Boosting Li-storage performance of LiMn0.5Fe0.5PO4/C cathode via Zn-mediated lattice modulation

Abstract

LiMn_0.5Fe_0.5PO₄ is regarded as a cathode material with extensive potential for lithium-ion batteries (LIBs), offering advantages such as excellent safety characteristics, cost-effective production, and co-friendly attributes. However, the inherent slow conductivity and manganese ion dissolution pose challenges to its commercial viability. To overcome these limitations, cation doping strategies can significantly improve material performance by enhancing crystal structure stability, improving electronic conductivity, and facilitating Li-ion transport. Herein, a citric acid-assisted sol-gel technique has been employed to perform Zn²⁺ doping at the Fe²⁺ site of LiMn_0.5Fe_0.5PO₄/C. Our experimental investigations reveal that Zn²⁺ mitigates the structural collapse caused by volume expansion and lattice distortion at charging-discharging cycles, thereby enhancing the structural stability of the material. Additionally, DFT computations were performed to evaluate the impact of Zn²⁺ doping on the density of states, the trace amount of zinc doping can enhance electronic transmission capability and mitigate the intensity of Jahn-Teller distortion, then reinforcing our experimental observations. Notably, the doped LiMn_0.5Fe_0.49Zn_0.01PO₄/C cathode exhibits exceptional discharge capacity of 116.5 mAh g⁻¹ even at 10C, alongside boasting remarkable long-term cyclic stability with only about decay of 5.05 % capacity retention after undergoing 300 cycles at 1C. This strategic design offers an efficient solution to enhance the characteristics of lithium manganese iron phosphate cathode material, making it more suitable for high-performance LIB applications.