A Fully Sodiated NaVOPO4 with Layered Structure for High-Voltage and Long-Lifespan Sodium-Ion Batteries

Sodium-ion batteries are the primary candidate for a low-cost and resource-abundant alternative to lithium-ion batteries for large-scale electric storage applications. However, the development of sodium-ion batteries is hindered by the lack of suitable cathode materials that have sufficient specific energy density and cycle life. Here, we report layered NaVOPO4 as a cathode material that exhibits high voltage (∼3.5 V versus Na/Na+), high discharge capacity (144 mAh g−1 at 0.05 C), and remarkable cyclability with 67% capacity retention over 1,000 cycles. The excellent performances result from the high Na+ ion diffusion rate in the two-dimensional path and the reversible transformation behavior of (de)sodiation. Particularly, this layered structure and its synthetic procedure can be extended to other alkali-metal intercalation materials, leading to other metal-ion battery systems, which opens a new avenue for large-scale energy storage systems with the development of high-energy-density and long-life cathodes for electric storage applications.