Porous polyimide separator promotes uniform lithium plating for lithium‐free cells

Abstract

Electrospun polyimide (PI) separators were found to reduce the charge‐transfer resistance of Li plating/stripping and the overpotentials of Li nucleation/growth onto Cu foils in the 1.2 M LiPF6/(ethylene carbonate/dimethyl carbonate = 1/1) electrolyte without any additives in comparison with polyethylene (PE) separators. Lithium deposition through the PI separator led to the formation of a granular morphology of 15–30 µm in diameter compared to lithium dendrites using PE. A similar trend of lithium deposition was observed in LiFePO4//Cu cells. The PI separator was found to enhance the discharge capacity and cycle life of Li plating/stripping in the Li//Cu and LiFePO4//Cu cells containing 40 µl electrolytes, verifying that the PI separator provides dendrite inhibition capability for the lithium‐metal‐free cells.

Mesoporous Polyimide Thin Films as Dendrite-Suppressing Separators for Lithium–Metal Batteries

“…22,34 Similarly, in the phase inversion process, the nonsolvent forms macro-scale domains in the wet polyimide film, thus producing macropores as wide as hundreds of nanometers to micrometers. 35,36 The electrospinning produces a polyimide fiber mat with porosity up to 95%, 42 and the spacious interfiber voids result in micrometer-scale pores. 38−42 Different from those aforementioned strategies, the microphase separation of polyimide-based block copolymer forms mesoscale domains of tens of nanometers, holding promise for preparing mesoporous polyimides.…”

“…Compared with PE and PP, polyimides have superior mechanical performance, but controlling the pore size in polyimides on the mesoscale remains challenging. Polyimide-based separators have been produced via porogens, , phase inversion, − electrospinning, − and thermolysis of polyimide-based block copolymers. , The porogens with predefined sizes were embedded in the polyimide films and then selectively removed to template pores, i.e., silica nanospheres etched by hydrofluoric acid. , The macroscale porogens produce macropores as wide as hundreds of nanometers. , Similarly, in the phase inversion process, the nonsolvent forms macro-scale domains in the wet polyimide film, thus producing macropores as wide as hundreds of nanometers to micrometers. , The electrospinning produces a polyimide fiber mat with porosity up to 95%, and the spacious interfiber voids result in micrometer-scale pores. − Different from those aforementioned strategies, the microphase separation of polyimide-based block copolymer forms mesoscale domains of tens of nanometers, holding promise for preparing mesoporous polyimides. , We adopted the strategy to prepare porous polyimides using ABA triblock copolymers comprising polyimide and thermally labile blocks. To synthesize polyimide-based triblock copolymers, various thermally labile blocks have been deployed, such as poly­(methyl methacrylate), polystyrene, , poly­(α-methylstyrene), , polycaprolactone, − poly­(ethylene oxide), and poly­(propylene oxide). − The triblock copolymers microphase-separate to form domains in tens of nanometers.…”

Effect of Cross-Linking and Surface Treatment on the Functional Properties of Electrospun Polybenzimidazole Separators for Lithium Metal Batteries

“…The electrospun polyimide (PI) and their copolymer-based composite separators possess high thermo-dimensional stability, porosity, as well as excellent electrochemical performance and ideal thermal shutdown function. Moreover, the polyimide separators are of benefit to the compatibility with electrolyte and reduce nucleation and plating overpotentials to form dendrite-like lithium deposit on the electrodes to enhance the cycle life. − Polyacrylonitrile (PAN) nanofiber membranes prepared by Dong et al showed conductivity higher than that of commercial Celgard and a Coulomb efficiency as high as 98.7% after 50 cycles of battery performance at 0.5 C . Even though the electrospun separators have an excellent porous structure, the low mechanical strength of various polymeric materials cannot meet the requirement of battery assembly and limits its application as battery separators …”