Quasi-solid-state supercapacitors (QSSCs) utilizing bio-derived polymers represent a pivotal technology for sustainable energy storage, bridging high power density with environmental compatibility [1]. This study proposes an integrated, sequential layer-by-layer fabrication strategy for QSSCs that exploits the multifunctional properties of carboxymethylcellulose (CMC). This protocol uniquely employs CMC as a bifunctional material, acting simultaneously as a sustainable, biodegradable binder in the electrodes and as the host polymer matrix in the electrolyte [1]. This dual role ensures superior chemical and mechanical compatibility between components [1, 2].
Unlike conventional methods relying on fluorinated binders and toxic solvents, the electrode paste preparation adopts a green aqueous processing route. The formulation adapts the standard 80:10:10 mass ratio of Activated Carbon (AC), Carbon Black (CB), and binder established [3], strategically substituting the conventional binder with CMC. To ensure the integrity of the conductive network, the mixture undergoes ultrasonication (10–30 min); this homogenization step induces cavitation forces critical for uniformly dispersing the amphiphilic CMC and breaking down particle agglomeration, thereby yielding a robust dry electrode with optimized percolation pathways [4, 5].
Device assembly is performed in a single stage directly on metal current collectors. The applied electrode paste undergoes controlled pre-drying at 60–70 °C. This specific thermal range is critical; it is sufficient to evaporate free water (thermal peak onset ≈ 62.76 °C [6]) while strictly preserving coordinated water, which is vital for cation solvation and ionic mobility within the polymer matrix [6, 7]. Subsequently, the highly viscous CMC/Na2SO4 gel electrolyte [8] is deposited, followed by the application of the second electrode layer. The resulting sandwich structure is consolidated under a controlled contact pressure of 0.5 MPa [5, 7]. This mechanical compression optimizes interfacial contact by promoting conformal adhesion and filling surface roughness, effectively reducing equivalent series resistance (ESR) without the need for external separators [5, 7].
Finally, device validation employs a comprehensive characterization suite. Structural properties and polymer-salt complexation are investigated via X-ray Diffraction (XRD) and Fourier Transform Infrared Spectroscopy (FTIR) [6]. Surface morphology and electrode/gel interfacial integrity are examined by Scanning Electron Microscopy (SEM) [6]. Thermal stability, free and coordinated water management, and polymer degradation transitions are investigated using Thermogravimetric Analysis (TGA) coupled with Derivative Thermogravimetry (DTG) and by Differential Scanning Calorimetry (DSC) [6, 7]. Electrochemical performance is rigorously evaluated using Electrochemical Impedance Spectroscopy (EIS) across a frequency range of 100 mHz to 10 kHz [8], alongside Cyclic Voltammetry (CV) and Galvanostatic Charge/Discharge (GCD). These assays are designed to confirm operational stability within extended potential windows and validate the efficiency of ionic transport across the quasi-solid interface [8].
This integrated fabrication protocol represents a methodological framework for developing fully bio-derived supercapacitors using CMC in dual functional roles. By consolidating the literature evidence regarding CMC processability, polymer-salt chemistry, and electrochemical device assembly, this approach offers a rational design strategy for quasi-solid-state energy storage systems. If validated through experimental implementation, this methodology could enable the development of supercapacitors with reduced reliance on fluorinated polymers and synthetic separators, potentially expanding the applicability of bio-derived materials in energy storage and grid-scale applications. The sequential layer-by-layer assembly strategy presented herein provides a foundation for future optimization of bio-based electrochemical device architectures.
References
[1] Akhlaq, M., et al(2023). Carboxymethyl cellulose-based materials as an alternative source for sustainable electrochemical devices: A review. RSC Advances, 13(9), 5723–5743. https://doi.org/10.1039/D2RA08244F
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[3] Demarconnay, L., et al. (2010). A symmetric carbon/carbon supercapacitor operating at 1.6 V by using a neutral aqueous solution. Electrochemistry Communications, 12(10), 1275–1278. https://doi.org/10.1016/j.elecom.2010.06.036
[4] Gordon, R., et al. (2020). Effect of polymeric binders on dispersion of active particles in aqueous LiFePO4-based cathode slurries as well as on mechanical and electrical properties of corresponding dry layers. ACS Omega, 5(20), 11455–11465. https://doi.org/10.1021/acsomega.0c00477
[5] Xu, L., et al. (2023). Nanocellulose-carboxymethylcellulose electrolyte for stable high-rate zinc-ion batteries. Advanced Functional Materials, 33(16), 2302098. https://doi.org/10.1002/adfm.202302098
[6] Darmawan, D. A., et al. (2023). Fabrication of solid polymer electrolyte based on carboxymethyl cellulose complexed with lithium acetate salt as Lithium-ion battery separator. Polymer Composites, 45(1), 273-285. https://doi.org/10.1002/pc.27902
[7] Tombolesi, S., et al. (2023). A sustainable gel polymer electrolyte for solid-state electrochemical devices. Polymers, 15(14), 3087. https://doi.org/10.3390/polym15143087
[8] Li, Z., et al. (2019). High-energy quasi-solid-state supercapacitors enabled by carbon nanofoam from biowaste and high-voltage inorganic gel electrolyte. Carbon, 149, 273–280. https://doi.org/10.1016/j.carbon.2019.04.056
