LiF-Dominated SEI Formation via a Lychee-Like Primary Interphase for Fast-Charging Natural Graphite Anodes

Abstract

Natural graphite, with its lower production cost, higher capacity, and superior electrical conductivity than artificial graphite, currently accounts for approximately 40% of the global lithium-ion battery anode market. However, the inadequate compatibility of natural graphite with commercial carbonate ester electrolytes leads to irreversible capacity loss, reduce coulombic efficiency, and rapid capacity decline during cycling. Applying an oxygen-deficient titanium dioxide (TiO2-x) protective layer to natural graphite anodes has been noted as a successful method for improving their structural integrity and cycling stability; however, the fragile solid–electrolyte interphase (SEI) limits their fast-charging capability. In this study, nitrogen atoms are strategically incorporated into the TiO2-x surface structures, creating a lychee-like primary interphase that regulated the interfacial electrochemistry and facilitated the development of a LiF-dominated SEI. The robust LiF-dominated SEI, as examined through ex situ X-ray photoelectron spectroscopy analysis and kinetic evaluations, successfully mitigates interfacial side reactions and enhances bulk charge transfer. Consequently, the modified natural graphite anodes exhibit improved capacities at higher current densities, delivering a stable reversible capacity of 388.9 mAh g−1 after 200 cycles at a rate of 5 C.