LiMnPO_4 Nanoplates with In-Situ Growth of a sp~2-Carbon Surface Layer from a Liquid Precursor, Phase Stability, and Tailored Impedance Properties

摘要

Background: Olivine structured LiMnPO_4 is a pioneering energy-storage material of Li~+-ion batteries. Its synthesis in a shape of small plates (large free-surfaces) bonding over a C-sp~2 surface layer is demanded in harvesting its functional properties. Objective: In situ synthesis of grafted LiMnPO_4 of nanopaltes with a C-sp~2 surface layer, with tailored impedance properties. Method: A simple hydrothermal reaction is explored in a solution LiOH·H_2O, MnSO_4·H_2O and H_3PO_4 with sodium dodecyl sulphate (a surfactant) to synthesize LiMnPO_4 of small plates. A phase pure LiMnPO_4 is obtained in 8-12 h heating a precursor solution at 150°C in an autoclave, and then washing a recovered powder in hot water. Results: The sample LiMnPO_4 contains nanoplates of a Pmnb orthorhombic crystal structure, 20-40 m~2/g surface area, 30-40 nm thickness, and self-assemblies. The lattice parameters a = 0.6104 nm, b = 1.0468 nm and c = 0.4758 nm describe a marked 0.43 % lattice expansion over the bulk phase, with an enhanced aspect ratio c/a = 0.7795 above the bulk value 0.7777, which likely promotes the charge-carrier dynamics. In the HRTEM images, the LiMnPO_4 plates wear a GO-surface layer of a conductive 2D-network with sp~2-C electrons. Uniquely, a cell made of the sample yields largely enhanced (i) conductivity of Li~+ ions and electrons at a 10~(-6) S-cm~(-1) scale and (ii) Li~+ diffusion coefficient 3.291×10~(-14) cm~2s~(-1) at room temperature. Conclusion: The results describe LiMnPO_4 nanoplates with an inbuilt surface C-sp~2 layer extend fast charge diffusion kinetics useful for powerful Li~+- ion batteries.