Single-ion conducting polymer electrolytes with temperature-independent modulus using cellulose nanocrystal-MXene and Poly(tetramethylene glycol)-based waterborne polyurethane and PEO

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 (sigma) among polymers despite facing challenges including loss of thermomechanical stability around 60 degrees C and low lithium-ion (Li+) transference number (t(Li+)similar to 0.25). 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 (t(Li+) (t(Li+) >= 0.700). High CNC loading (10wt%) made elastic modulus (E ') independent of temperature with terminal E 'similar to 10MPa, while improving sigma and t(Li+). These achievements were attributed to CNCs competing with Li+ over oxygen atoms of PEO and the formation of a strong CNC network. MXene was able to increase sigma from 0.61 x 10(-5) to 0.98x10(-4) attributed to intercalation of PEO into its interlayer spaces while also increasing t(Li+) to 0.897. The SPEs showed a high electrochemical stability window. The optimal electrolyte showed high Coulombic efficiency and stable cycling performance.