Commercial Separator Research Articles

Mitigating polysulfide crossover in lithium–sulfur batteries with polymer-coated separators

Initiated chemical vapor deposition (iCVD) coating of commercial battery separators enhance Li–S cell performance through mitigation of polysulfide crossover and stabilization of the Li anode/electrolyte interface.

Construction of an ultrathin multi-functional polymer electrolyte for safe and stable all-solid-state batteries.

The ever-increasing demand for safe and high-energy-density batteries urges the exploration of ultrathin, lightweight solid electrolytes with high ionic conductivity. Solid polymer electrolytes (SPEs) with high flexibility, reduced interfacial resistance and excellent processability have been attracting significant attentions. However, reducing the thickness of SPEs to be comparable with that of commercial separators increases the risk of short-circuiting. Herein, an ultrathin (≈7 μm), flexible and mechanical robust SPE was constructed from a rationally designed multi-functional polymer network, i.e., poly[2,2,2-trifluoroethyl methacrylate-r-(2-ethylhexyl acrylate)-r-methyl methacrylate-r-1,4-bis(acryloyloxy)butane] (PTEM) and porous polyethylene (PE). The resultant PTEM@PE electrolyte possesses a high tensile strength of 128.0 MPa with extensibility up to 34.8%, which could effectively prevent short-circuiting and minimize the interfacial resistance of cells. The obtained all-solid-state Li|PTEM@PE|LiFePO4 cell exhibited stable cycling performance over 1500 cycles at 0.5 C with a capacity retention of 74.4%. With high-voltage NCM811 as the cathode, the cell fabricated with PTEM@PE showed a remarkable capacity retention of 84.2% over 500 cycles. Even with the high-mass loading (≈3 mA h cm-2) NCM811 cathode, the cell could be operated at ambient temperature, demonstrating superior ion-migration kinetics. The current design provides a promising strategy to develop ultrathin and multifunctional solid electrolytes for safe, long-cycling and high-energy-density all-solid-state batteries.

A Separator with Double Layers Individually Modified by LiAlO2 Solid Electrolyte and Conductive Carbon for High‐performance Lithium–Sulfur Batteries

AbstractThe “shuttle effect” and the unchecked growth of lithium dendrites during operation in lithium–sulfur (Li–S) batteries seriously impact their practical applications. Besides, the performances of Li–S batteries at high current densities and sulfur loadings hold the key to bridge the gap between laboratory research and practical applications. To address the above issues and facilitate the practical utilization of Li–S batteries, the commercial separator is modified with solid electrolyte (nanorod LiAlO2, LAO) and conductive carbon (Super P) to obtain a double coated separator (SPLAOMS). The SPLAOMS can physically barrier polysulfides and accelerate reaction kinetics. In addition, it enhances uniform lithium deposition, boosts ionic conductivity, and increases the utilization of active sulfur substances. The prepared Li–S batteries exhibit excellent cycling stability under harsh conditions (high sulfur loadings and high current densities) with an initial capacity of 733 mAh g−1 and a capacity attenuation of 0.03% per cycle at 5C in 500 cycle life. Under ultra‐high sulfur loading (8.2 mg cm−2), the prepared battery maintains a satisfactory capacity of 800 mAh g−1 during cycling, demonstrating enormous commercial application potential. This study serves as a pivotal reference for the commercialization of high‐performance Li–S batteries.

Electrospun Poly(vinyl Alcohol)/Chitin Nanofiber Membrane as a Sustainable Lithium-Ion Battery Separator.

Commercial battery separators are made of polyolefin polymers due to their desired mechanical strength and chemical stability. However, these materials are not biodegradable and are challenging to recycle. Considering the environmental issues from polyolefins, biodegradable polymers can be developed as separators to reduce the potential waste from polyolefin separators. In this work, we investigated the potential of poly(vinyl alcohol)/chitin nanofiber (PVA/CHNF) nanofiber as a sustainable lithium-ion battery separator, which was successfully fabricated via the electrospinning and cross-linking method. The PVA/CHNF separator is biodegradable and has an ionic conductivity (1.41 mS cm-1), desirable porosity (86%), good thermal stability (1.4% shrinkage upon heating at 90 °C for 1 h), as well as high electrolyte uptake (388%). The PVA/CHNF separator is also evaluated in the assembled Li//LiFePO4 cells, showing an improved performance compared to the cell with the commercial separator. It shows a discharge capacity of 142 mAh g-1, which is stable throughout 120 charge-discharge cycles. Hence, according to these resulting properties, the PVA/CHNF separator shows promise as a sustainable and environmentally friendly lithium-ion battery separator, offering a high-value use of waste chitin materials.

Nanoparticles-Dotted 3D Porous Nanofiber Skeleton Separator for Advanced Supercapacitors.

As one of the key components of supercapacitors (SCs), separators can directly affect the energy density, output power, and safety stability of SCs. However, it is still a challenge to prepare separators that simultaneously combine large pore size, ultrathin thickness, and excellent mechanical properties. Herein, a 5 μm ultrathin separator with a three-dimensional (3D) porous nanofiber skeleton dotted by fumed Al2O3 nanoparticles has been developed using biaxial stretching. The unique structure of the 3D porous nanofiber skeleton ensures a mechanical strength up to 40 MPa, while the fumed Al2O3 nanoparticles dotted on the 3D skeleton and the incorporation of the annealing process achieve a large average pore size of 130.8 nm, thus harmoniously resolving the contradiction between strength and large average pore size for ultrathin composite separators. The ultrathin thickness greatly shortens the ion transmission channel and effectively reduces ion transmission resistance. Moreover, the fumed Al2O3 nanoparticles exposed on the surface of the 3D porous nanofiber skeleton enhance the wettability of the electrolyte as well as the thermal stability of the separator, achieving a low bulk resistance of 0.3 Ω and zero shrinkage at 130 °C. Due to the unique structure, UAPFS7 offers a better overall performance compared to commercial separators. These findings indicate that the developed separators exhibit excellent comprehensive performance and have the potential to promote the large-scale application of next-generation energy storage devices.

Design of a LiF-rich solid electrolyte interphase layer through a fluorinated carbon (CFX) complex separator for stable lithium metal batteries

The formation of a stable solid electrolyte interphase (SEI) layer is very important for improving the cycling stability and safety of lithium metal batteries (LMBs). However, since the reactivity of lithium metal anodes (LMAs) is very high, controlling the movement of Li+ at the anode/electrolyte interface remains challenging. In this study, an approach involving coating a fluorine functional-controlled fluorinated carbon (CFX) layer onto a commercial PE separator to form a stable SEI layer was proposed. The strong reaction between the fluorine functional groups constituting CFX and Li+ facilitated the rapid formation of a LiF-rich SEI layer in the resting and initial cycling stages. This initial stable SEI layer promoted a subsequent homogeneous Li+ flux, thus improving the LMA stability. In addition, the mechanism by which the total amount of fluorine and the fluorine functional groups control the Li+ dynamics through the CFX-coated PE separator with controlled fluorine functional groups was used to identify the mechanism by which the total amount of fluorine and the fluorine functional groups provide the advantage of the creation of a stable SEI layer. Therefore, this study contributes to the energy storage field by solving the cycling stability problem related to LMAs and emphasizes that a stable SEI layer can be formed based on the important interface control according to the type of fluorine functional group.

Electrospun PAN membrane encapsulated in PEO as a polymer electrolyte for lithium metal batteries

The novel two-step fabrication method of polymer electrolyte membrane was proposed. In the first step, the polyacrylonitrile nano fibrous membrane was prepared with the help of electrospinning. In the second step, the polyethylene oxide solution was prepared along with lithium salt and plasticizers. The solution was poured on the electrospun polyacrylonitrile to get polymer electrolyte membrane in the form of PAN membrane encapsulated in PEO. The polymer electrolyte membrane was boosted by the liquid LiPF6 before assembled in the lithium metal batteries. The polymer electrolyte membrane was compared with the commercial Celgard separator when assembled in coin cell for the application of lithium metal batteries. The polymer electrolyte membrane outperformed and exhibited a good ultimate tensile strength of 20 MPa and the better thermal stability of 97 % at 305 °C. Moreover, the polymer electrolyte membrane also exhibited excellent ionic conductivity of 1.2 mS cm−1, good lithium-ion transference number of 0.57 and uniform lithium plating/stripping cycles for up to 500 cycles without internal short circuiting. The polymer electrolyte membrane represented outstanding rate capability and exhibited the good discharge capacity of 141 mA h g−1 after 100 cycles at 0.5 C rate.

Regulating chiral nematic liquid crystal of hydroxypropyl methylcellulose coating on separator for High-Safety Lithium-Ion batteries

The conventional commercial polypropylene separator (PP) struggles to inhibit the thermal runaway triggered by dendrite short circuits, and its safety cannot meet the needs of the development of high-energy–density batteries. Herein, an easily commercializable design strategy was employed to induce the aqueous solution of natural polymer hydroxypropylmethylcellulose (HPMC) to self-assemble on the surface of the PP separator by Na2SO4, MnSO4, and Al2(SO4)3 to form the chiral nematic liquid crystal (CLC) with excellent performance, and finally the thermally stable separators (H-Na@PP, H-Mn@PP, and H-Al@PP) were obtained. Theoretical calculations and experiments demonstrate that the CLC induced by Na+, Mn2+, and Al3+ can interact with the electrolyte solvent to form a desolvation structure of Li+, which reduces the migration barrier of Li+ through the separator and accelerate the Li+ transport. Furthermore, the ordered CLC structure can ensure uniform electric field and Li+ flux. Hence, Li//LFP, Li (50 μm)//LFP, and Li//NCM811cells are assembled using these modified separators, featuring remarkable cycling stability and high Coulombic efficiency. As the result, H-Na@PP, H-Mn@PP, and H-Al@PP separators in Li//LFP cell display a high initial capacity of 141.2 mAh/g, 146.7 mAh/g and 130.7 mAh/g at 1C, respectively and stable cycling performance over 1000 cycles. Notably, the capacity retention rate remains high at 87 %, 69 %, and 59 % even after 700 cycles, respectively, which are higher than the 21 % capacity retention rate of PP separator. Meanwhile, the pouch cells equipped with these separators deliver exceptional electrochemical performance and show a lower temperature distribution without thermal runaway behavior under the Φ3 mm nail penetration test, indicating its feasibility for high-safety energy storage systems.

Fire-retardant and thermally conductive polyacrylonitrile-based separators enabling the safety of lithium-ion batteries.

Lithium-ion batteries (LIBs) have broad application prospects in many fields because of their high energy density. However, the poor heat resistance of polyolefin membranes and uneven lithium deposition result in battery failure and even infamous thermal runaway behavior. To improve the intrinsic safety of batteries, fire-retardant, thermally conductive, electrospinning strategies are employed to acquire a functional polyacrylonitrile (PAN) nanofiber separator (PAN@FBN/TPP) containing modified boron nitride (FBN) and triphenyl phosphate (TPP). Compared with those of the Celgard separator, the porosity, contact angle, and electrolyte uptake of the Celgard separator are greatly improved. Moreover, the designed separator shows excellent thermal stability without shrinkage when heated at 220°C. The char residue at 800°C is 43.7wt%, which is much greater than that of the Celgard separator (∼0.26wt%). The maximal peak heat release rate (PHRRmax) is only 30% that of the Celgard separator. The improvement in heat resistance laid a solid foundation for the preparation of high-safety LIBs. The advantages of a uniform pore size distribution and extremely high porosity provide abundant active sites and convenient channels for Li+ migration. The cell with the PAN@FBN/TPP separator shows excellent cycle stability and rate performance. Owing to the high heat resistance of PAN and the excellent flame-retardant capability of FBN, the LIBs presented the highest self-heating temperature (T0) and thermal runaway temperature (T1) and the smallest maximum temperature (Tmax) and heat release rate (HRRmax) in the safety performance test; compared with those of commercial separator batteries, the above thermal safety parameters increased by 16.9%, 6.5%, 21.8% and 81.5%, respectively. Overall, this work may provide an effective way to fabricate LIBs with high thermal safety.

Magnetism-Induced Homogenization of Charge and Ionic Distributions Realized By Cu-Ni Core-Shell Nano-Necklace for Stable Lithium Metal Batteries

One-dimensional nanostructures such as nanowires and nanobelts exhibit unique characteristics. Nano-necklace structures, in particular, have demonstrated superior properties in certain applications compared to nanowire structures due to their enlarged active sites and surface area, ample transport channels as well as, multiscale surficial roughness.Various methods exist for fabricating nano-necklace structures, including chemical synthesis, self-assembly, template assistance, and electrospinning. The method we approached was to modify the chemical reduction method in an economical, facile, and quick way for large scale synthesis. In our synthetic approach, we utilized ethylenediamine as a capping and shape-directing agent in a strong base solution, which enable the mass production of Cu-Ni core-shell nano-necklace (CNNN) with a high yield within 30 minutes. Moreover, by changing the type of basic solution, we successfully obtained Cu-Ni core-shell nanowire (CNNW) as a typical 1D nanostructure.The physiochemical properties of as-obtained CNNN and CNNW were systematically investigated. Microscopic analyses demonstrated that both CNNN and CNNW are constituted by two major components: 1) surficial Ni coating layers with a thickness of about 40 nm and 2) inner Cu clusters as a shell and a core, respectively. Experimental results suggest that CNNN exhibits much stronger ferromagnetic properties with much higher specific surface area compared to CNNN, which hold potentials for various applications.To demonstrate one of the potential applications of CNNN, we employed CNNN as a charge and ionic re-distributor for stable lithium metal batteries (LMB). The electrochemical analyses demonstrated that CNNN enabled uniform charge and ionic distributions when coated on a commercial separator, which suppresses notorious dendrite formation of Li metal anodes, due to its excellent ferromagnetic properties and enlarged active sites with Li ions. Therefore, CNNN enabled the stable operation of LMB with LiFePO4 and LiNi8Co1Mn1O2 cathode. Figure 1

Investigation of Electrospun Lignin Fiber Separators for Supercapacitor Applications

This research work investigates the potential of fossil-free electrospun lignin fibers (ELFs) as separators in supercapacitors, contrasting with commonly used commercial separators. We focus on ELFs derived from both hardwood and softwood wood derivatives, along with electrospun ELF with reduced graphene oxide (rGO), comparing their performance to eco-friendly cellulose separators.While polyolefin-based separators are prevalent in the industry, they often suffer from high production costs and limited performance due to sluggish ionic transfer kinetics and poor thermal stability 1. Separators play a critical role in battery performance, providing a microchannel for ion migration and affecting mechanical properties and safety. Lignin, with its high biocompatibility and stable aromatic rings, presents an attractive alternative material for separators2. Previous studies have demonstrated the potential of lignin-based separators, exhibiting high-rate capability and capacity retention compared to commercial separators. Lignin-polymer composite fibers, especially those with polyacrylonitrile (PAN) as the host polymer, have shown improved thermal stability, electrolyte affinity, and electrochemical performance. In our work, we aim to explore further the suitability of lignin-derived separators, particularly fossil-free ELFs and lignin nonwovens, for supercapacitor applications. By synthesizing nanofibers via electrospinning, we create separators with desirable pore properties and mechanical strength3. Our initial electrochemical investigations indicate promising results for ELF derived from both softwood and hardwood lignin, exhibiting specific capacitances of 174 F/g and 170 F/g, respectively. The nonwovens on the other hand demonstrate notably high specific capacitances, with 187 F/g surpassing conventional cellulose nonwovens at 173 F/g. These findings suggest that ELFs perform comparably to cellulose nonwovens, while lignin-based nonwovens exhibit superior performance. In large-scale applications, it's crucial to reduce the overall weight of individual supercapacitor devices. This helps improve their efficiency and ultimately makes them more affordable. One way to do this is by reducing the weight of separators inside the devices. Notably, the reduced mass of ELFs, nearly five times less than nonwoven counterparts, presents an avenue for improving overall component mass. Furthermore, ELFs demonstrate satisfactory rate capabilities comparable to nonwoven materials, further highlighting their potential for various applications. Moreover, lignin's substantially lower raw material costs compared to cellulose, even at its highest quality priced at 100-300 USD/milli ton, position it as an economically feasible alternative for separator material exploration 4. Employing lignin in nonwoven separators, particularly when utilizing inexpensive variants, offers a cost-effective solution for large-scale production of simple nonwoven fabrics. However, electrospinning, despite its advantages such as high surface area and precise fiber morphology control, typically entails higher expenses. Nevertheless, with the declining cost of lignin raw materials, electrospinning may become a more viable option. However, a thorough cost analysis, encompassing all relevant factors, remains essential for evaluating specific cases comprehensively. Furthermore, we intend to discuss more about the electrolyte absorption, mechanical properties, and thermal stability of these lignin-based separators compared to the commercial counterparts with continued investigation of this study. Therefore, through detailed characterization and electrochemical testing, we seek to elucidate the performance of the different separators in supercapacitors. Our findings aim to contribute to the development of sustainable and high-performance energy storage devices, leveraging lignin-derived materials as eco-friendly alternatives to traditional separators.

Next Generation Solid-State Batteries for Electric Aviation

Energy storage will play a critical role in the success of future NASA missions that require batteries with higher energy density, higher power, and most critically improved safety. These performance requirements, which extend beyond those for electric automobile markets, must be satisfied to enable widespread adoption of electric aviation. One approach to improve battery safety and energy is to transition to non-volatile solid-state electrolytes (SSE) which promise many advantages over traditional flammable liquid electrolytes and may also be an enabling technology for next generation chemistries such as lithium-sulfur (Li-S). However, significant manufacturing challenges must be overcome before the adoption of such technology. This study will discuss development of solid electrolytes specifically designed to meet future NASA electric aviation targets. Separator films were processed with densified thickness between 20-30 microns using solvent processing techniques [1]. These films were produced 10-15 times thinner than comparable bulk pressed powder electrolytes and achieved thicknesses comparable to commercial polyolefin separators (25 micron) used in commercial liquid containing lithium-ion cells. Furthermore, design considerations and fabrication techniques of novel cathode composites optimized through the integration of experiment and particle dynamics modeling will be discussed [2] [3]. [1] Donald A. Dornbusch, Rocco P. Viggiano, John W. Connell, Yi Lin, Vadim F. Lvovich. Practical considerations in designing solid state Li-S cells for electric aviation, Electrochimica Acta, 2021, 139406, ISSN 0013-4686,[2] Vesselin I. Yamakov, April A. Rains, Jin Ho Kang, Lopamudra Das, Rehan Rashid, Ji Su, Rocco P. Viggiano, John W. Connell, Yi Lin. Pressure Dependence of Solid Electrolyte Ionic Conductivity: A Particle Dynamics Study. ACS Applied Materials & Interfaces 2023, 15 (22) , 27243-27252.[3] Elizabeth A. Barrios, April A. Rains, Yi Lin, Ji Su, John W. Connell, Rocco P. Viggiano, Donald A. Dornbusch, James J. Wu, and Vesselin Yamakov. Li-Ion Permeability of Holey Graphene in Solid State Batteries: A Particle Dynamics Study. ACS Appl. Mater. Interfaces 2022, 14, 18, 21363–21370.

Mechanical shutdown of battery separators: Silicon anode failure

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

Realization of a Long-Lifespan Thin Li Metal Batteries Capable of Self-Recovery with a Functional Separator

Due to the rapid expansion of the electric vehicles (EVs) market, the demand for large-scale batteries is increasing. Particularly, EVs face several limitations in terms of battery volume and weight. Therefore, achieving high energy density in limited spaces requires a significant reduction in the volume of the anode. Recently, the research is underway on batteries that employ thin Li metal anodes, typically around 20-25μm thick, as the next generation of lithium-ion batteries. However, thin Li anodes present various challenges regarding their cycle life. Compared to Li metal, thin Li metal faces scarcity in lithium sources. Furthermore, due to the unstable formation and destruction of the Solid Electrolyte Interphase (SEI) during the plating-stripping process in Li metal anode charging and discharging, lithium ions and electrolyte are constantly consumed. These side reactions lead to decreased capacity and deteriorated lifespan characteristics. To maintain stable charging and discharging properties, it is necessary to minimize electrolyte decomposition by forming a stable SEI in the early cycle and continuously supplying consumed Li ions throughout the cycling process. Commonly used methods to supplement the limited lithium source of the thin Li anode and replenish consumed Li ions during charging and discharging represent the employing the high-concentration electrolytes (HCE). However, HCE have limits on the dissolved concentration of salts in the electrolyte, and the method of dissolving salts in the entire electrolyte is not attractive a cost perspective. Additionally, as the electrolyte concentration increases, viscosity also increases, leading to a decrease in ion mobility.In this study, high-concentration lithium bis(fluoromethanesulfonyl)imide (LiFSI) salts are coated onto commercial separators to provide a locally high-concentration environment at the electrode/electrolyte interface. This coating layer dissolves as Li ions are consumed, replenishing the depleted Li ions. Furthermore, the presence of high-concentration Li ions in the electrolyte eliminates free solvent. Reducing free solvent suppresses electrolyte consumption further. Additionally, by adopting LiFSI as the salt, rapid decomposition of anions in the initial cycle facilitates the formation of a stable LiF layer. The densely formed LiF layer exhibits high mechanical strength and electrochemical stability, aiding in achieving long-term characteristics.Li||Li symmetric cells were tested using commercial electrolytes, including 1M LiFSI in diethylene glycol dimethyl ether (DME) and 1M lithium hexafluorophosphate (LiPF6) in ethylene carbonate/ diethylene carbonate (EC/DEC). Both electrolytes showed improved cycle stability and lower polarization in cells using an ionically conductive salt-coated separator (SDL) compared to polyethylene (PE) separators. Particularly, the nucleation polarization observed during the initial charging process, when Li ions are deposited onto bare lithium metal, significantly decreased in SDL cells, indicating better Li ion affinity on the lithium surface of SDL cells. Tafel plots were used to analyze the exchange current at the electrode/electrolyte interface. The exchange current for PE was 1.09 mA/cm2, while for SDL, it was 1.52 mA/cm2, suggesting faster interfacial kinetics in SDL compared to PE. The results were also evident in rate capability tests, with the largest capacity difference observed at 5C. Scanning electron microscope (SEM) images revealed distinctly different Li ion deposits on the Cu foil. PE showed vigorous dendrite growth with many voids, while SDL exhibited dense Li deposition, attributed to the presence of high-concentration salts at the interphase, suppressing dendrite growth and inducing uniform Li ion flux. The stable interfacial characteristics were analyzed using X-ray photoelectron spectroscopy (XPS). After 100 cycles, PE showed a high proportion of electrolyte decomposition components, while SDL exhibited a higher proportion of LiF formation. These results demonstrate coated separator with LiFSI effectively suppressed electrolyte decomposition. Additionally, boehmite was pre-coated on the PE separator to endow with coating adhesion, resulting in improved surface morphology. When various commercial electrolytes were applied after salt coating, significantly enhanced wettability was observed compared to PE. Ultimately, half-cells were constructed using thin-film Li metal for galvanostatic charge-discharge tests, achieving superior cycle stability of over 200 cycles with SDL. Figure 1

CeVO4/KB Nanoparticles on Shuttle Effect Inhibition in Lithium-Sulfur Battery Separator Modification.

Lithium-sulfur (Li-S) batteries display promise as redox-based batteries, where separators are an essential part of preventing short-circuiting of the positive and negative electrodes, while the shuttle effect is a critical issue of separators. Currently, commercial PP separators are weak in inhibiting the polysulfides shuttling, so modified separators are needed to inhibit it to improve the battery performance. This paper reports that CeVO4/KB composites act as separator materials. CeVO4/KB modified PP separators enhanced the adsorption of LiPSs, accelerated the rate of Li+ migration, and catalyzed the conversion of LiPSs. These bring about the effect that CeVO4/KB/PP batteries reach 1200.9 mAh g-1 in the first cycle with a capacity retention rate of 86.5 % after 100 cycles at 0.2 C and reach 882.7 mAh g-1 of the initial cycle with a capacity decay rate of 0.063 % after 1000 cycles at 3 C. This work introduces rare earth metal vanadates to modify the separator, adding new ideas for designing separators for good-performance batteries.

Calcium Alginate Fibers/Boron Nitride Composite Lithium-Ion Battery Separators with Excellent Thermal Stability and Cycling Performance.

As one of the most critical components in lithium-ion batteries (LIBs), commercial polyolefin separators suffer from drawbacks such as poor thermal stability and the inability to inhibit the growth of dendrites, which seriously threaten the safety of LIBs. In this study, we prepared calcium alginate fiber/boron nitride-compliant separators (CA@BN) through paper-making technology and the surface coating method using calcium alginate fiber and boron nitride. The CA@BN had favorable electrolyte wettability, flame retardancy, and thermal dimensional stability of the biomass fiber separator. Meanwhile, the boron nitride coating provided excellent thermal conductivity and mechanical strength for the composite separator, which inhibited the growth of lithium dendrites and enabled lithium-ion symmetric batteries to achieve more than 1000 stable and long cycles at a current density of 0.5 mA cm-2. The interwoven fiber mesh formed by the boron nitride coating and the calcium alginate provided multiple pathways for ion migration, which enhanced the storage capacity of the electrolyte, improved the interfacial compatibility between the separator and the electrode, widened the window of electrochemical stability, and enhanced ionic migration. This eco-friendly bio-based separator paves a new insight for the design of heat-resistance separators as well as the safe running of LIBs.

Review and prospect on Metal-organic framework-based Separators for Lithium–Sulfur Battery

With the continuous advancement of technology, wearable smart devices and electric vehicles (EVs) have become an integral part of our daily lives. The increasing demand for energy from these devices and vehicles has driven the pursuit of high-performance rechargeable battery technology. In particular, the widespread adoption of electric vehicles has set higher standards for the energy density and cycle life of batteries. However, the energy density of the widely used lithium-ion batteries is currently limited by the theoretical capacity of commercial cathode materials, and there are certain challenges in terms of safety and cost-effectiveness. Therefore, the development of a new generation of rechargeable batteries with higher energy density, better safety, and more economical cost is particularly urgent. Lithium-sulfur batteries, due to their high energy density, high economic benefits, and high environmental friendliness, are considered to be one of the most promising successors to the widely used lithium-ion batteries. However, in practical applications, the electrochemical performance of lithium-sulfur batteries still needs to be improved. In particular, the poor conductivity of sulfur/lithium and the shuttle effect of polysulfides make the cycle life of the battery less than ideal, and lithium-sulfur batteries (LSB) are still far from achieving large-scale commercialization. The separator used in lithium-sulfur batteries plays a crucial role in its cycle performance and safety. The current commercial separator lacks the ability to effectively regulate the shuttle of polysulfides and is prone to thermal runaway at high temperatures. Therefore, to improve these issues, various functional materials have been used to modify the separator. Among them, as a new type of porous coordination polymer, metal organic frameworks (MOFs) have become a promising material for modifying separators due to their large specific surface area and highly ordered tunable nano-holes.At the same time, their rich inorganic nodes and designable organic ligands allow for the customization of pore chemistry at the molecular level, which can interact with the electroactive components in lithium-sulfur batteries in a tunable manner. This article reviews the reaction mechanism of lithium-sulfur batteries and the structural advantages of MOFs in terms of pore chemistry and morphology and briefly introduces the research progress of MOF-based interfacial layers for the functionalization of LSB separators in recent years. It elaborates on the mechanisms by which various modified separators improve electrochemical performance and provides a prospect for the development prospects of the field.

A Quasi-Solid-State Polymer Lithium-Metal Battery with Minimal Excess Lithium, Ultrathin Separator, and High-Mass Loading NMC811 Cathode.

Solid-state batteries with lithium metal anodes are considered the next major technology leap with respect to today's lithium-ion batteries, as they promise a significant increase in energy density. Expectations for solid-state batteries from the automotive and aviation sectors are high, but their implementation in industrial production remains challenging. Here, we report a solid-state lithium-metal battery enabled by a polymer electrolyte consisting of a poly(DMADAFSI) cationic polymer and LiFSI in Pyr13FSI as plasticizer. The polymer electrolyte is infiltrated and solidified in the pores of a commercial LiNi0.8Mn0.1Co0.1O2 (NMC811) cathode with up to 2.8 mAh cm-2 nominal areal capacity and in the pores of a 25 μm thin commercial polypropylene separator. Cathode and separator are finally laminated into a cell in combination with a commercial 20 μm thin lithium metal anode. Our demonstration of a solid-state polymer battery cycling at full nominal capacity employing exclusively commercially available components available at industrial scale represents a critical step forward toward the commercialization of a competitive all-solid-state battery technology.

A polyolefin separator reinforced inorganic/organic composite electrolyte for quasi-solid-state Lithium-sulfur batteries with high cycle stability and long lifespan

Lithium-sulfur (Li-S) batteries are considered a promising next-generation energy storage system due to the high energy density and the low cost. However, the severe shuttle effect of polysulfide and the security issue caused by organic liquid electrolyte and lithium metal anode have hindered their commercial application. Herein we achieved a polyolefin commercial separator reinforced inorganic/organic composite electrolyte (denoted as Com-LATP) via coating the polypropylene (PP) separator with the composite of polymethyl methacrylate/poly(vinylidene fluoride) (PMMA/PVDF) modified with Li1.3Al0.3Ti1.7(PO4)3 (LATP). The Com-LATP electrolyte (thickness: ∼30 um) exhibits remarkable tensile strength of 103 MPa, an ionic conductivity of 0.47·mS cm-1 with the Li+ transfer number of 0.45, which is beneficial for the uniform Li+ flux and the stable striping and plating of Li metal. The Li symmetrical batteries equipped with this Com-LATP exhibited stable cycling for over 350 h. Meanwhile, the Com-LATP electrolyte with the special dense structure can hinder the polysulfide diffusion. The developed quasi-solid-state lithium-sulfur batteries have demonstrated impressive cycling stability with an initial specific capacity of 1184.8 mA h g-1 at a discharge rate of 0.2 C, maintaining performance over 200 cycles. Additionally, they exhibited outstanding rate capability, retaining a reversible capacity of 710.4 mA h g-1 even at a higher discharge rate of 2 C. This research introduces an innovative structural design approach for high-performance quasi-solid-state Li-S batteries, which holds significant promise for advancing the commercialization of lithium-sulfur battery technology.

Constructing a Spider‐Web Polymer Blocking Layer on Separator for the High‐Loading Li‐S Battery

AbstractThe cycling performance of high‐loading Li−S batteries is still puzzled by the serious shuttle effect of polysulfides. Modifying the commercial separator with polysulfide anchoring materials has been demonstrated as an economical and effective approach to block the polysulfide shuttle. Herein, a cobweb‐like polymer polysulfide‐blocking layer has been constructed via crosslinking between lithium polysilicate (LP) inorganic oligomer and tannic acid (TA) dendritic polymer. Owing to the strongly polar Si−O and Si=O bonds in LP, the spider‐web polymer possesses robust affinity towards polysulfides, indicated by the theoretical calculations. Dendritic polymer TA as the skeleton contributes to effectively exposing the abundant polar functional groups to powerfully capture the polysulfides. As a result, the cycling stability of high‐loading Li−S batteries has been obviously improved. The Li−S battery with sulfur loading of 3.44 mg cm−2 can stably cycle 100 cycles with a high capacity of 685.1 mAh g−1 and columbic efficiency of 99.82 %. Even the sulfur loading increases to 7.15 mg cm−2, the Li−S battery can still deliver a high areal capacity of 5.26 mAh cm−2 after 50 cycles.