Carbon-Reinforced Nb₂CT_x MXene/MoS₂ Nanosheets as a Superior Rate and High-Capacity Anode for Sodium-Ion Batteries.

Abstract

Sodium-ion batteries operating at room temperature have emerged as a generation of energy storage devices to replace lithium-ion batteries; however, they are limited by a lack of anode materials with both an adequate lifespan and excellent rate capability. To address this issue, we developed Nb₂CT_x MXene-framework MoS₂ nanosheets coated with carbon (Nb₂CT_x@MoS₂@C) and constructed a robust three-dimensional cross-linked structure. In such a design, highly conductive Nb₂CT_x MXene nanosheets prevent the restacking of MoS₂ sheets and provide efficient channels for charge transfer and diffusion. Additionally, the hierarchical carbon coating has a certain level of volume elasticity and excellent electrical conductivity to guarantee the intercalation of sodium ions, facilitating both fast kinetics and long-term stability. As a result, the Nb₂CT_x@MoS₂@C anode delivers an ultrahigh reversible capacity of 530 mA h g^-1 at 0.1 A g^-1 after 200 cycles and very long cycling stability with a capacity of 403 mA h g^-1 and only 0.01% degradation per cycle for 2000 cycles at 1.0 A g^-1. Moreover, this anode has an outstanding capacity retention rate of approximately 88.4% from 0.1 to 1 A g^-1 in regard to rate performance. Most importantly, the Nb₂CT_x@MoS₂@C anode can realize a quick charge and discharge at current densities of 20 or even 40 A g^-1 with capacities of 340 and 260 mAh g^-1, respectively, which will increase the number of practical applications for sodium-ion batteries.