Electrochemical study of 3D hierarchical dandelion-fiber flake-like structure of Al(OH)3/MnO2 nanocomposite thin film for future supercapacitor applications

Hierarchical electrodes with superior cycling performance using porous material based on cellulose nanofiber as flexible substrate

The development and application of flexible electrodes with extended cycle life have long been a focal point in the field of energy research. In this study, positively charged polyethylene imine (PEI) and conductive polymer poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) with negative charge were alternately deposited onto a cellulose nanofiber (CNF) porous material utilizing pressure gradient-assisted layer-by-layer (LbL) self-assembly technology. The flexible substrate, characterized by a three-dimensional porous structure reinforced with stiff CNF, not only facilitated high charge storage but also enhanced the electrode's cycling life by reducing the volume changes of PEDOT:PSS. Furthermore, the exceptional wettability of PEI by the electrolyte could promote efficient charge transport within the electrode. The electrode with 10 PEI/PEDOT:PSS bilayer exhibits a capacitance of 63.71 F g-1 at the scan rate of 5 mV s-1 and a remarkable capacitance retention of 128 % after 3000 charge-discharge cycles. The investigation into the nanoscale layers of the LbL multilayer structure indicated that the exceptional cyclic performance was primarily attributed to the spatial constraints imposed by the rigid porous substrate layered structure on the deformation of PEDOT:PSS. This work is expected to make a significant contribution to the development of electrodes with high charge storage capacity and ultra-long cycling life.

Over-Reduction-Controlled Mixed-Valent Manganese Oxide with Tunable Mn2+/Mn3+ Ratio for High-Performance Asymmetric Supercapacitor with Enhanced Cycling Stability

Manganese oxides composed of various valence states Mn^x+ (x = 2, 3, and 4) have attracted wide attention as promising electrode materials for asymmetric supercapacitor. However, the poor electrical conductivity limited their performance and application. Appropriate regulation content of Mn^x+ in mixed-valent manganese oxide can tune the electronic structure and further improve their conductivity and performance. Herein, we prepared manganese oxides with different Mn²⁺/Mn³⁺ ratios through an over-reduction (OR) strategy for tuning the internal electron structure of mixed-valent manganese, which could make these material oxides a good platform for researching the structure-property relationships. The Mn²⁺/Mn³⁺ ratio of manganese oxide could be precisely tuned from 0.6 to 1.7 by controlling the amount of reducing agent for manipulating the redox processes, where the manganese oxide electrode with the most appropriate Mn²⁺/Mn³⁺ ratio, as 1.65 (OR4) exhibits large capacitance (274 F g^-1) and the assembling asymmetric supercapacitors by combining OR4 (positive) and the commercial activated carbon (as negative) achieved large 2.0 V voltage window and high energy density of 27.7 Wh kg^-1 (power density of 500 W kg^-1). The cycle lifespan of the OR4//AC could keep about 92.9% after 10 000-cycle tests owing to the Jahn-Teller distortion of the Mn(III)O₆ octahedron, which is more competitive compared to other work. Moreover, a red-light-emitting diode (LED) can easily be lit for 15 min by two all-solid supercapacitor devices in a series.