Ten concerns of Zn metal anode for rechargeable aqueous zinc batteries

Context & scaleAqueous Zn-ion batteries are attractive for stationary electrochemical energy storage. However, the poor stability/reversibility of the Zn-metal anode (ZMA), owing to dendrite growth and free-water-induced side reactions, and some ambiguous and even misunderstood issues related to the electro-deposition/dissolution process of Zn2+, limit its practical application. In this perspective, we not only propose and clarify existing concerns/issues—including scientific concepts (nucleation overpotential [ηn] and growth overpotential [ηg], exposed crystal face [ECF] and electro-crystallization orientation [ECO], and corrosion current density or exchange current density), non-scientific engineering factors (cell assessment modes and assembly parameters), reaction mechanisms of modification strategies, and limitations of typically used XRD/SEM characterizations—but also appeal to establish accurate and targeted modification strategy/in situ characterization techniques (in situ FTIR/XRD/DEMS) to guide the subsequent optimization. We hope for this perspective to awaken research status of blind advance on Zn-metal batteries and to provide constructive guidance for building theory models and designing modification strategies for narrowing the gap between laboratory research and commercial application of Zn-metal batteries.SummaryThousands of articles have been reported to enhance the electrochemical stability/reversibility of the Zn-metal anode (ZMA). However, some scientific concepts, engineering factors, mechanism models, and characterization limitations are still not comprehensively understood. Here, based on fair experiments, we proposed ten critical concerns on ZMAs, including the following: (1) scientific concepts misunderstanding on basic electrochemistry and crystallography terms, (2) non-scientific engineering factors affecting Coulombic efficiency (CE) assessment based on operation modes and "edge effect," and cell parameters on regulating battery performance, (3) influence mechanisms of coating modifications and Zn4(OH)6SO4·xH2O (ZHS) byproduct, and (4) limitations of typically used characterization tools and accuracy of advanced in situ technique paradigms. We not only proposed existing dilemmas but also provided the right medicine for corresponding pains. This perspective hopes to awaken research status of blind advance on aqueous zinc batteries and provide constructive guidance for building theory models and designing modification strategies to meet the challenges of energy storage scientifically and effectively.