Vertically-aligned nanostructures for electrochemical energy storage

Energy storage devices with high energy and power densities are highly attractive for various applications ranging from portable electronics to electric vehicles and grid-level energy storage, such as rechargeable batteries and supercapacitors. One limiting factor in power density is the ion transport in electrolyte, particularly in tortuous electrode materials with low porosity. A viable approach to enhance ion transport in electrolyte is to create vertically aligned structures and thus reduce electrode tortuosity. In the past decades, various methods have been explored to develop vertically aligned structures. This review summarizes battery kinetics to illustrate the importance of low tortuosity in electrodes, and then introduces various methods to create vertically aligned nanostructures, such as direct growth, templating and microfabrications. The electrochemical performance of electrodes or electrolytes created by each method is presented. At the end, this paper discusses challenges with these structures and the directions these technologies can be taken in the future.