Optimization of Na-doping enhancing the ionic conductivity for high electrochemical performance LiMnxFe1−xPO4 cathode

Abstract

Owing to its higher energy density and low cost, lithium manganese iron phosphate (LiMnₓFe_1−xPO₄) has emerged as a promising cathode material. However, the practical application of LiMnₓFe_1−xPO₄ is hindered by its poor rate performance and cycle life, primarily because of its low electronic/ionic conductivity and the Jahn–Teller effect. Using a dry–wet hybrid solid-phase ball-milling method combined with in situ sodium doping at the lithium sites, this study explores the synthesis of LiMn_0.5Fe_0.5PO₄ -Na_i composite cathodes. Sodium doping enhances the lattice spacing, improves lithium-ion diffusion coefficients, and stabilizes the lattice structure, thereby improving the cycling stability. The material with a sodium doping level of 0.008 shows optimal electrochemical performance, achieving discharge capacities of 146.8 and 93.9 mAh g⁻¹ at 28 °C under current densities of 0.1 and 10 C, respectively. After 800 cycles at 1 C, the capacity retention is 95.3 %. Even at 45 °C, the material exhibits a discharge capacity of 103.6 mAh g⁻¹ at 10 C with a capacity retention of 98.6 % after 2000 cycles. The results reveal that sodium doping is an effective modification method to enhance the performance of LiMnₓFe_1−xPO₄ cathode.