High-Entropy Doping Enabling Ultrahigh Power Density for Advanced Sodium-Ion Batteries

Area of Science:

• Materials Science
• Electrochemistry
• Energy Storage

Background:

• Sodium-ion batteries (SIBs) are a promising alternative to lithium-ion batteries for large-scale energy storage due to abundant sodium resources.
• Na3V2(PO4)2F3 (NVPF) is a potential SIB cathode material, but suffers from low electronic conductivity, poor cycling stability, and low energy density.

Purpose of the Study:

• To improve the performance of Na3V2(PO4)2F3 (NVPF) cathode materials for sodium-ion batteries.
• To investigate the effects of high-entropy doping on the electronic structure and ion diffusion kinetics of NVPF.
• To enhance the energy density, power density, and cycling stability of NVPF-based SIBs.

Main Methods:

• High-entropy strategy employing multielement low-concentration doping.
• Density functional theory (DFT) calculations to analyze electronic structure and band gap.
• Advanced analysis to study fluorine vacancies, V-O bond contraction, and sodium-ion rearrangement.
• Electrochemical testing to evaluate energy density, power density, and cycling stability.

Main Results:

• High-entropy doping narrowed the band gap from 1.59 to 0.68 eV, significantly enhancing electronic conductivity.
• The strategy induced fluorine vacancies, V-O bond contraction, and optimized sodium-ion diffusion pathways.
• The doped NVPF cathode achieved an energy density of 460.6 W h kg-1 at 0.5C and a power density of 15.3 kW kg-1 at 100C.
• Exceptional cycling stability was demonstrated with 70.5% capacity retention at 50C after 12,000 cycles.

Conclusions:

• High-entropy doping is an effective strategy to overcome the limitations of NVPF cathode materials for SIBs.
• The enhanced electronic conductivity and improved sodium-ion kinetics lead to superior electrochemical performance.
• This research offers significant advancements for the development of next-generation sodium-ion batteries.