The improved electro-chemical performance of β-LiVOPO4 by relieved strain via a post ball milling annealing process as a cathode material for lithium ion batteries

Electro-active lithium vanadyl phosphate, beta-LiVOPO4, was synthesized by solid-state method and post ball milling annealing treatment. SEM/TEM showed diminished particle size and thin amorphous surface layer after high energy ball milling. Deconvolution analysis based on Rietveld refinement revealed significantly relieved lattice strain. These factors contributed to the significantly improved electro-chemical performance of strain-relief beta-LiVOPO4 (S-LVOP). The initial discharge specific capacity of S-LVOP was 154.5 mAh g(-1 )at the current density of 16 mA g(-1), ca. 93% of the theoretical capacity of 166 mAh g(-1), and that was only 61.6 mAh g(-1) for pristine LVOP. It also remained 106.4 mAh g(-1) after 80 cycles. Better rate performance was also observed. Moving boundary model based GITT method showed that the lithium ion diffusion coefficients in the two phase region varied in the range of 1.5 x 10(-11) cm(2) s(-1) - 6.0 x 10(-1)1 cm(2) s(-1), 2-4 orders of magnitude higher than that obtained by traditional GITT method.