Urea Induces Uniform Tin Deposition for Long Cycle-Life Tin-based Redox Flow Battery

Among multivalent redox flow batteries, the Zn-based redox flow battery (RFB) has the advantages of high energy density, nontoxicity, and low cost. However, the severe dendrite issue hinders its deployment. Therefore, the Sn-based RFB is reported as a prospective alternative, particularly in alkaline systems, due to its lower redox potential and four electrons transfer in redox reactions. However, the continuous growth of Sn during charge forms large Sn bulk, which increases the risk of “dead Sn” formation. By combining experiments and theoretical calculations, urea is proposed as an electrolyte additive to regulate Sn deposition on graphite felt. This is achieved through the enhanced adsorption and robust reaction of Sn(OH) 6 2− with graphite felt. Consequently, a more uniform morphology ensues, reducing “dead Sn” formation and thus improving the average discharge voltage and areal capacity. Moreover, the Columbic efficiency becomes more stable, extending the cycle life to over 420 h (>200 cycles) without deep discharge during cycling. This study demonstrates the role of urea in achieving high-performance Sn-I flow battery with long cycle life, paving the way for further development of metal-based hybrid RFBs.