Impact of Die Exit Temperature on the Crystalline Orientation and Performance of Polypropylene Battery Separators

Poly(vinylidene fluoride)-based composite membranes with continuous metal–organic framework layer for high-performance separators of lithium-ion batteries

Characterization of Kneading Block Performance in Co-Rotating Twin Screw Extruders

Lithium battery separators play a critical role in the performance and safety of lithium batteries. In this work, four kinds of polymer particle adhesives (G1–G4) for lithium battery separators were synthesized via dispersion polymerization, using styrene, butyl acrylate and acrylonitrile as monomers. The particle size/size distributions, particle morphologies and glass transition temperatures (Tg) of polymer particle adhesives were explored using laser particle size analysis, scanning electron microscopy (SEM) and differential scanning calorimetry (DSC), respectively. The adhesion strengths between the battery separators and the poles piece were examined using a tensile machine. The prepared polymer particle adhesive with a uniform distribution of particle size was obtained when the mass ratio of ethanol to water reached 85:15. Compared with the other three polymer particle adhesives, the prepared G3 coated on the surface of the battery separator exhibited a stronger adhesion with the battery pole piece. In addition, the Land battery test system was applied to examine the electrochemical performance of the lithium battery assembled with the battery separator with the prepared polymer particle adhesives. The results suggest that the electrochemical performance of the lithium battery assembled with the battery separator with polymer particle adhesive G3 is the best among the four counterparts.

This chapter describes the fabrication of a novel modified polyethylene (PE) membrane using plasma technology to create high-performance separator membrane for practical applications in rechargeable lithium-ion polymer battery. The surface of PE membrane as a separator for lithium-ion polymer battery was modified with acrylonitrile via plasmainduced coating technique. The plasma-induced acrylonitrile coated PE (PiAN-PE) membrane was characterized by X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and contact angle measurements. The electrochemical performance of lithium-ion polymer cell assembly fabricated with PiAN-PE membranes was also analyzed. The surface characterization demonstrates that the enhanced adhesion of PiAN-PE membrane resulted from the increased polar component of surface energy. The presence of PiAN induced onto the surface of PE membrane via plasma modification process plays a critical role in improving the wettability and electrolyte retention, the interfacial adhesion between the electrodes and the separator, and the cycle performance of the resulting lithium-ion polymer cell assembly. This plasma-modified PE membrane holds a great potential to be a promising polymer membrane as a high-performance and cost-effective separator for lithium-ion polymer battery. This chapter also suggests that the performance of lithium-ion polymer battery can be greatly enhanced by the plasma modification of commercial separators with proper functional materials for targeted application.

A battery separator physically and electronically separates the anode and cathode but permits Li+ transport between them. Battery separators play a critical role in battery safety by providing, e.g., thermal shutdown functionality in abusive events, or, by preventing lithium metal dendrites or other defects in the cell from penetrating the membrane which can cause internal short circuit leading to uncontrolled thermal runaway, as in the case of the Boeing 787 battery fire incident [1]. One of the challenges with designing safe battery separators is the trade-off between mechanical robustness and porosity/transport properties. For example, high separator tortuosity is good for dendrite resistance but can lead to higher separator resistance [2]. Separator design is further complicated by additional constrains including tolerance to abuse conditions, stable at high voltages (e.g., > 4V), chemically inert to other cell materials, and low cost to meet the performance and cost targets. There is a need to tailor design battery separators that enable high energy/power density with engineered functionality for safety, without adversely affecting performance. Here we present our efforts to develop a nanoporous battery separator that is highly tunable in physical/mechanical properties (e.g., porosity, elastic modulus, toughness) and safety characteristics (e.g., thermal shutdown temperature). Our nanoporous separators are derived from functionalized block copolymers (polyolefins) with low cost precursors [3, 4, 5]. We will also present a hybrid separator concept where the rapid thermal shutdown-capable nanoporous separator developed is hybridized with a highly porous, mechanically and thermally robust separator. This approach renders a hybrid separator technology that affords high energy density, high rate capability, long cycle life and unprecedented safety characteristics for the next generation Li-ion batteries. Figure 1 shows scanning electron microscopy (SEM) images of a representative, synthesized nanoporous polyethylene (NPE) membrane samples, ~ 25 mm in thickness, revealing the desired bicontinuous cubic morphology and percolating pore architecture. Figure 2 shows separator impedance as a function of temperature, for NEP1-3 membrane samples and a commercial separator. An environment (EV) chamber was programmed to increase the temperature at a very low rate of 0.5°C/min for accurate temperature shutdown measurements. The onset of the impedance rise corresponded to ~ 120°C for the NPE separators and ~ 130°C for the commercial separator. The increase of the separator impedance is a result of the separator thermal shutdown, i.e., micropore closing due to the melting/shrinking of the separator, which impedes the ionic motion. It is interesting to note that the separator impedance increased by one to two orders of magnitude at the peak of the thermal shutdown comparing with the initial impedance value. The drastic separator impedance increase associated with the separator thermal shutdown is responsible for providing the safety feature to the otherwise normal operation of Li-ion batteries. The enhanced thermal shutdown features seen in the NPE separators will render earlier, much more rapid and effective thermal shutdown at abusive events (e.g., short circuit, overcharge, etc.), which leads to much improved safety charasteristics for batteries. Our study shows that the molecularly engineered nanoporous membranes are very promising to allow exquisite tuning of mechanical properties (e.g., porosity, elastic modulus, toughness) and safety features (e.g., thermal shutdown temperature). The NPE-based hybrid separator approach will afford an unprecedented performance and safety characteristics for the next generation batteries. Figure 1

PVDF/lithiated sulfonated poly (ether ether ketone) blend coated PE separators for high-performance lithium metal batteries

Enhanced cycle stability of LiCoPO 4 by using three-dimensionally ordered macroporous polyimide separator

A battery separator physically and electronically separates the anode and cathode but permits Li+ transport between them. Battery separators play a critical role in battery safety by providing, e.g., thermal shutdown functionality in abusive events, or, by preventing lithium metal dendrites or other defects in the cell from penetrating the membrane which can cause internal short circuit leading to uncontrolled thermal runaway, as in the case of the Boeing 787 battery fire incident [1]. One of the challenges with designing safe battery separators is the trade-off between mechanical robustness and porosity/transport properties. For example, high separator tortuosity is good for dendrite resistance but can lead to higher separator resistance [2]. Separator design is further complicated by additional constrains including tolerance to abuse conditions, stable at high voltages (e.g., > 4V), chemically inert to other cell materials, and low cost to meet the performance and cost targets. There is a need to tailor design battery separators that enable high energy and power with engineered functionality for safety, without adversely affecting cost. Here we present ADA efforts, in collaboration with university researchers, to develop a nanoporous battery separator that is highly tunable in safety characteristics (e.g., thermal shutdown temperature) and is derived from functionalized block copolymers (polyolefins) with low cost precursors [3, 4, 5]. In particular, we will present a hybrid separator concept where the rapid thermal shutdown-capable nanoporous separator developed is hybridized with a highly porous, mechanically and thermally robust separator. This approach renders a hybrid separator technology that affords high energy density, high rate capability, long cycle life and unprecedented safety characteristics for the next generation Li-ion batteries. Figure 1 shows scanning electron microscopy (SEM) images of the synthesized nanoporous polyethylene (NPE) membranes, an average 25 mm thickness, revealing the desired bicontinuous cubic morphology and percolating pore architecture. Our membranes possess a narrower pore size distribution and a high porosity, as intended based on our chemistry design selection, compared with the commercial separator. Figure 2 shows separator impedance as a function of temperature, for NEP Gen1, NPE Gen2, and a commercial separator. The onset of the impedance rise corresponded to 80°C, 115°C and 130°C for NPE Gen2, NPE Gen1, and the commercial separator, respectively. The increase of the separator impedance is a result of the separator thermal shutdown, i.e., micropore closing due to the melting/shrinking of the separator, which impedes the ionic motion. The drastic separator impedance increase associated with the separator thermal shutdown is responsible for providing the safety feature to the otherwise normal operation of Li-ion batteries. The enhanced thermal shutdown features seen in the NPE separators will render earlier, much more rapid and effective thermal shutdown at abusive events (e.g., short circuit, overcharge, etc.), which leads to much improved safety charasteristics for Li-ion batteries. Figure 3 shows charge/discharge voltage vs. specific capacity for a representative graphite/LiCoO2 (LCO) full cell using a NPE-based hybrid separator. The full cell displayed a good discharge specific capacity of ~ 120 mAh/g (LCO active mass). Figure 4 shows a rate capability test. The NPE-based hybrid separator demonstrated superior rate capability than the commercial separator at C rates ≥ 5C. At 20C rate, the NPE hybrid separator based Li-ion cells demonstrated an impressive rate capability of > 73% capacity retention, 2.5 times that of the commercial counterpart (29%). Figure 5 shows discharge capacity retention vs. cycle number of the Li-ion full cells using NPE-based hybrid separator and a commercial separator (control). The NPE hybrid separator based Li-ion full cells showed excellent cycle life performance with capacity retention of 88% after 300 cycles. It is noticed that the NPE-based hybrid separator demonstrated very compatible cycle life performance as the commercial separator. This result illustrates an excellent chemical and electrochemical compatibility of the NPE-based hybrid separator. Our study shows that the strategy of preparing block copolymer derived nanoporous separators provides a very promising and powerful tool to allow exquisite tuning of performance and safety features (e.g., thermal shutdown temperature) of the nanostructured separator. The NPE-based hybrid separator technology will afford an unprecedented performance and safety characteristics for the next generation Li-ion batteries. References National Transportation Safety Board Incident Report, NTSB/AIR-14/01, PB2014-108867, Jan 7, 2013.Pankaj Arora and Zhengming (John) Zhang, Rev. 104, 4419-4462, (2004).Louis M. Pitet, Mark A. Amendt, and Marc A. Hillmyer, AM. CHEM. SOC. 132, 8230–8231 (2010).Bielawski, C. W.; Grubbs, R. H. Polym. Sci. 32, 1–29 (2007).Pitet, L. M.; Hillmyer, M. A. Macromolecules, 42, 3674–3680 (2009). Figure 1

An unusual delamination phenomenon on three kinds of lithium‐ion battery separators was investigated in this study, which is closely associated with the compression resistance of the separator. The delamination trends of three kinds of polymer separators were analyzed systematically. Scanning electron microscopy, two‐dimensional wide‐angle X‐ray diffraction, compression and delamination tests show that a separator prepared by the dry process with uniaxial stretching delaminate hardest due to abundant connection or support structure along the thickness direction. However, the multilayer structure stacked along the thickness direction can be seen clearly for separators experiencing biaxial stretching, both for the dry process and wet process. In particular, a separator prepared by the wet process has the poorest connection or support structure along the thickness direction, leading to the strongest delamination trend and the worst compression resistance. Based on this, we control the delamination trend of the separator by adjusting the condensed structure of the precursor film. Besides, the delamination test can quantify the delamination trend of different kinds of separators accurately and further supplement the evaluation criteria of lithium‐ion battery separators, which can help us to better understand and design a separator with optimal microporous structure. © 2020 Society of Industrial Chemistry

Covalent organic frameworks (COFs) that selectively enable lithium ions transport by their abundant sub-nano or nanosized pores and polar skeleton are considered as emerging coating materials for separators of lithium metal batteries. However, the COF-coated separators that combine high ionic conductivity with excellent lithium ions transference number ($$ {t_{L i^{+}} } $$ ) are still challenging, as the coating layer may increase the transport resistance of ions through the separator due to the elongated pathway. Different from conventional strategies that always focus on developing COFs with distinct structural motifs, this work proposes a crystallinity engineering tactic to improve the ion transport behaviors and thus battery performance. Amorphous (AM-CTF) and highly crystalline covalent triazine frameworks (HC-CTF) were successfully synthesized, and the effect of crystallinity of CTFs on the electrochemical properties of the separators and the battery performance are fully studied. Compared to amorphous covalent triazine framework, HC-CTF features a more regular structure and higher surface area, which further improves the $$ {t_{L i^{+}} } $$ (0.60) and ionic conductivity (0.67 mS cm-1) of the coated separators. The LiFePO4/Li cells assembled with the HC-CTF-coated separator exhibit an ultralong lifespan and extremely high-capacity retention (45.4% at 1 C for 1,000 cycles). This work opens up a new strategy for designing high-performance separators of lithium batteries.

Mechanically robust, nonflammable and surface cross-linking composite membranes with high wettability for dendrite-proof and high-safety lithium-ion batteries

Eco-friendly and strong lignin-containing microfibrillated cellulose films for high-performance separators of aqueous zinc batteries.

Coaxial electrospun core-shell lithium-ion battery separator with flame retardant and thermal shutdown functions

The advanced anion-exchange membranes with the poly(3,3’-(hexyl)bis(1-vinylimidazolium)bromide), PHVB, was synthesized by inter-polymerization of a 3,3'-(hexyl)bis(1-vinylimidazolium) bromide in poly(vinyl chloride), PVC, solution. We confirmed the successful preparation of the advanced anion-exchange membrane (AEM) such as ionic conductivity (S/cm), water uptake (%), ion-exchange capacity (meq/g), vanadium permeability, thermal properties, and SEM analysis, respectively. The vanadium redox flow battery (VRFB) performances using the prepared AEM based on PHVB/PVC composite polymers in organic electrolytes was examined. In the prepared advanced AEM, the maximum voltages reached 2.5 V under the fixed current value of 0.005mA. The synthesized advanced AEM has also good stability with organic electrolyte by battery performance under 1000 cycles. As results, the advanced AEM based on PHVB/PVC prepared by the inter-polymerization is suitable for use as a battery separator in VRFB.

Electrospun polyacrylonitrile nanofibrous membranes with varied fiber diameters and different membrane porosities as lithium-ion battery separators