Trends in new materials for solid electrolytes and electrodes

Solid State Ionics 5 (1981) 3 8 North-Holland Publishing Company

TRENDS IN NEW MATERIALS FOR SOLID ELECTROLYTES AND ELECTRODES

Nerner Neppner Department of Materials Science and Engineering Stanford U n i v e r s i t y , Stanford, C a l i f o r n i a 94305 and M a x - P l a n c k - l n s t i t u t f~r FestkBrperforschung D-7000 S t u t t g a r t - 8 D , Federal Republic of Germany

An overview of recent developments in the f i e l d of f a s t s o l i d l i t h i u m ion and proton conductors is presented. The important role of water in both types of conductors is described. Fast s o l i d electrode materials are presented. Several general aspects such as thermodynamic s t a b i l i t y ranges, transport mechanisms, enhancement of ionic c o n d u c t i v i t y in 2-phase mixtures, influence of e l e c t r o n i c p r o p e r t i e s on ionic transport in e l e c t r o l y t e s and electrodes and e f f e c t s of s t o i c h i o m e t r i c v a r i a t i o n s of the compounds are discussed.

Recent experimental studies have resulted in a r a p i d l y increasing number of fast solid ionic conductors and several f a s t mixed e l e c t r o n i c ionic conductors. A large f r a c t i o n of i n t e r e s t was r e l a t e d to s o l i d lithium ion and more r e c e n t l y also to proton conductors. Obvious reasons are t h e i r dominant role with regard to practical applications. This paper focuses on these materials but emphasizes several general features. SOLID LITHIUM ION CONDUCTORS Early i n v e s t i g a t i o n s of l i t h i u m ion conductors have e s s e n t i a l l y c o n t r i b u t e d to tile d e f i n i t i o n and development of r e l i a b l e experimental techniques in order to a r r i v e at meaningful characteri s t i c k i n e t i c materials p r o p e r t i e s . T h e y have also provided evidence that f a s t ion conduction in s o l i d s is a common phenomenon and not r e s t r i c t e d to a few e x o t i c "magic ion" conductors. Figure I shows a compilation ~f the c o n d u c t i v i t i e s o ( m u l t i p l i e d by tile absolute temperature T) as a f u n c t i o n of tile temperature of prominent solid lithium ion conductors k n o w n today. Besides a long l i s t of o r d i n a r y ionic conductors, e.g., LiScOz [ I ] , LizZrO 3 [ I ] , Li~ZrOw [ 1 } , LizO 12] and p o l y c r y s t a l l i n e LisA10~ [21, a large number of m a t e r i a l s have been i d e n t i f i e d which show c o n d u c t i v i t i e s t h a t are higher than t h a t observed f o r L i I [3] and are s u f f i c i e n t l y high f o r practical applications. A m o n g those compounds are glassy LisA1Ow [ 4 ] , LiAICI~ [ 5 ] , LigNzCI3 [6], Li~Zn(GeO~)~ ( " L i s i c o n " ) [7], l i t h i u m s i l i c a t e phosphate s o l i d s o l u t i o n s [ 8 ] , L i l (+AlzO3 as second phase) [9] and LiAI11017 ( L i - 8 alumina) [I0]. It is remarkable that approximately the same pre-exponential f a c t o r is observed for a l l compounds i n d i c a t i n g an almost material-independent attempt frequency for l i t h i u m jumps in s o l i d s .

The highest c o n d u c t i v i t y at low temperatures reported so far is for the layer s t r u c t u r e material L i a N [11,121 in which ionic motion is reported to occur predominantly in the hexagonally dense packed "LizN" layer. It was r e c e n t l y pointed out that the c o n d u c t i v i t y is enhanced by the presence of hydrogen which presumably associates with tile nitrogen ion, leaving vacancies in the l i t h i u m s u b l a t t i c e , but is l i m i t e d by the low s o l u b i l i t y of hydrogen [13]. Major disadvantages in view of p r a c t i c a l a p p l i cations are the low thermodynamic decomposition voltage, e . g . , 0.445 V at 25°C [14] and the f o r mation of e l e c t r i c a l l y s h o r t - c i r c u i t i n g m e t a l l i c dendrites. The l a t t e r phenomenon may be c l o s e l y related to the presence of a layered s t r u c t u r e . These problems were overcome by adding another s a l t which has a much higher thermodynamic stab i l i t y than the l i t h i u m n i t r i d e , e.g., one of the l i t h i u m halides, to form new ternary l i t h i u m compounds which have two d i f f e r e n t anionic species but tile same L i - c a t i o n [ 6 , 1 5 ] . Since a l l the binary s a l t s involved are stable in contact with elemental lithium, and no other ternary compounds e x i s t with higher l i t h i u m content, tile new l i t h i u m n i t r i d e halides are also stable against reaction with lithium. Elemental l i t h i u m may therefore be conveniently used as an anode m a t e r i a l . The decomposition voltages are in betweeen those of L i a N and the respective halide. Experiments have shown a value of e . g . , 2.52 V at I00°C for the best conducting compound LigNzCla (Lil.aNo.~Clo,6) [15]. I t should be noted that tile ternary compounds form new s t r u c t u r e s in comparison with LiaN or the l i t h i u m halidds and t h e i r c o n d u c t i v i t i e s are lower at low temperatures in s p i t e of tile much higher degree of disorder in some of the ternary compounds. LigNzCla, e . g . , has an a n t i f l u o r i t e type s t r u c ture with 10% of the l i t h i u m s i t e s being vacant [16]. This s t r u c t u r a l property turned out to be very favorable in the case of a number of good anion conductors.

0 167-2738/81/0000-0000/$02.75 © North-Holland Publishing Company

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W. Weppner / New materials/or solid electrolytes and electrudes

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lithium activities, however o v e r a wide r a n g e c o r r e s p o n d i n g to a potential range of 1.68 to 4.36 V versus l i t h i u m at 25°0 [18]. The l i t h i u m a c t i v i t i e s of both anodes and cathodes h a v e to be kept in t h i s range during the e n t i r e d i s charge and charge process. This requirement may be d i f f i c u l t to f u l f i l l f o r high energy density b a t t e r i e s but is much less l i m i t i n g in the case of other a p p l i c a t i o n s , e . g . , electrochromic d i s plays where the p o t e n t i a l d i f f e r e n c e across the e l e c t r o l y t e is not of primary Importance and the r e v e r s i b l e charge f l u x is sma11. A p r a g m a t i c a p p r o a c h to t h e s e a r c h f o r new s o l i d lithium i o n c o n d u c t o r s has r e v e a l e d an e f f e c t of probably quite general validity i n the o b s e r v a t i o n o f t h e enhancement o f i o n i c c o n d u c t i v i t y by orders of magnitude in dispersed 2-phase m~xt u r e s o f L i I and AlzO 3 or SiO 2 , w h i c h may n o t be attributed to t i l e formation of d e f e c t s by a classical doping process [9]. Structural properties of the e l e c t r i c a ] l y i n e r t second phase were f o u n d to be of m i n o r i n f l u e n c e whereas the particle s i z e has shown a dramatic effect [19]. The c o n d u c t i v i t y increases ~ith decreasing partic|e s i z e and therefore increasing interface a r e a between the two p h a s e s .

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Figure I: Compilation of representative s o l i d lithium ion conductors as known today. Tile product of the c o n d u c t i v i t y ~ and the absolute temperature T is p l o t t e d vs. the inverse absolute temperature. For references, see t e x t .

Nhen a c u r r e n t o f l i t h i u m i o n s i s passed t h r o u g h tile p e l l e t s of the cubic material, no t e n d e n c y to form dendrites could be observed [ 1 5 ] . In view of t h i s r e s u l t and the high thermodynamic decomposition voltage i t seems f e a s i b l e to apply thin f i l m s of t h i s e l e c t r o l y t e in order to compensate f o r the higher resistance of tile material. In f a c t , a battery with e x t r a o r d i n a r i l y high energy density, based on t h i s e l e c t r o l y t e family has recently been announced [17].

The employed procedure did not f o l l o w the pattern of c l a s s i c a l p a r t i a l s u b s t i t u t i o n of the mobile ionic species by other p r e f e r a b l y a l i o v a lent ions as was successfully done in the case of s i l v e r s a l t s , e i t h e r to increase the concent r a t i o n of defects or to form thermodynamically stable compounds at room temperature. As a consequence of the high thermodynamic s t a b i l i t y of most l i t h i u m s a l t s compared to other s a l t s with the same anion, s t a b i l i t y against reaction with elemental l i t h i u m would disappear. In t h i s coilt e x t i t was found that LiAIO]~ which contains 2 d i f f e r e n t c a t i o n i c species is only stable at low

M o i s t u r e was assumed to p l a y a dominant role in controlling the conductivity of t h i s type and various other related lithium ion conductors. Hany l i t h i u m salts are n o t o r i o u s l y hygroscopic, and a l u m i n a and s i l i c a are w e l l known to p h y s i sorb water readily ~hioh is difficult to remove even t h r o u g h e x t e n d e d p e r i o d s of h e a t t r e a t m e n t .

The effect of water was therefore recently investigated separately from tile issue of the dispersed second phase, Phase equilibrium studies by various techniques (DTA, temperature scanning Guinier-Simon X-ray and thermogravlmetric techniques) have disclosed that tile mono-, di- and trihydrates of Lil are the only phases that exist in tile system LiI-HzO [20]. Earlier statements of several intermediate phases could not be confirmed. Lithium iodide monohydrate has all interesting cubic structure of the perovskite type. Tile I- ions form the corners of the elementary ceil. Rotating water molecules are located at tile body-centered position and the lithium ions occupy statistically I/3 of the available face-centered positions [21]. The conductivity has been measured in several laboratories. The r e s u l t s a r e c o m p i l e d in F i g u r e 2. The discrepancies are probably related to the difficulties and differences in preparing and storing samples of single phase materials, Curve a was measured when tile sample was sealed in a small container, whereas samples flushed by slow streams of dry argon gas have shoun the results indicated by b [20]. The compound melts at 12800, Pack, Owens and Nagner [22] have reported curve c for the virgin sample. Curves d and e were f o u n d upon a n n e a l i n g at 70 and 1O0°C, respectively. The higher temperature part is a continuation of curve e. Recent measurements w i t h the d e u t e r i u m analogue [23] are also presented.

W. Weppner / New materials for solid electrolytes and electrodes

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nevertheless e x t r a o r d i n a r i l y low (5xi0 "s ~-Icm'1 at 2DO°C) and is exceeded by those of the other l i t h i u m hydroxide halides. T h e y are a l t o g e t h e r rather moderate s o l i d ionic conductors. The c o n d u o t i v i t i e s are lower than that observed for L i l (+40 m/o Alz03). In s p i t e of various experimental discrepancies agreement is found t h a t none of tile l i t h i u m iodide hydrates or hydroxides is responsible for the observed enllancement of the ionic conductivi t y in the systems LiI-AlzO~/SiOz. Instead, tile idea of a more general phenomenon of enhanced ionic conduction in dispersed 2-phase mixtures compared to both single c o n s t i t u e n t phases has become strengthened. Also, dispersed mixtures of curl and AIz03 at 84°C [ 2 5 ] , Agl and AIz03 in dried and undried conditions at 27°C [26] as well as Agl and Alz03 of d i f f e r e n t grain sizes at 27°C [27] have shown c o n d u c t i v i t i e s which are enhanced by several orders of magnitude. The second dispersed phase may likewise be an ionic conductor instead of an e l e c t r i c a l insulator. I t was shown that mixtures of Agl and AgBr [ 2 8 ] , Lil and LiI.HzO, Liz(NH~)31s and Lil or Liz(NH~)31s and NH~I [29] may also h a v e orders of magnitude higher c o n d u e t i v i t i e s than does the best conducting c o n s t i t u e n t phase. SOLID PROTON CONDUCTORS

,".,... 35

Conductivities as a f u n c t i o n of tempthe LiI-hydrates compared with LiI, For r e f e r e n c e s , see t e x t .

L i l . 2 H z O has a low structural symmetry. The conductivity has a h i g h activation e n t h a l p y and is indicated by the long broken line [20]. Several Lil-based systems show a drastic increase in c o n d u c t i v i t y t h a t corresponds to tile temperature range in which Lil.2HzO becomes s i g nificantly conducting and e v e n t u a l l y melts at 80°C. Lil.3HzO c r y s t a l l i z e s in a hexagonal structure, melts at 70°C and shows a moderature ionic c o n d u c t i v i t y [ 2 0 ] . For comparison, the c o n d u c t i v i t i e s of L i l + 40 m/o Alz03 [ 9 ] , LizO [ 2 ] , LiOH [2] and several samples o f a n h y d r o u s L i l ( a " [3], b" [ 2 2 ] , c' [ 2 0 ] , d" [ 2 3 ] ) are a l s o p r e s e n t e d in F i g u r e 2. Another influence of water may be sought in the formation of h y d r o l y t i c decomposition products. Such a process may be r e a d i l y catalyzed by the presence of Alz03 or SiO z. LiON might be formed and react with the o r i g i n a l l i t h i u m s a l t . Phase e q u i l i b r i u m studies of the systems LiOH-lithium halide show the existence of several intermediate phases [ 2 4 ] . Among t h o s e , L i z ( O H ) 3 B r has a cubic p r i m i t i v e a n t i - p e r o v s k i t e type s t r u c t u r e s i m i l a r to LiI.HzO. A s t r u c t u r a l disorder keeps 1/3 of the positions of the Li-sublattice vacant. The ionic c o n d u c t i v i t y of t h i s phase is

Compared to l i t h i u m e l e c t r o l y t e s the present s i t u a t i o n is quite d i f f e r e n t for s o l i d proton conductors. In general, the c o n d u c t i v i t y of the i n v e s t i g a t e d organic compounds is orders of magnitude less than that of tile inorganic materials [30]. Reliable work was not s t a r t e d u n t i l a few years ago despite many e a r l i e r claims of proton conduction in a series of s o l i d s [ 3 0 , 3 1 ] . The features of proton conduction in s o l i d s a r e unique due to the missing electron cloud. The repulsive force of tile small p o s i t i v e l y charged species is d r a m a t i c a l l y lowered as i t approaches any n e u t r a l or n e g a t i v e l y charged species. It may be a b l e to imbed itself in tile electron c l o u d s of o t h e r i o n s , atoms, or m o l e c u l e s and may n o t be e a s i l y d i s l o d g e d [ 3 2 ] . A compilation of solid proton conductors is p r e s e n t e d in F i g u r e 3. A few examples from t h e l a r g e c l a s s o f p r o t o n c o n d u c t o r s w i t h r a t h e r low conductivities at r o o m temperature are KHF z [ 3 3 ] , H30+-B a l u m i n a [ 3 4 ] , KHzPO~ ( " K D P " ) [35), ~ - Z r ( H P O ~ ) z . HzO [ 3 6 ] and NH~HzPOw U'ADP") [35]. Li(NzHs)SO, is a one-dimensional proton conductor, with values a factor of more t h a n 10 z greater parallel t h a n normal to t h e c - a x i s [ 3 7 ] . I t was n o t u n t i l r e c e n t y e a r s t h a t a few m a t e r i als with very fast proton conduction at low t e m p e r a t u r e s became i d e n t i f i e d such as p b o s p h o molybdic and - t u n g s t i c acids (H3PMolzO~o,nNzO ( " P M A " ) , H3PNlzO~o.nHzO ( " P H A " ) [ 3 8 ] ) , perfluorocarbonsulfonic a c i d p o l y m e r s (~NAFION") [39], hydrogen uranyl p h o s p h a t e HUOzPOw.4NzO ("HUP") [40], hydrogen uranyl arsenate NUOzAsO~.4NzO U'NUAs') (a [ ~ l ] , b [37], under slightly reduced

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IV. Weppner / New materials for solid electrolytes al2d electrodes

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Several i n d i c a t i o n s observed recently with tile one-dimensional proton conductor LiNzHsS04 and tlle two-dimensional proton conductors HUOzPOh.4HzO and HUOzASO~.4HzO seem to confirm the vehicle mechanism [37]. The measurement of the diffusion coefficient of water in HUOzAsO4.4HzO by dehydration as a function of temperature has ]ed to a calculated value f o r the c o n d u c t i v i t y (assuming that a l l water molecules are mobile) w h i c h is of the same order of magnitude and shows approximate]y the same a c t i vation enthalpy as tile e l e c t r i c a l l y measured proton c o n d u c t i v i t y (curve c in Figure 3) [37]. Arguments supporting tile mechanism in the case of LiNzHsSO~ include the observation of large thermal diffuse X-ray s c a t t e r i n g of those r e f l e c t i o n s which have high c o n t r i b u t i o n s from the hydrazinium p o s i t i o n s , the loss of hydrazinium at s l i g h t l y increased temperatures, p r a o t i caIIv i d e n t i c a l a c t i v a t i o n enthalpies f o r the a c - c o n d u c t i v i t y and the NMR value f o r t r a n s l a t i o n a l motion of NzHs÷ as c l e a r l y d i s t i n c t fro~ the value f o r the r e o r i e n t a t i o n of NzHs+, important f o r motion in a Grotthus mechanis~;~. FAST SOLID ELECTRODES

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-E . 1 0 3 / T [ K -1] Figure 3: Conductivities o f representative f a s t s o l i d p r o t o n c o n d u c t o r s as a f u n c t i o n o f t e m p e r a t u r e . References in t e x t .

w a t e r c o n t e n t : d [ 3 7 ] ) , hydrogen u r a n y l p e r i o d a t e HsUOz(IO6)z.4HzO [ 4 2 } , NH~+-H(HzO)×*-B"-alumina [ 3 4 ] , SnOz.2H20 [ 4 3 } , Z r O z , l . 7 5 HzO [ 4 3 ] and H*and H - A ] - m o n t m o r i ] l o n i t e c ] a y s [44} f o r which a range o f conductivities depending on the w a t e r content is given. A l l t h e s e m a t e r i a ] s have some important transport-related properties in common. They a l l contain s t r u c t u r a l Water, have an obvious a c i d i c character and contain i~igh valent cations. Many f a s t proton conductors are p r a c t i c a l ion-exchange materials [43]. I t is a p p a r e n t that the f a s t proton conductors have protons associated with oxygen or nitrogen in order to form larger s t r u c t u r a l units such as H30 +, NH~ +, NZHS + or OH'. Two models for the macroscopic transport of protons are c o n c e i v a ble. In a p r e v i o u s l y commonly employed p i c t u r e , the p r o t o n t r a n s p o r t i s d e s c r i b e d by the movement from one h y d r o n i u m o r ammonium i o n to an adjacent water or ammonia m o ] e c u l e ("Grotthus mechanism"). Alternatively, i t was proposed that the movement of the whole s t r u c t u r a l group to which the proton is associated ( e . g . , H30÷, NHw÷, NzHs~ or OH-) might occur upon the a p p ] i cation of an e l e c t r i c f i e l d . Such a process was called a " v e h i c l e mechanism" [3?].

Mixed ionic and e l e c t r o n i c conducting solids expand the number of materials d r a s t i c a l l y f o r fundamental studies of the k i n e t i c properties of solids. Various electrochemical techniques were developed and employed advantageously in recent years in order to analyze tile various k i n e t i c parameters c o r r e c t l y w h i c h may become apparent in quite d i f f e r e n t ways in m i x e d conductors [45]. Thosemixed i o n i c - e l e c t r o n i c conducting materials which e q u i l i b r a t e fast with respect to compositiona] inhomogeneities are called fast s o l i d electrodes ("FSEs') {46]. Many fundamental similarities exist with regard to tile ionic transport mechanisms between solid e l e c t r o l y t e s and electrodes. There are, however, a]so s t r i k i n g d i f f e r e n c e s re]ated to tile r o l e of the e l e c t r o n i c species in the s o l i d s . Predominant ionic conduction may be in most cases regarded as tile result of electronic properties: the presence of trapped or hopping electronic species which show low mobilities, e.g., of the order of some 10 .4 cmZ/Vsec at 9OO°C which has been reported in tlle case of zirconia [47, 4~]. If one assumes mobilities of the order of severa] hundred cmZ/Vsec (typical for electronic semiconductors) ]ow partial electronic ccnductivities will require very ]ow e]ectronic concentrations. These are very sensitive to, and may be readily increased by i m p u r i t i e s and, more importantly, v a r i a t i o n s in stoichiometry. Predominant e l e c t r o n i c conduction will be the result. On the other hand, fast electronic species are required for fast transport in mixed conducting electrode materials. Internal e l e c t r i c a l f i e l d s may be present as a unique feature o f the s o l i d state in mixed conductors to enhance tile e f f e c t i v e ionic d i f f u sion by severa] orders of magnitude compared to tile d i f f u s i v i t y in tile absence of compositional

W. Weppner / New materials for solid electrolytes and electrodes

gradients [ 4 6 , 4 9 ] . Semiconductor technology is similarly the result of high internal electrical fields in solid state; in this case, however, at junctions.

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In many cases, chemical diffusion as fast as in liquids and in some cases as fast as in gases may be observed in solids. These materials are of practical interest in combination with both solid and liquid electrolytes. A collection of data is presented in Figure 4. High electronic concentrations, often stated as a major requirement for electrodes, are in fact of disadvantage since these shield o f f the electrical field a h i c h t h e n becomes i n e f f e c t i v e f o r t h e m o t i o n of ions. Electronically semiconducting materials generally provide a better choice. There s h o u l d be a small number o f electronic species with high mobility in o r d e r to c r e a t e the internal electrical f i e l d by d i f f u s i n g ahead of t h e i o n s if a gradient of t h e c h e m i c a l p o t e n t i a l of t h e n e u t r a l components exists. The p a r t i a l electronic conductivity s h o u l d be n e v e r t h e l e s s s t i l l larger than the partial ionic conductivity in the electrode. I t i s o b v i o u s t h a t a s m a l l number of electronic s p e c i e s may show a d r a s t i c relative change w i t h t h e variation of t h e s t o i chiometry of the compound. The e q u i l i b r a t i o n rate is therefore often dependent on the composi t i o n of the mixed conductor. In the c a s e of "LiAI" for instance, the chemical diffusion coefficient is about 2 orders of magnitude higher when the sample is in e q u i l i b r i u m with AI than when the sample is in e q u i l i b r i u m with the next more l i t h i u m r i c h phase, " L i 3 A l z " , at 4OO°C [50]. It was even found that B-AgzS e q u i l i b rates f a s t e r at low temperatures than at higher temperatures at the ideal s t o i c h i o m e t r i c composi t i o n (51]. The explanation is the increasing e l e c t r o n i c concentration with temperature and a corresponding " s e l f - d e s t r u c t i o n " of the e l e c t r i c f i e l d by the electrons or holes.

O t h e r compounds b e s i d e s AgzS t h a t are known to show e x t r e m e l y f a s t c h e m i c a l d i f f u s i o n s r e AgzSe 152] and CuzS [ 5 3 ] . Liquid like diffusion is reported in t h e compounds Li3Bi [54], Li3Sb [54], several L i - S n and L i - S i compounds [ 5 5 ] , Cuz0 [ 5 3 ] , " F e S " [ 5 3 ] and w ~ s t i t e { 5 6 ] . The e l e c t r o n i c species a l s o d e t e r m i n e fundamental tllermodynamic quantities of semiconducting compounds [ 4 6 ] . Due t o t h i s common o r i g i n o f kinetic and t h e r m o d y n a m i c d a t a , it is possible 1o use t h e r m o d y n a m i c i n f o r m a t i o n to p r e d i c t the kinetic properties o f compounds. CONCLUDING REMARKS AND SUMMARY Many interesting developments of new solid electrolytes and electrodes could not be considered in tills short overview. Instead, a few major aspects of general interest are emphasized: Thermodynamic considerations have led to the systematic development of practical solid lithium electrolytes which are stable against lithium and have h i g h d e c o m p o s i t i o n v o l t a g e s . Many lithium ion conductors are extremely sensitive to water. Solid or molten hydrates

¶AgzSe

(e) Cu 2S

-2

e•Lil3Sns (el Cu20

e~LizBi Liz~ns---e L i t 3 S i 4 ~ L i AI" LiizSi~'Liz2Sis'Li sSnz ~1 e-Li3 Sb Li-/Si3.Li~Sn3

E

(J w _~

=Q

(el "FeS" Li Sn--e FeollgO

-6

" 06

~r-~FeOg40

I Q8

I

I

I

1

12

14

~103/T

I

I

16 1.8 [ K -t]

Chemical d i f f u s i o n F i g u r e 4: various presently identified c o n d u c t o r s as a f u n c t i o n of references, see t e x t .

I

J

2

22

coefficients fast solid temperature.

24

D of mixed For

a r e r e a d i l y formed a l o n g c o n t i n u o u s p a t h s a c r o s s polycrystalline samples. Tile enhancement o f ionic conductivity in 2-phase mixtures is apparently a general effect and n o t r e s t r i c t e d t o t h e system L i I - A l z 0 3 . The second phase may be a n o t h e r i o n i c c o n d u c t o r . Protons form l a r g e structural groups which may be used as t r a n s p o r t vehicles to pass through the lattice. Electronic properties may g u i d e t h e s e l e c t i o n of potential materials for solid electrolytes or electrodes. Electrons are often trapped in pred o m i n a n t i o n i c c o n d u c t o r s and a r e v e r y m o b i l e a t low c o n c e n t r a t i o n s in f a s t s o l i d e l e c t r o d e s . The unique f e a t u r e of the solid state to allow high internal electrical f i e l d s may be utilized f o r t h e enhancement of t h e i o n i c m o t i o n in mixed conductors. Variations of the stoichiometry may change t o a large extent the kinetic properties of b o t h solid electrolytes and e l e c t r o d e s . ACKNOWLEDGEHENT The a u t h o r gratefully acknowledges many s t i m u lating discussions with P r o f e s s o r R.A. Huggins and Dr. I.D. Raistrick, S t a n f o r d and P r o f e s s o r A. Rabenau, S t u t t g a r t .

8

W. Weppner / New materials ,f?)r solid electroh'tes arid electrodes

REFERENCES [1] [2] [3] [4] [5] I6] [7]

[8] [9] [lOI

Ill] [12] [13] [14]

I15]

[16]

[17] [18]

[19] [20] [21] [22] [23] [24] {25] [26]

127]

Hellstrom, E.E. and van Gool, W., Solid S t a t e I o n i c s 2 (1981) 53. B i e f e l d , R.M. and Johnson, J r . , R.T., J. E l e c t r o c h e m . Soc. 126 (1979) 1. Jackson, J.H. and Young, D.A., J. Phys. Chem. S o l . 30 (1969) 1973. G l a s s , A.M. and Nassau, K . , J. A p p l . Phys. 51 (1980) 3756. Neppner, N. and Huggins, R . A . , J. Electrochem. Soc. 124 (1977) 35. H a r t w i g , P., Neppner, N., and N i c h e l h a u s , N., Mat. Res. B u l l . 14 (1979) 493. Hong, H . Y . - P . , Mat. Res. Bull. 13 (1978) 117; v. A l p e n , U., B e l l , M . F . , N i c h e l h a u s , N., Cheung, K . Y . , and D u d l e y , G.F., Electrocbim. Acta 23 (1978) 1395. Hu, Y.N., Raistrick, l.D., and Huggins, R . A . , J E l e c t r o c h e m . Soc. 124 (1977) 1240. Liang, C.C., J. Electrochem. Soc. 120 (1973) 1289. M b i t t i n g h a m , M.S. and Huggins, R.A., in: S o l i d S t a t e Chem., eds. Roth, R.S. and S c h n e i d e r , S . J . , NBS Spec. Publ. 364 ( N a t l . Bureau of Standards, Nashington, D.C., 1972) p. 139. Boukamp, B.A. and Huggins, R.A., Phys. Left. 58A (1976) 231. v. A l p e n , U., T a l a t , G.H. and Rabenau, A . , A p p l . Phys. L e t t . 30 (1977) 621. Yah1, J . , S o l i d S t a t e Comm. 29 (1979) 485. O ' H a r e , P.A.G. and Johnson, G.K., J. Chem. Thermodyn. 7 (1975) 13; Yonco, R.M., V e l e c k i s , E., and M a r o n i , V.A., J. Nuct. Mat. 57 (1975) 317. H a r t w i g , P., Neppner, N., Nichelhaus, N., and Rabenau, A., Solid S t a t e Commun. 30 (1979) 601; Angew. Chem. I n t . Ed. 19 (1980) 74; H a r t w i 9 , P., Rabenau, A . , and Neppner, N., J. Less Common M e t a l s , in p r e s s . Sattlegger, H. and Hahn, H., N a t u r w i s s . 51 (1954) 534, Z. Anor9. Allg. Chem. 379 (1970) 293; S a t t l e g g e r , H., Dissertation, N ~ r z b u r g , N. Germany ( 1 9 6 4 ) . N . N . , Chem. ~ Eng. News, Nov. 24 (1980) 34. Weppner, W. and Huggins, R . A . , in: Fast Ion T r a n p o r t in S o l i d s , eds. V a s h i s h t a , P., Mundy, J.N. and Shenoy, G.K. (Elsevier North-Holland, New Y o r k , NY, 1979) 475, S o l i d S t a t e I o n i c s I (1980) 3. Chen, L-C, and Gang, M., p r i v . commun. Rude, K . , Hartwig, P., and Neppner, N., Rev. Chim. m i n 6 r . 17 (1980) 420. N e i s s , E., Z. Anorg. A119em. Chem. 341 (1965) 203. Pack, S . , Owens, B., and Wagner, J r . , J . B . , J. E l e c t r o c h e m . Soc. 127 (1980) 2177. Pou]sen, F . M . , S o l . St. I o n i c s 2 (1981) 53, H a r t w i g , P., Rabenau, A . , and Neppner, W., J. Less Common M e t a l s 78 (1981) 227. Jew, T. and Magnet, J r . , J . B . , J. Electrochem. Soc. 126 (1979) 163. S h a h i , K. and Magnet, J r . , J . B . , Electrochem. Soc. M e e t . , Boston, Mass., May 1979, Abstract No. 369. Wagner, Jr., J.B., Mat. Res. Bull. 15

(1980) 1691. [28] Shahi, K. and Nagner, Jr., J.B., 3rd Intl. Meet, Solid Electrolytes, Tokyo, Sept. 1980, A b s t r a c t No. C301. [ 2 9 ] t l a r t w i g , P., Rude, K., and Meppner, N., unpublished results. [30] B r u i n i n k , J., J. App]. Electrochem. 2 (1972) 239. [31] G l a s s e r , L . , Chem. Rev. 75 (1975) 21. [ 3 2 ] E r n s b e r g e r , F . M . , J. N o n - c r y s t a l l i n e Solids 38 8 39 (1980) 557. [33] P o l l o c k , J.M. and Sharan, M., J. Chem. Phys. 47 (1967) 4064. [34] Farrington, G.C. and Briant, J.L,, in: Fast Ion Transport in Solids, eds. Vashishta, P., Mundy, J.N., and Shenoy, G.K. (Elsevier North-Holland, New Y o r k , NY, 1979) p. 395. [ 3 5 ] T a k a h a s h i , T . , Tanase, S., Yamamoto, 0., Yamauchi, S., and Kabeya, H., Int. d. Hydrogen Energy 4 (1979) 327. [35] A l b e r t i , G., C a s c i o l a , M., C o s t a n t i n o , U., and R a d i , R, Gazz. Chim. I t . 109 (1979) 421. [ 3 7 ] K r e u e r , K . D . , Rabenau, A . , and i4eppner, N., S o l i d S t a t e I o n i c s , in p r e s s . [ 3 8 ] Nakamura, 0 . , Kodama, T . , Ogino, I., and M i y a k e , Y . , Chem. L e f t . (1979) 17. [ 3 9 ] U.S. P a t e n t 298,922 ( 1 9 7 2 ) . [40] S h i l t o n , M.G. and Howe, A . T . , Mat. Res. Bull. 12 (1977) 701; Howe, A.T. and S h i l t o n , M.G., J. S o l i d S t a t e Chem. 28 (1979) 345; C h i l d s , P . E . , flowe, A . T . , and S h i l t o n , M.G., J. Power Sources 3 (1978) 105. [ 4 1 ] Howe, A.T. and S h i l t o n , M.G., J. Solid S t a t e Chem. 34 (1980) 149. [ 4 2 ] S h i l t o n , M.G. and Howe, A . T . , i n : Fast Ion T r a n s p o r t in S o l i d s , eds. Vashishta, P., Mundy, J.N., and Shenoy, G.K. (Elsevier N o r t h - H o l l a n d , New Y o r k , NY, 1979) p. 727. [ 4 3 ] England, N . A . , Cross, M.G., Hamnett, A., Niseman, P . J . , and Goodenough, J . B . , Solid S t a t e I o n i c s 1 (1980) 231. [44] S h e f f i e l d , S.H. and Ho~e, A . T . , Mat. Res. Bull. 14 (1979) 929. [ 4 5 ] Neppner, N. and Huggins, R . A . , Ann. Rev. M a t e r . S c i . 8 (1978) 269. [ 4 6 ] Meppner, W., in: M a t e r i a l s f o r Advanced Batteries, eds. Murphy, D.W., Broadhead, J . , and S t e e l e , B.C.H. (Plenum, 1980) 269. [47] Heppner, N, J. S o l . S t . Chem. 20 (1977) 305. [48] Meppner, 14, E l e c t r o c h i m . A c t a 22 (1977) 721, [ 4 9 ] Neppner, N. and Huggins, R . A . , J. Electrochem. Soc. 124 (1977) 1569. [ 5 0 ] Wen, C . J . , Boukamp, B . A . , Huggins, R.A. and Meppner, W., J. Electrochem. Soc. 12B (1979) 2258. [ 5 1 ] Weppner, N., S o l i d S t a t e I o n i c s , i n p r e s s . [ 5 2 ] Ohachi, T . , T h e s i s , Doshisha U n i v . , Kyoto, Japan ( 1 9 7 4 ) . [ 5 3 ] Mrowec, S., D e f e c t s and D i f f u s i o n in S o l i d s , E l s e v i e r , Amsterdam, 1980. [ 5 4 ] Neppner, W. and Huggins, R.A., d. Solid S t a t e Chem. 22 (1977) 297. [ 5 5 ] [4en, C . J . , Pb.D. Thesis, Stanford University (1980). [ 5 6 ] R i c k e r t , H. and Neppner, N., Z. N a t u r f o r s c h 29a (1974) 1849.