The development of a biodegradable cellulose-based separator with excellent performance has been of great research significance and application potential for the green development of supercapacitors. Herein, the regenerated porous cellulose/Polyvinyl alcohol films (CP-10, CP-15, CP-20, CP-25) with different mass ratio were successfully fabricated by a simple blending and phase inversion process. Their electrochemical properties as separators in assembled supercapacitor were evaluated. Fourier transform infrared spectroscopy and x-ray diffraction analysis indicate that intermolecular and intramolecular hydrogen bonding existed between cellulose and polyvinyl alcohol of the CP films. Compared with other CP films, the CP-20 film shows higher mechanical strength (28.02 MPa), better wettability (79.06°), higher porosity (59.69%) and electrolyte uptake (281.26 wt%). These properties of CP-20 are expected to show better electrochemical performance as separator. Indeed, the electrochemical tests, including electrochemical impedance spectroscopy, cyclic voltammetry, galvanostatic charge discharge, demonstrate that the SC-20 capacitor (with CP-20 as separator) shows the lowest equivalent series resistance of 0.57 Ω, the highest areal capacitance of 1.98 F cm−2 at 10 mV s−1, specific capacitance of 134.41 F g−1 and charge-discharge efficiency of 98.62% at 1 A g−1 among the four capacitors with CP films as separators. Comparing the assembled SC-40 and SC-30 with two commercial separators (TF4040 and MPF30AC) and SC-PVA with Polyvinyl alcohol (PVA) separator, the CV and GCD curves of SC-20 maintain the quasi rectangular and symmetrical triangular profiles respectively at different scan rates in potential window of 0–1 V. SC-20 exhibits the highest value of 28.24 Wh kg−1 at 0.5 A g−1 with a power density of 0.26 kW kg−1, and 13.41 Wh kg−1 at 10 A g−1 with a power density of 6.04 kW kg−1. SC-20 also shows the lowest voltage drop and the highest areal and specific capacitance. Moreover, SC-20 maintains the highest value of 86.81% after 4000 cycles compared to 21.18% of SC-40, 75.07% of SC-30, and 6.66% of SC-PVA, showing a superior rate capability of a supercapacitor. These results indicate that CP films can be served as promising separators for supercapacitors.
Shaped-stabilized reversible thermochromic phase change materials of (TBC-LB, TBB-LB) were assembled by impregnation the TBC (crystal violet lactone/ bisphenol A/tetradecanol) or TBB (3,3 0 -Bis (1-n-octyl-2-methylindol-3-yl) phthalide/bisphenol A/tetradecanol) into lignin-retained bamboo (LB) for energy storage. Analysis of the chemical structure of lignin-retained wood showed that the removal of part of lignin from the bamboo contributes to the penetration of the compound, and the partial retention of lignin is advantageous for maintaining high mechanical properties. The SEM micrographs of TBC-LB and TBB-LB indicate that TBC and TBB are well immersed into the porous LB. The TBC-LB showed an endothermic peak at 40.8 C with ΔH m of 113.3 J g −1 and two exothermic peaks at 28.8 C and 21.9 C with ΔH L+S of 110.2 J g −1 , and the value is basically equal to the pure TBC compound, indicating that TBC has been fully immersed in LB to form a composite phase change material. For phase change latent heat and melting-cooling temperature, TBB-LB and TBC-LB showed the same trend. About 100 heating-cooling cycles were performed to evaluate the reliability of TBC-LB and TBB-LB, showing excellent cycle stability. It is foreseen that the prepared shape-stable TBC-LB and TBB-LB have great potential for applying insulation systems in reversible thermochromic phase change energy storage. K E Y W O R D S composite, lignin-retained bamboo, phase change, properties, reversible thermochromic compound
The cellulose-based polydopamine
modified separator (LID-PDA) and
polydopamine/graphene/polypyrrole modified electrode (LID-PDA-GR/PPy)
were successfully fabricated by dissolving–regenerating and
phase-inversion methods via dopamine polymerization and doping modification
of graphene (GR) and polypyrrole (PPy) in a lithium chloride/N,N-dimethylacetamide solvent system. The
structure and physical properties of the LID-PDA film material play
a positive role in its application in supercapacitor separators and
electrodes. The effect of PPy content on the electrochemical performance
of the electrode shows that the LID-PDA-GR/PPy-30 electrode has the
best performance (2.2 Ω, 237.2 F/g at 0.5 A/g). The cellulose-based
supercapacitor assembled from the LID-PDA-GR/PPy-30 electrode and
LID-PDA separator shows good electrochemical energy storage properties
(439.0 F/g at 0.2 A/g, 36.2 Wh/kg corresponding to 2.2 kW/kg). Based
on the microstructural properties of natural and renewable cellulose
substrates, combining polymerization and doping to realize the complementarity
between materials is meaningful for the application and development
of energy storage materials.
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