A Dendrite‐Free Tin Anode for High‐Energy Aqueous Redox Flow Batteries

Metal‐based aqueous redox flow batteries (ARFBs) such as zinc‐based ARFBs have attracted remarkable attention owing to their intrinsic high energy density. However, severe dendrite issues limit their efficiency and lifespan. Here an aqueous metal anode operating between Sn(OH)62− (stannate) and metal Sn is presented, providing a reversible four‐electron transfer at −0.921 V vs standard hydrogen electrode. In strong contrast to severe Zn dendrites, the Sn(OH)62−/Sn electrode shows smooth and dendrite‐free morphology, which can be attributed to its intrinsic low‐surface‐energy anisotropy which facilitates isotropic crystal growth of Sn metal. By coupling with iodide/tri‐iodide (I−/I3−), the static Sn–I cell demonstrates a stable cycling for 500 cycles (more than 2 months). In contrast, the state‐of‐the‐art Zn anode suffers from serious dendrites and lasts less than 45 cycles (190 h) in Zn–I cells. A stable continuous flow cycling of Sn–I cell achieves a Sn areal capacity of 73.07 mAh cm−2 at an average discharge voltage of 1.3 V for 350 h. The alkaline Sn electrode demonstrates dendrite‐free morphology and superior performance in cycle life and areal capacity compared to state‐of‐the‐art Zn metal anodes, offering a promising metal anode for high‐energy ARFBs and other metal‐based rechargeable aqueous batteries. A metal anode based on the Sn(OH)62−/Sn redox couple at −0.921 V vs standard hydrogen electrode is reported. In contrast to severe Zn dendrites, Sn metal prefers isotropic crystal growth without dendrites, leading to superior performance in lifespan and areal capacity in Sn–I cells. The Sn anode represents a promising electrode candidate for metal‐based rechargeable aqueous batteries.