Enhancing low-temperature electrochemical kinetics and high-temperature cycling stability by decreasing ionic packing factor

Abstract

Present-day Li⁺ storage materials generally suffer from sluggish low-temperature electrochemical kinetics and poor high-temperature cycling stability. Herein, based on a Ca²⁺ substituted Mg₂Nb₃₄O₈₇ anode material, we demonstrate that decreasing the ionic packing factor is a two-fold strategy to enhance the low-temperature electrochemical kinetics and high-temperature cyclic stability. The resulting Mg_1.5Ca_0.5Nb₃₄O₈₇ shows the smallest ionic packing factor among Wadsley–Roth niobate materials. Compared with Mg₂Nb₃₄O₈₇, Mg_1.5Ca_0.5Nb₃₄O₈₇ delivers a 1.6 times faster Li​⁺ ​diffusivity at −20 ​°C, leading to 56% larger reversible capacity and 1.5 times higher rate capability. Furthermore, Mg_1.5Ca_0.5Nb₃₄O₈₇ exhibits an 11% smaller maximum unit-cell volume expansion upon lithiation at 60 ​°C, resulting in better cyclic stability; at 10C after 500 cycles, it has a 7.1% higher capacity retention, and its reversible capacity at 10C is 57% larger. Therefore, Mg_1.5Ca_0.5Nb₃₄O₈₇ is an all-climate anode material capable of working at harsh temperatures, even when its particle sizes are in the order of micrometers.