Optimization of Rate Capability and Cyclability Performance in Li VO Anode Material through Ca Doping.

A series of Ca-doped lithium vanadates Li Ca VO (x=0, 0.01, 0.03, and 0.05) are synthesized successfully through a simple sol-gel method. XRD patterns and energy-dispersive X-ray spectroscopy (EDS) mappings reveal that the doped Ca ions enter into the lattice successfully and are distributed uniformly throughout the Li VO (LVO) grains. XRD spectra and SEM images show that Ca doping can lead to an enlarged lattice and refined Li VO particles. A small quantity of V ions will transfer from V to V in the Ca-doped samples, as demonstrated by the X-ray photoelectron spectroscopy (XPS) analysis, which leads to an increase of an order of magnitude in the electronic conductivity. Improved rate capability and cycling stability are observed for the Ca-doped samples, and Li Ca VO exhibits the best electrochemical performance among the studied materials. The initial charge/discharge capacities at 0.1 C increase from 480/645 to 527/702 mA h g as x varies from 0 to 0.03. The charge capacity of Li Ca VO at 1 C retains 95.3 % of its initial value after 180 cycles, whereas the capacity retention is only 40 % for the pristine sample. Moreover, Li Ca VO maintains a high discharge capacity of 301.7 mA h g at a high discharge rate (4 C), whereas the corresponding value is only 95.2 mA h g for the pristine LVO sample. The enhanced cycling and rate performances are ascribed to the increased lithium ion diffusivity and electrical conductivity induced by Ca doping.