Solvothermal synthesized LiMn1−xFexPO4@C nanopowders with excellent high rate and low temperature performances for lithium-ion batteries

Abstract

Mixed-carbon coated LiMn_1−xFe_xPO₄ (x = 0, 0.2, 0.5, 1) nano-particles are synthesized by a novel solvothermal approach. All of these powders possess a uniform particle size distribution around 150 nm and a carbon coating layer of about 2 nm. The LiMn_1−xFe_xPO₄@C samples with a carbon content of 2 wt% have an optimal electrochemical performance. The average voltage platform of LiMn_1−xFe_xPO₄@C increases with the increased Mn/Fe ratio, but declines gradually during electrochemical cycling. The LiMn_0.5Fe_0.5PO₄ sample shows a high energy density (568 W h kg⁻¹), good cycleability (97.1%, 100 cycles) and excellent rate capability (120.2 mA h g⁻¹, 20C) at room temperature. Simultaneously, the LiMn_0.5Fe_0.5PO₄ and LiFePO₄ samples also show excellent low temperature electrochemical performance with specific capacities of 109.4 and 138.8 mA h g⁻¹ with average discharge voltages of 3.476 V and 3.385 V, respectively, at −12 °C. Even at −20 °C, their discharge specific capacities are 71.7 and 82.3 mA h g⁻¹ at 3C, respectively.