Constructing Dense Morphology of Sn with High Reversibility under High Areal‐capacity for Anode‐Free Tin Batteries

Sn electrode possesses high reversibility, redox kinetics and corrosion resistance, as well as non-toxic and environmental compatibility, which is competitive candidate for aqueous batteries. However, due to huge size of deposition particles and "dead Sn", it is a great challenge to obtain high areal-capacity (>5 mAh cm^-2) and high coulombic efficiency (>99 %) simultaneously. Here, we demonstrate a highly reversible Sn redox electrochemistry with high areal-capacity enabled by thiourea additive. Systematical investigations reveal the participation of thiourea molecules in the electrical double layer, reducing exchange current density and suppressing rampant two-dimensional diffusion. As a result, flat and dense scale-like deposition Sn morphology is obtained, which enables high cycle stability with high areal-capacity of 10 mAh cm^-2 for symmetrical cell with lean electrolyte (25 μL cm^-2), and delivering a high average coulombic efficiency of 99.85 % with practical high 5 mAh cm^-2 area-capacity for asymmetrical cell. More importantly, anode-free Organic||Sn battery is developed, and 62 % capacity retention can be obtained after 570 cycles.