Solid State Chemistry of Energy Conversion and Storage

12 The Sodium-Sulfur Battery:

Downloaded by UNIV OF CALIFORNIA SAN DIEGO on February 10, 2016 | http://pubs.acs.org Publication Date: June 1, 1977 | doi: 10.1021/ba-1977-0163.ch012

Problems and Promises S. A. WEINER Research Staff, Ford Motor Co., Dearborn, Mich. 48121

The current status of work on the sodium-sulfur battery is reviewed, with emphasis on the ceramic electrolyte and container and electrode materials for the sulfur electrode. The baseline studies for the cell testing program are run on cells constructed of carbon, glass, and β"-alumina and con taining no metal other than sodium. In sodium—sodium test cells ceramic life has exceeded 1000 A-h/cm one way. Sodium-sulfur cell life still remains short of sodium-sodium cell life. Separate cells designed to maximize energy and power density, respectively, were studied. The high energy cell #89 delivered 2.3 Wh/cm at 64% efficiency. The high power cell delivered 0.35 W/cm at 62% electrical efficiency and with long life. Cost studies indicate the ceramic to be the high cost item with a materials cost of 11.6 cents/cm . While problems still remain, there is no known fundamental obstacle that precludes the commercial development of the sodium—sulfur battery. 2

2

2

2

T P h e s o d i u m - s u l f u r b a t t e r y consists of t w o l i q u i d electrodes,

sodium

a n d sulfur, a n d a ceramic electrolyte membrane a l l o w i n g the trans p o r t of s o d i u m ions ( 1 ) . T h e s o d i u m electrode is w e l l c h a r a c t e r i z e d a n d does n o t present m a t e r i a l p r o b l e m s .

E x c e s s s o d i u m is u s e d to k e e p t h e

c e r a m i c e l e c t r o l y t e c o m p l e t e l y c o v e r e d at a l l t i m e s . T h e use of excess s o d i u m together w i t h a stainless steel s o d i u m c o n t a i n e r e l i m i n a t e s t h e need for a n electrical feed-through.

T h e / ^ " - a l u m i n a e l e c t r o l y t e consists

of N a 0 , A 1 0 , s t a b i l i z e d b y L i 0 .

T y p i c a l l y i t has a s t r e n g t h o n t h e

2

2

3

2

o r d e r of 20 k p s i a n d a r e s i s t i v i t y of 5 o h m - c m at 3 0 0 ° C . T h e o p e r a t i o n of t h e s u l f u r electrode is q u i t e c o m p l e x .

B e c a u s e ele

m e n t a l s u l f u r is a n e l e c t r o n i c i n s u l a t o r , g r a p h i t e felt is a d d e d to p r o v i d e 205

In Solid State Chemistry of Energy Conversion and Storage; Goodenough, John B., et al.; Advances in Chemistry; American Chemical Society: Washington, DC, 1977.

206

SOLID STATE

CHEMISTRY

a large area electrode. O n discharge f r o m s o d i u m a n d sulfur, the s o d i u m p o l y s u l f i d e f o r m e d is n o t s o l u b l e i n s u l f u r . T h u s t h e s u l f u r e l e c t r o d e contains t w o

l i q u i d phases t h r o u g h o u t s o m e 6 0 %

of

the

discharge.

B e y o n d t h i s p o i n t essentially n o e l e m e n t a l s u l f u r r e m a i n s , a n d a l l of t h e p o l y s u l f i d e s are m i s c i b l e , f o n n i n g one phase. t h r o u g h o u t its c o m p o s i t i o n a l r a n g e ( N a S 2

operate

B

T o k e e p this p h a s e l i q u i d

to N a S ) i t is necessary t o 2

3

above 2 7 0 ° C w i t h t y p i c a l operating temperatures falling

at


3 0 0 ° - 3 7 5 ° C . A s c h e m a t i c of a c e l l w i t h a c y l i n d r i c a l c e r a m i c e l e c t r o l y t e is s h o w n i n F i g u r e 1.

Figure 1.

Schematic of a sodium-sulfur

cell


12.

WEINER

The Sodium-Sulfur

207

Battery

T h e two major applications currently envisioned for the s o d i u m s u l f u r b a t t e r y are e l e c t r i c u t i l i t y l o a d l e v e l i n g a n d a u t o m o t i v e p r o p u l s i o n . F o r l o a d l e v e l i n g the s u l f u r electrode m u s t m e e t stringent e l e c t r i c a l effi c i e n c y r e q u i r e m e n t s w i t h less i m p o r t a n c e p l a c e d o n a c h i e v i n g h i g h u t i l i z a t i o n of reactants since w e i g h t a n d v o l u m e

are n o t as c r i t i c a l .

In

contrast, h i g h reactant u t i l i z a t i o n is m o r e i m p o r t a n t t h a n e v e n the o p e r a t i n g efficiency of the v e h i c u l a r b a t t e r y .

Furthermore, the battery for


a u t o m o t i v e p r o p u l s i o n m u s t h a v e a h i g h e r p o w e r d e n s i t y t h a n the b a t t e r y u s e d for l o a d l e v e l i n g . O u r p r o g r a m has t w o goals: the d e v e l o p m e n t a n efficient h i g h e n e r g y b a t t e r y a n d t h e d e v e l o p m e n t

of

of a l o w w e i g h t ,

h i g h power battery. I n o r d e r to c o m p a r e

current laboratory achievement w i t h overall

p r o g r a m goals, the goals of t h e p r o g r a m h a v e b e e n t r a n s l a t e d f r o m u n i t s of W / k g a n d W h / k g to W / c m

2

and W h / c m

2

w h e r e the u n i t of area is

t h e surface area of the / ? " - a l u m i n a c e r a m i c electrolyte.

T h e goals

are

g i v e n i n T a b l e I . T h e t r a n s l a t i o n f r o m u n i t s of w e i g h t to u n i t s of e l e c t r o l y t e area w a s necessary b e c a u s e t h e b u l k of t h e l a b o r a t o r y results w e r e o b t a i n e d u s i n g cells c o n s t r u c t e d m a i n l y f r o m c a r b o n a n d glass to a v o i d t h e effects of

corrosion

products

originating from metallic

electrode

containers or c u r r e n t collectors i n contact w i t h the s u l f u r / p o l y s u l f i d e melt. Table I.

C e l l Goals High Energy Cell

Variable E n e r g y density ( W h / c m ) 2

A v e r a g e power d e n s i t y ( W / c m ) 2

U t i l i z a t i o n of reagents (%) E l e c t r i c a l efficiency (%) Capacity (A-h/cm ) D i s c h a r g e t i m e (h) Durability (A-h/cm ) C y c l e life 2

2

High

2 (265 W h / k g ) 0.2-0.4 (55-110 W / k g ) 50 65 1.0 5-10 2500 2500

° The goal for peak power density is 0.7 W / c m

2

or 280

Power Cell

0.15 (60 W h / k g ) 0.35 (140 W / k g ) 25 70 0.1 0.4 100 1000

β

W/kg.

U l t i m a t e l y the use of the s o d i u m - s u l f u r b a t t e r y w i l l d e p e n d o n its a b i l i t y to c o m p e t e e c o n o m i c a l l y w i t h t h e alternate means a v a i l a b l e f o r l o a d l e v e l i n g a n d a u t o m o t i v e p r o p u l s i o n . P r e s e n t l y t h e l i m i t s of c e l l d u r a b i l i t y a n d cost are set b y the ^ " - a l u m i n a electrolyte.

both

Accord

i n g l y this p a p e r emphasizes the c e r a m i c electrolyte.


208

SOLID STATE C H E M I S T R Y

Results

of

Cell

Testing

F o r c e r a m i c e v a l u a t i o n s o d i u m - s o d i u m test cells

(Figure 2)

c o n s t r u c t e d a n d r u n at r e l a t i v e l y h i g h c u r r e n t densities of A/cm

2

so that s u b s t a n t i a l i o n i c currents c a n b e

passed

are

0.75-1.25

through

the

e l e c t r o l y t e i n a reasonable p e r i o d of t i m e . D u r i n g t e s t i n g c e l l p o l a r i t i e s are r e v e r s e d p e r i o d i c a l l y . T h i s subjects e a c h surface of the c e r a m i c e l e c


t r o l y t e to b o t h a c h a r g i n g o p e r a t i o n i n w h i c h s o d i u m ions are c o n v e r t e d to s o d i u m m e t a l a n d a d i s c h a r g e o p e r a t i o n i n w h i c h s o d i u m m e t a l is c o n v e r t e d to s o d i u m ions. T h e c h a r a c t e r i z a t i o n of i n d i v i d u a l s o d i u m - s u l f u r cells i n v o l v e s t w o distinct testing programs—endurance (2).

testing a n d p e r f o r m a n c e

testing

T h e p u r p o s e of the e n d u r a n c e test p r o g r a m is to e s t a b l i s h the d u r a

b i l i t y of the c e l l a n d its c o m p o n e n t s b y m o n i t o r i n g t h e e l e c t r i c a l p e r f o r m a n c e at fixed o p e r a t i n g c o n d i t i o n s as a f u n c t i o n of t i m e a n d c o n d i t i o n s of use. I n a d d i t i o n to the t i m e to f a i l u r e , the rates of d e t e r i o r a t i o n of c e l l performance

(e.g., c a p a c i t y , i n t e r n a l resistance) are o b t a i n e d .

T h e goal

of p e r f o r m a n c e t e s t i n g is the c h a r a c t e r i z a t i o n of the e l e c t r i c a l b e h a v i o r of a c e l l at v a r i o u s o p e r a t i n g c o n d i t i o n s (e.g., t e m p e r a t u r e , charge, a n d d i s c h a r g e rates) d u r i n g the e a r l y stages of c e l l l i f e .

S p e c i f i c a l l y these

tests i n v o l v e d e t e r m i n i n g t h e c a p a c i t y vs. rate of c h a r g e a n d d i s c h a r g e

Figure 2.

Schematic of a sodium-sodium

cell


12.

WEINER

The Sodium-Sulfur

209

Battery

a n d t h e m e a s u r e m e n t of o h r n i c a n d c o n c e n t r a t i o n p o l a r i z a t i o n s as a f u n c t i o n of t e m p e r a t u r e , rate, a n d state of c h a r g e of t h e c e l l . A t t h e c o n c l u s i o n of t h e e l e c t r i c a l test p r o g r a m e a c h c e l l is d i s s e c t e d a n d e x a m i n e d visually.

Cell

components

are prepared

f o r f u r t h e r e x a m i n a t i o n as

appropriate.


Sodium—Sodium

Cells

O n e of t h e m a j o r uses of t h e s o d i u m - s o d i u m c e l l test p r o g r a m h a s b e e n t o evaluate different c e r a m i c c o m p o s i t i o n s .

S e v e r a l of t h e c o m p o

sitions tested p a s s e d over 1000 A - h / c m i n o n e d i r e c t i o n , w h e r e a s others 2

s h o w e d clear e v i d e n c e of e l e c t r o l y t i c d e g r a d a t i o n . T h e m a j o r f a c t o r i n t h e e l e c t r o l y t i c d e g r a d a t i o n of β''-alumina w h e n s u b j e c t e d to h i g h c u r r e n t densities i n a c h a r g i n g m o d e is t h e L i 0 c o n c e n t r a t i o n . W h i l e t h e N a 0 2

2

content m a y v a r y w i t h i n certain limits, ^ " - a l u m i n a compositions

con

t a i n i n g L i 0 ^ 0 . 8 % a p p e a r t o b e s i g n i f i c a n t l y m o r e resistant to e l e c t r o 2

l y t i c d e g r a d a t i o n a t h i g h c u r r e n t densities t h a n / ^ ' ' - a l u m i n a c o m p o s i t i o n s containing L i

2

^ 0.9%.

A s a f u r t h e r result of this s t u d y t h e c o m p o s i t i o n 9 . 0 % N a O / 0 . 8 % 2

Li 0 2

is b e i n g tested i n s o d i u m - s u l f u r cells.

C e l l s 1723-1 a n d 1723-2

e a c h passed over 1000 A - h / c m u n d i r e c t i o n a l l y w i t h o u t d e t e r i o r a t i o n at 2

a c u r r e n t d e n s i t y of 1.25 A / c m . T h e r e s i s t i v i t y of t h e m a t e r i a l ( 5 . 3 Ω-cm 2

at 3 0 0 ° C ) is c o m p a r a b l e w i t h t h a t o f t h e 8 . 7 % N a O / 0 . 7 % L i 0 p r e v i 2

2

o u s l y u s e d (5.0 Ω-cm at 3 0 0 ° C ) , w h i l e its s t r e n g t h is greater (19,000 p s i vs. 16,000 p s i ) . F u r t h e r m o r e , ^ " - a l u m i n a of t h e 9 . 0 % N a O / 0 . 8 % 2

Li 0 2

c o m p o s i t i o n is easier to process t h a n / 3 " - a l u m i n a of t h e 8 . 7 % N a O / 0 . 7 % 2

Li 0 2

composition.

C o m p a r i s o n of t h e p e r f o r m a n c e i n N a - N a cells of

c e r a m i c of these t w o c o m p o s i t i o n s is g i v e n i n T a b l e I I . T e s t i n g of cells 1266-1, 1266-2, 1266-3, a n d 1487-1 w a s d i s c o n t i n u e d b e c a u s e of f a i l u r e of t h e outer glass e n v e l o p e . Table II.

Cell Number 1266-1 1266-2 1266-3 1578-1 1269-3 1723-1 1723-2

T e s t i n g of cells 1269-3,

Summary of D a t a from H i g h C u r r e n t Density Na—Na Test Cells

Current Density (A/cm ) 2

0.75 0.75 0.75 1.00 1.25 1.25 1.25

Composition

T

Approx.

Specific Capacity

™ ° Test

U-h/cm») One

i

% Na 0

% Li 0 2

(Mo)

8.7 8.7 8.7 8.7 8.7 9.0 9.0

0.7 0.7 0.7 0.7 0.7 0.8 0.8

1.3 6 1.5 1.9 1.3 2.1 3.2

2

n

Direction 377 1512 378 636 525 1155 1575


210

SOLID S T A T E

CHEMISTRY

1723-1, a n d 1723-2 w a s d i s c o n t i n u e d b e c a u s e of m a l f u n c t i o n of the c e l l test c o n t r o l l e r . A f t e r c e l l t e r r n i n a t i o n m o s t of the c e r a m i c

membranes

w e r e e x a m i n e d b y a v a r i e t y of m e t h o d s i n c l u d i n g l i g h t m i c r o s c o p y , s c a n n i n g electron microscopy ( S E M ) , x-ray diffraction, a n d x-ray

fluorescence.

O n l y t h e c e r a m i c f r o m c e l l 1578-1 w a s f o u n d to b e c r a c k e d . S o m e a n o m a lies w e r e o b s e r v e d , h o w e v e r , i n t h e e x a m i n a t i o n of other ceramics.

The

p r e s e n c e of Κ a n d C I w a s f o u n d b y S E M i n c r a c k e d areas of t u b e 1578-1, Downloaded by UNIV OF CALIFORNIA SAN DIEGO on February 10, 2016 | http://pubs.acs.org Publication Date: June 1, 1977 | doi: 10.1021/ba-1977-0163.ch012

b u t n o t i n u n d a m a g e d sections.

T h e r e w e r e s e v e r a l i n d i c a t i o n s of s e a l

d a m a g e that c o u l d not p r o p e r l y b e c a l l e d seal f a i l u r e s i n t h e f o u r cells b u i l t w i t h c e r a m i c of c o m p o s i t i o n 9 . 0 % N a O / 0 . 8 % L i 0 . I n these cases 2

2

t h e «-Al 0 -glass-)S' -alumina seals w e r e b a d l y d i s c o l o r e d or p i t t e d b u t 2

/

3

not broken. T y p i c a l l y c e r a m i c electrolytes t h a t h a v e f a i l e d o n h i g h c u r r e n t test i n g e x h i b i t m u l t i p l e c r a c k patterns a n d a p p e a r w e a k e n e d e v e n i n areas w h e r e there are n o v i s i b l e c r a c k patterns. T h e r e h a v e also b e e n i n d i c a tions of f a i l u r e c a u s e d b y d e t e r i o r a t i o n of t h e / ? " - a l u m i n a i n the v i c i n i t y of the seal. I n one case cracks w e r e f o r m e d i n a / ? " - a l u m i n a t u b e adjacent t o t h e /3"-glass-« seal b u t not i n o t h e r p o r t i o n s of the t u b e . T h i s r a i s e d t h e p o s s i b i l i t y of stress c o r r o s i o n c a u s e d b y the seal. T o test this p o s s i b i l i t y p e r p e n d i c u l a r p a i r s of strain gauges w e r e m o u n t e d o n ^ ' ' - a l u m i n a t u b e s at distances of 0.5 c m a n d 2 c m f r o m p r e v i o u s l y f o r m e d β''-glass-a seals. A f t e r i n i t i a l r e a d i n g s w e r e t a k e n , the tubes w e r e c u t w i t h a l o w - s p e e d d i a m o n d s a w at p o i n t s b e t w e e n t h e seals a n d t h e s t r a i n gauges

closest

to t h e m . T h e c h a n g e i n s t r a i n w a s t h e n m e a s u r e d a n d the stress c a l c u lated u s i n g the expression: Ε

where G

=

Gy

=

a x i a l stress i n p s i

Ε

=

Youngs modulus «

«ν

= strain i n p p m , circumferential — strain i n p p m , axial

V

=- P o i s s o n s r a t i o «

x

c i r c u m f e r e n t i a l stress i n p s i 28.04 X 1 0 p s i 8

0.259

T h e v a l u e s of Ε a n d ν w e r e d e t e r m i n e d f o r t h e c o m p o s i t i o n

9.0%

N a O / 0 . 8 % L i 0 . T h e v a l u e of Ε differs f r o m t h a t r e p o r t e d f o r t h e c o m 2

2

position 8.7%

N a / 0 . 7 % L i 0 , i.e., 18 X 2

2

10

e

psi (3).

T h i s d e g r e e of


12.

WEINER

The Sodium-Sulfur

211

Battery

v a r i a t i o n is n o t u n r e a s o n a b l e , h o w e v e r , as the v a l u e of Ε is i n f l u e n c e d b y s a m p l e p o r o s i t y a n d does n o t affect the c o n c l u s i o n s i g n i f i c a n t l y . A l l tubes w e r e s e a l e d to α - Α 1 0 2

3

tubes w i t h s e a l i n g glass i n t h e

c u s t o m a r y m a n n e r . T u b e s of the f o l l o w i n g c o m p o s i t i o n s w e r e e x a m i n e d : (a)

9.5%

N a - N a cell.

Na O/0.9% Li O. 2

z

T h e tube h a d been degraded i n a

C r a c k s w e r e o b s e r v e d n e a r the seal, b u t n o cracks w e r e


f o u n d 2 c m or f a r t h e r a w a y f r o m t h e seal. (b)

9.5% N a O / 0 . 9 % L i 0 .

(c)

9 . 5 % N a O / 0 . 8 % L i 0 . T h e t u b e h a d b e e n s u b j e c t e d to c u r r e n t

2

2

2

T h e tube was new.

2

of 1.25 A / c m i n a N a - N a c e l l . It w a s u n d a m a g e d . 2

(d)

8.7% N a O / 0 . 7 % L i 0 . T h e tube was freshly prepared. 2

2

T h e s e d a t a are s u m m a r i z e d i n T a b l e I I I . T h e r e is a n a p p a r e n t c o r relation between strain a n d ceramic degradation, a n d it w o u l d be tempt i n g to ascribe the o b s e r v e d

c e r a m i c d e g r a d a t i o n t o stress

corrosion.

H o w e v e r , the stresses c a l c u l a t e d f r o m t h e m e a s u r e d strains n o r m a l l y w o u l d n o t b e e x p e c t e d to c o n t r i b u t e s i g n i f i c a n t l y to stress c o r r o s i o n . M o r e recent w o r k b y A . V i r k a r , U n i v e r s i t y of U t a h , has s h o w n t h a t /?"a l u m i n a is subject to stress c o r r o s i o n i n l i q u i d s o d i u m . I n these e x p e r i m e n t s , the K - V d i a g r a m w a s generated.

T h e stress c o r r o s i o n effects are

s m a l l a n d are s o m e w h a t a f u n c t i o n of c o m p o s i t i o n of c e r a m i c . M o r e r e c e n t l y the N a - N a test c e l l p r o g r a m has b e e n u s e d to e v a l u a t e t h e c e r a m i c e l e c t r o l y t e p r o d u c e d at t h e U n i v e r s i t y of U t a h . O f t h e f o u r

Table III.

Stress and Strain on ^ " - A l u m i n a Tubes N e a r Seals % Composition

Na 0/Li O 2

t

9.5/0.9

9.5/0.9

9.6/0.8

8.7/0.7

N a - N a cell degraded n e a r seal

Fresh

N a - N a cell undamaged

Fresh

0.5 c m f r o m seal : ty ( p p m ) G (psi)

22 856

28 1075

4 159

-13 -157

0.5 c m f r o m seal : t (ppm) G (psi)

25 922

30 1119

5 181

30 800

2 c m f r o m seal : €y ( p p m ) G„ (psi)

2 146

13 523

0 31

8 263

2 cm from seal: t (ppm) G (psi)

11 346

17 612

4 120

3 152

History

y

x

x

m

x

e

* Negative values indicate compression.


212

SOLID S T A T E C H E M I S T R Y

cens c o n t a i n i n g U t a h - p r o d u c e d ^ " - a l u m i n a c e r a m i c of c o m p o s i t i o n

9.0%

Na O/0.8%

way,

2

L i 0 one has f a i l e d after p a s s i n g 1415 A - h / c m 2

2

one

a n d t h e others are s t i l l i n o p e r a t i o n . P r e s e n t p l a n s c a l l f o r u s i n g N a - N a cells to test the effects of process a n d r a w m a t e r i a l changes m a d e b y t h e U n i v e r s i t y of U t a h . A l t h o u g h N a - N a c e l l t e s t i n g r e m a i n s a u s e f u l t o o l f o r c e r a m i c e v a l u a t i o n , w e h a v e f o u n d t h a t the c r a c k patterns e x h i b i t e d b y ^ " - a l u m i n a electrolytes after N a - N a t e s t i n g are different f r o m those Downloaded by UNIV OF CALIFORNIA SAN DIEGO on February 10, 2016 | http://pubs.acs.org Publication Date: June 1, 1977 | doi: 10.1021/ba-1977-0163.ch012

observed on N a - S cell testing. F u r t h e r m o r e , w h i l e w e have established o u r p r e f e r r e d c o m p o s i t i o n o n the basis of N a - N a c e l l tests, w e h a v e n o t established w h y one composition behaves differently f r o m another similar c o m p o s i t i o n n o r w h y a n d b y w h a t m e c h a n i s m ( s ) / T ' - a l u m i n a electrolytes degrade. Sodium-Sulfur

Cells

C e l l d e s i g n i n v o l v e s c r e a t i n g a n o v e r a l l c e l l c o n f i g u r a t i o n w h i c h is c o m p a t i b l e w i t h the / T ' - a l u m i n a e l e c t r o l y t e , seals, c o n t a i n e r m a t e r i a l s , a n d assembly procedures. sistent w i t h

(a)

T h e c e l l c o m p o n e n t s m u s t b e s i z e d to b e c o n

the e l e c t r i c a l r e q u i r e m e n t s of

capacity, power,

and

efficiency, a n d ( b ) t h e m e c h a n i c a l r e q u i r e m e n t s of s t r e n g t h , r u g g e d n e s s , a n d s i m p l i c i t y of a s s e m b l y set b y o p e r a t i o n a l a n d f a b r i c a t i o n l o a d s . T h e s o d i u m - s u l f u r c e l l t e s t i n g p r o g r a m is d i r e c t e d t o w a r d i m p r o v i n g t h e e l e c t r i c a l p e r f o r m a n c e of cells, d e v e l o p i n g a n u n d e r s t a n d i n g of those factors w h i c h c o n t r o l c e l l p e r f o r m a n c e , e s t a b l i s h i n g c e l l d u r a b i l i t y , a n d i d e n t i f y i n g factors w h i c h l i m i t c e l l l i f e . W h i l e the p r e s e n t l i m i t to c e l l l i f e f o r those cells c o n s t r u c t e d m a i n l y of c a r b o n a n d glass is set b y t h e d u r a b i l i t y of / ? " - a l u m i n a electrolytes, t h e f a c t that cells b u i l t u s i n g o t h e r

TEST CELL

CROSS SECTION

Figure 3.

Schematic of Cell 89


12.

WEINER

The Sodium-Sulfur

213

Battery


CELL CAPACITY-Ah

SPECIFIC CAPACITY-Ah-cm"

Figure 4.

Performance

2

of Cell 89

m a t e r i a l s of c o n s t r u c t i o n h a v e shorter lives u n d e r l i n e s t h e i m p o r t a n c e of factors s u c h as t h e presence of m e t a l ions w h o s e i n f l u e n c e o n / ? " - a l u m i n a c e r a m i c e l e c t r o l y t e d u r a b i l i t y is n o t yet u n d e r s t o o d . A c e l l incorporating a shaped graphite felt electrode designed for v e r y h i g h e n e r g y storage ( F i g u r e 3 ) gave l o w i n t e r n a l losses a n d h i g h u t i l i z a t i o n of reactants ( F i g u r e 4 ) .

I n attempts to o b t a i n f u r t h e r i m

p r o v e m e n t s i n c e l l o p e r a t i o n at t e m p e r a t u r e s of a b o u t 3 5 0 ° C a n d to a i d i n d e v e l o p i n g a n u n d e r s t a n d i n g of the effects of electrode shape a series of three cells, d e s i g n a t e d cells 93, 94, a n d 95 i n F i g u r e 5, w a s c o n s t r u c t e d to c o m p a r e the effect of o p e n v o l u m e s a n d the l o c a t i o n of the

open

c h a n n e l s r e l a t i v e to t h e c e r a m i c surface. T h e results o b t a i n e d w i t h c e l l 94 are s h o w n i n F i g u r e 6. T h i s c e l l shows g o o d d i s c h a r g e

performance

a n d f a i r c h a r g e a b i l i t y — u t i l i z i n g a s i z e a b l e f r a c t i o n of t h e reactants a n d o p e r a t i n g m o d e r a t e l y d e e p i n t o the t w o p h a s e r e g i o n of the N a - S p h a s e d i a g r a m . T h e results o b t a i n e d w i t h c e l l 93 are s h o w n i n F i g u r e 7. I t is c l e a r t h a t the c e l l w i t h u n c o v e r e d c e r a m i c is c a p a b l e of r e c h a r g i n g m u c h m o r e c o m p l e t e l y , r e t u r n i n g to n e a r l y p u r e s u l f u r , a l t h o u g h w i t h a s t e a d i l y i n c r e a s i n g p o l a r i z a t i o n as c h a r g i n g c o n t i n u e s .

T h e losses for this c e l l

are a b o u t d o u b l e those i n c e l l 94. T h e s e results c a n b e i n t e r p r e t e d i n terms of mass transfer b y c o n v e c t i o n , w i c k i n g , a n d d i f f u s i o n . C e l l 94 w a s c a p a b l e of d i s c h a r g i n g w e l l because the reaction product—polysulfldes—formed i n the thin r i n g was a b l e to diffuse to t h e e d g e of the f e l t a n d r e a c t or c o n v e c t a w a y . L a r g e scale c o n v e c t i o n i n t h e o p e n channels b r o u g h t s u l f u r u p t o t h e f e l t t o s u p p l y i t to t h e r e a c t i n g z o n e .

B e c a u s e a l l the / T ' - a l u m i n a c e r a m i c w a s

u t i l i z e d a n d the r e a c t i o n zone w a s close to the c e r a m i c , t h e i n t e r n a l losses were low. O n charge, however, the sodium pentasulfide was prevented f r o m r e a c h i n g the c e r a m i c at a sufficient r a t e b e c a u s e t h e g r a p h i t e

fibers



214


CELL DESIGNEZ" Figure

5.

Schematic of Cells

93-95

are w e t t e d better b y s u l f u r . T h e charge is l i m i t e d t h e r e b y to a s m a l l p o r t i o n of t h e t w o - p h a s e r e g i o n . F o r c e l l 93 this i n t e r p r e t a t i o n w o u l d suggest that o n d i s c h a r g e , t h e losses w o u l d b e h i g h e r b e c a u s e o n l y a b o u t h a l f of t h e c e r a m i c is f u l l y active. T h e p o r t i o n of t h e c e r a m i c area n o t c o v e r e d b y felt is i n a c t i v e , since i t is c o v e r e d b y s u l f u r i n i t i a l l y .

A s p o l y s u l f i d e is f o r m e d

during

d i s c h a r g e a n d fills t h e o p e n channels, t h e p o r t i o n of c e r a m i c c o v e r e d b y

100 m A / c m

5

10

2

15

S T A T E OF C H A R G E - Ah

Figure

6.

Performance

of Cell 94


12.

WEINER

The

Sodium-Sulfur

215

Battery

p o l y s u l f i d e b e c o m e s a c t i v e . I n this r e g i o n t h e i o n i c p a t h extends t h r o u g h t h e c e r a m i c a n d t h r o u g h the p o l y s u l f i d e m e l t i n the o p e n c h a n n e l a n d terminates o n t h e g r a p h i t e fiber surfaces o n the edges of the s h a p e d felt. T h e c o n t r i b u t i o n of this c o n d u c t i o n p a t h is p r o p o r t i o n a l to t h e h e i g h t of the p o l y s u l f i d e i n t h e o p e n channels a n d is p r o b a b l y

a small factor

t h r o u g h o u t t h e d i s c h a r g e c y c l e , a l t h o u g h i t is r e s p o n s i b l e f o r t h e i m p r o v e m e n t i n c h a r g e a b i l i t y of the c e l l . A s w i t h m o s t cells, there are n o Downloaded by UNIV OF CALIFORNIA SAN DIEGO on February 10, 2016 | http://pubs.acs.org Publication Date: June 1, 1977 | doi: 10.1021/ba-1977-0163.ch012

p r o b l e m s associated w i t h c h a r g i n g t h r o u g h the one-phase r e g i o n b e c a u s e of d i f f u s i o n a n d c h e m i c a l reactions. O n c e pentasulfide has f o r m e d , h o w ever, t h e p o r t i o n of c e r a m i c c o v e r e d b y felt is e x p e c t e d to b e c o m e i n a c t i v e b e c a u s e of s u l f u r film f o r m a t i o n w h i c h b l o c k s the felt s u r f a c e adjacent to the c e r a m i c . T h e o n l y r e m a i n i n g i o n i c p a t h is t h r o u g h the u n c o v e r e d c e r a m i c surface. W e b e l i e v e t h a t the g r a p h i t e fiber surfaces at the e d g e

CAPACITY-Ah Figure 7.

Performance of Cell 93

of the felt r e m a i n a c t i v e b e c a u s e these surfaces are e x p o s e d to a f r e e l y c o n v e c t i n g l i q u i d p h a s e that c a n r e m o v e t h e s u l f u r film b y

convection.

A c c o r d i n g to this m o d e l w e w o u l d expect the c e l l c o n d u c t a n c e to decrease i n p r o p o r t i o n to t h e r e m a i n i n g h e i g h t of p o l y s u l f i d e i n the o p e n regions, i n q u a l i t a t i v e agreement w i t h d a t a f r o m c e l l 93. A c e l l d e s i g n e d for a m o r e q a u n t i t a t i v e test of this c o n c e p t is s h o w n i n F i g u r e 8. T h e i n n e r h o l e i n the e l e c t r o d e w a s e n l a r g e d to p r o v i d e a 1-mm g a p b e t w e e n the c e r a m i c surface a n d t h e electrode. d i s c h a r g e characteristics of this c e l l ( c e l l 102)

The

charge/

are g i v e n i n F i g u r e 9.

T h e results c a n b e i n t e r p r e t e d i n terms of changes i n g e o m e t r y

associated

w i t h the v a r y i n g l e v e l of pentasulfide as t h e state of c h a r g e is v a r i e d . I f p h a s e s e p a r a t i o n o c c u r s r a p i d l y , t h e a r e a of c e r a m i c c o v e r e d b y i o n i c a l l y c o n d u c t i n g p o l y s u l f i d e varies i n p r o p o r t i o n to t h e a m o u n t


the of

216

SOLID S T A T E

polysulfide present in the cell.

CHEMISTRY

T o a first approximation the cell con-

ductance should vary linearly with the state of charge as shown in Figure 10. ALPHA ALUMINA


GRAPHITE ROD

TEST CELL

CROSS SECTION Figure 8.

Examination

of

Sodium—Sulfur

Schematic of Cell 102

Cells

after

Testing

After high-temperature testing was completed, cell 89 was returned to 3 0 0 ° C . Its performance had degraded significantly. The charge cycle appeared to have become limited to the single-phase region even at low rates of charge. The cell was taken out of service after three months of operation and examined.

T h e major finding was that the "cemented"

felt arms had become detached from an eroded graphite current collector, thus reducing the electrical contact between the current collector and the electrode to that provided by a few pressure contacts.

Under this


12.

WEINER

The Sodium-Sulfur


J

I Ο

c

217

Battery

= 5 0 , 100, 150, 2 0 0 , 3 0 0 m A / c m

I 10

Figure 9.

2

I I 20 30 STATE OF CHARGE-Ah Performance

Ι 40

of Cell 102

c o n d i t i o n , o n l y t h e i n n e r w a l l of the c y l i n d r i c a l c u r r e n t c o l l e c t o r r e m a i n s a c t i v e as t h e electrode.

T h e c e r a m i c e l e c t r o l y t e w a s f o u n d to b e i n t a c t .

E x a m i n a t i o n of f r a c t u r e surfaces u s i n g s c a n n i n g e l e c t r o n m i c r o s c o p y d i d n o t r e v e a l a n y signs of d e g r a d a t i o n .

Figure 10.

Plot of cell conductance vs. state of charge


218

SOLID STATE

CHEMISTRY

T h e p e r f o r m a n c e of c e l l 93 d e t e r i o r a t e d s l o w l y . E x a m i n a t i o n of the c e l l after its f a i l u r e s h o w e d t h a t t h e " c e m e n t e d " g r a p h i t e f e l t slabs h a d b e c o m e d e t a c h e d , as h a d o c c u r r e d i n c e l l 89. C e l l 94 f a i l e d b e f o r e extensive e l e c t r i c a l t e s t i n g c o u l d b e

accom

p l i s h e d . O n l y t h e i n i t i a l c h a r g e / d i s c h a r g e characteristics w e r e o b t a i n e d . U n e x p e c t e d l y , c e l l 95 also c h a r g e d f a r i n t o the t w o - p h a s e r e g i o n , c o n t r a r y to a l l p r e v i o u s results o n s u c h cells h a v i n g t h i c k f u l l r i n g electrodes. Downloaded by UNIV OF CALIFORNIA SAN DIEGO on February 10, 2016 | http://pubs.acs.org Publication Date: June 1, 1977 | doi: 10.1021/ba-1977-0163.ch012

T h e c e l l b e c a m e n o n - c o u l o m b i c , h o w e v e r , b e f o r e its c h a r g e / d i s c h a r g e characteristics c o u l d b e e s t a b l i s h e d f u l l y . C e r a m i c tubes w e r e r e m o v e d f r o m 93 a n d 94 a n d , after c l e a n i n g , w e r e c u t i n t o segments. W h e n feasible, r i n g s w e r e c u t f r o m u n d a m a g e d p o r t i o n s of the t u b e for d i a m e t r i c a l s t r e n g t h tests, m i c r o s t r u c t u r e s w e r e d e t e r m i n e d , a n d surfaces w e r e a n a l y z e d b y s c a n n i n g e l e c t r o n m i c r o s c o p y ( S E M ) . I n selected cases e l e c t r o n m i c r o p r o b e , A u g e r , a n d x - r a y c e n c e w e r e also u s e d .

I n a d d i t i o n , c e r a m i c tubes also w e r e

fluores

removed

f r o m cells Ε 5, Ε 16, a n d Ε 23. T h e s e cells w e r e b u i l t w i t h a n e l e c t r o d e shape s i m i l a r to c e l l 95 (see

F i g u r e s 5 a n d 11) a n d u s e d o n l y c a r b o n

a n d glass m a t e r i a l s of c o n s t r u c t i o n . C e l l s Ε 5 a n d Ε 16 h a d b e e n c y c l e d s o m e 6000 a n d 2200 times r e s p e c t i v e l y i n t h e single-phase r e g i o n .

Cell

Ε 5 h a d passed 925 A - h / c m of s o d i u m i o n one w a y p r i o r to b e i n g t e r m i 2

n a t e d w h i l e s t i l l f u n c t i o n i n g p r o p e r l y . C e l l s 89, 9 3 - 9 5 , Ε 16, a n d Ε 23 u s e d c e r a m i c of c o m p o s i t i o n 8 . 7 %

Na O/0.7% Li 0. 2

2

C e l l Ε 5 used

c e r a m i c of c o m p o s i t i o n 9 . 2 5 % N a O / 0 . 2 5 % L i 0 . 2

2

GRAPHITE THREAD PYREX GRAPHITE

TUBE ALPHA ALUMINA

GRAPHITE CEMENT

r=l

MACHINED GRAPHITE ROD

CONDUCTIVE CERAMIC

GRAPHITE FELT PYREX CONTAINER

TEST CELL CELL Figure 11.

DESIGN I

Schematic of "metal-free' cell 9



12.

WEINER

Figure 12.

The Sodium-Sulfur

219

Battery

SEM scan of outside surface of ceramic from Cell Ε 23

T h e ^ " - a l u m i n a e l e c t r o l y t e f r o m c e l l Ε 23 was u n d a m a g e d , a n d n o i m p u r i t i e s w e r e f o u n d o n e i t h e r t h e i n n e r surface ( w h i c h h a d b e e n i n contact w i t h N a ) or the outer surface ( w h i c h h a d b e e n i n contact w i t h s u l f u r ) . D i a m e t r a l tests i n d i c a t e d n o d e t e r i o r a t i o n i n s t r e n g t h . T h i s s a m p l e w a s u s e d as a s t a n d a r d , a n d s u b s e q u e n t r e f e r e n c e to c o n t a m i n a t i o n or i m p u r i t y levels are m a d e r e l a t i v e to Ε 23 ( F i g u r e 1 2 ) .

T h i s reduces

the p r o b a b i l i t y of m i s i n t e r p r e t i n g t h e p r e s e n c e of v e r y l o w l e v e l i m p u r i ties r e s u l t i n g f r o m n o r m a l c e l l c o n s t r u c t i o n . T h e a p p e a r a n c e of

tubes

f r o m cells Ε 5, Ε 16, 93, a n d 94 w a s q u i t e different f r o m that of a t y p i c a l c e r a m i c d e g r a d e d i n a N a - N a c e l l . T u b e s f r o m cells Ε 5, 93, a n d 94 d i s p l a y e d a s i n g l e l o n g c r a c k , w i t h s o m e b r a n c h i n g i n t h e l o w e r p o r t i o n of the t u b e . T h e t u b e f r o m c e l l Ε 16 d i v i d e d i n t o t w o parts b y a u n i f o r m c i r c u l a r c r a c k i n the u p p e r p o r t i o n of the t u b e . T h e r e w a s s o m e e r o s i o n at the edges of t h e c r a c k s , b u t this w a s f o u n d o n l y o n t h e outer surfaces. T h e erosion was probably caused w h e n the crack f o r m e d a n d s o d i u m c a m e i n t o e x p l o s i v e contact w i t h s u l f u r . T h e areas a w a y f r o m the c r a c k a p p e a r e d u n d a m a g e d , a n d d i a m e t r a l s t r e n g t h tests i n d i c a t e d n o loss of s t r e n g t h f o r tubes Ε 16, 93, a n d 94. D e g r a d a t i o n is u s u a l l y m a n i f e s t e d i n N a - N a cells as m u l t i p l e u n c o n n e c t e d c r a c k s .


220


T h e S E M t e c h n i q u e s u s e d for most of the r e p o r t e d surface analysis i n v o l v e s the analysis of p o i n t s o n a surface. T h i s raises t h e p o s s i b i l i t y of a n y one p o i n t b e i n g a t y p i c a l b e c a u s e of r a n d o m c o n t a m i n a t i o n . T h e r e fore, m a n y points w e r e a n a l y z e d for e a c h s a m p l e . S o m e t y p i c a l d a t a are s h o w n i n F i g u r e s 1 2 - 1 5 . C e l l Ε 5 h a d b e e n i n service for 15 m o n t h s p r i o r to f a i l u r e . A n a l y s i s of b o t h i n n e r a n d outer surfaces u s i n g S E M i n d i c a t e d s m a l l b u t r e a l a m o u n t s of p o t a s s i u m . Cross-sections 25/x, f r o m t h e outer Downloaded by UNIV OF CALIFORNIA SAN DIEGO on February 10, 2016 | http://pubs.acs.org Publication Date: June 1, 1977 | doi: 10.1021/ba-1977-0163.ch012

surface, h o w e v e r , h a d p o t a s s i u m levels 2 5 % h i g h e r t h a n t h a t f o u n d at t h e other p o i n t s .

Figure 13.

SEM scan of outside surface of ceramic from Cell 93

T h e m a j o r i m p u r i t y i n a l l of t h e d e g r a d e d samples w a s p o t a s s i u m . C a l c i u m w a s often present w i t h t h e p o t a s s i u m b u t a l w a y s at l o w e r levels. C a l c i u m w a s n e v e r f o u n d alone.

T r a c e s of i r o n , s i l i c o n , a n d c h l o r i n e

w e r e also f o u n d i n s e v e r a l cases. T h e p o t a s s i u m i m p u r i t i e s w e r e f o u n d o n the o u t e r surfaces m o r e f r e q u e n t l y t h a n o n t h e i n n e r surfaces.

The

p o t a s s i u m levels f o u n d o n o u t e r surfaces w e r e o f t e n h i g h e r , b u t n e v e r l o w e r , t h a n t h e p o t a s s i u m levels f o u n d o n i n n e r surfaces.

Apparently

p o t a s s i u m is n o t p r e s e n t i n t h e o r i g i n a l c e r a m i c a n d diffuses i n t o t h e ceramic d u r i n g cell operation.

A t this stage i t w o u l d b e i m p r o p e r to

c o n c l u d e t h a t p o t a s s i u m c a u s e d the c e r a m i c d e g r a d a t i o n , b u t t h e r e are e n o u g h i n d i c a t i o n s to w a r r a n t f u r t h e r s t u d y .

M o r e recently, some pre-



WEINER

The Sodium-Sulfur

Battery

Figure 14.

SEM scan of outside surface of ceramic from Cell 94

Figure 15.

SEM scan of inside surface of ceramic from Cell 94


222

SOLID STATE

l i m i n a r y experiments i n w h i c h samples of ^ " - a l u m i n a of 9.0%

Na O/0.8% Li 0 2

NaN03-KN0

2

3

CHEMISTRY

composition

w e r e i m m e r s e d f o r 16 h o u r s at 3 5 0 ° C i n a

m e l t c o n t a i n i n g 0 - 4 . 5 m o l % p o t a s s i u m suggest t h a t s m a l l

a m o u n t s of p o t a s s i u m r e d u c e the s t r e n g t h of ^ " - a l u m i n a b y s o m e f e w thousand psi. R e c e n t l y w e h a v e s h i f t e d o u r emphasis f r o m c o n s t r u c t i o n of glass a n d c a r b o n cells to c o n s t r u c t i o n of m o r e r e a l i s t i c p r o t o t y p e s of l a r g e r Downloaded by UNIV OF CALIFORNIA SAN DIEGO on February 10, 2016 | http://pubs.acs.org Publication Date: June 1, 1977 | doi: 10.1021/ba-1977-0163.ch012

size u s i n g m e t a l s o d i u m a n d s u l f u r containers. W e are c o n t i n u i n g o u r efforts, h o w e v e r , to define t h e effects of s u c h c e l l v a r i a b l e s as t e m p e r a t u r e , m e t a l ions, c u r r e n t d e n s i t y , e l e c t r o d e

shape, a n d t h e extent

of

t w o - p h a s e ( s u l f u r -\- s o d i u m p o l y s u l f i d e ) o p e r a t i o n o n β''-alumina d u r a b i l i t y . I t w i l l b e necessary f o r some t i m e to p e r f o r m experiments i n a n a t t e m p t to d e l i n e a t e h o w these c e l l v a r i a b l e s i n t e r a c t w i t h / ? " - a l u m i n a electrolytes of v a r y i n g c o m p o s i t i o n , i n t e r n a l stress levels, a n d v a r i o u s microstructures.

Materials Costs Estimate for a Sodium—Sulfur Cell A cost target of $ 2 0 / k W h has b e e n chosen f o r the l o a d l e v e l i n g application based on published data ( 4 ) .

T h e cost of c o n s t r u c t i o n of

present l a b o r a t o r y cells w i l l p r o v i d e a n u p p e r l i m i t f o r c e l l costs. d i r e c t cost elements c a n b e b r o k e n d o w n i n t o f o u r m a j o r ( a ) t h e costs of r a w m a t e r i a l s , ( b ) (c)

The

categories:

t h e costs of c o m p o n e n t f a b r i c a t i o n ,

t h e costs of c e l l filling a n d a s s e m b l y , a n d ( d )

the costs of e x t e r n a l

c o m p o n e n t s s u c h as leads, etc. P r e s e n t l y w e s h a l l c o n c e r n ourselves w i t h o n l y t h e a c t u a l costs of r a w m a t e r i a l s u s e d i n c o n s t r u c t i o n of l a b o r a t o r y cells. F o r purposes

of c a l c u l a t i o n w e h a v e a s s u m e d a m a t e r i a l s usage

efficiency of 1 0 0 % a n d h a v e b a s e d a l l of o u r costs i n terms of u n i t a r e a o f c e r a m i c electrolyte ( c m ) . 2

T o c o n v e r t f r o m area of e l e c t r o l y t e to

k W h w e h a v e u s e d a f a c t o r of 2.3 W h / c m

2

or 435 c m c e r a m i c e l e c t r o l y t e 2

p e r k W h d e l i v e r e d . T h i s e n e r g y d e n s i t y w a s a c h i e v e d i n c e l l 89 w h i c h Table I V .

Major Materials Costs for Laboratory Cells Cost

Material G r a p h i t e felt Stainless steel α-Alumina header /?"-Alumina Sodium Sulfur

75 2 10 —

0.4 0.1

Amount (g/cm of β"-Alumina) 2

Cost (t/kWh) 6.57 4.86 3.18 50.46 0.79 0.36

0.091 2.53 0.35 0.32 2.06 3.71 Total

62.22


12.

WEINER

The

Sodium-Sulfur

223

Battery

w a s d e s i g n e d s p e c i f i c a l l y for l o a d l e v e l i n g . U s i n g these assumptions t h e m a j o r r a w m a t e r i a l s costs w e r e d e t e r m i n e d ( T a b l e T h e cost of $ 3 . 1 8 / k W h f o r o - A l 0 2

headers

3

IV). can be

expected

decrease at least o n e o r d e r of m a g n i t u d e i n terms of p r o d u c t i o n

to

costs.

A cost r e d u c t i o n of a f a c t o r of f o u r c a n b e a c h i e v e d s i m p l y b y u s i n g 1-in l o n g headers r a t h e r t h a n the 4 - i n l o n g headers c u r r e n t l y u s e d i n f a b r i c a t i o n of l a b o r a t o r y cells.


It is w o r t h w h i l e to take a s o m e w h a t closer l o o k at the costs associ a t e d w i t h p r o d u c i n g u n i t s of / T ' - a l u m i n a e l e c t r o l y t e j o i n e d to a n a - A l O 2

i n s u l a t o r . I n the past w e h a v e u s e d a cost target of $ 0 . 0 1 / c m electrolyte.

2

s

of c e r a m i c

U s i n g t h e c o n v e r s i o n f a c t o r of 2.3 W h / c m , this translates 2

to a cost of $ 4 . 3 5 / k W h of energy d e l i v e r e d . T h e r a w m a t e r i a l s costs associated w i t h / ^ " - a l u m i n a f a b r i c a t i o n are shown in Table V . Table V .

Material

(Unit)

α - Α 1 0 (lb) Na C0 (lb) LiN0 (lb) P t (troy o u n c e ) Polyurethane (boots) 2

Ceramic Materials

Cost

Amount ( g/cm )

($/unit)

0.07 0.19 0.06 0.02 0.41

3.60 17.50 200.00 8.90 10.00

2

3

2

Costs

e

3

3

b

β

b

Total β 5

(t/cm?) 0.06 2.6 8.0 0.04 0.9

(39)

1

11.6

The conversion factor is 1.5 X 10~ boots/cm . The cost of the Pt is $0.39/cm , but 80% of the cost is recovered. 3

2

2

T h e cost o f the p o l y u r e t h a n e boots ( m o l d s ) c a n b e d e c r e a s e d

by

e x t e n d i n g b o o t l i f e w h i c h is n o w o n the o r d e r of 15 pressings. T h e cost associated w i t h the p l a t i n u m u s e d d u r i n g s i n t e r i n g is s h o w n as 2 0 %

of

the cost of the f o r m e d p l a t i n u m , t h e r e m a i n i n g 8 0 % t a k e n as scrap v a l u e . T h e results g i v e n i n T a b l e s I V a n d V i n d i c a t e t h a t the h i g h e s t cost i t e m b y f a r is the β''-alumina c e r a m i c electrolyte.

T o m e e t target costs

the cost of / ^ ' - a l u m i n a r a w m a t e r i a l s m u s t b e r e d u c e d b y m o r e t h a n a n o r d e r of m a g n i t u d e . R e s e a r c h is c o n t i n u i n g t o w a r d o u r g o a l of cost r e d u c t i o n . W e e x p l o r i n g t h e use of r a w « - A l 0 2

3

are

p o w d e r s w h i c h cost less t h a n $ 1 . 0 0 / l b

or 0 . 0 9 0 / c m , the e l i m i n a t i o n of p l a t i n u m e n c a p s u l a t i o n , a n d the use of 2

l u b r i c a n t s to e x t e n d the l i f e of the p o l y u r e t h a n e boots.

A l t h o u g h the

progress at U t a h i n f o r m i n g c e r a m i c electrolyte b y isostatic p r e s s i n g has e x c e e d e d that m a d e u s i n g e x t r u s i o n , w e m a y s t i l l b e a b l e to use a n e x t r u s i o n process w h i c h w o u l d b e o n e w a y to e l i m i n a t e t h e costs associ a t e d w i t h p o l y u r e t h a n e boots.


224

SOLID S T A T E

CHEMISTRY

Summary R e s u l t s o n t e s t i n g l a b o r a t o r y s o d i u m - s u l f u r cells c o n t i n u e to d e m o n strate the p o t e n t i a l of this system to m e e t the goals r e q u i r e d f o r leveling a n d automotive propulsion.

load

W h i l e m u c h v a l u a b l e r e s e a r c h has

b e e n d o n e , t h e r a p i d a d v a n c e of this t e c h n o l o g y w o u l d b e a i d e d g r e a t l y b y answers to s o m e of the f u n d a m e n t a l questions t h a t r e m a i n . T h e n e e d


to u n d e r s t a n d the causes of c e l l a n d c e r a m i c f a i l u r e are p e r h a p s

demon

s t r a t e d m o s t c l e a r l y b y stating that l o a d l e v e l i n g systems s h o u l d last at least 10 years. Acknowledgment I t h a n k m y colleagues at F o r d — T i s c h e r , M i n c k , G u p t a , L u d w i g , M i k k o r , Lingscheit, Tennenhouse,

Oei, Winterbottom, and

Seaver—for

a l l o w i n g m e to cite t h e i r w o r k a n d h e l p i n g m e to p r e p a r e this m a n u s c r i p t .

Literature Cited 1. Kummer, J. T., Weber, N., "A Sodium-Sulfur Secondary Battery," SAE Transactions (1967) 76, paper 670179. 2. Weiner, S. Α., "Research on Electrodes and Electrolyte for the Ford SodiumSulfur Battery," Annual Report to the National Science Foundation under Contract No. NSF-C805, July 1975. 3. Virkar, Α. V., Tennenhouse, G. J.,Gordon, R. S., J. Am. Ceram. Soc. (1974) 57, 508. 4. Yao, N . P., Birk, J. R., "Battery Energy Storage for Utility Load Leveling and Electric Vehicles: A Review of Advanced Secondary Batteries," 10th Intersociety Energy Conversion Engineering Conference, Newark, Dela ware, August 18-22, 1975, paper 759166. July 27, 1976. Work supported in part by the National Science Foundation—RANN Program under contract NSF-C805. RECEIVED


Solid State Chemistry of Energy Conversion and Storage

Recommend Documents