N,P-Doped Carbon-Based Freestanding Electrodes Enabled by Cellulose Nanofibers for Superior Asymmetric Supercapacitors
Haolin Liu, Wenjie Fan, Haoran Lv, Wenzhe Zhang, Jing Shi, Minghua Huang, Shuai Liu, Huanlei Wang
Abstract
The preparation of freestanding electrodes with excellent conductivity and mechanical strength plays a vital role in simplifying the electrode fabrication process and reducing the electrode cost. Herein, a N,P-doped self-supporting carbon electrode is synthesized via a combined templating/activating coassisted carbonization procedure and vacuum filtration process. The glucose precursor was first transformed into N,P-doped carbon nanosheets (NPCNs) with a large specific surface area (2073 m2 g–1) and rich heteroatom-doping (phosphorus: 2.1 atom %; nitrogen: 4.1 atom %) with the assistance of P2O5 and dicyandiamide, and then the compact freestanding electrode (NPCN-f) with outstanding mechanical strength was constructed via vacuum filtration using a mixture of NPCN and conductive cellulose nanofibers. The resultant freestanding electrode exhibits a high capacitance of 318 F g–1 at 1 A g–1 and retains 188 F g–1 at 100 A g–1 in an alkaline electrolyte. Furthermore, excellent electrochemical performances are also exhibited in the asymmetric supercapacitor assembled using NPCN-f as the negative electrode and NPCN/MnO2-f synthesized by a self-controlled redox process as the positive electrode. The asymmetric device can deliver a high energy density of 41.5 Wh kg–1 at a power density of 182.0 W kg–1 and excellent cyclability with 93% capacitance retention after 10 000 cycles in a neutral electrolyte. This work sheds light on the design of self-supporting electrodes for advanced energy storage devices.