Commercial Polyethylene Separator Research Articles

Mechanical shutdown of battery separators: Silicon anode failure

The pulverization of silicon (Si) anode materials is recognized as a major cause of their poor cycling performance, yet a mechanistic understanding of this degradation from a full cell perspective remains elusive. Here, we identify an overlooked contributor to Si anode failure: mechanical shutdown of separators. Through mechano-structural characterization of Si full cells, combined with digital-twin simulation, we demonstrate that the volume expansion of Si exerts localized compressive stress on commercial polyethylene separators, leading to pore collapse. This structural disruption impairs ion transport across the separator, exacerbating redox nonuniformity and Si pulverization. Compression simulation reveals that a Young’s modulus greater than 1 GPa is required for separators to withstand the volume expansion of Si. To fulfill this requirement, we design a high modulus separator, enabling a high-areal-capacity pouch-type Si full cell to retain 88% capacity after 400 cycles at a fast charge rate of 4.5 mA cm−2.

Thickness regulation of electric double layer via electronegative separator to realize High-Performance Lithium-Metal batteries

Lithium metal anode is considered as a promising electrode material for next-generation energy storage systems due to their high theoretical capacity and a low redox potential. However, the uncontrollable growth of Li dendrites severely hindered its practical application. Separators, a vital component in batteries, offer a promising solution to this issue, which can regulate the transport of lithium ions (Li+) and guide the homogenous deposition of Li+. In this study, a three-dimensional porous structure coating layer is constructed on the surface of the commercial polyethylene separator by polymer-induced phase separation (PIPS) and UV-induced cross-linking reactions. The incorporation of synthetized sulfonated SiO2 particles (S-SiO2) enable the successful construction of a negatively charged separator (PE@S-SiO2) based on negatively charged moieties on the surface, which compresses the thickness of the electric double layer (EDL) to optimize the Li+ transport dynamics and suppress dendritic growth. The resulting PE@S-SiO2 separator displays superior electrolyte wettability, much higher thermal resistance, high lithium transference number (0.86), and ionic conductivity (1.15 mS/cm). Consequently, when assembled into lithium metal batteries, the negatively charged separator endows stable cycling over 800 h at a current density of 1 mA cm−2.

Aging Behavior of Polyethylene and Ceramics-Coated Separators under the Simulated Lithium-Ion Battery Service Compression and Temperature Field

In this paper, a device was set up, which could simulate the separator environment in the battery to track the influence of compression, temperature, and the electrolyte on the structure and electrochemical performance of separators. A commercial polyethylene separator and alumina- or boehmite-coated separators were selected, and the high-temperature cyclic compression was carried out in a mixed solvent environment with a ratio of vinyl carbonate and diethyl carbonate of 1:1. Compared with that compressed for 50 cycles under room temperature, the compression at 60 °C resulted in pore structure deterioration in the polyethylene separator. The oxidative voltage limit was reduced to 3.6 V, and after 200 charge and discharge cycles, the capacity was reduced by more than 50%. For the coated separator, the presence of a coating layer exhibited some protective effects, and the microporous structure in the base membrane was preserved. The oxidative voltage limit was above 4.2 V. However, as a result of the compression, the coating particles were still inserted into the pore structure, leading to a decrease in porosity and a decrease in discharge capacity, especially at a rate of 4 C. Compared with that coated with alumina particles, the interface resistance for the separator coated with boehmite particles was minimally affected, and the electrochemical performance after cyclic compression under 60 °C was better, exhibiting higher application ability.

Ultrathin Composite Separator Based on Lithiated COF Nanosheet for High Stability Lithium Metal Batteries

AbstractLithium metal is considered as the ultimate anode material for high‐energy‐density rechargeable batteries. However, lithium metal batteries (LMBs) with commercial separators still face some challenges such as low cycling efficiency and uncontrollable Li dendrite growth, which seriously hampers the commercialization of LMBs. In this study, a novel kind of ultrathin (6.2 µm) multifunctional composite separator (TpPa‐SO3Li@PE) is designed and prepared via coating lithiated covalent organic framework nanosheet (TpPa‐SO3Li) on the surface of commercial polyethylene separator (PE). TpPa‐SO3Li@PE integrates features of the nanochannel arrays and abundant immobilized anionic sites, leading to efficient Li+ conduction and homogeneous Li+ flow. As a result, TpPa‐SO3Li@PE exhibits excellent Li+ conductivity (0.96 mS cm−1) and Li+ transference number (0.83) at room temperature, and Li/Li symmetric cell using TpPa‐SO3Li@PE separator possesses highly stable Li plating/striping (over 2600 h) at high current density (5 mA cm−2). Moreover, Li/LiFePO4 full cells with TpPa‐SO3Li@PE separator show excellent cycling performance (high capacity retention of 94.9% after 300 cycles at 1 C) and superior rate performance (high specific capacity of 113.6 mAh g−1 at 5 C).

Unveiling high-power and high-safety lithium-ion battery separator based on interlayer of ZIF-67/cellulose nanofiber with electrospun poly(vinyl alcohol)/melamine nonwoven membranes

Due to the poor thermal stability of conventional separators, lithium-ion batteries require a suitable separator to maintain system safety for long-term cycling performance. It must have high porosity, superior electrolyte uptake ability, and good ion-conducting properties even at high temperatures. In this work, we demonstrate a novel composite membrane based on sandwiching of zeolitic imidazole frameworks-67 decorated cellulose acetate nanofibers (ZIF-67@CA) with electrospun poly(vinyl alcohol)/melamine (denoted as PVAM) nonwoven membranes. The as-prepared sandwich-type membranes are called PVAM/x%ZIF-67@CA/PVAM. The middle layer of composite membranes is primarily filled with different weight percentages of ZIF-67 nanoparticles (x = 5, 15, and 25 wt%), which both reduces the non-uniform porous structure of CA and increases its thermal stability. Therefore, our sandwich-type PVAM/x%ZIF-67@CA/PVAM membrane exhibits a higher thermal shrinkage effect at 200 °C than the commercial polyethylene (PE) separator. Due to its high electrolyte uptake (646.8%) and porosity (85.2%), PVAM/15%ZIF-67@CA/PVAM membrane achieved high ionic conductivity of 1.46 × 10-3 S cm−1 at 70 °C, as compared to the commercial PE separator (ca. 6.01 × 10-4 S cm−1 at 70 °C). Besides, the cell with PVAM/15%ZIF-67@CA/PVAM membrane shows an excellent discharge capacity of about 167.5 mAh g−1after 100 cycles at a 1C rate with a capacity retention of 90.3%. The ZIF-67 fillers in our sandwich-type composite membrane strongly attract anions (PF6-) through Lewis' acid-base interaction, allowing uniform Li+ ion transport and suppressing Li dendrites. As a result, we found that the PVAM/15%ZIF-67@CA/PVAM composite nonwoven membrane is applicable to high-power, high-safety lithium-ion battery systems that can be used in electric vehicles (EVs).

Thermally Resistant, Mechanically Robust, Enamel‐Inspired Hydroxyapatite/Polyethylene Nanocomposite Battery Separator

AbstractMicroporous polyethylene (PE) membrane is a representative lithium‐ion battery (LIB) separators but regularly shrinks especially in high‐temperature conditions, and is facilely pierced while growing Li dendrites, leading to severe consequences such as short circuits, thermal runaway, and even explosion. Herein, this article reports a quasi‐continuous strategy that utilizes in situ enamel mineralization engineering followed by thermal treatment to easily develop a large‐area, 3D interlaced hydroxyapatite nanosheets array‐reinforced PE nanocomposite separator with robust mechanical properties and excellent resistance to thermal shrinkage. Specifically, the 120 °C‐heated nanocomposite possesses excellent breaking stress, an ultrahigh toughness of ≈434.4 MJ m−3, and an enhanced friction coefficient of ≈0.69, which are distinctly higher than those of commercial PE separators, respectively, and far exceeding those of reported ceramic modified‐PE separators. The elongation of the resultant nanocomposite can achieve an extraordinary ≈2456.4% without any fracture under a 180 °C‐heating temperature. In situ observation and finite element simulation indicate that the impressive mechanical and thermostable integration profits from the co‐effect of efficient energy dissipation at organic–inorganic interfaces and mechanically interlocked, mutually‐supported hybrid microstructure. The enamel‐inspired separator can be potentially applied in safer high‐temperature LIBs and this strategy provides a valuable guide to develop other high‐performance polymer‐based nanocomposites.

Cellulose nanofibrils derived from pulp as a high performance separator for lithium‐ion batteries

AbstractCellulose nanofibrils (CNFs) from hardwood bleached kraft pulp (HwBKP) are produced via enzymatic, chemical, and mechanical treatment. A nanoporous structured CNF‐based separator is produced, and the electrochemical performance, morphology, and thermal stability analyses are performed in comparison to the commercial polyethylene separator. The results obtained show that the electrolyte‐philic CNF separator has capacity retention of 88.6% over 200 cycles and very good ionic conductivity and wettability results due to its high hydrophilic nature. At 140°C, the CNF separator was resilient to heat and remained intact. The CNF separator reflects high thermal resistance and good electrolyte uptake properties that are among the mandatory requirements of a separator hence, a promising contender for use in lithium‐ion batteries.

Swelling of lignin-based gel in salt-containing organic solvents and its application as gel electrolyte

Abstract A lignin-based gel prepared by the chemical crosslinking of hardwood acetic acid lignin (AL) with poly(ethylene glycol) diglycidyl ether has been reported to shrink in water and organic solvents but swell specifically in aqueous binary solutions. In this study, the AL-based gel was also found to swell in lithium-salt-containing organic solvents, namely, liquid electrolytes. The uptake of salt solutions reached five times the dry weight of the gel. The ionic conductivity of the gel swollen with 1 M LiBF4 in propylene carbonate or a mixed solution (1:1, v/v) of ethylene carbonate and dimethyl carbonate exceeded 1 mS cm−1 at room temperature (25 °C), suggesting that this gel can be applied as a gel electrolyte for lithium-ion batteries (LIBs). A prototype LIB was assembled with the AL-based gel electrolyte and LiCoO2/graphite-based electrodes and exhibited low bulk and charge transfer resistances of 4.1 and 9.7 Ω, respectively. Moreover, its initial specific capacity reached 104 mAh g−1 at a current density of 28 mA g−1, which is comparable to that of a reference LIB assembled using a commercial polyethylene separator. These results indicate the significant potential of this lignin-based gel for application in energy storage devices.

Multi-functional Al2O3-coated separators for high-performance lithium-ion batteries: Critical effects of particle shape

The technology of coating polyolefin-type separators with ceramics is gradually developing as an effective method to improve the safety of lithium-ion batteries (LIBs). However, the powder properties of ceramics can adversely affect the surface structure and ionic conductivity of separators; therefore, a new approach is required regarding the powder properties that affect the performance of the separator. Herein, the effect of the Al2O3 particle shape on the physical properties of Al2O3-coated separators and the performance of LIBs is investigated. In the separator coated with angular-shaped Al2O3 particles (Al2O3-A), the pores in the coating layer are uniformly distributed, improving physical properties such as porosity and wettability. The thermal shrinkage of separator is <10% when exposed to 150 °C for 1 h, considerably smaller than that of the commercial polyethylene separator (approximately 83%) under the same conditions. Moreover, the Al2O3-A-coated separator shows the highest ionic conductivity (0.531 mS cm−1), and the LiNi0.8Mn0.1Co0.1O2/Al2O3-A-coated separator/Li battery displays improved stability than using the polyethylene separator under a current density of 5C. This proposes approach to improve the separator's performance through the shape control of ceramic particles paves the way for separators to contribute to the high-temperature safety and long cycle life of batteries.

Facile one-pot synthesis of biomass-derived activated carbon as an interlayer material for a BAC/PE/Al2O3 dual coated separator in Li-S batteries.

Lithium-sulfur batteries (LSB) are an attractive alternative electrochemical energy storage device compared to conventional lithium-ion batteries due to their higher theoretical capacity and energy density. Despite these advantages, it is still difficult to commercialize LSB because of poor electrochemical performance caused by the dissolution of soluble lithium polysulfides (LiPS). To solve these critical issues, a multi-functional separator was prepared using biomass-derived activated carbon (BAC) and a ceramic layer on the polyethylene (PE) separator. For this purpose, BAC was synthesized by a facile one-pot synthesis method by a specifically designed furnace using various forms of milk waste. The multi-functional separator suppresses the effect of LiPS dissolution and increases the Li+ diffusion kinetics. BAC was able to absorb the LiPS shuttle, as confirmed by UV-vis measurements and X-ray photoelectron spectroscopy (XPS). LSB cells assembled using this multi-functional separator show a higher discharge capacity of 1092.5 mA h g-1 at 0.1 C-rate, while commercial PE separators deliver a specific capacity of 811.8 mA h g-1. These novel separators were also able to suppress lithium dendrites during cycling. This work offers a novel and simple approach for streamlining the synthesis process of BAC and applying it to LSB, aiding in the development of sustainable energy sources.

A high-stable polyacrylonitrile/ceramic composite membranes for high-voltage lithium-ion batteries

Polymer/ceramic composite gel electrolytes are considered promising alternatives to conventional liquid electrolytes for developing high-energy and safer lithium-ion batteries (LIBs). In this study, we prepare three polyacrylonitrile (PAN)/ceramic composite membranes with 40 wt% Al2O3, BaTiO3, and TiO2 ceramic nanoparticles and compared their properties with those of pristine PAN. Structural and morphological investigations confirm the formation of the polymer/ceramic composites. The interconnected microporous structure PAN/ceramic composites efficiently entrapped a large amount of liquid electrolyte and exhibit improved ionic conductivity compared to that of the pristine PAN electrolyte. The PAN/Al2O3 composite electrolyte displays the highest ionic conductivity of 5.2 × 10−3 S cm−1 under ambient conditions with low Li+-coordinated EC and high free PF6− concentration. Thermal shrinkage tests indicate that the addition of ceramic particles enhance the thermal stability of the PAN/ceramic membranes, as compared to that of commercial polyethylene separators. The PAN/ceramic composite electrolytes are tested as separator-cum-electrolytes in lithium-ion batteries using a LiNi0.8Co0.1Mn0.1O2 (NCM811) high-voltage cathode, and a lithium metal anode. The LIB with the PAN/Al2O3 composite electrolyte delivers a high capacity of 184 mAh g−1 at 0.5 C, which is retained at 85% after 100 cycles, demonstrating the best rate performance among all tested composite electrolytes.

LiF-rich and self-repairing interface induced by MgF2 engineered separator enables dendrite-free lithium metal batteries

Lithium metal batteries (LMBs) are promising for high-energy density rechargeable batteries while suffer from uncontrolled dendrites growth and unstable solid electrolyte interface (SEI) layer on the surface of lithium (Li) metal anodes. In this study, a facile and low-cost strategy is proposed to enable dendrite-free and long-life LMBs by coating MgF2 onto commercial polyethylene separator. The composite separator possesses excellent wettability and high thermal stability. When the MgF2 coating contacts Li metal anode directly, an artificial SEI layer is in-situ formed due to the spontaneously reaction of MgF2 and Li metal, which is composed of LiF and lithiophilic Mg. More importantly, a small amount of dissolved MgF2 can fill the micro-gaps between un-contact MgF2 coating and Li anode and repair the tiny cracks in the SEI generated during repeated charge–discharge process. Hence, a continuous SEI layer is formed throughout the entire surface of Li metal anode with lithiophilic, LiF-rich and self-repairing capabilities, protecting Li metal anode, reducing the nucleation overpotential, promoting smooth Li plating and inhibiting Li dendrites growth. The Li||Li symmetric cells, Cu||Li asymmetric cells and full cells with the MgF2 coated separators delivers significantly enhanced coulombic efficiency and cycle life in both ether-based and carbonate-based electrolyte. This design of artificial LiF-rich SEI with self-repairing capability by separator engineering paves a new insight for the application of alkali metal batteries.

Lithiophilic perovskite-CaTiO3 engineered separator for dendrite-suppressing 5 V-class lithium metal batteries with commercial carbonate-based electrolyte

High theoretical specific capacity and the lowest electrochemical potential of Li metal have made it one of the most promising materials for metal anode. Nonetheless, shortened lifespan and even safety issues induced by uncontrollable growth of Li dendrite severely impede the development of lithium metal batteries (LMBs). In this work, a facile and economic strategy is introduced by casting lithiophilic CaTiO3 micro-particles onto the commercial polyethylene separators. The CaTiO3 coating could not only enhance the thermal stability of the separator, but also decrease the nucleation overpotential and facilitate homogeneous Li deposition, finally achieving suppression of the Li dendrite. Consequently, with the CaTiO3-coated separators, the cycling lifespan of Li||Li symmetric cells was remarkably improved to 1500 h in carbonate electrolyte. Moreover, 5 V-class full cells coupled with CaTiO3-coated separators exhibit prolonged lifespan and superior rate performance, indicating the good potential of the modified separators for application. Considering the fabrication of CaTiO3-coated separators is completely industry-available, this work could accelerate the proceeding of practical application of high-energy-density lithium metal battery systems.

Scalable Synthesis of Nano-Sized Bi for Separator Modifying in 5V-Class Lithium Metal Batteries and Potassium Ion Batteries Anodes.

With the advantages of high theoretical-specific capacity and lowest working potential, lithium metal anode is considered as the most promising anode for next-generation batteries. Here, a scalable dealloying method is developed to prepare nano-sized bismuth (Bi). It is found that the Bi-modification can not only enhance the wettability of the commercial polyethylene separator but also suppresses the lithium dendrite growth. With the nano-sized Bi modified separator, 5V-class lithium metal batteries with commercial carbonate-based electrolyte show a 91% capacity retention ratio after 800 cycles. First-principle calculations prove that lithium atoms tend to deposit smoothly on the Bi surface. Moreover, for potassium ion batteries, nano-sized Bi shows a stable cycling performance and high capacity. The results may be useful for the development of high-energy and high-safety batteries.

Influence of flexible gelatinous coating layer on electrochemical performance and fatigue failure of lithium battery separator

Recently, the battery security issue receives widespread attention. Investigating the compression performance and failure mode of the battery separator, and then simulating the internal soft short-circuit of the battery due to separator rupture becomes the current focus. In this work, commercial polyethylene separators are coated with a Al2O3 composite organic silicone - acrylic acid gel layer and the electrochemical performance are characterized. The coated battery separator (PEAE-5) exhibits the lowest charge transfer resistance and increases the electrochemical stability window to 5.3 V, since the silicone exhibits oxidation resistance and the acrylic provides flexibility in polar electrolyte solvents. Subsequently, the battery separator is punched in cycles to simulate fatigue failure of the separator under external compression. The results indicate that the separator (PEAE-5) coated with a 5% solid content of organic silicone - acrylic acid emulsion exhibits the best combined physical-mechanical and electrochemical properties, maintaining nearly 80% of the original cycling performance after 50 cycles of compression. The separator coated with the composite organic silicone - acrylic acid gel layer suffers the least from cycle fatigue. The existence of the flexible gelatinous coating layer affords an efficient method to protect the battery separator from destruction.

Binder-Free, Thin-Film Ceramic-Coated Separators for Improved Safety of Lithium-Ion Batteries.

Separators play a crucial role in ensuring the safety of lithium-ion batteries (LIBs). Commercial polyolefin-based separators such as polyethylene (PE) still possess serious safety risks under abuse conditions because of their poor thermal stability. In this work, a novel type of binder-free, thin ceramic-coated separators with superior safety characteristics is demonstrated. A thin layer of alumina (Al2O3) is coated on commercial PE separators using the electron-beam physical vapor deposition (EB-PVD) technique. Scanning electron microscopy (SEM), contact angle, impedance spectroscopy, and adhesion test techniques were employed to evaluate structure–property correlations. When compared to commercial slurry-coated separators, the EB-PVD-coated separators display (i) higher thermal stability, (ii) stronger ceramic–polymer adhesion, and (iii) competitive electrochemical performance of full LIB cells. Thermal stability, in terms of improved shutdown and breakdown characteristics of the separator, was studied using the in situ impedance technique up to 190 °C. In addition, the improved adhesion of the ceramic layer deposited on the PE separator was studied following the tape adhesion strength test. We prove that the thin (binder-free) ceramic layer coated by EB-PVD is far more effective in improving separator safety than those made using the conventional thick slurry coating.

Construction of silica-oxygen-borate hybrid networks on Al2O3-coated polyethylene separators realizing multifunction for high-performance lithium ion batteries

The separator, an essential component in lithium ion batteries, faces more challenges with the increasing diversification of electrode materials towards higher energy density and longer life. Herein we report the performance improvements of lithium ion batteries enabled by the multifunctional separator, which is fabricated by constructing the silica-oxygen-borate (Si–O–B) thin layer on Al2O3-coated polyethylene separators through surface engineering. This separator inherits the advantage of Al2O3-coated polyethylene separators in terms of excellent thermal stability and puncture strength, and no obvious dimensional change at 200 °C. The Si–O–B thin layer provides abundant Lewis acid sites and excellent electrolyte uptake to desolvate Li+ ions and traps anions, and therefore favors excellent lithium ion transport properties and lithium/electrolyte interfacial stability. More importantly, the Si–O–B hybrid thin layer endows an additional function of scavenging HF and H2O molecules. The benefits offered by this separator are demonstrated by the enhanced C-rates capability and cycling performance of both LiCoO2/Li half-cell and NCM/graphite full cell, which lies far beyond those achievable with commercial polyethylene separators and Al2O3-coated polyethylene separators. This work presents a simple and efficient strategy to construct multifunctional separators with excellent comprehensive properties, and provides inspiration for the rational design of advanced separators towards next-generation high-performance batteries.

Rational design of perfluorinated sulfonic acid ionic sieve modified separator for high-performance Li-S battery

Practical application of Li-S battery is limited by the fast capacity decay and low coulombic efficiency caused by the shuttling phenomenon. Modification of the battery separator to impart the separator with ionic sieving property is an effective strategy to alleviate the shuttling phenomenon. In this study, perfluorinated sulfonic acid (PFSA) ionomers with different equivalent weight (EW) values are used to modify the commercial polyethylene separator, and the electrochemical performance of these separators is systematically investigated. Our results show that the separator modified using PFSA ionomer with a low EW value of 830 shows optimal battery performance owing to its unique structure of the ionic cluster. The Li-S battery with this modified separator shows an initial discharge capacity of 1352 mAh g−1 and a retained capacity of 931.6 mAh g−1 after cycling 100 times at 0.2 C, which demonstrates the effectiveness of this modification strategy. Furthermore, the correlation between the properties of PFSA ionomers and the electrochemical performance of the modified separator unveiled in this study may provide insight for the rational design of advanced separator for battery applications.

Organic‐Inorganic Composite Porous Membrane for Stable and High‐Performance Lithium‐Ion Battery

AbstractThe ionic conductivity of the separator is the essential parameter for performance of lithium ion batteries. Herein, we synthesize a new composite separator through coating of the mixture of poly (methyl methacrylate) and alpha alumina on the surface of commercial polyethylene separator. Benefiting from the excellent electrolyte wettability and high ionic conductivity of the poly (methyl methacrylate), the synthesized separator exhibits promising electrochemical properties. The lithium ion diffusion coefficient of the synthesized separator is 1.48×10−15 cm2 s–1, higher than that of the pristine polyethylene separator (0.808×10−15 cm2 s–1). Furthermore, the introduced alumina can prevent the blockage of the ion transport channels from the electrolyte absorption‐induced swelling of poly (methyl methacrylate), which in turn can improve the cycle performance of the thus‐assembled cells. it means that the cell assembled form the synthesized composite separator shows high charge–discharge cyclability, i. e. the cell assembled from the synthesized composite separator maintains 93.9% of initial discharge capacity after 200 charge‐discharge cycles under the rate of 1 C.

Novel Polyimide Separator Prepared with Two Porogens for Safe Lithium-Ion Batteries.

A porous polyimide (PI) membrane is successfully prepared via nonsolvent-induced phase separation with two porogens: dibutyl phthalate and glycerin. The as-prepared uniform porous PI membrane shows excellent separator properties for lithium-ion batteries (LIBs). Compared with the commercial polyethylene (PE) separator, the PI separator exhibits significant thermal stability, better ionic conductivity, and wettability both in carbonate and ether electrolytes for LIBs. The battery coin-cells assembled with the PI separator is more robust and still works even after heating at 140 °C for 1 h, while the cells with the commercial PE separator could not charge any more due to the shrinkage of the PE under the same condition.