Advances and opportunities of hydrogels for metal-ion batteries

Following the growing need for battery chemistries and designs that rely on more sustainable materials, much research and development have focused on low-cost, abundant, safe, environmentally sustainable and functional materials for advancing battery technology. Numerous promising candidates, especially metals, have been explored. However, there remains the need to improve battery cycling performance and capacity. Besides, most of these candidates are toxic, and their inappropriate disposal can cause fire, water and ecosystem contamination. In recent times, hydrogels have been attracting attention for energy storage and conversion devices as promising alternative materials. Compared with metals, hydrogels are affordable, sustainable, safe, and can be efficiently designed to achieve specific/desired structures for facilitating ion transport and enhancing performance. Functionalized hydrogels can enhance electrochemical performance by endowing other functional properties under harsh conditions such as stretching, bending, cut/fracture, and extreme temperatures. This work highlights the benefits and prospects of hydrogels as an appealing candidate for battery. Recent advances in which hydrogels are applied as electrolytes, electrodes for anode, binders, separators and battery management systems to address current battery challenges are discussed and analyzed. Further, a series of challenges of using hydrogels in batteries are presented, and solutions and perspectives are proposed to facilitate further research and development.