Multifunctional surfactants for synthesizing high-performance energy storage materials

Due to a steady increase of electrical energy consumption, the demand for high-performance energy storage materials becomes more urgent than ever. Compared to other synthetic technologies, surfactant templating method offers the most efficient way to improve electrochemical performances of energy storage materials. In the synthesis of energy storage materials prepared, various surfactants are often used and play a crucial role in determining the properties of final products. Multifunctional surfactants can effectively tailor and control particle size, crystallinity, morphology, porosity, structure and composition of energy storage materials, achieving significant enhancement in rate capability and cycle stability. Herein, we summarize various surfactants, including classic alkyl-based surfactants, polymers, biological ligands and other surface active molecules. This review highlights the essential roles of surfactants, working as structure-directing agents, carbon sources, porogens and stabilizer agents, etc., in controlling nanostructure of energy storage materials and improving their properties. For different batteries (such as lithium-ion batteries, sodium-ion batteries, lithium-sulfur batteries, lithium-oxygen batteries and alkaline batteries) and supercapacitors, similarities and differences in surfactant mechanism, functions, electrochemical performances of the synthesized materials, challenges and opportunities are discussed as well. To facilitate further development of surfactant template method, some future research trends and directions are finally put forward.