Towards a high-rate and long-life LiVPO_4F/C cathode material for lithium ion batteries by potassium and zirconium co-doping

摘要

As a high-potential and high-stability cathode material, LiVPO4F/C is modified by K+ and Zr4+ co-doping to significantly improve its high-rate and long-life performance. K+ assisted by Zr4+ slightly enlarges the unit cell volume to expand Li+ migration pathway. K+ substituting Li+ can also achieve pillar effect to increase the structural stability. Hall effect reveals that Zr4+ substituting V3+ is a donor doping, leading to the transformation of conductive type from p-type to n-type and a great increase of carrier density by 10(6) times. Therefore, the electronic conductivity (1.1 x 10(-2)S cm(-1)) increases by a factor of similar to 10(4). The charge transfer resistance decreases to 82.81 Omega and the Li+ diffusion coefficient (9.83 x 10(-13) cm(2) s(-1)) increases to 7 times that of sin doped LiVPO4F/C. The discharge capacities of Li0.99K0.01V0.995Zr0.005PO4F/C at 0.1C and 1C are 143.3 mA h g(-1) and 135.5 mA h g(-1), respectively. The capacity retention at the charge/discharge rate of 10C is as high as 80.0% after 2000 cycles with an initial capacity of 108.1 mA h g(-1). Even at the discharge rate of 60C (charging at 1C), the capacity reaches 105.7 mA h g(-1).