Abstract
Rechargeable lithium-ion batteries (LIBs) have emerged as a key technology to meet the demand for electric vehicles, energy storage systems, and portable electronics. In LIBs, a permeable porous membrane (separator) is an essential component located between positive and negative electrodes to prevent physical contact between the two electrodes and transfer lithium ions. Among several types, microporous polyolefin membranes have dominated the commercial separator market for LIBs operated with liquid electrolytes, favored for their chemical and electrochemical stability, high mechanical strength, uniform pore size, and inexpensive manufacturing and materials cost. In this review, we summarize the principles and theoretical background underlying conventional manufacturing processes and newly emerging microporous polyolefin separators. Based on their mechanical and physical properties, as collected from the literature, we introduce a number of processing type-dependent characteristics and universal correlations among their properties. This will provide a macroscopic view on the subject and a guideline for the development of next-generation separators.
Highlights
With the rapidly growing demand for power consumption, lithium-ion batteries (LIBs) have emerged as a sustainable energy source for portable electronic devices and energy storage systems owing to their high specific energy and power (Figure 1a), flexible and lightweight design, and long lifespan compared with other battery technologies [1]
In various types of commercial LIBs, the main function of the separator is to prevent short circuits caused by physical contact of the two electrodes (Figure 2) [3]
Edxempearnimdsenfotarlerneesrugltys dreepnosirttye,dminanthyesltiutedriaetsuhreavheavaeimdeedmtoonismtrpatreodvethat the slope of a the energy densifitytteodf liLnIeBos.f l[o7g4(–G77u]rleAyl/otnhgickwniethss)thaendinlotrgoΦduisct−io3n.2,owf hsitcrhucitsucrlaolsley toantdhe estimated value thermally instabloefn−ic3k(eFli-griucrhe c9aat)h. odes, attempts have been made to make polyolefin microporous separators thinner. This route toward the development of next-generation LIBs will potentially lead to more serious safety concerns
Summary
With the rapidly growing demand for power consumption, lithium-ion batteries (LIBs) have emerged as a sustainable energy source for portable electronic devices and energy storage systems owing to their high specific energy and power (Figure 1a), flexible and lightweight design, and long lifespan compared with other battery technologies [1]. The separator should not be dissolved by or react with the electrolyte solution, which is mainly composed of organic carbonates and esters mixed with Li salts, such as lithium hexafluorophosphate [4] It must be electrochemically stable during cell operation and mechanically strong enough to withstand the high tension in the course of battery assembly [5]. Crystals 2021, 11, 1013 larger mean pore size and higher porosity generally result in lower ionic resistance and high specific battery power [12] In this case, the poorer mechanical strength is expected to increase the possibility of inner-battery electrical short circuiting. This may allow for the proper design of next-generation separators and the tailoring of their mechanical and physical properties
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