Highly Stable Porous Polyimide Sponge as a Separator for Lithium-Metal Secondary Batteries

Abstract

To inhibit Li-dendrite growth on lithium (Li)-metal electrodes, which causes capacity deterioration and safety issues in Li-ion batteries, we prepared a porous polyimide (PI) sponge using a solution-processable high internal-phase emulsion technique with a water-soluble PI precursor solution; the process is not only simple but also environmentally friendly. The prepared PI sponge was processed into porous PI separators and used for Li-metal electrodes. The physical properties (e.g., thermal stability, liquid electrolyte uptake, and ionic conductivity) of the porous PI separators and their effect on the Li-metal anodes (e.g., self-discharge and open-circuit voltage properties after storage, cycle performance, rate capability, and morphological changes) were investigated. Owing to the thermally stable properties of the PI polymer, the porous PI separators demonstrated no dimensional changes up to 180 °C. In comparison with commercialized polyethylene (PE) separators, the porous PI separators exhibited improved wetting ability for liquid electrolytes; thus, the latter improved not only the physical properties (e.g., improved the electrolyte uptake and ionic conductivity) but also the electrochemical properties of Li-metal electrodes (e.g., maintained stable self-discharge capacity and open-circuit voltage features after storage and improved the cycle performance and rate capability) in comparison with PE separators.

Al2O3 Ceramic/Nanocellulose-Coated Non-Woven Separator for Lithium-Metal Batteries

“…By contrast, Li deposits in the cell using the Al 2 O 3 /NC-3 separator showed a relatively dense and smooth surface. These SEM results prove that the Al 2 O 3 /NC coating layer uniformly distributed the Li ions through the pores of the coating layer and also inhibited the extensive growth of Li dendrites owing to its relatively high mechanical strength [51][52][53].…”

Review—Challenges and Opportunities in Lithium Metal Battery Technology

“…Different types of high-performance separators may include ceramic filled, ceramic filled and coated, polyimide-based and Aramid coated separators. [64][65][66][67] Current ongoing research in the field of separator includes layered separators of these materials and wetting of the separator interface with advanced electrolytes. 68 Another important role of separator is to improve battery safety, Most of the commercial separators are made up of polyethylene (PE) or polypropylene (PP) which melt between 130 and 170 °C, thereby blocking Li-ion flow and shutting down battery operation.…”

Highly Macroporous Polyimide with Chemical Versatility Prepared from Poly(amic acid) Salt-Stabilized High Internal Phase Emulsion Template

“…Furthermore, porous PI was successfully obtained by converting the PAAS to PI scaffold via a well-known thermal imidization process. [39][40][41][42]44 The Macro PI obtained via our emulsion template method is thermally stable with elastic properties and is useful as a solar desalination membrane and separator in Li-metal batteries. Nevertheless, the limitations of the PAAS-mediated emulsion template method remain, including (1) the limited combination in chemical diversity of the polymer backbone and organic base, (2) a lack of understanding of the design of the PAAS polymer for use in the emulsion, and (3) the control of the pore size and porosity of the resulting polymer.…”

“…As an alternative approach, our group suggested the use of the poly­(amic acid) salt (PAAS) polymer as the macrosurfactant of an oil-in-water (o/w) HIPE. , The water-soluble PAAS polymer displays an intrinsic amphiphilicity due to its chemical structure consisting of the aromatic polymer backbone conjugated with protonated organic bases. − The PAAS polymer poly­(3,3′,4,4′-biphenyltetracarboxylic dianhydride- co - m -tolidine) conjugated with N,N′ -dimethylethanolamine (BPDA-mTB/DMEA) exhibits a sufficient amphiphilicity to form a (o/w) HIPE having an internal volume of >80 vol %, even at a low PAAS mass content (∼3 wt %). Furthermore, porous PI was successfully obtained by converting the PAAS to PI scaffold via a well-known thermal imidization process. − , The Macro PI obtained via our emulsion template method is thermally stable with elastic properties and is useful as a solar desalination membrane and separator in Li-metal batteries. Nevertheless, the limitations of the PAAS-mediated emulsion template method remain, including (1) the limited combination in chemical diversity of the polymer backbone and organic base, (2) a lack of understanding of the design of the PAAS polymer for use in the emulsion, and (3) the control of the pore size and porosity of the resulting polymer.…”

“…As an alternative approach, our group suggested the use of the poly(amic acid) salt (PAAS) polymer as the macrosurfactant of an oil-in-water (o/w) HIPE. 38 , 39 The water-soluble PAAS polymer displays an intrinsic amphiphilicity due to its chemical structure consisting of the aromatic polymer backbone conjugated with protonated organic bases. 40 − 43 The PAAS polymer poly(3,3′,4,4′-biphenyltetracarboxylic dianhydride- co - m -tolidine) conjugated with N,N′ -dimethylethanolamine (BPDA-mTB/DMEA) exhibits a sufficient amphiphilicity to form a (o/w) HIPE having an internal volume of >80 vol %, even at a low PAAS mass content (∼3 wt %).…”