# Orbital hybridization-mediated synergistic multi-electron redox in a NASICON cathode unlocking solid-solution reactions for ultrafast and durable sodium storage

## TL;DR

This paper introduces a new strategy for improving sodium-ion battery cathode materials by using Ti/Fe co-doping to enhance performance and durability.

## Contribution

The novel Ti/Fe co-doping strategy enables single-step desodiation and improves structural stability in SIB cathodes.

## Key findings

- Ti/Fe co-doping creates a 3d–3d metallic network, enabling continuous multi-orbital hybridization.
- The material retains 73% capacity after 2000 cycles at 10C, showing excellent cycling stability.
- The d-band energy level difference is narrowed, enhancing electron delocalization and conductivity.

## Abstract

Na4VMn(PO4)3, as a high-energy-density and low-cost cathode material for sodium-ion batteries (SIBs), holds promising application prospects. However, its practical performance is limited by the stepwise redox reactions of V and Mn, which induce significant phase transitions and sluggish kinetics, particularly during the second desodiation process. To address this issue, we propose an orbital hybridization regulation strategy based on Ti/Fe co-doping. By tailoring the local coordination environment, the introduced Ti/Fe constructs a 3d–3d metallic network, inducing continuous multi-orbital hybridization. This transforms the V/Mn redox process from stepwise to simultaneous, eliminating sharp phase boundaries and overcoming the kinetic bottleneck in the second desodiation step. Additionally, the d-band energy level difference between V and Mn is narrowed to 0.701 eV, enhancing electron delocalization and intrinsic conductivity, thereby enabling highly reversible multi-electron transfer processes. The optimized Na3.75V0.75Mn0.75Ti0.25Fe0.25(PO4)3 effectively mitigates volumetric stress and local phase transitions, ensuring structural integrity. Consequently, the material retains 73% capacity after 2000 cycles at 10C, demonstrating superior rate capability and cycling stability. This work provides crucial electronic-level insights and a novel design paradigm for high-performance SIB cathode materials.

Ti/Fe co-doping modulates the electronic structure of NVMTFP, enabling single-step desodiation. It reduces the Na+ migration energy barrier, accelerates ion diffusion, and alleviates lattice distortion.