电化学储能应用中类共晶凝胶电解质的纳米尺度水限域与配位驱动离子传输

        The rapid expansion of renewable energy systems, portable electronics, electric vehicles, and smart grid technologies has intensified the demand for advanced electrochemical energy storage devices capable of delivering high power density, long cycling life, operational safety, and environmental sustainability. Among these technologies, supercapacitors have attracted considerable attention because of their rapid charge-discharge capability, excellent cycling stability, and high-power performance.             
           However, their relatively low energy density remains a critical limitation that restricts their broader practical application. Since the energy density of supercapacitors scales with the square of the operating voltage, expanding the electrochemical stability window of the electrolyte represents one of the most effective strategies for improving device performance. Conventional aqueous electrolytes offer high ionic conductivity, low cost, nonflammability, and environmental compatibility, yet their voltage window is fundamentally restricted by water decomposition. In contrast, organic electrolytes and ionic liquids can provide higher operating voltages but often suffer from drawbacks such as flammability, toxicity, high viscosity, low ionic conductivity, moisture sensitivity, and elevated cost. Quasisolid-state gel electrolytes have emerged as promising alternatives because they combine liquid-like ionic transport with solid-like mechanical stability while reducing leakage and improving device safety.
       Nevertheless, many conventional hydrogel electrolytes still contain free water that remains susceptible to freezing, evaporation, and electrochemical decomposition, while dense polymer networks may hinder ion mobility. This thesis presents the development of a nanoionically engineered Eutectic@CMC Eutectogel electrolyte based on the integration of carboxymethyl cellulose (CMC) with reline, a choline chloride/urea deep eutectic solvent (DES). The electrolyte composition was systematically optimized by varying the eutectic-to-CMC ratio to achieve an effective balance between ionic conductivity, water confinement, and quasi-solid structural integrity. Among the investigated formulations, the 2:1 Eutectic@CMC composition exhibited the optimal electrochemical and physicochemical performance. In this system, the DES phase supplied abundant mobile ionic species, while the CMC network immobilized water molecules into a non-freezable bound state through strong hydrogen bonding and polymer-DES-water interactions. Spectroscopic and thermal analyses confirmed the suppression of freezable water and the formation of a strongly interconnected hydrogen-bonded network, while molecular dynamics simulations revealed persistent N⁺–COO⁻ coordination between choline cations and CMC chains.
       The optimized electrolyte enabled stable supercapacitor operation over an expanded voltage window of 2.7 V, delivering a specific capacitance of 141 F g⁻¹, the maximum energy density of 142.6 Wh kg⁻¹, and the maximum power density of 48.6 kW kg⁻¹, with 83% capacitance retention after 19,000 charge-discharge cycles. These improvements are attributed to the formation of continuous ion-rich percolation pathways within the quasi-solid matrix, where coordinated nanochannels facilitate collective ion migration despite reduced individual ion diffusivity under polymer confinement. Overall, this work establishes a molecular-level design framework in which water immobilization, polymer-DES coordination, and structureassisted ion transport synergistically overcome the conventional trade-off between ionic conductivity, voltage stability, thermal resilience, and mechanical integrity. The proposed Eutectic@CMC platform, therefore, represents a scalable and climate-resilient electrolyte strategy for next-generation high-voltage quasi-solid-state supercapacitors.