Identifying the role of Zn self-dissolution in the anode corrosion process in Zn-ion batteries

Zn-ion batteries for practical applications face several challenges, some of which arise from the inevitable degradation of the Zn metal anode. The intrinsic thermodynamic instability of Zn metal anodes in mildly acidic Zn-ion batteries can trigger spontaneous interfacial corrosion, which leads to hydrogen evolution, the formation of byproducts, and the irreversible loss of active species during both storage and operation. Here, we delve into the intricate corrosion processes of the Zn metal anode in mildly acidic electrolytes. With the help of operando electrochemical liquid cell transmission electron microscopy, the self-dissolution of Zn is observed, and the capacity loss due to such corrosion behaviour during the cell rest period is quantified. This dissolution of Zn is found to be closely related to the initial pH value of the electrolyte and can be mitigated by pH adjustment through the slight addition of a pH buffer additive. The self-dissolution of Zn, which causes an increase in the local pH, is a prelude to the formation of corrosion byproducts that continues throughout the entire storage and cycling period. These corrosion issues are exacerbated by the presence of excess Zn metal in the system, suggesting that the feasibility of using excess Zn metal in Zn-ion batteries should be carefully evaluated. These findings further emphasise the importance of considering electrolyte pH in future electrolyte modification research, as well as its potential impacts on the stability of both the anode and cathode, and the shelf life of the entire battery.