Xuan Wang, Ting Xu, Han Zhang, Junjie Qi, Meng Zhang, Tairan Pang, Liyu Zhu, Kun Liu, Chuanling Si
ABSTRACT Functional fibers assembled from cellulose offer advantages including renewability, outstanding mechanical properties, ease of chemical modification, demonstrating significant potential in energy storage and harvesting. However, there is a scarcity of comprehensive paper elucidating the formation mechanisms of cellulose functional fibers, as well as the relationship between the physical and chemical structural characteristics of the fibers and their energy storage and energy harvesting properties. Herein, a systemic review is provided, covering from dispersion and dissolution of cellulose, assembly mechanisms of fiber materials, key features of cellulose functional fibers for energy storage and harvesting systems. This paper first demonstrates typical chemical–physical properties of cellulose, elucidating the mechanisms of action for natural cellulose and its derivatives in spinning dopes. Subsequently, it focuses on assembling mechanism and structural regulation strategies for cellulose functional fibers, including micro‐fibers and nanofiber membranes. Then, it examines the working principles and key features of cellulose functional fibers, emphasizing the decisive role of ion transport, electron conduction, and interfacial compatibility. This paper also provides a critical overview of representative applications within energy storage and harvesting technologies, including supercapacitors, lithium‐ion batteries, zinc‐ion batteries, triboelectric nanogenerators, and piezoelectric nanogenerators. Perspectives on sustainable design, scalable fabrication, and multifunctional integration are addressed.