Improving the Electrochemical Properties of a Cathode Material Based on Lithium–Manganese Phosphate through the Partial Substitution of Mn for Ni

Abstract

Lithium and transition-metal phosphates are promising cathode materials for lithium-ion batteries. Lithium manganese phosphate LiMnPO₄ has a higher specific energy density than LiFePO₄ used in practice: theoretical values of 700 and 580 W h/kg, respectively. However, its use is hampered by a number of disadvantages: reduced electronic and ionic conductivity, inferior stability of the structure in the charged form, and large changes in the volume during (de)lithiation. LiMnPO₄ and LiMn_0.95Ni_0.05PO₄ samples are synthesized by the solvothermal method and studied using X-ray powder diffraction, low-temperature nitrogen adsorption, scanning electron microscopy, and electrochemical methods. It is shown that a small degree of substitution of Mn for Ni (5 at %) leads to an increase in the capacity and Coulombic efficiency of LiMnPO₄, a decrease in charge-transfer resistance, and an increase in Li⁺ diffusion coefficients.