Single-Pot Fabrication of Cellulose-Reinforced Solid Polymer Lithium-Ion Conductors

Flexible power sources are essential to enable the autonomous operation of portable electronic systems. Conventional liquid electrolytes are not desirable for flexible batteries because of safety concerns surrounding the use of flammable organic solvents. A polymer electrolyte presents a promising alternative due to its higher mechanical integrity and lower risk of leaking solvent. Though they have such advantages, these electrolytes have lower ionic conductivity compared to conventional liquid electrolytes and are typically prepared using multistep process sequences. Here, we demonstrate a "single-pot" synthetic approach that affords a flexible, free-standing solid polymer electrolyte comprising cellulose-based nanocrystals and a cross-linked interpenetrating polymer network. Polyethylene oxide (PEO) is blended with poly(ethylene glycol) dimethacrylate (PEGDMA), cellulose nanocrystals, and a lithium salt to afford the cross-linked polymer electrolyte upon UV irradiation. The cross-linked PEGDMA matrix provides good mechanical properties, while PEO is known for excellent electrochemical stability and its ability to solubilize lithium salts. The nontoxic cellulose additive also contributes to good mechanical properties and serves as a reinforcing filler. Soft and flexible polymer electrolytes were prepared with this approach. When the cellulose nanocrystal content reached 10 wt % relative to the PEO fraction, ionic conductivity was retained at 20 °C compared to the PEO control. The results provide a path toward sustainable, polymer electrolytes with performance metrics suitable for applications having a lower energy demand.