Effect of Zr4+ doping on the morphological features and electrochemical performance of monoclinic Li3V2(PO4)3/C cathode material synthesized by an improved sol-gel combustion technique

Abstract

Abstract Monoclinic Li3V2−xZrx(PO4)3/C composites with different Zr4+ doping amounts (x = 0.00, 0.01, 0.05 and 0.09) were prepared by an improved sol-gel combustion technique. An expansion in the lattice volume was caused by the incorporation of Zr4+ in the V3+ sites of Li3V2(PO4)3, thus providing enlarged Li+ diffusion channels that are conducive to the reversible intercalation and deintercalation of Li+. Moreover, the amount of Zr4+ doping had an obvious impact on the morphological characteristics of Li3V2(PO4)3, while the undoped Li3V2(PO4)3 contained a mixed morphology with porous particles and needles. The volume fraction and sizes of the needles decreased with increasing amounts of Zr4+ doping. No needles were observed when the amount of Zr4+ doping was increased to x = 0.09. Furthermore, the ohmic and charge-transfer resistances were reduced, and the reversibility and Li+ diffusion coefficient were improved, after Zr4+ doping. All Zr4+-doped samples displayed better electrochemical performance when compared to pristine Li3V2(PO4)3. The optimized Li3V1.95Zr0.05(PO4)3/C sample with an adequate level of Zr4+ doping exhibited the highest tap density and demonstrated excellent electrochemical properties. It delivered a specific discharge capacity of 112.2 mAh g−1 at 10 C rate and a high capacity retention of 86.1% over 1000 cycles ranging from 3.0 to 4.3 V.