Study on discharge voltage and discharge capacity of LiFe_1−xMn_xPO₄ with high Mn content

Rod-like LiFe_1−xMn_xPO₄/C cathode with particle size of about 300–500 nm was fabricated successfully via simple hydrothermal method. By means of adjusting the manganese content of LiFe_1−xMn_xPO₄, the electrochemical property was studied to clarify the effect of manganese content. LiFe_1−xMn_xPO₄/C sample with x = 0.70 showed the superior specific discharge capacity of 153.1 mAh g⁻¹ at a rate of 0.1 C, and the electrochemical mechanism analyzed by electrochemical impedance spectra demonstrated that the LiFe_0.30Mn_0.70PO₄/C exhibited the smallest charge transfer impedance and the largest lithium-ion diffusion coefficient. With the increase of manganese content, the reduction of discharge capacity is attributed to the linear decrease of Mn²⁺/Mn³⁺ reduction reaction. When x = 0.80, the two discharge platforms located at 3.5 and 3.9 V, respectively, reach a maximum, which result from the reduction electromotive force of Fe²⁺/Fe³⁺ affected by the addition of manganese ions since the discharge platform of LiMnPO₄ is higher than that of LiFePO₄.