Multi-Redox (V5+/V4+/V3+/V2+) Driven Asymmetric Sodium (De)intercalation Reactions in NASICON-Na3VIn(PO4)3 Cathode

NASICON-Na3V2−xMx(PO4)3 (M = Al3+, Cr3+, Fe3+ & Ga3+) cathodes are attractive for sodium-ion battery application due to their high voltage multi-redox (V5+/V4+/V3+) couples and faster sodium-ion diffusivity. However, they suffer from rapid capacity decay due to irreversible structural changes occurring at high voltages. Herein, we present the structural and electrochemical sodium (de)intercalation properties of NASICON-Na3VIn(PO4)3 (NVIP) cathode. Although, this In3+-substituted cathode also undergoes similar high voltage structural degradation, but its structure is rejuvenated through the following low voltage deep-sodiation process, resulting in reversible capacities of ∼145 mA h g−1 (i.e., equivalent to ∼2.82 moles of Na per vanadium). Our combined electrochemical, in-operando X-ray diffraction and exsitu X-ray absorption spectroscopy analyses reveal asymmetric sodium (de)intercalation pathways of the NVIP cathode in the window of 4.2–1.2 V vs Na+/Na0 that is driven by multi-redox (V5+/V4+/V3+/V2+) couples.