Phase-Inversion Polymer Composite Separators Based on Hexagonal Boron Nitride Nanosheets for High-Temperature Lithium-Ion Batteries

Abstract

By preventing electrical contact between anode and cathode electrodes while promoting ionic transport, separators are critical components in the safe operation of rechargeable battery technologies. However, traditional polymer-based separators have limited thermal stability, which has contributed to catastrophic thermal runaway failure modes that have conspicuously plagued lithium-ion batteries. Here, we describe the development of phase-inversion composite separators based on carbon-coated hexagonal boron nitride (hBN) nanosheets and poly­(vinylidene fluoride) (PVDF) polymers that possess high porosity, electrolyte wettability, and thermal stability. The carbon-coated hBN nanosheets are obtained through a scalable liquid-phase shear exfoliation method using ethyl cellulose as a polymer stabilizer and source of the carbon coating following thermal pyrolysis. When incorporated within the PVDF matrix, the carbon-coated hBN nanosheets promote favorable interfacial interactions during the phase-inversion process, resulting in porous, flexible, free-standing composite separators. The unique chemical composition of these carbon-coated hBN separators implies high wettability for a wide range of liquid electrolytes. This combination of high porosity and electrolyte wettability enables enhanced ionic conductivity and lithium-ion battery electrochemical performance that exceeds incumbent polyolefin separators over a wide range of operating conditions. The hBN nanosheets also impart high thermal stability, providing safe lithium-ion battery operation up to 120 °C.

Poly(vinylidene fluoride) separators for next‐generation lithium based batteries

“…The PVDF/PEG/BaTiO 3 composite separator improves the porosity and electrolyte wettability of the separator, and has a larger electrolyte retention rate. At the same time, the PVDF/PEG/BaTiO 3 separator has excellent mechanical [67] Copyright 2020, American Chemical Society properties and thermal stability. These good physical properties result in the batteries exhibiting outstanding electrochemical properties.…”

“…The process of TIPS is shown in Figure 4B. [67] Liang et al [68] fabricated dual-asymmetric PVDF separators by TIPS method with the mixed diluents of dimethyl sulfone (DMSO2) and glycerol. This dual-asymmetric porous structure has a porous volume and two surfaces with large interconnected pores and small pores, respectively.…”

“…B, The process of TIPS. [67] Copyright 2020, American Chemical Society. C, The contact angle images of electrolyte solvent dripping on PVDF and Celgard 2400 separators, (D) Thermal contraction behavior of PVDF and Celgard 2400 separators.…”

Synthesis and Modification of Boron Nitride Nanomaterials for Electrochemical Energy Storage: From Theory to Application

“…e–g) Reproduced with permission. [ 116 ] Copyright 2020, American Chemical Society. h) Thermal infrared images of different separators.…”

Thermoregulating Separators Based on Phase‐Change Materials for Safe Lithium‐Ion Batteries

“…[21] Recently, inorganic and organic materials have been coated onto separators to improve thermal resistance and wettability. [22][23][24][25] Nevertheless, the coating layer may increase the thickness and decrease the porosity of the separators. More importantly, rationally designed separators with multiple functions are proposed to improve the safety of LIBs.…”