Hexagonal Boron Nitride-Coated Polyimide Ion Track Etched Separator with Enhanced Thermal Conductivity and High-Temperature Stability for Lithium-Ion Batteries

Abstract

The separator plays a vital role in preventing thermal runaway in lithium-ion batteries (LIBs). Herein, a PI/hBN (polyimide/hexagonal boron nitride) separator with excellent thermal stability and enhanced thermal conductivity is successfully prepared by ion track etching and doctor blade coating to achieve highly safe LIBs. The PI/hBN separator displays good electrolyte wettability, high mechanical strength, excellent thermal stability, and enhanced in-plane thermal conductivity, as well as good electrochemical performance when applied in LIBs. Specifically, PI track-etched membranes have been used to prepare separators with rigid structures and functional groups in polymer chains, thereby enabling the separators to be stable at temperatures as high as 500 °C. Moreover, hBN-coated nanoplates enhance the in-plane thermal conductivity of the separator to reduce the local heat accumulation in the battery while also promoting interfacial compatibility to facilitate the conduction of lithium ions. Lithium iron phosphate/lithium cells with the PI/hBN separator deliver better rate capability and superior capacity retention. The PI/hBN separator is a promising candidate for achieving highly safe LIBs, and this work paves the way for engineering roll-to-roll techniques to suppress thermal runaway and improve battery safety.

Overview on Theoretical Simulations of Lithium‐Ion Batteries and Their Application to Battery Separators

“…[92] The thickness of the separators typically varies between 25 and 40 µm, depending on the type of battery, they show a degree of porosity larger than 40% with an average pore size below 1 µm and are stable at temperatures up to 150 °C. Additionally, to improve the thermal and mechanical properties and wettability of the conventional separators based on PE and PP, new separators based on covalent organic framework (COF) into poly(arylene ether benzimidazole) (OPBI), [93] polyacrylonitrile (PAN) composite separators with cellulose acetate and nano-hydroxyapatite, [94] PAN with aluminum diethylphosphinate (ADEP), [95] polyimide (PI) polymer, [96] PI with polyethylene oxide (PEO) processed by electrospinning technique, [97] PI with zirconia (ZrO 2 ), [98] PI with graphene, [99] PI with hexagonal boron nitride, [100] PI with nano-tiO 2 , [101] PI with organic montmorillonite (OMMT), [102] PEO with para-aramid nanofibers (ANFs), [103] PVDF/SiO 2 , [104] poly(ethylene glycol) diacrylate (PEGDA), [105] polyurethane separator coated Al 2 O 3 particles, [89a] and poly(vinyl alcohol) with nano architecture halloysite nanotubes (NHNTs) composite separator (OPVA/NHNTs separator, [106] and new coatings of boehmite (γ-AlO(OH)) nanofibers, [107] inorganic oxide solid electrolyte layers (Li 1.3 Al 0.3 Ti 1.7 (PO 4 ) 3 , LATP), [108] SiO 2 with acrylamide (AM), [81a] Ca 3 (PO 4 ) 2 inorganic layer, [91] polyimide microsphere, [109] and plasma treatment plus zwitterion grafting [110] were developed. Further, it has been also explored the replacement of these synthetic polymers by natural polymers such as, natural wood, [111] cellulose, [96,112] silk fibroin, [113] silk fibroin with sericin, [114] poly(vinyl alcohol) (PVA), [115] lignin, [116] carrageenan, [117] among others.…”

A multifunctional composite membrane for high-safety lithium-ion batteries

“…In view of this, some researchers have proposed that the battery performance will be greatly improved if inorganic llers can be introduced inside another suitable polymer matrix, instead of coating onto the polyolen surface. 16,17 Typically, several kinds of advanced polymers have been emphatically investigated as the LIBs separator, such as poly(vinylidene uoride) (PVDF) [18][19][20] and its copolymer poly(vinylidene uorideco-hexauoropropylene) (PVDF-HFP), 21,22 poly(ethylene oxide) (PEO), 23 polyimide (PI) 24,25 and poly(acrylonitrile) (PAN). 26 Among them, PVDF is recognized as a promising polymer matrix because of its good processibility, excellent chemical stability and satisfactory thermal stability.…”

Core–Shell Structured Polyimide@γ-Al2O3 Nanofiber Separators for Lithium-Ion Batteries

“…To address the shortcomings of the polyolefin separator discussed above, a new generation of separators with excellent thermal stability are put forward. The polyimide (PI) nanofiber membrane obtained via the electrospinning process has been widely applied and highly appreciated in relevant businesses due to its outstanding thermal stability, tremendous electrolyte uptake, and ease of preparation. − However, the PI nanofiber membrane obtained via the electrospinning process is fragile because of the commonly overlapped internal fiber structure and the disordered arrangement. − In addition, the bulkiness structure of the nanofiber membrane will be damaged after long-term charge–discharge cycles . Therefore, the triple crosslinking strategies, including pre-rolling, solvent, and chemical imidization crosslinking of the PI nanofiber membrane were proposed to improve the mechanical strength of the PI nanofiber membrane in our previous study …”