Open-framework Layered Na2[(VO)2(HPO4)2(C2O4)] for High Voltage/Rate Sodium-ion Batteries via Ion Intercalation Mechanism

The exponentially growing global demand for lithium resources has accelerated the development of sodium-ion batteries (SIBs) as a promising alternative to conventional lithium-ion batteries. In this work, we successfully synthesized a novel open-framework layered material, Na2[(VO)2(HPO4)2(C2O4)] (designated as NaVPC), through an eco-friendly one-step hydrothermal method that eliminates energy-intensive post-calcination processes. The unique architecture of NaVPC features (1) three-dimensional ion diffusion channels enabling reversible Na+ extraction/insertion, (2) minimal lattice contraction (<3%) during cycling, and (3) an exceptional average operating voltage of 3.8 V vs Na+/Na. When composited with single-walled carbon nanotubes, the hybrid electrode delivers enhanced electrochemical performance, achieving a specific capacity of 80.6 mAh g−1 at 0.1 C and maintaining 91.7% capacity retention after 100 cycles at 2 C. Through a combination of ex situ X-ray diffraction, X-ray photoelectron spectroscopy, and density functional theory calculations, we systematically investigated the structural evolution and Na+ migration mechanism, establishing a fundamental framework for understanding the charge storage behavior in this open-framework material.