A simple pre-sodiation strategy to improve performance and energy density of sodium ion batteries with Na4V2(PO4)3 as cathode material
Sodium-ion batteries are considered as a surrogate to conventional lithium-ion batteries for the commercial sector. One of the most auspicious anode materials for sodium-ion batteries is hard carbon. However, its performance is affected by the largely irreversible capacity loss (I.C.L.) in the initial charging process. This study proposes the Na4V2(PO4)3 (Na4VP) cathode as a possible solution for matching the hard carbon anode. The process uses a recently developed electrochemical pre-sodiation strategy, where the first step converts Na3V2(PO4)3 (Na3VP) to a Na4VP cathode by a sodiation step. After that, a de-sodiation step of Na4VP is carried out below 2.2 V (vs. Na+/Na) to entirely compensate for the I.C.L. of the anode and the resulting Na3VP directly acts as a cathode. As a result, the Na4VP||H.C. full cell achieves a substantially high specific energy of 265 Wh kg-1, that is 76% higher than Na3VP||H.C. full cell. Moreover, the Na4VP||HC full cell shows excellent rate performance (62.32 mAh g-1 at 10C) and cycling stability (about 80.0% capacity retention after 100 cycles at 1C). This work forms a precursor to further study of other battery and hybrid capacitor systems, where the pre-sodiation plays an important role to improve their performance.