Win–win strategy: zinc-ion anchoring crosslinked hydrogels and regulating electronic structure to achieve V3+/V4+/V5+ redox reaction of Na3V2(PO4)3 with high thermal stability and zero strain characteristics

Abstract

Poor conductivity and serious lattice distortion limit the development of Na₃V₂(PO₄)₃ (NVP). Meanwhile, a single redox reaction of V³⁺/V⁴⁺ leads to a relatively low capacity and energy for NVP. Beside, numerous studies consider NVP possesses excellent thermal stability but few verifies this by solid experimental data. Currently, an ingenious win–win strategy is proposed involving Zn²⁺-induced modification of the NVP system. Specifically, moderate Zn²⁺-substituted NVP attached in the Zn²⁺-anchored crosslinked chitosan hydrogel substrate is successfully synthesized. The replacement of V³⁺ by Zn²⁺ generates favorable P-type doping effects and then produces abundant hole carriers to modify the electronic structure of NVP, as demonstrated by the DFT calculations. Meanwhile, the Zn²⁺-anchored hydrogel forms a unique three-dimensional porous coral-like carbon matrix. Furthermore, in situ subsistent N/Cl elements from the hydrogel provide beneficial defects and active sites for Na⁺ storage. Deeply, the excellent chemical and structural stability of the optimized NVP/C-Znx@CHACC is confirmed by ex situ XPS (HCl Etched) and ex situ XRD. After undergoing a charge–discharge procedure, it maintains a 0.25% volume shrinkage rate, indicating nearly zero strain characteristics. In addition, a multi-redox reaction involving V³⁺/V⁴⁺/V⁵⁺ is activated, and the working mechanism is verified using ex situ XRD and electrochemical ex situ XPS. The newly generated V⁴⁺/V⁵⁺ couple results in a high voltage platform at 3.9 V, which is derived from the deintercalation of Na⁺ at the Na(1) site. Notably, an accelerating rate calorimeter (ARC) is utilized to evaluate the thermal stability and further quantify the thermal runaway temperature, indicating that the win–win strategy effectively elevates the safety property of SIBs.