Study of phase changes during 500 full cycles of Li/composite polymer electrolyte/FeS2 battery

There is a growing demand for the development of high-energy-density lithiu m batteries for a number of applications including electric vehicles (EV), energy storage and space. The Li/composite polymer electrolyte (CPE)/pyrite battery, which has a high theoretical energy density (about 810 Wh kg(-1) based on 2.8e/FeS2), and is made of cheap, non-toxic and green compounds is a good candidate for EV applications. Materials cost is estimated at 50$ k Wh(-1) five times lower than that of other lithium and lithium-ion batterie s. Over 500 1000/o DOD cycles (at c(3) rate) with a capacity fading rate of less than 0.1% per cycle were carried out in a small (1 cm(2) area) labora tory prototype cells with 7 mu m-thick cathodes. Charge-discharge processes in the Li/Lil-(PEO)(n)-Al2O3-based CPE/pyrite battery during long-term cyc le life have been analyzed with the use of dq/dV curves. These studies furn ish insights into the electrochemical behavior of pyrite in polymer electro lyte-systems. Up to seven phases have been identified and found to change d uring the first 50-100 cycles. These phases do not change much over the sub sequent 400 cycles. The major phases have been recently identified by EXAFS and NEXAFS measurements. It was proved that reduction of the ferrous disul fide proceeds as a multi-stage process, first to Li2FeS2 and finally to met allic iron. No evidence of FeS was found. When he battery is charged to 2.2 5 V, Li-2, FeS2 is formed. (C) 2000 Elsevier Science Ltd. All rights reserv ed.