Preparation In Polyol/Water System And CeO₂/C Hybrid Coating Modification Of LiMnPO₄

Lithium manganese phosphate(LiMnPO4) cathode material has attracted many attentions in recent years, due to its advantaged properties of high energy density, good stability, environmental benignity, low cost and so on. However, the inherent low electronic conductivity and sluggish lithium ion diffusion kinetics have seriously restricted the practical application of LiMnPO4. Many efforts have been adopted to enhance the electrochemical performance, such as optimizing the synthesize conditions, surface coating as well as metal ions doping.A polyol reflux method was adopted to synthesize LiMnPO4 and the effects of reaction temperature, time and the kinds of surfactant on the electrochemical performance have been investigated systematically. The results indicated the optimum temperature and time in the polyol process were 115 °C and 12 h. The surfactant was selected as PEG2000 and the mass ratio of PEG2000 to LiMnPO4 was 4:1. The sample obtained under such conditions with plate morphology was packed tightly by the primary particles and the crystallinity was low, so the initial discharge capacity at 0.1 C could only reach 58.0 mAh g-1.The influence of different raw materials on the morphology and electrochemical performance of LiMnPO4 was studied in a polyol-assistant hydrothermal process. It was found that the combination of MnSO4·H2O and Li3PO4 was optimal to prepare LiMnPO4 with good performance. The sample which exhibited flaky-like morphology could attain a capacity of 105.0 mAh g-1 at 0.1 C and showed good cycling stability.The hybrid coating of CeO2 and carbon on LiMnPO4 surface was prepared via a wet chemical method. In comparation with the LiMnPO4 sample which was only coated with carbon, the CeO2/C hybrid coating could not only enhance the discharge capacity, but also improve the cycling stability of LiMnPO4. The optimal CeO2 content was 0.25 wt.% of LiMnPO4 and the initial discharge capacity of the CeO2/C hybrid coated sample at 0.1 C was 139.9 mAh g-1. The capacity retention after 50 cycles was 86.1 %. The results of XRD, SEM and TEM indicated that CeO2 and carbon could coat on LiMnPO4 surface successfully, and CeO2 could fill in the vacancies of the un-continuous carbon layer. In addition, the CeO2/C hybrid coating could effectively enhance the electronic conductivity and keep the structure stability of the bulk material, which could be verified by the EIS and CV tests.