In situ Ni matrix for kinetic enhancement and Li-F cleavage catalysis enabled high-performance conversion fluoride electrodes

Abstract

Fluorides are considered potential replacements for intercalation electrodes in high-performance lithium-ion batteries (LIBs), owing to the high energy density achieved through conversion reactions for lithium storage. However, their practical application is hindered by severe polarization effects due to sluggish charge transport and electrochemical kinetics of LiF reactions. Herein, a dual-conductivity-enhanced Ni-CoF₂@CNT electrode is developed through CNT modulation and in situ reduction of Co_xNi_yF₂ solid solutions. Electrochemical characterizations and XPS confirm the irreversible transformation of NiF₂ into metallic Ni. Kinetic analyses reveal that the composite electrode exhibits low interfacial impedance, rapid interfacial charge transfer, and a lithium-ion diffusion coefficient three times than that of pristine CoF₂. Morphological regulation promotes Faradaic reactions into pseudocapacitance, mitigating diffusion limitations under high-rate conditions. Notably, density functional theory (DFT) calculations and ex situ XPS demonstrate that the Ni(111) crystal plane catalyzes LiF cleavage during charging, reducing the energy barrier from 3.620 eV for direct cleavage to 0.871 eV. The designed electrode exhibits outstanding cycling stability and rate performance, retaining a capacity of 405 mAh g⁻¹ with 94 % retention after 1000 cycles at 1 A g⁻¹. This study presents a straightforward and effective in situ reduction strategy for incorporating metallic phases into fluorides, providing a promising pathway for high-performance conversion electrodes.