Side reactions at the Zn anode: what we know and how we deal with them

Aqueous Zn-ion batteries (AZIBs) have been widely regarded as promising alternatives to Li-ion batteries (LIBs) owing to their intrinsic safety and cost-effectiveness. Nonetheless, spontaneous side reactions at the Zn anode dominate the platelet packing mode of Zn plating/stripping, thus undermining the anode's reversibility. To enable the future development of AZIBs, undesirable side reactions at the Zn anode need to be fully unveiled to understand intrinsic Zn plating/stripping processes. This review offers innovative and comprehensive insights to mitigate the side reactions at the Zn anode that have not been reported to date. It commences with a profound understanding of Zn redox chemistry with side reactions involved. Subsequently, the main initiators of side reactions are discussed; the mainstream strategies used to decouple main/side reactions are considered and analyzed from the thermodynamics and kinetics viewpoints based on different mechanisms; and cutting-edge research breakthroughs are summarized. Additionally, advanced characterization technologies are expounded, equipping readers with measures to intuitively detect side reactions. Finally, current challenges related to side reactions are presented, accompanied by proposed feasible solutions to inspire readers for the future development of AZIBs.