(Invited) Hexagonal Boron Nitride Ionogel Electrolytes for Solid-State Batteries

Abstract

Ionogel electrolytes based on ionic liquids (ILs) and a gelling solid matrix are an attractive alternative to conventional liquid electrolytes for energy storage applications. In particular, ILs offer several advantages as an electrolyte including nonflammability, nonvolatility, high electrochemical stability, and high ionic conductivity. Moreover, combining ILs with a gelling solid matrix leads to a solid-state electrolyte that is sufficiently mechanically robust to replace both the liquid electrolyte and separator in a single component, thus allowing easier packaging, streamlined manufacturing, and minimal risk of leakage. For ionogel electrolytes, hexagonal boron nitride (hBN) is an especially desirable solid matrix due to its excellent chemical and thermal stability in addition to its mechanical robustness [1]. This talk will address recent efforts to realize high-performance hBN/IL ionogel electrolytes using hBN that has been solution-exfoliated into two-dimensional nanosheets using ethyl cellulose (EC) stabilizing polymers [2]. In addition to the intrinsic advantages of hBN, EC-exfoliated hBN nanosheets significantly enhance both ionic conductivity (> 1 mS/cm) and mechanical strength (storage modulus > 1 MPa) compared to conventional hBN microparticles, providing additional competitive advantages for energy storage applications [3]. The high thermal stability of hBN/IL ionogel electrolytes also enables safe, high-rate operation (up to 10C charge/discharge rate) at high temperatures up to 175 °C, which represents the highest operating temperature to date for solid-state lithium-ion batteries.[1] K.-S. Chen, et al., ACS Energy Letters, 2, 2026 (2017).[2] A. C. M. de Moraes, et al., Advanced Functional Materials, 29, 1902245 (2019).[3] W. J. Hyun, et al., ACS Nano, 13, 9664 (2019).