Transport and electrochemical properties of high potential tavorite LiVPO4F

Abstract

Tavorite-structured 4 V-class LiVPO4F as a safe and durable cathode material for lithium-ion batteries (LIBs) has been studied. The electrical transport and ionic diffusion properties of LiVPO4F at different temperature and at different charge-discharge states have been systemically investigated for the first time. At room temperature, LiVPO 4F shows a relatively high bulk ionic conductivity of ~ 8 × 10- 7 S cm- 1 but a poor electronic conductivity of ~ 10- 11 S cm- 1. This work uncovers an abnormal non-Arrhenius temperature dependence of electrical conductivity in the temperature range of 30-90 C for tavorite LiVPO4F. Li+ diffusivity of Li1 - xVPO4F (0 ≤ x ≤ 1) at different delithiated/lithiated states and have been comprehensively studied for the first time, through galvanostatic charge-discharge, galvanostatic intermittent titration technique (GITT), electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). The electronic insulating nature may be the main bottleneck towards high rate performances for LiVPO4F at room temperature. To tackle this challenge, the strategy of carbon coating has been adopted in this work. The LiVPO4F/C composite exhibits impressive rate capability and good long-term cyclability at both room temperature and elevated temperature (55 C). © 2013 Elsevier B.V.