An Na3VMn0.5Ti0.5(PO4)3 NASICON cathode with multielectron reactions for sustainable energy storage

Abstract

Rechargeable hybrid aqueous batteries (ReHABs) have emerged as a promising solution to overcome the safety and environmental challenges associated with non-aqueous sodium-ion batteries. Although Na₃V₂(PO₄)₃ is a promising candidate for ReHAB cathodes, its reliance on expensive and toxic vanadium highlights the need for more sustainable alternatives. Despite efforts to explore alternative NASICON-type materials, there remains a lack of viable cathodes that can offer comparable electrochemical performance while reducing or eliminating vanadium content. This constitutes a critical knowledge gap in the development of low-cost, eco-friendly cathode materials for ReHABs. Therefore, this study aims to develop a NASICON-type cathode, Na₃VMn_0.5Ti_0.5(PO₄)₃ (NVMTP), by substituting vanadium with manganese and titanium. The resulting cathode demonstrates promising electrochemical performance across various voltage windows. Furthermore, it exhibits 94.9 and 70.6% capacity retentions over 100 and 400 cycles, respectively, at a current rate of 0.4 A g⁻¹. Activating a multielectron reaction mechanism involving Na- and Zn-ions significantly enhances the overall capacity. This multielectron reaction capability aligns with the objective of achieving higher energy densities while maintaining the structural integrity of the cathode material. In situ synchrotron X-ray diffraction confirms a stable one-phase reaction mechanism of NVMTP. These findings highlight the potential of NVMTP as a low-cost, eco-friendly cathode for ReHABs, paving the way for further exploration of NASICON materials in energy storage applications.