Water-based zinc ion batteries are characterized by high power density, low cost, and inherent safety, making them promising for energy storage applications. Recently, researchers Yang Weishen and Zhu Kaiyue from the Dalian Institute of Chemical Physics, Chinese Academy of Sciences, have made a breakthrough in the development of electrolytes for water-based zinc ion batteries. They have prepared Janus water gel membranes with different hydrophilicities on each side and a gradient pore structure, which are used as electrolytes for water-based zinc ion batteries. These membranes not only reduce the water activity at the negative electrode to suppress hydrogen evolution reactions but also ensure sufficient proton insertion at the positive electrode to enhance battery capacity, achieving long-term stable cycling of zinc ion batteries. The related research findings have been published in "Energy & Environmental Science."
Currently, issues such as negative electrode corrosion, zinc dendrite formation, low positive electrode capacity, and dissolution pose challenges during the cycling of water-based zinc ion batteries, limiting their large-scale application. From a microscopic molecular reaction perspective, the attack of highly active water molecules in the aqueous electrolyte on both positive and negative electrodes is a key factor leading to these problems. While solvent water is crucial for enhancing battery capacity, it also reduces the cycling stability of both electrodes, with the negative electrode requiring lower water activity than the positive electrode. Traditional electrolyte regulation strategies typically uniformly adjust water molecule activity to enhance negative electrode reversibility, making it difficult to simultaneously regulate both electrodes and often overlooking the significant impact on the positive electrode side, resulting in suboptimal performance of zinc ion batteries.
In this work, the research team innovatively proposes the construction of Janus water gel electrolytes by controlling the gradient distribution of hydrophilic and hydrophobic monomers. By utilizing the quasi-solid-state nature of water gels and designing membranes with different hydrophilic surfaces and gradient pore structures, the team meets the different water molecule activity requirements of the positive and negative electrodes. The team uses the lower water activity and dense network structure on the less hydrophilic side to inhibit negative electrode corrosion and zinc dendrite formation, while the higher water content and strong hydrogen bond network structure on the more hydrophilic side promote proton insertion at the positive electrode, thereby increasing battery capacity and enhancing stability. The research shows that button batteries using this Janus water gel electrolyte exhibit a high capacity of 470mAh/g at a current density of 0.5A/g and still maintain 87% capacity retention after 100 cycles, outperforming symmetric uniform water gels and traditional aqueous zinc sulfate electrolytes. Moreover, soft pouch batteries assembled with this Janus water gel electrolyte demonstrate a high capacity of 48mAh, with an 85% capacity retention after 150 cycles, and remain stable even under extreme conditions such as shear, heavy pressure, or bending.
This work introduces an integrally formed Janus water gel membrane with different skeleton structures and modified functional groups on both surfaces, enabling precise control of water molecule activity at the positive and negative electrode interfaces. This suppresses negative electrode corrosion, dendrite formation, and positive electrode dissolution reactions while ensuring sufficient and rapid proton and ion insertion at the positive electrode, leading to stable and efficient operation of zinc ion battery systems. These findings provide new insights and methods for the design of electrolyte/positive-negative electrode interfaces in zinc ion batteries, potentially accelerating the practical application of inherently safe water-based zinc ion battery technology.
Related Paper Information: https://doi.org/10.1039/D4EE01018C
