Negatively charged nanoporous membrane for a dendrite-free alkaline zinc-based flow battery with long cycle life

Recent Development in Composite Membranes for Flow Batteries

Flow batteries (FBs) are one of the most attractive candidates for stationary energy storage and vital in realizing the wide application of renewable energies. Membranes play an important role in isolating redox couples while transporting ions to close the internal electrical circuit. Therefore, membranes with high selectivity and conductivity are highly important. Among different membranes, a composite membrane with independent design of support layer and thin selective top layer becomes one of the most promising candidates to break the trade-off between selectivity and conductivity. In this Review, recent studies on composite membranes for FBs and the principles of membrane design in different systems are discussed and summarized. Finally, the future direction on membrane design for different FBs is presented, which will provide an extensive, comprehensive reference to design and construct high-performance composite membranes for FBs.

Inhibition of Zinc Dendrites in Zinc-Based Flow Batteries

Zinc-based flow batteries have gained widespread attention and are considered to be one of the most promising large-scale energy storage devices for increasing the utilization of intermittently sustainable energy. However, the formation of zinc dendrites at anodes has seriously depressed their cycling life, security, coulombic efficiency, and charging capacity. Inhibition of zinc dendrites is thus the bottleneck to further improving the performance of zinc-based flow batteries, but it remains a major challenge. Considering recent developments, this mini review analyzes the formation mechanism and growth process of zinc dendrites and presents and summarizes the strategies for preventing zinc dendrites by regulating the interfaces between anodes and electrolytes. Four typical strategies, namely electrolyte modification, anode engineering, electric field regulation, and ion transfer control, are comprehensively highlighted. Finally, remaining challenges and promising directions are outlined and anticipated for zinc dendrites in zinc-based flow batteries.

A Boron Nitride Nanosheets Composite Membrane for a Long-Life Zinc-Based Flow Battery

The capability to maintain a constant system temperature is vital in nature, since it endows the system with enhanced lifetime. This trait also works for zinc-based batteries, because their cycle-life is limited by notorious zinc dendrite/accumulation, which are highly affected by the inhomogeneous distribution of temperature on electrode and relatively low mechanical strength of membrane. Herein, boron nitride nanosheets (BNNSs) with high mechanical strength serving as heat-porter are introduced onto a porous substrate to enable uniform deposition of zinc and further a zinc-based flow battery with long-cycle life. The results indicate that BNNSs can effectively adjust the deposited zinc from needle-like to French fries-like morphology, thus affording the battery with a stable performance for nearly 500 cycles at 80 mA cm^-2 . Most importantly, an energy efficiency of above 80 % can be obtained even at 200 mA cm^-2 , which is by far the highest value ever reported among zinc-based flow batteries.

Dendrite-Free Zinc Deposition Induced by Tin-Modified Multifunctional 3D Host for Stable Zinc-Based Flow Battery

Zinc (Zn) plating/stripping is a promising anodic electrochemical reaction for aqueous batteries because of its high safety, low cost, two electron transfer, and rapid reaction kinetics. However, the notorious dendrite growth of Zn has become one of the biggest obstacles hindering its further commercialization. A multifunctional binder-free tin (Sn)-modified 3D carbon felt anodic host (SH) is constructed for aqueous zinc-based flow batteries (ZFB) via a facile and scalable strategy. Compared with the pristine carbon felt host (PH), the as-fabricated SH affords more robust Zn nucleation sites, lower hydrogen evolution reaction potential and lower nucleation overpotential of Zn and thus better induces uniform Zn plating/stripping with very high Coulombic efficiency (CE). Based on such an SH, a symmetrical flow battery exhibits superior CE (290 cycles with average CE of 99.4%) and a zinc-bromine flow battery demonstrates a longer cycle life (142 cycles with average CE of 97.2%), much better than pristine PH. This is a simple, novel, and effective way to suppress Zn dendrites and improve the performance of ZFBs.

Advanced Materials for Zinc-Based Flow Battery: Development and Challenge

Zinc-based flow batteries (ZFBs) are well suitable for stationary energy storage applications because of their high energy density and low-cost advantages. Nevertheless, their wide application is still confronted with challenges, which are mainly from advanced materials. Therefore, research on advanced materials for ZFBs in terms of electrodes, membranes, and electrolytes as well as their chemistries are of the utmost importance. Herein, the focus is on the scientific understandings of the fundamental design of these advanced materials and their chemistries in relation to the battery performance. The principles of using different materials in different ZFB technologies, the functions and structure of the materials, and further material improvements are discussed in detail. Finally, the challenges and prospects of ZFBs are summarized as well. This review provides valuable instruction on how to design and develop new materials as well as new chemistries for ZFBs.

Lignin@Nafion Membranes Forming Zn Solid-Electrolyte Interfaces Enhance the Cycle Life for Rechargeable Zinc-Ion Batteries

Metallic zinc is an ideal anode material for rechargeable zinc-ion batteries (ZIBs), taking us beyond the lithium-ion era. In-depth understanding of the Zn metal surface is currently required owing to diverse but uncorrelated data about the Zn surface in mild environments. Herein, the surface chemistry of Zn is elucidated and the formation and growth of a zinc layer hydroxide is verified as an effective solid-electrolyte interface (SEI) during stripping/plating in mild electrolyte. The effects of battery separators/membranes on the growth of an effective SEI and deposited Zn are then investigated from the perspectives of structure, morphology, compositions, and interfacial impedance. Nafion-based membranes enable the formation of a planar SEI, which protects the metal surface and prevents short circuiting. Biomass@Nafion membranes are developed and assessed with a long cycle life of over 400 h compared with below 200 h for physical separators. The mechanism behind this is attributed to interaction between the membranes and Zn²⁺ , which enables reshaping of the Zn²⁺ coordination in an aqueous medium. Together with the advantages of using the membranes in β-MnO₂ |ZnSO₄ |Zn, our work provides a feasible way to design an effective SEI for advancing the use of Zn anodes in rechargeable ZIBs.

Prototype System of Rocking-Chair Zn-Ion Battery Adopting Zinc Chevrel Phase Anode and Rhombohedral Zinc Hexacyanoferrate Cathode

Zinc-ion batteries (ZIBs) have received attention as one type of multivalent-ion batteries due to their potential applications in large-scale energy storage systems. Here we report a prototype of rocking-chair ZIB system employing Zn2Mo6S8 (zinc Chevrel phase) as an anode operating at 0.35 V, and K0.02(H2O)0.22Zn2.94[Fe(CN)6]2 (rhombohedral zinc Prussian-blue analogue) as a cathode operating at 1.75 V (vs. Zn/Zn2+) in ZnSO4 aqueous electrolyte. This type of cell has a benefit due to its intrinsic zinc-dendrite-free nature. The cell is designed to be positive-limited with a capacity of 62.3 mAh g−1. The full-cell shows a reversible cycle with an average discharge cell voltage of ~1.40 V, demonstrating a successful rocking-chair zinc-ion battery system.

MoS2-modified graphite felt as a high performance electrode material for zinc–polyiodide redox flow batteries

MoS₂ nanoplates were in situ grafted onto graphite felt to enable high performance zinc–polyiodine redox flow batteries.