In situ formation of solid electrolyte interphase facilitates anode-free aqueous zinc battery

Aqueous Zn batteries (AZBs) suffer from poor Zn anode reversibility. To address this issue, excess Zn foil is often utilized to prolong the cycle life, but it reduces the actual battery energy density. In this work, we use methylurea molecules to in situ form a solid electrolyte interphase (SEI) layer on the Zn anode, achieving reversible Zn plating/stripping with a maximal Coulombic efficiency (CE) of 99.99% and extending the anode's lifespan to 4500 cycles. Leveraging this highly reversible chemistry, we fabricate and test various anode-free Zn batteries. An anode-free Zn–AC cell exhibits stable cycling for exceeding 5000 cycles, an anode-free Zn–I 2 battery with high specific capacities achieves a stable cycle life of 1000 cycles, and an anode-free Zn–Br 2 battery with a high areal capacity of 4 mAh cm −2 demonstrates a stable cycle life of 450 cycles. Characterization of the SEI using TEM and DFT calculations reveal the formation mechanisms of the ZnCO 3 - and ZnS-rich amorphous SEI layer. These results indicate that the design of desirable SEI compositions could pave the way for developing low-cost, high-performance anode-free AZBs. • Methylurea additive forms a ZnCO 3 - and ZnS-rich SEI, achieving 99.93 ​% ACE and 4500 cycles of Zn plating/stripping. • Facilitated by the in situ SEI layer, a Zn–Zn symmetric cell demonstrates a long cycle life of 4500 ​h. • Anode-free Zn–AC full cells retain 80 ​% capacity after 3000 cycles and achieve 5000 cycles, with ACEs close to 100 ​%, showcasing excellent reversibility. • SEI stabilization via methylurea chemistry accelerates the development of low-cost, high-performance aqueous Zn batteries.