High-performance honeycombed FeF3@C cathodes enabling practical lithium pouch cells and silicon−metal fluoride batteries

Abstract

Metal fluoride cathodes are promising candidates for next-generation rechargeable lithium metal batteries (LMBs). However, the sluggish reaction kinetics limits their electrochemical applications, especially at high mass loadings. Moreover, current designs on fluoride cathodes hardly achieve the related practical pouch cells and full cells. A honeycombed FeF3@C nanocomposite with high specific surface area (SSA) of 191.6 m2 g−1, is successfully synthesized herein, where the nanosized FeF3 particles (less than 40 nm) are uniformly embedded in the honeycombed carbon matrix. Benefiting from the unique configuration, it can provide an efficient mixed Li+/e− conduction networks then enable excellent lithium storage performance under three-electron transfer reaction even at high mass loadings. The high-loading honeycombed FeF3@C (∼3.5 mg cm−2) cathode offers a reversible specific capacity of 369.9 mAh g−1 after 500 cycles in a Li half-cell, corresponding to noticeable areal capacity of ∼1.25 mAh cm−2. In order to further investigate their practical applications, as-produced FeF3@C−Li pouch cell is constructed, delivering average nominal capacity of ∼50 mAh per cycle. Furthermore, the FeF3−prelithiated Si (PLSi) full cell is produced for the first time, demonstrating cycle life over 200 cycles and rate capability up to 5C. Notably, the as-produced cathodes show partially reversible phase transition during discharge/charge, which offers abundant fresh phase interface, contributing to growing pseudocapacitance and Li+ migration ability as the cycle proceeds. The pseudocapacitance compensates for lost capacity caused by incompletely reversible phase transition, and enables superior electrochemical properties.