United States Patent (19)
`Jacobs et al.
`
`54 RECHARGEABLE LITHIUM BATTERY
`HAVING IMPROWED REVERSIBLE
`CAPACITY
`
`76 Inventors: James K. Jacobs, The Electrofuel
`Manufacturing Co. 21 Hanna Avenue.
`Toronto, Canada; Sankar Dasgupta,
`The Electrofuel Manuf. Co. 21 Hanna
`Avenue. Toronto, Canada
`21 Appl. No.: 604,220
`pp. No.:
`22 Filed:
`Feb. 22, 1996
`HO1M 10/40
`(51) Int. Cl.
`52 U.S.C. ..."429/60.425218. 429
`0
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`429/9, 60,209
`29,218,220.223,224 194. 29,623
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`References Cited
`U.S. P.
`DOC
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`56
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`S
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`USOO5721067A
`Patent Number:
`11
`45 Date of Patent:
`
`5,721,067
`Feb. 24, 1998
`
`5,162,176 11/1992 Herr et al. .............................. 429/194
`5,238,760 8/1993 Takahashi et al. .........
`... 429/194
`5,340,670 8/1994 Takami et al. .......................... 429/194
`5,422,203 6/1995 Guyomard et al. ..................... 429/194
`5,432,029 7/1995 Mitate et al. ........................... 429,194
`5,436,093 7/1995 Huang et al. ........................... 429/217
`5,595,837
`1/1997 Olsen et al. ............................ 429/94
`5,605,772 2/1997 Yazami et al. .......................... 429/90
`
`
`
`Primary Examiner-Anthony Skapars
`57
`ABSTRACT
`An improved rechargeable lithium battery is described com
`prising a transition metal compound as cathode active mate
`rial and carbonaceous particles as anode active material,
`having prior intercalated lithium ions in the carbonaceous
`particles in the anode of the assembled lithium battery,
`thereby reducing the weight of the cathode active material
`required. The rechargeable lithium battery has increased
`energy density per unit weight and per unit volume.
`
`4,980,250 12/1990 Takahashi et al. ...................... 429/194
`
`12 Claims, 2 Drawing Sheets
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`U.S. Patent
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`Feb. 24, 1998
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`Sheet 1 of 2
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`U.S. Patent
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`Feb. 24, 1998
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`Sheet 2 of 2
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`5,721,067
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`1.
`RECHARGEABLE LITHIUM BATTERY
`HAVING IMPROVED REVERSIBLE
`CAPACTY
`
`FIELD OF INVENTION
`This invention is related to rechargeable non-aqueous
`lithium batteries.
`
`BACKGROUND TO THE INVENTION
`Most rechargeable lithium ion batteries have a negative
`electrode containing elemental lithium, which is usually
`intercalated in some carbonaceous substance, a positive
`electrode bearing a chalcogenide, which is capable of incor
`porating lithium ions in its structure, an electrolyte contain
`ing mobile lithium ions, located between the negative and
`positive electrodes and, optionally, a separator. The positive
`electrode also contains lithium either as ions incorporated in
`the structure of the chalcogenide or as a lithium compound
`having dissociable lithium ions ready to be incorporated in
`the structure of the chalcogenide, a binder mixed with the
`chalcogenide, and optionally carbon added to increase the
`conductivity of the mixture. The chalcogenide in the positive
`electrode is usually a transition metal oxide but may also be
`a transition metal sulphide. In some instances the chalco
`genide may be replaced with a suitable organic compound.
`The electrolyte is commonly a solid organic polymer or a
`non-aqueous liquid, which has a lithium salt dissolved in it
`or contains dissociable lithium ions in some other form. The
`electrolyte may also be a microporous solid polymer which
`has been impregnated with an organic liquid containing a
`dissociable lithium salt. The electrolyte which is non
`conductive of electrons, provides ionic passage for the
`lithium ions. Lithium ions move from the elemental lithium
`containing negative electrode or anode to the transition
`metal oxide containing positive electrode or cathode, on
`discharge of the battery. Lithium ions are moved from the
`cathode or positive electrode through the electrolyte to the
`negative electrode in the charging step.
`Lithium batteries often utilize carbonaceous particles
`which are capable of intercalating lithium ions to serve as
`the cathode active material in the negative electrode. It is
`common practice that the carbonaceous particles provided in
`the negative electrode and compacted into a layer with the
`aid of an organic binder, are initially devoid of lithium ions.
`The lithium ions to be utilized in the battery are usually
`added as a component in the transition metal oxide capable
`of incorporating lithium ions in its structure in the positive
`electrode, and in the non-aqueous lithium bearing electro
`lyte. It is to be noted that this procedure is common in
`assembling planar, spirally wound and button shaped
`rechargeable lithium batteries. The assembled lithium bat
`tery is first charged by applying a voltage of about 4.5 volts
`between the electrodes of the lithium battery to move the
`lithium ions in the positive electrode for intercalation in the
`carbonaceous particles constituting the negative electrode.
`Most of the lithium added in the positive electrode can be
`moved by applying an electric charge, however, there is a
`limit of the lithium concentration within the transition metal
`oxide below which the oxide crystal structure is irreversibly
`changed. Furthermore, the first charging of the assembled
`battery is a slow process to be conducted under carefully
`controlled conditions.
`A portion of the lithium ions moved out of the lithium
`transition metal compound serving as the positive active
`material, by the imposed external potential for intercalation
`in the carbonaceous particles, will be permanently lodged in
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`or attached to the surface of the carbonaceous particles
`serving as the negative active material, or will be appended
`to the interface between the carbonaceous particles and the
`non-aqueous electrolyte. The type of bonding by which a
`portion of the lithium ion becomes immobilizable is not
`known exactly; the bonding of the immobilizable lithium
`may be related to the structure of the carbonaceous particles
`or to the nature of the bonding of the mobile lithium ion in
`the electrolyte, or to the interaction between the lithium
`bearing electrolyte and the lithium intercalated in the car
`bonaceous particles or to similar features of the lithium
`battery, however, such immobilizable portion of the lithium
`ioninitially present in the rechargeable lithium battery is lost
`to subsequent charging-discharging process steps. The por
`tion of the lithium ions that becomes non-mobilizable in
`subsequent charging-discharging process steps usually con
`stitutes 20-30% or even higher, of the total amount of
`lithium contained in the rechargeable lithiumbattery and is
`usually referred to as the irreversible capacity loss of the
`lithium battery. The non-mobilizable lithium portion, that is
`the irreversible capacity, will thus be influenced by many
`factors such as the sites available for the lithium ion for
`intercalation, i.e. the nature of the carbon particles utilized,
`the nature and type of non-aqueous lithium bearing electro
`lyte employed, as well as the kind of transition metal oxide
`utilized in the positive electrode. U.S. Pat. No. 5.340,670
`issued to Norio Takami et al. on Aug. 23, 1994, describes as
`the negative active material in a rechargeable lithium
`battery, graphite particles obtained in a high temperature
`treatment step and of specific crystal structure, having
`advantageous properties with respect to irreversible capacity
`loss. U.S. Pat. 5.432,029 issued to Takehito Mitate et al. on
`Jul. 11, 1995, teaches the utilization of copper oxide attached
`to the graphite or similar carbonaceous particles incorpo
`rated in the negative electrode for diminishing the irrevers
`ible capacity loss in a rechargeable lithium battery. Domi
`nique Guyomard et al. in U.S. Pat. No. 5,422.203 issued on
`Jun. 6, 1995, describe a lithium bearing electrolyte compo
`sition to be utilized for reducing the irreversible capacity
`loss in a lithium battery. The above are merely listed as
`examples of attempts of defining the nature of irreversible
`capacity loss in a rechargeable lithium battery and methods
`for diminishing such irreversible capacity losses.
`It can be seen that the irreversible capacity loss of a
`rechargeable lithium battery may be related to both the
`negative active material and to the positive active material.
`It is to be noted that the type of irreversibility associated
`with the negative electrode and its interface with the elec
`trolyte is different from the irreversibility exhibited by the
`positive active material in the positive electrode, however,
`both kinds of irreversibilities are usually compensated by
`adding an excess amount of lithium containing transition
`metal compound to the battery. The excess lithium-transition
`metal compound is a necessary component of a conventional
`lithium battery but is not taking part in subsequent charging
`recharging steps and may amount to 25% or more extra
`battery weight. The mobilizable lithium ion portion in the
`rechargeable lithium battery, related to the carbonaceous
`particles in the negative electrode, is usually referred to as
`the anode specific reversible capacity measured in
`milliampere-hours per gram of carbonaceous particles
`(mAh/g), and that related to the transition metal compound
`the positive electrode, is usually referred to as the cathode
`specific reversible capacity measured in milliampere-hours
`per gram of transition metal compound (mAh/g).
`It is also to be noted that the first charging step due to its
`prolonged nature and controlled conditions, is costly even if
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`excess lithium is added in the form of extra lithium
`transition metal compound. There are known methods for
`incorporating lithium in the carbonaceous particles prior to
`assembling the lithium battery comprising an electrolyte and
`negative and positive electrodes. U.S. Pat No. 4,980,250
`issued to Yuzuru Takahashietal, on Dec. 25, 1990, describes
`carbon moulded articles made of carbon fibre or carbon
`powder having lithium introduced electrolytically in the
`moulded article prior to the incorporation of the carbon
`moulded article into a lithium battery. Cheng-Kuo Huang et
`al. in U.S. Pat, No. 5,436,093, teach a method for introduc
`ing lithium into carbon particles from a liquid electrolyte
`containing lithium ions by the application of more than one
`electrical charging steps. The carbon particles are carried by
`a nickel grid acting as the negatively charged electrode. The
`positive electrode in the pretreatment process is at least one
`lithium sheet immersed in the electrolyte. The lithium con
`taining carbon particles are withdrawn from the pretreating
`electrolyte and are used subsequently as negative active
`material in a rechargeable lithium battery. There is, however,
`no clear indication that all or any portion of the lithium
`introduced by the above described methods contributes to
`the reversible anode capacity of the carbon particles in
`subsequent repeated charging-discharging of the obtained
`lithium battery, thereby eliminates the need for adding an
`extra amount of lithium ion containing transition metal
`compound to operate the rechargeable lithium ion battery
`satisfactorily, and hence provide a lighter lithium battery.
`SUMMARY OF THE INVENTION
`One of the objects of the present invention is to provide
`a rechargeable lithium battery which incorporates the non
`mobilizable lithium ion portion in the negative electrode
`coupled to the non-aqueous electrolyte in the lithium battery
`in the stage prior to the final packaging of the rechargeable
`lithium battery and prior to the full charging of the battery,
`thereby avoiding having to add extra weight in the positive
`electrode.
`Another object of the present invention is to reduce the
`length of time required in the first full charging step of the
`assembled lithium battery.
`Yet another object of the present invention is to provide
`substantially all the mobilizable lithium ion portion as that
`contained in the positive electrode and the dissociable
`lithium ion in the non-aqueous electrolyte of the resulting
`assembled lithium battery, and thereby obtaining a lithium
`battery having high energy density per unit weight.
`A rechargeable lithium battery is described hereinbelow
`which has improved reversible capacity. The improved
`50
`rechargeable lithium battery has a positive electrode com
`prising a transition metal compound capable of incorporat
`ing lithium ions in its structure as the positive active material
`in the cathode, the cathode having a cathode specific revers
`ible capacity (mAh/g), a negative electrode containing
`carbonaceous particles capable of intercalating lithium ions
`as the negative active material in the anode, the anode
`having an anode specific reversible capacity (mAh/g), as
`well as a non-aqueous electrolyte conductive of lithium ions,
`and a total amount of lithium ions distributed between the
`electrodes and the non-aqueous lithium ion bearing electro
`lyte. In the improved rechargeable lithium battery of the
`present invention the weight of the negative active material
`in the negative electrode(w) and the weight of the positive
`active material in the positive electrode (w) are adjusted
`such that the ratio of the anode specific reversible capacity
`multiplied by the weight of the negative active material
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`4
`contained in the rechargeable lithium battery to the cathode
`specific reversible capacity multiplied by the weight of the
`positive active material contained in the rechargeable
`lithium ion battery has a value between 0.85 and 1.15, that
`is mAh/gxw: mAh/gxw=0.85-1.15. The improved
`rechargeable lithium battery has an energy density in excess
`of 320 watt hour?liter or 130 watt-hour/kg.
`BRIEF DESCRIPTION OF THE DRAWINGS
`FIG. 1 is a schematic circuit diagram illustrating the initial
`transfer of lithium into the anode of the lithium battery
`according to the present invention.
`FIG. 2 shows the performance of a lithium battery of the
`present invention in repeated charging-discharging cycles.
`DETAILED DESCRIPTION OF THE
`PREFERRED EMBODIMENTS
`As it has been briefly mentioned above, the energy density
`per unit weight of a rechargeable lithium battery is of
`significance in the commercial utilization of lithium
`batteries, in particular of planar lithium batteries. One of the
`desired features in lithium battery technology is to reduce
`the weight of the battery components as much as it is
`possible without loss of battery efficiency and output.
`The transition metal compound utilized in rechargeable
`lithium batteries is usually a transition metal chalcogenide,
`most frequently a transition metal oxide but may also be a
`transition metal sulphide. The composition of the transition
`metal oxide incorporating lithium ions in its structure
`depends on the type and kind of transition metal oxide
`utilized. For example, lithium-cobalt oxide has a composi
`tion of LiCoO, where x is less than 1, similarly lithium
`bearing nickel oxide has a composition of LiNiO. On the
`other hand, lithium bearing manganese oxide may be
`described as LiMn.0, where 0<y<2. The transition metal
`compound may also be an oxide of chromium, copper,
`vanadium, tungsten or alloys of the above mentioned metals
`with other metals, which are capable of incorporating
`lithium ions in their structure. The most often utilized
`transition metal sulphide is TiS, but other transition metal
`sulphides, such as iron sulphide, may also serve as cathode
`active materials. Some organic compounds which are
`capable of incorporating lithium ions reversibly and are also
`electronic conductors, may also be utilized in the positive
`electrode of a rechargeable lithium battery. In theory, virtu
`ally all the lithium ions incorporated in the structure of
`transition metal compound may be moved by an imposed
`direct potential, however, as mentioned above, below a
`certain lithium concentration that is characteristic of each
`transition metal compound the crystal structure, in particu
`lar the lattice dimensions of the transition metal compound
`is likely to change irreversibly. Hence a certain portion of
`the lithium in the battery has to be retained in the positive
`electrode being incorporated in an unavoidable extra cath
`ode material weight. The positive electrode may also contain
`fine carbon to increase the electrical conductivity of the
`electrode and a binder substance. The positive electrode is
`usually in contact with some form of a current collector.
`The cathode or positive electrode of a rechargeable
`lithium battery will have a reversible capacity depending on
`the nature of the cathode active material contained in the
`electrode and to a lesser degree, on the binder. The cathode
`specific reversible capacity is usually calculated per unit
`weight of the cathode active material in the electrode and is
`expressed in milliampere-hours per gram (mAh/g).
`The non-aqueous electrolyte of a rechargeable lithium
`battery is usually either a solid polymer electrolyte contain
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`ing lithium in a dissociable form, or a porous polymer
`separator impregnated with an organic liquid containing
`dissolved therein a lithium salt capable of dissociating. For
`obvious reasons, the electrolyte is conductive only of ions
`and non-conductive of electrons. There are various ways to
`keep the electrolyte weight in the battery as low as possible,
`which is beyond the scope of the present invention.
`The negative electrode of a rechargeable, or secondary
`lithium battery usually has some form of carbonaceous
`particles capable of intercalating lithium, as the negative
`active material. The carbonaceous particles most often uti
`lized in a rechargeable lithium battery include graphite,
`glassy or pyrolytic carbon, petroleum coke, carbon fibres
`and any other form of carbon particles that can intercalate
`lithium under normal circumstances. The preferred particle
`size of the carbonaceous particles is less than 60m but
`greater than 5 m. It is known that the lithium intercalated
`in carbon has the general formula of LiC but other lithium
`to carbon ratios have also been recorded. It is also known
`that a portion of the lithium subsequent to the first intro
`duction of lithium into the carbonaceous particles, that is in
`the initial lithium charging step of a lithium battery, is
`irreversibly retained in the carbon structure. As discussed
`above, it is not known exactly whether the irreversibly
`bonded lithium attaches itself to some structural elements of
`the carbon or to the surface of the particles, or is located on
`the interface between the carbonaceous particles and the
`lithium ion conducting electrolyte. It has been observed that
`such irreversible capacity loss may depend on the type and
`history of the carbonaceous particles, on the binder sub
`stance utilized, on the nature of the electrolyte composition
`and so forth. Whatever is the reason, a portion of the
`transferred lithium is lost for subsequent battery charging
`discharging process steps. As mentioned hereinabove, in
`conventional rechargeable lithium batteries the irreversibly
`bonded lithium is compensated by an extra amount of
`lithium-transition metal compound added in the cathode,
`thus increasing the total weight of the battery.
`The anode or negative electrode of a rechargeable lithium
`battery will have a reversible capacity depending on the
`nature of the cathode active material, that is on the type of
`carbonaceous particles contained in the anode and to a
`limited degree, on the binder. The anode specific reversible
`capacity is usually calculated per unit weight of the anode
`active material present in the electrode and is expressed in
`milliampere-hours per gram (mAh/g).
`It is known to introduce lithium into the carbonaceous
`particles by various methods prior to the carbonaceous
`material being incorporated in the anode of the lithium
`battery, however it is believed, these methods have not been
`successful in eliminating an additional irreversible capacity
`loss that occurs during the first, charging of the lithium
`battery. In other words, an extra amount of lithium
`transitional metal compound is still needed over and above
`the reversibly incorporated lithium requirement of the car
`bonaceous particles in the anode.
`It has now been surprisingly found that if the lithium is
`added electrolytically during the first charging of the
`assembled rechargeable lithium battery in such a manner
`that the lithium transferred from the positive electrode for
`initially charging the anode, is replaced from a third lithium
`electrode, no extra amount of lithium-transition metal con
`pound is required to compensate for the irreversible capacity
`loss in the anode. The improved rechargeable lithium battery
`of the present invention undergoes a first charging or pre
`charging step of the battery in an electrical circuit which
`incorporates a third lithium containing electrode, which is
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`most often an elemental lithium bearing electrode. The third
`electrode is separated from the lithium-transition metal
`compound containing cathode by another non-aqueous
`lithium ion containing electrolyte but is electrically
`(ionically) in contact with it. In practice, a positive potential
`is applied to the third, usually elemental lithium containing
`electrode, thereby forcing lithium ions to enter into the
`electrolyte separating the third electrode from the lithium
`transition metal compound containing cathode of the lithium
`battery. The arriving lithium ions, in turn, force an equiva
`lent amount of lithium ions to leave the cathode to enter by
`way of the electrolyte within the lithium battery into the
`anode to be intercalated by the carbonaceous particles in the
`negative electrode. As usual in the charging step, the anode
`carries a negative potential, thus closing the circuit. The
`pre-charging is conducted at the usual charging potential of
`a lithium battery, that is at about 4.5 volts at the conven
`tionally required current density for an appropriate length of
`time. The assembled pre-charged lithium battery is discon
`nected from the third electrode and the additional or tem
`porary electrolyte, and is subsequently sealed and packaged
`with appropriate current collectors and electric leads in the
`usual manner.
`The temporary electrolyte in contact with the third elec
`trode containing a source of lithium ions may have the same
`composition as the electrolyte of the assembled rechargeable
`lithium battery, or may be a different electrolyte such as an
`organic liquid having a lithium salt dissolved therein. The
`third electrode may be a lithium foil immersed in the organic
`liquid or an alloy of lithium or may be another lithium ion
`containing compound. Any convenient lithium source that is
`capable of providing lithium ions to the positive electrode of
`the rechargeable lithium battery and can be incorporated in
`an electrical circuit, is suitable for facilitating the pre
`charging of the rechargeable lithium battery in accordance
`with the present invention. FIG. 1 represents a schematic
`diagram of the electrical circuit of the pre-charging process
`step of the battery, where 2 is the negative electrode bearing
`carbonaceous particles which do not contain any lithium
`before the pre-charging process step, 4 represents the lithium
`battery electrolyte and 6 is the lithium-transition metal
`compound containing positive electrode. The positive elec
`trode is in contact with the pre-charging temporary electro
`lyte 8, which in turn is in electrolytic contact with the third,
`usually but not necessarily, elemental lithium containing
`electrode 10. In the preferred embodiment the third electrode
`is lithium metal or an elemental lithium containing alloy.
`Reference numeral 12 represents the external potential
`source, providing the current for the pre-charging process
`step of the rechargeable lithium battery. The broken line 14
`around the schematically drawn rechargeable lithium battery
`components represents conventional sealers, current collec
`tors and electrical leads which encase the rechargeable
`lithium battery subsequent to the pre-charging step.
`For the sake of clarity, in the present description pre
`charging of the lithium battery is understood to mean the
`first transfer of lithium ions to be intercalated in the car
`bonaceous particles of the anode or negative electrode, by
`means of applying a positive electrical potential to a third
`electrode which acts as a source of lithium ions. In the
`pre-charging step the third electrode as connected by means
`of a non-aqueous electrolyte referred to as temporary
`electrolyte, to the positive electrode of the lithium battery.
`The temporary electrolyte is disconnected from the lithium
`battery after the pre-charging has taken place.
`It is noted that the rechargeable lithium battery may not be
`fully charged in the pre-charging step and additional charg
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`ing of the lithium battery may still be required after the
`rechargeable lithium battery has been separated from the
`third electrode and its electrolyte, sealed and packaged in the
`conventional manner. Whether the battery is fully charged or
`only partially charged in the pre-charging step, depends on
`the composition of the cathode active material and may also
`be dictated by other aspects of convenience. Optionally, the
`fully pre-charged lithium battery is allowed to discharge to
`attain its conventional low voltage level and is subsequently
`packaged and sealed.
`One of the important features of the present invention is
`that the bonding between the electrolyte, shown as 4 on FIG.
`1. and the lithium bearing carbonaceous particle-containing
`anode 2 formed in the pre-charging step, is not disturbed or
`broken in the subsequent sealing and packaging of the
`rechargeable lithium battery. In other words, the lithium is
`transferred through the same electrolyte-anode interface in
`the pre-charging step as in subsequent charging-discharging
`steps taking place in utilizing the rechargeable lithium
`battery of the present invention.
`The above described pre-charging process may be applied
`to planar, spirally wound and button-shaped rechargeable
`lithium batteries.
`The specific reversible capacity of a rechargeable lithium
`battery refers to the total reversible capacity of the
`assembled lithium battery and is expressed in milliampere
`hours per the total weight of the active components of the
`lithium battery, that is the sum of the weights of the anode
`active material, the cathode active material and the non
`30
`aqueous electrolyte comprised in the lithium battery (mAh/
`g). The reversible capacity of the rechargeable lithium
`battery made in accordance with the present invention is
`usually not much lower than the value of the lesser of the
`reversible capacities of the electrodes. It should be noted that
`in practical applications the values of the electrode revers
`ible capacities within a rechargeable lithium battery are
`similar to one another.
`The present invention will now be illustrated by working
`examples.
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`EXAMPLE 1.
`A commercially available planar rechargeable lithium
`battery A, having lithium-cobalt oxide as cathode active
`component and graphite as anode active component, was
`charged in the conventional manner by applying 4.2 volts to
`its external electrical leads at a current level controlled to
`complete charging in a 24 hour period. After charging
`battery A exhibited full battery voltage of 4.05 volts. Battery
`A had conventional anode film made of graphite of average
`particle size of 15 um containing 5 wt % polyvinylidene
`fluoride binder. The electrolyte of battery A was porous
`polyethylene impregnated with ethylene carbonate-diethyl
`carbonate mixed in 1:1 ratio, containing LiPF in 10 mole
`concentration. It is known that conventional lithium-cobalt
`oxide has specific reversible capacity of 123 mAh/g. The
`specific anode reversible capacity of the graphite utilized in
`the battery is 370 mAh/g. The reversible capacity of battery
`A was measured in the usual manner and the component
`layers of battery A were subsequently separated and ana
`60
`lyzed. The specific reversible capacity of lithium battery A
`was then obtained as 52 mAh/g; in the calculation g was the
`sun total of the weights of the anode active graphite,
`cathode active lithium-cobalt oxide and the impregnated
`microporous polyethylene electrolyte comprised in a 100
`65
`cm area of battery A. The 100 cm segment of battery Awas
`found to contain 1.35 g anode active graphite particles and
`
`55
`
`8
`6.08 g cathode active lithium-cobalt oxide, that is the weight
`ratio of graphite to lithium-cobalt oxide in the anode and
`cathode layers respectively, was found to be 4:18. It was
`calculated that the value of the ratio of the anode capacity to
`the cathode capacity of battery A, that is: mAh/gxw
`divided by mAh/gxw=370x1.35 : 123x6.08=0.67. This
`ratio is well below 1, thus indicating that excess weight is
`carried in the cathode.
`Battery B was made up of the same commercially avail
`able lithium-cobalt oxide and graphite particles, utilizing the
`same amount of polyvinylidene fluoride binder and other
`additives in the anode and cathode, respectively, as in battery
`A, however, the weight ratio of the anode active graphite
`particles to the cathode active lithium-cobalt oxide was
`4:13.2. The electrolyte of battery B had the same composi
`tion as that of battery A, but the weight per unit area of
`battery B was lower than that of battery A. The assembled
`lithium battery B was immersed in an electrolyte solution
`made of ethylene carbonate-diethyl carbonate, containing
`LiPF in 1 Molar concentration. A 1 mm thick 100 mm wide
`lithium foil mounted on a stainless steel carrier was also
`immersed in the electrolyte solution. A direct potential of 4.2
`volts was applied between the lithium foil-third electrode
`and the anode of lithium battery B containing graphite
`particles as negative active material, the latter having nega
`tive polarity in the circuit. The direct current was applied
`until the anode of lithium battery Battained a potential of 2.9
`volts against the lithium-cobalt oxide bearing cathode of
`lithium battery B. Battery B was then disconnected from the
`pre-charging direct potential and removed from the tempo
`rary electrolyte. Battery B was subsequently fitted with
`appropriate current collectors and electrical leads, and
`sealed in the conventional manner. Battery B was then
`charged to the full potential value it was capable of attaining,
`i.e. 4.05 volts, in conventional manner.
`Battery B was subjected to several charging-discharging
`cycles and it was found to perform just as satisfactorily as
`battery A under similar cycling conditions.
`In a subsequent series of tests the capacity of battery B
`was first measured in charging and discharging cycles at 25
`mA current, which was then followed by charging and
`discharging cycles conducted at 40 mA current. The revers
`ible capacities manifested in the cycling of battery B are
`shown on FIG. 2, indicating that the rechargeable lithium
`battery made in accordance with the present invention has
`high capacity and is capable of rendering reliable service.
`Following the cycling series, battery B was dismantled
`and the relevant component layers in a 100 cm area were
`weighed and analyzed. It was found that battery B contained
`1.35 gram of graphite and 4.42 grams of lithium-cobalt
`oxide in the corresponding battery B cathode layer volume.
`Thus the rati