Electronic Confinement-Restrained Anti-Site Defects in Sodium-Rich Phosphates Toward Multi-Electron Transfer and High Energy Efficiency

Sodium (Na) super-ionic conductor structured NaMnTi(PO) (NMTP) cathodes have garnered interest owing to their cost-effectiveness and high operating voltages. However, the voltage hysteresis phenomenon triggered by anti-site defects ( -ASD), namely, the occupation of Mn in the Na2 vacancies in NMTP, leads to sluggish diffusion kinetics and low energy efficiency. This study employs an innovative electronic confinement-restrained strategy to achieve the regulation of -ASD. Partial replacement of titanium (Ti) with electron-rich vanadium (V) favors strong electronic interactions with Mn, restraining Mn migration. The results suggest that this strategy can significantly increase the vacancy formation energy and migration energy barrier of manganese (Mn), thus inhibiting -ASD formation. As proof of this concept, an Na-rich NaMnTiV(PO) (NMTVP) material is designed, wherein the electronic interaction enhanced the redox activity and achieved more Na storage under high-voltage. The NMTVP cathode delivered a reversible specific capacity of up to 182.7 mAh g and output an excellent specific energy of 513.8 Wh kg, corresponding to ≈3.2 electron transfer processes, wherein the energy efficiency increased by 35.5% at 30 C. Through the confinement effect of electron interactions, this strategy provides novel perspectives for the exploitation and breakthrough of high-energy-density cathode materials in Na-ion batteries.