Multi-Redox (V <sup>5+</sup> /V <sup>4+</sup> /V <sup>3+</sup> /V <sup>2+</sup> ) Driven Asymmetric Sodium (De)intercalation Reactions in NASICON-Na <sub>3</sub> VIn(PO <sub>4</sub> ) <sub>3</sub> Cathode
Subham Ghosh, Nirmal Jose, Baskar Senthilkumar, Penphitcha Amonpattaratkit, Premkumar Senguttuvan
Abstract
NASICON-Na 3 V 2−x M x (PO 4 ) 3 (M = Al 3+ , Cr 3+ , Fe 3+ & Ga 3+ ) cathodes are attractive for sodium-ion battery application due to their high voltage multi-redox (V 5+ /V 4+ /V 3+ ) 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-Na 3 VIn(PO 4 ) 3 (NVIP) cathode. Although, this In 3+ -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 + /Na 0 that is driven by multi-redox (V 5+ /V 4+ /V 3+ /V 2+ ) couples.