Inhibiting VOPO4⋅x H2O Decomposition and Dissolution in Rechargeable Aqueous Zinc Batteries to Promote Voltage and Capacity Stabilities

• Published in: Angewandte Chemie International Edition 2019-11, Vol.58 (45), p.16057-16061
• Main Authors: Shi, Hua‐Yu, Song, Yu, Qin, Zengming, Li, Cuicui, Guo, Di, Liu, Xiao‐Xia, Sun, Xiaoqi
• Format: Article
• Language: eng ; jpn
• Subjects: cathode materials; cycling stability; intercalation; polyanions; zinc batteries
• ISSN: 1433-7851; 1521-3773
• DOI: 10.1002/anie.201908853

VOPO4⋅x H2O has been proposed as a cathode for rechargeable aqueous zinc batteries. However, it undergoes significant voltage decay in conventional Zn(OTf)2 electrolyte. Investigations show the decomposition of VOPO4⋅x H2O into VOx in the electrolyte and voltage drops after losing the inductive effect from polyanions.PO43− was thus added to shift the decomposition equilibrium. A high concentration of cheap, highly soluble ZnCl2 salt in the electrolyte further prevents VOPO4⋅x H2O dissolution. The cathode shows stable capacity and voltage retentions in 13 m ZnCl2/0.8 m H3PO4 aqueous electrolyte, in direct contrast to that in Zn(OTf)2 where the decomposition product VOx provides most electrochemical activity over cycling. Sequential H+ and Zn2+ intercalations into the structure are revealed, delivering a high capacity (170 mAh g−1). This work shows the potential issue with polyanion cathodes in zinc batteries and proposes an effective solution using fundamental chemical principles. The VOPO4⋅x H2O cathode undergoes decomposition and dissolution in rechargeable aqueous Zn batteries. A 13 m ZnCl2/0.8 m H3PO4 aqueous electrolyte is designed to inhibit its degradation, allowing stable capacity and voltage retentions over cycling. Sequential H+ and Zn2+ intercalations into the structure deliver a high capacity of 170 mAh g−1.