The synergistic effect of multiple doping on structure and electrochemical performance of LiFe1-x-y-zZnxMnyCazPO4

This paper is focused on the synergistic effect of Fe site multi-doping, which is a promising target to adequately enhance the electrochemical performance of LiFePO4 by means of cation doping method. Ca, Mn and Zn are selected as the doping elements, and the doping amounts are designed as inequality and equality multi-doping. The effects on structure micro-variation are evaluated in terms of cell parameters and LiO bond length according to the Rietveld refinement results. The effect tendency on structure micro-variation is approximately corresponding with the electrochemical performance, which can be concluded mainly as (i) in the case of inequality amount doping, Zn predominant doping exhibits more beneficial effect than Mn predominant doping, while Ca predominant doping is beneficial for cycling performance but harmful for rate capability; (ii) in the case of equality amount doping, appropriate doping amount (LiFe0.94Zn0.02Mn0.02Ca0.02PO4) exhibits both merits of Zn predominant doping for rate capability and Ca predominant doping for cycling performance, while high doping amount (LiFe0.88Zn0.04Mn0.04Ca0.04PO4) just exhibits merit of Ca predominant doping; (iii) among these multi-doping samples, LiFe0.95Zn0.03Mn0.01Ca0.01PO4 and LiFe0.94Zn0.02Mn0.02Ca0.02PO4 exhibit better electrochemical performance. This study of synergistic effect has reference significance for the development of cation doping method of modifying LiFePO4. Series of designed Zn, Mn and Ca multi-doped LiFePO4/C are prepared to investigate the synergistic effect of multiple doping. [Display omitted] •The synergistic effect of Fe site multi-doping of LiFePO4 is investigated.•Series of designed Zn, Mn, Ca multi-doped LiFePO4/C samples are prepared.•Structure micro-variations are evaluated through Rietveld refinement method.•The effect rules of the multi-doping on electrochemical performance are indicated.