SnF2 -Catalyzed Formation of Polymerized Dioxolane as Solid Electrolyte and its Thermal Decomposition Behavior.

Abstract

Polymerized-dioxolane(P-DOL) is of potential as a solid-polymer-electrolyte(SPE) due to its high Li+ -conductivity, good compatibility with Li-metal and desired preparation method of in situ polymerization in cells. In this study, SnF2 was demonstrated not only to be an efficient catalyst for the polymerization of DOL at room temperature, but also an effective additive for improving interfacial wettability and suppressing dendrite through the reaction with Li-metal and the formation of LiF/Lix Sn based composite solid electrolyte interlayer(SEI). Using the SnF2 polymerized P-DOL containing 1 M LiTFSI as SPE(P-DOL-SPE), obviously denser Li-deposition was obtained, and the all-solid-state(ASS) Li/LiFePO4 cell delivered stable cycling over 350 cycles at 45 °C. At the same time, the irreversible decomposition of P-DOL-SPE into formaldehyde and small molecule epoxides are observed at 110 °C, which is even initiated at lower temperature of 40 °C under vacuum. This thermal decomposition of P-DOL-SPE in pouch cell causes huge volume swell, and therefore putting a strict limitation on the operating temperature window for the P-DOL based electrolytes.