Promising Battery Coating Fails After Months of Use, Raising Questions About Technology Timeline

<p>Liquid metal coatings are applied to the surfaces of metallic zinc anodes in rechargeable aqueous Zn-ion batteries to promote dendrite-free zinc plating and stripping, enhance electron transport, and improve the overall electrochemical cycling performance. In this study, we utilized a Ga–Sn–Zn eutectic alloy as a surface coating on the Zn anode in a mildly acidic 1 M ZnSO4 electrolyte, both in symmetric and full cells incorporating copper hexacyanoferrate as the cathode. The Ga–Sn–Zn coating exhibited promising performance during the initial stages of cycling, up to 200 cycles at 8C. However, during extended cycling periods up to 1000 cycles at 1C, erratic behavior was observed. Postmortem analyses revealed an inherent instability of the Ga–Sn–Zn alloy, resulting in the rapid loss of its characteristic liquid nature and its transformation into a crystalline solid. X-ray photoelectron spectroscopy confirmed compositional changes in the alloy with depletion of both Ga and Sn from the surface. These changes led to embrittlement of the entire anode, causing it to shatter, even upon light handling during cell disassembly. The cells with the Ga–Sn–Zn alloy displayed severe erratic electrochemical behavior in later stages of cycling, leading to premature failure. These findings underscore the need for a thorough assessment of Ga-based liquid metal alloys as a protective anode coating against dendritic growth in aqueous Zn-ion batteries, as it compromises the overall mechanical stability of Zn electrodes.</p>