The rapid progress in energy storage technologies demands innovative solutions to challenges related to sustainability, cost, and performance. Aqueous zinc-based energy storage systems, such as zinc metal batteries (AZMBs) and zinc-hybrid capacitors (ZHCs), offer promising possibilities due to their inherent safety, cost-effectiveness, and scalability.[1] Nonetheless, complications like hydrogen evolution reactions, dendritic growth, and water-induced parasitic reactions are major obstacles to be overcome before these technologies can be practically employed on a large scale. The following abstract summarizes findings from three new central studies that place MCEs at the forefront in driving a new generation of research breakthroughs to overcome these challenges and improve performance in aqueous zinc systems.

The first study investigates an advanced MCE containing a combination of Zn(TFSI)₂, LiTFSI, and polyethylene glycol (PEG400) to improve the performance of Zn//LFP hybrid batteries.[2] By confining water molecules and reducing free water activity, the optimized MCE enhances the reversibility of Zn plating/stripping and significantly improves long-term cyclability. The Zn//LFP battery, in turn, showed quite high capacities of 120 mAh g⁻¹ with excellent stability-65% capacity retention after 200 cycles-whereas the self-discharge rate is reduced and parasitic reactions are suppressed compared to conventional electrolytes. These confirm the effectiveness of MCEs for solutions of major anode and cathode problems in AZMBs.

The second investigation is concerned with a Zn//V₂O₅ battery, which works out a newly developed MCE, using Zn(TFSI)₂ as the main salt.[3] The electrolyte formulation in this work enhances ionic conductivity, hence boosting ion transport properties to further ensure superior rate capability and decent cycle stability. It obtains excellent performance metrics of the Zn//V₂O₅ system, such as 78% capacity retention after 1000 cycles and an impressive reduction in self-discharge. Mitigation of free water activity hence improved the stability window, which assured reversible Zn plating/stripping and placed the MCE as a versatile strategy toward the advancement of AZMBs for practical applications.

Another study investigates the use of PEGDME-based MCE in ZHCs as means to solve such Zn anode problems but without sacrificing its practicability.[4] The advanced MCE obtained had a widened electrochemical stability window of up to 2.7 V, which reduced the water activity and hence improved anti-corrosion properties that enabled superior performance in Zn//Cu and Zn//Zn symmetric cells. The hybrid system of Zn/MCE/AC achieved energy density at 138 Wh/kg, perfect capacitance of 281 F/g, and superlative cyclability, with capacity retained up to 100% after 19,100 cycles. These results really underline the big capability of MCEs in providing high-power, long-life energy storage solutions.

Collectively, these works highlight how MCEs will be game-changing in overcoming fundamental challenges in aqueous-based zinc energy storage systems. By taking advantage of novel electrolyte chemistries to suppress parasitic reactions, enhance ionic transport, and stabilize electrode interfaces, MCEs will provide a route toward safe, efficient, and sustainable energy storage systems. This work presents an important milestone toward successful practice application of AZMBs and ZHCs and in particular provides for impactful solutions to global challenges in energy storage.