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 Mg1.5Ca0.5Nb34O87 shows the smallest ionic packing factor among Wadsley–Roth niobate materials. Compared with Mg2Nb34O87, Mg1.5Ca0.5Nb34O87 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, Mg1.5Ca0.5Nb34O87 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, Mg1.5Ca0.5Nb34O87 is an all-climate anode material capable of working at harsh temperatures, even when its particle sizes are in the order of micrometers.

Keywords

• Ionic packing factor
• Low-temperature electrochemical kinetics
• High-temperature cycling stability
• Wadsley–Roth niobate
• Substitution
• In situ characterization