Ascorbic acid acts as both an antioxidant and a surfactant to form organic groups (first carbon source) on the surface of as-solvothermal products, in which the-OH (or H 2 O) groups of glucose (second carbon source) are closely bonded to the surface to form a uniform adsorption layer. Uniform mixed-carbon-coated LiMn 0.4 Fe 0.6 PO 4 nanopowders are formed after calcination, which demonstrate excellent electrochemical performances.

A simple two-step solid-state-reaction process is adopted to synthesize carbon-coated Mg-doped Li(Mn,Fe)PO 4 (LMMFP) nano-particles. As positive electrode materials for lithium-ion batteries, the carbon-coated LMMFP samples show excellent electrochemical properties in a temperature range from-20 to 55°C. For example, LiMn 0.48 Fe 0.5 Mg 0.02 PO 4 can deliver a capacity of 146.2 mAh g-1 at 3C rate and retain 95.3% after 450 cycles at 25°C. It can also deliver 160.7 mAh g-1 at 1C and retain 97.7% after 100 cycles at 55°C. Even at-20°C, it gives a capacity of 109.5 mAh g-1 with an average discharge voltage of 3.37 V at 0.2C. In Na/LMMFP cells, the LMMFP electrodes can be electrochemically converted into Mg-doped Na(Mn,Fe)PO 4 (NMMFP) electrodes for sodium-ion batteries (SIBs). Ex-situ XRD