Single‐ion conducting polymer electrolytes with temperature‐independent modulus using cellulose nanocrystal‐ <scp>MXene</scp> and <scp>Poly(tetramethylene glycol)</scp> ‐based waterborne polyurethane and <scp>PEO</scp>

Abstract With the rapid progress of electric vehicles, the focus on high‐energy‐density anodes has increased substantially. Lithium metal (Li) possesses a high energy density of 3800 mAh/g. However, it poses safety issues for liquid electrolytes, mandating the use of safer replacements like solid polymer electrolytes (SPEs). In this regard, polyethylene oxide (PEO), as the most prominent SPE, shows the highest ionic conductivity ( σ ) among polymers despite facing challenges including loss of thermomechanical stability around 60°C and low lithium‐ion (Li + ) transference number (). Here, we designed SPEs consisting of PEO, poly (tetramethylene glycol)‐based waterborne polyurethane (WPU), cellulose nanocrystal (CNC), and MXene. The presence of WPU was quite effective at increasing (). High CNC loading () made elastic modulus () independent of temperature with terminal , while improving σ and . These achievements were attributed to CNCs competing with over oxygen atoms of PEO and the formation of a strong CNC network. was able to increase σ from attributed to intercalation of PEO into its interlayer spaces while also increasing to 0.897. The SPEs showed a high electrochemical stability window. The optimal electrolyte showed high Coulombic efficiency and stable cycling performance. Highlights Ionomeric units resulted in a high lithium‐ion transference number () Hydrogen bonding was partially responsible for increased Cellulose nanocrystals (CNCs) increased ionic conductivity and CNCs suppressed PEO spherulites' size and increased thermomechanical stability MXene disrupts PEO crystal growth and provides a new route for conduction