Synthesis And Electrochemical Performance Of LiMnPO₄Nanomaterials As A Cathode Material For Lithium-ion Batteries

Olivine structured lithium manganese phosphate (LiMnPO4) has attracted considerable attention as a new type of potential cathode material for lithium ion batteries (LIBs). It has some advantages such as high voltage, good environmental compatibility, low cost and stable cycle performance. However, this material has a low electronic conductivity and poor ionic conductivity that limit its practical application.In order to struggle against these issues, we have discussed the ways that come over these problems in two aspects, nanoscale and carbon coated. Wherein the nanoscaled electrode material can shorten the diffusion path of lithium ions, then improve its rate performance; carbon coated material can increase the conductivity of the electrode, then promote the transport of charge. The morphology, structure and electrochemical performances of these materials were characterized by XRD, SEM, TEM, HRTEM, TGA, Raman spectra, galvanostatic charge/discharge, CV and EIS. The main works of this paper are as follows:1. LiMnPO4nanoparticles with various morphologies were synthesized by hydrothermal/solvothermal method. By regulating the reaction conditions of the solvothermal, it was found that the rod-like LiMnPO4could be prepared at a neutral solution of DEG with the concentration of Mn2+at0.16M. The product reveals that the average length and diameter are approximately100and60nm, respectively. Experiment results also revealed that LiMnPO4nanoplates with the thickness less than20nm were prepared at suitable pH value by using TTEG as solvent.2. In order to improve the electrical conductivity and ionic conductivity of LiMnPO4, we modified its surface through the path of carbon-coating. Herein, we mainly studied the smaller sized LiMnPO4of rod-like morphology. By ball milled with organic carbon source followed high-temperature annealing, its electrochemical performance was improved. The organic carbon sources were citric acid, ascorbic acid, glucose, sucrose, and beta-cyclodextrin. Results showed that beta-cyclodextrin can be considered as the best carbon source. It showed a reversible capacity of153.4mAh·g-1at a rate of0.1C and maintained it at120mAh·g-1after50cycles. Correlated to the molecule structure, we analyzed this result. It is believed that larger molecules with more oxygenous groups are beneficial to their uniform adsorption on the electrodes and then produce a better electron-conductive carbon layer after calcinations.