2023 AIChE Annual Meeting
Hexagonal Boron Nitride Modulates Crystallinity and Charge Mobility in PEO–NaNO3 Electrolytes
Composite polymer electrolytes (CPEs) hold great promise for the development of safe and sustainable batteries. In this study, we find that 2D hexagonal boron nitride (h-BN) as a filler has a non-monotonic effect on polymer crystallinity and total ionic conductivity in PEO-NaNO3 electrolytes. The dual Lewis acidity and basicity of hexagonal boron nitride (h-BN) allows it to interact with dissociated salt ions and the polymer matrix itself. PEO crystallinity was quantified using differential scanning calorimetry (DSC) and X-ray diffraction (XRD), and complex formation between NaNO3, PEO, and h-BN was studied using ATR-Fourier Transform IR (FTIR) spectroscopy. Total ionic conductivity was determined using electrochemical impedance spectroscopy (EIS) as a function of temperature. We find that h-BN has two competing effects in CPEs: 1) nucleation-enhanced crystallization of PEO on h-BN surfaces at low h-BN loading, and 2) spherulitic confinement of PEO at higher h-BN weight loading. These competing effects reveal that h-BN modulates both polymer crystallinity and charge mobility in our CPEs. Density Functional Theory (DFT) calculations confirm strong attractive interactions between h-BN and both free ions (Na+ and NO3-), and we also find lesser attractive interactions between h-BN and PEO. These new findings for Na-polymer electrolytes support our experimental results. Our findings highlight the importance of filler geometry and chemical characteristics in designing future CPEs for Na-ion batteries.