Enhanced electrochemical performance of Ni2+ doped carbon coated LiMn0.5Fe0.5PO4 nanocomposites as cathode materials for lithium-ion batteries

Abstract

To highlight the complementary advantages between LiFePO₄ and LiMnPO₄, the orthorhombic phosphor-olivine structured LiMn_1-xFe_xPO₄ (0<x<1) has been attracting significant attention as cathode material for lithium ion battery due to its series of appealing features. However, LiMn_1-xFe_xPO₄ (0<x<1) suffers from low electronic and ionic conductivity and slow lithium ion diffusion. Therefore, in this work, Ni²⁺ doped carbon coated LiMn_0.5Fe_0.5PO₄ nanocomposites were synthesized by a facile solvothermal method followed by calcination under an Ar atmosphere with 10 % (v/v) H₂ and investigated electrochemically. The results show that Ni²⁺ doping could tune the morphology and cell parameters of carbon coated LiMn_0.5Fe_0.5PO₄ crystal composites to form carbon coated LiMn_0.5Fe_0.5-xNi_xPO₄ solid solution, thus affect its electrochemical performance. In comparison, carbon coated LiMn_0.5Fe_0.499Ni_0.01PO₄ nanocomposite exhibits excellent rate capability and superb cycle stability due to its reinforced crystal structure stability, improved electrical conductivity and fast lithium ion diffusion rate, indicating that the appropriate amount of Ni²⁺ doping could greatly ameliorate the electrochemical performance of carbon coated LiMn_0.5Fe_0.5PO₄ cathode material. This offers the guidance of designing the stable structurally LiMn_1-xFe_xPO₄ composite cathode for the next generation of lithium ion battery.