Surface Chemistry-Controlled SEI Layer on Silicon Electrodes by Regulating Electrolyte Decomposition

Unstable solid electrolyte interface (SEI) layers induced by significant volume changes and subsequent side reactions at the interface have prevented Si anodes from practical application in lithium-ion batteries. The interface stability plays an important role in the electrochemical performance of Si electrodes. Here, we modify the interface of a Si electrode with ion-conductive poly(ethylene glycol) diglycidyl ether (PEGDE), which controls the electrolyte decomposition route and stabilizes the SEI layer. It enables the Si electrode to achieve a capacity of more than 1800 mAh g–1 at a current density of 2 A g–1, with a capacity retention of 77.25% after 300 cycles. The PEGDE-decorated Si electrode also shows greatly improved rate capability, with specific capacity up to 777 mAh g–1 even at 20 A g–1. We demonstrate that PEGDE decoration greatly increases the Li2CO3 ratio in the SEI layer, which improves the interface stability and Li+ conductivity and hence suppresses continuous electrolyte decomposition. As a result, the structural integrity of the Si particles is maintained and capacity fading is retarded. This work reveals that surface design can effectively regulate the SEI layer composition and improve interface stability, which is a promising strategy for Si-electrode manufacture.