Improvement of electrochemical properties of LiFe0.9Zn0.1-xMnxPO4 (x=0, 0.05, 0.075, 0.1) by double doping with Zn2+, Mn2+

Zn²⁺ and Mn²⁺ co-doped LiFe_0.9Zn_0.1-xMn_xPO₄ (where x = 0, 0.05, 0.075, 0.1) composites are synthesized by a simple one-step hydrothermal method. The composition, structure, morphology and electrochemical properties of the materials are fully characterized using XRD, SEM, TEM, EDS, CV and AC impedance tests. The results show that the co-doping of Zn²⁺ and Mn²⁺ preserves the olivine structure of LiFePO₄ and also stabilizes the crystal structure, reduces the charge transfer resistance and improves the Li⁺ diffusion rate. When the initial specific capacity of the cathode material with the doping ratio of Zn = 0.025 and Mn = 0.075 is 161.8 mAh·g⁻¹, the discharge specific capacity after 200 cycles is still as high as 157.8 mAh·g⁻¹ with a capacity retention of 97.5 %, which is obviously better than the rest of the materials.