New polymer lithium secondary batteries based on ORMOCER ® electrolytes–inorganic–organic polymers

Abstract

Based on new plasticized inorganic–organic polymer electrolytes [M. Popall, M. Andrei, J. Kappel, J. Kron, K. Olma, B. Olsowski, ‘ORMOCERs as Inorganic–organic Electrolytes for New Solid State Lithium Batteries and Supercapacitors’, Electrochim. Acta 43 (1998) 1155] new flexible foil-batteries in ‘coffee bag arrangement’ were assembled and tested. The electrolyte works as separator and binder for the cathodes. Self-diffusion NMR studies on the system (EC/PC/Li +N(SO 2CF 3) 2 −/ORMOCER ®) resulted in cationic transport numbers ( t +) of 0.42 for the EC/PC/salt system and 0.35 for the ternary electrolyte, typical for polymer electrolytes. Cycling tests (more than 900 cycles) proved that the unplasticized electrolyte can act as binder in composite cathodes of lithium secondary batteries [2]. Charge/discharge cycles of complete batteries like (Cu/active carbon/ORMOCER ®/LiCoO 2/Al) with an ORMOCER ® as separator electrolyte were measured. The voltage drop of these batteries is very similar to cells with standard liquid electrolytes and the efficiency is close to 100%. Cycling the batteries with a current density of 0.25 mA cm −2 between the voltage limits of 3.1 and 4.1 V results in a charge/discharge capacity (referring to the cathode mass) of 100 mAh g −1 at the beginning and after a slight decrease in a stabilised capacity of 75 mAh g −1 after 15 cycles. These promising results could be optimised by using highly purified components.