Study on discharge voltage and discharge capacity of LiFe1−xMnxPO4 with high Mn content

Abstract

Rod-like LiFe1−xMnxPO4/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 LiFe1−xMnxPO4, the electrochemical property was studied to clarify the effect of manganese content. LiFe1−xMnxPO4/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 LiFe0.30Mn0.70PO4/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.