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

Abstract

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 Highly Reversible Low-Cost Aqueous Sulfur–Manganese Redox Flow Battery

“…The time-voltage profiles indicated stable operations for the S–Mn cell (Figure c), but a dramatic voltage fluctuation and voltage drop were observed during the charging process for the Zn–Mn cell, and it is more severe with zinc accumulation after long cycling (Figure d). The zinc electrode after cycling showed large zinc clusters and dendrites with zinc flakes in different orientations , (Figure S11), which is consistent with the poor cycling performance for the Zn–Mn cell.…”

“…In addition to the Zn–Mn system, − ,− various metal–Mn 2+ /MnO 2 (s) batteries were proposed, including copper–manganese, , bismuth–manganese, ,, cadmium–manganese, aluminum–manganese, and antimony–manganese batteries, etc. However, these systems suffer from poor cycling life with limited areal capacity (normally <10 mAh cm –2 ) due to metal dendrites , and positive electrode passivation. In our recent work, we resolved the dead MnO 2 exfoliation and cathode passivation through a mediator strategy by dissolving the accumulated dead MnO 2 with a spontaneous chemical reaction between MnO 2 and the mediator iodide, achieving a high areal capacity of 50 mAh cm –2 in a Zn–Mn 2+ /MnO 2 (s) battery .…”

A Highly Reversible Zinc Anode for Rechargeable Aqueous Batteries

“…The widespread adoption of renewable energies ( e.g. , solar and wind) requires efficient and economical grid-scale energy storage technologies to ensure stable power output. , Rechargeable batteries are regarded as one of the most promising candidates for this application, owing to the merits of high energy efficiency, good site independency, and excellent scalability. , Among various candidates, rechargeable aqueous batteries are especially attractive because of their unique advantages, including high safety, high power capability, low cost, and environmental friendliness. − Particularly, aqueous zinc (Zn) metal batteries have gained enormous research interest owing to the outstanding properties of Zn anodes, which have a high theoretical capacity (820 mA h g –1 and 5855 mA h cm –3 ), favorable redox potential (−0.76 V vs standard hydrogen electrode), and good stability in an aqueous environment. − Although great progress has been made in several types of aqueous Zn batteries ( e.g. , Zn–Ni and Zn–air batteries) over the past several decades, , state-of-the-art rechargeable Zn batteries employing alkaline electrolytes are still confronted with some insurmountable challenges, such as severe side reactions, including hydrogen evolution reactions and surface passivation, shape change, and dendrite growth. − Recently, it is found that using a mild/neutral electrolyte in Zn batteries could mitigate the problems of Zn electrodes to some extent, which has thereby aroused enormous research interest in these systems. − However, dendrite growth and side reactions with electrolytes still exist in mildly acidic aqueous electrolytes, which contribute to the poor cyclability, low efficiency, and even short-circuit-induced failure of aqueous Zn batteries. , …”

Unleashing energy storage ability of aqueous battery electrolytes

“…Moreover, in an alkaline electrolyte, the Sn(OH) 6 2− /Sn electrode shows a smooth and dendrite-free morphology due to the intrinsic low-surface-energy anisotropy that facilitates the isotropic crystal growth of the Sn metal. As a result, the Sn(OH) 6 2− /Sn anolyte offers high reversibility of up to 500 stable cycles (more than two months) [85].…”