1-Hydroxyethylidene-1, 1-diphosphonic acid: A multifunctional interface modifier for eliminating HF in silicon anode

Abstract Fluoroethylene carbonate (FEC) is an important electrolyte additive in silicon (Si) anodes. However, it is easily defluorinated by Lewis acids (PF5−) to form harmful corrosive substances (HF). To overcome this problem, 1-Hydroxyethylidene-1, 1-diphosphonic acid (HEDP), a novel multifunctional surface modifier is developed on the Si surface. It can not only consume HF, but also participate in the formation of a solid electrolyte interphase (SEI) film with excellent electrochemical stability, high lithium conductivity, and good thermal stability. In addition, Si@HEDP anode with polyvinylidene fluoride (PVDF) binder exhibits much improved electrochemical performance. After 500 cycles at 30 °C, a high reversible capacity of 1831.8 mAh g − 1 is obtained; and after 200 cycles at 60 °C, it still maintains 2163.8 mAh g − 1; which are in sharp contrast to the reference Si anode of almost zero capacity after 25 cycles. This work overcomes the fundamental challenges of using FEC electrolyte additive and PVDF binder in Si-based batteries.