Separators For Lithium-ion Batteries Research Articles

Elastically anisotropic architected metamaterials with enhanced energy absorption

Materials and structures featuring a combination of high stiffness, strength, and energy absorption are highly demanded. Current studies are focused on the improvement of these mechanical properties without considering their directional dependence. In practice, directional-dependent mechanical properties are crucial to structural integrity and performance, for instance, in the application of anisotropic bone scaffolds for load bearing and battery separators for ion conductivity. Recently, tunable anisotropic stiffness in mechanical metamaterials has been obtained by tailoring the microstructures using data-driven approaches. However, energy absorption behavior, which plays a critical role in the presence of large deformation, has largely been neglected. In this work, we propose a new type of elastically anisotropic architected metamaterials (AAMs) inspired by the current lithium-ion battery separator porous microstructure to acquire tunable anisotropy while exhibiting superior energy absorption. The integrated study presented herein, which combines an experimental investigation with numerical simulations, reveals that the anisotropy can be engineered across a broad range. Compared with two existing lattice and shell-based architected materials, it is shown that the energy absorption of the newly developed AAMs is increased by 120% and 13%. The findings in this work provide a new strategy to expand the existing metamaterial design space, with the potential to enable innovative solutions for applications where directional-dependent stiffness and energy absorption are needed.

Coupled Effect of Low Temperature and Electrolyte Immersion on the Tensile Properties of Separators in Lithium-Ion Batteries.

The performance degradation at low temperatures and frequent safety accidents have aggravated security risks and inhibited the long-term service of lithium-ion batteries (LIBs). As a key component of LIBs, the separator has a great impact on the performance and safety of the battery. In this study, tensile tests of two commercial polyolefin separators (Celgard 2325 and Celgard PE) are performed under low-temperature and immersion conditions. Four representative temperature points and dimethyl carbonate [(DMC), the common solvent in electrolytes] are selected to investigate the coupling effect on the mechanical properties of the separators. The results show that both the separators have anisotropy, but the performance of Celgard 2325 varies more significantly than that of Celgard PE along different directions. Additionally, it is found that with a decrease in the temperature, the tensile strength of the two separators increases, while the elongation decreases. Electrolyte immersion induces a softening tendency in Celgard 2325. Due to the special effect of the residual electrolyte on polyethylene fibers, Celgard PE shows the opposite result. Furthermore, the effect of low temperature is revealed by the analysis of the crystallinity and molecular structure, which can be obtained by X-ray diffraction and Raman spectroscopy, respectively. In addition, the contact angle is measured to describe the wettability variation related to low temperature. The present work provides a theoretical basis and experimental data for the application and development of separators.

LiFePO4 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.

Partially Neutralized Polyacrylic Acid as an Efficient Binder for Aqueous Ceramic-Coated Separators for Lithium-Ion Batteries.

A partially neutralized polyacrylic acid (Pn-PAA) is used for coating sub-micron-sized α-alumina on a conventional microporous polyolefin separator, fabricating a ceramic-coated separator (CCS). Pn-PAA acts as a dispersant and binder by adsorbing itself on alpha(α)-alumina surfaces under acidic condition through the columbic interaction, providing a repulsive force to disperse fine alumina in aqueous suspension, and binds alumina strongly on plasma-treated separator through hydrogen bonding. This CCS shows favorable wettability in carbonate-based liquid electrolyte and ionic conduction due to the high hydrophilicity of Pn-PAA and alumina. With that, this study found that Pn-PAA-made-CCS yields a substantial adhesion strength of ~106 N/m with enhanced cycle stability, a specific capacity of 145.0 mAh/g after 200 cycles at 1 C at room temperature in half cells (LFP/Li metal).

The fabrication of high-performance α-Al2O3 coated PE separator for lithium-ion batteries based on multiple hydrogen bonds

The separator acts as a crucial role in lithium-ion batteries (LIBs). However, commercial separators possess serious shortcomings such as poor thermal stability and compatibility with liquid electrolyte. Although the coating of ceramic powder on the separator can alleviate these disadvantages, it is still challenging to solve the problem of ceramic coating falling off the separators surface. Herein, by improving the surface structure of PE separator and α-Al2O3 particles, KH550 modified α-Al2O3 (mAl2O3) is anchored on the surface of dopamine modified PE separator (PDA-PE) with multiple hydrogen bonds to prepare high-performance battery separator (PDA@mAl2O3-PE). The results demonstrate that the PDA@mAl2O3-PE separator has excellent thermal stability, mechanical performance and electrolyte wettability. Moreover, the ionic conductivity of the PDA@mAl2O3-PE separator increases from 0.531 mS cm−1 for the pristine PE separator to 0.693 mS cm−1. When the PDA@mAl2O3-PE separator is used in LIBs, the LiCoO2/Li batteries present superior cycling capability with a discharge capacity of 132 mAh g − 1 at 1 C after 100 cycles and the capacity retention rate is 95.8%, much higher than that of the batteries with PE separator (86.4%), suggesting that the PDA@mAl2O3-PE separator has a stable ceramic surface anchored by multiple hydrogen bonds and has greater compatibility with electrolyte, leading to a quicker lithium-ion diffusion and outstanding cycling stability.

Polyvinylidene Fluoride as an advanced polymer for multifunctional applications- a review

With the advancement of technological development, polymers are grabbing huge consideration in developing Energy Harvesting and Electromechanical devices. Polyvinylidene Fluoride, commonly referred to as PVDF, a semicrystalline polymer from the fluoropolymer family, has received tremendous interest among the research community. This polymer is astonishing to researchers with its excellent piezoelectric and dielectric properties. Apart from this, properties like outstanding thermal stability, flexible processing, anticorrosive, and mechanical strength make them more appropriate for applications such as wearable sensors, nanogenerators, spin valve ultrafiltration membranes, and separators in lithium-ion batteries. Furthermore, while exploring deep through its electrical properties, PVDF is a ferroelectric non-polar insulating matrix and is majorly adopted in insulating materials. But few researchers have resulted that incorporating certain fillers into PVDF can improve their electroactive crystalline phase without an external poling process. This enhancement enhances their piezoelectric properties and makes them an advanced polymer for multifunctional applications such as shielding material for Electromagnetic Interference (EMI), Acoustic sensors, energy storage and smart scaffolds. Hence this review discusses PVDF as an advanced polymer for Multifunctional applications.

Pure cellulose nanofiber separator with high ionic conductivity and cycling stability for lithium-ion batteries

Conventional polyolefin separators are constrained by poor electrolyte wettability, inferior thermal stability, and low ionic conductivity, which seriously restrict their application in high-performance lithium-ion batteries (LIBs). Herein, cellulose nanofiber (CNF) as the matrix and tert-butyl alcohol (TBA) as the dispersion medium were used to prepare the pure CNF separators for LIBs by a facile filtration method. The effects of the drying temperature on the pore structure, electrolyte wettability, mechanical properties, thermal stability, and ionic conductivity of the separators were comprehensively investigated. The results showed that the freeze-dried separator at −80 °C with TBA as the dispersion medium (TBA-FD) had the best overall performance, with the porosity and electrolyte uptake up to 70.8 % and 296 %, respectively, as well as the ionic conductivity up to 1.90 mS/cm. The CNF separators had no apparent thermal shrinkage at 160 °C, illustrating good thermal stability. Moreover, the LiFePO4/lithium metal battery assembled with the TBA-HD (tert-butyl alcohol as the dispersion medium for heat-drying at 80 °C) and TBA-FD separators displayed superior cycling stability (with a capacity retention rate up to 97.5 % and 96.4 %, respectively) and rate performance. The pure CNF separators with good performance prepared by the facile method are greatly promising for high-performance LIBs.

In situ aluminide armored polyimide nanofiber separators with ultrahigh strength and high wettability for advanced lithium-ion batteries

Polyimide (PI) has been widely used in aerospace, electronic information, novel energy, and other industries due to its excellent high- and low-temperature, radiation, and chemical corrosion resistance. However, the use of electrospun PI separators in lithium-ion batteries (LIBs) is limited due to their poor electrolyte wettability and insufficient mechanical strength. Inorganic materials such as aluminide have typically been used in the coating composition of PI separators. To investigate the effects of different aluminide components, in this work, PI materials were prepared by the complexation–hydrolysis method and used as separators for LIBs. The physicochemical and electrochemical properties of the different nanofiber membranes were studied by adjusting the calcination temperature. The results showed that the sample with the highest tensile strength was 107.6 MPa, which is close to the commercial polyolefin separator. When the calcination temperature increased to 300 °C and then exceeded 400 °C, the aluminide shell initially transformed into thin boehmite and then into γ-Al2O3 phases. The mechanical properties of the nanofiber membranes were enhanced, and the wettability and electrochemical characteristics also improved to some extent. Furthermore, the nanofiber structure was destroyed at 500 °C and could not meet the long-term battery cycles. Therefore, when the calcination temperature was controlled between 300 °C and 400 °C, the aluminide-armored PI nanofiber membranes exhibited better comprehensive performance and were suitable for use as separators in LIBs, which was of great significance for improving the safety and stability of LIBs, especially power batteries.

Green synthesis of sulfonated cellulose/polyether block amide/polyethylene glycol diacrylate (SC/PEBAX/PEGDA) composite membrane by gamma radiation and sulfonation techniques for battery application

Sulfonated cellulose (SC) was successfully prepared through a two-step process of gamma radiation and subsequently sulfonation with potassium metabisulfite of microcrystalline cellulose extracted from sugarcane bagasse. The effect of gamma radiation dose on cellulose showed an increment of oxidation degree, which was evidenced by the intensity ratio of I1718 (carbonyl)/ I2892 (aliphatic) from FTIR analysis. The obtained SC was introduced into polyether block amide/polyethylene glycol diacrylate (PEBAX/PEGDA) polymer matrix as a reinforcement and hydrophilic filler for improving electrolyte affinity and thermal stability of its composite membrane. The increase of SC in PEBAX/PEGDA composite membranes resulted in enhancement of hydrophilicity, electrolyte uptake, and thermal stability compared to pristine composite membranes. However, the excess SC content in the composite membrane exhibited the low physical properties, caused by negligible dispersion on the surface membrane. With the optimum 2.0 wt% SC in PEBAX/PEGDA, the porosity, contact angle and electrolyte uptake capacity was found to be 64.0 %, 12.8° and 37.5 %, respectively. 2.0 wt% SC/PEBAX/PEGDA showed the outstanding thermal stability with negligible shrinkage <10 % at 150 °C whereas pristine PEBAX/PEGDA showed the shrinkage of 29 %. The obtained SC/PEBAX/PEGDA composite membrane is considered as a potential candidate to replace the commercial polyolefin-based separator in lithium-ion batteries.

Nanofibrillar aerogels produced via one-pot chitin nanofibrils liquid exfoliation and self-crosslinking in the DMSO/KOH pseudosolvent system for high-performance lithium-ion batteries

Herein, we demonstrate a facile and effective method to construct chitin nanofibrils (ChNFs) aerogels from the DMSO/KOH pseudosolvent systems, which overcome high cost, complicated processes and energy-consumption of traditional procedures. Pseudosolvent treatment allows chitin to fully swell, leading to the delamination of closely packed ChNFs bundles into long and thin nanofibrils and thereby easy formation of strong and entangled nanofibrils networks. The ChNFs aerogels prepared by removing the pseudosolvent possess unique nanofibrous networks with tortuous pore channels, excellent mechanical flexibility and shapeability, good thermal stability as raw chitin, high specific surface area up to 274.9 m2/g and low densities on the order of 10 mg/cm3. This combination offers an opportunity of applying chitin aerogels as distinct biobased separators for lithium-ion batteries (LIBs). Compared with commercial Celgard separator, our chitin separators with higher electrolyte absorption (3278%) and ionic conductivity (1.77 mS/cm−1 at 30 °C) endow LIBs with better rate performance (92.2 mAh/g at 20C) and cycle life (98.2% after 500 cycles). This work provides a sustainable one-pot liquid exfoliation and self-crosslinking of chitin nanofibrils in the pseudosolvent system, which can impart high porosity, low density, large specific surface area and shapeability to chitin, promoting the high-value utilization of agricultural waste chitin.

Effect of battery fast cyclic charging on the mechanical and fracture behavior of the lithium-ion battery separator

The effect of cyclic fast charging on the mechanical and physicochemical properties of the lithium-ion battery separator is investigated. For that purpose, six battery pouch cells were cycled at 4C charge and 0.5C discharge rates for up to 400, 800, and 1600 cycles. Once the fast charging cycles were completed, the battery pouch cells were fully discharged and carefully disassembled. The physical and chemical microstructural properties of pristine and cycled separators were investigated using scanning electron micrographs (SEM), X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared spectroscopy (FTIR). Additionally, the mechanical behavior of the pristine and cycled separators was also investigated through uniaxial tensile and biaxial punch tests. While the XPS and FTIR analyses of the cycled separator surfaces did not reveal the presence of chemical degradation, the mechanical properties presented a decrease in toughness and ductility with an increased number of charging cycles. A thorough discussion of the possible degradation mechanisms of the cycled separator is provided by combining the results of our analysis and of those reported in the literature.

Fluorine-Initiated Carboxyl Group Enhanced Combination Properties of the Polyethylene Separator for Lithium-Ion Batteries

Fluorine-Initiated Carboxyl Group Enhanced Combination Properties of the Polyethylene Separator for Lithium-Ion Batteries

A novel high-performance electrospun of polyimide/lignin nanofibers with unique electrochemical properties and its application as lithium-ion batteries separators

Polypropylene is currently one of the most widely used separators in lithium batteries because of its low cost and chemical stability. However, it also has some intrinsic flaws that hamper the battery performance, such as poor wettability, low ionic conductivity, and some safety issues. This work introduces a novel electrospun nanofibrous consisting of polyimide (PI) blended with lignin (L) to serve as a new class of bio-based separators for lithium-ion batteries. The morphology and properties of the prepared membranes were studied in detail and compared with those of a commercial polypropylene separator. Interestingly, the polar groups in lignin promoted the affinity to the electrolytes and improved the liquid absorption properties of the PI-L membrane. Besides, the PI-L separator showed a higher ionic conductivity (1.78 × 10−3 S/cm) and Li+ transference number (0.787). Furthermore, the battery's cycle and rate performance improved due to adding of lignin. The capacity retention of the assembled LiFePO4 | PI-L | Li Battery was 95.1 % after 100 cycles at 1C current density, which was higher than that of the PP (90 %). Based on the results, PI-L, a bio-based battery separator, can potentially replace the current PP separators in lithium metal batteries.

Multi-functional Al2O3-coated separators for high-performance lithium-ion batteries: Critical effects of particle shape

The technology of coating polyolefin-type separators with ceramics is gradually developing as an effective method to improve the safety of lithium-ion batteries (LIBs). However, the powder properties of ceramics can adversely affect the surface structure and ionic conductivity of separators; therefore, a new approach is required regarding the powder properties that affect the performance of the separator. Herein, the effect of the Al2O3 particle shape on the physical properties of Al2O3-coated separators and the performance of LIBs is investigated. In the separator coated with angular-shaped Al2O3 particles (Al2O3-A), the pores in the coating layer are uniformly distributed, improving physical properties such as porosity and wettability. The thermal shrinkage of separator is <10% when exposed to 150 °C for 1 h, considerably smaller than that of the commercial polyethylene separator (approximately 83%) under the same conditions. Moreover, the Al2O3-A-coated separator shows the highest ionic conductivity (0.531 mS cm−1), and the LiNi0.8Mn0.1Co0.1O2/Al2O3-A-coated separator/Li battery displays improved stability than using the polyethylene separator under a current density of 5C. This proposes approach to improve the separator's performance through the shape control of ceramic particles paves the way for separators to contribute to the high-temperature safety and long cycle life of batteries.

Nanodiamond-Enhanced Nanofiber Separators for High-Energy Lithium-Ion Batteries.

Current lithium-ion battery separators made from polyolefins such as polypropylene and polyethylene generally suffer from low porosity, low wettability, and slow ionic conductivity and tend to perform poorly against heat-triggering reactions that may cause potentially catastrophic issues, such as fire. To overcome these limitations, here we report that a porous composite membrane consisting of poly(vinylidene fluoride-co-hexafluoropropylene) nanofibers functionalized with nanodiamonds (NDs) can realize a thermally resistant, mechanically robust, and ionically conductive separator. We critically reveal the role of NDs in the polymer matrix of the membrane to improve the thermal, mechanical, crystalline, and electrochemical properties of the composites. Taking advantages of these characteristics, the ND-functionalized nanofiber separator enables high-capacity and stable cycling of lithium cells with LiNi0.8Mn0.1Co0.1O2 (NMC811) as the cathode, much superior to those using conventional polyolefin separators in otherwise identical cells.

Electrospun PVDF-HFP/PAN bicomponent nanofibers as separators in lithium-ion batteries with high thermal stability and electrolyte wettability

Electrospun PVDF-HFP/PAN bicomponent nanofibers as separators in lithium-ion batteries with high thermal stability and electrolyte wettability

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/PVDF-HFP 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 °C is only 5%, which is notably lower than those of PVDF-HFP and Celgard2500. The commercial LiFePO4 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 °C. 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.

Grafting Polyethyleneimine-Poly(ethylene glycol) Gel onto a Heat-Resistant Polyimide Nanofiber Separator for Improving Lithium-Ion Transporting Ability in Lithium-Ion Batteries.

To improve the lithium-ion transporting ability in lithium-ion batteries, a high-performance polyimide-based lithium-ion battery separator (PI-mod) was prepared by chemically grafting poly(ethylene glycol) (PEG) onto the surface of a heat-resistant polyimide nanofiber matrix with the assistance of amino-rich polyethyleneimine (PEI). The resulted PEI-PEG polymer coating exhibited unique gel-like properties with an electrolyte uptake rate of 168%, an area resistance as low as 2.60 Ω·cm2, and an ionic conductivity up to 2.33 mS·cm-1, which are 3.5, 0.10, and 12.3 times that of the commercial separator Celgard 2320, respectively. Meanwhile, the heat-resistant polyimide skeleton can effectively avoid thermal shrinkage of the modified separator even after 200 °C treatment for 0.5 h, which ensures the safety of the battery working under extreme conditions. The modified PI separator possessed a high electrochemical stability window of 4.5 V. Compared with the batteries from the commercial separator Celgard 2320 and the pure polyimide matrix, the assembled coin cell with the PI-mod separator showed much better rate capabilities and capacity retention due to the high electrolyte affinity of the PEI-PEG polymer coating. The developed strategy of using the electrolyte-swollen polymer to modify the thermal-resistant separator network provides an efficient way for establishing high-power lithium-ion batteries with good safety performance.

Graphene-Based Materials for the Separator Functionalization of Lithium-Ion/Metal/Sulfur Batteries.

With the escalating demand for electrochemical energy storage, commercial lithium-ion and metal battery systems have been increasingly developed. As an indispensable component of batteries, the separator plays a crucial role in determining their electrochemical performance. Conventional polymer separators have been extensively investigated over the past few decades. Nevertheless, their inadequate mechanical strength, deficient thermal stability, and constrained porosity constitute serious impediments to the development of electric vehicle power batteries and the progress of energy storage devices. Advanced graphene-based materials have emerged as an adaptable solution to these challenges, owing to their exceptional electrical conductivity, large specific surface area, and outstanding mechanical properties. Incorporating advanced graphene-based materials into the separator of lithium-ion and metal batteries has been identified as an effective strategy to overcome the aforementioned issues and enhance the specific capacity, cycle stability, and safety of batteries. This review paper provides an overview of the preparation of advanced graphene-based materials and their applications in lithium-ion, lithium-metal, and lithium-sulfur batteries. It systematically elaborates on the advantages of advanced graphene-based materials as novel separator materials and outlines future research directions in this field.

Sustainable lithium-ion battery separators based on cellulose and soy protein membranes

The food industry produces millions of tons of natural by-products. Through this study, we followed an environmentally friendly strategy using discards, such as soy protein isolate (SPI) from soya oil production and marine cellulose (Cell) from the agar industry, in order to achieve added-value applications. In particular, this work focuses on the development of membranes based on soy protein and cellulose, and their validation as battery separator membranes toward sustainable energy storage systems. SPI membranes with Cell show excellent compatibility with the electrolyte based on physical interactions. These physical interactions favor the swelling of the membranes, reaching swelling values of 1000% after three days in the liquid electrolyte. The membranes are thermally stable up to 180 °C. After being subjected to the liquid electrolyte, it is observed that the microstructure of the membranes change, but the porous structure is maintained, while the materials remain easy to handle. The ionic conductivity value, lithium transference number and battery performance in cathodic half-cells are ∼ 5.8 mS.cm−1, 0.77, and 112 mAh.g−1 at 1C-rate, respectively. Overall, considering environmental issues and circular economy, it is proven that it is possible to obtain more sustainable high-performance lithium-ion batteries based on waste materials.