Energy Storage Materials and Devices Lecture 2

Energy Storage Materials and Devices Lecture 2

1. SEE902 – Energy Storage Materials and Devices Week 3, Lecture 6: Electrode Reactions Dr. Sudarshan Narayanan Assistant Professor Dept. of Sustainable Energy Engg ., IIT Kanpur

2. Contents Binary electrodes under near-equilibrium conditions Li-Sb system Li-Bi system Insertion reactions Solid-solutions Guest species Layered structures Type I, II, and III reactions Sequential reactions and other concepts

3. ELECTROCHEMICAL POTENTIAL DEPENDENCE ON ELECTRODE COMPOSITION

4. Binary Electrodes Un d er Ne a r Equilibrium Conditions Accord i ng t o t he G ibbs Phase Ru l e, a l l in t ens i ve proper t ies inc l ud i ng e l ec t rical po t en t ial va r y con t inual l y w i t h the co m position w i t hin sing l e - pha s e regions in a b i nary s y s t em. Ho w eve r , t hese proper t ies w ill not change in t he region con t a i n i ng mo r e t han a sing l e phase.

5. Binary Electrodes Un d er Ne a r Equilibrium Conditions Let us t ry t o p l ot t he d i scharge curve f or h y pothe t ical AB s y s t em at T 1 t empe r a t ure Ex a mple with Line Phas e s

6. Binary Electrodes Un d er Ne a r Equilibrium Conditions R e al S y ste m : L i - Sb S y stem 2 L i  Sb  L i 2 Sb L i 2 Sb  L i  L i 3 Sb T w o L i ne com p o u n d s e x ists in th i s s y stem NOTE th a t L i w i l l s e rv e a s an a nod e w h i l e Sb w i l l b e a c a th od e T = 360 o C

7. Binary Electrodes Un d er Ne a r Equilibrium Conditions Another Real System : L i - Bi S y stem A co n si d er a b l e so l u b i l ity of Bi in li q u i d Li at 3 6 o C Cell voltage vs composition at 3 6 o C Coulometric titration measurements within the composition range of the phase “Li 3 Bi”, at 3 6 o C

8. Ins e rti o n r ea ct i o n i s a m a j o r fe a ture i n s o m e o f the m o st i mpo rta n t el e c t r od e us e d i n m o d ern b a t t ery s y stem s . With a surp r ise d i scovery of ions mo v ing fa st inside certain solids (so l id electrol y te), it w as r e al i zed that some ions could mo v e r apid l y into and out of some other mate r ial s. Instead of react i ons occur r ing on the surface of solid electrodes, the phenomena oc c u r ring in s ide the ele ctr o des i s of critical impo r tance. Insertion Reaction: Introduction Insertion/e x tract i on react i ons occur r ing i n both cathode and anode of the L i - ion batter y . Host structure Mob i le guest spe c ies T he terms intercalation/de-in t er c alat i on are used (instead of insertion/e x tr a cti o n) w hen the insertion occurs into a la y ered host matri x .

9. Insertion Reaction: Reconstitution It is im p ort a nt t o c o ns i der t he G i bbs Pha s e Ru l e while pr ed ic t ing de p e n d e n c e of the potential o n compositio n . Ch ar g ing LiFeP O 4 → FeP O 4 + L i + + e - It is known th a t the p o te n ti a l pla t e a u is observed wh e n th e re are two p h ases pr e sent in tw o -com p o n e n t system. Insertion-driven reconstitution reaction occurring in FePO4 Fl a t pl a t e au obs e rved in t h e charg e -dischar g e curve is d u e to the m o ving in t erf a ce reconsti t ut i on re a ctio n .

10. Insertion Reaction: Solid-solution Reactions Si n ce i ns e rti o n/ e x tract i on r e a ctio n s i n v ol ve a ch a n ge i n the chemical composition, th e se re a ctio n s are a l so ca l l e d so l i d -so l uti o n re a ctio n s . In s ert i on rea ct i ons are topota ct i c s in c e there exi s ts a 3 - d i men s ional c orre s ponden c e bet w een the c r y s tal s tru c tures of parent and produ ct. Examples: A large amount of h y drogen can be i nserted into Pd and i ts allo y s. Clay w ith a la y ered structure is often used to remove the contam i nant from w ater by ab s orbing them into the cr y stal structure

11. Insertion Reaction: Guest Species T he guest spec i es shou l d have a relative l y small size t o squeeze t hrough t he nar r ow confines of t he host cr y s t al s t ruc t ure. Most important guest species in connection with batteries are H+, Li+ and Na+. e- It has been demonstrated that in a few materials, anionic species can also be inserted into the crystal structure. Electrostatic energy consideration dictates that the neutral combination of species can be added. If Li+ is inserted, electrons should also be added. If Li+ is extracted, electrons should also be removed. e-

12. Insertion Reaction: Layered structures Ma n y mater i a l s have c r y s t al s t ruc t ures t h a t c ons i st o f rather s t i f f cova l e n t ly bonded slabs contain i ng several la y ers of a t om s . T he ad j acent slabs are bound t o each o t her by w eak V an der W aa l s force s . T he space be t w een t he t w o sl a bs i s ca l led t he ga l lery s p ace a nd t he add i t ional guest spec i es can reside i n t h i s space. In a pillared la y ered structure, slabs are rig i dly conne c ted to e ach other by pillar atoms w hich partially fill the galleries through w hich the guest spec i es move. Cr y stal Structure of Cd I 2 sho w ing hexagonal ABABA B - t y pe stacking Gallery Space Pillar ato m s

13. Insertion Reaction: Types (Type I) T here are several t y pes of inser t ions reac t ions. T y p e I G ue st spe c ies random l y occupy sites w ithin a l l the gallerie s, gradually filling them as the concentration of guest spec i es increase s. In this t y pe of insertion rea c tion, there e x ists a transient compo s ition gradient w ithin the gallery spa c e, and the electric potent i al variat i on w ith compo s ition indicates a singl e - pha s e soli d - solution react i on. S i ngle pha s e solid - solution r e act i on is oc c u r ring sugge s ting monotonous de c line of potent i al w ith compo s ition R a n d om d i f fusi o n of g u est sp e ci e s

14. T y pe II If gue st spe c ies cau s es a mod i fication in the ho st structure, the insertion rea c tion occurs by the mot i on of an i nterface. This interface separates the region into w hich the gue st spe c ies ha v e mo v ed from the region in w hich there are no, or fe w e r , gue st spe c ies. Mov i ng i n terface d u ri n g the ins e rtion re a ction Insertion Reaction: Types (Type II) This t y pe of insertion rea c tion has a characteri s tic of recon s titution react i on and the potent i al titration curves show the plateau during the insertion rea c tion

15. T y pe III The r e may be t w o or more t y pe of sites in the gallery spa c e (of the ho st structure) w ith di f ferent energies. The gue st spe c ies preferentia l ly res i de on the sites w ith low energies. The change i n overall con c entration of mob i le spe c ies require the trans l ation of the interface separating the occupied and uno c cupied region s. Gu e st sp e ci e s pr e fer e nti a l l y res i d i ng on certa i n sites Insertion Reaction: Types (Type III) This t y pe of insertion rea c tion aga i n has a characteri s tic of recon s titution react i on and the potent i al titration curves show the plateau during the insertion reaction

16. Insertion Reaction: Sequential reactions If there are several types of si t es present in the host struc t ure with di f fere n t en e rgies, the insertion ge n erally occurs first o n one type of si t es, f ollow e d by the occupat i on of an o ther type. Exam p le: Po t e n ti a l titra t ion curve of Li inser t ion in NiP S 3 T wo type of sites are avai l a b le in NiP S 3 Ran d om occupa t ion of first type of sites Ran d om occupa t ion of other type of sites Rea c tion involve th r ee seque n tial steps. Up to 0. 4, random occupation of 1 st set of site s. In s ertion of another 0.4 Li into another set of sites in an order e d arran g eme n t . Next, insertion of one additional Li into anoth e r order e d structu re . Reconstitution Rea c tions Example: Potential titration curve of Li insertion in K x V 2 O 5

17. Staging is a ph e nome no n in which gu e st species selectively occupy galle r ies in materials with a layered cry s tal structure. Insertion Reaction: Other concepts (Staging) Exam p le: Grap h ite M o d e l d e p i cti n g sta g i n g p h e n o m e n on in Gr a p h ite Sta g e 1 : All the g a ll e ries are occupi e d in the structure. St a ge 2 : Every a l t e rn a te g a ll e ry is occupi e d in the structure. Sta g e 3 : Every t hird g a ll e ry i s occupi e d in the structure.

18. Insertion Reaction: Other Concepts (Parallel Tunnels) Parall e l T unn e ls I n s ertion o f g ue st s pec i es al s o occurs i n ma t erials with pa r al l el lin ear t u n ne l s allowing only on e dimension di f fusion. Exam p le: Hol l a n di t e At low te m p e rat u res, the g u est sp e cies form an or d er e d arra n g e m e nt u p on the avai l a b le sites. In a d di t io n , there is coord i n a ti o n b etw e en the arra n g e m e nt in o n e tu n n e l with respect to a n ot h er n e ar b y tu n n e l. On incre a sing the te m p e rat u re, the th e rmal e n er g y dist u rbs the or d er e d arra n g e m e nt of g u est sp e cies b e twe e n t he tu n n e ls. On fur t h e r incre a se in the te m p e rat u re, the or d er e d arra n g e m e nt of g u est species with i n the tu n n e ls is also lost Ho l l a n di te Crystal Str u cture

19. Bard, Allen J., and Larry R. Faulkner.  Electrochemical Methods: Fundamentals and Applications . 2nd ed. Wiley, 2000. ISBN: 9780471043720. Huggins, Robert A.  Energy Storage: Fundamentals, Materials and Applications. 2 nd ed. Springer, 2016. ISBN: 9783319212388. Reddy, Thomas B. Handbook of Batteries . Fourth ed. McGraw-Hill, 2011. Further Readings

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