Structure, performance, morphology and component transformation mechanism of LiMn0·8Fe0·2PO4/C nanocrystal with excellent stability

LiMn0·8Fe0·2PO4/C nanocrystal was synthesized by a facile solvothermal reaction. The pH and concentration of lithium ion are changing with the increase of LiOH. The deposition law of precursor ions is investigated, in which Li+ exceeds the necessary stoichiometric ratio even in the lowest amount of LiOH. Mn2+ and Fe2+ possess the similar fixation tendency, and 87.88% Mn2+ are deposited at the pH of 3.30. However, nearly all Fe2+ are precipitated in a wide pH range (2.96–3.85). The morphology changes from nanosheet to nanoellipsoid under the cooperation of pH and precursor ions. The components of LiMnPO4 and LiFePO4 in LiMn0·8Fe0·2PO4/C are predicted and their contributions to capacity are close to the actual results. Sample S-2.6 delivers the optimum electrochemical performance with a capacity of 150.9, 134.6 and 107.5 mA h·g−1 at 0.05, 1 and 5 C, respectively. It also exhibits high reversibility, low charge transfer resistance (41.2 Ω) and excellent diffusion coefficient (5.38 × 10−11 cm2·s−1). The capacity retention of sample S-2.6 reaches 96.03% after 200 cycles and it maintains original structure without obvious change according to the ex-situ XRD results. The morphology of the cycled cathode film also maintains its integrity without evident cracks. The low dissolution of Mn2+ and Fe2+ from LiMn0·8Fe0·2PO4/C shows the enhanced chemical stability.