1 Poly Elect total

(1)

Polymer Electrolytes

Jong Hak Kim

Chemical Engineering

Yonsei University

Jong Hak Kim

(2)

Polym e r Ele c t rolyt e s (PEs)

●

N e w e st solid ionic s

: for E ge ne ra t ion, st ora ge , dist ribut ion - Applic a t ions t o e le c t roc he m ic a l de vic e s

- Synt he sis of ne w polym e r e le c t rolyt e s

- Physic a l st udie s of t he ir st ruc t ure & c ha rge t ra nsport - T he ore t ic a l m ode ling of c ha rge t ra nsport proc e sse s

●

Cha rge t ra nsport m e c ha nism s

- I norga nic : ion “hopping m e c ha nism ”

- PEs: loc a l m ot ion of polym e r (se gm e nt a l m ot ion) in t he vic init y of t he ion

●

T w o ge ne ra l t ype s

(3)

Solid I onic s

●

Cryst a lline solid e le c t rolyt e s

- H+_{, Li}+_{, N a}+_{, K}+_{, Ag}+_{, F}-_{, O}

2-, & di- or t riva le nt ions c onduc t ors - (i) a high c onc e nt ra t ion of m obile ions, (ii) a low a c t iva t ion

e ne rgy for ionic m ot ion from sit e t o sit e

- c onduc t ivit y: hopping m e c ha nism a long c ha nne ls - in c ryst a l st ruc t ure : 1 -, 2 -, 3 -D ne t w ork of c ha nne ls

●

Gla ss e le c t rolyt e s

: a m orphous solid c onduc t ors

●

M olt e n e le c t rolyt e s

- m olt e n sa lt s or m ix t ure s high c onduc t ivit ie s (> 1 Sc m-1) - e .g., LiCl-K Cl e ut e c t ic (m .p. 3 5 5 °C < LiCl a t 6 1 3 °C)

(4)

●

Polym e ric e le c t rolyt e s

(5)

●

Prope rt ie s of polym e r e le c t rolyt e

- a de qua t e c onduc t ivit y for pra c t ic a l purpose s

- low e le c t ronic c onduc t ivit y

- good m e c ha nic a l prope rt ie s

- high c he m ic a l, e le c t roc he m ic a l a nd phot oc he m ic a l

st a bilit y

(6)

Funda m e nt a ls of polym e r e le c t rolyt e

1 . Solve nt (liquid) fre e syst e m : ionic a lly c onduc t ing pha se is form e d by dissolving sa lt s in polym e r.

2 . Ge l e le c t rolyt e : form e d by dissolving sa lt in pola r liquid a nd a dding ina c t ive polym e ric m a t e ria l.

3 . Pla st ic ize d e le c t rolyt e : e sse nt ia lly a ge l e le c t rolyt e but is usua lly a ssoc ia t e d w it h t he a ddit ion of sm a ll a m ount s of a high die le c t ric c onst a nt solve nt t o e nha nc e it s c onduc t ivit y

4 . I onic rubbe r: a liquid e le c t rolyt e c om prising a low

t e m pe ra t ure m olt e n sa lt m ix t ure , re duc e d t o a rubbe ry

c ondit ion by a ddit ion of a sm a ll a m ount of high Mw polym e r

(7)

T he rm odyna m ic s of sa lt dissolut ion

● Dissolut ion of sa lt s → re duc t ion in ∆G of t he syst e m a t c onst a nt T & P → c onside r ∆H , ∆S

∆G = ∆H - T∆S

● Ove ra ll e nt ropy c ha nge on dissolut ion

(+) : due t o t he bre a k up of c ryst a l la t t ic e a nd t he subse que nt disorde ring of ions in t he syst e m

(−) : c a use d by t he st iffe ning of c ha ins a s t he y c oordina t e t o c a t ions

(8)

Polym e r solve nt s

• A polym e r t ha t is c a pa ble of st rongly c oordina t ing c a t ions • polye t he rs, polye st e rs, polyim ine s, polyt hiols

• ha ve st rong c oordina t ing groups t o dissolve sa lt s e a sily • H igh M w PEO-ba se d polym e r e le c t rolyt e s

- poor c onduc t ors in c ryst a lline

- a m orphous; loss of m e c ha nic a l st a bilit y

● At a c t ic PPO

- a m orphous sinc e ra ndom a rra nge m e nt of m e t hyl group

● Ra ndom polye t he rs

(-(OCH₂CH₂)_m-OCH₂-)_n: a m orphous, dim e t hyl silox y unit s

● Com b-bra nc he d c opolym e rs

- e nha nc e fle x ibilit y of t he syst e m & c onduc t ivit y

● N e t w ork s

(9)

H ost Polym e rs

Rubbe ry & Am orphous

●

PEO

- T < 6 0 °C, pre se nc e of c ryst a lline pa rt → re duc e c onduc t ivit y

●

At a c t ic poly(propyle ne ox ide ), PPO

- ra ndom a rra nge m e nt of CH₃ a long t he c ha in

→ pre ve nt t he orde r ne c e ssa ry for c ryst a lliza t ion of polym e r

→ not be st e le c t rolyt e (∵st e ric hindra nc e of CH₃ side group)

1 ) lim it s t he se gm e nt a l m ot ion

(10)

●

Poly (m e t hyle ne ox ide ), (CH

₂

O)

_n

- supe rfic ia lly good be c a use of it s high c onc . pola r groups

- but not good in pra c t ic e sinc e ha rd w it h high c ohe sive e ne rgy

●

Am orphous poly(e t hyle ne ox ide ), PEO

- c onsist s of m e dium but ra ndom ly-va ria ble le ngt h se gm e nt s of PEO joine d by m e t hyle ne ox ide unit s

→ m e t hyle ne ox ide unit s bre a k up t he re gula r he lic a l pa t t e rn of PEO a nd suppre ss c ryst a lliza t ion

●

PEO w it h DM S unit s

(11)

●

Am orphous c om b polym e rs

- short c ha in polye t he rs a t t a c he d t o a polyphospha ze ne or a

polysilox a ne ba c k bone

- e x c e lle nt host s for a lk a li m e t a l sa lt s sinc e high fle x ibilit y of PN ba c k bone t o prom ot e ion t ra nsport

●

Bra nc he d & N e t w ork polym e r ionic s

- a t a m ic rosc opic le ve l, t he de gre e of c rosslink ing m ust not be so gre a t a s t o m a k e t he loc a l polym e r se gm e nt s rigid, t he re by inc re a sing Tg a nd re duc ing ion t ra nsport

(12)

● Addit ive s: sm a ll pola r m ole c ule s int o PEs - im prove m e nt in c onduc t ivit y

i) pla st ic ize polym e r → high fle x ibilit y & se gm e nt a l m ot ion ii) solva t e c a t ion (or a nion) → re duc e ion-ion int e ra c t ions

- e .g., propyle ne c a rbona t e

poly(a c rylonit rile ) & poly(vinyl pyrrolidone ) + LiClO₄+ PC

→ high c onduc t ivit ie s (1 .7 x 1 0-3 _{a t 2 0}°_C)

● Addit ive s: sm a ll c he la t ing a ge nt s

(13)

O

th

e

r

P

o

ly

m

e

r

H

o

s

(14)

● Polya t om ic a nions w it h m onova le nt c ha rge a re t he be st c a ndida t e s (∵ w e a k a nion solva t ion).

• e .g., w a t e r soluble LiF (st rong solva t ion of F by w at e r)

→ LiF insoluble in PEO

→ LiClO₄highly soluble in PEO

● La rge , pola riza ble , m onova le nt a nions low la t t ic e E

→ be t t e r dissolut ion

→ ClO₄-_{, CF}

3SO3-, (CF3SO2)2N-, (CF3SO2)3C-, AsF6-, PF6

-→ I- _{& Br}- _{(but Cl}-_{, F}- _{poor solubilit y)}

● Solva t ion H of sa lt de pe nds on c a t ion-polym e r int e ra c t ion → dissolut ion only oc c urs if a t om s w hic h a re c a pa ble of

c oordina t ing t he c a t ions a re a va ila ble on t he polym e r c ha ins

(15)

● We a k e r solva t ion of (-CH₂-O-)_n& (-CH₂-CH₂-CH₂-O-)_n

- t he c ha ins w ra p a round c a t ion w it hout e x c e ss st ra in

→ right spa c ing of (-CH₂-CH₂-O-)_nunit

- ot he r c oordina t ion groups: -N R- , -N H - a nd

–S-● I nt e ra c t ion st re ngt h bt n. c a t ion a nd c oordina t ing group c la ssifie d a c c ording t o ha rd/soft a c id ba se t he ory (H SAB) → H A pre fe r H B a nd SA do SB; e .g., polye t he r vs Li+

1 ) ha rd/soft a c ids

(a ) ha rd: sm a ll c a t ions w it h no va le nc e e le c t rons, e .g., a lk a li, a lk a line e a rt h ions, M g2 +

(b) soft : la rge r c a t ions w it h se ve ra l va le nc e e le c t rons, H g₂+

2 ) ha rd/soft ba se s

(a ) ha rd: non-pola riza ble liga nds of high e le c t rone ga t ivit y (-O-) (b) soft : m ore pola riza ble groups, e .g., t hio group

(16)

-S-Polye le c t rolyt e s

• M a t e ria ls t ha t ha ve polym e ric ba c k bone s w it h c ova le nt ly bonde d ionizing groups a t t a c he d t o t he m

• Com m on func t iona l group: SO₃-_{, COO}-_{, N H}

3+, = N H2+

Ge l e le c t rolyt e s

• Gre a t int e re st c om m e rc ia lly a s a lt e rna t ive t o t he solve nt -fre e syst e m s → highe r, m ore pra c t ic a l ionic c onduc t ivit ie s

• Form e d by dissolving sa lt in pola r liquid a nd a dding polym e r ne t w ork t o give t he m a t e ria l m e c ha nic a l st a bilit y

• T w o m e t hods t o a c hie ve m a c rosc opic im m obiliza t ion of solv. 1 ) inc re a se t he visc osit y of liq. e le c t rolyt e by a dding soluble

polym e r, e .g., PEO, PM M A, PAN unt il ge l c onsist e nc y is a c hie ve d

(17)

• Low m ole c ula r solve nt s

- propyle ne c a rbona t e (PC), e t hyle ne c a rbona t e (EC), N ,N -dim e t hyl form a m ide (DM F), γ-but yrola c t one (GBL) - high die le c t ric c onst a nt , high B.P.

- inc re a se sa lt dissoc ia t ion

- low visc osit y → high ionic m obilit y

• Polym e ric m a t e ria ls: PAN , PV DF, PV C, PM M A

• Be llc ore (U SA) Co.

- c om m e rc ia lly a va ila ble ge l e le c t rolyt e (for Li ba t t e ry) - PV dF-c o-H FP (he x a fluoropropyle ne ) e le c t rolyt e

(Li sa lt solut ion in m ix e d c a rbona t e e st e rs)

- H FP → de c re a se c ryst a llinit y of PV dF c om pone nt & e nha nc ing it s a bilit y t o a bsorb liquid

(18)

Break ???

(19)

M e c ha nism s of ion c onduc t ion

• ‘dry’ polym e r e le c t rolyt e : polym e r it se lf is im m obile (m a c rosc opic a lly)

→ ions a re t ra nsport e d by t he

(20)

Solve nt & ion t ra nsport

• c a t ions in liquids or low MW polym e r; ions c a n m ove t oge t he r w it h t he ir c oordina t e d solve nt, not in high MW polym e r

• Whe n M_W > 3 2 0 0 g/m ol, M_W of polym e r ha s no signific a nt e ffe c t on c a t ion m obilit y.

(21)

• For high M_W polym e r host s,

- c ha in diffusion is sm a ll a nd m a k e s lit t le c ont ribut ion t o m e c ha nism for ion t ra nsport

- t he m ot ion of ions in polym e r e le c t rolyt e s is st rongly de pe nde nt on se gm e nt a l m ot ion of t he polym e r host

●

Dyna m ic bond pe rc ola t ion t he ory (DBP)

- M ic rosc opic m ode l → c onduc t ivit y due t o c om bina t ion of ion/polym e r c oope ra t ive m ot ion w it h t he oc c a siona l

inde pe nde nt ion m ove m e nt .

- T im e sc a le for t he la t t e r is m uc h short e r t ha n for polym e r re la x a t ion, diffe re nt c a t ion a nd a nion m ot ions.

• c a t ion→ m a k ing a nd bre a k ing of c oordina t e bonds w it h m ot ion be t w e e n c oordina t ing sit e s

(22)

M a c rosc opic a pproa c h

●

Em piric a l re la t ionship: c onduc t ivit y vs. t e m pe ra t ure

- a m orphous PEs de pa rt from t he c la ssic a l Arrhe nius re la t ion

σ = σ₀e x p [ - E_a / k_B T ]

- V oge l-T a m m a n-Fulc he r (V T F) e qua t ion: ions a re t ra nsport e d by se m i-ra ndom m ot ion of short polym e r se gm e nt s

σ = σ₀e x p [ - B / (T -T₀) ]

●

Fre e volum e -ba se d m ode ls: m ot ion oc c urs a s a re sult of t he re dist ribut ion of fre e volum e w it hin t he syst e m

●

Configura t iona l e nt ropy m ode l: ba se d upon e nt ropy, not volum e , w it h t ra nsport m ode le d on group c oope ra t ive re a rra nge m e nt s of polym e r c ha ins ra t he r t ha n a void-t o-void jum ping

(23)

M orphology

● Ge ne ra l t e c hnique s t o c ha ra c t e rize polym e r e le c t rolyt e st ruc t ure a nd m orphology

- opt ic a l m ic rosc opy, DSC, N M R, X RD

(24)

Pre pa ra t ive T e c hnique s

●

Solve nt -fre e e le c t rolyt e film

1 ) Solve nt c a st ing

c a st ing

→

solve nt e va p.

→

he a t ing unde r va c uum

2 ) H ot pre ssing m e t hod

-

grinding

polym e r & sa lt a t liquid N

₂

T e m p.

→

hot

pre sse d

; t ot a lly solve nt fre e

(25)

● M inim um re quire m e nt s

- ionic c onduc t ivit y: 1 0-2 – 1 0-3 Sc m-1 ide a l a t RT

(m in. 1 0-5 _{Sc m}-1 _{for pra c t ic a l use}₎

- e le c t roc he m ic a l st a bilit y in a volt a ge w indow -c om pa t ibilit y: c he m ic a lly & e le c t roc he m ic a lly c om pa t ible w it h e le c t rode s - T he rm a l st a bilit y

- M e c ha nic a l st a bilit y

- Ava ila bilit y: a va ila ble & ine x pe nsive

● Ele c t rode -e le c t rolyt e int e rfa c e

- diffe re nt int e rfa c ia l proc e sse s, e .g., e le c t ron t ra nsfe r m e c ha nism s

(26)

●

Lit hium a node

- lit hium m e t a l/PEO → t hin la ye r of t hird pha se form e d be t w e e n t w o bulk pha se s

- pa ssive la ye r c om posit ion: LiF (for LiCF₃SO₃ e le c t rolyt e ) or Li₂O

(for LiClO₄ e le c t rolyt e s), inhom oge ne ous

(27)

●

I nt e rc a la t ion c a t hode

- provide a m e c ha nism for re ve rsible a nd k ine t ic a lly fa st solid-st a t e e le c t roc he m ic a l re a c t ions

- Li se c onda ry ba t t e ry, e le c t roc hrom ic s, se nsors, sola r c e lls

M X_n + a Li+ _{+ a e}- → _Li

aM Xn

- e .g., V₂O₅/PEO e le c t rolyt e s w it h LiClO₄ - t w o se m ic irc le in a .c . im pe da nc e

→ high fre que nc y se m ic irc le ; ionic a lly c onduc t ing surfa c e la ye r t ha t grow s on t he V₂O₅

→ low fre que nc y se m ic irc le ; c ha rge t ra nsfe r be t w e e n surfa c e la ye r a nd t he e le c t rode

(28)

●

N a noc om posit e polym e r e le c t rolyt e s

M ix e d pha se e le c t rolyt e s & na noc om posit e s

• c e ra m ic or gla ssy e le c t rolyt e s vs. polym e r e le c t rolyt e s - highe r c onduc t ivit y, be t t e r t he rm odyna m ic st a bilit y

• polym e r vs. c e ra m ic /gla ssy e le c t rolyt e s - fle x ible , supe rior int e rfa c ia l c ont a c t s - proc e sse d a s t hin la rge a re a film s

• m ix e d pha se PEs-c e ra m ic s of na nom e t e r gra in size

(29)

• Conduc t ivit y: a be ne fic ia l e ffe c t of c e ra m ic a ddit ive s

• I nt e rfa c ia l prope rt ie s: I m prove d st a bilit y by na noc om posit e

(30)

• Why c e ra m ic or gla ss pow de r re nde r t he int e rfa c e m ore st a ble ? 1 ) Re a c t ivit y

: form a t ion of highly c onduc t ing produc t (Li₃N ) t o fa c ilit a t e ion t ra nsport

2 ) Shie lding e ffe c t

(31)

●

Prot on c onduc t ors

→ a nhydrous c onduc t ors: PEO-H₃PO₄, PEI -H₂SO₄ or H₃PO₄, PV P-H₃PO₄; high c onduc t ivit y (∵ high int rinsic c onduc t ivit y of a c id)

→ prot on-va c a nc y c onduc t ing polym e rs: PEO_nN H₂SO₂N H₂

→ hydra t e d prot on c onduc t ing m e m bra ne s: polye le c t rolyt e + w a t e r

→ polym e r e le c t rolyt e fue l c e ll e m ploy hydra t e d pe rfluorosulfonic a c id suc h a s N a fion (DuPont ), Dow X U S-1 3 2 0 4 .1 0 , Chlorine

(32)

Polym e r e le c t rode s

: c onjuga t e d polym e r

Polya c e t yle ne

• (CH )x ; room T c onduc t ivit y;

1 0-5 _{Sc m}-1 _{for t ra ns, 1 0}-9 _{Sc m}-1 _{for c is}

(33)

● Ex posure t o ox idizing or re duc ing a ge nt s

→ inc re a se se ve ra l orde rs of c onduc t ivit y

(34)

●

p-doping proc e ss

- e x posure t o

ox idizing a ge nt (X )

- form a t ion of

posit ive ly c ha rge d polym e r

c om ple x &

re duc t ion of X

(CH )

_x

→

[(CH

y+

)]

x

+ (x y)e

-(x y)X + -(x y)e

-

→

(x y)X

-w it h t ot a l re a c t ion

(CH )

_x

+ (x y)X

→

[(CH

y+

)]

x

+ (x y)X

-

→

[(CH

y+

)X

y-

]

x

w he re X

-

= I

-

, Br

-

…

X

-

→

dopa nt c ount e r a nion

y: ra t io bt n. dopa nt ion a nd polym e r re pe a t ing unit

→

doping le ve l

(35)

●

n-doping proc e ss

- e x posure t o

re duc ing a ge nt (M )

- form a t ion of

ne ga t ive ly c ha rge d polym e r

c om ple x &

ox ida t ion of M

(CH )

_x

+ (x y)e

-

→

[(CH

y-

)]

x

(x y)M

→

(x y)M

+

+ (x y)e

-w it h t ot a l re a c t ion

(CH )

_x

+ (x y)M

→

[(CH

y-

)]

x

+ (x y)M

+

→

[M

y

+(CH

y-

)]

x

(36)

●

H e t e roc yc lic polym e rs

• polypyrrole & polyt hiophe ne

●

Polya c e t yle ne

(37)

• doping → not induc e c ha nge s in t he num be r of e le c t rons a ssoc ia t e d w it h t he polym e r c ha in, but re la t e d t o a highly sym m e t ric a l π- de loc a lize d st ruc t ure

• c onduc t ivit y vs. T ; polym e r ~ SC

●

Polya niline

(38)

M e c ha nism of doping proc e sse s

• “doping”: sa m e t e rm inology w it h inorga nic se m ic onduc t or, but t he doping proc e sse s of c onduc t ing polym e rs a re quit e diffe re nt from t hose of inorga nic se m ic onduc t ors

● Se m ic onduc t or: rigid la t t ic e , doping is w e ll de sc ribe d by ba nd m ode ls

→ doping proc e sse s; int roduc t ion of im purit ie s int o t he c ryst a l la t t ic e w it h t he int e rga p e ne rgy le ve ls ne a r CB or V B; c onduc t ion proc e e ds via a c ohe re nt propa ga t ion of e le c t rons a nd/or hole s a c ross t he la t t ic e

● Polym e r: fle x ible c ha ins, fa vor loc a lize d c ha in de form a t ion → im purit ie s or doping a ge nt s do not be c om e pa rt of t he st ruc t ure , ra t he r a re

(39)

●

T w o c ont ribut ions

- I nt ra c ha in t ra nsport: a ve ra ge c onjuga t ion le ngt h of c ha ins - I nt e rc ha in t ra nsport: re gula rit y of polym e r st ruc t ure

(∵c onduc t ivit y inc re a se s by orde ring of st ruc t ure )

● M e t hods for m onit oring t he doping proc e sse s

- Opt ic a l a bsorpt ion: int e rga p t ra nsit ion c ha nge s a bsorpt ion - in sit u spe c t roe le c t roc he m ic a l c e ll m e a sure m e nt

(40)

- M ic roba la nc e (QCM , qua rt z c ryst a l )

- Cyc lic volt a m m e t ry & a .c . im pe da nc e e .g., CV of (CH )_x in LiClO₄-PC:

a nodic (doping) & c a t hodic (undoping) pe a k s

(41)

●

Ba t t e rie s ; lit hium /polypyrrole ba t t e rie s

Li / LiClO4-PC / (C4H5N )v

Cha ra c t e rize d by t he follow ing e le c t roc he m ic a l proc e ss:

(C₄H₅N )_v + (x y)LiClO₄ (C₄H₅N3 +_)(ClO

4-)x y]v +(x y)Li c ha rge

disc ha rge

●

Opt ic a l displa y (e le c t roc hrom ic de vic e )

Li / LI ClO4-PC / [C5H7S]v , I T O, gla ss

Displa y is a ba t t e ry w it h a c olor c ha nge . Ele c t ro-c he m ic a l proc e ss:

[C₅H₇S]_v + (x y)LiClO₄ [(C₅H₇S7 +_)(ClO

4-)x y]v + (x y)Li

(re d) (blue )

doping

undoping