Multiscalar Investigation of FeVO₄ Conversion Cathode for a Low Concentration Zn(CF₃SO₃)₂ Rechargeable Zn-Ion Aqueous Battery

Battery cathode materials operating on multivalent-ion intercalation are prone to short operational lifetimes, traditionally explained to be due to poor solid-state diffusion. Here, we overcome this problem by using a conversion-type cathode material and demonstrate the benefits in a FeVO₄ host structure. The rechargeable Zn-ion battery exhibits stability for an unprecedented operational lifetime of 57 days with a high capacity of 272 mAh g⁻¹ (60 mA g⁻¹) over 140 cycles. We use a combination of synchrotron-based XAS, SRXTM, Raman, XRD and HRTEM techniques to elucidate the cathode material evolution at multilength-scale for understanding the Zn-ion storage mechanism. We further highlight the benefits of using a low-salt concentration electrolyte and pH-consideration analysis in aqueous battery development, the optimization of which leads to a 4-fold increase in battery performance as compared to conventional high-salt concentration electrolyte formulations.