LAUSR

Abstract NASICON (Na superionic conductor) type electrode materials are known for their wide range of electrochemical potentials, high ionic conductivity, and most importantly their structural and thermal stabilities. Li2M2(MoO4)3 (M=Zn, Cu), belonging to molybdenum-based NASICON family, are successfully synthesized by simple sol-gel method. The structure evolution caused by the substitution of Zn2+ by Cu2+ within Li2Zn2-xCux(MoO4)3 (0 ≤ x ≤ 2) has been investigated. Rietveld refinement results reveals that the priority order of copper atoms replacing zinc atoms in Li2Zn2(MoO4)3. Furthermore, both Li2Zn2(MoO4)3 and Li2Cu2(MoO4)3 electrodes deliver excellent electrochemical performance, and high reversible capacities of 864 mAh g−1 and 747 mAh g−1 can be acquired at a current density of 0.1 A g−1, respectively. In addition, the in-operando X-ray diffraction measurements indicate the formation of cubic mesophase Li4MoO5 both in Li2Zn2(MoO4)3 and Li2Cu2(MoO4)3 during the initial lithium insertion, which irreversibly converts into the amorphous phases on further discharge at subsequent discharge and charge process.