Ultrafast Sodium-Ion Storage in Self-Doped 2D PVP-VS₄/Ti₃C₂T_x Hybrids for High-Performance Sodium-Ion Half/Full Batteries

Abstract

Transition metal sulfides demonstrate remarkable theoretical specific capacities, making them highly desirable anode materials for sodium-ion batteries (SIBs). Nevertheless, low electrical conductivity and restacking seriously limit their electrochemical activity, resulting in suboptimal specific capacity and cycling stability. Herein, it is demonstrated that self-doped PVP-VS₄/Ti₃C₂T_x presents multidirectional open conductive channels and sufficient vacancies for reversible and fast Na⁺ insertion/extraction. The PVP-VS₄/Ti₃C₂T_x exhibits excellent rate performance (80.5% capacity retention from 0.1 to 10.0 A g⁻¹) and superior cycling stability (711 mAh g⁻¹ after 1000 cycles at 5 A g⁻¹ and 518 mAh g⁻¹ after 600 cycles at 10 A g⁻¹). The sodium storage mechanism of the PVP-VS₄/Ti₃C₂T_x anode was elucidated through in situ XRD, ex situ HRTEM, and ex situ XPS analyses. The DFT calculation demonstrates that the interfacial structure of PVP-VS₄/Ti₃C₂T_x significantly enhances the electronic conductivity as an anode. Impressively, the assembled NaFePO₄//PVP-VS₄/Ti₃C₂T_x full cell retained 87.2% of capacity after 500 cycles at 0.5 C, and still allowed the LEDs to remain lighted after cycling. This study offers a fresh perspective on improving the electrochemical performance of vanadium tetrasulfide through Ti₃C₂T_x as a conductive base to support PVP-induced VS₄.

Keywords

full cells / sodium-ion batteries / Ti₃C₂T_x MXenes / vacancies engineering / VS₄

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