Assessment of Polymer-Electrolyte Batteries for EV and Ambient Temperature Applications

Assessment of Polymer-Electrolyte Batteries for EV and Ambient Temperature Applications

M. Gauthier,* D. Fauteux,* G. Vassort,* A. B61anger,* and M. Duval

Institut de recherche d'Hydro-Qu~bec (IREQ), Varennes, Quebec, Canada JOL 2PO

P. Ricoux, J.-M. Chabagno, D. Muller, and P. Rigaud

Direction Recherche, D~veloppement et Innovation, Soci~t~ Nationale Elf Aquitaine (SNEA), 75739 Paris Cedex 15, France

M. B. Armand* and D. Deroo

Laboratoire d'Energ~tique Electrochimique (LEE), 38402 Grenoble, France

ABSTRACT

The feasibility of polyether-based all-solid-state cells has been assessed in a joint research and development program. At 80~176 cells using TiSE or VsO,3 positive-electrode material and excess l i thium show high material utilization at 0.5-1.0 mA/cm 2 and can be cycled more than 250 times. Furthermore, a new family of polyether electrolytes has been found that allows room temperature (26~ operation at 3-20 ~A/cmt

A joint research and development project ("ACEP' Project") between Soci~t~ Nationale Elf Aquitaine (SNEA), Institut. de recherche d'Hydro-Qu~bec (IREQ), and ANVAR 2 acting for Laboratoire d'Energ~tique ~.lectrochimique (LEE) has been under way since 1980 to develop thin film solid-state batteries based on polyether complexes. The starting point for this project was Armand's pioneering work, which suggested the use of polymer electrolytes for high energy-density batteries (1). Albeit only slightly conducting, these materials can be obtained in a high surface-to-thickness ratio, and they also maintain a good contact with the electrode materials.

The main interest of SNEA and IREQ in this joint project is to develop a battery for electric vehicle (EV) application. Consequently, the work was organized along the lines of the main technical tasks identified an essential for success (Fig. 1).

Only two of the aspects of the project shown in Fig. 1 are dealt with in the present paper: the performance of TiS2 and V60,3 positive composite electrodes and their cycling properties vs. an excess-lithium negative electrode, and the ambient temperature project. To meet the power density requirements for EV applications (>80 W/kg sustained power) while using polyethylene oxide (PEO, Mw = 5 x l0 g or 5M), the operating temperature was fixed at 80~176 for most of the tests. As shown below, PEO electrolytes have a very limited performance at temperatures below 40~ which precludes their use in electrochemical cells working at ambient temperature. In the course of research, however, a family of improved electrolytes was developed that appears to be useful for ambient temperature applications. Initial results on primary and rechargeable ceils at 26~ are presented to give an idea of the potential applications of this emerging technology.

Experimental The experimental work described here was done using

electrolyte and composite-electrode films obtained by so- lution casting techniques, as previously described ( 1, 2). Commercial PEO (5M and 0.9M) from Polyscience was used as received. The ratio between the number of mon'0- mer units (CH2-CH2-O) and the number of lithium in the salt (O/Li) was fixed at ~8/1 for both LiC104 (Ventron- Alfa Division) and LiCFgSO3 (Ozark-Mahoning) complexes.

The electrolyte thickness varied from 160 to 100 ~m for small electrochemical cells and from 80 to 50 ~m for

*Electrochemical Society Active Member. 1Accumulateurs ~ ~lectrolyte polym~re. 2Agence Nationale de Valorisation de la Recherche.

larger surface cells. The anodes were cut from freshly pressed Li ~ or from =100 ~m li thium foils. The TiS~ and V6Olg (< 37 ~m grain size) were prepared by in-house syn- thesis after adapting published procedures (6, 7).

Electrolytic MnO.~ (Trona Chemicals, Kerr-McGee Chemical Corporation) and MoO2 (Ventron-Alfa Division) (< 15 ~m grain size) were used after drying. The positive composite electrodes included the electrolyte (O/Li = 8/1), the active material (40-50 volume percent [v/o]) and acety- lene black (=10 v/o).

The 3.9 cm g cells were crimp-sealed button cells or the cell constituents were housed in containers such as illustrated in Fig. 2 and 3. As shown in Fig. 2a, a central Li ~ reference electrode was used on one side of the electro- ]yte, while in the configuration of Fig. 2b a LiA1-A1 reference electrode was made by inserting a 10 ~m aluminum strip during cell assembly and electrochemically charging it. The EMF of the latter reference electrode ranged from +400 to +360 mV vs. Li ~ between room temperature and 100~ (3).

Figure 3b shows a larger 70 cm 2 cell. Cells like this can be stacked in parallel for the scale-up tests described later. This design is convenient for laboratory tests. Optimization in terms of the energy density for future cells is presently under study.

The cycling mode used for this study is based on constant discharge and charge currents with high and low voltage limits.

ACEP PROJECT (solid-state thln-film polymer batteries)

MAIN GOAL: ELECTRIC VEHICLES

C o s t and r a a r k e t t n g New polymer-s~it complexes Negative electrodes: evaluatlons with improved conductivity: Li ~ rechar~eability Legal protection: preparation, characterization Li alloys patents, llcenees,

external contracts

First famil temperature

i

Optimization of known posl=ive-electrode materials Development of new active

compounds

"labl ommere aval e of ambient- C Jelly electrolytes materials

Processing technologies ] and assembly

SolutioJcasting

AMBIENT-TEMPE~TURE PROJECT

Scarred January 1983 - reassessed December i 9 8 a Applications: mieroelectronies; small rechargeable power sources

Fig. 1. ACEP Proiect organization

1333

) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 129.81.226.78Downloaded on 2014-09-07 to IP

http://ecsdl.org/site/terms_use

1334

Li~ reference electrode . . . ""r~.~..... AI20 ~ insulator

Stainless steet ~ ~,,, r ~ ~ I i i ~ BN holder

(~ electrode ~ ~

~ ~ " ;~i Electrolyte Li ~ ~ e l e c t r o d e ~

Stainless steeV

a) Central-type reference electrode

J. E lec t rochem. Sac.: E L E C T R O C H E M I C A L S C I E N C E A N D T E C H N O L O G Y J u n e ] 985

O) / - S S container and lid ~) . / (~ /--Glass-to-metal seal

I/ ~ - T i g weld IJ/ ~ • : ~ '[//--plastic insulators

Spring --~.~..~ ............. ~ .................. ~,~.~ SS holdinq ~ ... . . . . . . . . . . . . """" . . . . . . . . . . . . . . . . ~Elecf rochemico l

lates "~,#~:~:::~'- .~.=,-'-,..".-,~"~.~1 cell P I [ " . . . . . . . i i . . . . . . . . / i .............................. 9

(~ electrode

electrolyte (~ t 0 0 / ~ m ) ~ A I - LiAI

Q electrode / ~ - reference electrode

b) Strip-type reference electrode

Fig. 2. Electrochemical cells with reference electrodes, a: Central- type Li ~ electrode, b: Strip-type LiAI-AI electrode.

)OFm

~de

b) current collector

Fig. 3. a: Welded stainless steel cells with glass to metal seal. b: 70 cm ~ capacitor-type cell.

Results and Discussion The results presented here serve to establish the char-

acteristics of experimental Li/PEO/TiS2 and Li/PEO/V6013 cells with respect to their performance on cycling. The achieved power and energy densities represent only a first step towards performance optimization based on presently known or commercially available materials. Al- though the present work is based on the results of a large number of cells, efforts have been made in this presenta- tion to gather most of the studies into a limited number of cells. The results are then considered typical of the technology.

In the discussion of the cycling profiles, unless other- wise indicated, comparison is made between a discharge curve and the subsequent charge curve.

Li/PEO/TiS~ cell cycling profiles.--Figure 4 illustrates the cycling profile of a 2.9 mAh cell, showing the number of coulombs measured during discharge and charge vs.

cycling. During the tests, several parameters such as T (~ or the charge and discharge currents, Jc and JD, were modified and/or systematically studied.

The changes (a to k on cycle number scale in Fig. 4) observed are listed below. They are also illustrated by addi- tional figures.

a. At this point appears the effect of a lower discharging current on the number of coulombs followed by the effect of lower operating temperatures at constant current (Fig. 5).

b. This point shows charging/discharging at 70~ pursued for 14 cycles.

c. This marks the restorations, at 65~ of the initial utilization of the TiS~ electrode (previously observed at 100~ by the reduction of currents JD and Jc.

d. Here, cycling is continued at 44~ with a utilization lower than 10%. (Not shown here are some attempts at 26~ where, after a few hours, no current could be drawn from the cell.)

T i S z l P E O 5 M - L i C l 0 4 IL l ~ Q Theoretical capacity: 2.9 rnAh (11 C) Area : 5 .8 cm 2

, 0 0 C - , 0 , - - i , - 6 I - 5 4 I ~ , - 4 4 - , - 9 6 , l H ' , - - - - , 2 2 - I t00 F 7

! [ . . . . . C,or~ i 4t' ............ ...... :d . ~ . . . . . . . . . . . . . . . . . . D i s c h a r g e f " " .. " ' " "

, I-- II / /A f il - 41- -w'3, "/ \ i I ',', -

/ . a . ,bt c , , ~ . d ~ _ ~ f , ig h , j+ k n l ~ ~ ~ ~ I i ~ h t ' ~ l ~ I I t i ~ i i I i I t ~ ~ Jvl i = ~ ~ ~ t J ~ . [ - - ( - l ' " i " - v i v~ ! ! ITI t i i i i i i i i i i i i i - i "~ "0 5 t0 I~ 30 55 40 45 ~ 70 75 I ' 405 t'10 4'15

Cycle number Fig. 4. Cycling profile of a 2.9 mAh TiS2/Li cell: effect of temperature and cycling conditions on the number of coulombs observed on discharge (full

lines) and charge (dotted lines). The discharge and charge currents, JD and Jc, are represented as - and +0 respectively.



Vol. 132, No. 6 POLYMER-ELECTROLYTE BATTERIES 1335

50

2.0

>o

lO

% ,

i I i I i I i I

JD=270FAlcm 2 Theoretical capacity =2.9 mAh

65~ 75~ tO0~

I

m

I t I I I t I t 20 40 60 80 100

Utilization of TiS2 electrode (%)

Fig. 5. Effect of the temperature on percentage of utilization of TiS2 at 0 .27 mA/cm 2 during discharge. The number on each curve corresponds to the cycle number.

e. At this point is marked the appearance of dendrites on charge after 24 cycles at 44~ (50h), a phenomenon be- lieved to be related to the onset of crystallization of the PEO/LiC104 complex. The test temperature is relatively close to a eutectic temperature in the PEO/LiC104 phase diagram presently under study (4).

f. The initial utilization of TiS2 is restored when the temperature increases to =100~

g. This marks continuation of cycling under initial conditions.

h. At this point, the increase of the operating temperature to 122~ results in a high utilization but leads to inefficient and anomalous recharge plateaus (Fig. 6).

i. This point indicates a return to operating temperature of 100~ which leads to initial utilization on discharge (Fig. 7) but to slightly less efficient recharge. (Possible damage resulted from previous high temperature cycles, (Fig. 6)).

j. A dendrite at the end of the l l 8 th recharge plateau appears here (Fig. 6). This phenomenon was not observed in other experiments, not reported herein, when Li ~ was replaced by an LiA1 alloy, which seems to confirm that lithium dendrite formation is involved.

k. This marks the return to stable performance of the cycle observed before the dendrite appearance; this suggests that (i) the dendrite is burnt by the Joule effect and (i i) no permanent damage results from occasional dendrites owing to the self-healing properties of the polymer electrolyte.

The second cycling profile (Fig. 8) also for a Li/PEO/TiS2 cell with a 3.3 mAh capacity was used princi-

t ] ' ] , I i I , 1 , ] r ] , ]

_

(D:C) C-I02 /,~,S.4~, C-119~

~ ~ C-I06

2.c o Charge plateaus of TiS2 I PEO 5M- LICe041 Li o

Theoretical capacity = 2.9mAh (IIC) Area = 3.8cm 2 JD = 0.500 mA/cm z

Is Jc = 0.125 mA/cm 2

0(~ J I i I l I t I t I t I t I t I 2 4 6 8 10 12 t4 16

Number of coulombs on charge Fig. 6. Typical charge plateaus of TiS2/LI ~ cell at different cycle num-

bers. C-102: Efficient charge plateau (C = D). C-106: Double-wave charge plateau of TiS2 at 122~ C- 112: Slightly inefficient charge plateau after 10 cycles at 122~ C-118: Charge plateau showing a dendrite occurrence. C-117/119: Charge plateaus before and after C-118.

pally to establish the relations between the charge and discharge currents and the utilization of the TiS2 electrode, especially for power and energy evaluation. The main observations are described below.

Points a, a', and a" mark the appearance of occasional dendrites observed during charge, similar to cycle C-118 of Fig. 6.

Points b and b' indicate where several cycles are run at 100 ~ and 80~ to establish a relation between the utilization of TiS2 and the discharge current JD (mA/cm 2) (Fig. 9 and 10). The results at 100~ (Fig. 9) show very good agreement with the theory of the insertion of an alkali metal in a composite electrode (5), which proves that the limiting mechanism at 100~ is the li thium diffusion in TiS.~ and not the polymer electrolyte conductivity.

Points c and c' mark improved utilization, of the 's electrode at 80~ as a result of the lower charging current.

Point d shows the effect of a t ime delay (lh) between the end of a discharge and the next charge, indicating the presence of local concentration gradients in the Li/TiS2 cell at 80~

Point e marks drop in utilization of the TiS2 electrode resulting from a relatively high charging current (1 mA/cm2).

Point f indicates cycling at JD = 0.5 mA/cm 2 and Jc = 1.0 mA/cm 2 for more than 90 cycles without any evidence of dendrite formation or significant performance degrada- tion.

Point g marks the appearance of a certain inefficiency of the charge half-cycle (5-10%) after 275 cycles (already illustrated for cycle C-112 in Fig. 6). This test was pursued under similar conditions for more than 450 cycles.

A third cycling profile illustrated in Fig. 11 is also based on a Li/PEO/TiS2 cell of 3.7 mAh capacity. It is a study of the effect of uninterrupted deep-discharge/ charge cycles on the cell performance at 100~

The area between a and a' is an area of stable performance of the cell and the balanced discharge and charge plateaus over the first 36 cycles.

At point b, ~95% overall energy efficiency (energy out at C/2)/(energy in at C/7) was observed at cycle 16 (Fig. 12).

The span from c to c' encompasses the appearance of a slight inefficiency of the charge half-cycle at cycle 31, in- creasing to ~10% at cycle 89.

At point d, a temporary reduction in the observed charge inefficiency took place through an increase in the charge current (cycles 90-100).

Point e shows the stabilization of the charge half-cycle inefficiency vs . cycling from cycles 100 to beyond 250.

>

E o

4.0

5 s

2.0

t I I I J I i I i

Discharge plateaus of TiSz I PEO 5M-L iCL041L i ~ Theoretical capacity = 2.9 mAh ( 11 C) Area = .5.8 cm 2 JD = 0.500 mA/cm 2 Jc = 0.125 mA/cm 2

D- t02 (96~

t n , ~ I I I I t I I ~0 2 4 6 8 40

Number of coulombs on discharge Fig. 7. Discharge plateaus corresponding to the cycle number and

charge plateaus of Fig. 6. ) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 129.81.226.78Downloaded on 2014-09-07 to IP


1336 J. Electrochem. Soc.: ELECTROCHEMICAL SCIENCE AND TECHNOLOGY June 1985

14

t3

t2

1t r

~ 9

~8 r ,

E 7=7

5

4

0

-~,,,l,,,,l,,i, . I00~

~C) =0.49 mA/cm 2

�9 , . . .

- I

- i I

TISzlPEO 5M- LiCl04 I L i ~ (~) Theoretical copocity = 3.3 mAh (t2.5 C) Are(] : 3.8 cm 2

il,,,, I

I

"Jr---O.39J--

- - Charge .............. Discharge

; / ............... b ~ '-tic'

II lJ liIIIii,llli~llllIIIi i

I - a a' ',b a" ,,,,I,,,,I',,~,I ,liT,,

5 40 ' ' 4 5

.... , , , , . , , , , , , , , , , , , , , , , , , , , , , . .oo . . . . . . . . . . . . . . ! . , , , , , , , , , , , , , , , , 1 -4 5- o.73 -" o.t221 . . . . I- o.975] . . . . I-- o.t22 0.122

70 75 80 85 90 Cycle number

L . . , . , , - - " ' " , ~ , ,

e f I , , , ~ l l , J , l l l I

'175 t80 185

i

g -

275 280

Fig. 8. Cycling profile of a 3.3 mAh TiSJLi ~ celh effect of discharge current vs. temperature and cycling. The discharge and charge currents, JD and Jo are represented as - and +, respectively.

> V

(D

o 2 0 0

I I I I t I = I I

Theoretical capacity = 3.5 mAh 3.0 Area = & 8 c m 2

It T = 100 ~ Jc = 0.125 mA/cm 2

~ - - ~ " ~ " ~ ' ~ - - - - ~ J D : I mA/cm 2 _ ~ ~ ~ . . _ / JD:OZSmA/cm~

- < ~ ~ . . : . ~ 2 - j,., = 2 m/A/~ mZ-'--./...... -" ~ ~.-..-.,.,.,..~- ~---___~ JD=O5 mA/cm "~ . . . . . . . . . / ~ ~ ~ ' ~ " " " ~ . ,4

- ~, . . . . . . . . . . \ \ "'~::,", '%

25 22 18 8 7 54

1 . 0 -

w

m

I I I I I I .... t I I 0 20 40 60 80

Utilization of TiSz electrode (%) Fig. 9. Utilization of TiSJLi cell vs. discharge current densities at 100~ The number on each curve corresponds to the cycle number

100



Vol. 132, No. 6 P O L Y M E R - E L E C T R O L Y T E B A T T E R I E S 1337

I i I i I i I i I i

T : 80~ Theoretical capacity :5.5 mAh

3.0 Area : 3.8 crn 2, Jc: 0.t25 mA/cm 2

8 2.O-

dD= 075 mMcm 2 JD=0.50 mMcm 2 do = 0.25 mA,'crn 2

i n i I i I I I i I i ~o 20 40 60 80 400

Utilization of TiSz electrode (%)

Fig. 10. Utilization of TiS2Li ~ cell vs. discharge current densities at 80~

40

5.0

o a~

ts

I I I

TiS2; 16th cycle Theoretical capacity: 3.7 mAh,t00~ do: 0-5 rnA/c m2

\ Jr = 0.t25 mA/cm 2 E~nergy efficiency: = 95%

=-

D-16

I I I 25 50 75

Utilization of TiS2 electrode (%)

Fig. 12. Energy efficiency of Li/TiS2 cell at 16th cycle

100

Nature of the l i thium salt .--All cells described so far were prepared with li thium perchlorate complexes (O/Li = 8/1) present in the electrolyte and in the TiS2 composite electrode. However, other cells were prepared which con- tained li thium salt only in the electrolyte and not in the composite electrode (where only pure PEO was used) when they were assembled. The results presented in Fig. 13 and 9 (at 100~ and 0.5 mA/cm 2) afford the conclusion that there is no significant difference in performance whichever of the two methods of cell preparation is used.

Furthermore, if for a given cell LiC104 was replaced by LiCF~SO3, the utilization of the TiS~ electrode dropped from 80% to =15% to 100~ and 0.5 mA/cm 2. To obtain an equivalent performance with LiCF3SO~, the operating temperature had to be increased to >130~ and the current density reduced by half. This large difference in the performance of LiC104- and LiCF3SO~-based cells at 100~ is expected considering that the conductivity of LiCF3SO3 8/1 complexes is much lower than that of LiC104 8/1 complexes (1.9 x 10 -5 vs. 1.6 x 10 -4 ~l-' cm-' at 100~ furthermore, the LiCF3SO3-PEO phase diagram predicts the presence of crystalline phases in the electrolyte. An addi- tional explanation could be a higher anionic transference number in PEO-LiCF3SO3 vs. PEO-LiClO4 complexes.

Origin of the polarizat ion.--The in situ LiA1-A1 reference electrode described in Fig. 2b was used (3) on several occasions in the present study in order to determine

the origin of the polarization that limits the Li/PEO/TiS2 cell performance. Figure 14 illustrates a test in which the cell potential is recorded simultaneously with the potential of the TiS2 electrode vs. the LiA1 reference electrode. It is clear from the similarity of the two curves at 100~ that the cell potential is largely controlled by the positive compositive electrode. This behavior, typical of most of the present results, was obtained against a negative Li ~ electrode.

Li/PEO/V60,3 cells.--V60,3 has many practical advantages as a positive-electrode material for EV application, namely, its light weight, high voltage, and number of lithium inserted per vanadium. These advantages compen- sate for the relatively sharp decrease in performance during the first few cycles (illustrated in Fig. 15 for a 2.42 mAh cell tested at 80~ This behavior is typical of a high purity acicular V60,3-C (x-ray diffraction). Up to 0.5 mAJcm 2, the initial utilization of this positive-electrode material is close to 90-95% (vs. LisV60~3). However, in the subsequent cycles this value decreases and stabilizes at about 60% for a current density of 0.5 mA]cm 2. These results are in agreement with those obtained by Murphy (6) for liquid organic electrolytes (0.7 Li/V). Under these conditions, V60,~ electrodes appear to compare well with TiS2 electrodes in terms of energy and power densities.

Larger cells (140 cm 2) made up of two 70 cm 2 units con- nected in parallel (represented in Fig. 3b) were assem-

TiS2, T:101% *- 2~ Q Theoretical capacity: 5.7 mAh (13 C) Area : 5.8 cm z

t6 , , , , i , , , , , , , , , , , , , , , , , , , l , , , , l l , , , i , , , , , , , , l , , , , i , , , , i l l ! ! l i l i l i i ,

. . . . . . . . . - . =.__ ~ . . . . . . . . . . . . . . . . . . . . . . . . . . . ~ . . . . . . , . . j - - ................ _.... I - ' " ' " ' - - . . . .............. _.

- - Charge ................. Discharge

( ~ : 0 . 4 9 mA/cm2~ . . . . . . ; "

( ~ = 0.t25 mA/cm 2 _,_-,- L. 0.25 mA/cm 2--'~ ' l

0 , c I~ -

,,,,,,,,,,,,,T,,,,,,,,,,,,,,,,,,,;;,, ,,,,,, 5 t0 45 20 25 30 35 85 90 95 425 13(

Cycle number Fig. ! ]. Cycling profile of a 3.7 mAh TiSJLi ~ cell: effect of uninterrupted deep-discharge/charge cycles. The discharge and charge currents, JD and

]c , are represented as - and + , respectively.

.~t2 E - , i O

~ 8 - ~, -

E

z 4 i i

_a 0;r,



1338 J. Electrochem. Sac.: ELECTROCHEMICAL SCIENCE AND TECHNOLOGY June 1985

Li/PEO-LiX, 9/1 I TiSz Theoretical capacity = 3.5 mAh

5D Area: 5.8 cm 2 - - - - TiS2 (PEO electrode)

PEO- LiC~04 electrolyte o~ k TiSz (PEO electrode)

~ PEO-LiCF3S03 electrolyte

\ ....... ,oooc \ ~ ~ ........ ~ Jo =0.25mA/cm 2

JD =0.5 mA/cm 2 JD=0.75 mA/cm ~ JD=O.4mA/crn ~ T~IO0~ I 150% 11300C I

4.C 20 40 60 80 100 Utilization of TiS2 electrode (%)

Fig. ] 3. Utilization of Li/TiS= cells prepared without lithium salt in the composite electrode vs . a LiCIO~ (dotted line) or a LiCF~SO~ containing electrolyte (full line).

>o

i I i I i ] t I i " Theoretical capacity :3.3 mAh -

5.0 Area: 5.8cm 2 T=lO0~

~ cell

tO

I I I I I I I I I 20 40 60 80 I00

Utilization of TiS2 electrode (%}

Fig. 14. Comparison of the Li/TiS2 cell voltage with the signal of the same positive composite electrode vs . LiAI-AI reference electrode.

' I ' I ' I ' I ' J 5.2-- /

~, Theoretical capacity = 2.42 mAh -~ 2 . 8 ~ ~eOc: 589 cm2 -~

"~ - D-3 to D-7 ",

.1.2 - t I I I t I '" I l I i 0 20 40 60 80 t00

Utilization of Vs013 electrode (to LisVs013) (%}

Fig. 15. Evolution of the discharge plateaus of a Li/V60,~-C cell during cycling at 80~

bled, one w i t h V~O,3-C, t he o the r w i t h a lower pur i ty V60,3-B c o n t a i n i n g a sma l l p e r c e n t a g e of v a n a d i u m ox- ides s u c h as V205. T he p e r f o r m a n c e of the 98 m A h V60,~-B cell, cyc led a t 100~ p r e s e n t e d in Fig. 16 is ve ry close to t h a t o b s e r v e d for smal l cel ls m a d e w i t h t he s ame b a t c h of V60,~. E x c e p t for t he in i t ia l cycles, t h e s e exper i - m e n t s s h o w a c o u l o m b i c eff ic iency of a b o u t 100% be- t w e e n d i s c h a r g e a n d cha rge w i t h o u t any f o r m a t i o n of dendr i t e s .

S tab i l i zed u t i l iza t ion , b o t h for la rge a n d smal l cells, a t h i g h c u r r e n t d r a i n s (C/2.7 or C/1.5) d e p e n d s on t he qua l i ty of t h e V60,3: 60-65% for V~O,3-C v s . 40% for V60,~-B at 0.5 m A / c m ~ for 140 c m 2 cells a n d 60-70% for V~O,3-C v s .

50-60% for V6OL3-B at 0.5 m A / c m = for 3.9 c m '2 cells.

5.0

t.0

I I I Theoretical capacity =98 mAh

k- Area = 140 cm 2 _ tI-B , 100 ~

- D - l O f ~ ~ D ' 6 "~'~',',.~, / ~ D ' 9 ~ 3 4 ''!i\ ~D-1

JD:O.500 mA Do ,:, o

-- d 0 =0.285mA/crn 2 Jo = 3"5/~A/cm 2 -~

Utilization of V 6 013 electrode (to LiBV6013) (%) Fig. 16. Behavior of a 140 cm2 Li/V60,3-B cell with cycling at ]O0~

ACEP Technology at 80~176 T a b l e I c o n t a i n s e s t ima te s of t he p o w e r a n d e n e r g y den-

s i t ies a long w i t h o the r charac te r i s t i c s d e d u c e d f rom t h e p r e s e n t resu l t s o b t a i n e d m o s t l y o n Li/TiS2 cells. T h e s e es- t i m a t e s are b a s e d on e x p e r i m e n t a l l y d e t e r m i n e d va lues s u c h as t he u t i l iza t ion , t he e l ec t rode t h i c k n e s s , etc. The on ly a rb i t ra r i ly f ixed va lues are t h e nega t i ve e l ec t rode capac i ty a n d a 10 /~m p rov i s ion for t he c u r r e n t col lector a n d t he e lec t r ica l insu la t ion .

The p o w e r a n d e n e r g y dens i t i e s p r e s e n t e d in Tab le I c o r r e s p o n d to a f irst s tep t o w a r d s t he op t imiza t ion of t he pos i t ive c o m p o s i t e e lec t rodes , bu t , a l ready, t hey c lear ly d e m o n s t r a t e t he p o w e r d e n s i t y of po lymer -e l ec t ro ly te ba t ter ies . This c an b e a t t r i b u t e d to t h e p o l y m e r electro-

Table I. Present performance of ACEP technology based on positive-electrode-limited Li/TiS2 cells

Calculations are based on 3.1 C/cm 2 Li/TiS2 cell characteristics and performance: average discharge plateau voltage V, electrode composition, thickness, and utilization at 2, 1, and 0.5 mA]cm 2. Elec- trolyte thickness of 50, 1O0, and 150/~m. The anode capacity is three times that of the cathode. Provision of 10/~m is made for collectors and/or insulators.

Electrolyte Energy density Sustained power thickness

(Wh/kg) (Wh/liter) (W/kg) (W/liter) (~m)

O.5mA/cm 2 101 154 68 104 50 (C/1.7) 71 103 48 70 100

55 77 37 52 150

1.OmA]cm 2 87 133 130 198 50 (1.2 C) 61 89 92 132 100

47 67 71 1O0 150 2.0mA/cm 2 56 86 260 397 50 (2.3 C) 40 58 183 266 I00

31 43 141 199 150

Peak power (5-10s) 1O0~ 8O~

Full charge Half-charge Full charge Half-charge 1553 W/liter 1435 W/liter 888 W/liter 431 W/liter

(9 mA/cm 2 at (9 mA/cm 2 at (6.4 mA/cm ~ at (2.6 mA]cm 2 at 1.7V) 1.37V) 1.36V) 1.65V)

Li~ Li~

LiiTiS~

Cycling performance at 100~C (% Util.)

250 discharges > 80 100 discharges > 60

Energy efficiency at 100~ Wh out (C/2)

95% Wh in (C/7)



Vol. 132, No. 6 P O L Y M E R - E L E C T R O L Y T E B A T T E R I E S 1339

lyte's unique combination of solid-state characteristics with plastic behavior, which is particularly well suited to the power and cycling performance of positive composite electrodes.

The cycling values presented in Table I were obtained with excess-lithium electrode capacity and constitute in- direct evidence of the efficiency of l i thium redeposition from polymer electrolytes. However, systematic work with lithium-limited cells is under way and tends to confirm the high efficiency of the electrodeposition process. As for the dendrite problem, it appears to be an occasional phenomenon, dependent on the control of several technological parameters, which does not affect the cycling capacity of small or larger (70-140 cm 2) cells built with li thium negative electrodes. Moreover, the polymer electrolyte appears to possess self healing properties since the dendrites do not seem to affect the following cycles.

The projected energy efficiency of large-scale practical Li/PEO/TiS2 cells is notably higher than that found with existing rechargeable batteries. This will certainly con- tribute to the thermal management of large installations of thin film batteries.

A m b i e n t T e m p e r a t u r e C e l l s As mentioned earlier, at room temperature the P E a

conductivity is too low for this material to be used in practical cells, even at a very low drain (see first cycling profile in Fig. 4). In the ACEP Project, therefore, new polymer-salt complexes were developed with improved electrochemical and transport properties which allow operation of all-solid-state primary and secondary cells at ambient temperature.

Several cells have already been built and tested at low to moderate current drains. Figures 17 and 18 illustrate typical performances. The primary high voltage MnO2 electrode and the reversible low voltage MoO2 electrode both show utilizations in excess of 80% at rates up to C/37. In addition, nonoptimized MoO2 cells have confirmed the feasibility of a large number of cycles: > 20 cycles at deep discharges (> 75%) have already been demonstrated at C/36, while 400 cycles have been obtained with the same cell but at rates between C/50 and C/10 at 27~ Figure 20 shows that good electrochemical properties have been maintained at C/50 even after 300 cycles at C/10.

Moreover, the results presented in Fig. 19, based on a MoOJLi cell with a larger surface area (70 cm2), suggest that scale-up is possible and that the results obtained with small cells will be repeated.

Although the technology used for the construction of such ambient temperature cells has not reached a high level of development, a first attempt has been made to establish some of the characteristics of ACEP batteries at room temperature (see Table II). At the time these tests

4.0

5.0

>o

2.0

Is

I I I Theoretical co,city = 1.0 mAh Area = 3.9 cm z T = 26~ C/57

I I 1 25 50 75

Utilization of MnOz electrode (%) Fig. 17. Utilization of primary Li /Mn02 cell at 26~

100

I I I I i I

3.0~ Theoretical capacity = 0.9 mAh -

~_ Area = 3.9 cm z

8 1.0

O[" i t i I ~ I i 0 25 50 75 t00

Utilization of MoO 2 electrode (%)

Fig. ] 8. Utilization of rechargeable Li/Mo02 cell vs. cycling at 26~ The number on each curve corresponds to the cycle number.

2s -&

4.C I t i

3.C

1s

I I 20

Mn02//Li ~ Theoretical capacity : 55.6 mAh Area = 70 crn 2 C/125, 26~

i I I I i I i 40 60 80 t00

Utilization of Mn02 electrode (%)

Fig. 19. Discharge plateau of a scaled-up (36 mAh) Li/Mo02 cell at 26~

i I I l I ) 1 )

~n~- Theoretical capacity : t.21 mAh _ v .v | Area = 3.t4 cm 2

[ - MoO2//Li ~ T=27~

._o I\x~.._ 2"adischarge at C/t0 - i

o I-\o t"e'scharoe 0t 0'50

L ,~-~" ,L 50tth'-506thdischarge at C/50 [ rth-3oothdischarge at C/t0 , l

01 t I a I i i f 0 25 50 75 100

Utilization of MoO2 electrode (%) Fig. 20. Discharge plateau of a nenoptimized Li/Mo02 cell at C/10

and C/50 for more than 300 cycles at 27~

were conducted, the temperature observed in the glove box was =25~176 Based on more recent results, the authors consider that the performances presented here are still representative of ACEP technology at 20~ for example.

The authors believe that this emerging technology based on polymer electrolytes is promising for microelec- tronic and other applications, especially those requiring a rechargeable power source.

Conclusions In conclusion, the present work, although incomplete,

suggests the feasibility of thin film polymer electrolytes in high energy- and power-density batteries for EV applications.

Projected energy densities of -~100 Wh/kg were shown to be possible associated with a sustained power of >- 200 W/kg and peak power over 900 W/kg at half-charge and at



1340 J. E lec t rochem. Soc.: E L E C T R O C H E M I C A L S C I E N C E A N D T E C H N O L O G Y J u n e 1985

Table II. Performance of ACEP technology at ambient temperature Electrolytes: aprotic polyethers + lithium salt complexes

Calculations based on observedcharacteristics of positive composite electrodes and electrolyte: V, utilization of positive electrode material thickness, etc. Arbitrarily fixed parameters were (i) the anode capacity is three times that of the cathode, and (ii) provision of 10 tLm is made for collectors and/or insulators.

LifMnO2 systems 0.1-0.17 Wh/cm 3 at C/15-C/40 for 0.3 mAhJcm 2 + 0.2-0.4 Wh/cm '~ at C/250-C/600 for 2 mAh/cm 2 + Projected performance of primary cells:

0.3-0.5 Wh]cm '~ at C/10 to C/400 LifMoO2, Li/TiS2

0.5-0.1 Wh]cm ~ at C/15-C/30 for 0.3 mAh/cm 2 + 0.1-0.17 Wh/cm 3 at C/60-C/160 for 1 mAh/cm 2 + For 20 cycles (75%), projected performance of secondary cells:

0.15-0.3 Wh/cm ~ at C/10-C/200 > 100 cycles State of the art

= 0.07 Wh/cm 3 for packaged Ni-Cd at C]I0 Other characteristics: (i) no self-discharge or performance losses

after storage for 1 month at 71~ or > 6 months at ambient temperature; (ii) no liquid electrolyte (thus reducing sealing problems), and (iii) scale-up demonstrated at 70 and 150 cm 2.

100~ Also, an energy eff ic iency in excess of 90% and a cycl ing pe r fo rmance of -> 250 deep discharges (or 450 me- d i u m to deep discharges) have been demonst ra ted .

In the au thors ' opinion, the resul ts obta ined in the present study, especia l ly in t e rms of power densi ty, m a y be a t - t r ibuted most ly to the u n i q u e combina t ion of solid-state proper t ies wi th those of plast ic materials , such as the deformabi l i ty inhe ren t in po lymer electrolytes. This appears desi rable as a means of main ta in ing the electro- chemica l in tegr i ty of the e lec t rode/e lec t ro lyte interfaces, especial ly wi th respect to the cycl ing proper t ies of com- posi te e lectrodes.

In addit ion, it has been shown tha t po lymer electrolyte cells can be opera ted at r o o m tempera tu re wi th lower rate capaci t ies (C/15-C/300) for pr imary and secondary systems. These p re l iminary resul ts appear ve ry p romis ing for small r echargeab le applicat ions.

The fact that recent ly the pe r fo rmance obta ined on small cells has been successful ly repea ted at 100 ~ and 26~ wi th cell areas greater t han 100 cm 2 has led to the ini- t ia t ion of a demons t r a t ion program. In this program, the large-scale prepara t ion t echn iques n o w used at both S N E A and I R E Q will be adapted to the present manufac- tur ing p rocedure in order to bui ld a first generat ion of cells wi th capaci t ies of 10-50 Ah. These cells will serve to es tabl ish realist ic pe r fo rmances for the A C E P technology and to assess the scale-up prob lems and manufac tur ing costs.

These act ivi t ies will be pursued in parallel wi th the research into new famil ies of e lect rolytes and e lec t rode materials and on pe r fo rmance opt imizat ion in part icular by increas ing the surface capaci t ies of the posi t ive e lec t rode in order to improve the energy dens i ty ye t main ta in similar power densit ies.

Acknowledgments The authors t hank M. C. Anerot , R. Bel lemare , E. Bon,

F. Brochu, R. Gillard, Y. Gigu~re, P. E. Harvey, B. Kapfer, C. Robitail le, M. Robitai l le , S. Sempe , and Y. Tauzy for their va luab le cont r ibu t ion to this work. Thanks are due to Hydro-Qu6bec and to Soci6t6 Nat ionale Elf Aqui ta ine for the f inancial suppor t of this work.

Manuscr ip t submi t t ed J u n e 5; 1984; revised manusc r ip t rece ived Feb. 6, 1985.

Institut de Recherche d'Hydro-Qu~bec assisted in meet- ing the publication costs of this article.

R E F E R E N C E S 1. M.B. Armand , J. M. Chabagno, and M. J. Duclot , in "Fas t

Ion Transfer in Solids," P. Vashishta , Editor, p. 131, Nor th Holland, New York (1979).

2. A. Hoope r and J. M. North, Solid State Ionics, 9-10, 1161 (1983).

3. D. Fau teux , Ph.D. thesis in preparat ion, INRS-]~nergie, Varennes , Qu6bec, Canada.

4. C. Robitai l le , Persona l communica t ion . 5. S. Atlung, K. West, and T. Jacobson , This Journal, 126,

1311 (1979). 6. D. W. M u r p h y , P. A. C h r i s t i a n , F. J . D i s a l v o , J . IN.

Carides, and J. V. Waszczak, ibid., 128, 2053 (1981). 7. S. Whi t t ingham, Prog. Solid State Chem., 12, 41 (1978).

Ionic Conductivity in Solid Solutions of the Na3YSi309 Type Chy Hyung Kim, Bingyi Qiu 1 and Ephraim Banks*

Department of Chemistry, Polytechnic Institute of New York, Brooklyn, New York 11201

A B S T R A C T

Samples based on the Na3MSi309 s t ructure (M = Sin, Eu, Gd, Dy, Ho, Er, Tm, Yb, Lu, and Y) were prepared. A com- b ina t ion of phosphorus subs t i tu t ion and reduc t ion of M '~§ con ten t pe rmi t t ed increas ing sod ium content , the m a x i m u m sod ium conten t be ing 3.3. Conduc t iv i ty of this sample, measu red by pulse and two- te rmina l ac methods , was about 5.5 • 10 -4 (i2-cm)- ' at 320~ compared to 9 x 10 -6 (~l-cm)-' for Na3YSi309 at the same tempera ture . Act ivat ion energies were sl ightly lowered wi th increas ing sod ium content , f rom 15 to 14 kcaYmol. In compos i t ions wi th o ther rare earths, conduc- t ivi ty increased wi th increas ing ionic radius of the rare ear th ion. L i th ium ions were in t roduced by ion e x c h a n g e in mol- ten L i N Q . The conduct iv i t ies were sl ightly lower than those of the cor responding sod ium samples, bu t decreased with increas ing rare ear th radius.

The c o m p o u n d s of the type Na~MSi309 (M = Y, Dy, Gd) were p repa red by S h a n n o n et al. (1). The sod ium ion conduct iv i ty of Na3YSi:~O~ was repor ted to be 6 x 10 -6 (gt-cm)-' at 300~

In our s tudy of Na~MSi~Og-type compounds , it was found that excess sod ium could be in t roduced into the structure. Also, r educ t ion of M :*+ con ten t (M = Y, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb, Lu) and subs t i tu t ion of small amoun t s of phosphorus for si l icon wi thou t dis tor t ion of the Na~MSi30, s t ruc ture were possible, as ev idenced by x-ray analysis. The conduct iv i t les of these modif ied corn-

*Electrochemical Society Active Member. 1Present Address: Peking University, Beijing, China.

pounds i m p r o v e d wi th the values be ing in the range of 10 -4 (t2-cm) -I at 300~

Experimental Star t ing mater ia ls Na2CO3, SIO2, and M.,O3 of reagent

grade were m i x e d and fired overn igh t at 900~176 in covered p la t inum crucibles. The p rocedure of gr inding and heat ing each of the samples was repea ted to insure that the react ions were complete . The x-ray pat terns were obta ined on a Phi l ips Di f f rac tometer us ing CuKa radia- tion. The x-ray pat terns of p roduc t s obta ined by quench ing at the react ion t empera tu re and by anneal ing were essent ia l ly the same.



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