Battery Separator Research Articles

The preparation of intrinsic DOPO-Cinnamic flame-retardant cellulose and its application for lithium-ion battery separator

A renewable and superior intrinsic thermal-resistant cellulose-based nonwoven was explored as lithium-ion battery separator via phase separation mechanism. Herein, we sparked a robust strategy for improving the flammability of cellulose, namely DOPO- Cinnamoyl Cellulose (DCC) with intrinsic flame retardant was obtained via the incorporation of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) and Cinnamoyl Chloride attached on the backbone of cellulose. It demonstrates that the heat release rate and total heat release significantly reduced. Meanwhile the membrane displayed excellent self-extinction. Additionally, after the DCC membrane assembled into lithium battery, under the optimum formulation situation, the electrochemical properties established that the LIBs showed superior electrochemical performance compared with PP separator. The interface impedance of DCC separator was less than 300 Ω, which was much smaller than that of commercial separator of 410 Ω. After 50 cycles, the battery with DCC-0.11 separator retained 84.2% of its initial discharge capacity, which was higher than the commercial polypropylene separator with the numeric of 79.1%. In sum, this novel, environmental friendly and intrinsic DOPO-Cinnamic flame-retardant cellulose based separator can be considered as an expectant candidate for lithium ion battery separator with high performance.

Layer-by-Layer Assembly of Strong Thin Films with High Lithium Ion Conductance for Batteries and Beyond.

Polyethylene oxide (PEO) is one of the most widely used polymeric ion conductors which has the potential for a wide range of applications in energy storage. The enhancement of ionic conductivity of PEO-based electrolytes is generally achieved by sacrificing the mechanical properties. Using layer-by-layer (LbL) self-assembly with a nanoscale precision, mechanically strong and self-healable PEO/polyacrylic acid composite thin films with a high Li+ conductivity of 2.3± 0.8 × 10-4 S cm-1 at 30°C, and a strength of 3.7MPa is prepared. These values make the LbL composite among the best recorded multifunctional solid electrolytes. The electrolyte thin film withstands at least 1000 cycles of striping/plating of Li at 0.05mA cm-2 . It is further shown that the LbL thin films can be used as separators for Li-ion batteries to deliver a capacity of 116 mAh g-1 at 0.1 C in an all-LbL-assembled lithium iron phosphate/lithium titanate battery. Finally, it is demonstrated that the thin films can be used as ion-conducting substrates for flexible electrochemical devices, including micro supercapacitors and electrochemical transistors.

Non-woven polyaramid porous membranes as separators for Li-ion batteries?

Macroporous separators play a crucial role regarding safety in current Li-ion batteries. Most separators used in battery applications are based on polyolefin and present shrinkage and a decrease in mechanical properties when used at high temperatures, both detrimental in the battery performance. In search of more suitable alternatives that render to more stable and safer batteries, in this work, non-woven separators based on polyacrylonitrile blended with cellulose and para-aramid fibers are systematically investigated. This study has been carried out in terms of microstructure, mechanical properties, ionic conductivity and thermal and electrochemical stability (using Li4Ti5O12/LiCoO2 full cells with a nominal potential of ≈2.5 V). Although conductivity values of separators are somewhat modest, the electrochemical performance developed when used in Li4Ti5O12/LiCoO2 cells are, at moderate C rates, comparable to commercial Celgard©2400 separator. At high C rates, in particular at 2C, DwG40 exhibits much higher capacities than the whole of the separators, including Celgard®2400. This study responds to the continuous need reflected not only by the scientific community but also by the industrial one when new materials for electrolytes and electrodes should be tested, since there is a lack of reports characterizing such elements in the literature.

Insight into Lithium–Sulfur Batteries with Novel Modified Separators: Recent Progress and Perspectives

Lithium-sulfur (Li-S) batteries have been found to have sky-scraping theoretical gravimetric energy density and have gained a lot of interest. However, owing to low electrical conductivity, a conducting substance must be coupled with the sulfur cathode. The first important concern in Li-S is diffusion of lithium polysulfides (PSs), resulting in a shuttle linking both the cathode and anode and rapid capacity of degradation. Plating conventional separators is a kind of alleviation of the shuttle issue. To achieve an advanced Li-S battery, understanding of the structure of PSs needs to be considered to design efficient separator coating materials. The main object of this work is to review the most promising recent challenges and address the application of modified coatings on the polypropylene (PP), polyethylene (PE), and glass fiber (GF) separators for high-performance Li-S batteries. The particular focus has been placed on functioning of various functional layers on the surface of PP, PE, and GF, including polymers, carbons, nanomaterials, and their composites. Finally, the polar host materials in the cathode that influence the Li-S performance are summarized. © 2021 American Chemical Society. All rights reserved.

Lithium-Ion Battery Separator Prepared by Double-Matrix Encapsulation and Penetration

Lithium-Ion Battery Separator Prepared by Double-Matrix Encapsulation and Penetration

Facile Fabrication of Functionalized Separators for Lithium-Ion Batteries with Ionic Conduction Path Modifications via the γ-Ray Co-irradiation Grafting Process.

Separators play a vital role in electronic insulation and ionic conduction in lithium-ion batteries. The common improvement strategy of polyolefin separators is mostly based on modifications with a coating layer, which is simple and effective to some extent. However, the improvement is often accompanied by negative effects such as the increase of the thickness and the blockage of the porous structure, resulting in the decrease of energy density and power density. The porous structure of the separators serves as a conduction path for ions to travel back and forth between the anode and cathode, which has an important impact on the performance of lithium-ion batteries. If the porous structure of the separators can be modified, it will essentially affect the ionic transport behavior through the whole conduction path. Herein, we provide a simple and effective method to functionalize the porous polyolefin separator via the γ-ray co-irradiation grafting process, where high-energy γ-ray is used to generate active sites on the polymer chain to initiate the grafting polymerization of chosen monomers with selected functional groups. In this work, 4,4,5,5-tetramethyl-2-vinyl-1,3,2-dioxaborolane, a kind of borane molecule with an electron-deficient group, was chosen as the grafting monomer. After the γ-ray co-irradiation grafting process, both the surface and pores of the polyolefin separators were functionalized by electron-deficient groups in the borane molecule and the whole electrolyte conduction path within the separator was activated. Due to the electron-deficient effect of the B atom, the lithium-ion conduction is promoted and the lithium-ion transference number can be increased to 0.5. As a result, the half-cell assembled with the functionalized separator shows better cycle stability and better capacity retention under high current rate.

Effect of hydroxyls and particle size on the electrochemical performance of boehmite coated PE separators for lithium-ion batteries

Boehmite particles with or without hydroxyls and those of different particle sizes were coated on PE membrane with water-based slurry, and properties of coated separators were characterized. Scanning electron microscope (SEM) was used to examine the uniformity and integrity of the coatings. X-ray diffractometer (XRD) and Fourier transform infrared spectrometer (FT-IR) were used to identify the phases and hydroxyls, respectively. Half cells were assembled with metal Li and LiFePO4 as working electrodes, and their electrochemical performance were tested. It is found that coated separators with boehmite particles and those with hydroxyls removed do not show significant difference in water wettability, neither do corresponding cells in electrochemical performance. Although boehmite particles of all sizes investigated can be coated on PE to improve separator properties and cell electrochemical performance, particles with size distribution of (D10 0.35 μm, D50 0.50 μm, D90 0.67 μm) are the most effective.

Dualbeam Platform Applications in Lithium Battery Research

Lithium batteries are energy storage systems with highly complex microstructures. To understand the performance of the battery it is essential to accurately characterize the battery microstructure at multiple length scales. However, there are multiple challenges in battery characterization such as beam damage, imaging liquid phases and getting to representative volumes.The DualBeam, also known as focused ion beam–scanning electron microscope (FIB-SEM) technique is an analytical method combining an ion beam for materials processing and an electron column for imaging to enable 2D and 3D characterization at the nanometer scale. In this presentation the application of three different DualBeam techniques for battery characterization and how to handle the imaging challenges are discussed for different sample types.A battery separator is a beam sensitive sample and imaging conditions need to be optimized to avoid damaging the separator morphology. By using cryo techniques in a Ga-based FIBSEM, the cross-section and 3D structure of a separator sample is analyzed. The second example deals with a thick NMC electrode sample. Considering the thickness of the cathode (>70 µm) and the active particle size (~10 µm) particle size, a field of view >100 um is needed to get to a representative volume. The combination of Xe-plasma FIB (PFIB) with Avizo software is used to study the electrode microstructure evolution during cycling to better understand the degradation mechanism. The final example is about accessing the liquid-solid interphase inside of the electron microscope. By using a laser PFIB under cryogenic condition, the interphase of the liquid-solid in a Li-metal battery is explored, which is critical to decipher the root cause for cycling inefficiency.DualBeam technology enables new analytical capabilities for materials research while opening up exciting opportunities for advancing battery development. It is expected to remain an indispensable technique for supporting battery innovation in both academic and industrial environments.

A Functional PEO/LiTFSI-Coated Coated Separator for Electrochemical Lithium-Sulfur Battery

There is a strong interest in exploring next-generation rechargeable batteries that can deliver a high energy density for a long cycle life and a long shelf time at an affordable cost. The commercial lithium-ion battery systems have exhibited the advantages in satisfying all the above-mentioned requirements so that the lithium-ion technology has dominated the battery business for over 30 years. To obtain further upgrades in battery technologies, the current lithium-ion systems based on various lithium-insertion oxide cathodes are mature techniques and have faced the theoretical values in terms of their capacity and energy density values. Moreover, the increasing demands of commercial lithium-ion batteries have encountered the increasing prices and limited availability of the raw materials. To address these issues, the conversion-reaction cathodes featuring an enhanced energy density at an affordable cost garner significant attention.Sulfur cathodes have become appealing as they offer an order of magnitude higher capacity and are abundant. The electrochemical conversion reactions of sulfur with lithium ions provide lithium sulfide, involving two electrons per sulfur and providing a high charge-storage capacity of 1,672 mA∙h g-1. The high-capacity sulfur cathodes enable the packaged lithium-sulfur cells to attain 2-3 times higher energy density than that offered by the current lithium-ion batteries. However, several challenges prevent the practical application of lithium-sulfur batteries. The high resistivity of solid-state sulfur and its end-discharged lithium sulfides as well as the dissolution and diffusion of intermediate liquid-state lithium polysulfides cause the poor electrochemical utilization of sulfur, fast capacity fade, and low Coulombic efficiency of the cell in a short cycle life.Significant improvements have been made in the modification of the material and the structure of the sulfur cathodes and the separators in recent years. This presentation will focus on lithium-sulfur battery separator with a coating layer of mixtures containing poly(ethylene oxide) (PEO) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) on a polypropylene membrane, forming a functional gel polymer electrolyte (GPE) / separator composite. The PEO/LiTFSI-coated polypropylene membrane is configurated to face the sulfur cathode and functions as the restrict film to cease the fast diffusion of liquid-state polysulfides and to stabilize the liquid-state active materials within the cathode region of the cell as the catholyte for enhancing the electrochemical reaction kinetics and stability. As a result, our findings show that the lithium-sulfur cells with the PEO/LiTFSI-coated polypropylene membrane show a high discharge capacity of 1,200 mA∙h g-1, a long cycle life of 200 cycles, and high Coulombic efficiency of above 99%. As a comparison, the same cell with a PEO-coated polypropylene membrane reveals a poor electrochemical utilization and efficiency due to the lack of LiTFSI as the ion-diffusion matrix, resulting in low discharge capacity of 662 mA∙h g-1and poor capacity retention. On the other hand, the same cell with a regular unmodified separator membrane suffers the fast loss of the liquid-state active material, showing a short cycle life of less than 100 cycles. According to the material analysis and electrochemical comparison, the PEO/LiTFSI-coated polypropylene membrane proves its capability in blocking the uncontrolled migration of polysulfides, while allowing the smooth diffusion of lithium ions. In conclusion, our experimental and analytical results prove the PEO/LiTFSI-coated polypropylene membrane as an advanced and a facile separator design in the development of high-loading/content sulfur cathodes in lithium-sulfur batteries for realizing a high energy density.

Phase-Inversion Polymer Composite Separators for Printable Lithium-Ion Batteries

Separators isolate the anode and cathode electrodes in Lithium-ion (Li-ion) batteries and play a critical role in facilitating ion transport while enabling safe battery operation. Commercial polyolefin separators made of polypropylene (PP) and polyethylene (PE) are used widely in traditional liquid electrolyte Li-ion batteries. However, these materials have limited thermal stability and are not compatible with additive manufacturing approaches for fabrication of new battery electrode architectures [1]. Researchers have investigated phase-inversion composite separators as a means to solve these problems, but there is limited data available on the relative effects of material composition and processing conditions on final separator morphology and performance. In our work, we analyze the effects of solvents, inorganic additives and phase inversion processing conditions on the separator’s ionic conductivity, rate capability, and mechanical integrity. Silica (SiO2), alumina (Al2O3), and glass particles are used as inorganic additives in varying combinations and ratios in a polyvinylidene fluoride (PVDF) polymer matrix. The PVDF concentration in our solvent solution is varied to understand the impact of solution viscosity on the phase inversion process and resultant mechanical performance of our separators. Through this study we begin to elucidate relationships between processing conditions, material composition and electrochemical and mechanical performance to facilitate further development of alternative Li-ion battery separators that are compatible with additive manufacturing.[1] Cobb, C. L.; Ho, C. C. Electrochem. Soc. Interface 2016, 25 (1), 75–78. Acknowledgement This work was funded in part by a Defense Advanced Research Projects Agency (DARPA) Young Faculty Award under grant number D19AP00038. The views, opinions, and/or findings expressed are those of the authors and should not be interpreted as representing the official views or policies of the Department of Defense or the U.S. Government.

Unraveling the Catalytic Activity of Fe–Based Compounds toward Li2Sx in Li–S Chemical System from d–p Bands

AbstractLithium–sulfur batteries have ultra–high energy density and are considered to be one of the most promising energy storage systems among all battery systems. However, due to various thorny problems, their commercial production has not yet been realized. The current experimental research normally lacks a systematic investigation into the conversion mechanism of the sulfur cathode from the electronic structure level. Actually, there is still a lack of powerful theoretical guidance for the design of high–performance Li–S batteries and the selection of modified materials still seems blind. In this article, with the chelated Fe‐polyvinyl pyrrolidone as the precursor, a series of Fe–based materials (e.g., Fe3O4@C, FeS@C, Fe3N@C) are synthesized as modified layers for battery separators, and the performance differences between them are systematically studied. It is found that the d–p band center model developed based on the d band center can reasonably combine the reaction potential of Li2S4 and performance differences. Simultaneously, the interaction between Li2S6 and the adsorption interface is simulated by ab initio molecular dynamics. This current work sheds light on promising material design for superior Li–S batteries both from a theoretical and experimental perspective.

Porous polyetherimide separators controlled in‐situ by tetrabutyl titanate as polymer electrolyte with ionic liquid for lithium‐oxygen batteries

Due to its advantages in specific capacity, lithium-oxygen batteries are expected to increase the recharge mileage of electric vehicles. However, the safety and cycle stability problems of lithium-oxygen batteries have not been completely resolved. Herein, through the non-solvent-induced phase separation method combined with the in-situ hydrolysis modification strategy of tetrabutyl titanate, a type of polyetherimide (PEI) separator with typical finger-shaped pores and honeycomb-shaped supporting layer pore structure was prepared. After being infiltrated by EMIM-BF4 ionic liquid electrolyte, the ionic conductivity of the separator can reach 0.75 mS cm−1. Due to the low crystallinity, high thermal stability, and stable ion transport pore structure of the separators, the assembled lithium-oxygen batteries can stably cycle for more than 75 cycles under the condition of a limit of 1000 mAh g−1. In addition, under the strategy of high-performance cathode catalysts and electrolyte additives, the application of the porous PEI separators in lithium-oxygen batteries will be further expanded.

Multi-scale modeling study on fibrous network of cellulose separator for lithium-ion battery

Separator is an essential component of lithium-ion battery, affecting the electrochemical performance and safety of battery. The material-structure-tensile property relationship is significant, herein, a multi-scale modeling method is proposed to explore cellulose separator. Theoretical calculation is utilized to study the composite material in material scale. A multi-layered model is established to survey single fiber in micro scale. Random fibrous networks are applied as representative volumetric element (RVE) models to investigate the fibrous network in meso scale. The multi-scale modeling method manages to conduct reliable simulation on tensile property of cellulose separator, and provide behavior predicting function on further study. A multi-scale modelling method is proposed for cellulose separator Scales including composite materials, single fiber, and fibrous network are studied One-step method is realized combining modelling and simulation of RVE models Relationship between structural parameters. A multi-scale modelling method is proposed for cellulose separator Scales including composite materials, single fiber, and fibrous network are studied One-step method is realized combining modelling and simulation of RVE models Relationship between structural parameters and tensile properties are predicted and tensile properties are predicted.

Meltblown Polyvinylidene Difluoride as a Li-Ion Battery Separator

Meltblown Polyvinylidene Difluoride as a Li-Ion Battery Separator

Revealing Anion Adsorption Mechanism for Coating Layer on Separator toward Practical Li Metal Batteries.

Using a coating layer to modify the separator in a practical Li metal battery has attracted wide attention; however, its function on Li-ion diffusion and Li plating/stripping has not been systematically investigated. Herein, in situ electrochemical Raman characterization using modified coin cell configuration is employed to directly reveal the anion adsorption mechanism of the coating layer. The adsorption ability of the MOF-based coating layer on the commercial separator is able to preserve high concentration of anions near the electrolyte/Li interface, which generates high local Li-ion concentration that delays the drain of Li+ to uniform Li plating. The feasible and large-area fabrication of GO/ZIF-8-modified separator enables the assembly of pouch cell strictly following practical parameters. 0.4 Ah pouch cell (Li/NCM811) delivers stable capacity for over 100 cycles. The deep understanding of the mechanism of how a coating layer affects Li plating behavior is helpful for the designing and preparation of high-performance separators for Li metal batteries.

Synergistic Composite Coating for Separators in Lithium Metal Batteries

Despite their conspicuous advantages in energy density, lithium metal batteries (LMBs) are still in the research stage owing to uncontrolled lithium dendrite growth, which deteriorates their cycle ...

Porous Composite Bifunctional Membranes for Lithium‐Ion Battery Separator and Photocatalytic Degradation Applications: Toward Multifunctionality for Circular Economy

Circular economy paradigms will benefit materials with multifunctional properties allowing to be implemented in more than one application, after processed, or in one application after already being used in another. In this context, membranes based on TiO2/poly(vinylidene fluoride‐co‐trifluoroethylene) (PVDF‐TrFE) with different filler contents were prepared for battery and photocatalytic degradation of pollutants by a temperature‐induced phase separation process (TIPS). It has been shown that the morphological, thermal and mechanical properties, porosity, contact angle, the ionic conductivity and lithium transference number are dependent on the TiO2 content. The membranes with 10 wt% TiO2 content show an ionic conductivity of 0.59 mS cm−1, lithium transference number of 0.72, discharge capacity of 128 mAh g−1 and low capacity fade (17%) at 2C. Further, this membrane presents a high photocatalytic response, being able to be used for ciprofloxacin remediation from water after 300 min of exposure to UV. Further, a second life was confirmed for this membrane by being implemented as a lithium ion battery separator after its use for water remediation applications. This work explores a new concept for the efficient use of the same membranes in very different applications, demonstrating the multifunctionality of the material in the scope of the circular economy paradigm.

Research and Development on the Separators of Li-ion Batteries

With the rapid development of the lithium-ion batteries, the lithium-ion battery separator, as a critical component of lithium-ion batteries, had been extensively studied. In this paper, the main function and performance indicators about the separator materials, recent research and development status at home and abroad of lithium ion battery separators were reviewed. The types and existing problems of mainstream diaphragms in the existing market were described. The production methods of the separators were discussed mainly. It simply introduces the status of the separator’s modification and development of new type of battery separator. Finally, the future development trend of battery separators was forecasted.

Ultraviolet-Cured Al2O3-Polyethylene Terephthalate/Polyvinylidene Fluoride Composite Separator with Asymmetric Design and Its Performance in Lithium Batteries

An Al2O3/polyethylene terephthalate (Al2O3/PET) film can be used as a practical battery separator with superior thermostability, but particle shedding inhibits wide application of this material. We...

Stable Na Electrodeposition Enabled by Agarose-Based Water-Soluble Sodium Ion Battery Separators.

Developing efficient energy storage technologies is at the core of current strategies toward a decarbonized society. Energy storage systems based on renewable, nontoxic, and degradable materials represent a circular economy approach to address the environmental pollution issues associated with conventional batteries, that is, resource depletion and inadequate disposal. Here we tap into that prospect using a marine biopolymer together with a water-soluble polymer to develop sodium ion battery (NIB) separators. Mesoporous membranes comprising agarose, an algae-derived polysaccharide, and poly(vinyl alcohol) are synthesized via nonsolvent-induced phase separation. Obtained membranes outperform conventional nondegradable NIB separators in terms of thermal stability, electrolyte wettability, and Na+ conductivity. Thanks to the good interfacial adhesion with metallic Na promoted by the hydroxyl and ether functional groups of agarose, the separators enable a stable and homogeneous Na deposition with limited dendrite growth. As a result, membranes can operate at 200 μA cm–2, in contrast with Celgard and glass microfiber, which short circuit at 50 and 100 μA cm–2, respectively. When evaluated in Na3V2(PO4)3/Na half-cells, agarose-based separators deliver 108 mA h g–1 after 50 cycles at C/10, together with a remarkable rate capability. This work opens up new possibilities for the use of water-degradable separators, reducing the environmental burdens arising from the uncontrolled accumulation of electronic waste in marine or land environments.