Commercial Separator Research Articles

O-doping induced abundant active-sites in MoS2 nanosheets for propelling polysulfide conversion of Li-S batteries

The oxygen doped MoS2 nanosheets were in-situ grown into the three-dimensional (3D) porous graphene frameworks (O-MoS2/G) through a facile hydrothermal method, and then used to coat the commercial PP separators for Li-S batteries. The relatively low hydrothermal temperature should be a key factor for achieving the O-doped MoS2. The O dopants could expand and disturb interlayer structures of MoS2 to produce abundant active edge sites for adsorption and catalytic conversion of polysulfides. Moreover, the basal planes of MoS2 should be also activated by the O doping and exhibit enhanced chemical adsorption strength towards polysulfides for propelling electrochemical conversion. Owing to the synergistic effects of the 3D porous graphene frameworks and the inlaid O-MoS2 nanosheets, the Li-S cells with high S areal loading cathodes and O-MoS2/G@PP separators exhibit excellent electrochemical performances with a high specific capacity of 1141 mAh g−1 at the 1st cycle at 0.1 C, reversible capacities of 772 mAh g−1 at the 50th cycle at 0.2 C and 583 mAh g−1 at the 100th cycle at 0.5 C. These encouraging results provide that the heteroatom doping should be a promising approach to improve the adsorption and catalytic activity of MoS2 for propelling the polysulfide conversion in Li-S batteries.

Regulating Electronic Structure of Fe–N4 Single Atomic Catalyst via Neighboring Sulfur Doping for High Performance Lithium–Sulfur Batteries

AbstractConstructing high performance electrocatalysts for lithium polysulfides (LiPSs) adsorption and fast conversion is the effective way to boost practical energy density and cycle life of rechargeable lithium–sulfur (Li–S) batteries, which have been regarded as the most promising next generation high energy density battery but still suffering from LiPSs shuttle effect and slow sulfur redox kinetics. Herein, a single atomic catalyst of Fe–N4 moiety doping periphery with S (Fe–NSC) is theoretically and experimentally demonstrated to enhance LiPSs adsorption and facilitated sulfur conversion, due to more charge density accumulated around Fe–NSC configuration relative to bare Fe–N4 moiety. Thereafter, the graphene oxide supported Fe–NSC catalyst (Fe–NSC@GO) is modified to the commercial separator through a simple slurry casting method. Thus, Li–S cells with Fe–NSC@GO modified separators display high discharge capacity and excellent cyclability, showing 1156 mAh g−1 at 1 C rate and a low capacity decay of only 0.022% per cycle over 1000 cycles. Even with a high sulfur loading of 5.1 mg cm−2, the cell still delivers excellent cycling stability. This work provides a fresh insight into electrocatalyst structural tuning to improve the electrochemical performance of Li–S batteries.

Toward Safe and High-Performance Lithium–Sulfur Batteries via Polyimide Nanosheets-Modified Separator

Lithium–sulfur batteries (LSBs) have broad application prospects in high density energy storage. Nevertheless, LSBs present serious safety concerns and rapid capacity decay due to the flammability and contractility of commercial separators at high temperatures and lithium polysulfide (LiPSs) dissolution. In view of this, a multifunctional modified separator is developed by combining a commercial polypropylene (PP) separator with a polyimide (PI)-Super P functional coating and a rigid nonflammable PI matrix. This PI/PP/PI-Super P separator provides multiple advantages: (i) strong physical blocking and chemical trapping/conversion ability for LiPSs, (ii) high flame-retardancy and dimensional stability, and (iii) superior electrolyte wettability and high efficiency lithium dendritic growth inhibition. As a result, the LSBs assembled with PI/PP/PI-Super P separators and pure sulfur cathodes exhibit an ultrahigh discharge specific capacity of 1611.8 mAh/g and excellent cycling performance (the average capacity attenuation within 100 cycles at 1 C is 0.469%) at 80 °C, which exceed the advanced results reported previously. More importantly, even when sulfur and organic electrolyte are adsorbed on PI/PP/PI-Super P, the modified separator still shows good flame retardancy. Additionally, this modified separator is also suitable for LSBs with high sulfur loading. This work offers an innovative design concept for safe and high-performance LSBs.

High‐performance nano‐TiO2@polyvinylidene fluoride composite separators prepared by electrospinning for safe lithium‐ion battery

AbstractTraditional polyolefin separators cannot guarantee safety for lithium‐ion batteries at high temperature due to their low melting point, especially for high power discharge. Therefore, it is imperative to develop separators with excellent thermal stability. In this paper, we have prepared TiO2 modified PVDF composite separators by electrospinning. When compared with commercial PE separators, this kind of composite separators show superior thermal stability at 160°C. In addition, it is found that the 0.5‐TiO2@PVDF separator exhibits excellent flame retardant and optimal tension strength. Meanwhile, the 0.5‐TiO2@PVDF separator exhibits ideal liquid electrolyte storage capacity, which improves the ionic conductivity (0.68 mS cm−1). As a result, the LiCoO2||Li cells with 0.5‐TiO2@PVDF separator have high discharge capacity retention rate at a current density of 1 C (300 cycles) and excellent rate performance (1.75 mAh at 5 C). In short, nano‐TiO2 modified PVDF separator has a great application prospect in high‐performance and high‐safety lithium‐ion batteries.

Crystallization-templated high-performance PVDF separator used in lithium-ion batteries

In this work, high-performance PVDF separators have been successfully fabricated for lithium-ion batteries (LIBs) based on crystallization template in PVDF/PBSU blends. The crystallization of PVDF produces co-continuous structures of crystalline phase and amorphous phase. On one hand, the continuous state of PBSU enables its removal via selective solvent extraction, yielding 3D interpenetrated nanochannels which have been confirmed with the help of X-ray imaging technology. On the other hand, the continuous PVDF crystal framework contributes to superior mechanical performance and heat resistance of resultant separator, playing crucial roles in the inhibition of Li dendrite growth and improvement of LIBs safety. The optimal specimen of PVDF-30 (from PVDF/PBSU 30/70) exhibits higher discharge capacity (135.5 mA h g−1), higher coulombic efficiency (∼99.9% after 200 cycles) and enhanced cycle stability relative to the reference (commercial polypropylene separator). Such a significant improvement can be attributed to the combination of excellent connectivity of diffusion channels, outstanding mechanical performance and higher electrolyte uptake resulting from stronger polarity of PVDF. Our results provide a novel strategy for fabricating PVDF separators with superior performances used in lithium-ion batteries.

Solid polymer electrolytes reinforced with porous polypropylene separators for all-solid-state supercapacitors.

Solid polymer electrolytes (SPEs) encounter the challenge of balancing high ionic conductivity and mechanical strength. Ionic liquids, which are among the contenders to be used in high-performance supercapacitors, have difficulty infiltrating commercial polyolefin separators for combined applications. In this study, a novel SPE involving uniform infiltration in the micropores of commercial polyolefin separators with polyethylene oxide (PEO), lithium salt, and different proportions of added ionic liquid was developed. The composite membranes combining ionic liquid-filled SPE with polypropylene (PP) microporous separators simultaneously achieve excellent mechanical strength and high-ionic conductivity. The low wettability of pure ionic liquids and commercial polyolefin-based separators is addressed. The 70 wt% IL-filled solid electrolyte composite membrane (PLI(70)@PP) exhibits a high ionic conductivity (2.9 × 10-3 S cm-1), low resistance at the electrolyte-electrode interface and excellent mechanical strength (128 MPa) at 25 °C. The all-solid-state supercapacitor using PLI(70)@PP exhibits a specific capacitance of 158 F g-1 at 0.1 A g-1 and stable cycle performance. The proposed method can be performed via high-volume roll-to-roll processing to obtain high-performance all-solid-state supercapacitors (ASSCs) for engineering applications.

IMPRESSÃO 3D DE SEPARADOR MAGNÉTICO: UMA ABORDAGEM ACESSÍVEL PARA O PREPARO DE AMOSTRAS NO DIAGNÓSTICO DA COVID-19

3D PRINTING OF MAGNETIC SEPARATOR: AN AFFORDABLE APPROACH TO SAMPLE PREPARATION IN THE COVID-19 DIAGNOSIS. This report describes the fabrication of a low-cost magnetic separator holder combining 3D printing and compact neodymium blocks for allowing magnetic extraction and purification of RNA from samples collected by nasopharyngeal swab from patients infected by SARS-CoV-2. The device was designed to contain 24 entrances for plastic microtubes in an arrangement like a commercial device. The proof of concept of the proposed device was successfully demonstrated through the sample extraction and purification of swab samples collected from eight patients suspected of SARS-CoV-2 infection. The sample preparation protocol was performed using a commercial kit containing magnetic beads and different solutions. The performance of the printed device was compared to a commercial magnetic separator, usually employed in the golden standard techniques. The fabrication of the 3D printed magnetic separator was completed under optimized printing conditions within 6 h at cost of 4 USD per unit. The RNA extracted from samples using both devices was analyzed by reverse transcriptase quantitative polymerase chain reaction (RT-qPCR) and the achieved results have indicated no statistical different at confidence level of 95%. Based on the achievements, the use of 3D printing and neodymium blocks have demonstrated an alternative route to be used in routing analysis associated to COVID-19 diagnosis.

A CF4 plasma functionalized polypropylene separator for dendrite-free lithium metal anodes

A simple and effective plasma functionalization technique for grafting fluorine-containing functional groups on commercial PP separators to induce the formation of LiF-rich SEI films has been proposed.

Oxygen-deficient TiO2-x interlayer enabling Li-rich Mn-based layered oxide cathodes with enhanced reversible capacity and cyclability.

The unique anion redox mechanism of Li-rich Mn-based layered oxide (LMLO) cathodes endows them with a higher specific capacity compared with conventional cathodes. However, the irreversible anion redox reactions can cause structural degradation and sluggish electrochemical kinetics in the cathode, resulting in a poor electrochemical performance in the batteries. Thus, to address these issues, a single-sided conductive oxygen-deficient TiO2-x interlayer was applied on a commercial Celgard separator as a coating layer towards the LMLO cathode. After coating TiO2-x, the initial coulombic efficiency (ICE) of the cathode increased from 92.1% to 95.8%, the capacity retention improved from 84.2% to 91.7% after 100 cycles, and the rate performance of the cathode was significantly enhanced from 91.3 mA h g-1 to 203.9 mA h g-1 at 5C. Operando differential electrochemical mass spectroscopy (DEMS) showed that the coating layer could restrain the release of oxygen in the battery, especially from the initial formation process. The X-ray photoelectron spectroscopy (XPS) results demonstrated that the favorable oxygen absorption by the TiO2-x interlayer benefitted the suppression of side reactions and cathode structural evolution and favored the formation of a uniform cathode-electrolyte interphase on the LMLO cathode. This work provides an alternative path to address the issue of oxygen release in LMLO cathodes.

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.

Recent advances in modified commercial separators for lithium–sulfur batteries

Lithium–sulfur batteries (LSBs) are one of the most promising next-generation batteries because they have higher theoretical capacities, lower cost, and smaller environmental impact than lithium-ion batteries (LIBs).

Catalytic effects of Ni nanoparticles encapsulated in few-layer N-doped graphene and supported by N-doped graphitic carbon in Li-S batteries.

Although lithium-sulfur batteries possess the highest theoretical capacity and lowest cost among all known rechargeable batteries, their commercialization is still hampered by the intrinsic disadvantages of low conductivity of sulfur and polysulfide shuttle effect, which is most critical. Considerable research efforts have been dedicated to solving these difficulties for every part of Li-S batteries. Separator modification with metal electrocatalysts is a promising approach to overcome the major part of these disadvantages. This work focuses on the development of Ni nanoparticles encapsulated in a few-layer nitrogen-doped graphene supported by nitrogen-doped graphitic carbon (Ni@NGC) with different metal loadings as separator modifications. The effect of metal loading on the Li-S electrochemical reaction kinetics and performance of Li-S batteries was investigated. Controlling the Ni loading allowed for the modulation of the surface area-to-metal content ratio, which influenced the reaction kinetics and cycling performance of Li-S cells. Among the separators with different Ni loadings, the one with 9 wt% Ni exhibited the most efficient acceleration of the polysulfide redox reaction and minimized the polysulfide shuttling effect. Batteries with this separator retained 77.2% capacity after 200 cycles at 0.5C, with a high sulfur loading of ∼4.0 mg cm-2, while a bare separator showed 51.3% capacity retention after 200 cycles under the same conditions. This work reveals that there is a vast utility space for carbon-encapsulated Ni nanoparticles in electrochemical energy storage devices with optimal selection and rational design.

Class of Boehmite/Polyacrylonitrile Membranes with Different Thermal Shutdown Temperatures for High-Performance Lithium-Ion Batteries.

Nowadays, lithium-ion batteries are required to have a higher energy density and safety because of their wide applications. Current commercial separators have poor wettability and thermal stability, which significantly impact the performance and safety of batteries. In this study, a class of boehmite particles with different grain sizes was synthesized by adjusting hydrothermal temperatures and used to fabricate boehmite/polyacrylonitrile (BM/PAN) membranes. All of these BM/PAN membranes can not only maintain excellent thermal dimensional stability above 200 °C but also have good electrolyte wettability and high porosity. More interestingly, the BM/PAN membranes' thermal shutdown temperature can be adjusted by changing the grain size of boehmite particles. The lithium-ion batteries assembled with BM/PAN separators exhibit different thermal stability phenomena at 150 °C and have excellent rate performance and cycle stability at room temperature. After 120 cycles at 1C, the LiFePO4 half-cell assembled by the best BM/PAN separator has almost unchanged discharge capacity, whereas the capacity retention of Celgard 2325 is only about 85%. Meanwhile, the NCM523 half-cell assembled with the best BM/PAN separator shows superb cycle stability after 500 cycles at 8C, with a capacity retention of 79% compared with 56% for Celgard 2325.

Coupling multifunctional catalytic active sites into metal carbide catalysts to promote the multipath bidirectional conversion of Li-S redox

Li-S batteries are hampered by sluggish liquidsolid redox and shuttle effects. Herein, a strategy of coupling multifunctional catalytic sites is proposed to fabricate bidirectional catalysts to promote multipath bidirectional Li-S redox conversion. By engineering Co or Zr dopants into Ni3C/C, the obtained Co0.30Ni2.70C/C and Zr0.30Ni2.70C/C electrocatalysts play different roles in polysulfide adsorption and multipath bidirectional conversion. During the discharging/charging process, due to limited electron transfer between the Co3+/Co2+ pair and polysulfides, Co sites themselves are catalytically inactive for the conversion of polysulfides and only act as promoters to improve the catalytic activity of Ni sites. In contrast, in addition to being promoters, Zr sites serve as electron acceptors and donors to catalyze bidirectional Li-S redox due to the flexible electron transfer between the Zr4+/Zr2+ pair and polysulfides. Such bidirectional electron transfer is accompanied by thiosulfate-mediated redox. Therefore, Zr doping not only accelerates the inherent solid (S8)-liquid (polysulfide)-solid (Li2S) conversion pathway but also propels the reversible thiosulfate-mediated conversion pathway. As a result, when the Zr0.30Ni2.70C/C nanosheets were used to modify the commercial PP separator, the Li-S batteries exhibit improved electrochemical performance (a decay of 0.0756 % over 200 cycles with a sulfur loading of 5.0 mgs cm−2).

An electrolyte-locked thermally stable composite separator for safe lithium ion batteries

The safety issue of lithium ion batteries has always received extensive attention and become the main obstacle restricting their development and applications. Commercial polyolefin separators own poor thermal stability, which cannot ensure the safe operation of lithium ion batteries after heating. Herein, an electrolyte-locked thermally stable composite separator polyimide/poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP@PI) is constructed through coating a layer of PVDF-HFP on the electrospun PI fibers membrane. In this structure, the high electrolyte retention ability and excellent thermal dimensional stability of PVDF-HFP@PI effectively inhibit the continuous reaction between electrolyte and Li anode, and prevent the battery failure after heating. In addition, the prepared PVDF-HFP@PI has good mechanical properties and high ionic conductivity of up to 1.79 mS cm−1, which significantly improves the electrochemical performance of the batteries. Therefore, the pouch cell with PVDF-HFP@PI retains 77.4 % of the original capacity after 300 cycles at 0.1 C. More importantly, the cell with PVDF-HFP@PI can work normally after heated under 140 °C for 1 h, exhibiting high heat tolerance.

A Janus MXene/MOF separator for the all-in-one enhancement of lithium-sulfur batteries

Rapid capacity fading and poor safety originating from the shuttle effect of S cathodes and the dendritic growth of Li anodes hinder the practical applications of lithium-sulfur batteries. Herein, we designed a thin (MXene/PP/Cu-TCPP) Janus separator with anisotropic spatial heterogeneity regarding the sulfophile for the cathode-facing surface, while maintaining the opposite side as a multifunctional ionic sieve. Asymmetry was realized by plating nanometer-thick MXene and MOF layers onto the two different sides of a commercial separator. The highly-conductive MXene, rich with polar surface functional groups, acted as an expanded S host that confined sulfur and its intermediates on the cathode-facing surface, which boosted the conversion. The insulating and porous MOF layer on the anode-facing surface served as an “ionic sieve” that further intercepted polysulfides and guided the uniform deposition of Li and blocked Li dendrite growth. This design endowed lithium-sulfur batteries with all-in-one enhanced cycling performance, with a high discharge capacity and low self-discharge shuttle constant of 0.0004 h−1, as well as a low polarization voltage of 20 mV at 0.5 mA cm−2 for a Li||Li symmetrical cell.

Assembly of electric double-layer capacitors with hardwood kraft lignin-based electrodes and separator together with ionic liquid electrolyte

Abstract This study aimed to assemble a high-performance electric double-layer capacitor (EDLC) using a hardwood kraft lignin (HKL)-based separator and HKL-based electrodes, which were fabricated from a nonwoven mat of electrospun HKL fibers. The separator was prepared by the thermostabilization of the mat derived from a mixed dope of HKL, hexamethylenetetramine, and polyethylene glycol (1.66/0.50/0.09, w/w) for electrospinning. Although a mat-type HKL-based electrode containing conductive carbon black (CB) has been reported to be suitable for a commercial cellulosic separator, this electrode was found to be unsuitable for the HKL-based separator because of its rough surface and poor contact with the separator interface. Hence, a powder-type electrode with a smooth surface was fabricated by grinding the mat, followed by casting with a carboxymethyl cellulose aqueous solution, and its EDLC possessed high energy (49 Wh kg−1) and power densities (151 kW kg−1). Moreover, to provide a simple process for electrode fabrication, another mat-type electrode was fabricated by adding CB to the mixed dope, followed by electrospinning, carbonization, and steam activation. The resultant EDLC exhibited excellent electrochemical performance with energy (58 Wh kg−1) and power densities (55 kW kg−1).

Covalent Organic Frameworks for Separator Modification of Lithium-Sulfur Batteries.

Lithium-sulfur (Li-S) batteries are regarded as one of the promising energy storage systems. However, rapid capacity attenuation caused by shuttle effect of soluble polysulfides is major challenge in practical application. The separator modification is regarded as one countermeasure besides the construction of sulfur host materials. Covalent organic frameworks (COFs) are one type of outstanding candidates for suppressing shuttle effect of polysulfides. Herein, recent advances of COFs in the application as commercial separator modifiers are summarized. COFs serve as ionic sieves, the importance of porous size and surface environments in inhibiting soluble polysulfides shuttling and promoting lithium ions conduction is highlighted. The superiority of charge-neutral COFs, ionic COFs, and the composites of COFs with conductive materials for improving reversible capacity and cycling stability is demonstrated. Some new strategies for the design of COF-based separator modifiers are proposed to achieving high energy density. The review provides new perspectives for future development of high-performance Li-S batteries.

Aqueous Colloid Flow Batteries Based on Redox-Reversible Polyoxometalate Clusters and Size-Exclusive Membranes

Aqueous redox flow batteries (ARFBs) exhibit great potential for large-scale energy storage, but the cross-contamination, limited ion conductivity, and high costs of ion-exchange membranes restrict the wide application of ARFBs. Herein, we report the construction of aqueous colloid flow batteries (ACFBs) based on redox-active polyoxometalate (POM) colloid electrolytes and size-exclusive membrane separators. The aqueous suspensions of POM clusters, such as [N(C3H7)4]4[H12(VO2)12(C6H5PO3)8]·xH2O and [N(C3H7)4]4[H12(VO2)12(4-FC6H4PO3)8]·xH2O, deliver good reversibility, high redox kinetics, and long cycling life. The nanoscale sizes of POM clusters make them compatible with cheap commercial dialysis membrane separators to replace expensive ion-exchange membranes, thus inhibiting the cross-contamination of active species via size exclusion. The ACFBs achieve a high energy efficiency of ∼90% and an ultralow capacity fade rate of 0.004% per cycle. This work highlights the great potential of ACFBs based on redox-reversible POM clusters and size-exclusion membrane separators toward grid-scale and sustainable energy storage applications.

In-situ constructing “ceramer” electrolytes with robust-flexible interfaces enabling long-cycling lithium metal batteries

² Novel “ceramer” electrolyte with robust-flexible interfaces is in-situ synthesized ² Ceramer electrolyte enables the dendrite-free stripping/plating cycle of Li metal ² Li/Li cells stably cycle over 3600 h at 0.5 mA cm −2 with a constant overpotential ² LFP/Li cells maintain high capacity retention of up to 90.3% at 1C after 500 cycles ² NCM811/Li cell stably cycles for up to 600 cycles at 1C with a high capacity The lifetime and safety of lithium metal batteries (LMBs) with commercial polyolefin separators and liquid electrolytes are deteriorated by the lithium dendrites, as well as leakage and combustion of liquid electrolytes. To effectively address these issues, a “ceramer” electrolyte is in-situ synthesized to exquisitely combine meritorious properties of both cera mic silica (e.g. high modulus) and poly mer poly-1,3-dioxolane (e.g. flexibility/good interface with electrodes), leading to excellent performance for the LMBs. The lithium anodes with the novel “ceramer” electrolyte exhibit ultra-long cycle life and lithium dendrite-free property that is confirmed by in-situ optical microscope. The Li/Li symmetric cells stably plat and strip for up to 3,600 h at 0.5 mA cm −2 with a constant low overpotential. The LiFePO 4 /Li cells present up to 90.3% capacity retention and 99.9 % coulombic efficiency at 1 C after 500 cycles. Even at a higher current density of 2 C, the cell performs an excellent long-term cycle stability with a capacity decay of only 0.0285% per cycle. More significantly, the assembled coin cells (LiNi 0.8 Co 0.1 Mn 0.1 O 2 /Li) delivers high capacity retention of 80.2% at 1 C after 500 cycles, and the pouch cell with high cathode loading (10 mg cm −2 ) and thin lithium anode (∼50 µm) is operated stably. This research provides a very promising strategy to construct a unique organic-inorganic electrolyte with excellent comprehensive properties effectively enabling long-cycle and high-safety LMBs. A “ceramer” electrolyte is in-situ synthesized to exquisitely combine meritorious properties of both ceramic silica and polymer poly-1,3-dioxolane, leading to excellent comprehensive performance for the lithium metal batteries.