Sodium Ion Storage in Na4MnV(PO4)3@C Free-Standing Electrode

To enhance the energy density of batteries and explore intrinsic charge storage mechanism of the active materials, it is important to reduce or eliminate the use of non-active materials in electrodes, such as binder and conductive additives. Herein, free-standing Na4MnV(PO4)(3)@C (F-NMVP@C) fiber membrane is fabricated and directly used as a sodium-ion battery (SIB) cathode. In situ X-ray diffraction reveals that the V3+/V4+ redox reaction occurs through a solid-solution reaction while a two-phase Mn2+/Mn3+ redox reaction is identified, and both are highly reversible. Meanwhile, ex situ electrochemical impedance spectroscopy reveals that both the ion diffusion coefficient and charge transfer resistance of F-NMVP@C change reversibly during the Na+ intercalation/de-intercalation. Battery full cells are assembled based on the free-standing F-NMVP@C cathodes and F-Sb@C anodes, which manifests a high energy density (293 Wh kg(-1)) and good cyclability (87.5% after 100 cycles at 1 C). The high-performance free-standing cathodes and anodes shed light on the development of flexible SIBs.

Automated summary

To enhance battery energy density and understand the charge storage mechanism, it is important to reduce non-active materials in electrodes. In this study, a free-standing Na4MnV(PO4)(3)@C fiber membrane was used as a sodium-ion battery cathode, showing reversible redox reactions and ion diffusion behavior. The assembled battery exhibited high energy density and good cyclability.