Regulating Lithium-Ion Transference Number of a Poly(vinyl alcohol)-Based Gel Electrolyte by the Incorporation of H₃BO₃ as an Anion Trapper

Gel electrolytes hold great promise for improving the safety of lithium-ion batteries (LIBs); however, their low lithium-ion transference number (tLi+ < 0.4) remains to be improved. Herein, boron-containing poly(vinyl alcohol) (B-PVA) solutions are prepared based on the simple reaction between PVA and H3BO3 and then electrospun to obtain the B-PVA nanofiber matrices. The gel electrolytes are formed by loading the liquid electrolytes into the as-obtained porous B-PVA matrices. We demonstrate that the tLi+ of B-PVA8 (with 8 wt % H3BO3 added) gel electrolyte can reach 0.81, much higher than that of the conventional PVA gel electrolyte (0.32). The B-PVA8 gel electrolyte also shows the highest Li+ conductivity of 1.81 × 10–3 S cm–1 compared to PVA. The B-PVA8 gel electrolyte enables a small Li nucleation overpotential of 129.8 mV when Li is plated and reduces the concentration polarization of Li||Li batteries. The mesocarbon microbead (MCMB) half-coin cells with the B-PVA8 gel electrolyte exhibit excellent rate capability and exceptional charge/discharge cycling stability.