High-performance Separator Research Articles

In Situ Armoring: A Robust, High-Wettability, and Fire-Resistant Hybrid Separator for Advanced and Safe Batteries.

Development of nonflammable separators with excellent properties is in urgent need by next-generation advanced and safe energy storage devices. However, it has been extremely challenging to simultaneously achieve fire resistance, high mechanical strength, good thermomechanical stability, and low ion-transport resistance for polymeric separators. Herein, to address all these needs, we report an in situ formed silica@silica-imbedded polyimide (in situ SiO2@(PI/SiO2)) nanofabric as a new high-performance inorganic-organic hybrid separator. Different from conventional ceramics-modified separators, this in situ SiO2@(PI/SiO2) hybrid separator is realized for the first time via an inverse in situ hydrolysis process. Benefiting from the in situ formed silica nanoshell, the in situ SiO2@(PI/SiO2) hybrid separator shows the highest tensile strength of 42 MPa among all reported nanofiber-based separators, excellent wettability to the electrolyte, good thermomechanical stability at 300 °C, and fire resistance. The LiFePO4 half-cell assembled with this hybrid separator showed a high capacity of 139 mAh·g-1@5C, which is much higher than that of the battery with the pristine PI separator (126.2 mAh·g-1@5C) and Celgard-2400 separator (95.1 mAh·g-1@5C). More importantly, the battery showed excellent cycling stability with no capacity decay over 100 cycles at the high temperature of 120 °C. This study provides a novel method for the fabrication of high-performance and nonflammable polymeric-inorganic hybrid battery separators.

Nanoporous and lyophilic battery separator from regenerated eggshell membrane with effective suppression of dendritic lithium growth

Lithium metal-based batteries are attractive energy storage systems owing to the high theoretical capacity of lithium metal anode and the known lowest potential among existing anodes. However, lithium anodes usually suffer from severe growth of lithium dendrites, a main reason of safety concern. Engineering the structure of separators could be an effective solution for resolving this issue. Herein, we demonstrate that eggshell membrane (ESM) extracted from waste eggshell is a promising candidate as high-performance separator. Furthermore, we have developed a biomimetic and economic strategy to produce large-area and flat regenerated ESM (RESM) to overcome the size and shape limits of raw ESM. The ESM and RESM are highly lyophilic to electrolytes; their well-distributed pores and high electrolyte uptake allow fast ion-diffusion; and their high mechanical and thermal stability ensure the safety and cyclability of batteries. Most impressively, the nanoporous structure and the negatively-charged surface of ESM and RESM separators can effectively suppress the formation of lithium dendrites, even after long-term cycling under high rate. Lithium-ion batteries, lithium-sulfur batteries, and sodium-ion batteries using RESM separators all show boosted rate capability and cycling retention, outperforming commercial separators on almost all fronts. Even at a high temperature (120 °C), lithium-ion batteries with RESM separators can still operate normally. Our findings indicate the nanoporous RESM film can meet most if not all requirements of an ideal separator for metal ion batteries.

A convenient oil-water separator from polybutylmethacrylate/graphene-deposited polyethylene terephthalate nonwoven fabricated by a facile coating method

Abstract A convenient oil-water separator of polybutylmethacrylate/graphene (PBMA/GE)-deposited polyethylene terephthalate (PET) nonwoven was fabricated by a casting coating method. The resulting nonwovens were characterized by Scanning electron microscopy (SEM), Fourier transform infrared (FTIR), X-ray photoelectron spectroscopy (XPS) and contact angle measurements. The results reveal a hydrophobic and oleophilic surface with micro-nanoscale hierarchical network structures was formed by PBMA, GE and PET fiber web. Furthermore, we demonstrate the separation of oil–water mixtures using a facile apparatus, solely driven by gravity. As-prepared PBMA/GE-coated nonwovens exhibit high oil-water separation efficiency of over 95% up to eight cycles. Our finding as a facile, inexpensive, high-performance oil-water separator have a promising practical application in the oil spill cleanup and the removal of organic pollutants from water surface.

Fluoro-methyl sulfonated poly(arylene ether ketone-co-benzimidazole) amphoteric ion-exchange membranes for vanadium redox flow battery

In this work, amphoteric ion-exchange membranes (AIEMs) prepared from fluoro-methyl sulfonated poly(arylene ether ketone-co-benzimidazole)s have been systematically evaluated for their potential usage in all vanadium redox battery (VRB). Our investigation has demonstrated that the compacted structure originated from the self-assembly ionic cross-linking and the positive charged benzimidazole moiety in AIEM matrix could synergistically reduce the vanadium species cross-contamination. The self-discharge time of a single cell assembled with AIEM of optimized chemical structure is over 3 times longer than that with Nafion117, and a desirable conductivity/permeability trade-off can be achieved by tuning the content of benzimidazole moiety. Single cell assembled with the optimized AIEM exhibit higher battery efficiencies and lower capacity loss than that with Nafion117 at current densities of 30, 50 or 70 mA cm−2. Furthermore, the AIEMs are able to tolerate the strong oxidizing VO2+ and remain intact for over 370 days, as revealed from ex-situ chemical stability tests. These findings strongly suggest that the as-prepared AIEM can be a good candidate for low-cost and high-performance separator in VRB application.

High performance separator coated with amino-functionalized SiO2 particles for safety enhanced lithium-ion batteries

Amino-functionalized SiO2 (N-SiO2) particles were synthesized and used to coat both sides of a porous polyethylene separator. The N-SiO2 coated separator exhibited good wettability by liquid electrolyte, high ionic conductivity when soaked with liquid electrolyte and enhanced thermal stability at high temperatures. By employing the N-SiO2 coated separator in fabricating the lithium-ion cell composed of a graphite negative electrode and a LiNi1/3Co1/3Mn1/3O2 positive electrode, its cycling stability was improved compared to a cell assembled with either a conventional polyethylene separator or a SiO2 coated polyethylene separator. The N-SiO2 coated separator is a promising separator to enhance the cycling stability and thermal safety of lithium-ion battery.

Electrospun polyacrylonitrile nanofibrous membranes with varied fiber diameters and different membrane porosities as lithium-ion battery separators

In this study, nine types of polyacrylonitrile (PAN) nanofibrous membranes with varied fiber diameters and different membrane porosities are prepared by electrospinning followed by hot-pressing. Subsequently, these membranes are explored as Li-ion battery (LIB) separators. The impacts of fiber diameter and membrane porosity on electrolyte uptake, Li+ ion transport through the membrane, electrochemical oxidation potential, and membrane performance as LIB separator (during charge/discharge cycling and rate capability tests of a cathodic half-cell) have been investigated. When compared to commercial Celgard PP separator, hot-pressed electrospun PAN nanofibrous membranes exhibit larger electrolyte uptake, higher thermal stability, wider electrochemical potential window, higher Li+ ion permeability, and better electrochemical performance in LiMn2O4/separator/Li half-cell. The results also indicate that the PAN-based membrane/separator with small fiber diameters of 200–300nm and hot-pressed under high pressure of 20MPa surpasses all other membranes/separators and demonstrates the best performance, leading to the highest discharge capacity (89.5mAhg−1 at C/2 rate) and cycle life (with capacity retention ratio being 97.7%) of the half-cell. In summary, this study has revealed that the hot-pressed electrospun PAN nanofibrous membranes (particularly those consisting of thin nanofibers) are promising as high-performance LIB separators.

High temperature stable Li-ion battery separators based on polyetherimides with improved electrolyte compatibility

Abstract We report (electro-)chemically stable, high temperature resistant and fast wetting Li-ion battery separators produced through a phase inversion process using novel polyetherimides (PEI) based on bisphenol-aceton diphthalic anhydride (BPADA) and para -phenylenediamine (pPD). In contrast to previous studies using PEI based on BPADA and meta -phenylenediamine (mPD), the separators reported herein show limited swelling in electrolytes and do not require fillers to render sufficient mechanical strength and ionic conductivity. In this work, the produced 15–25 μm thick PEI-pPD separators show excellent electrolyte compatibility, proven by low degrees of swelling in electrolyte solvents, low contact angles, fast electrolyte wicking and high electrolyte uptake. The separators cover a tunable range of morphologies and properties, leading to a wide range of ionic conductivities as studied by Electrochemical Impedance Spectroscopy (EIS). Dynamic Mechanical Analysis (DMA) demonstrated dimensional stability up to 220 °C. Finally, single layer graphite/lithium nickel manganese cobalt oxide (NMC) pouch cells were assembled using this novel PEI-pPD separator, showing an excellent capacity retention of 89.3% after 1000 1C/2C cycles, with a mean Coulombic efficiency of 99.77% and limited resistance build-up. We conclude that PEI-pPD is a promising new material candidate for high performance separators.

Hollow mesoporous silica sphere-embedded composite separator for high-performance lithium-ion battery

A high-performance composite separator based on hollow mesoporous silica spheres, poly(vinylidene fluoride-co-hexafluoropropylene) (PVdF-HFP), and poly(ethylene terephthalate) nonwoven was explored as lithium-ion battery separator via a dip coating technique followed by a phase separation wet process. Systematical investigations including morphology characterization, porosity measurement, electrolyte wettability, thermal shrinkage testing, and cell performance examination are carried out. It is demonstrated that the unique mesoporous structures of silica spheres endow the composite separator with well-defined microporous structure. Owing to the preferable microstructure and relatively polar constituents, the composite separator exhibits higher porosity, superior electrolyte wettability, and outstanding thermal stability. Based on the above advantages, the composite separator shows better electrochemical performances, such as the discharge C-rate capability and cycling performance, as compared to the commercialized PE separator. This research presents a simple approach to prepare high-performance separator, which is demonstrated to be a good candidate for lithium-ion batteries.

Al2O3/poly(ethylene terephthalate) composite separator for high-safety lithium-ion batteries

Separators have garnered substantial attention from researchers and developers in regard to their crucial role in the safety of lithium-ion batteries. In this study, a composite separator was prepared by coating cubic Al2O3 nanoparticles on non-woven poly(ethylene terephthalate) (PET) via a simple dip-coating process. The basic properties of the Al2O3-coated PET non-woven composite separator were characterized by scanning electron microscopy and other specific measurements in respect to its morphology, porosity, electrolyte wettability, and thermal shrinkage as well as its application in lithium-ion batteries. We found that the composite separator has outstanding thermostability, which may improve battery safety. Additionally, by comparison against the commercial Celgard 2500 separator, the proposed composite separator exhibits higher porosity, superior electrolyte wettability, and higher ionic conductivity. More importantly, the lithium-ion battery assembled with this composite separator shows better electrochemical performance (e.g., cycling and discharge C-rate capability) compared to that with the Celgard 2500 separator. The results of this study represent a simple approach to preparing high-performance separators that can be used to enhance the safety of lithium-ion batteries.

Water-Based Organic–Inorganic Hybrid Coating for a High-Performance Separator

With the development of electric vehicles, the traditional polyolefin separators can not meet the increasing requirements of lithium ion batteries with high power density, high energy density, and high safety performance. Herein, a novel water-based binder is synthesized by grafting carboxyl groups onto cellulose diacetate. When the polyethylene (PE) separator is coated by this binder and SiO2 nanoparticles, the thermal shrinkage of the modified separator is observed to be almost 0% after exposure at 200 °C for 30 min. The puncture strength significantly increase from 5.10 MPa (PE separator) to 7.64 MPa. More importantly, the capacity retention of the cells assembled with modified separators after 100 cycles at 0.5 C increase from 73.3% (cells assembled with PE separator) to 81.6%, owing to the excellent electrolyte uptake and the good compatibility with lithium electrode. Besides, the modified separator shows excellent surface stability after 100 cycles. Considering the above excellent properties, this c...

High Performance Separator Coated with Amino-Functionalized SiO2 Nanoparticles for Safety Enhanced Lithium-Ion Battery

The use of lithium-ion batteries has been rapidly expanding in portable electronic devices, electric vehicles and energy storage systems due to their high energy density and long cycle life. In lithium-ion batteries, a separator is a critical component which prevents physical contact of the positive and negative electrodes while permitting free ionic transport within the cell. Most of the separators currently used in lithium-ion batteries are based on microporous polyolefin membranes such as polyethylene (PE) and polypropylene (PP) as well as various combinations of the two [1,2]. Although these separators offer excellent mechanical strength and chemical stability, they shrink and even melt at high temperatures, which causes short circuit between electrodes in the case of unusual heat generation. Furthermore, the large difference in polarity between the non-polar polyolefin separator and the polar organic electrolyte leads to poor wettability. In order to solve these problems, ceramic-coated separators have been developed by combining the characteristics of a polymeric separator and ceramic materials. In this study, we tried to improve the thermal safety and cycling performance of lithium-ion cells by using separators coated by amino-functionalized SiO2 (A-SiO2) nanoparticles. These separators exhibited enhanced thermal stability and melt integrity. Due to the high affinity of A-SiO2 with liquid electrolyte, the A-SiO2 coated separators exhibited good wettability and high ionic conductivity. Furthermore, A-SiO2 nanoparticles played a role as HF scavenger, which suppressed HF generation and electrolyte decomposition at elevated temperature. As a result, the lithium-ion cells assembled with A-SiO2 coated separator exhibited the improved cycling performance at both ambient temperature and elevated temperature.

Low-Permeability Poly(ether Ether Ketone)-Based Ampholytic Membranes.

Ion-exchange membranes based on sulfonated and sulfaminated poly(ether ether ketone) were prepared by a modified sulfamination route. In a first step, poly(ether ether ketone) was sulfonated. The sulfonic acid groups were then transformed into chlorosulfonic moieties by reaction with thionyl chloride. A proportion of the chlorosulfonic functionalities reacted with dimethylamine to give basic sulfonamide groups, whereas those remaining were hydrolyzed back to sulfonate moieties obtaining, after immersion in acidic solution, an ampholytic polymer. The thermal, mechanical, electrical, and permeability properties of these amphoteric membranes were characterized. These membranes exhibit good thermal and mechanical stability and ultra-low vanadium ion permeability. The type and value of ion conductivity can be adjusted by the choice of acidic or basic medium. The tunable ion conductivity and the low ion permeability are suitable characteristics for the development of high-performance separator membranes.

Ultrastrong Polyoxyzole Nanofiber Membranes for Dendrite-Proof and Heat-Resistant Battery Separators.

Polymeric nanomaterials emerge as key building blocks for engineering materials in a variety of applications. In particular, the high modulus polymeric nanofibers are suitable to prepare flexible yet strong membrane separators to prevent the growth and penetration of lithium dendrites for safe and reliable high energy lithium metal-based batteries. High ionic conductance, scalability, and low cost are other required attributes of the separator important for practical implementations. Available materials so far are difficult to comply with such stringent criteria. Here, we demonstrate a high-yield exfoliation of ultrastrong poly(p-phenylene benzobisoxazole) nanofibers from the Zylon microfibers. A highly scalable blade casting process is used to assemble these nanofibers into nanoporous membranes. These membranes possess ultimate strengths of 525 MPa, Young's moduli of 20 GPa, thermal stability up to 600 °C, and impressively low ionic resistance, enabling their use as dendrite-suppressing membrane separators in electrochemical cells. With such high-performance separators, reliable lithium-metal based batteries operated at 150 °C are also demonstrated. Those polyoxyzole nanofibers would enrich the existing library of strong nanomaterials and serve as a promising material for large-scale and cost-effective safe energy storage.

Silica/polyacrylonitrile hybrid nanofiber membrane separators via sol-gel and electrospinning techniques for lithium-ion batteries

Silica/polyacrylonitrile (SiO2/PAN) hybrid nanofiber membranes were fabricated by using sol-gel and electrospinning techniques and their electrochemical performance was evaluated for use as separators in lithium-ion batteries. The aim of this study was to design high-performance separator membranes with enhanced electrochemical performance and good thermal stability compared to microporous polyolefin membranes. In this study, SiO2 nanoparticle content up to 27 wt% was achieved in the membranes by using sol-gel technique. It was found that SiO2/PAN hybrid nanofiber membranes had superior electrochemical performance with good thermal stability due to their high SiO2 content and large porosity. Compared with commercial microporous polyolefin membranes, SiO2/PAN hybrid nanofiber membranes had larger liquid electrolyte uptake, higher electrochemical oxidation limit, and lower interfacial resistance with lithium. SiO2/PAN hybrid nanofiber membranes with different SiO2 contents (0, 16, 19 and 27 wt%) were also assembled into lithium/lithium iron phosphate cells, and high cell capacities and good cycling performance were demonstrated at room temperature. In addition, cells using SiO2/PAN hybrid nanofiber membranes with high SiO2 contents showed superior C-rate performance compared to those with low SiO2 contents and commercial microporous polyolefin membrane.

Ceramic coated polypropylene separators for lithium-ion batteries with improved safety: effects of high melting point organic binder

A study on Al2O3/poly(vinyl alcohol) coated polypropylene separators is presented providing insights into designing high-performance LIB separators with improved safety.

Preparation and electrochemical performance of ZrO2 nanoparticle-embedded nonwoven composite separator for lithium-ion batteries

To improve the safety of lithium-ion batteries, a high performance composite separator based on ZrO2 nanoparticles and poly (ethylene terephthalate) nonwoven was successfully prepared. Systematical investigations including morphology characterization, porosity measurement, electrolyte wettability, thermal shrinkage testing, and cell performance examination were carried out. The results show that ZrO2 nanoparticles and nonwoven substrate endow the composite separator with outstanding thermostability, which may lead to improved safety of the batteries. Meanwhile, the composite separator possesses unique porous structure formed between ZrO2 particles. Owing to the relatively polar constituents and well-developed microstructure, the composite separator exhibits higher air permeability and porosity, as well as superior electrolyte wettability compared to the commercialized polyethylene separator. Based on the above advantages, this composite separator shows better electrochemical properties, such as the discharge C-rate capability and cycling performance, as compared to the polyethylene separator. This research presents a simple approach to prepare high performance separator, which is demonstrated to be a good candidate for lithium-ion batteries.

Preparation and performance of poly(vinyl alcohol) porous separator for lithium-ion batteries

Poly(vinyl alcohol) (PVA) separator with highly developed porous structure is facilely prepared by a non-solvent induced phase separation (NIPS) wet-process and investigated in lithium-ion batteries. In this method, deionized water and ethanol are used as solvent and non-solvent for PVA material, respectively, and no pore forming additives are employed. Systematical investigations including morphology characterization, porosity measurement, electrolyte contact angle testing, electrolyte uptake/retention examination, and thermal shrinkage testing are carried out. The results demonstrate that this PVA separator possesses notable features, such as uniform and porous surface morphology, symmetric interconnected porous structure all through the separator thickness, and excellent electrolyte wettability, thus resulting in superior electrolyte adsorption/retention capacity, lower thermal shrinkage, and higher ionic conductivity, in comparison to the commercial polypropylene (PP) separator. Based on the above advantages, the PVA separator exhibits better electrochemical performances, such as the discharge C-rate capability and cycling performance, as compared to PP separator. This research presents a low-cost and environment-friendly approach to prepare a high performance separator, which is demonstrated to be a good candidate for lithium-ion batteries.

Development of plasma-treated polypropylene nonwoven-based composites for high-performance lithium-ion battery separators

Separators have drawn substantial attention because of their important role in achieving the safety and good electrochemical performance of lithium-ion batteries. In this study, we report a new type of composite membrane prepared by a combination of fluorinated polypropylene (PP) nonwoven fabric, poly(vinylidene fluoride-co-hexafluoropropylene) (PVdF-HFP) and SiO2 nanoparticles. 2, 2, 3, 3, 4, 4, 5, 5-Octafluoropentyl methacrylate (OFPMA) is first grafted on the surface of PP nonwoven by plasma treatment to improve the nonwoven’s adhesion with PVdF-HFP. Two kinds of composite separators have been prepared by using the different PP nonwovens together with PVdF-HFP and SiO2 nanoparticles. They were separately designated as PHS for commercially raw PP nonwoven system and PHS-n for OFPMA-modified PP nonwoven systems (n means plasma treatment time). The morphology, electrolyte uptake, ionic conductivity and electrochemical properties of the composite separators have been analyzed by scanning electron microscope (SEM) analysis, impedance measurement, charge-discharge cycle and C-rate tests, respectively. The results indicate that PHS-10 composite separator using the modified PP nonwoven treated by plasma for 10min exhibits much better properties than PHS separator, including an improved mechanical property, thermal stability, electrolyte uptake (290wt%) and ionic conductivity (1.76mScm−1). More importantly, the LiFePO4/Li half-cell assembled with PHS-10 composite separator displays a good C-rate performance, which shows an enhancement in the chemical stability and discharge capacity. The capacity keeps above 150mAhg−1 after 100 charge–discharge cycles. These performances endow this composite membrane as a promising candidate for high-performance lithium-ion battery separators.

Polymethylmethacrylate/Polyacrylonitrile Membranes via Centrifugal Spinning as Separator in Li-Ion Batteries

Electrospun nanofiber membranes have been extensively studied as separators in Li-ion batteries due to their large porosity, unique pore structure, and high electrolyte uptake. However, the electrospinning process has some serious drawbacks, such as low spinning rate and high production cost. The centrifugal spinning technique can be used as a fast, cost-effective and safe technique to fabricate high-performance fiber-based separators. In this work, polymethylmethacrylate (PMMA)/polyacrylonitrile (PAN) membranes with different blend ratios were produced via centrifugal spinning and characterized by using different electrochemical techniques for use as separators in Li-ion batteries. Compared with commercial microporous polyolefin membrane, centrifugally-spun PMMA/PAN membranes had larger ionic conductivity, higher electrochemical oxidation limit, and lower interfacial resistance with lithium. Centrifugally-spun PMMA/PAN membrane separators were assembled into Li/LiFePO4 cells and these cells delivered high capacities and exhibited good cycling performance at room temperature. In addition, cells using centrifugally-spun PMMA/PAN membrane separators showed superior C-rate performance compared to those using microporous polypropylene (PP) membranes. It is, therefore, demonstrated that centrifugally-spun PMMA/PAN membranes are promising separator candidate for high-performance Li-ion batteries.

Preparation of hydroentangled CMC composite nonwoven fabrics as high performance separator for nickel metal hydride battery

Hydroentangling nonwoven process has been attempted to fabricate carding fiber web/meltblown/carding fiber web (CMC) composite nonwoven fabrics with the view to improve the chemical stability and long-term performance of nickel metal hydride (Ni-MH) battery. Hydrophilic polypropylene (PP) meltblown nonwoven fabric was prepared by adding hydrophilic additives in PP melt. Then it was sandwiched into two layers of carding PP fiber web and bonded by hydroentangling process. The mechanical strength, pore size, electrolyte absorption and retention capacity, chemical stability, and electrolytic resistance were investigated in comparison with a commercial sulfonated post-treated separator. The cell performance of hydroentangled CMC composite nonwoven fabrics before and after electrolyte storage was tested by using a stacked Ni-MH battery. These results indicate that hydroentangled CMC composite nonwoven fabric is a kind of promising materials to replace the traditional wet-laid nonwoven fabric as Ni-MH battery separator with better long-term cell performance.