Hybrid LiV3O8/carbon encapsulated Li1.2Mn0.54Co0.13Ni0.13O2 with improved electrochemical properties for lithium ion batteries

Abstract

A low coulombic efficiency in the first cycle and poor rate capability limit the practical application of a lithium rich manganese-based solid solution (LMSS) in lithium ion batteries. To resolve these problems, a core–shell type of Li_1.2Mn_0.54Co_0.13Ni_0.13O₂@LiV₃O₈/C (LMSSVC) composite material was prepared using a sol–gel process, in which NH₄VO₃-derived V₂O₅ chemically leached lithium from the LMSS and formed the LiV₃O₈ during high temperature annealing. The effect of the hybrid LiV₃O₈/C layer on the electrochemical properties of the LMSS is investigated using cyclic voltammetry, electrochemical impedance spectroscopy and galvanostatic charge–discharge measurements. The as-prepared LiV₃O₈ nanoparticles are embedded within the carbon matrix uniformly, which becomes an outer shell to encapsulate the LMSS nanoparticles. Because of the Li-host nature of LiV₃O₈ and the electronic conductivity of carbon, the LMSSVC can deliver a capacity of 269 mA h g⁻¹ at a 0.1C rate in the first cycle over the voltage range of 2.0–4.8 V together with a coulombic efficiency of 94%, and retain 94% of the initial capacity after 50 cycles. It can deliver capacities of 258, 245, 229, 207 and 176 mA h g⁻¹ at the rates of 0.2C, 0.5C, 1C, 2C and 5C, respectively. The results indicate that surface coating of the hybrid LiV₃O₈/C layer can improve not only the initial coulombic efficiency but also the rate capability of the LMSS material.