Facilitating the redox conversion of CoSe2 nanorods by Ti3C2Tx to improve the electrode durability as anodes for sodium-ion batteries

Abstract

Nanostructured metal selenides based on conversion reactions are promising anode materials for sodium-ion batteries (SIBs). However, the repeat structural degradation accompanied by the detrimental intermediate of sodium selenides (Na_xSe) leads them to suffer from continuous capacity decaying and under-voltage failure. In this work, CoSe₂ is chosen as a representative by the introduction of a polar Ti₃C₂T_x matrix to alleviate the performance deterioration caused by the crystal structure evolution. CoSe₂ nanorods are in situ grown on the Ti₃C₂T_x (CoSe₂/Ti₃C₂T_x) surface by a simple one-step hydrothermal reaction during the reduction environment. A tight chemical bonding is formed between CoSe₂ and Ti₃C₂T_x by oxygen bridging, which maintains the stable charge and ion transport during cycling. Meanwhile, Ti₃C₂T_x facilitates copper coming from the collector being diffused in the electrode, and is involved in the electrochemical reaction in an ether-based electrolyte, resulting in CoSe₂ being partially converted to Cu_2−xSe after long cycles. Synchronously, Ti₃C₂T_x improves the mutual transformation of Na_xSe ↔ Na₂Se during the intercalation/de-intercalation of metal selenides. Therefore, via optimizing the content of Ti₃C₂T_x, the CoSe₂/Ti₃C₂T_x-10 composite obtains excellent long cycle stability, delivering a specific capacity of 343 mA h g⁻¹ at 0.3 A g⁻¹ after 1200 cycles with a capacity retention of 98%. Even at 10.0 A g⁻¹, CoSe₂/Ti₃C₂T_x-10 exerts about 200 mA h g⁻¹ initial capacity, and remains at 140 mA h g⁻¹ after 1400 cycles. The strategy of introducing a polar matrix to improve the long cycling stability of the metal selenide provides a new opportunity for the development of new anode materials for SIBs.