Role of 1, 3-Propane Sultone and Vinylene Carbonate in Solid Electrolyte Interface (SEI) Formation and Gas Generation

The cycling performance, ex-situ surface analysis, and in-situ gas analysis of lithium ion batteries containing the widely used electrolyte additives VC and PS has been investigated.  All of the electrolytes have good cycling performance at 25°C.  However, the electrolytes containing additives have better discharge capacity retention and coulombic efficiency upon cycling at 55°C. Analysis of the differential capacity plots suggest that both VC and PS are reduced prior to the carbonates and alter the structure of the anode SEI.   Ex-situ surface analysis confirms structural differences of the anode SEI.  Electrodes cycled in the presence of PS contain lithium alkyl sulphonate (RSO₃Li) on the surface of the anodes.  The presence of the lithium alkyl sulfonate leads to higher lithium ion conductivity of the anode SEI.  Electrodes cycled with added VC contain poly(VC) in the anode SEI.  The presence of the poly(VC) leads to improved stability of the SEI.  Anodes cycled with both VC and PS contain lithium alkyl sulphonate and poly(VC) which leads to an SEI with both high conductivity and high thermal stability. In-situ gas analysis shows that both additives, VC and PS, are able to reduce the ethylene evolution during SEI formation by nearly 70 %. The formation of poly(VC) for electrodes cycled in VC is accompanied by CO₂ evolution. The presence of the lithium sulfonate for PS leads to a lower onset potential of ethylene evolution. For VC, the only gaseous byproduct during reduction is CO₂, while PS shows no gaseous reduction products. The combination of both additives leads to a superposition of the described phenomena. The reduction of gas evolution during SEI formation would allow a faster and easier industrial formation procedure for Li-ion batteries.