Status and Opportunities of Zinc Ion Hybrid Capacitors: Focus on Carbon Materials, Current Collectors, and Separators

Zinc ion hybrid capacitors(ZIHCs), which integrate the features of the high power of supercapacitors and the high energy of zinc ion batteries, are promising competitors in future electrochemical energy storage applications. Carbon-based materials are deemed the competitive candidates for cathodes of ZIHC due to their cost-effectiveness, high electronic conductivity, chemical inertness, controllable surface states, and tunable pore architectures. In recent years, great research efforts have been devoted to further improving the energy density and cycling stability of ZIHCs. Reasonable modification and optimization of carbon-based materials offer a remedy for these challenges. In this review, the structural design, and electrochemical properties of carbon-based cathode materials with different dimensions, as well as the selection of compatible, robust current collectors and separators for ZIHCs are discussed. The challenges and prospects of ZIHCs are showcased to guide the innovative development of carbon-based cathode materials and the development of novel ZIHCs.

Suppression of Self-Discharge in Aqueous Supercapacitor Devices Incorporating Highly Polar Nanofiber Separators

One of the major problems limiting the applications of electric double-layer(EDLC)supercapacitor devices is their inability to maintain their cell voltage over a significant period.Self-discharge is a spontaneous decay in charged energy,often resulting in fully depleted devices in a matter of hours.Here,a new method for suppressing this self-discharge phenomenon is proposed by using directionally polarized piezoelectric electrospun nanofiber films as separator materials.Tailored engineering of polyvinylidene fluoride(PVDF)nanofiber films containing a small concentration of sodium dodecyl sulfate(SDS)results in a high proportion of polarβphases,reaching 380.5%of the total material.Inducing polarity into the separator material provides a reverse-diode mechanism in the device,such that it drops from an initial voltage of 1.6 down to 1 V after 10 h,as opposed to 0.3 V with a nonpolarized,commercial separator material.Thus,the energy retained for the polarized separator is 37%and 4%for the nonpolarized separator,making supercapacitors a more attractive solution for long-term energy storage.

LiFePO_(4) as a dual-functional coating for separators in lithium-ion batteries:A new strategy for improving capacity and safety

Lithium-ion batteries(LIBs)require separators with high performance and safety to meet the increasing demands for energy storage applications.Coating electrochemically inert ceramic materials on conventional polyolefin separators can enhance stability but comes at the cost of increased weight and decreased capacity of the battery.Herein,a novel separator coated with lithium iron phosphate(LFP),an active cathode material,is developed via a simple and scalable process.The LFP-coated separator exhibits superior thermal stability,mechanical strength,electrolyte wettability,and ionic conductivity than the conventional polyethylene(PE)separator.Moreover,the LFP coating can actively participate in the electrochemical reaction during the charge-discharge process,thus enhancing the capacity of the battery.The results show that the LFP-coated separator can increase the cell capacity by 26%,and improve the rate capability by 29%at 4 C compared with the conventional PE separator.The LFP-coated separator exhibits only 1.1%thermal shrinkage at 140°C,a temperature even above the melting point of PE.This work introduces a new strategy for designing separators with dual functions for the next-generation LIBs with improved performance and safety.

An upgraded polymeric composite with interparticle chemical bonding microstructure toward lithium-ion battery separators with enhanced safety and electrochemical performances

A composite separator of SiC/PVDF-HFP was synthesized for lithium-ion batteries with high thermal and mechanical stabilities.Benefiting from the nanoscale,high hardness,and melting point of SiC,SiC/PVDFHFP with highly uniform microstructure was obtained.This polarization caused by barrier penetration was significantly restrained.Due to the Si-F bond between SiC and PVDF-HFP,the structural stability has been obviously enhanced,which could suppress the growth of lithium(Li) dendrite.Furthermore,some 3D reticulated Si nanowires are found on the surface of Li anode,which also greatly inhibit Li dendrites and result in irregular flakes of Li metal.Especially,the shrinkage of 6% SiC/PVDF-HFP at 150℃ is only 5%,which is notably lower than those of PVDF-HFP and Celgard2500.The commercial LiFePO_(4) cell assembled with 6% SiC/PVDF-HFP possesses a specific capacity of 157.8 mA h g^(-1) and coulomb efficiency of 98% at 80℃.In addition,the tensile strength and modulus of 6% SiC/PVDF-HFP could reach 14.6 and 562 MPa,respectively.And a small deformation(1000 nm) and strong deformation recovery are obtained under a high additional load(2.3 mN).Compared with PVDF-HFP and Celgard2500,the symmetric Li cell assembled with 6% SiC/PVDF-HFP has not polarized after 900 cycles due to its excellent mechanical stabilities.This strategy provides a feasible solution for the composite separator of high-safety batteries with a high temperature and impact resistance.

Thermal Stability and Electrochemical Properties of Separators for Lithium-ion Batteries

The mechanical properties,contact angle,thermomechanical and electrochemical properties of PE,PVDF,and ceramic separators were compared.The experimental results show that the PE separator has the largest porosity,the PVDF separator has the best mechanical properties,wettability,and heat resistance.Three kinds of separators were assembled into lithium-ion batteries for electrochemical tests.Among them,the PE separator has the best rate performance,and the ceramic separator has poor performance in charge-discharge cycles.At the same time,the PE and ceramic separators were tested with different amounts of electrolytes at room temperature and a high temperature,and it is found that the capacity of the PE separator is higher at room temperature,while the performance of the ceramic separator is better at a high temperature.The amount of electrolyte also has a certain influence on its electrochemical performance.

Research status and prospect of separators for magnesium-sulfur batteries

Magnesium-sulfur(Mg-S)batteries have attracted wide research attention in recent years,and are considered as one of the major candidates to replace lithium-ion batteries due to the high theoretical energy density,low costs of active materials,and high safety.However,there are still significant challenges that need to be overcome before they can reach the large-scale practical applications.The key issue is the dissolution and shuttle effect of magnesium polysulfides(Mg-PSs),which leads to severe capacity degradation and shortens cycling life,greatly limiting the development of Mg-S batteries.In order to overcome these challenges,great efforts have been made in cathode materials,electrolytes,and separators.Herein,we review the investigations on suppressing the shuttle effect of Mg-PSs via the modification of separators,including schemes such as coating the functional materials that can hold Mg-PSs on the surface of polyolefin-based or glass fiber(GF)separators,forming gel polymer separators via cross-linking polymerization reactions,and developing gel polymer electrolytes coupled with GF separators.Furthermore,an outlook is proposed for the future design on separator exploitation to accelerate the development of Mg-S battery technology.

Microporous Cyclodextrin Film with Funnel-type Channel Polymerized on Electrospun Cellulose Acetate Membrane as Separators for Strong Trapping Polysulfides and Boosting Charging in Lithium-Sulfur Batteries

The“shuttle effect”of polysulfides hampers the commercialization of lithium-sulfur(Li-S)batteries.Here,a thin molecular sieve film was decorated on the surface of an electrospun cellulose acetate(CA)membrane derived from recycled cigarette filters,where the truncated cone structureβ-cyclodextrin(β-CD)was selected as the building block to physically block and chemically trap polysulfides while simultaneously dramatically speeding up ion transport.Furthermore,on theβ-CD free side of the separator facing the cathode,graphite carbon(C)was sputtered as an upper current collector,which barely increases the thickness.These benefits result in an initial discharge performance of 1378.24 mAh g^(−1) and long-term cycling stability of 863.78 mAh g^(−1) after 1000 cycles at 0.2 C for the battery with theβ-CD/CA/C separator,which is more than three times that of the PP separator after 500 cycles.Surprisingly,the funnel-type channel ofβ-CD generates a differential ionic fluid pressure on both sides,speeding up ion transport by up to 69%,and a 65.3%faster charging rate of 9484 mA g^(−1) was achieved.The“funnel effect”of a separator is regarded as a novel and high-efficiency solution for fast charging of Li-S and other lithium secondary batteries.

Optimization of Control Loops and Operating Parameters for Three-Phase Separators Used in Oilfield Central Processing Facilities

In this study,the Stokes formula is used to analyze the separation effect of three-phase separators used in a Oilfield Central Processing Facility.The considered main influencing factors include(but are not limited to)the typical size of oil and water droplets,the residence time and temperature of fluid and the dosage of demulsifier.Using the“Specification for Oil and Gas Separators”as a basis,the control loops and operating parameters of each separator are optimized Considering the Halfaya Oilfield as a testbed,it is shown that the proposed approach can lead to good results in the production stage.

Rational design and low-cost fabrication of multifunctional separators enabling high sulfur utilization in long-life lithium-sulfur batteries

The lithium-sulfur(Li-S)battery with an ultrahigh theoretical energy density has emerged as a promising rechargeable battery system.However,the practical applications of Li-S batteries are severely plagued by the sluggish reaction kinetics of sulfur species and notorious shuttling of soluble lithium polysulfides(LiPSs)intermediates that result in low sulfur utilization.The introduction of functional layers on separators has been considered as an effective strategy to improve the sulfur utilization in Li-S batteries by achieving effective regulation of LiPSs.Herein,a promising self-assembly strategy is proposed to achieve the low-cost fabrication of hollow and hierarchically porous Fe_(3)O_(4)nanospheres(p-Fe_(3)O_(4)-NSs)assembled by numerous extremely-small primary nanocrystals as building blocks.The rationally-designed p-Fe_(3)O_(4)-NSs are utilized as a multifunctional layer on the separator with highly efficient trapping and conversion features toward LiPSs.Results demonstrate that the nanostructured p-Fe_(3)O_(4)-NSs provide chemical adsorption toward LiPSs and kinetically promote the mutual transformation between LiPSs and Li_(2)S_(2)/Li_(2)S during cycling,thus inhibiting the LiPSs shuttling and boosting the redox reaction kinetics via a chemisorption-catalytic conversion mechanism.The enhanced wettability of the p-Fe_(3)O_(4)-NSs-based separator with the electrolyte enables fast transportation of lithium ions.Benefitting from these alluring properties,the functionalized separator with p-Fe_(3)O_(4)-NSs endows the battery with an admirable rate performance of 877 mAh g^(−1)at 2 C,an ultra-durable cycling performance of up to 2176 cycles at 1 C,and a promising areal capacity of 4.55 mAh cm^(−2)under high-sulfur-loading and lean-electrolyte conditions(4.29 mg cm^(−2),electrolyte/ratio:8μl mg^(−1)).This study will offer fresh insights on the rational design and low-cost fabrication of multifunctional separator to strengthen electrochemical reaction kinetics by regulating LiPSs conversion for developing efficient and long-life Li-S batteries.

Metal-Organic Frameworks Functionalized Separators for Robust Aqueous Zinc-Ion Batteries

Aqueous zinc-ion batteries(AZIBs)are one of the promising energy storage systems,which consist of electrode materials,electrolyte,and separator.The first two have been significantly received ample development,while the prominent role of the separators in manipulating the stability of the electrode has not attracted sufficient attention.In this work,a separator(UiO-66-GF)modified by Zr-based metal organic framework for robust AZIBs is proposed.UiO-66-GF effectively enhances the transport ability of charge carriers and demonstrates preferential orientation of(002)crystal plane,which is favorable for corrosion resistance and dendrite-free zinc deposition.Consequently,Zn|UiO-66-GF-2.2|Zn cells exhibit highly reversible plating/stripping behavior with long cycle life over 1650 h at 2.0 mA cm^(−2),and Zn|UiO-66-GF-2.2|MnO_(2) cells show excellent long-term stability with capacity retention of 85%after 1000 cycles.The reasonable design and application of multifunctional metal organic frameworks modified separators provide useful guidance for constructing durable AZIBs.

Polyimide separators for rechargeable batteries

Separators are indispensable components of modern electrochemical energy storage devices such as lithium-ion batteries(LIBs).They perform the critical function of physically separating the electrodes to prevent short-circuits while permitting the ions to pass through.While conventional separators using polypropylene(PP) and polyethylene(PE) are prone to shrinkage and melting at relatively high temperatures(150℃ or above) causing short circuits and thermal runaway,separators made of thermally stable polyimides(PIs) are electrochemically stable and resistant to high temperatures,and possess good mechanical strength-making them a promising solution to the safety concerns of LIBs.In this review,the research progress on PI separators for use in LIBs is summarized with a special focus on molecular design and microstructural control.In view of the significant progress in advanced chemistries beyond LIBs,recent advances in PI-based membranes for applications in lithium-sulfur,lithium-metal,and solid-state batteries are also reviewed.Finally,practical issues are also discussed along with their prospects.

Rational design on separators and liquid electrolytes for safer lithium-ion batteries

As the energy density of lithium-ion batteries (LIBs) continues to increase,their safety has become a great concern for further practical large-scale applications.One of the ultimate solution of the safety issue is to develop intrinsically safe battery components,where the battery separators and liquid electrolytes are critical for the battery thermal runaway process.In this review,we summarize recent progress in the rational materials design on battery separators and liquid electrolyte towards the goal of improving the safety of LIBs.Also,some strategies for further improving safety of LIBs are also briefly outlooked.

Research on High-Efficiency Cyclone Separators and Their Optimum Design

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Dendrite-free lithium anode achieved under lean-electrolyte condition through the modification of separators with F-functionalized Ti_(3)C_(2)nanosheets

An unstable solid electrolyte interphase(SEI)and chaotic lithium ion fux are key impediments to commercial high-energy-density lithium batteries because of the uncontrolled growth of rigid lithium dendrites,which would pierce through the conventional polypropylene(PP)separator,causing short circuit and safety issues.Herein,the homogenization of lithium ion fux and the generation of stable SEI layers on lithium anodes were achieved via coating a fuorine-functionalized Ti_(3)C_(2)(F-Ti_(3)C_(2))nanosheets on PP separator(F-Ti_(3)C_(2)@PP).F-Ti_(3)C_(2)nanosheets provide abundant ions pathways to homogeneously manipulate lithium ion fux and increase the Young’s modulus and electrolyte wettability of the separators.In addition,F species derived from the F-Ti_(3)C_(2)nanosheets would promote the formation of Li F-rich SEI film.The synergistic effect contribute to the uniform lithium deposition.Symmetric Li|Li,asymmetric Li|Cu and full Li|Li Fe PO4cells incorporated with the modified separators exhibit improved electrochemical performance even under lean electrolyte conditions.This work provides a feasible strategy to improve the performance of lithium batteries through both fuoridized SEI formation and lithium ion fux manipulation.

Radiation graft of acrylamide onto polyethylene separators for lithium-ion batteries

To improve the affinity between separators and electrolyte in lithium-ion battery,microporous polyethylene(PE) separator was grafted of polyacrylamide(PAAm) by radiation.Chemical structure of the PAAmgrafted PE separators(denoted as PE-g-PAAm) was characterized by Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy.Properties of the pristine PE and PE-g-PAAm were tested by scanning electron microscope,liquid electrolyte uptake and lithium-ion conductivity.Electrochemical performances of the grafted PE separators(up to 0.76 × 10^(-3) S/cm of ionic conductivity at room temperature) were much better than pristine PE,and performance of the battery with the grafted separator behaved better than with the virgin PE separator,under the same condition(assembled in Ar-filled glove box).

Development an Easy-to-Use Simulator to Thermodynamic Design of Gas Condensate Reservoir’s Separators

Separator design in petroleum engineering is so important because of its important role in the evaluation of optimum parameters and also to achieve to maximum stock tank liquid. However, no simulator exists that simultaneously and directly optimizes the parameters “pressure”, “temperature”, and so on. On the other hands, Commercial simulators fix one parameter and vary another parameter to achieve the optimum conditions. So, they need long-time simulation. Moreover, gas condensate reservoirs, like another reservoirs, have this problem as well. In present paper, a self-developed simulator applied in the optimized design of gas condensate reservoir’s separators by determining optimized pressure, temperature, and number of separators in order to obtain maximized tank liquid volume and minimized tank liquid density utilizing Matlab software and other commercial simulators such as Aspen-Plus, Aspen-Hysys, and PVTi to do a comparison. Also, each software was separately tested with one, two, and three separators to obtain the optimum number of separators. Additionally, Peng-Robinson equation of state (PR EOS) has been applied in the simulation. For simulation input, a set of field data of gas condensate reservoir has been utilized, as well. The results show a good compatibility of this simulator with other simulators but in so little runtime (this simulator calculates the optimum pressure and temperature in a wide range of pressures and temperatures with the help of a simultaneous optimization algorithm in one stage) and the highest stock tank liquid is calculated with this simulator in comparison to other simulators. Also, with the help of this simulator, we are able to obtain the optimum pressure, temperature, and the number of separators in the gas condensate reservoir’s separators with any desired properties. Finally, this simulator optimizes the temperatures for each separator and obtains very good results despite the other simulators that fix temperatures for all separators in most times.

Review on current development of polybenzimidazole membrane for lithium battery

With the rapid development of portable technology,lithium batteries have emerged as potential candidates for high-performance energy storage systems owing to their high energy density and cycling stability.Among the key components of a lithium battery system,the separator plays a critical role as it directly influences the battery performance benchmark(cycling performance and safety).However,traditional polyolefin separators(polypropylene/polyethylene)are unable to meet the demands of highperformance and safer battery systems due to their poor electrolyte compatibility,thermal runaways,and ultimate growth of dendrites.In contrast,membranes fabricated using polybenzimidazole(PBI)exhibit excellent electrolyte wettability and outstanding thermal dimensional stability,thus holding great potential as separators for high-performance and high-safety batteries.In this paper,we present a comprehensive review of the general requirements for separators,synthesis technology for separators,and research trends focusing PBI membranes in lithium batteries to alleviate the current commercial challenges faced by conventional polyolefin separators.In addition,we discuss the future development direction for PBI battery separators by considering various factors such as production cost,ecological footprint,preparation technology,and battery component compatibility.By exploring these perspectives,we aim to promote the continued application and exploration of PBI-based materials to advance lithium battery technology.

Numerical investigation on dynamic characteristics of flow field in cyclone separators with different dust hopper structures

The dynamic characteristics of flow field in cyclone separators with different dust hopper structures were studied by coupling Reynolds Stress Model(RSM)and Lagrangian Particle Tracking(LPT)methods.The characteristic frequencies of cylinder section,cone section and dust hopper were calculated as f_(1)=53 Hz,f_(2)=65 Hz,and f_(3)=8 Hz by using Fast Fourier Transform(FFT)method,respectively.Based on the effects of f3 on the motion of vortex,the separated space was divided into none affected region,weakly affected region,and strongly affected region.The characteristic frequency of dust hopper increased with the decrease of dust hopper diameter,while it was independent of the height.The dust hopper with d=1.5D(model D3)and h=1.5D(model H3)can significantly decrease the effect of back-mixing on the motion of inner vortex,which is beneficial to improve the efficiency of cyclone separator.

Nitrogen doped hollow carbon nanospheres as efficient polysulfide restricted layer on commercial separators for high-performance lithium-sulfur batteries

The polysulfide shuttle limits the development of lithium-sulfur(Li-S) batteries with high energy density and long lifespan. Herein, nitrogen doped hollow carbon nanospheres(NHCS) derived from polymerization of dopamine on SiO_(2)nanospheres are employed to modify the commercial polypropylene/polyethylene/polypropylene tri-layer separators(PP/PE/PP@NHCS). The abundant nitrogen heteroatoms in NHCS exhibit strong chemical adsorption toward polysulfides, which can effectively suppress the lithium polysulfides shuttle and further enhance the utilization of active sulfur. Lithium-sulfur batteries employing the PP/PE/PP@NHCS deliver an initial discharge capacity of 1355 mAh/g and retain high capacity of 921 mAh/g after 100 cycles at 0.2 C. At a high rate of 2 C, the lithium-sulfur batteries exhibit capacity of 461 mAh/g after 1000 cycles with a capacity fading rate of 0.049% per cycle. This work demonstrates that the NHCS coated PP/PE/PP separator is promising for future commercial applications of lithium-sulfur batteries with improved electrochemical performances.

Cathodic biofouling control by microbial separators in air-breathing microbial fuel cells

Microbial fuel cells(MFCs)incorporating air-breathing cathodes have emerged as a promising ecofriendly wastewater treatment technology capable of operating on an energy-free basis.However,the inevitable biofouling of these devices rapidly decreases cathodic catalytic activity and also reduces the stability of MFCs during long-term operation.The present work developed a novel microbial separator for use in air-breathing MFCs that protects cathodic catalytic activity.In these modified devices,microbes preferentially grow on the microbial separator rather than the cathodic surface such that biofouling is prevented.Trials showed that this concept provided low charge transfer and mass diffusion resistance values during the cathodic oxygen reduction reaction of 4.6±1.3 and 17.3±6.8 U,respectively,after prolonged operation.The maximum power density was found to be stable at 1.06±0.07 W m
2 throughout a long-term test and the chemical oxygen demand removal efficiency was increased to 92%compared with a value of 83%for MFCs exhibiting serious biofouling.In addition,a cathode combined with a microbial separator demonstrated less cross-cathode diffusion of oxygen to the anolyte.This effect indirectly induced the growth of electroactive bacteria and produced higher currents in air-breathing MFCs.Most importantly,the present microbial separator concept enhances both the lifespan and economics of air-breathing MFCs by removing the need to replace or regenerate the cathode during longterm operation.These results indicate that the installation of a microbial separator is an effective means of stabilizing power generation and ensuring the cost-effective performance of air-breathing MFCs intended for future industrial applications.