Deep etching assisted hollow-carbon-skeleton structured porous Co0.85Se nanocubes anchored on MXene nanosheets for superior sodium storage toward ultrahigh initial Coulombic efficiency

Cobalt selenide (CoSe _x ), as a significant member of transition-metal selenides (TMSe), has attracted great interest as anode materials of sodium ion batteries (SIBs), owing to the superior sodium storage capacity. However, the low initial Coulombic efficiency (ICE), inferior rate capability and terrible cycling stability still restrict its practical application. Thus, we develop a method of tannic acid (TA) deep-etching to build up hollow Co metal-organic frameworks (Co-MOF), then combined with MXene nanosheets through the electrostatic self-assembly and meanwhile tailored the solid electrolyte interface (SEI) simultaneously to address above existing problems of CoSe _x anode. The hollow-carbon-skeleton structured porous Co _0.85 Se nanocubes anchored on the MXene nanosheets (TA-Co _0.85Se-MXene) greatly buffer the huge volume changes, reinforce the structure of the electrode and accelerate the Na ⁺/electron-transport kinetics. Furthermore, an ideal SEI film has been formed by employing the chosen ether-based electrolytes. Owing to the fabricated structure and tailored SEI, the TA-Co _0.85Se-MXene anode exhibits ultrahigh ICE of 91 %, superior rate capability of 389 mA h g ⁻¹ at 5 A g ⁻¹, and outstanding long-term cycling stability of 418 mA h g ⁻¹ at 1 A g ⁻¹ for 1000 cycles. This work proposes an effective strategy to design transition metal selenides anodes with ultrahigh ICE and superior sodium storage properties.