Structural composite energy storage devices — a review

Structural composite energy storage devices (SCESDs) which enable both structural mechanical load bearing (sufficient stiffness and strength) and electrochemical energy storage (adequate capacity) have been developing rapidly in the past two decades. The capabilities of SCESDs to function as both structural elements and energy storage units in a single engineering structure lead to reduction of volume/mass of the overall system. The designs of SCESDs can be largely divided into two categories. One is based on carbon fiber-reinforced polymer, where surface-modified high-performance carbon fibers are used as energy storage electrodes and mechanical reinforcement. The other is based on embedded energy storage devices in structural composite to provide multifunctionality. This review summarizes the reported structural composite batteries and supercapacitors with detailed development of carbon fiber-based electrodes and solid-state polymer electrolytes. Particularly, we discuss the impact of different separators on system performance and propose a new efficiency factor to evaluate the multifunctional performance. In addition, several new structural designs of SCESDs have been proposed along with the discussion of existing structures. Looking forward to the future, it is expected that SCESDs will play a revolutionary role in many engineering applications, such as portable electronic devices, electric vehicles, drones, and even civil constructions.