Porous TiP2O7/nitrogen-doped carbon composite with tailored crystal orientation as diffusion-controlled high-rate anode for lithium-ion batteries

Abstract

TiP₂O₇ is a lithium-ion batteries anode material with outstanding stability and high safety due to its strong polyanion three-dimensional frame structure. However, poor electrical conductivity severely represses the rate capability of TiP₂O₇ anode. Herein, a porous TiP₂O₇/nitrogen-doped carbon (CN) composite with tailored (6 3 0) and (6 0 0) preferential crystallographic orientation is achieved by the ball-milling and thermal treatment strategy. The TiP₂O₇/CN (6 3 0) anode retains specific capacities of 194.3 and 128.9 mA h/g at high current densities of 5 and 10 A/g, respectively, superior than that of the TiP₂O₇/CN (6 0 0). Remarkably, kinetic analysis reveals that the charge storage process in the TiP₂O₇/CN (6 3 0) anode is predominantly diffusion-controlled, with the diffusion-controlled capacity contributing up to 52 % even at a high scan rate of 2 mV/s. Density functional theory calculation confirms the lower lithium ions migration energy barrier of (6 3 0) crystallographic orientation of TiP₂O₇. In addition, due to the homogeneity of porous structure and composition, the TiP₂O₇/CN (6 3 0) anode maintains a capacity of 389mA h/g after 1000 cycles at 1 A/g. Thereby, the synthesis strategy for preferred orientation TiP₂O₇-based anode is instructive for the structural design of high-rate metal-based composite oxides for lithium-ion batteries.