Robust sodium storage enabled medium entropy Na _3.5 V _0.5 Mn _0.5 Fe _0.5 Ti _0.5 (PO ₄ ) ₃ NASICON with multielectron reaction for sodium‐ion battery

Abstract Sodium superionic conductors (NASICONs) have attracted enormous attention owing to their excellent ionic diffusion and structural stability. However, the high cost of vanadium, limited capacity due to fewer redox reactions, and low electronic conductivity restrict their practical application. Herein, we designed Na 3.5 V 0.5 Mn 0.5 Fe 0.5 Ti 0.5 (PO 4 ) 3 (NVMFTP) medium entropy NASICON with multi‐electron reactions as a fast sodium storage cathode for sodium‐ion batteries (SIBs). The incorporation of Fe, Mn and Ti not only reduces the cost but also activates multi‐redox reactions of V 2+ /V 3+ , Ti 3+ /Ti 4+ , Fe 2+ /Fe 3+ , V 3+ /V 4+ , Mn 2+ /Mn 3+ , V 4+ /V 5+ . Owing to distinctive structural design with medium entropy, the NVMFTP delivered 168 mAh·g −1 at 0.5C with a remarkable rate capability of 93.51 mAh·g −1 at 60C and steady long‐term cycling performance till 5000 cycles. More importantly, NVMFTP takes only 11 min to achieve 80% SOC at 5C. The in‐situ and ex‐situ X‐ray diffraction (XRD) further demonstrate reversible multi‐electron reaction mechanisms of slow charging and fast charging. NVMFTP/HC full cell shows 110 mAh·g −1 capacity and 208 Wh·kg −1 energy density. This study will provide comprehensive insight into developing low‐cost, cutting‐edge materials for SIBs.