Boosting Solid-State Reconversion Reactivity to Mitigate Lithium Trapping for High Initial Coulombic Efficiency

Abstract

An initial Coulombic efficiency (ICE) higher than 90% is crucial for industrial lithium-ion batteries, but numerous electrode materials are not standards compliant. Lithium trapping, due to i) incomplete solid-state reaction of Li+ generation and ii) sluggish Li+ diffusion, undermines ICE in high-capacity electrodes (e.g., conversion-type electrodes). Current approaches mitigating lithium trapping emphasize ii) nanoscaling (<50 nm) to minimize Li+ diffusion distance, followed by severe solid electrolyte interphase formation and inferior volumetric energy density. Herein, this work accentuates i) instead, to demonstrate that the lithium trapping can be mitigated by boosting the solid-state reaction reactivity. As a proof-of-concept, ternary LiFeO2 anodes, whose discharged products contain highly reactive vacancy-rich Fe nanoparticles, can alleviate lithium trapping and enable a remarkable average ICE of ≈92.77%, much higher than binary Fe2O3 anodes (≈75.19%). Synchrotron-based techniques and theoretical simulations reveal that the solid-state reconversion reaction for Li+ generation between Fe and Li2O can be effectively promoted by the Fe-vacancy-rich local chemical environment. The superior ICE is further demonstrated by assembled pouch cells. This work proposes a novel paradigm of regulating intrinsic solid-state chemistry to ameliorate electrochemical performance and facilitate industrial applications of various advanced electrode materials.