Realization of Ti Doping by Electrostatic Assembly to Improve the Stability of LiCoO2 Cycled to 4.5 V

Abstract

LiCoO2 has a theoretical capacity of up to 274 mAh g−1. However, the cycle based on LiCoO2 battery to voltage higher than 4.35 V caused obvious structural instability and serious capacity attenuation. Naturally, the maximum capacity shown by a commercial LiCoO2 is only 175 mAh g−1. Here, we have developed a Ti doping technique to solve the problem of long-term cycle instability and increase the capacity of LiCoO2. The positively charged Co(OH)2-xx+ nano-disk and the negatively charged Ti2-x/4□x/4O4x− nano-sheet were assembled by electrostatic gravity, and then calcined with LiOH at high temperature to form Ti-doped LiCoO2. We have used a detailed electrochemical impedance, cycle voltammetry analysis, galvanostatic intermittent titration technique and hybrid pulse power characterization to establish quantitatively dependence of the phase transition, lithium ion diffusion coefficient and structural distortion on cyclic performance in lithium ion batteries. After doping Ti, the transmission coefficient of Li+ remains unchanged, and the phase transition in the cycle is suppressed at the same time of stabilizing the structure. Even at a cutoff voltage of 4.5 V, Ti-doped LiCoO2 exhibits a very high capacity of 205 mAh g−1. After 200 cycles, the capacity retention rate is 97%, and the rate performance is obviously enhanced.