Multi-element coupling driven high performance sodium-ion phosphate cathode

Balancing energy density and lifespan is an essential issue for NASICON-type cathodes. Fully integrating electrochemical properties of vanadium, manganese and iron elements, regulating voltage plateaus and introducing entropy effects rationally, this work proposes a novel Na_11/3(V,Mn,Fe)_2/3(PO₄)₃ (ME-NVMFP) cathode with a capacity of 111.9 mAh g⁻¹ and high energy density of 339.0 Wh kg⁻¹. Ascribed to reasonable components design, ME-NVMFP achieves an ultra-long cycling lifespan (a capacity retention over 70 % after 4000 cycles at 5 C) and potential application in fast charging realm (a capacity retention of 87.6 % after 1300 cycles at 20 C). Notably, ME-NVMFP exhibits admirable low temperature adaptability under 0 °C (91.6 % at 10 C over 1800 cycles) and can still operate well even under -20 °C (92.3 % at 5 C over 1000 cycles). DRT analysis was conducted to explore sodium-ion storage mechanism, verifying highly reversible evolution of CEI on cathode surface. Ex-situ XRD analysis were performed, revealing an inspiring volume variation ratio of 2.4 % and probing the structural evolution of ME-NVMFP. What's more, ME-NVMFP||Hard Carbon cell delivers a high energy density of 330.9 Wh kg⁻¹ at 0.2 C. This article provides a promising strategy of multi-element coupling design to optimize the overall performance of polyanion sodium ion cathodes.