| As the demand for high voltage and high capacity battery becomes more and more urgent, LiFePO4 materials can’t adapt to the new requirement because of the low energy density. However, the electrochemical properties of LiMnPO4 are poor. New anode materials LiFexMn1-xPO4 which combine the advantages of both LiFePO4 and LiMnPO4 are intensively investigated. The introduction of Mn can increase the energy density of the material compared to LiFePO4, on the other side, the introduction of Fe can improve the electronic conductivity and ionic conductivity of the anode materials, obtaining excellent rate and cycle performance.First part of this paper is based on the laboratory’s previous work. LiFexMn1-xPO4 (x≤15%) with high performance is synthesized by solvothermal method. In this work, we synthesized ultrathin cuboid-like LiFexMn1-xPO4 (x<0.15) nanoplates by a facile, controllable method. The plate-like LiFexMn1-xPO4 with a small lateral size (40-100 nm) and thickness (10-20 nm) exhibits high electrochemical activity, excellent rate capability and superior cycle stability after carbon coating. Among them, LiFe0.15Mn0.85PO4/C shows the best electrochemical performance. It exhibits excellent rate capability, delivering high discharge capacities of 138.0,130.0 and 120.9 mAhg-1, respectively, at 5 C,10 C, and 20 C. Even at a current density as high as 50C, it can still deliver a discharge capacity of 96.2 mAhg-1, where the discharge process can be completed in only 40 s. LiFe0.15Mn0.85PO4/C can sustain a long-term cycling up to 1000 cycles at 10 C with a capacity retention close to 70%. The excellent rate capability is ascribed to the small size and enhanced electrode kinetics by Fe doping. The long cycle life can be attributed to the uniform distribution of Fe in Mn sites that relieves the Mn2+ dissolution and lattice distortion, and to the small size of the plates the facilitates the diffusion of Li ions and the release of lattice strain.At another part of this paper, we propose a facile route to prepare nano-LiMnPO4 (30-50 nm) by using citric acid (CA) as the surfactant. The addition of a small amount of CA in precursor leads to obvious size reduction of LiMnPO4. After carbon-coated nano-LiMnPO4 exhibits excellent rate capability and long cycle life at high rate because of the small size and uniform/thin carbon coating. The discharge capacities of LMP-3.0 are 158.6,152.3,147.9,140.0 and 126.1 mAhg-1 at 0.1 C,0.5 C,1 C,2 C and 5 C, respectively. At 10 C and 20 C, this sample can still deliver high capacities of 113.0 and 96.6 mAhg=1, respectively. LiMnPO4/C also exhibits long cycle life with ／70% capacity retained after 500 cycles at 10 C. The excellent rate capability is attributed to the small size with easy Li-ion transport on electrode/electrolyte interface and in bulk material, and to the uniform/thin carbon layer with enhanced electron transport. The long cycle life is ascribed to the small size which alleviates the lattice strains and the uniform carbon coating which refrains the Mn dissolution. |
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