Construction of high performance N-doped carbon coated LiMn0.8Fe0.2PO4 nanocrystal cathode for lithium-ion batteries

Abstract

N-doped carbon coated LiMn0.8Fe0.2PO4 nanocrystal for lithium-ion batteries was prepared by a facile solvothermal method. The doping effect of nitrogen is regulated by altering the addition amount of nitrogen source melamine. Result shows that the introduction of N atoms does not change the crystal structure of LiMn0.8Fe0.2PO4/C. The ‒NH2 functional groups in melamine can react with the ‒OH groups in pyrolytic carbon generated by the pre-sintering of sucrose. Then, multiple nanosheets in LMFP-0 are combined together and the morphology of LiMn0.8Fe0.2PO4/C is transformed to nano particle-like in LMFP-7. The doped nitrogen in the forms of pyridinic, pyrrolic and graphitic N are derived from the combination of pyrolytic carbon and melamine, which can generate active defective sites and improve the electronic conductivity and diffusion rate of lithium ions. Sample LMFP-7 delivers the best electrochemical performance with a capacity of 154.7, 144.2 and 110.0 mA h g−1 at 0.1, 1 and 5 C, respectively. The LiMn0.8Fe0.2PO4/C cathode exhibits good electrochemical reversibility, low charge transfer resistance (46.9 Ω) and high diffusion coefficient (1.35 × 10−13 cm2 s−1). It also delivers excellent cyclic performance, structural stability and chemical stability.