Nanocellulose-Based Conductive Membranes for Free-Standing Supercapacitors: A Review

There is currently strong demand for the development of advanced energy storage devices with inexpensive, flexibility, lightweight, and eco-friendly materials. Cellulose is considered as a suitable material that has the potential to meet the requirements of the advanced energy storage devices. Specifically, nanocellulose has been shown to be an environmentally friendly material that has low density and high specific strength, Young's modulus, and surface-to-volume ratio compared to synthetic materials. Furthermore, it can be isolated from a variety of plants through several simple and rapid methods. Cellulose-based conductive composite membranes can be assembled into supercapacitors to achieve free-standing, lightweight, and flexible energy storage devices. Therefore, they have attracted extensive research interest for the development of small-size wearable devices, implantable sensors, and smart skin. Various conductive materials can be loaded onto nanocellulose substrates to endow or enhance the electrochemical performance of supercapacitors by taking advantage of the high loading capacity of nanocellulose membranes for brittle conductive materials. Several factors can impact the electronic performance of a nanocellulose-based supercapacitor, such as the methods of loading conductive materials and the types of conductive materials, as will be discussed in this review.