High Performance Carbon Fiber Structural Batteries Using Cellulose Nanocrystal Reinforced Polymer Electrolyte

In recent years, structural batteries have received great attention for future automotive application in which a load-bearing car panel is used as an energy storage. However, based on the current advances, achieving both high ionic conductivity and mechanical performance has remained a challenge. To address this challenge, this study introduces a cellulose nanocrystal (CNC) reinforced structural battery electrolyte (CSBE) consisting of CNC, triethylene glycol dimethyl ether (TriG) electrolyte containing a quasi-solid additive, e.g., cyclohexanedimethanol (CHDM), in a vinyl ester polymer. This green and renewable CSBE electrolyte system was in situ polymerized via reaction induced phase transition to form a high performance multidimensional channel electrolyte to be used in structural carbon fiber-based battery fabrication. The effect of various concentrations of CNC on the electrolyte ionic conductivity and mechanical properties was obtained in their relation to intermolecular interactions, interpreted by FTIR, Raman, Li NMR results. Compared to the neat SBE system, the optimized CSBE nanocomposite containing 2 wt % CNC shows a remarkable ionic conductivity of 1.1 × 10^-3 S cm^-1 at 30 °C, which reveals ∼300% improvement, alongside higher thermal stability. Based on the FTIR, Raman, Li NMR results, the content of CNC in the CSBE structure plays a crucial role not only in the formation of cellulose network skeleton but also in physical interaction with polymer matrix, providing an efficient Li⁺ pathway through the electrolyte matrix. The carbon fiber composite was fabricated by 2 wt % CNC reinforced SBE electrolyte to evaluate as a battery half-cell. The results demonstrated that by addition of 2 wt % CNC into SBE system, 7.6% and 33.9% improvements were achieved in specific capacity at 0.33 C and tensile strength, respectively, implying outstanding potential of ion conduction and mechanical load transfer between the carbon fibers and the electrolyte.