In-situ Homogenized Fluorination Strategy via Active Prelithiation Enabling LiF Solid Electrolyte Interphases for Stable Silicon Anodes

Abstract

Silicon-based anodes, with exceptionally high theoretical specific capacity, are still hindered in practical applications due to significant volume expansion and unstable solid electrolyte interphases (SEI). LiF-rich SEI has been confirmed to suppress electrode swelling and maintain interface stability. Unfortunately, it is usually achieved by electrolyte engineering, leading to undesired side reaction products. Herein, we propose a pre-lithiation/in situ fluorination strategy to pre-construct a stable LiF layer on the surface of Si particles for obtaining an ideal SEI. The LiF layer effectively mitigates volume expansion and suppresses electrolyte decomposition. This mechanism is revealed via in-situ confocal optical microscope and finite element analysis. Consequently, the LiF-modified Si anode exhibits minimal expansion and stable SEI throughout cycling. The 1.2 Ah pouch cells using NCM811 cathode and modified Si/graphite anode demonstrate a high capacity retention of 94.5% after 1000 cycles at 1C. Moreover, the cells show superior storage performance (capacity retention of 94.5% after 7 days at 60 °C) and outstanding cycling stability (capacity retention of 80.8% after 650 cycles at 45 °C) at high temperature. The proposed in-situ homogenized fluorination strategy offers a promising approach to construct controllable protective LiF layer for improving the interfacial stability of high-capacity anode materials in LIBs.