Mixed-carbon-coated LiMn0.4Fe0.6PO4 nanopowders with excellent high rate and low temperature performances for lithium-ion batteries

A novel solvothermal approach with ascorbic acid as both an antioxidant and a first-time carbon coating source is developed to synthesize LiMn0.4Fe0.6PO4 nano-particles with a uniform particle size distribution around 150 nm. A calcination step for the second-time carbon coating and further crystallization is adopted following the solvothermal step. The structures and electrochemical properties of the obtained samples are studied by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, Raman spectroscopy, Fourier transformation infrared, Infrared carbon-sulfur analyzer and galvanostatic cell cycling. Ascorbic acid plays a crucial role in the formation of uniform carbon layer and nano-particles. Compared with single-carbon-coated LiMn0.4Fe0.6PO4 without adding ascorbic acid, the mixed-carbon-coated LiMn0.4Fe0.6PO4 shows much better electrochemical performance. It can deliver specific capacities of 154.8 and 128.5 mAh g−1 at 1C and 20C, respectively, at 25 °C. Even at −20 °C, its specific capacities are 106.6 and 68.8 mAh g−1 at 0.2C and 5C, respectively.