Cation-Disordered Lithium-Excess Li-Fe-Ti Oxide Cathode Materials for Enhanced Li-Ion Storage

Cation-disordered Li-excess lithium-transition metal (Li-TM) oxides designed based on the percolation theory are regarded as a promising new type of high-performance cathode material for Li-ion batteries. Herein, cation-disordered rocksalt-type Li-Fe-Ti oxides of Li_0.89Fe_0.44Ti_0.45O₂, Li_1.18Fe_0.34Ti_0.45O₂, and Li_1.24Fe_0.38Ti_0.38O₂ with different Li-to-transition metal ratios (Li/TM = 1, 1.49, or 1.63) are investigated to understand the effect of a Li excess on the electrochemical Li-ion storage properties. The Li excess leads to local structural fluctuations of the as-prepared Li-Fe-Ti oxides, contributing to the formation of 0-TM diffusion channels for rapid Li-ion migration. The as-prepared Li-excess Li-Fe-Ti oxide cathodes (Li/TM = 1.49 and Li/TM = 1.63) deliver a higher reversible capacity of over 220 mAh g^-1 and a better rate capability compared to the Li/TM = 1 electrode, which possesses a maximum discharge capacity of only about 165 mAh g^-1. The redox reactions of Fe²⁺/Fe³⁺ and O^2-/O₂^2- achieve the main capacity of the Li-excess Li-Fe-Ti oxide cathodes during cycling, as supported by ⁵⁷Fe Mössbauer spectroscopy, O 1s X-ray photoelectron spectroscopy, and O K-edge soft X-ray absorption spectroscopy.