US00558
`7133A
`5,587,133
`Patent Numb
`United States Patent
`Patent
`Number:
`
`Amatucci et al.
`[45] Date of Patent:
`Dec. 24, 1996
`
`[19]
`
`[11]
`
`UCTCUPRY
`
`[54] DELITHIATED COBALT OXIDE AND
`NICKEL OXIDE PHASES AND METHOD OF
`PREPARING SAME
`
`[75]
`
`.
`
`‘
`
`Stans
`
`Inventors: Teeeeeeeville
`
`both of N.J.
`
`5,011,748
`5,192,629
`5,264,201
`5,296,318
`5,296,319
`
`5,401,599
`
`4/1991 Shacklette et al. wu. essen 429/218
`3/1993 Guyomardetal.....
`wee 429/197
`11/1993 Dahnetal. ........
`wee 423/594
`3/1994 Gozdz etal.
`......
`wee 429/192
`3/1994 Bito etal. wu...
`wee 429/218
`
`
`
`scssssssnsessemeene 429/218
`
`3/1995 Tahara et al.
`
`OTHER PUBLICATIONS
`
`[73] Assignee: Bell Communications Research,Inc.,
`Morristown, N.J.
`
`Ohzuku et al., J. Electrochem. Soc., vol. 141, No. 11, Nov.
`1994, pp. 2972-2977,
`Ohzuku et al., J. Electrochem. Soc., vol. 140, No. 7, Jul.
`[21] Appl. No.: 383,401
`1993, pp. 1862-1870.
`[22]
`Filed:
`Feb. 3, 1995
`;
`.
`[51]
`Inte Cho iccccssssstencsssen C01D 1/02; C01G 49/02;
`CO01G 51/04=Primary Examiner—Kathryn Gorgos
`[52] US. Checscs 423/138; 423/592; 423/179.5;
`Attorney, Agent, or Firm—Lionel N. White
`423/594; 429/49; 429/50; 429/52; 429/218;
`205/538; 205/548
`(58] Field of Search occ 429/49, 50, 52,
`429/218; 204/140, 141.5; 423/138, 592,
`179.5, 594; 205/538, 548
`
`(57]
`
`ABSTRACT
`
`LiCoO, and LiNiO, are fully delithiated electrochemically
`using solid state electrolytic cells and oxidation resistant
`electrolytes to yield new phases of CoO, and NiO,.
`
`[56]
`
`References Cited
`U.S. PATENT DOCUMENTS
`
`4,818,647
`
`4/1989 Plichta et al.
`
`.......ssscsessseseseeee 429/218
`
`10 Claims, 10 Drawing Sheets
`
`APPLE-1025
`
`APPLE-1025
`
`1
`
`

`

`U.S. Patent
`
`Dec. 24, 1996
`
`Sheet 1 of 10
`
`
`
`
`
`Intensityarbitrary-
`
`5,587,133
`
`Monoclinic
`a=4.835
`b=2.775
`c=4.928
`
`units
`
`2
`
`

`

`U.S. Patent
`
`Sheet 2 of 10
`
`5,587,133
`
`Hexagonal
`a=2.8222
`(110) O=12.879
`(203)
`
`(106)
`
`Intensity-arbitrary
`
`units Dec. 24, 1996
`
`
`
`
`
`)jBeelahe onal
`(104)
`x=0.15Li
`g=2.ei
`(107)
`(110) b=14.219
`(113)
`
`50
`
`60
`
`70
`
`80
`
`Angle, 20 - degrees
`
`FIG. 2
`
`3
`
`

`

`U.S. Patent
`
`Dec. 24, 1996
`
`Sheet 3 of 10
`
`5,587,133
`
`-V
`
`Voltage
`
`0
`
`02
`
`04
`
`06
`
`O8
`
`1.0
`
`X in Li,CoO,
`
`FIG. 3
`
`4
`
`

`

`U.S. Patent
`
`Dec.24, 1996
`
`Sheet 4 of 10
`
`5,587,133
`
`4.5
`
`4.0
`
`3.5
`
`Voltage
`
`Voltage
`
`-V 3.0 2.5
`-V
`
`0
`
`02
`
`04
`
`06
`
`O08
`
`1.0
`
`X in Li,NiO,
`
`FIG. 4
`
`0
`
`02
`
`04
`
`06
`
`O08
`
`1.0
`
`X in Li,NiO»
`
`FIG. 5
`
`5
`
`

`

`U.S. Patent
`
`Dec. 24, 1996
`
`Sheet 5 of 10
`
`5,587,133
`
`0.30
`
`NiO»
`
`0-184 Coo,
`
`O®2@
`
`E
`
`0.00
`
`-40
`
`40
`
`120
`
`200
`
`280
`
`360
`
`Temperature - °C
`
`FIG. 6
`
`6
`
`

`

`U.S. Patent
`
`Dec. 24, 1996
`
`Sheet 6 of 10
`
`5,587,133
`
`After DSC
`
`units
`Intensityarbitrary-
`
`
`
`Angle, 29 - degrees
`
`FIG. 7
`
`7
`
`

`

`U.S. Patent
`
`Dec. 24, 1996
`
`Sheet 7 of 10
`
`5,587,133
`
`After DSC
`300°C
`
`units
`Intensityarbitrary-
`
`
`
`22, 1189
`NiO
`
`20
`
`30
`
`40
`
`50
`
`60
`
`70
`
`80
`
`Angle, 26 - degrees
`
`FIG. 8
`
`8
`
`

`

`US. Patent
`
`Dec. 24, 1996
`
`Sheet 8 of 10
`
`5,587,133
`
`4.5
`
`-VNhwoGoaSonoOno.oOo
`
`Voltage
`
`NO oO
`
`aonk. O1
`
`CoO,
`
`Nap g5C0O>
`
`0
`
`0.2
`
`0.4
`
`0.6
`
`X in NayCoO,
`
`FIG. 9
`
`9
`
`

`

`U.S. Patent
`
`Dec. 24, 1996
`
`Sheet 9 of 10
`
`5,587,133
`
`units
`Intensityarbitrary-
`
`
`
`20
`
`~3=30
`
`40
`50
`60
`Angle, 26 - degrees
`
`70
`
`80
`
`FIG. 10
`
`10
`
`

`

`U.S. Patent
`
`Dec. 24, 1996
`
`Sheet 10 of 10
`
`5,587,133
`
`units
`
`Intensityarbitrary-
`
`
`Angle, 20 - degrees
`
`FIG. 17
`
`11
`
`

`

`5,587,133
`
`1
`DELITHIATED COBALT OXIDE AND
`NICKEL OXIDE PHASES AND METHOD OF
`PREPARING SAME
`
`BACKGROUNDOF THE INVENTION
`
`The increasing commercial importance of rechargeable
`lithium ion battery cells has prompted a desire to identify
`and to prepare cathode materials better able to reversibly
`intercalate and deintercalate lithium ions at greater voltages.
`There are three prominent reversible lithium intercalation
`compounds used for lithium ion rechargeable batteries:
`lithium cobalt oxide (LiCoO,) and lithium nickel oxide
`(LiNiO,) compounds, as well as lithium magnesese oxide
`(LiMn,O,) spinel.
`LiCoO, cells are of particular interest because of their
`ability to insert/deinsert
`lithium reversibly at voltages
`greater than 4 V resulting in batteries that have an output
`voltage and an energy density 3 times greater than Ni—Cd.
`The theoretical charge capacity of LiCoO, cells is large at
`about 275 Amp-hours/kilogram (A-h/kg). In practical appli-
`cation, however,
`the maximum obtainable capacity for
`LiCoO,cells has been only about 140 A-h/kg, correspond-
`ing to a maximum charge voltage of about 4.2 V.
`Previous attempts to exceed this charge cutoff voltage in
`LiCoO,cells have caused poor cell performance manifested
`by severe loss of charge capacity in subsequent charge-
`discharge cycles. The commonly-held reason for the 4.2 volt
`chargelimitation for LiCoO, cells was that electrochemical
`delithiation of LiCoO, above this voltage destabilized the
`structure of the partially delithiated LiCoO, phase, impair-
`ing intercalation of lithium in subsequent charge-discharge
`cycles.
`Lithium cobalt oxide adopts a hexagonal structure con-
`sisting of CoO, layers separated by a Van der Waals gap. The
`octahedral sites within the Van der Waals gap are occupied
`by the Li* ions. This results in the reversible intercalation of
`lithium.
`
`In such compounds,lithium acts as a glue or cement,
`screening the repulsive interactions between the negatively
`charged CoO, layers. When the compoundis fully lithiated
`LiCoO,,
`the screening effect
`is greatest. As lithium is
`removed,the screening effect is decreased and the repulsions
`between the two CoO, layers are enhanced resulting in an
`expansion of the c-axis parameter. Due to the screening
`effect of lithium,
`it was believed that complete lithium
`deintercalation to form CoO, was not possible.
`Ohzuku et al., J. Electrochem. Soc., Vol. 141, No. 11, Nov.
`1994, p. 2972, have succeeded in removing approximately
`85% of the lithium. Their efforts revealed a monoclinic
`phase and questioned the existence of a CoO, phase.
`In another theory, Reimers and Dahn, J. Electrochem.
`Soc., 139, 2091, (1992), states that excess Co** destroys the
`crystallinity of the lithium cobalt oxide structure. Appar-
`ently, it inhibits the formation of highly crystalline phases at
`low lithium contents.
`
`15
`
`20
`
`25
`
`35
`
`45
`
`Wizansky, Rauch, and DiSalvo, Journal of Solid State
`Chemistry, 81, 203-207 (1989), investigated the delithiation
`of LiCOO,through the use of powerful oxidizing agents
`such as NO,* and MoF,. Their results showed that this
`approach merely decomposes the LiCoQ,.
`LiNiO,is isostructural with LiCoO, and is commercially
`viable for use in secondary lithium ionbatteries. Heretofore,
`no one has been capable of obtaining the delithiated NiO,
`phase. Ohzuku et al., J. Electrochem. Soc., Vol. 140, No. 7,
`
`60
`
`65
`
`2
`July 1993, working with the nickel oxide reported
`Lig.ogNiO. and approximated that this was the end phase.
`Lithium secondary batteries are generally recognized and
`are described for instance in U.S. Pat. No. 5,296,318 to
`Gozdzet. al., which is incorporated in its entirety herein by
`reference. Lithium metal-free “rocking-chair” batteries may
`thus be viewed as comprising two lithium-ion-absorbing
`electrode “sponges” separated by a lithium-ion-conducting
`electrolyte, usually comprising a Li* salt dissolved in a
`non-aqueous solvent or mixture of such solvents. Numerous
`such salts and solvents are knownin the arts, as evidence in
`Canadian Pat. Publication No. 2,022,191, dated 30 Jan.
`1991.
`
`When cells comprising these previously-available elec-
`trolytes are cycled to a voltage even slightly greater than 4.3
`V, electrolyte oxidation occurs. Although small, this oxida-
`tion can jeopardize the capacity, cycle life, and safety of the
`battery cell. For example, the electrode oxidation reaction
`consumes part of the charging current, which cannot be
`recovered when discharging the cell. The result is a con-
`tinuous loss in the cell capacity over subsequent cycles.
`Further, if during each charge a small part of the electrolyte
`is consumed, excess electrolyte must be included when the
`cell is assembled. The excess electrolyte reduces the amount
`of active material for a constant volume battery body,
`thereby decreasinginitial capacity. In addition, the oxidation
`of the electrolyte often generates solid and gaseous by-
`products. The solid by-products build up a passivating layer
`onthe particles of the active material, essentially increasing
`the polarization of the cell and lowering the output voltage.
`Simultaneously, and more importantly,
`the gaseous by-
`products increase the internal pressure of the cell, thereby
`increasing the risk of explosion and leading to unsafe and
`unacceptable operating conditions.
`U.S. Pat. No. 5,192,629, which is herein incorporated by
`reference in its entirety, provides a class of electrolyte
`compositions that are exceptionally useful for minimizing
`electrolyte decomposition in secondary batteries comprising
`strongly oxidizing positive electrode materials. These elec-
`trolytes are thus uniquely capable of enhancingthe cyclelife
`and improving the temperature performance of practical
`“rocking chair” cells. These electrolyte compositions have a
`range ofeffective stability extending up to about 5.0 V at 55°
`C., as well as at room temperature (about 25° C.).
`Electrolytes that are substantially inert
`to oxidation
`include a 0.5M to 2M solution of LiPF,, or LiPF, with up
`to about an equal amount of LiBF, added, in a mixture of
`dimethylcarbonate (DMC) and ethylene carbonate (EC)
`within the weight percent ratio range from about 95 DMC:5
`EC to 20 DMC:80 EC.In a preferredelectrolyte solution, the
`solvent ratio range is about 80 DMC:20 EC to 20 DMC:80
`EC. An optimum composition for operation at room tem-
`perature and below is an approximately 1.5M LiPF, solution
`in a solvent mixture of about 67 DMC:33 EC. A battery
`operating at room temperature and higher, e.g., in the range
`of 55° C., optimally utilizes an electrolyte consisting essen-
`tially of an approximately 1.5M LiPF, solution in a solvent
`combination of about 33 DMC:67 EC. An additionally
`useful electrolyte consists essentially of an approximately
`1M to 2M solution of equal pares of LiPF, and LiBF, in a
`solvent mixture of about 50 DMC:50 EC.
`
`Negligible current increases, after the reversible Li inter-
`calations, at voltages up to about 5 V vs. Li indicates this
`remarkable stability that enables enhanced cell capacity not
`only in the “rocking chair” cells comprising negative elec-
`trodes of carbon, e.g., petroleum coke, but also in Li
`
`12
`
`12
`
`

`

`5,587,133
`
`4
`3
`explain the invention and its objects, advantages, and prin-
`negative electrode cells. Suchalithium metal cell utilizing
`ciples.
`a LiCoO,positive electrode may be reasonably expected to
`achieve normal operating ranges of about 4.3 to 5.1 V.
`With the aid of electrolytes which are substantially inert
`to oxidation and solid state electrolytic cells, fully delithi-
`ated phases of both CoO, and NiO, were obtained.
`SUMMARYOF THE INVENTION
`
`BRIEF DESCRIPTION OF THE DRAWING
`
`The present invention will be described with reference to
`the accompanying drawing of which:
`FIG. 1 is a series of x-ray diffraction diagrams taken
`during electrochemical delithiation of LiCoO, to form the
`CoO, phase;
`FIG. 2 is a series of x-ray diffraction diagrams taken
`during electrochemical
`intercalation of lithium into the
`CoO, phase;
`FIG.3 plots charge and discharge voltage versus lithium
`content for a cell utilizing the CoO, phase;
`FIGS. 4 and 5 plot charge and discharge voltage versus
`lithium content for a cell having a LiNiO, cathode that has
`been delithiated to the NiO, phase according to the inven-
`tion;
`FIG.6 plots decomposition reaction heat versus tempera-
`ture for the CoO, and NiO, phase;
`FIGS. 7 and 8 are x-ray diffraction diagrams for the
`thermal decomposition products of the CoO, and NiO,
`phases;
`FIG.9 plots charge and discharge voltages versus sodium
`content for a cell using the CoO, phase of this invention
`intercalated with sodium ions;
`FIG. 10 is an x-ray diffraction diagram taken during
`electrochemical delithiation of LiNiO. to form the NiO,
`phase; and
`FIG. 11 is an x-ray diffraction diagram illustrating the
`effect of atmospheric water on the CoO, phase.
`
`DESCRIPTION OF THE INVENTION
`
`Onehindrance to the achievement of the CoO, and NiO,
`phases of the present invention, was removed by the devel-
`opmentofelectrolytes that are stable (inert to oxidation) at
`the high voltages thought necessary to achieve the delithi-
`ated CoO, phase. These electrolytes are exemplified by
`those described in U.S. Pat. No. 5,192,629, the disclosure of
`which is incorporated herein by reference. Nonetheless, it
`was commonly held that the CoO, phase was unattainable
`because in the complete absence of lithium ions in the Van
`der Waals gap between the negatively-charged CoO, layers,
`the repulsive force between the layers would be too great
`and a completely delithiated CoO, phase would never be
`stable.
`
`Using an electrolytic cell incorporating an LiCoO, cath-
`ode material described herein and a high voltage-stable
`electrolyte, the CoO, phase can be prepared by applying to
`the cell a charge voltage of 5.2 V, which will deintercalate
`substantially all
`the lithium from the LiCoO, cathode,
`forming the CoO, phase. The CoO, phase is metastable and
`decomposes above 200° C.
`Similarly, in an electrolytic cell using a high voltage-
`stable electrolyte and a LiNiO, cathode, a substantially
`complete delithiation to a NiO, phase can be achieved by
`applying a charge voltage of 5.1 V.
`Once obtained, the CoO, and NiO, phases of the present
`invention can be reintercalated with lithium, or by other ions
`such as hydrogen nuclei, sodium (Example 4), potassium, or
`rubidium. Reintercalation of lithium or other ionic species
`into the CoO, or NiO, phases can be accomplished by
`electrochemical insertion or by vapor phase transport at
`
`Accordingly, the present invention is directed to meta-
`stable CoO, and NiO. phases and their use as intercalation
`compoundsfor use in lithium ion secondary batteries. Fea-
`tures and advantages of this invention are set forth in the
`description that follows, and they will be apparent from that
`description or can be learned by practice of the invention.
`In one aspect, this invention relates to an electrochemical
`method for preparing a stable cobalt dioxide phase that
`includes preparing an electrolytic cell having an anode, an
`electrolyte substantially inert to oxidation, and a cathode
`including a lithium cobalt oxide intercalation complex; and
`applying a voltage to the cell sufficient
`to completely
`deintercalate lithium from the lithium cobalt oxide interca-
`lation complex, thereby forming a stable cobalt dioxide
`phase in the cathode.
`In a further aspect, this invention relates to a stable cobalt
`dioxide phase prepared by the foregoing method.
`In a further aspect, this invention relates to a stable cobalt
`dioxide phase having the x-ray diffraction pattern:
`
`d(A)
`4.30 + 0.02
`2.44 + 0.02
`2.12 + 0,02
`1.61 + 0,02
`1.41 + 0,02
`1.34 + 0.02
`1.17 + 0,02
`
`In a further aspect, this invention relates to an electro-
`chemical method for preparing a stable nickel dioxide phase
`that includes providing a lithium nickel oxide intercalation
`complex having the formula Li,NiO, wherein x is preferably
`0.8 to 1.0, preparing an electrolytic cell having a cathode
`including the lithium nickel oxide intercalation complex,
`and applying a voltage to the cell sufficient to delithiate
`completely the lithium nickel oxide intercalation complex.
`In a further aspect, this invention relates to a stable nickel
`dioxide phase prepared by the above described process. In a
`further aspect,
`this invention relates to a stable nickel
`dioxide phase having the x-ray diffraction pattern:
`
`d(A)
`4.47 + 0.02
`2.40 + 0.02
`2.29 + 0.02
`1,97 + 0.02
`1,51 £0.02
`1.41 + 0.02
`1.38 + 0.02
`
`In a further aspect, the invention relates to the a method
`of making a secondary electrolytic cell including the stable
`CoO, or NiO, phase and the cell formed thereby.
`The accompanying drawings, which are incorporated in
`and constitute a part of this specification,illustrate embodi-
`ments of the invention and with the description serve to
`
`20
`
`25
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`13
`
`13
`
`

`

`5,587,133
`
`5
`is
`temperatures below 200° C. Vapor phase transport
`described in a paper by Tarascon et al., “Synthesis and
`peculiar properties of InMo,S,.,Sey and Hg,Mo,S,,Se,”,
`Physical Review B, Vol. 31, NO. 2, 1985, which is incor-
`porated herein by reference in its entirety.
`Following reintercalation, these phases can, for example,
`be cycled with lithium between 3 V and 4.2 V for the CoO,
`phase and 2.8 V and 4.1 V for the NiO, phase withoutloss
`of cell capacity.
`After formation of the CoO, phase, CoOOOH may be
`formed by exposure of the phase to atmospheric water. As
`can be seen from FIG. 11, CoO. may be formedin situ in an
`electrochemical cell. After exposure to air for approximately
`30 minutes,
`two phases are present. After 3 days in air
`CoOOHwasformed, because at an open circuit voltage >4
`V the following reaction occurs:
`
`2H,0—4e"-0,+4H*
`
`CoOgtx &+x HtH,CoO,
`
`The CoOOH maybe used as an electronic conductor in
`other battery technology. This includes application in the Ni
`electrode or NiMeH, Ni—H or Ni—Cdbatteries in which
`cobalt is already used.
`Asan alternative, once formed, these phases can be used
`in any variety of manners. In one preferred embodiment, the
`cathode ofa plastic solid state cell is not laminated to the
`underlying electrolyte/anode structure, thus allowing ease of
`removal of the CoO, or NiO, phase in a plastic matrix. This
`plasticized phase can then easily be transported to other
`environments. For the reasons discussed abave,if the pure
`CoO, phase is desired, handling under inert (anhydrous)
`conditions is preferred.
`In another embodiment, this plasticized phase is placed
`into a cell containing, for example, a sodium containing
`electrolyte and a compatible electrolyte and then the cobalt
`or nickel oxide phase is reintercalated with the sodium ions.
`This reintcrcalation may be stopped short of completion and,
`in that way, a second or subsequent ion may be addedto the
`reintercalated metal oxide phase.
`In yet another embodiment, the nickel or cobalt oxide
`phase may be combined with an organic componentto form,
`for example, either a composite polymer or an activated
`metal oxidecarrier. The redox potential of this phase is high
`making it potentially useful
`in many areas. Anticipated
`applications include, for example, forming inorganic poly-
`mer structures and as a biochemical carrier. Such applica-
`tions would be clearly recognizable to the skilled artisan.
`The following examples exemplify the practice of the
`present invention to the prior art. It will be appreciated by
`those skilled in the art that these examples are not to be
`construed as limiting the present invention.
`EXAMPLE1
`
`A plastic electrolytic cell was constructed comprising a
`matrix of polyvinylidene fluoride (PVdF) and hexafluoro-
`propylene (HFP) and incorporating an electrolyte composi-
`tion of 2 parts EC to one part DMC and 1M LiPF,, which
`was inert to oxidation at high voltages. The cathode con-
`tained LiCoO, as an active material and the anode contained
`carbon. The anode and the solid state electrolyte were
`laminated to one another and the cathode wasplaced there-
`over.
`
`This cell was charged to 5.2 V, at which point the LiCoO,
`was fully delithiate to form the CoO, phase. The existence
`of this phase is confirmed by the x-ray data depicted in FIG.
`
`6
`the end of
`1 depicts the diffraction pattern at
`1. FIG.
`deintercalation of LiCoO, beginning at approximately the
`last known phase disclosed in the prior literature,
`i.e.,
`monoclinic (Lig ,;CoO,)
`and proceeding to complete
`delithiation at a voltage of 5.2 V.
`The x-ray diffraction patterns were obtained in-situ
`through the use of an X-ray diffraction apparatus that allows
`the use of high voltages without corrosion of the beryllium
`window.
`
`The final x-ray diffraction pattern obtained at 5.2 V is the
`hexagonal structure associated with the CoO, phase. More-
`over, once obtained, the CoO, phase reconverted to the
`LiCoO, phase during discharge of the cell as shown by the
`series of x-ray diffraction patterns in FIG. 2. Following
`attainment of the CoO, phase in the cathode and reinterca-
`lation of lithium to form the LiCoO, phase, this cell was
`cycled between 3 V and 4.2 V with little loss of charge
`capacity, as seen in FIG.3.
`During the charge cycle of a partially delithiated cobalt
`oxide, reinsertion of the lithium forms a monoclinic phase;
`however, reinsertion of lithium into the fully delithiated
`cobalt oxide resulted in a hexagonal structure, which is the
`sameas the structure of the LiCoO, originally incorporated
`into the electrolytic cell.
`
`EXAMPLE2
`
`A plastic electrolytic cell was constructed as in Example
`1, incorporating an electrolyte composition inert to oxida-
`tion at high voltages and a cathode made from LiNiO,. This
`cell was charged to 5.1 V, at which voltage substantially all
`of the lithium was removed from the LiNiO, phase to form
`the NiO, phase. The existence of the NiO, phase is con-
`firmed by the x-ray data depicted in FIG. 10.
`Thecell was discharged at 200 pA, whereupon 70% ofthe
`lithium intercalated back into the NiO, structure, as seen in
`FIG.4. Subsequent cycling this cell between 2.8 V and 4.0
`V without capacity fading confirmed that the reversible
`charge characteristics of the Li,NiO, were not destroyed by
`the attainment of the NiO, phase. Reducing the discharge
`current to 150 pA resulted in intercalation of all of the
`lithium to form the LiNiO, phase. As shown in FIG. 5,
`subsequent cycling of this cell between 2.8 V and 4.1 V
`resulted in a high capacity (greater than 190 A-h/kg) with
`minimal! polarization and slight irreversibility characteristic
`of LiNiO,. These results show that total removal of lithium
`from LiNiO, produces a structure that remains electro-
`chemically active.
`
`EXAMPLE3
`
`A study of the thermal stability of the CoO, phase and
`NiO, phase was undertaken. Plastic electrodes of LiCoO,
`and LiNiO, brought to the CoO, phase and the NiO, phase
`in the manners described in Examples 1 and 2, respectively,
`were dissolved separately in a dilute acetone solvent at room
`temperature. The plastic portions of the electrodes dissolved
`in the solvent, and the insoluble metal oxides settled to the
`bottomofthe vessels. The metal oxides were separated from
`the solution and analyzed using differential scanning cale-
`rimetry (DSC) ramped to 300° C. at 10° C./min.
`As seen in FIG.6, a relatively strong exothermic reaction
`occurred at 200° C. for both the CoO, and NiO, phases.
`Analysis of the samples by x-ray diffraction after DSC
`revealed that both phases reduced with attendant oxygen
`loss according to the reaction
`
`20
`
`25
`
`30
`
`40
`
`50
`
`55
`
`60
`
`65
`
`14
`
`14
`
`

`

`5,587,133
`
`MO,>M0+40,
`
`7
`
`The x-ray diffraction patterns depicted in FIGS. 7 and 8
`confirm that the samples transformed into the mixed rocksalt
`structures of CoO and NiO, which are knownto beeleciro-
`chemically inactive to lithium intercalation.
`
`EXAMPLE4
`
`A cell was constructed as in Example 1. The CoO, phase
`was formed by delithiating the plastic cell at 5.2 V for 15
`hours. After the CoO, phase was formed, the plasticized
`CoO, was removed from the electrolyte/anode structure and
`then incorporated into a similarly constructed cell contained
`sodium.
`
`The new cell was constructed using the plastic CoO,
`cathode, an NaCiO, electrolyte and a sodium metal anode.
`Sodium wasintroduced into the CoO, phase by discharging
`the cell at 2.2 V to insert the sodium. The cell was then
`cycled between 2.2 V and 4.1 V, as shown in FIG.9.
`What is claimed is:
`1. A method of preparing a stable cobalt dioxide phase
`comprising:
`a) preparing an electrolytic cell having an anode, an
`electrolyte inert to oxidation, and a cathode comprising
`a lithium cobalt oxide intercalation complex; and
`b) applying a voltage in excess of about 5.0 V to deinter-
`calate substantially all lithium from said lithium cobalt
`oxide intercalation complex.
`2. A stable dioxide phase prepared according to the
`method of claim 1.
`3. A stable cobalt dioxide phase prepared according to
`claim 2 having the x-ray diffraction pattern:
`
`5
`
`10
`
`15
`
`25
`
`30
`
`a(A)
`4.30 + 0.02
`2.44 + 0.02
`2.12 + 0.02
`1.61 + 0.02
`1.41 + 0.02
`1.34 + 0.02
`1.17 £ 0.02.
`
`8
`4. A secondary electrolytic cell including an anode, an
`electrolyte, and a cathode comprising the cobalt dioxide
`phase of claim 2.
`5. A method according to claim 1 wherein said electrolyte
`comprises a0.5M to 2M solution of LiPF,, or LiPF, with up
`to about an equal amount of LiBF, added, in a mixture of
`dimethylcarbonate (DMC) and ethylene carbonate (EC)
`within the weight percent ratio range from about 95 DMC:5
`EC to 20 DMC:80 EC.
`6. A method of preparing a stable nickel dioxide phase
`comprising:
`a) providing a lithium nickel oxide intercalation complex
`having the formula Li,NiO, wherein x is 0.8 to 1.0,
`b) preparing an electrolytic cell having an anode, an
`electrolyte inert to oxidation, and a cathode comprising
`said lithium nickel oxide intercalation complex; and
`c) applying to said cell a voltage in excess of about 5.0 V
`to deintercalate substantially all
`lithium from said
`lithium nickel oxide intercalation complex.
`7. A stable nickel dioxide phase prepared according to the
`method of claim 6.
`8. A stable nickel dioxide phase according to claim 7
`having the X-ray diffraction pattern:
`
`d(A)
`4.47 + 0.02
`2.40 + 0.02
`2.29 + 0.02
`1.97 + 0.02
`1.51 + 0.02
`1.41 + 0.02
`1.38 + 0.02.
`
`9. A secondary electrolytic cell including an anode, an
`electrolyte, and a cathode comprising the nickel dioxide
`phase of claim 7.
`.
`10. A method according to claim 6 wherein said electro-
`lyte comprises a 0.5M to 2M solution of LiPF,, or LiPF,
`with up to about an equal amount of LiBF, added, in a
`mixture of dimethylcarbonate (DMC)and ethylene carbon-
`ate (EC) within the weight percentratio range from about 95
`DMC:5 EC to 20 DMC:80 EC.
`
`*
`
`ke
`
`#k RF
`
`15
`
`15
`
`