Overcoming the Unfavorable Kinetics of Na3V2(PO4)2F3//SnPx Full‐Cell Sodium‐Ion Batteries for High Specific Energy and Energy Efficiency

Abstract In this work, a full‐cell sodium‐ion battery (SIB) with a high specific energy approaching 300 Wh kg −1 is realized using a sodium vanadium fluorophosphate (Na 3 V 2 (PO 4 ) 2 F 3 , NVPF) cathode and a tin phosphide (SnP x ) anode, despite both electrode materials having greatly unbalanced specific capacities. The use of a cathode employing an areal loading more than eight times larger than that of the anode can be achieved by designing a nanostructured nanosized NVPF (n‐NVPF) cathode with well‐defined particle size, porosity, and conductivity. Furthermore, the high rate capability and high potential window of the full‐cell can be obtained by tuning the Sn/P ratio (4/3, 1/1, and 1/2) and the nanostructure of an SnP x /carbon composite anode. As a result, the full‐cell SIBs employing the nanostructured n‐NVPF cathode and the SnP x /carbon composite anode (Sn/P = 1/1) exhibit outstanding specific energy (≈280 Wh kg −1 (cathode+anode) ) and energy efficiency (≈78%); furthermore, the results are comparable to those of state‐of‐the‐art lithium‐ion batteries.