Comparison of LiVPO4F to Li4Ti5O12 as anode materials for lithium-ion batteries.

In this paper, we reported on a comparison of LiVPO4F to Li4Ti5O12 as anode materials for lithium-ion batteries. Combined with powder X-ray diffraction, scanning electron microscopy, high-resolution transmission electron microscopy, galvanostatic discharge/charge tests and in situ X-ray diffraction technologies, we explore and compare the insertion/extraction mechanisms of LiVPO4F based on the V3+/V2+/V+ redox couples and Li4Ti5O12 based on the Ti4+/Ti3+ redox couple cycled in 1.0-3.0 V and 0.0-3.0 V. The electrochemical results indicate that both LiVPO4F and Li4Ti5O12 are solid electrolyte interphase free materials in 1.0-3.0 V. The insertion/extraction mechanisms of LiVPO4F and Li4Ti5O12 are similar with each other in 1.0-3.0 V as proved by in situ X-ray diffraction. It also demonstrates that both samples possess stable structure in 0.0-3.0 V. Additionally, the electrochemical performance tests of LiVPO4F and Li4Ti5O12 indicate that both samples cycled in 0.0-3.0 V exhibit much higher capacities than those cycled in 1.0-3.0 V but display worse cycle performance. The rate performance of Li4Ti5O12 far exceeds that of LiVPO4F in the same electrochemical potential window. In particular, the capacity retention of Li4Ti5O12 cycled in 1.0-3.0 V is as high as 98.2% after 20 cycles. By contrast, Li4Ti5O12 is expected to be a candidate anode material considering its high working potential, structural zero-strain property, and excellent cycle stability and rate performance.