Abstract: Nanocellulose is a green nanomaterial obtained from natural plants, several marine animals and exceptional microbes. As the results of its unique network structure, outstanding mechanical properties and high specific surface area, nanocellulose can be effectively compounded via layer-by-layer self-assembling, in-situ chemical polymerization and electrochemical deposition with various nanoparticles such as metal oxides, conductive polymers, and two-dimension nanomaterials,to form different nanocellulose-based porous film material and electroconductive composites. These nanocomposites have great application prospects in the separator and electrode materials for mental ion battery and supercapacitor. Based on the differences in source materials, preparation methods, and fiber morphology, nanocellulose is divideed into cellulose nanocrystal, cellulose nanofibril, bacterial nanocelluloe, and electrospun cellulose, and the former three are widely used for energy storage materials. Naturally, nanocellulose is frequently mixed with water and maintains in the stable colloidal state. After the loss of water, the nanocellulose mixture is able to form self-assembled nanocellulose film with outstanding mechanical properties and thermal stability. The film exhibits good ability of moisturizing in electrolyte solution and smoothness for free ion and electron transfer as a promising choice for separator in green energy storage. Due to the advantages of sufficient active groups, unique network and easiness to form film, nanocellulose, incorporating with other conductive active ingredients such as carbon nanomaterials, metal oxide, and conductive polymers, plays significant role of skeleton material in the preparation of electrode for energy storage. The nanocellulose can also be directly carbonized for electrode materials, and its electrochemical performance is closely related to the degree of graphitization. To improve the electrochemical performance, the carbonized nanocellulose is often further treated by N-and C-doping. Currently, the major nanocellulose based electrode materials include nano-cellulose carbon fiber materials, two-dimension nanomaterials, conductive polymer materials and multi-component materials. Although nanocelluse poses incomparable merits and perspective future in the application to green energy storage, it still faces huge challenges in the incorporation pattern between nanocellulose and electrode active material, poor interfacial compatibility and microstructure regulation. It is suggested that the future work would focus on the tough problems of maximizing the size effect in nanometer and instinctive network structure, building more elaborate nano-system and designing energy storage device with higher conversion efficiency. This paper briefly introduces varieties and properties of nanocellulose, highlights its present application status in separator materials and novel electrode materials, and predicts its future development.

Key words: nanocellulose, electrode materials, separator materials, energy storage device