Enhancing High-Rate Performance and Cyclability of LiFePO4 Cathode Materials for Lithium-Ion Batteries by Optimizing the Li/Fe Ratio

Abstract

Lithium iron phosphate (LiFePO₄) has garnered significant attention as a key cathode material for lithium-ion batteries due to its exceptional safety, long cycle life, and environmentally friendly characteristics. However, its electrochemical performance is influenced by several factors, with the Li/Fe molar ratio being one of the key determinants. In this study, a series of LiFePO₄ samples with Li/Fe molar ratios of 0.99, 1.00, 1.01, 1.03, 1.05, and 1.07 were synthesized via a solid-state method. The impact of varying the Li/Fe molar ratios on the physical and electrochemical properties of LiFePO₄ was systematically investigated. The results indicate that at a Li/Fe molar ratio of 1.05, the material exhibits optimal electrochemical performance, achieving a discharge capacity of 165.30 mA h g^–1 at a 0.1 C rate and 158.38 mA h g^–1 at a 1 C rate. A range of characterization techniques, including electrochemical impedance spectroscopy (EIS), differential capacity versus voltage (dQ/dV), and galvanostatic intermittent titration technique (GITT), confirmed that the sample with a Li/Fe molar ratio of 1.05 exhibits the lowest polarization and the highest lithium ion diffusion coefficient (3.24 × 10^–12 cm² s^–1). These results demonstrate that the optimal Li/Fe molar ratio of 1.05 expands the Li⁺ transport channels within the LiO₆ octahedra, reduces polarization, and enhances lithium-ion diffusion, thereby improving the electrochemical performance of the material.