Roll-to-Roll Functionalization of Polyolefin Separators for High-Performance Lithium-Ion Batteries

Abstract

Modified polyolefin separators fabricated via a roll-to-roll system exhibit markedly improved compatibility with lithium ion battery electrolytes. Zwitterionic molecules containing a perfluorophenyl azide functional group were synthesized and covalently bound to the surface of commercial polyolefin separators via UV-activated photochemistry. A roll-to-roll prototype system was constructed allowing for the functionalization of large areas of separator under ambient conditions at low cost. Lithium-ion battery cells containing the modified separators exhibit superior electrochemical performance using a common commercial electrolyte. The modified separators, both monolayer PE and trilayer PP/PE/PP, are wetted instantly upon contact with liquid electrolytes lacking linear carbonates. These electrolytes have been designed for use in batteries with advanced thermal stability properties and/or higher voltage windows, which have previously been hindered by incompatibility with commercial trilayer polyolefin separators. This scalable modification technique is able to meet the rapidly growing demand for low-cost, high-performance separators for safer lithium-ion batteries.

Ionic Covalent Organic Frameworks for Energy Devices

“…[ 220,221 ] However, these polymers generally lack functional groups and have low electrolyte wettability; thus, they exhibit low electrochemical energy conversion, which limits their use in low‐form‐factor electronic devices. [ 222 ] These problems have been addressed by modifying high‐porosity semicrystalline polyolefins in several ways, such as by plasma processing, [ 223 ] electron‐beam treatment, [ 224 ] ultraviolet irradiation, [ 225 ] or grafting with hydrophilic groups. [ 226,227 ]…”

“…[220,221] However, these polymers generally lack functional groups and have low electrolyte wettability; thus, they exhibit low electrochemical energy conversion, which limits their use in low-form-factor electronic devices. [222] These problems have been addressed by modifying high-porosity semicrystalline polyolefins in several ways, such as by plasma processing, [223] electron-beam treatment, [224] ultraviolet irradiation, [225] or grafting with hydrophilic groups. [226,227] Research has also been pursued on the development of porous nanomaterials for the construction of electrodes with improved conductivity and stability; this has been achieved, for example, by enhancing S-loading masses, and inhibiting the polysulfide shuttle effect.…”

Recent developments in natural mineral-based separators for lithium-ion batteries

“…At present, polyolefin separators, such as polyethylene (PE), polypropylene (PP), are used in commercial LIBs due to their low cost, good mechanical properties, excellent chemically inert, non-toxicity, etc. 13 While, there are still some issues, for example, poor electrolyte wettability and thermal stability, low porosity and melting point, leading to safety issues and severely affecting electrochemical performance. 7,14 Natural minerals with abundant pore structure, excellent thermal/chemical stability and mechanical properties have attracted widespread attention.…”

Intercalated Montmorillonite Reinforced Polyimide Separator Prepared by Solution Blow Spinning for Lithium-Ion Batteries

“…Lithium-ion batteries (LIBs) are currently the most competitive power source for high capacity energy storage in virtue of their high energy density, excellent power capability, low self-discharge rate, and long cycle lifetime. − Considering the continuous expansion of the LIB market prospect, the potential security issue has proved to be the foremost challenge for their wide commercialized applications . A separator is of crucial importance in a battery, which preserves the liquid electrolyte and keeps the anode and the cathode apart to avoid internal short circuit, while permitting rapid transport of ionic charge carriers. − Typically, commercial separators used in LIBs are porous polyolefin materials prepared by a wet or dry stretching process, predominantly polypropylene (PP), microporous polyethylene (PE), or their combinations (such as PP/PE/PP) because of their acceptable costs, chemical stability, and robust mechanical properties. − In spite of these superior properties, they still suffer from several inherent drawbacks, for instance, low porosity, poor compatibility with polar electrolytes, and weak thermal stability . The aforementioned drawbacks could inhibit the performance of batteries and particularly cause security issues under harsh conditions, and even more severely, nonflame-retardant separators may aggravate their deterioration.…”