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`APPLE 1025
`
`1
`
`

`

` TECHNICAL PAPERS
`
`ELECTROCHEMICAL SCIENCE AND TECHNOLOGY
`
`Rechargeable LiNiO,/Carbon Cells
`
`J.R. Dahn
`
`Department of Physics, Simon Fraser University, Burnaby, British Columbia, Canada, VoA 186
`
`U. von Sacken, M. W. Juzkow,* and H. Al-Janaby
`Moli Energy (1990) Limited , Burnaby, British Columbia, Canada, V5C 4G2
`
`ABSTRACT
`
`
`
`Rechargeable cells can be made using two different intercalation compounds, in which the chemical potential of the
`intercalant differs by several eV, for the electrodes. We discuss the factors that play a role in the selection of‘appropriate
`lithium intercalation compounds for such cells. For ease of cell assembly the cathode should be stable in air when it is
`fully intercalated, like LiNiO,. For the anode, the chemical potential of the intercalated Li should be close to that of Li
`metal, like it is in Li,C,. We discuss the intercalation of Li in LiNiO, and then in petroleum coke. Then, we show that
`LiNiO,/coke cells have high energy density, long cycle life, excellent high-temperature performance, low self-discharge
`rates, can be repeatedly discharged to zero volts without damage,andare easily fabricated. In our opinionthis type of cell
`shows far more promise for widespread applications than traditional secondary Li cells using metallic Li anodes.
`
`wound secondary Li cell. As long as Li metal anodes are
`used,
`the uniaxial pressure requirement precludes the
`construction of flat or prismatic cells with thin-walled
`cases.
`
`Rechargeable Li batteries like Li/MnO,(1) have several
`advantages over conventional secondary systems like
`NiCad or new technologies like Ni-metal hydride. Second-
`ary Li cells promise higher energy, higher voltage, and
`longer shelf life than competitive technologies (2). How-
`Secondary Li cells with Li metal anodes require thin
`ever, secondary Li batteries also have numerous disadvan-
`electrode technologies. Generally, the anode and cathode
`tages which maypreclude their widespread acceptancein
`thicknesses are about 100 pm. Thin electrodes are required
`the marketplace.
`because:(1) The thicknessof the stripped and plated Li de-
`Secondary Li batteries generally have a lowercycle life
`posit is proportional to the cathode thickness; electrode
`than NiCad cells. This results from the inability of at-
`thicknesses are kept thin to minimize the risk of dendrite
`taining 100% Li cycling efficiency. Even in commercial Li/
`penetration of the separator during the plating of the Li.
`MoS,cells (8) there is a three-to fourfold stoichiometric ex-
`(ii) The conductivity of nonaqueouselectrolytes are typi-
`cess of Li compared to that needed to fully intercalate the
`cally two orders of magnitudeless than the aqueousclec-
`cathode. If the Li cycling efficiency is 99%, then 1% of the
`trolytes used in NiCad cells. To obtain reasonable rate cap-
`cycled Li is lost on each cycle. Therefore, to obtain 200
`ability, electrode separations and thicknesses must be
`deep discharge cycles, at least a three-fold excess of Li is
`roughly an order of magnitude less than in NiCad. The thin
`required.
`electrode technology, the excess Li, the need for assembly
`The excess Li in these cells can cause other problemsif
`equipment to be located in dry rooms, andtherelatively.
`the cells are allowed to discharge to low voltages outside
`expensive separators all contribute to the relatively high
`cost of secondary Li cells compared to NiCad.
`their normal operating range. Manyintercalation cathodes
`decompose(e.g., to form Li,S or Li,O) if allowed to react
`Secondary Li cells typically use recharge currents which
`with excess lithium (4). The cells are then only poorly re-
`correspond to C/10 (10 h for full recharge) rates (3). This is
`chargeable becauseofirreversible chemical and structural
`because the risk of dendrite penetration of the separators
`changes in the cathode. In addition, the reactions that
`increases as the recharge current is increased and because
`the Li cycling efficiency is improved when the current
`occur at low voltage can often totally consume the Li
`anode, making charging difficult.
`density used for plating the Li is substantially less than
`The relatively: poor cycling efficiency of the Li anode
`that used for stripping(1, 3). This represents a major disad-
`arises because it is not thermodynamically stable in typi-
`vantage for secondary Li cells since NiCad cells and: Ni-
`cal nonaqueous electrolytes. The surface of the Liis
`metal hydride cells can be charged in one hourorless.
`covered with a film of the reaction products between the
`The safety of AA size secondary Li cells with metallic Li
`Li and the electrolyte (5, 6). Every time the Li is stripped
`anodes is presently less than satisfactory (11, 12). There
`and plated, some new Li surface is exposed and hence
`have been reported incidentsof fires involving equipment
`passivated, consuming Li. Mucheffort has been expended
`powered by secondary Li/MoS§,cells which led to a prad-
`uct recall (13, 14). There have even been similar recalls in-
`to improve the cycling efficiency of the Li anode through
`changes to the electrolyte (7, 8) or through the application
`volving primary Li/MnO,cells (15) suggesting that safety is
`a central issue which must be resolved to makethis a via-
`of uniaxial pressure to the Li surface (9, 10). Practical cells
`use both optimum electrolytes and pressures of about 1.4
`ble technology.
`MPa on the Li electrode to achieve efficiencies of up to
`It is clear that although the use of metallic Li leads to
`99% (3). Special separators which can withstand high uni-
`higher energies, higher voltages, and longershelflife than
`axial pressures and which haveaporesize smaller than the
`conventional cells, the many disadvantages of this tech-
`diameter of typical Li dendrites must be used in these
`nology severely limit its application. Here we show that
`cells. These separators, generally polypropylene or poly-
`cells using two different Li intercalation compounds,in
`ethylene microporousfilms, are relatively expensive and
`which the chemical potential of the intercalated Li differs
`contribute significantly to the raw materials cost ofa spiral
`by several eV, for the electrodes eliminate mostof the dis-
`advantages discussed above while retaining the essential
`advantages of secondary Li cells. There is, of course, a
`
`* Electrochemical Society Active Member.
`
`J. Electrochem. Soc., Vol. 138, No. 8, August 1991 © The Electrochemical Society, Inc.
`
`2207
`
`2
`
`

`

` 0
`
`O14 02 03 04 05 0.6
`y in Li(y—y)Ni0g
`Fig. 2. Voltage of Li/Li,_,NiOz cells vs. y for the first charge and dis-
`chargeof the ceil. The current was chosen so that a change Ay = 1 oc-
`curred in 40 h.
`
`than 4.0 V) the oxidation of the nonaquecus electrolytes
`used in secondary Li cells can occur (23). This electrolyte
`oxidation is to be avoided if long cycle life cells are to be
`made. The voltage-composition profile for Li/Lij_,NiO,
`cells is shown in Fig. 2. The cells cycle reversibly for
`Ay = 0.5 below 4.0 V.
`The anode should be selected from those materials
`which have chemical potentials close to that of lithium
`metal. Of these, carbonslike graphite and petroleum coke
`are especially well suited (24, 25). Graphite and petroleum
`coke can intercalate Li to composition limits of LiC, (cor-
`responding to 0.37 Ah/g) and LiysC,, respectively (25). The
`voltage-composition profile for Li/petroleum cokecells is
`shown in Fig. 3. Li/graphite cells have a much “flatter”
`voltage-composition profile, which varies from about
`0.25 V near x = 0 to about 0.70 V near x = 1 in Li,C, (25).
`For reasons discussed below, we chose petroleum coke
`over graphite for our electrodes even though graphite
`gives twice the specific capacity.
`In earlier studies of Li/gtaphite and Li/coke cells (24) we
`showedthat duringthefirst electrochemical intercalation
`of Li into carbon, some Liis irreversibly consumed. The
`
`(volts)
`
`Voltage
`
`Oo
`
`O01
`
`0.2
`
`#03
`
`O04
`
`0.5
`
`x in Li,Cg
`Fig. 3. Voltage of Li/Li,C, cells vs. x for the second discharge and
`charge of the cell. The carbon in the positive electrode is petroleum
`coke. The current was chosen so that a change Ax = 1 occurred in
`80h.
`
`2208
`
`small penalty to be paid in cell voltage and in cell energy.
`Cells of this design are often called “rocking chair cells”
`(16) because the Li shuttles or “rocks” between the elec-
`trodes as the cell is charged or discharged. At least one
`Japanese company announcedits plans to commercialize
`this technology (17).
`First we discuss the selection of appropriate materials
`for the electrodes of “rocking chair” cells and show that
`LiNiO, and petroleum coke are good candidates for the
`cathode and anode,respectively. Next, we review the elec-
`trochemical intercalation of Li in these two materials.
`Then we describe the construction of 1225 coin cells using
`LiNiO, and petroleum coke as electrode materials. The re-
`sults of cycle testing these cells under a variety of condi-
`tions demonstrate that most of the disadvantages associ-
`ated with secondary Li cells are eliminated. Finally, we
`summarize our work and comment on the key problems
`remaining in the further development of rocking chair
`cells,
`
`Electrode Materials for “Rocking Chair Cells”
`The voltage, V, of an electrochemical cell based on the
`intercalation of Li into a host electrode, relative to Li
`metal, is
`
`V=—-ple
`
`[1]
`
`where ,» is the chemical potential of the Li intercalated in
`the host and e is the magnitude ofthe electron charge (18).
`Normally, the voltage varies with the composition of the
`intercalation compound. Figure 1 shows the chemical po-
`tential ranges of intercalated Li in a variety of compounds.
`Clearly it is possible to find materials where the chemical
`potential differs by several eV.
`In a practical rocking chair cell it is necessary to ensure
`that one of the electrodes is loaded with lithium prior to
`cell assembly. Most powdered intercalation compounds
`are pyrophoric when loaded with Li. However, the Li will
`not deintercalate to react with air or moistureif it is suffi-
`ciently tightly boundin the intercalation compound. When
`the chemical potential is less than about —3.5 eV,lithium
`intercalation compoundsare generally observed by x-ray
`diffraction to be air stable. Fortunately, there are several
`well-known Li
`insertion
`compounds which
`have
`p< —8.5 eV even when the material is loaded with sub-
`stantial Li. Of
`these, Lij_,NiO, (0<y< 0.8)
`(19, 20),
`Li, ,CoO, (@ < y < 0.8) (21), and Li,_,Mn.O, (0 < y < 1) (22)
`are currently the most studied.
`Li,_,NiO, was selected for the cathodein our studies be-
`cause it has a lowervoltage vs. Li than either Li;_,CoO, or
`Li,_yMn,O,. At sufficiently high voltages (generally greater
`
`oO eV
`
`Li metal
`LiGraphite
`
`-1 eV
`
`-2 eV
`
`LE WO.
`Li Moo
`K 2
`Li Tis
`x
`
`~2
`
`LiCoke
`
`Li Mos
`x
`
`"2
`
`-3 ev
`
`Li MnO (O<x<1.0)
`x
`2
`
`AS
`(AU ev
`Ro
`L
`E
`
`-5 ev
`
`Lt NiO,
`Iry
`Li, C00,
`y
`
`Fig. 1. Showing the chemical potential ranges of intercalated Li in a
`variety of compounds. Chemical potentials are measured relative to Li
`metal.
`
`J. Electrochem. Soc., Vol. 138, No. 8, August 1991 © The Electrochemical Society,Inc.
`
`
`4.2
`
`(volts)
`
`
` Discharge Voltage
`
`3
`
`

`

`J. Electrochem. Soc., Vol. 138, No. 8, August 1991 © The Electrochemical Society,Inc.
`
`2209
`
`amount of Li consumed was shownto be proportional to
`the surface area of coke electrodes, suggesting that a passi-
`vating film of constant thickness was being formed. In the
`case of graphite electrodes, there was additional irrever-
`sible consumption of Li. This was thoughtto be associated
`with electrolyte reduction occurring on fresh surfaces of
`graphite exposed during partial exfoliation of graphite
`caused by the cointercalation of electrolyte solvent. Since
`the amountof Li in a rocking chair cell is entirely supplied
`by that initially loaded into the cathode, it is very impor-
`tant to minimize any possible loss of Li to film forming or
`other irreversible reactions. Therefore, we decided to use
`low surface area petroleum coke electrodes in ourfirst
`cells.
`
`LiNiO,/COKE 1225 CELL
`0.5 mA at 21°C
`
`5
`
`w»
`
`VOLTAGE(V) 20
`
`80
`
`Experimental
`LiNiO, was prepared as outlined in Ref. (20). The mate-
`rial used in the 1225 coin cells had an actual stoichiometry
`of LigggNi,Or. Top premium petroleum needle coke des-
`ignated XP was obtained from Conoco, Incorporated
`(Houston, Texas) in the form of lumps about 1 cm*. This
`material is about 99.5 weight percent (w/o) carbon with sul-
`60
`40
`fur (0.3 w/o) as the major impurity. The spacing between
`TIME (HOURS)
`carbon planes, d(002) = 3.46Ais typical for needle cokes.
`The petroleum coke was ground and then sized using
`standard sieves. The coke used to fabricate electrodes was
`Fig. 4. First cycles of a LiIN‘O2/coke 1225 coin cell at 21°C. The cell
`is charging and discharging between 3.9 and 0.7 V using a constant
`—200/+400 mesh (i.e., 75 wm > particle diameter > 38 ym).
`current of 0.5 mA.
`Stainless steel 1225 coin cell hardware (12 mm outside
`diameter and 2.5 mm thickness) obtained from Rayovac
`Corporation (Madison, WIwas used. A polypropylene gas-
`ket is used to make the seal. Leak tests of coin cells filled
`only with dimethyoxyethane (DME)(about 70 mg) showed
`no measureable weightloss (<0.1 mg) after 1 week at 55°C
`in a vacuum oven, proving that the leak rates at these tem-
`peratures are negligible.
`Disk-shaped tablet electrodes were prepared from a
`mixture of the active powders with binder and carbon
`biack followed by pressing. A laboratory scale rotary
`tablet press (Stokes 511) was used to press tablets with uni-
`form thickness and mass. The tablet thickness and mass
`were adjusted so that: (i) The thickness of the tablets plus
`separator was equal to the inside height to the cell. Each
`tablet was approximately 1.0 mm thick. (ii) The masses are
`adjusted so that at the completion ofthe first charge of the
`cell the cathode stoichiometry is Li);NiO, while the anode
`stoichiometry is simultaneously Li,,;C,. The calculation ac-
`counts for that Li irreversibly consumed by the carbon
`anode. Typical active massesfor the LiNiO, and petroleum
`coke electrodes were 93 and 61 mg,respectively.
`LiN(CF;SO,), was obtained from 3M Corporation (Min-
`neapolis, MN) and was dried under vacuum at 140°C before
`use. Typical electrolytes used in these cells were 1M solu-
`tions of this salt in a 50:50 mixture of propylene carbonate
`(PC) and DMEorin a 50:50 mixture of ethylene carbonate
`and DME.Weobserved no difference in performance be-
`tween cells using PC or EC as a cosolvent. PC and EC
`(Texaco) were purified by vacuum distillation. DME from
`Aldrich was used as received or was repurified from Li
`benzophenoneketyl solutions. Electrolytes were not used
`ifthe moisture content determined by Karl-Fishertitration
`exceeded 100 ppm.
`Celanese No. 2502 microporous films were used as sepa-
`rators in most cells. In some cells we used nonwovenpoly-
`propylene separators and observed similar results. All
`cells reported here were assembled in a dry room with
`RH < 0.5%. Cells were charged and discharged using com-
`puter-controlled battery cyclers capable of constant cur-
`rent cycling between fixed voltage limits, constant capac-
`ity cycling, or discharge througha fixed load followed by a
`chargingto a voltage cutoff. These chargers were designed
`and built at Moli Energy (1990) Limited.
`
`of the intercalated coke (24) and is hence unavailable for
`the next discharge of the cell. The cell capacity on the sec-
`ond cycle is about 10mAh when the cell is charged to
`4.0 V. Figure 5 shows the capacity vs. cycle numberfor a
`cell at room temperature. On thescale of Fig. 5 the charge
`and discharge capacities are indistinguishable after the
`first cycle. Apart from a small amount of early capacity
`fade, these cells exhibit good reversibility. Since there is
`no excess Li in these cells, each Li atom lost to an irrevers-
`ible reaction will be unavailable for cycling and capacity
`loss will result. The data in Fig. 5 prove that the interca-
`lation of Li in Li,_,NiO, and in Li,C, is nearly 100% revers-
`ible. Once the capacity loss associated with the first charg-
`ing ofthe cell has been eliminated,very little further loss is
`seen. At the time of this writing cells have been tested con-
`tinuously for 11 months and show nosign of impending
`failure as evidenced by increases in charge or discharge
`overvoltages or by capacity loss.
`These rocking chair cells have no excess Li in the anode
`or cathode, so they should be tolerant to repeated dis-
`charges to zero volts. At zero volts, all the available Li has
`been removed from Li,C, and inserted into Li,_,NiO,. Fig-
`ure 6 showsthevoltage vs. time for cycles 10 and 11 and for
`
`Results and Discussion
`Figure 4 showsthefirst cycles of a LiNiO./coke 1225 coin
`cell. During the first charge, Li is deintercalated from
`Li,_NiO, andis intercalated into Li,C,. The capacity of the
`first charge is about 18% larger than that of the subsequent
`eycles. The Li which has been consumedis thought to be
`now incorporated into the passivation film on the surface
`
`6
`
`300
`200
`100
`CYCLE NUMBER
`
`400
`
`Fig. 5. Capacity vs. cycle number for LiNiO./coke 1225 coin cells cy-
`cled at 21°C using constant current (0.5 mA). The voltage limits are in-
`dicated in the figure.
`
`0.010
`
`30.008
`
`A~hr~—0.008
`
`0.004
`
`CAPACITY 0.002 0.0006
`
`4
`
`

`

`J. Electrochem. Soc., Val. 138, No. 8, August 1991 © The Electrochemical Society,Inc.
`
`0.012
`
`0.010
`
`0.008
`
`2210
`
`
`
`VOLTAGE(V)o
`
`e
`
`0.002 0.060
`
`CAPACITY(A-hr) 28
`
`LiNiO,/COKE 1225 cells
`1.0 mA at 55°C
`solid ~ 3.7V to 0.7V
`small dash — 3.85V to 0.7V
`large dash — 4.0V to 0.7V
`
`50
`CYCLE NUMBER
`
`Fig. 8. Capacity vs. cycle number for LiNiO,/coke 1225coincells cy-
`cled at 55°C. The cycling current was 1.0 mA. The voltage limits are
`given in the figure.
`
`LiNiO./coke cells were discharged to a fixed capacity at
`85°C and then recharged to 3.7 V. Figure 9 showsthe volt-
`age reached at the end of each constant capacity discharge
`plotted vs. cycle numberfor cells dischargedto 1, 2, 4, and
`6mAh. The tests were stopped when the cell voltage
`reached 2.0 V. Over 1000 cycles were obtained for the
`1 mAhdischarge (10% DOD). Thesecells were weighed be-
`fore and after testing and a small weight loss, corre-
`sponding to about 15% of the weight of the DME, was ob-
`served. The boiling point of DME is 85°C and the
`permeability of the polypropylene seal increases with
`temperature. Thereforeit is likely that cell leakage contrib-
`uted to the failure of the cells cycled at 85°C. The data in
`Fig. 9 proves the suitability of this chemistry for high-tem-
`perature applications.
`The cells also show excellent storage properties. Fig-
`ure 10 shows the capacity vs. cycle number for a cell
`charged to 3.9 V and stored for 30 days at room tempera-
`ture after every ten cycles. After storage, the cells were dis-
`charged first. The first discharge after the storage period
`does not show appreciable capacity loss. The cells were cy-
`
`ENDVOLTAGE °o
`DISCHARGE
`
`200
`
`400
`1000
`800
`600
`CYCLE NUMBER
`
`1200
`
`sa
`
`ere2a
`
`40
`20
`TIME (HOURS)
`Fig. 6. Voltage vs. time for a LiNiO2/coke 1225 coin cell discharged
`through a 3 kO, load and then charged to 3.8 V. The 10th, 11th (solid),
`and 110th, and 111th (dashed) cycles are shown. The cell was at 21°C.
`
`60
`
`eycle 110 and 111 of a cell discharged through a 3 KQresis-
`tor and then charged to 3.8 V. The chargeis initiated 10h
`after the cell voltage drops below 0.1 V. Thus, the cell
`spends 10 h near zero volts on every cycle. Figure 7 shows
`the capacity fade for the cell of Fig. 6 and for an identical
`cell discharging through a 1 kQresistor. Both of these cells
`have cycled to zero volts hundreds of times without signif-
`icant capacity loss. Again, at the time of writing thesecells
`have been tested for 11 months with no signs of impending
`failure.
`Figure 8 shows capacity vs. cycle numberfor 3 LiNiO,/
`coke cells cycling at 55°C using a current of 1 mA for both
`charge and discharge. The rate of capacity loss increases
`when the upper voltage limit is raised, presumably be-
`cause the electrolyte oxidation rate increases at the higher
`voltages. Nevertheless, the cell charged to 3.7 V shows ex-
`cellent cycling behavior even at 55°C. At the timeofthis
`writing, the cell charging to 3.7 V has reached over 300 cy-
`cles and showsno signs of impendingfailure.
`
`0.010 +
`
`Pinigtoteeimmmenspene,
`
`0.008 4
`o
`/
`
`Petntet
`
`| o
`
`A<
`
`
`
`
`.008 +
`va
`4
`EH
`Oo 004 4
`a 0.
`{
`O
`
`4
`
`0.002 +4
`
`0.000 --
`0
`
`t
`
`T
`T
`200
`100
`CYCLE NUMBER
`
`T
`
`300
`
`Fig. 7. Capacity vs. cycle number for LiNiO,/coke 1225 coin cells
`discharged through t and 3 kO resistors. The lower capacity date are
`for the 3 kQ load. The cell voltage remains below 0.1 V for 10 h before
`each recharge (see text).
`
`Fig. 9. End of discharge voltage vs. cycle numberfor constant capac-
`ity discharges (1,0 mA) at 85°C. The LiNiO,/coke cells were charged
`to 3.7 V at 1.0 mA following each discharge. Four cells were tested
`using discharge capacities of 1, 2, 4, and 6 mAh.
`
`5
`
`

`

`J. Electrochem. Soc., Vol. 138, No. 8, August 1991 © The Electrochemical Society, Inc.
`
`2211
`
`
`
`
`0.002 5
`
`0.000
`
`0
`
`7
`
`T
`10
`
`soaco Discharge
`+++++ Recharge
`
`T
`
`T
`40
`20° «30
`Cycle Number
`
`T
`
`50
`
`Fig. 10. Capacity vs. cycle number for LiNiO;/coke 1225 coin cells
`with 30 day storage periods after every 10 cycles. The storage periods
`occurred after each vertical bar in the graph. The cycling currents are
`indicated in the figure. The cells were cycled between 3.9 and 2.5 V.
`
`cled using 1mA currents for the first five cycles and
`0.5 mA currents for the otherfive cycles ofall but the first
`cycling period. The capacity loss shown by thesecells is
`low even though they have been repeatedly stored and cy-
`cled. Other cells were charged to 3.9 V and then left open
`circuit. Their voltage was monitored daily. Within a few
`days the rate of cell voltage loss (—dV/dt) was less than
`lmV/day. After 100 days storage we found —dV/dt<
`0.5 mV/day. Since the cell voltage varies by more than 1 V
`over the useful capacity of the cell, this corresponds to a
`shelflife of order 2000 days.
`
`Conclusions
`We have shown that LiNiO,/coke cells have long cycle
`life, excellent high-temperature performance, low self-
`discharge rate, can be repeatedly discharged to zera volts
`without harm, and can be made with electrodes at least
`1mm thick. It is our opinion that this technology is well
`suited for consumerapplications in coin, prismatic, spiral-
`wound cylindrical, and small diameter(e.g., AAA) bobbin-
`type cells.
`We are presently studying the reactivity of Li interca-
`jated carbon with nonaqueous battery electrolytes using
`an accelerating rate calorimeter. These are similar to our
`studies of Li metal which were recently described (12).
`These preliminary results suggest that the safety of rock-
`ing chair cells will be greatly improved over secondary
`cells using Li metal. In addition, the absence of dendritic
`Li and excess Li in the LiNiO,/cokecells will also contrib-
`ute to increased cell safety.
`More work is required to further increase the capacity
`and energy of rocking chair cells. New materials with
`higher specific capacities for both the anode and cathode
`are needed. The approach discussed in Fig. 1 associated
`with the selection of electrodes for rocking chair cells
`should be extended to sodium intercalation compounds.
`Sodium is more abundant than Li and it is possible that
`the reactivity of sodium compounds with nonaqueous
`electrolytes could be significantly different than that of Li
`so that fundamentally safer cells might be obtained. Fi-
`nally, the rocking chair approach should be coupled to
`
`cells with polymerelectrolytes as this again may lead to
`safer cells. It is our opinion that rocking chair cells show
`far more promise than traditional secondary cells using
`metallic Li.
`
`Acknowledgments
`We thank Sid Megahed of Rayovac Corporation for sup-
`plying the 1225 coin cell hardware.
`Manuscript submitted Nov. 19, 1990; revised manuscript
`received Feb. 21, 1991. This was Paper 42 presented at the
`Seattle, WA, Meeting of the Society, Oct. 14-19, 1990.
`Moli Energy (1990) Limited assisted in meeting the publi-
`cation costs of this article.
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