(Invited) Zinc/ Sodium Vanadium Oxide (NaV₃O₈) Aqueous Electrolyte Batteries: Competing Proton and Zinc Ion Insertion

Large-scale energy storage systems suitable for pairing with renewable energy generation require low-cost materials and safety. A promising candidate for large scale storage is the aqueous Zn-ion battery (AZIB). Zinc metal is a useful anode for aqueous batteries as it possesses a high theoretical capacity (820 mAh/g), low redox potential (-0.76 V vs SHE), and allows for two electron transfers per Zn 2+ (de)insertion. Sodium vanadium oxides have been investigated as cathode materials for AZIBs as the size of Na + is larger than Zn 2+ facilitating ion diffusion within the lattice. Specifically, sodium vanadium oxide (NaV 3 O 8 , NVO) in an anhydrous form and its monohydrate (NaV 3 O 8 ·H2O) have been identified as candidate materials. Notably, one of the phases that forms during the discharge of these materials within a zinc battery system is zinc hydroxy-sulfate (Zn 4 (SO 4 )(OH) 6 ·5H 2 O (ZHS) and has been attributed to H + insertion in NVO where the H + insertion is accompanied by local pH change and precipitation of the ZHS. This presentation probes the competing zinc ion and proton insertion mechanisms for discharge of NVO. The impact of (dis)charge rate on reduction products formed is determined with quantitative Rietveld refinement analysis. Further, synchrotron based EDXRD providing spatio-temporally resolved data is used to determine phase evolution operando in different locations within thick porous NVO positive electrodes. Determining the reaction progression within thick electrodes while under load is an important aspect of scaling batteries appropriately, where these results can have relevance to development of future sustainable energy storage systems.