High-Modulus Hexagonal Boron Nitride Nanoplatelet Gel Electrolytes for Solid-State Rechargeable Lithium-Ion Batteries

Solid-state electrolytes based on ionic liquids and a gelling matrix are promising for rechargeable lithium-ion batteries due to their safety under diverse operating conditions, favorable electrochemical and thermal properties, and wide processing compatibility. However, gel electrolytes also suffer from low mechanical moduli, which imply poor structural integrity and thus an enhanced probability of electrical shorting, particularly under conditions that are favorable for lithium dendrite growth. Here, we realize high-modulus, ion-conductive gel electrolytes based on imidazolium ionic liquids and exfoliated hexagonal boron nitride (hBN) nanoplatelets. Compared to conventional bulk hBN microparticles, exfoliated hBN nanoplatelets improve the mechanical properties of gel electrolytes by 2 orders of magnitude (shear storage modulus ∼5 MPa), while retaining high ionic conductivity at room temperature (>1 mS cm^-1). Moreover, exfoliated hBN nanoplatelets are compatible with high-voltage cathodes (>5 V vs Li/Li⁺) and impart exceptional thermal stability that allows high-rate operation of solid-state rechargeable lithium-ion batteries at temperatures up to 175 °C.