Separators For Lithium-ion Batteries Research Articles

Composite Membrane of Poly(vinylidene fluoride) and 2D Ni(OH)2 Nanosheets for High-Performance Lithium-Ion Battery

For the first time, we explored the possibility of utilizing 2D nickel hydroxide nanosheets (NHNs) to prepare NHN/poly(vinylidene fluoride) composite membranes for battery separator applications. The effect of these ultrathin 2D nanosheets on the morphology, crystallization behaviors, porosity, electrolyte uptake ratio, ionic conductivity, and thermal stability of the composite membranes were systematically investigated. A low filler content of only 3 wt % NHNs into PVDF membranes not only promoted superior thermal stability (1.9% shrinkage at 130 °C for 0.5 h) but also led to a significant increase of β-phase content (85.0%), electrolyte affinity (327.6% uptake ratio), and ionic conductivity (1.5 mS cm–1). Strong interfacial interactions between 2D NHNs and polymer molecular chains are responsible for significant α to β crystalline phase conversion, benefiting to high ionic conductivity and electrochemical performance of cells. Moreover, in order to gain more insights for battery applications, this membrane was assembled and evaluated in Li/LiFePO4 half-cells, showing a good cycling performance and rate capability, with a capacity retention of 95.9% after 100 cycles at 2 C and a high specific capacity of 129.1 mAhg–1 at 2 C. Thus, this NHN/PVDF composite membrane could be a promising separator for next generation lithium-ion batteries requiring high safety and ultrafast rechargeability.

Improving Surface Functionality, Hydrophilicity, and Interfacial Adhesion Properties of High-Density Polyethylene with Activated Peroxides.

Polyolefins have had limited application in advanced technologies due to their low surface energy, hydrophobicity, and weak interfacial adhesion with polar coatings. Herein, we propose the use of transition metals at their lowest oxidation state and inorganic peroxides to improve the functionality, surface free energy, hydrophilicity, and adhesion properties of high-density polyethylene (HDPE). Among the nine combinations of transition metals and peroxides used in this study, the combination of Co(II) and peroxymonosulfate (PMS) peroxide was the most effective for surface modification of HDPE, followed closely by the combination of Ru(III) and PMS. After chemical treatment, HDPE's surface functionality, composition, and energy were analyzed via Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and contact angle measurements. Hydroxyl, carbonyl, and carboxylic acid functional groups were detected on the surface, which explained the improved hydrophilicity of the modified HDPE surface; the contact angle of HDPE with DI water decreased from 94.31 to 51.95° after surface treatment. To investigate the effect of HDPE's surface functionality on its interfacial properties, its adhesion to a commercial epoxy coating was measured via pull-off strength test according to ASTM D54541. After only 20 min of surface treatment with Co(II)/PMS solution, the adhesion strength at the interface of HDPE and the epoxy coating increased by 193%, confirming the importance of polyolefins' surface functionality on their interfacial adhesion properties. The method outlined herein can improve HDPE's surface functionality by introducing sulfate radicals. It improves HDPE's hydrophilicity and adhesion properties without requiring strong acids or time-consuming pre- or post-treatment processes. This process has the potential to increase the use of polyolefins in various industries, such as for protective coatings, high performance lithium-ion battery separators, and acoustic sensors.

Sustainable lithium-ion battery separators derived from polyethylene oxide/lignocellulose coated electrospun P(VDF-TrFE) nanofibrous membranes

A novel Polyethylene oxide/lignocellulose (PEO/LIGC) coated dimpled electrospun P(VDF-TrFE) nanofibrous membranes were prepared and are employed as a separator for lithium-ion battery. ESEM images revealed the dimpled morphology of electrospun fibers and PEO/LIGC is located on the surface as well as in the space between the fibers. Results of tensile studies prove that PEO/LIGC coating improves the mechanical strength and elongation at break. The wettability of the membrane with liquid electrolyte was studied by contact angle analysis and the results indicate that both the membranes are readily wetted by the electrolyte. The electrolyte uptake of ecofriendly LIGC coated sample is ∼ 440%, which is 647% higher than that of commercial Celgard separator. PEO/LIGC coated membrane shows ∼ 86% porosity, which is 226% higher than that of the Celgard separator. Ionic conductivity studies show that dip coated P(VDF-TrFE) exhibits a conductivity 7. 04 × 10−3 S cm−1. A 2320 type coin cell (Li/Separator/LiFePO4) were fabricated using PEO/LIGC coated P(VDF-TrFE) and the fabricated cell is superior to that of a Celgard 2320 separator. Thus, the study reveals that the lignocellulose, a sustainable material helps to enhance the overall performance of the battery.

High-Voltage Operation by Mechanical Interlocking Adhesion of Nickel-Rich Cathode and Functional Separator in Lithium-Ion Batteries

High-Voltage Operation by Mechanical Interlocking Adhesion of Nickel-Rich Cathode and Functional Separator in Lithium-Ion Batteries

The effect of [EMIm]BF4/Li+ Ionic liquid on PEO-based solid polymer electrolyte membranes characteristics as lithium-ion batteries separator

Lithium-ion batteries have liquid electrolytes, which are corrosive and volatile, that would cause leakage and explosion during the rechargeable process at high temperatures. To overcome these problems, it is necessary to change the liquid electrolyte into a solid one, namely a solid polymer electrolyte. This work has prepared the solidpolymer electrolyte membranes by casting various 1-ethyl-3-tetrafluoroborate, [EMIm]BF4/Li+ ionic liquid, and PEO. In this study, [EMIm]BF4/Li+ , a Li+ ion-attached ionic liquid, has been synthesized using a simple metathesis reaction between 1-ethyl-3- methylimidazolium-bromide, [EMIm]Br, and lithium tetrafluoroborate, LiBF4 salt. [EMIm]Br has been synthesized from 1- methylimidazole and bromoethane precursors using Microwave Assisted Organic Synthesis (MAOS) method. The functional groups and structures of [EMIm]Br and [EMIm]BF4/Li+ have been confirmed by Fourier Transform Infrared (FTIR) and Nuclear Magnetic Resonance (NMR) spectra analysis. The analysis of ionic conductivities, crystallinities, mechanical properties, surface morphologies, and thermal stabilities have been confirmed by using Electrochemical Impedance Spectroscopy (EIS), X-ray Diffraction (XRD), and tensile tester, Scanning Electron Microscopy (SEM), and Thermogravimetry Analysis (TGA), respectively. The highest ionic conductivity is 1.83 x 10-3 S.cm-1 at room temperature for polymer electrolyte membrane with 16% weight of the [EMIm]BF4/Li+ ionic liquid and also exhibits good mechanical flexibility and thermal stability

Natural wood-derived free-standing films as efficient and stable separators for high-performance lithium ion batteries.

A sustainable and low-cost separator is highly required for electrochemical energy storage systems. Herein, a type of modified natural wood film with excellent mechanical properties, ion conductivity and thermal stability is fabricated for high-performance lithium ion batteries. Using the modified natural wood film as a separator, the fabricated symmetric cell exhibits a more stable and lower plating/stripping voltage for Li than that of the cell with a commercialized polypropylene (PP) separator. The LiFePO4/Li half-cell with the modified wood film separator shows a small polarization voltage and high discharge capacity because of the multi-level nanostructure and abundant functional groups of the modified wood films. The results suggest that the modified wood films are a promising candidate for use as separators in lithium ion batteries. As desired, the LiFePO4/Li half-cells with the modified wood film separator deliver much higher discharge capacities and more stable Coulomb efficiency over two hundred charge/discharge cycles than the cell based on the PP separator. The present work systematically investigate the feasibility of abundant and cheap natural wood-derived materials for use as efficient separators instead of synthetic polymers for high-performance lithium ion batteries with long cycle life.

Research progress on preparation and purification of fluorine-containing chemicals in lithium-ion batteries

With the development of digital products, electric vehicles and energy storage technology, electronic chemicals play an increasingly prominent role in the field of new energy such as lithium-ion batteries. Electronic chemicals have attracted extensive attention in various fields. Characteristics of high-end electronic chemicals are high purity and low impurity content, which requires a very strict separation and purification process. At present, crystallization is a key technology for their separation and purification of electronic chemicals. In this work, the representative fluorine-containing compounds in cathode and anode materials, separator and electrolyte of lithium-ion batteries are introduced. The latest technologies for the preparation and purification of four kinds of fluorine-containing battery chemicals by crystallization technology are reviewed. In addition, the research prospects and suggestions are put forward for the separation of fluorine-containing battery chemicals.

High-performance composite separators based on the synergy of vermiculite and laponite for lithium-ion batteries.

The electrochemical performance and safe operation of the separator plays an important role in lithium-ion batteries. The introduction of inorganic nanoparticles into the separators with organic matter as the matrix effectively improves the thermal stability and wettability of the composite separators, but it also blocks some pores and adversely affects the electrochemical performance. Herein, vermiculite and laponite nanoparticles are introduced into a poly(vinylidene fluoride) matrix to prepare organic-inorganic composite separators for lithium-ion batteries and the synergistic effect of the two inorganic nanofillers is explored. By adding the same amount of the two nanoparticles into the polymer matrix, the prepared separator has the highest ionic conductivity (0.72 mS cm-1) at room temperature and the lowest interfacial impedance (283 Ω). It has an initial discharge capacity of 161.2 mA h g-1 at a rate of 0.5C, a coulombic efficiency of 99.5% after 100 cycles, and a high capacity retention rate of 98.4%, which shows excellent rate performance. The results show that the two clay nanoparticles exert their respective advantages and exhibit a synergistic enhancement effect on the battery performance, which inspires new ideas for the preparation of new organic-inorganic composite separators.

Cellulose Nanofibrils Derived from Pulp as a High-Performance Separator for Lithium-Ion Batteries

Cellulose Nanofibrils Derived from Pulp as a High-Performance Separator for Lithium-Ion Batteries

Highly Thermally Stable, Highly Electrolyte Wettable Hydroxyapatite/Cellulose Nanofibers Hybrid Separators for Lithium-Ion Batteries

Highly Thermally Stable, Highly Electrolyte Wettable Hydroxyapatite/Cellulose Nanofibers Hybrid Separators for Lithium-Ion Batteries

One-step fabrication of robust lithium ion battery separators by polymerization-induced phase separation

LIB electrolyte component and monomer undergo polymerization-induced phase separation to additively fabricate porous LIB separator.

Aramid Nanofibers/Polydopamine Coating Polyethylene Separator for Lithium-Ion Battery

Aramid Nanofibers/Polydopamine Coating Polyethylene Separator for Lithium-Ion Battery

Functional Role of Aramid Coated Separator for Dendrite Suppression in Lithium-Ion Batteries

The separator is an essential important key material in lithium-ion batteries (LIBs) because it is in contact with the positive and negative electrodes and the electrolyte. Aramid coated separators (ACS) are widely used in automotive and consumer batteries as high-performance separators for LIBs with high safety and excellent lifetime characteristics. Although much effort has been made to improve the electrolyte composition, the lithium deposition on the surface of the graphite electrode at low temperature and the high charge rate is still an unsolved problem in LIBs. In this work, lithium metal is used as a counter electrode, and a separator was placed between lithium metal and graphite composite electrode. The lithium was deposited on the surface of the graphite composite electrode through the separator. Then, the functional role of ACS in the initial deposition process was investigated. The dendrite blocking effect of ACS was studied by the observation of dendrite growth and pulse cycle performance.

Freestanding and Ultra-Flexible Pan/Zif67 Hybrid Membrane with Controlled Porosity for High-Performance and High-Safety Lithium-Ion Batteries Separator

Freestanding and Ultra-Flexible Pan/Zif67 Hybrid Membrane with Controlled Porosity for High-Performance and High-Safety Lithium-Ion Batteries Separator

Mechanical Behaviors and Ion Transport Variation of Lithium-Ion Battery Separators Under Various Compression Conditions

Mechanical Behaviors and Ion Transport Variation of Lithium-Ion Battery Separators Under Various Compression Conditions

THE ORGANIC MODIFICATION OF PRE-LITHIATED MONTMORILLONITE

The use of mineral/polyimide composites for lithium-ion battery separators provides an outstanding development direction. Minerals that can be used for lithium-ion battery separators are minerals that have good pores size and distribution, can be intercalated with lithium-ions, and are hydrophobic. Montmorillonite is a natural mineral belonging to the smectite group, and has the capacity to exchange cations but is hydrophilic so it is necessary to modify it to make it hydrophobic and to keep it rich in lithium ions for such purpose. In this study, organic modification has been carried out to change the hydrophilic nature of montmorillonite to become hydrophobic under lithium-ion-rich conditions. Montmorillonite was first isolated by sonicating the dispersion, then carefully separating its suspension after several days of aging. Afterward, the suspension was precipitated by centrifugation and finally dried at 80°C. Thereafter, carbonate cations, organic compounds, and metal oxides, especially ferrous oxide, are removed. The purified isolated montmorillonite is then lithiated with lithium chloride. Finally, the surface of the pre-lithiated montmorillonite was modified with cetyltrimethylammonium bromide to obtain organic-modified pre-lithiated montmorillonite. The results of characterization with an infrared spectrophotometer showed vibration peaks at 2928 cm-1, 2854 cm-1, and 1476 cm-1 as evidence of the presence of attached cetyltrimethylammonium, and vibration peaks at 520 cm-1 and 463 cm-1 as evidence of the presence of attached lithium. The results were also characterized by SEM and XRD which shows that the montmorillonite was organically modified, and lithium intercalated.

Para-Aramid Nanofiber Membranes for High-Performance and Multifunctional Materials

In recent years, high-strength electrospinning nanofiber membranes have important applications in many fields, such as tissue engineering, filtration, lithium-ion battery separator, etc. Improving the mechanical strength of electrospinning nanofiber membranes has always been an important research topic. In this work, for the first time, an ultra-high-strength para-aramid nanofiber membrane is prepared by electrospinning of para-aramid nanofibril dispersion with the assistance of polyethylene oxide (PEO). The rheology and solution properties are investigated to determine the optimal composition of spinning solution. Electrospinning process parameters are studied to obtain a uniform morphology of the membranes. In order to achieve higher strength, the membranes with different forms are prepared by adjusting the arrangement and orientation of nanofibers, random membranes, oriented membranes, and nanofiber bundles. Among them, the fiber diameter is relatively uniform, between 100 and 200 nm. For random and oriented membranes, the mechanical properties can be greatly improved by heat treatment because PEO can act as physical cross-points to realize welding of nanofibers. Compared with the untreated membranes, the tensile strength increases to 40.36 and 65.82 MPa, respectively, increasing by 308 and 83%. Meanwhile, the morphology of the nanofiber membrane is not affected, and the porosity decreases slightly to 76 and 52%, respectively, and a decrease of 8 and 2%. In addition, the strength of the random membrane washed with water for 2 h can reach 83.56 MPa after heat treatment. For nanofiber bundles, the tensile strength exceeds 400 MPa. This work successfully achieves the preparation of ultra-high-strength electrospinning para-aramid nanofiber membranes, which have great application prospects in the field of high-performance and multifunctional materials, such as lithium-ion battery separators, filtration materials, and reinforced composite materials, etc.

Facile Preparation of a Lithium-Ion Battery Separator with Thermal Shutdown Function Based on Polypropylene/Polyethylene Microsphere Composites

With the continuous development of energy density and charge–discharge rates of lithium-ion batteries in recent years, safety function has become the most concerning issue. In this work, a polypropylene (PP)/polyethylene (PE) composited separator with shutdown function is prepared by a facile dry process with biaxial stretching. Owing to the thermodynamic incompatibility between PP and PE, PE crystallizes initially upon cooling and separates from PP melt, forming ample nanoscale PE microspheres within the PP matrix. The weak interfaces between PE microspheres and PP debond during biaxial stretching to create numerous micropores directly. More importantly, as the temperature rises to 135 °C, PE within the separator melts to block the channels for Li-ion transport; meanwhile, the PP matrix maintains the overall dimensional stability of the separator to prevent the internal short circuiting. Compared with the commercial PP/PE/PP trilayer separator manufacturing technique, this approach has advantages of simple techniques, environmental friendliness, continuous fabrication, and low manufacturing cost, which can offer practical guidance for large-scale low-cost manufacturing of high-performance separators.

Poly(ethylene oxide)-ethylene carbonate solid binary electrolyte with higher conductivity, lower operating temperature and fully impregnated separator for all solid-state lithium ion batteries

Poly(ethylene oxide) (PEO) solid electrolyte suffers from the low conductivity and the high operating temperature owing to the cation is trapped in the highly crystalline domains and enmeshed in amorphous domains. Therefore, a tactic was attempted by forming the solid binary electrolyte with the solid cosolvent, ethylene carbonate (EC). X-ray diffraction revealed the crystallinity of the electrolyte progressively degraded at room temperature as EC was added, eventually disappeared, accompanying the endothermic peak continuously shifted to the lower temperature and then vanished in differential scanning calorimetry. Fourier transform infrared spectroscopy also indicated the surroundings around PEO chains mutated after addition of 50% EC (in EO ratio). More importantly, the conductivity was significantly improved ten times after 60% EC was added, still three times at 25 °C than the pristine electrolyte at 60 °C, which was further corroborated with cyclic voltammogram of LiFePO4 micro electrode. Based on the rate discharge, no less than 60% EC content was recommended for the application in the medium rate (<2C) at 25 °C. Additionally, another barrier, the poor wettability of polyolefin separator with the solid state electrolyte was also overcome completely by the facile surface modification.

Cross-linked cellulose/carboxylated polyimide nanofiber separator for lithium-ion battery application

Polyimide (PI) membranes with superior chemical resistance, insulation and self-extinguishing are attracting numerous attentions as the separators of lithium-ion batteries (LIBs), but significant challenges of low mechanical strength and poor electrolyte affinity still remain. Herein, a new kind of environmentally friendly hydrogen-bond (H-bond) cross-linked cellulose/carboxylated PI (Cellulose/PI-COOH) nanofiber composite separator is prepared via electrospinning followed by imidization and alkaline hydrolysis. Besides inheriting the high porosity of the pristine PI separator to absorb the electrolyte, the three-dimensional interconnected structure resulting from H-bond cross-linking is beneficial to improving the mechanical properties of the composite separator, and thereby delivers a tensile strength of 34.2 MPa, 5 times higher than that of the pristine PI separator (6.8 MPa). Meanwhile, the exposed hydroxyl groups on the cellulose, and carboxyl and imino groups on the carboxylated PI can also enhance the electrolyte affinity and wettability of the Cellulose/PI-COOH separator, which plays an important role in increasing the ionic conductivity (0.51 mS cm−1) and widening the electrochemical stability window (∼5.1 V). Consequently, compared with the polypropylene separator and PI separator, the H-bond cross-linked Cellulose/PI-COOH separators show better cycle performance and rate performance when adopted in lithium iron phosphate (LiFePO4) and lithium cobaltate (LiCoO2) half-cells. For example, the Cellulose/PI-COOH-based LiFePO4 half-cell demonstrates the highest initial discharge capacity of 166.2 mAh g−1 and capacity retention rate of 90%, much higher than the pristine PI-based LiFePO4 half-cell (114.6 mAh g−1, 86%). Furthermore, the much enhanced tensile strength, flexibility, thermal stability and flame-resistance of the Cellulose/PI-COOH separator are believed to greatly enhance the safety performance of the obtained LIBs.