Dynamic Covalent Chemistry Eliminates Structural Distortion of Na₄MnV(PO₄)₃: Unlocking Ultrafast and Durable Multielectron Redox in Sodium-Ion Batteries.

Abstract

Na₄MnV(PO₄)₃ stands as a promising cathode material for sodium-ion batteries owing to its low cost and multiple redox potentials. However, challenges such as drastic local distortion, irreversible phase evolution, and transition metal dissolution in multielectron redox processes, coupled with intrinsic low electronic conductivity jointly trouble its practical deployment. Herein, the Ti⁴⁺ with a d⁰ arrangement is employed to customize the TM-O bonds to eliminate the structural distortion in Na₄MnV(PO₄)₃. The coupling coordination effect of multiple transition metals activates the Mn^4+/3+ redox while reinforcing structural stability in over two-electron redox processes, enabling the Na_3.1(MnV)_0.7Ti_0.6(PO₄)₃ (MnVTi) cathode to realize a 2.4 e^- reversible transfer and deliver a specific capacity of 138.4 mAh g^-1. Experimental and theoretical calculations reveal that robust TM-O bonds with dynamic covalent chemistry, particularly the strong covalent Ti-O bonds, unlock ultrafast and durable cycling performance (78.4% capacity retention after 10,000 cycles at 20 C). Furthermore, the enhanced electronic conductivity and reaction kinetics contribute to the exceptional rate performance (74.2 mAh g^-1 at 50 C), fast-charging capability (1.77 min to reach 80% SOC), and fabulous all-weather adaptability (-40 to 50 °C). This work establishes a universal design paradigm for high-performance Mn-based polyanion cathodes through d⁰-metal coupling mediated by dynamic covalent chemistry.