A Rechargeable All‐Solid‐State Sodium Cell with Polymer Electrolyte

sodium with thicknesses between 50 ;~m and 100 ~m were obtained. Secondary lithium cells with intercalation or insertion materials as positive Polymer electrolyte sheets (-~30 ~m) electrodes are now an extensively stuWere prepared by evaporation of acetodied subject. However, only few papers nitrile solutions of poly-(ethylene covering the corresponding sodium sysoxide) (PEO) and the proper amount of terns have yet appeared. Ostensibly this Nal, recrystallized from acetonitrile is due to the lack of reversible sodium and vacuumdried at l~0~ The PEO (WSR /electrolyte half-cells functioning be301 Polyox, MW = 4.I0 ~, BDH) was used low 200~ higher temperatures most as received. The films were prepared electrode materials will react via and handled in an argon filled dry box. displacement reactions, which generally The Nal concentration in the films used have lower electrode potentials and do corresponded to a Na/O ratio of 1:10. not possess the inherent reversibility With this electrolyte, the operating of intercalation reactions, temperature of the cell is confined to the interval between 98~ (melting of Liquid organic electrolytes consisting sodium) and 65~ as the electrolyte of NaI dissolved in propylene carbonate conductivity decreases rapidly below have been used for electrochemical prethis temperature. paration of sodium intercalated TiS 2 (1,2). The Exxon group has cycled both Composite MoS 3 electrode films (-~50 ~m) Na/TiS~ and Na/MoS 3 using sodium triewith the overall composition: 72 w/o thyl [N-pyrrol) b~orate dissolved in MoS3, 20 w/o PEO, and 8 w/o Nal were 1.3-dioxolane as electrolyte (3,4). Most other groups have chosen to use two-electrolyte systems with an ionic conducting ceramic membrane. This membrane separates molten sodium from the liquid electrolyte forming contact to the active material in the positive electrode (5).