Tailoring a multifunctional, boron and fluoride-enriched solid-electrolyte interphase precursor towards high-rate and stable-cycling silicon anodes

Abstract

Rational design and construction of stable artificial interface for silicon (Si) anodes exhibits great promise in shielding the Si particles against their intrinsic volumetric changes and minimizing the side reactions, both constituting prerequisites towards the long-term stability of the high-energy density Si-based batteries. Herein, a multifunctional solid-electrolyte interphase (SEI) precursor of 4-trifluoromethylphenylboronic acid (TFPBA) nano-layer is tailored, which readily polymerizes to form 2,4,6-tris-4-(trifluoromethylphenyl)boroxine (TTFPB) on Si surface during high-temperature drying process of the electrodes. After one-electron reduction, the BO bonds in TTFPB molecule break where the radical molecules are thus generated, initiating the spontaneous polymerization to form the poly-4-trifluoromethylphenylboronic acid (PTFPBA) with repeated B–O chains. Such polymerized nano-layer not only manifests a desirable artificial SEI for its high robustness and elasticity in accommodating the volume expansions, but also effectively improves the electrolyte absorption rate of the electrode, providing accelerated kinetics for Li+ transfer. Under the stable framework formed by PTFPBA, preferential adsorption of LiPF6 molecules is enabled with the electron-deficient boron (B) species, further inducing a continuous and dense SEI rich in benzene rings and inorganic substances. As such, the as-obtained Si@TTFPB anode demonstrates significantly enhanced rate capability and long-cycle performance. After 500 cycles at 0.2 C rate, the modified Si electrode still delivers a capacity of 1778.7 mA h g−1, while the reference Si anode has almost no capacity.