New 4V-class and zero-strain cathode material for Na-ion batteries

Abstract

Here, we introduce Na3V(PO3)(3)N as a novel 4V-class and zero-strain cathode material for Na-ion batteries. Structural analysis based on a combination of neutron and X-ray diffraction (XRD) reveals that the Na3V(PO3)(3)N crystal contains three-dimensional channels that are suitable for facile Na diffusion. The Na (de)intercalation is observed to occur at similar to 4 V vs Na/Na+ in the Na cell via the V3+/V4+ redox reaction with similar to 67% retention of the initial capacity after over 3000 cycles. The remarkable cycle stability is attributed to the near-zero volume change (similar to 0.24%) and unique centrosymmetric distortion that occurs during a cycle despite the large ionic size of Na ions for (de)intercalation, as demonstrated by ex situ XRD analysis and first-principles calculations. We also demonstrate that the Na3V(PO3)(3)N electrode can display outstanding power capability with similar to 84% of the theoretical capacity retained at 10C, even though the particle sizes are on the micrometer scale (> 5 mu m), which is attributed to its intrinsic three-dimensional open-crystal framework. The combination of this high power capability and extraordinary cycle stability makes Na3V(PO3)(3)N a new potential cathode material for Na-ion batteries.