CA1091763A - Cathodes for solid state lithium cells - Google Patents
Cathodes for solid state lithium cellsInfo
- Publication number
- CA1091763A CA1091763A CA300,295A CA300295A CA1091763A CA 1091763 A CA1091763 A CA 1091763A CA 300295 A CA300295 A CA 300295A CA 1091763 A CA1091763 A CA 1091763A
- Authority
- CA
- Canada
- Prior art keywords
- solid state
- cell
- lithium
- cathode
- cells
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
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Classifications
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/36—Selection of substances as active materials, active masses, active liquids
- H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M6/00—Primary cells; Manufacture thereof
- H01M6/14—Cells with non-aqueous electrolyte
- H01M6/18—Cells with non-aqueous electrolyte with solid electrolyte
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
- Y02P70/50—Manufacturing or production processes characterised by the final manufactured product
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- Chemical & Material Sciences (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Electrochemistry (AREA)
- General Chemical & Material Sciences (AREA)
- Inorganic Chemistry (AREA)
- Engineering & Computer Science (AREA)
- Manufacturing & Machinery (AREA)
- Secondary Cells (AREA)
- Primary Cells (AREA)
- Battery Electrode And Active Subsutance (AREA)
- Conductive Materials (AREA)
Abstract
CATHODES FOR SOLID STATE LITHIUM CELLS ABSTRACT High energy density solid state cells using cathode materials of ionically and electronically con-ductive dischargeable compounds in combination with other non-conductive cathode active materials of higher energy density.
Description
: ~` lO9i71~3 This invention relates to high energy density cells utilizing solid electrolytes, solid active metal anodes and novel solid cathodes, and more particularly to such cells in which the cathodes contain an active material which is both ionically and electronically conductive.
Recently the state of electronics has achieved a ; high degree of sophistication especially in regard to devices utilizing integrated circuit chips which have been proliferating in items such as quartz crystal watches, calculators, cameras, pacemakers and the like. Miniaturization of these devices as well as low power drainage and relatively long lives under all types of conditions has resulted in a ~i demand for power sources which have characteristics of , rugged construction, long shelf life, high reliability, high energy density and an operating capability over a wide range of temperatures as well as concomitant miniaturization of the power source. These requirements pose problems for conventional cells having solution or even paste type electrolytes especially with regard to shelf life. The electrode materials in such cells may react with the electrolyte solutions and tend therefore to self discharge after periods of time which are relatively short when compared to the potential life of solid state batteries. There may also be evolu~ion of gases in such cells which could force the electrolyte to leak out of the battery seals, thus corroding other components in the circuit which in sophisticated componentry can be very damaging. Increasing closure ' :
;: M-3324-C
- 1091~763 " ~ .
reliability is both bulky and costly and will not eliminate ; the problem of self discharge. Additionally, solution cells ; have a limitedoperating temperature range dependent upon the , freezing and boiling points of the contained solutions.
Success in meeting the above demands without the drawbacks of solution electrolyte systems has been achieved with the use of solid electrolyte and electrode cells or ~`~ solid state cells which do not evolve gases, self discharge on long standing or have electrolyte leakage problems. These ,..~
systems however have had their own particular limitations and drawbacks not inherent in solution electrolyte cells.
Ideally a cell should have a high voltage, a high energy density, and a high current capability. Prior art solid state cells have however been deficient in one or more of the above desirable characteristics.
A first requirement and an important part of the operation of any solid state cell is the choice of solid electrolyte. In order to provide good current capability a solid electrolyte should have a high ionic conductivity which enables the transport of ions through defects in the crystalline electrolyte structure of the electrode-electrolyte system. An additional, and one of the most important require-ments for a solid electrolyte , is that it must be virtually solely an ionic conductor. Conductivity due to the mobility of electrons must be neglible because otherwise the resulting partial internal short circuiting would result in the consumption of electrode materials even under open circuit conditions.
Recently the state of electronics has achieved a ; high degree of sophistication especially in regard to devices utilizing integrated circuit chips which have been proliferating in items such as quartz crystal watches, calculators, cameras, pacemakers and the like. Miniaturization of these devices as well as low power drainage and relatively long lives under all types of conditions has resulted in a ~i demand for power sources which have characteristics of , rugged construction, long shelf life, high reliability, high energy density and an operating capability over a wide range of temperatures as well as concomitant miniaturization of the power source. These requirements pose problems for conventional cells having solution or even paste type electrolytes especially with regard to shelf life. The electrode materials in such cells may react with the electrolyte solutions and tend therefore to self discharge after periods of time which are relatively short when compared to the potential life of solid state batteries. There may also be evolu~ion of gases in such cells which could force the electrolyte to leak out of the battery seals, thus corroding other components in the circuit which in sophisticated componentry can be very damaging. Increasing closure ' :
;: M-3324-C
- 1091~763 " ~ .
reliability is both bulky and costly and will not eliminate ; the problem of self discharge. Additionally, solution cells ; have a limitedoperating temperature range dependent upon the , freezing and boiling points of the contained solutions.
Success in meeting the above demands without the drawbacks of solution electrolyte systems has been achieved with the use of solid electrolyte and electrode cells or ~`~ solid state cells which do not evolve gases, self discharge on long standing or have electrolyte leakage problems. These ,..~
systems however have had their own particular limitations and drawbacks not inherent in solution electrolyte cells.
Ideally a cell should have a high voltage, a high energy density, and a high current capability. Prior art solid state cells have however been deficient in one or more of the above desirable characteristics.
A first requirement and an important part of the operation of any solid state cell is the choice of solid electrolyte. In order to provide good current capability a solid electrolyte should have a high ionic conductivity which enables the transport of ions through defects in the crystalline electrolyte structure of the electrode-electrolyte system. An additional, and one of the most important require-ments for a solid electrolyte , is that it must be virtually solely an ionic conductor. Conductivity due to the mobility of electrons must be neglible because otherwise the resulting partial internal short circuiting would result in the consumption of electrode materials even under open circuit conditions.
-2-'-., -~
)91763 v Solution electrolyte cells include an electronically non-conductive separator between the electrode elements to prevent such a shortcircuit, whereas solid state cells utilize the solid electrolyte as both electronic separator - and the ionic conductive species.
High current capabilities for solid state cells have been attained with the use of materials which are . solely ionic conductors such as RbAg4I5 (.27 ohm lcm 1 room ; temperature conductivity). However these conductors are only ,,~,r,:, 10 useful as electrolytes in cells having low voltages and energy densities. As an example, a solid state Ag/RbAg4Is/RbI3 ~i~ cell is dischargeable at 40 mA/cm2 at room temperature but with about 0.2 Whr/in3 and an OCV of 0.66V. High energy density and high voltage anodic materials such as lithium are chemically reactive with such conductors thereby precluding the use of these conductors in such cells. Electrolytes which are chemically compatible with the high energy density and high voltage anode materials,such as LiI, even when doped for greater conductivity, do not exceed a conductivity of 5 x 10 5 ohm cm at room temperature. Thus, high energy density cells with an energy density ranging from about 5-10 Whr/in3 and a voltage at about 1.9 volts for a Li/LiI-doped/PbI, PbS,Pb cell currently being produced are precluded from having an effective high ' f current capability above 50 ~A/cm 2 at room temperature. A further ; aggravation of the reduced current capability of high energy density cells is the low conductivity (both electronic and ,''' :
)91763 v Solution electrolyte cells include an electronically non-conductive separator between the electrode elements to prevent such a shortcircuit, whereas solid state cells utilize the solid electrolyte as both electronic separator - and the ionic conductive species.
High current capabilities for solid state cells have been attained with the use of materials which are . solely ionic conductors such as RbAg4I5 (.27 ohm lcm 1 room ; temperature conductivity). However these conductors are only ,,~,r,:, 10 useful as electrolytes in cells having low voltages and energy densities. As an example, a solid state Ag/RbAg4Is/RbI3 ~i~ cell is dischargeable at 40 mA/cm2 at room temperature but with about 0.2 Whr/in3 and an OCV of 0.66V. High energy density and high voltage anodic materials such as lithium are chemically reactive with such conductors thereby precluding the use of these conductors in such cells. Electrolytes which are chemically compatible with the high energy density and high voltage anode materials,such as LiI, even when doped for greater conductivity, do not exceed a conductivity of 5 x 10 5 ohm cm at room temperature. Thus, high energy density cells with an energy density ranging from about 5-10 Whr/in3 and a voltage at about 1.9 volts for a Li/LiI-doped/PbI, PbS,Pb cell currently being produced are precluded from having an effective high ' f current capability above 50 ~A/cm 2 at room temperature. A further ; aggravation of the reduced current capability of high energy density cells is the low conductivity (both electronic and ,''' :
-3-. _ _ . . . .. ...
..
.
10:', ionic) of active cathode materials. Conductivity enhancers such as graphite for electronic conductivity and electrolyte for ionic conductivity,while increasing the current capability of the cell to the maximum allowed by the conductivity of the ~^, electrolyte, reduce the energy density of the cell because of their volume.
`~ Commercial feasibility in production of the - electrolyte material is another factor to be considered in the . construction of solid state cells. Thus, the physical properties of electrolytes such as BaMg5S5 and BaMg5Se6, which are compatible with a magnesium but not a lithium anode, and sodium beta aluminas such as Na20 11 A1203, which are compatible with sodium :
anodes, will preclude the fabrication of cells having a high energy density or current capability even when costly production steps are taken. These electrolytes have ceramic characteristics making them difficult to work with especially in manufacturing with processes involving grinding and pelletization,~such processes requiring a firing step for structural integrity. Furthermore, the glazed material so formed inhibits good surface contact with the electrodes with a result of poor conductivity leading to poor cell performance. These electrolytes are thus typically used in cells with molten electrodes.
It is therefore an object of the present invention to increase the conductivity of the cathode of solid state cells in conjunction with high energy density anodes and compat-ible electrolytes such that there is an increase in energy density without current capability losses, while maintaining chemical stability between the cell components.
_4_ 1~91763 Generally the present invention involves the incorpora-tiOll into the cakhode of a solid state cell of a material which has the characteristics of being both ionically and electronically conductive as well as being able to function as an active cathode material. Normally cathodes require the incorporation of sub-stantial amounts (e.g. over 20 percent by weight) of an ionic conductor such as that used as the electrolyte in order to facilitate ionic flow in the cathode during the cell reaction.
This is especially true if the cathodic material is an electronic conductor since otherwise a reduction product would form at the cathode-electrolyte interface which would eventually block off a substantial amount of the ionic flow during discharge. However the incorporated ionic conductors in prior art cells have not generally been cathode active materials with the result of significant capacity loss. Additionally, cathode active materials which are poor electronic conductors as well require the further incorporation of electronically conductive materials which further reduces the cells energy capacity. By combining the functions of electronic and ionic conductivity with cathode activity a higher energy density and current capability is attained with the need for space wasting conductors being obviated.
Examples of materials having the requisite character-istics of ionic and electronic conductivity and which are cathodically active as well as being compatible with electrolytes used in high energy density cells include the following metal chalcogenides: CoTe2, Cr2S3, HfS2, HfSe2~ HfTe2~ IrTe2~
MS2~ MSe2~ MTe2~ NbS2, NbSe2, NbTe2, NiTe2, PtS2, PtSe2, ,,~._ .. . . . . . .
.. ,' - ~ ~ , .
,. ~ .~ , , .
10917~;3 , .
PtTe2, SnS2, SnSSe, SnSe2, TaS2, TaSe2, TaTe2, TiS2, TiSe2, TiTe2, VS2, VSe2, VTe2, WS2, WSe2, WTe2, zrs2, ZrSe2, and ZrTe2, .
wherein the chalcogenide is a sulfide, selenide, telluride or a combination thereof.
Also included are the non-stoichiometric metal chalcogenide compounds such as LixTiS2 where x <1, which to some extent contain the complexed form of one of the cathode materials with the anodic cation and which are believed to be intermediate reaction products durinq cell discharge.
In order for the ionically-electronically conductive ., ;~ cathode active material to be commercially useful in high ,.
voltage cells with lithium anodes it should be able to provide a voltage couple with lithium of at least an O.C.V. of 1.5 volts and preferably above 2 volts.
The operating voltage of the ionically-electronically conductive cathode active material should preferably be roughly equivalent to the voltage of the higher energy density non-conductive cathode active material mixed therewith to avoid detrimental voltage fluctuations.
- 20 A further criteria for the above cathodic material is that both the ionic and electronic conductivities of the - cathode active material should range between 10 10and 102 ohm~
cm~l with a preferred ionic conductivity of more than 10-6 and an electronic conductivity greater than 10 1,~ t roome~a~re In addition, and most importantly, the ionically-electronically conductive,active cathode material must be compatible with the solid electrolytes used in the high energy density cells.
.~, .. _ _. _ .. . .. _ . . . ... . _ ., _ _ ~
. ~ , 1~)9i763 :
The solid electrolytes used in high energy density lithium cells are lithium salts and have ionic conductivities at room temperature.
greater than 1 x 10 9 ohm 1 cm 1~ These salts can either be in the pure form or combined with conductivity enhancers such that the current capability is improved thereby. Examples of lithium salts having the requisite conductivity for meaningful cell utilization include lithium iodide (LiI) and lithium iodide admixed with lithium hydroxide (LioH) and aluminum oxide (A1203), with the latter mixture being referred to as LLA and disclosed in U.S. patent no. 3,713,897.
It is postulated that the aforementioned ionically-electronically conductive,cathode active materials react with the ions of the anode (i.e. lithium cations) to form a non-stoichiometric complex during the discharge of the cell. This complexing of cations allows them to move from site to site .
thereby providing ionic conductivity. Additionally the above compounds provide the free electrons necessary for electronic conductivity.
The above compounds are admixed with other compounds or elements which provide a greater energy density but which cannot be utilized in and of themselves because of their inability to function as ionic and/or electronic conductors.
.. .
The inclusion of the ionically-electronically conductive,cathode active material thereby increases the capacity of the cell by obviating the need for non-dischargeable conductive materials.
Furthermore, when the conductive active material is homogeneously admixed with the higher energy density compound the realizable utilization of the so formed cells is approximately .. . .. . . ... _ .
,. .
1~)91763 '::
. .. .
' equal to the theoretical. A limiting factor in solid state cell ~: performance is the conductivity of the cell reaction product.
, ; A low conductivity product results in large internal resistance r''' losses which effectively terminate cell usefu~ess . Thus ~:;
in cells having the above ionically-electronically conductiv~, cathode active material the complexed reaction product retains conductivity thereby enabling full utilization of other active - cathode materials which are in proximity therewith.
Accordingly,high energy density cathodic materials such as sulfur and iodine as well as other solid chalcogens, Se and Te, and halogens such as bromine can be effectively utilized to greater potential. Solid state cells utilizing ; sulfur in conjunction with lithium anodes and lithium salt solid electrolytes have shown great promise in terms of voltage obtainable and total energy density.However, one of the draw-, `:;
backs has been the formation of the low ionically conductive lithium sulfide (Li2S~ as the cell reaction product and , especially at the cathode electrolyte interface. This build up has effectively choked off the further utilization of these ~;i 20 cells. However the inclusion of the ionically-electronically ~,............ . .
~conductive,cathode active materials provides a more uniform distribution of the reaction product throughout the cathode,:
structure because of their ionically conductive characteristics.
Since the reaction productsof the ionically conductive materials retain conductivity,further utilization of the cell is also - possible with the non-conductive active material in conductive proximity to the conductive active material.
A small amount of electrolyte can also be included _, :
~ M-3324-C
9iL763 -;
in the cathode structure in order to blur the interface between cathode and electrolyte thereby providing more intimate electrical contact between the cathode and the electrolyte.
This enables the cell to operate at higher current drains for : longer periods of time. Additionally,the electrolyte inclusion can increase the ionic conductivity of the cathode should the ionically conductive cathode active material have a lower conductivity than that of the electrolyte. This inclusion however, if made, should not exceed 10% by weight since greater amounts would merely decrease the energy density of the cell with little if any further tradeoff in terms of current drain capacity.
The following examples illustrate the high energy density and utilizability of a sulfur containing cathode in a ` solid state cell with the abovementioned ionically and electron-ically conductive cathode active metal chalcogenides. Sulfur in and of itself cannot be used as a cathode in a solid state cell unless it contains susbstantial amounts of ionic and electronic conductors which constitute 60% or more of the total cathode by weight. Thus the inclusion into a cathode of sulfur of an ionically and electronically conductive metal chalcogenide such as titanium disulfide enables the use of sulfur without the concomitant severe losses of energy capacity. Titanium disulfide is both a good ionic and electronic conductor (10 50hm 1cm room temperature ionic conductivity and greater than 10 ohm cm room temperature electronic conductivity) and also functions as a reactive species in the cell reaction with the lithium cations to form the nonstoichiometric LiXTiS2 which is alsc _ g_ 1~)9~7~3 .
ionically and electronically conductive thus further ameliorating the other problem of non-conductive reaction products choking off further cell reaction. In addition TiS2 generally discharges at a voltage similar to that of sulfur i.e. 2.3 volts and thus the cell voltage is steady without cell voltage fluctuations.
In the following examples as throughout the en~ire specification and claims all parts and percentages are parts by weight unless otherwise specified. The examples are given for illustrative purposes only, and specific details are not to be con-strued as limitations.
EXAMPLE I
A solid state cell is made from a lithium metal disc having dimensions of about 1.47 cm2 surface area by about 0.01 cm thickness; a cathode disc having dimensions of about 1.82 cm2 surface area by about 0.02 cm thickness, consisting of 80% TiS2 and 20% S, and weighing 100 mg; and a solid electrolyte there-- between with the same dimensions as the cathode and consisting of LiI, LioH, and A1203 in a 4:1:2 ratio. The electrolyte is first pressed to the cathode at a pressure of about 100,000 psi, - 20 and then the anode is pressed thereto at about 50,000 psi. The resulting cell is discharged at room temperature under a load of 100 k~b The cell provides 26 milliamp hours (mAH) to 2 volts, about 41 mAH to 1.5 volts, and in excess of 46 mAH to 1 volt.
The cell has a realizable capacity in excess of 12 watt hours/in3.
The following Table illustrates the results obtained from cells tested under condition of different loads or temperatures and having differing cathode weight, cathode-electrolyte interface surface area or relative percentages of TiS2 to S with resulting capacity limits to 2, 1.5 and 1 volt.
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10:', ionic) of active cathode materials. Conductivity enhancers such as graphite for electronic conductivity and electrolyte for ionic conductivity,while increasing the current capability of the cell to the maximum allowed by the conductivity of the ~^, electrolyte, reduce the energy density of the cell because of their volume.
`~ Commercial feasibility in production of the - electrolyte material is another factor to be considered in the . construction of solid state cells. Thus, the physical properties of electrolytes such as BaMg5S5 and BaMg5Se6, which are compatible with a magnesium but not a lithium anode, and sodium beta aluminas such as Na20 11 A1203, which are compatible with sodium :
anodes, will preclude the fabrication of cells having a high energy density or current capability even when costly production steps are taken. These electrolytes have ceramic characteristics making them difficult to work with especially in manufacturing with processes involving grinding and pelletization,~such processes requiring a firing step for structural integrity. Furthermore, the glazed material so formed inhibits good surface contact with the electrodes with a result of poor conductivity leading to poor cell performance. These electrolytes are thus typically used in cells with molten electrodes.
It is therefore an object of the present invention to increase the conductivity of the cathode of solid state cells in conjunction with high energy density anodes and compat-ible electrolytes such that there is an increase in energy density without current capability losses, while maintaining chemical stability between the cell components.
_4_ 1~91763 Generally the present invention involves the incorpora-tiOll into the cakhode of a solid state cell of a material which has the characteristics of being both ionically and electronically conductive as well as being able to function as an active cathode material. Normally cathodes require the incorporation of sub-stantial amounts (e.g. over 20 percent by weight) of an ionic conductor such as that used as the electrolyte in order to facilitate ionic flow in the cathode during the cell reaction.
This is especially true if the cathodic material is an electronic conductor since otherwise a reduction product would form at the cathode-electrolyte interface which would eventually block off a substantial amount of the ionic flow during discharge. However the incorporated ionic conductors in prior art cells have not generally been cathode active materials with the result of significant capacity loss. Additionally, cathode active materials which are poor electronic conductors as well require the further incorporation of electronically conductive materials which further reduces the cells energy capacity. By combining the functions of electronic and ionic conductivity with cathode activity a higher energy density and current capability is attained with the need for space wasting conductors being obviated.
Examples of materials having the requisite character-istics of ionic and electronic conductivity and which are cathodically active as well as being compatible with electrolytes used in high energy density cells include the following metal chalcogenides: CoTe2, Cr2S3, HfS2, HfSe2~ HfTe2~ IrTe2~
MS2~ MSe2~ MTe2~ NbS2, NbSe2, NbTe2, NiTe2, PtS2, PtSe2, ,,~._ .. . . . . . .
.. ,' - ~ ~ , .
,. ~ .~ , , .
10917~;3 , .
PtTe2, SnS2, SnSSe, SnSe2, TaS2, TaSe2, TaTe2, TiS2, TiSe2, TiTe2, VS2, VSe2, VTe2, WS2, WSe2, WTe2, zrs2, ZrSe2, and ZrTe2, .
wherein the chalcogenide is a sulfide, selenide, telluride or a combination thereof.
Also included are the non-stoichiometric metal chalcogenide compounds such as LixTiS2 where x <1, which to some extent contain the complexed form of one of the cathode materials with the anodic cation and which are believed to be intermediate reaction products durinq cell discharge.
In order for the ionically-electronically conductive ., ;~ cathode active material to be commercially useful in high ,.
voltage cells with lithium anodes it should be able to provide a voltage couple with lithium of at least an O.C.V. of 1.5 volts and preferably above 2 volts.
The operating voltage of the ionically-electronically conductive cathode active material should preferably be roughly equivalent to the voltage of the higher energy density non-conductive cathode active material mixed therewith to avoid detrimental voltage fluctuations.
- 20 A further criteria for the above cathodic material is that both the ionic and electronic conductivities of the - cathode active material should range between 10 10and 102 ohm~
cm~l with a preferred ionic conductivity of more than 10-6 and an electronic conductivity greater than 10 1,~ t roome~a~re In addition, and most importantly, the ionically-electronically conductive,active cathode material must be compatible with the solid electrolytes used in the high energy density cells.
.~, .. _ _. _ .. . .. _ . . . ... . _ ., _ _ ~
. ~ , 1~)9i763 :
The solid electrolytes used in high energy density lithium cells are lithium salts and have ionic conductivities at room temperature.
greater than 1 x 10 9 ohm 1 cm 1~ These salts can either be in the pure form or combined with conductivity enhancers such that the current capability is improved thereby. Examples of lithium salts having the requisite conductivity for meaningful cell utilization include lithium iodide (LiI) and lithium iodide admixed with lithium hydroxide (LioH) and aluminum oxide (A1203), with the latter mixture being referred to as LLA and disclosed in U.S. patent no. 3,713,897.
It is postulated that the aforementioned ionically-electronically conductive,cathode active materials react with the ions of the anode (i.e. lithium cations) to form a non-stoichiometric complex during the discharge of the cell. This complexing of cations allows them to move from site to site .
thereby providing ionic conductivity. Additionally the above compounds provide the free electrons necessary for electronic conductivity.
The above compounds are admixed with other compounds or elements which provide a greater energy density but which cannot be utilized in and of themselves because of their inability to function as ionic and/or electronic conductors.
.. .
The inclusion of the ionically-electronically conductive,cathode active material thereby increases the capacity of the cell by obviating the need for non-dischargeable conductive materials.
Furthermore, when the conductive active material is homogeneously admixed with the higher energy density compound the realizable utilization of the so formed cells is approximately .. . .. . . ... _ .
,. .
1~)91763 '::
. .. .
' equal to the theoretical. A limiting factor in solid state cell ~: performance is the conductivity of the cell reaction product.
, ; A low conductivity product results in large internal resistance r''' losses which effectively terminate cell usefu~ess . Thus ~:;
in cells having the above ionically-electronically conductiv~, cathode active material the complexed reaction product retains conductivity thereby enabling full utilization of other active - cathode materials which are in proximity therewith.
Accordingly,high energy density cathodic materials such as sulfur and iodine as well as other solid chalcogens, Se and Te, and halogens such as bromine can be effectively utilized to greater potential. Solid state cells utilizing ; sulfur in conjunction with lithium anodes and lithium salt solid electrolytes have shown great promise in terms of voltage obtainable and total energy density.However, one of the draw-, `:;
backs has been the formation of the low ionically conductive lithium sulfide (Li2S~ as the cell reaction product and , especially at the cathode electrolyte interface. This build up has effectively choked off the further utilization of these ~;i 20 cells. However the inclusion of the ionically-electronically ~,............ . .
~conductive,cathode active materials provides a more uniform distribution of the reaction product throughout the cathode,:
structure because of their ionically conductive characteristics.
Since the reaction productsof the ionically conductive materials retain conductivity,further utilization of the cell is also - possible with the non-conductive active material in conductive proximity to the conductive active material.
A small amount of electrolyte can also be included _, :
~ M-3324-C
9iL763 -;
in the cathode structure in order to blur the interface between cathode and electrolyte thereby providing more intimate electrical contact between the cathode and the electrolyte.
This enables the cell to operate at higher current drains for : longer periods of time. Additionally,the electrolyte inclusion can increase the ionic conductivity of the cathode should the ionically conductive cathode active material have a lower conductivity than that of the electrolyte. This inclusion however, if made, should not exceed 10% by weight since greater amounts would merely decrease the energy density of the cell with little if any further tradeoff in terms of current drain capacity.
The following examples illustrate the high energy density and utilizability of a sulfur containing cathode in a ` solid state cell with the abovementioned ionically and electron-ically conductive cathode active metal chalcogenides. Sulfur in and of itself cannot be used as a cathode in a solid state cell unless it contains susbstantial amounts of ionic and electronic conductors which constitute 60% or more of the total cathode by weight. Thus the inclusion into a cathode of sulfur of an ionically and electronically conductive metal chalcogenide such as titanium disulfide enables the use of sulfur without the concomitant severe losses of energy capacity. Titanium disulfide is both a good ionic and electronic conductor (10 50hm 1cm room temperature ionic conductivity and greater than 10 ohm cm room temperature electronic conductivity) and also functions as a reactive species in the cell reaction with the lithium cations to form the nonstoichiometric LiXTiS2 which is alsc _ g_ 1~)9~7~3 .
ionically and electronically conductive thus further ameliorating the other problem of non-conductive reaction products choking off further cell reaction. In addition TiS2 generally discharges at a voltage similar to that of sulfur i.e. 2.3 volts and thus the cell voltage is steady without cell voltage fluctuations.
In the following examples as throughout the en~ire specification and claims all parts and percentages are parts by weight unless otherwise specified. The examples are given for illustrative purposes only, and specific details are not to be con-strued as limitations.
EXAMPLE I
A solid state cell is made from a lithium metal disc having dimensions of about 1.47 cm2 surface area by about 0.01 cm thickness; a cathode disc having dimensions of about 1.82 cm2 surface area by about 0.02 cm thickness, consisting of 80% TiS2 and 20% S, and weighing 100 mg; and a solid electrolyte there-- between with the same dimensions as the cathode and consisting of LiI, LioH, and A1203 in a 4:1:2 ratio. The electrolyte is first pressed to the cathode at a pressure of about 100,000 psi, - 20 and then the anode is pressed thereto at about 50,000 psi. The resulting cell is discharged at room temperature under a load of 100 k~b The cell provides 26 milliamp hours (mAH) to 2 volts, about 41 mAH to 1.5 volts, and in excess of 46 mAH to 1 volt.
The cell has a realizable capacity in excess of 12 watt hours/in3.
The following Table illustrates the results obtained from cells tested under condition of different loads or temperatures and having differing cathode weight, cathode-electrolyte interface surface area or relative percentages of TiS2 to S with resulting capacity limits to 2, 1.5 and 1 volt.
. ~
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~09-1763 It should be noted from the Examples that cells dis-charged at 37C show even greater capacity than those cells discharged at room temperature and under the same load. Thus, since 37C is human body temperature, cells utilizing the present ; invention can be used in pacemakers with the capability of lasting in excess of 10 years,thereby greatly reducing the ` need for surgery necessitated by the need for implanting fresh batteries.
Additionally, the 80:20 ratio of TiS2 to S by weight, roughly equivalent to a mole-to-mole ratio, provides a greater useful capacity than the 60:40 ratio despite the increased ; amount of the higher energy density sulfur in the latter.
With the mole-to-mole ratio,three lithiums can react stoichio-metrically in the cell reactions i.e. 2Li + S -~Li2S and Li + TiS2-~ LiTiS2. These reactions provide a three electron change with both a high voltage and a high capacity. The mole -to-mole ratio of TiS2 to S provides for complete stoichiometric utilization and is thus highly preferred.
A cell made with the materials of Example l the dimensions of 1.258" OD and 0.085" thickness, a cathode of 1.5 grams is made as the back cover of a tritium illuminated liquid crystal display (LCD) watch. A limiting resistor of 330k~ limits the voltage applied to the watch.
The operating current for the abovementioned watch ranges between 1 and 3~A. Thus,with a stoichiometric capacity of 750 mAH and assuming a conservative utilizability of 2/3 capacity the cell is theoretically capable of powering the :, .
.' ~~
10~1763 , .
watch at an average drain rate of 2~lA and a voltage in excess of 2.2 volts for about 28.5 years. The lifetime of such cells is in excess of the lifetime of the currently produced watches themselves. Accordingly, with~the stability of solid state ., cells in general and the capacity of the present cell in particular, batteries can be made as integral parts of electrical componentry such as watches rather than as a part requiring constant replacement.
~'t`
A cell made in accordance with that of Example 1 is made but with tantalum disulfide (TaS2) in place of titanium disulfide (TiS2) and a wcight ratio to sulfur of 87.5:12.5.
Upon discharge of the cell at 72C under a load of lOk.~the cell realizes 6 mAH to 2 volts, 18 mAH to 1.5 volts and 24 mAH to volt.
EX~MPLE 25 A cell made in accordance with the previous Example is discharged at 72C under a load of 20k~. The cell realizes 14 mP~H to 2 volts, 25 mAH to 1.5 volts and about 28 mAH to 1 volt.
It is understood that changes and variations of the invention as described herein can be made without departing from the scope of the present invention as defined in the following claims.
_ ~
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U~ ~ ~ t~l, t~l E~ O o o o S~ 00 CO 0~ 0~
.' .
. ~ ~ O ~ ~
, X ~ ~ ~ ~
, .
_ r .. ~. .
..
~09-1763 It should be noted from the Examples that cells dis-charged at 37C show even greater capacity than those cells discharged at room temperature and under the same load. Thus, since 37C is human body temperature, cells utilizing the present ; invention can be used in pacemakers with the capability of lasting in excess of 10 years,thereby greatly reducing the ` need for surgery necessitated by the need for implanting fresh batteries.
Additionally, the 80:20 ratio of TiS2 to S by weight, roughly equivalent to a mole-to-mole ratio, provides a greater useful capacity than the 60:40 ratio despite the increased ; amount of the higher energy density sulfur in the latter.
With the mole-to-mole ratio,three lithiums can react stoichio-metrically in the cell reactions i.e. 2Li + S -~Li2S and Li + TiS2-~ LiTiS2. These reactions provide a three electron change with both a high voltage and a high capacity. The mole -to-mole ratio of TiS2 to S provides for complete stoichiometric utilization and is thus highly preferred.
A cell made with the materials of Example l the dimensions of 1.258" OD and 0.085" thickness, a cathode of 1.5 grams is made as the back cover of a tritium illuminated liquid crystal display (LCD) watch. A limiting resistor of 330k~ limits the voltage applied to the watch.
The operating current for the abovementioned watch ranges between 1 and 3~A. Thus,with a stoichiometric capacity of 750 mAH and assuming a conservative utilizability of 2/3 capacity the cell is theoretically capable of powering the :, .
.' ~~
10~1763 , .
watch at an average drain rate of 2~lA and a voltage in excess of 2.2 volts for about 28.5 years. The lifetime of such cells is in excess of the lifetime of the currently produced watches themselves. Accordingly, with~the stability of solid state ., cells in general and the capacity of the present cell in particular, batteries can be made as integral parts of electrical componentry such as watches rather than as a part requiring constant replacement.
~'t`
A cell made in accordance with that of Example 1 is made but with tantalum disulfide (TaS2) in place of titanium disulfide (TiS2) and a wcight ratio to sulfur of 87.5:12.5.
Upon discharge of the cell at 72C under a load of lOk.~the cell realizes 6 mAH to 2 volts, 18 mAH to 1.5 volts and 24 mAH to volt.
EX~MPLE 25 A cell made in accordance with the previous Example is discharged at 72C under a load of 20k~. The cell realizes 14 mP~H to 2 volts, 25 mAH to 1.5 volts and about 28 mAH to 1 volt.
It is understood that changes and variations of the invention as described herein can be made without departing from the scope of the present invention as defined in the following claims.
Claims (9)
1. A solid state electrochemical cell comprising a solid lithium anode; a solid electrolyte comprising one or more lithium salts and having an ionic conductivity in excess of 1 x 10-9 ohm-1cm-1 at room temperature and a solid cathode comprising an ionically and electronically conductive metal chalcogenide wherein said ionic and electronic conductivity ranges between 10-10 to 10-2 ohm-1cm-1 at room temperature and wherein said metal chalcogenide is cathodically active with said lithium anode, and said cathode further includes as a second cathode active material a member of the group consisting of sulfur, selenium, tellurium, bromine and iodine.
2. The solid state cell of claim 1 wherein said lithium salt is lithium iodide.
3. The solid state cell of claim 2 wherein said electrolyte further includes lithium hydroxide and aluminium oxide.
4. The solid state cell of claim 1 wherein said metal chalcogenide has a room temperature ionic conductivity in excess of 10-6ohm-1cm-1, a room temperature electronic conductivity in excess of 10-1ohm-1cm-1 and an open circuit voltage when coupled with said lithium anode in excess of 1.5 volts.
5. The solid state cell of claim 1 wherein said metal chalcogenide is titanium disulfide.
6. The solid state cell of claim 5 wherein said second cathode active material is sulfur.
7. The solid state cell of claim 6 wherein said titanium disulfide and said sulfur are in a mole to mole ratio.
8. The solid state cell of claim 7 wherein said lithium salt is lithium iodide.
9. The solid state cell of claim 8 wherein said electrolyte further includes lithium hydroxide and aluminum oxide.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US79080077A | 1977-04-25 | 1977-04-25 | |
| US790,800 | 1991-11-12 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1091763A true CA1091763A (en) | 1980-12-16 |
Family
ID=25151779
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA300,295A Expired CA1091763A (en) | 1977-04-25 | 1978-04-03 | Cathodes for solid state lithium cells |
Country Status (11)
| Country | Link |
|---|---|
| JP (1) | JPS53133730A (en) |
| BE (1) | BE866320A (en) |
| CA (1) | CA1091763A (en) |
| CH (1) | CH634955A5 (en) |
| DE (1) | DE2817776A1 (en) |
| DK (1) | DK177278A (en) |
| FR (1) | FR2389246B1 (en) |
| GB (1) | GB1599792A (en) |
| IL (1) | IL54397A (en) |
| IT (1) | IT1095321B (en) |
| NL (1) | NL7804332A (en) |
Families Citing this family (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE3026141A1 (en) * | 1980-07-10 | 1982-02-18 | Varta Batterie Ag, 3000 Hannover | GALVANIC FIXED ELECTROLYTE CELL |
| FR2508240A1 (en) * | 1981-06-17 | 1982-12-24 | Gipelec | Electrochemical cell with cation conductive vitreous electrolyte - formed by powder compaction on cathode with lithium disc superimposed |
| US4444857A (en) * | 1981-06-17 | 1984-04-24 | Societe Anonyme Dite: Gipelec | Electrochemical cell including a solid electrolyte made from a cation conductive vitreous compound |
| CN103650215A (en) * | 2011-07-11 | 2014-03-19 | 巴斯夫欧洲公司 | Electrode material comprising metal sulfide |
| US10566611B2 (en) | 2015-12-21 | 2020-02-18 | Johnson Ip Holding, Llc | Solid-state batteries, separators, electrodes, and methods of fabrication |
| US10218044B2 (en) | 2016-01-22 | 2019-02-26 | Johnson Ip Holding, Llc | Johnson lithium oxygen electrochemical engine |
| CN106065847B (en) * | 2016-08-10 | 2023-03-10 | 西安交通大学 | Variable cross-section wind power blade |
| WO2019126499A1 (en) | 2017-12-20 | 2019-06-27 | Cornell University | Titanium disulfide-sulfur composites |
Family Cites Families (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3827913A (en) * | 1972-05-08 | 1974-08-06 | Bell Telephone Labor Inc | Solid electrolyte power source |
| US3791867A (en) * | 1972-07-24 | 1974-02-12 | Bell Telephone Labor Inc | Rechargable nonaqueous battery |
| DE2254415C2 (en) * | 1972-11-07 | 1981-12-03 | P.R. Mallory & Co. Inc. (n.d.Ges.d.Staates Delaware), Indianapolis, Ind. | Galvanic element with solid electrolyte |
| CA1021844A (en) * | 1973-09-10 | 1977-11-29 | M. Stanley Whittingham | Rechargeable battery with chalcogenide cathode |
| US3959012A (en) * | 1974-04-25 | 1976-05-25 | P. R. Mallory & Co., Inc. | Composite cathode materials for solid state batteries |
| US3988164A (en) * | 1974-04-25 | 1976-10-26 | P. R. Mallory & Co., Inc. | Cathode material for solid state batteries |
| DE2450489B2 (en) * | 1974-10-24 | 1978-02-02 | Rheinisch-Westfälisches Elektrizitätswerk AG, 4300 Essen | GALVANIC ELEMENT |
-
1978
- 1978-03-30 IL IL54397A patent/IL54397A/en unknown
- 1978-04-03 CA CA300,295A patent/CA1091763A/en not_active Expired
- 1978-04-22 DE DE19782817776 patent/DE2817776A1/en not_active Ceased
- 1978-04-22 CH CH432478A patent/CH634955A5/en not_active IP Right Cessation
- 1978-04-24 JP JP4863478A patent/JPS53133730A/en active Pending
- 1978-04-24 NL NL7804332A patent/NL7804332A/en not_active Application Discontinuation
- 1978-04-24 FR FR7811997A patent/FR2389246B1/en not_active Expired
- 1978-04-24 IT IT22687/78A patent/IT1095321B/en active
- 1978-04-24 DK DK177278A patent/DK177278A/en unknown
- 1978-04-25 BE BE2056906A patent/BE866320A/en not_active IP Right Cessation
- 1978-04-25 GB GB16382/78A patent/GB1599792A/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| CH634955A5 (en) | 1983-02-28 |
| IL54397A (en) | 1981-07-31 |
| DE2817776A1 (en) | 1978-10-26 |
| DK177278A (en) | 1978-10-26 |
| FR2389246B1 (en) | 1986-02-21 |
| IL54397A0 (en) | 1978-06-15 |
| IT1095321B (en) | 1985-08-10 |
| FR2389246A1 (en) | 1978-11-24 |
| GB1599792A (en) | 1981-10-07 |
| IT7822687A0 (en) | 1978-04-24 |
| NL7804332A (en) | 1978-10-27 |
| JPS53133730A (en) | 1978-11-21 |
| BE866320A (en) | 1978-08-14 |
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