub.4, TiS.sub.2,
V.sub.2O.sub.5, V.sub.3O.sub.13 or the lithiated form of these
vanadium oxides. The layers are deposited by CVD, plating, casting
or similar known coating techniques, preferably by CVD. Contacts to
the anode and cathode are made on either the same side of the wafer
using masking, etching, and contact metal deposition, or using both
sides of the wafer.
By etching the substrate with macroporous cavities of various
shapes, the microbattery of the present invention has an increased
area available for thin film deposition by up to 100 fold. Since
the capacity of a battery is directly proportional to its volume,
for the same thin-film thickness (typically a few microns for each
layer of anode, electrode and cathode and up to a total of about 70
.mu.m), means an increase in volume of up to about two orders of
magnitude, i.e. capacity, to about 10,000 microAmp hour per 1
square cm.
For a circular cavity with diameter d in a wafer of thickness h
("aspect ratio"=h/d), the ratio k of surface area after etching to
the original, "planar" state is 2 h/d. For a square cavity with
side a in the same wafer, k=2 h/a. Thus, for a typical wafer with a
thickness of 400 .mu.m (e.g. h=400) and d or a=15 .mu.m, the
increase in area is: k=53, while for d=10 .mu.m, k=80.
The invention will be further described in more detail with the aid
of the following non-limiting examples.
EXAMPLE 1
A microbattery, consisting of a carbon anode, composite polymer
electrolyte and composite LiCoO.sub.2 cathode was fabricated in the
discharged state on a perforated 400 micron thick silicon wafer
which contains 100 micron in diameter through holes. A thin carbon
film was deposited by CVD at 850 Celsius by passing a
C.sub.2H.sub.4 (10%) Ar (90%) gas mixture for four minutes over the
wafer.
A second layer of a composite polymer electrolyte (CPE) was
deposited (inside an Ar filled glove box) over the carbon layer by
a short vacuum dipping at 50-65 Celsius in acetonitrile (30 ml)
suspension consisting of 0.6 g PEO (5.times.10.sup.6 MW), 0.05 g
EC, 0.1 g LiN(CF.sub.3SO.sub.2).sub.2 (imide) and 0.03 g alumina.
After drying, a second layer of CPE was deposited in the same way
to get the desired CPE thickness. A thin cathode layer was
deposited (inside the glove box) over the CPE layer by a short
vacuum dipping in cyclopentanone (10 ml) suspension consisting of 2
g of ball milled LiCoO.sub.2, 0.05 g alumina, 0.2 g PVDF copolymer
(ELF 2800) and 0.4 g sub-micron graphite powder. As an option for
improving cathode utilization and power capability, a forth
PVDF-graphite layer is deposited on the cathode.
Poly(ethylene oxide)(P(EO)) was purchased from Aldrich, (average
molecular weight 5.times.10.sup.6) and was vacuum dried at
45.degree. to 50.degree. C. for about 24 hours. The imide (Aldrich)
was vacuum dried at 200.degree. C. for about 4 hours. All
subsequent handling of these materials took place under an argon
atmosphere in a VAC glove box with an water content<10 ppm. A
polymer electrolyte slurry was prepared by dispersing known
quantities of P(EO), imide, and ethylene carbonate (EC) in
analytical grade acetonitrile together with the required amount of
an inorganic filler, such as Al.sub.2O.sub.3 (Buehler), or
SiO.sub.2 with an average diameter of about 150.ANG.. To ensure the
formation of a homogeneous suspension, an ultrasonic bath or
high-speed homogenizer was used. The suspension was stirred for
about 24 hours before the composite cathode was cast. The solvent
was allowed to evaporate slowly and then the wafers were vacuum
dried at 120.degree. C. for at least 5 hours. The electro-chemical
characteristics of the microbattery has been examined in the
experimental cell showed in FIG. 2, which comprises a hermetically
sealed glass container 5, provided with an outlet 1, connected to a
vacuum pump; the glass cover 3 of the glass container is equipped
with a Viton O-ring 4. On one side of the wafer a contact was made
to the carbon anode and on the other side a contact was made to the
cathode. The test cell illustrated in FIG. 2 is connected by wires
7 to tungsten rods 2 which pass through the cover. In the glass
container, the battery 6 was cycled between 2.5 and 4.1 V at 0.01
mA and at 25.degree. C. using a Maccor series 2000 battery test
system.
The cell delivered above 0.4 mAh per cycle for over 20 cycles. The
Faradaic efficiency was close to 100%.
EXAMPLE 2
A DLC, consisting of two carbon electrodes, and composite polymer
electrolyte was fabricated on a perforated 400 micron thick silicon
wafer which contains 100 micron in diameter through holes in a
similar way as described in Example 1. A thin high surface area
carbon powder (500 m.sup.2/g) (made by 1000 Celsius pyrolysis of
cotton) layer was deposited (inside the glove box) on the
perforated wafer by a short vacuum dipping in cyclopentanone (10
ml) suspension consisting of 1 g of ball milled carbon, 0.05 g
carbon black and 0.1 g PVDF copolymer (ELF 2800). A second layer of
a composite polymer electrolyte (CPE) was deposited (inside Ar
filled glove box) over the carbon layer by a short vacuum dipping
at 50-65 Celsius in an acetonitrile (30 ml) suspension consisting
of 0.6 g PEO (5.times.10.sup.6 MW), 0.05 g EC, 0.1 g
LiN(CF.sub.3SO.sub.2).sub.2 (imide) and 0.03 g alumina. After
drying, another layer of CPE was deposited in the same way to get
the desired CPE thickness. A third high surface area carbon layer
was deposited in the same way as the first one.
By using the procedure described in Example 1 above, the DLC was
cycled at 0.01 mA between 1.2 and 2.5 V for over 1000 cycles of 10
seconds each.
EXAMPLE 3
A microbattery, consisting of four thin films: a carbon anode, Al
doped Li.sub.2CO.sub.3 solid electrolyte, LiCoO.sub.2 cathode and
carbon current collector was fabricated in the discharged state on
a perforated 400 micron thick silicon wafer which contains 60
micron in diameter through holes. A thin carbon film was CVD
deposited at 850 Celsius by passing a C.sub.2H.sub.4 (10%) Ar (90%)
gas mixture for three minutes over the wafer. A second layer of
thin Al doped Li.sub.2CO.sub.3 solid electrolyte was deposited at
475 Celsius on the first one by CVD following the procedure
described in P. Fragnaul et al. J. Power Sources 54, 362 1995. A
third thin layer of LiCoO.sub.2 cathode was deposited at 500
Celsius on the second one following the procedure described in P.
Fragnaul et al. J. Power Sources 54, 362 1995. A fourth thin carbon
current collector layer was deposited at 800 Celsius on the third
one in the same way as the first one.
This cell was cycled (as described in example 1) at 0.01 mA and at
room temperature between 2.5 and 4.1 V for more than 10 stable
cycles.
* * * * *