Dramatic improvement in high-rate capability of LiMnPO4 nanosheets via crystallite size regulation

LiMnPO4 has gained much attention due to its higher electrode potential than that of the commercial LiFePO4. However, it suffers from worse electrode kinetics related to the extremely low electrical conductivity and Li+ ion diffusion rate. Reducing crystal size can shorten diffusion distance of Li+ ions, and suppress the negative effect of defect zones on Li+ ion diffusion during cycling, thereby improving the electrode activity. In this study, the effect of crystallite size and carbon coating of LiMnPO4 on the electrochemical behavior is systemically investigated. By facile acetic acid-assisted solvothermal synthesis method, the crystallite size of LiMnPO4 nanosheets (ca. 10–20 nm in thickness) is remarkably reduced to below 50 nm in length and width. The shortened Li+ ion diffusion distance, increased specific surface area, and improved electrical conduction via carbon layer coating lead to the excellent electrochemical performance. The resulting LiMnPO4/C cathode shows the good charge/discharge reversibility and high discharge specific capacities of 148.8 mAh g-1 and 96.4 mAh g-1 at 1 C and 20 C respectively. This work would greatly promote the development of high-performance Li-ion batteries balancing the energy density and safety.