Cu‐Driven Active Cu2Se@MXene Heterointerface Reconstruction and Co Electron Reservoir Toward Superior Sodium Storage

The electrochemically reconstructed active Cu₂Se@MXene heterostructure with abundant heterointerfaces exhibits enhanced Na⁺ adsorption and diffusion kinetics, as well as structural robustness. Additionally, the Co element serves as an electron reservoir, further accelerating the redox process of Cu₂Se. This will provide new insights and guidance for the development of advanced conversion-type anodes for sodium-ion batteries.

Abstract

Heterostructure engineering and active component reconstruction are effective strategies for efficient and rapid charge storage in advanced sodium-ion batteries (SIBs). Herein, sandwich-type CoSe₂@MXene composites are used as a model to reconstruct new active Cu₂Se@MXene heterostructures by in situ electrochemical driving. The MXene core provides interconnected pathways for electron and ion conduction, while also buffering volumetric expansion to stabilize the structure. This reconstructed Cu₂Se@MXene heterointerface features abundant sodium storage active sites, enhanced Na⁺ adsorption, and diffusion kinetics, thus increasing sodium storage capacity. Moreover, the elevated Co valence state during the discharge process allows it to act as an electron reservoir to provide additional electron supply for Cu₂Se conversion and accelerate the sodium storage kinetics. When employed as an anode in SIBs, the CoSe₂@MXene electrode exhibits high capacity (694 mAh g⁻¹ at 0.1 A g⁻¹), excellent rate performance (425 mAh g⁻¹ at 20 A g⁻¹), and exceptional durability (437 mAh g⁻¹ after 10 000 cycles at 5 A g⁻¹ with a 0.0014% capacity decay per cycle). The electrochemical reconstruction and sodium storage mechanism of Cu₂Se@MXene anode is further revealed through ex situ characterization and theoretical calculations. This work provides a new approach for designing advanced conversion-type anodes for SIBs.