Separators For Lithium-ion Batteries Research Articles

Self-Polymerized Dopamine Nanoparticles Modified Separators for Improving Electrochemical Performance and Enhancing Mechanical Strength of Lithium-Ion Batteries.

Separators in lithium-ion batteries (LIBs) play an important role for battery safety, so stable electrochemical performance and high mechanical strength of separators will always be of interest. On the basis of the fact that polydopamine (PDA) nanoparticles found in mussel have a strong adhesion ability, biomaterial surface nanoparticles modification methods are developed to increase electrochemical performance and enhance mechanical strength of polypropylene (PP) and polypropylene/polyethylene/polypropylene (PP/PE/PP) separators. The electrolyte uptake performance, ionic conductivities, discharging rate capabilities, yield stresses, and failure strains of PP and PP/PE/PP separators are all enhanced remarkably by PDA modification. Thermal shrinkage results show that thermal stabilities and the shrinkage percentage of PDA-modified separators are improved. The electrochemical testing results conclude that the discharging capacities of PP (increased by 3.77%~187.57%) and PP/PE/PP (increased by 2.31%~92.21%) separators increase remarkably from 0.1 C to 5.0 C. The ionic conductivities of PDA-modified PP and PP/PE/PP separators are 1.5 times and 6.1 times higher than that of unmodified PP and PP/PE/PP separators, which in turn increase the electrolyte uptake and ionic migration. In addition, mechanical properties of PP (yield stresses: 17.48%~100.11%; failure stresses: 13.45%~82.71%; failure strains: 4.08%~303.13%) and PP/PE/PP (yield stresses: 11.77%~296.00%; failure stresses: 12.50%~248.30%; failure strains: 16.53%~32.56%) separators are increased greatly.

A pore-controllable polyamine (PAI) layer-coated polyolefin (PE) separator for pouch lithium-ion batteries with enhanced safety

A series of pore-controllable polyamine (PAI) layer-coated polyolefin (PE) separators (PAI-PE-1, PAI-PE-2, and PAI-PE-3) are prepared by using a phase-transfer and gravure-printing method and used to improve the safety of pouch lithium-ion batteries (LIBs) based on a PAI “guest-host transition” and PE “pore on-off” cooperative strategy. And the safety mechanism for the LIBs using PAI-PE-1, PAI-PE-2, and PAI-PE-3 separators with pore sizes of approximately 0.02, 0.17, and 0.85 μm is discussed. In the overcharge, nail, and hot box tests, the LIBs with PAI-PE separators all meet safety requirements, while the LIBs with PE separators exhibit either fire or smoke issues. The LIBs with PAI-PE-1 separators have the lowest temperature of 102 °C and the highest residual voltage of 3.97 V in the nail and hot box tests, respectively, and the LIBs with PAI-PE-3 separators have the lowest temperature of 129 °C in the overcharge test. The mechanism for the enhanced safety of LIBs with PAI-PE separators is ascribed to a PAI “guest-host transition” and PE “pore on-off” cooperative process. These results indicate that this pore-controllable PAI-PE separator has promising prospects in the application of LIBs with enhanced safety requirements.

Preparation and Characterization of Biopolymer Electrolyte Membranes Based on LiClO4-Complexed Methyl Cellulose as Lithium-ion Battery Separator

The polymer electrolyte membrane is a main component of lithium-ion batteries (LiBs), serving as separator and electrolyte. In this work, we prepared biopolymer electrolyte (BPE) membranes of lithium perchlorate (LiClO4)-complexed methyl cellulose (MC). Methyl cellulose (MC), a cellulose derivative, has attractive properties for use as biopolymer electrolyte. The bulkier anion size of lithium salt (LiClO4) significantly enhances the performance of biopolymer electrolyte (BPE) membranes. The fabricated biopolymer electrolyte (BPE) membranes were characterized by FTIR, EIS, tensile tester, XRD and TGA. Biopolymer electrolyte membranes with various weight percentages of LiClO4 salt (0%, 5%, 10%, 15%, and 20%) were prepared using a simple solution casting technique. Incorporation of 10% weight of LiClO4 into the MC-based host polymer was selected as optimum condition, because this yielded good conductivity (3.66 x 10-5 S cm-1), good mechanical properties (tensile strength 35.97 MPa and elongation at break 14.47%), good thermal stability (208.4 to 338.2 °C) as well as ease of preparation and low cost of production. Based on its characteristics it can be stated that the 10% LiClO4-complexed MC membrane meets the requirements as a candidate separator for lithium-ion battery application.

Unveiling the effect of homogenization degree on electrochemical performance of TEMPO-mediated oxidized cellulose separators for lithium-ion batteries

Separator is an essential component for lithium-ion batteries, subtly providing transporting micro-channels for lithium ions and electric insulation between electrodes. In this paper, bleached eucalyptus cellulose pulp is implanted with TEMPO-mediated oxidization and high-pressure homogenization to attain cellulose pulps with both micro- and nano-sized fibers, where the blending ratio is regulated by homogenization times. Then the cellulose pulp is formed into separators through vacuum filtration after uniformly dispersed. Macro-properties, micro-structures, physical properties and electrochemical performance of the cellulosic separators are characterized and analyzed. And t commercial Celgard 2500 polypropylene separator is also investigated as comparison. The influence of homogenizing degree on comprehensive properties of the separators is investigated. Besides, the relationship between micro-structure and electrochemical performance is detailedly discussed. Results show that higher homogenization degree contributes to more nano-sized fibers and less micro-fibers, resulting in smaller porosity, poorer electrolyte uptake and larger contact angle. The nano-sized fibers are effective in promoting mechanical strength of separators, but are negative to the impedance performance. This study has unveiled the impact of high-pressure homogenization on the performance of separators, providing meaningful instruction for further development of qualified cellulose separators.

Electrospun PMIA and PVDF-HFP composite nanofibrous membranes with two different structures for improved lithium-ion battery separators

In this study, two methods were used to combine poly (m-phenylene isophthalamide) (PMIA) with polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP). The first PMIA@PVDF-HFP consisted of coaxial electrospinning and the second PMIA/PVDF-HFP was based on simultaneous electrospinning using two solutions. The morphology, mechanical and thermal properties, ionic conductivity and electrochemical stability of the as-obtained composite membranes were all investigated. Compared to properties of commercial Celgard membrane, the composite membranes PMIA@PVDF-HFP and PMIA/PVDF-HFP effectively combined the advantages of separate PMIA and PVDF-HFP. They exhibited not only excellent thermal stability and mechanical strength but also outstanding electrochemical stability and battery cycle performance. Moreover, PMIA@PVDF-HFP composite nanofibrous membrane with core (PMIA)-shell (PVDF-HFP) structure showed superior properties than PMIA/PVDF-HFP membrane prepared by simultaneous electrospinning. Hence, it could be used as ideal separator material in lithium-ion batteries.

Hybrid thermal resistant electrospun polymer membrane as the separator of lithium ion batteries

A heat resistant, anti-thermal-shrinkage, hybrid, electrospun nano-fibrous polymer membrane separator was synthesized. Three polyacrylonitrile (PAN)-based hybrid membranes were prepared by electrospinning different concentrations of pyromellitic dianhydride (PMDA) and 4,4′-oxydianiline (ODA) followed by oven drying to remove the residual solvent and thermal pressing to achieve the optimal strength and porosity in the membranes. The electrospun hybrid membranes were assessed as separators in lithium-ion batteries (LIBs) in a coin cell. Compared to the commercially available Celgard and PAN separator, the Hybrid3 membrane showed the highest porosity (73.36%), excellent electrolyte uptake (558.63%), and extraordinary ionic conductivity (2.39 mScm−1). Scanning electron microscopy, X-ray diffraction, and thermogravimetric analysis were applied to examine the electrospun nano-fibrous separator membranes. The Hybrid3 membrane separator exhibited good dimensional stability when exposed to a temperature of 250 °C for 1 h. Electrochemical measurements were applied to investigate the electrochemical performance of the commercial Celgard and hybrid electrospun nano-fibrous membranes. The Hybrid3 membrane exhibited better electrochemical stability towards the electrolyte than the commercial Celgard separator and other hybrid electrospun nano-fibrous membrane. The coin cell constructed by the Hybrid3 membrane separator exhibited high specific capacity (184 mAh.g−1) at 1C. Moreover, at 0.5C, the coin cell assembled using the Hybrid3 membrane showed good cyclability and capacity retention (95.57%), as well as better efficiency (99.8%). The Hybrid3 membrane is a capable separator to boost the cyclability and provide thermally safe LIBs.

A Glass Platelet Coating on Battery Electrodes and Its Use as a Separator for Lithium-Ion Batteries

Abstract A new type of separator for lithium-ion batteries (LIBs) has been developed using ultrathin micrometer-sized sodium borosilicate glass platelets coated directly on a battery electrode with a water-based binder. The coating process is described in detail, demonstrating coating thicknesses of the glass separator of less than 50 µm. The high-temperature stability has been investigated and it has been shown that the separator is dimensionally stable to at least 600 °C. With regard to the electrochemical performance, full-cell tests on graphite || lithium iron phosphate cells showed a very good behavior, according to which comparable properties of the electrode/separator compound to a commercial polymer-based separator were achieved. This glass separator/electrode composite shows an interesting property profile and is a temperature-stable alternative to conventional polymer-based separators.

Effect of monomer structure on properties of polyimide as LIB separator and its mechanism study

Polyimide (PI) has remarkable thermal stability and mechanical properties, and is considered as an important candidate material for the manufacture of high-security new separators of lithium ion batteries (LIBs). However, different types of PI may exhibit performance differences in battery applications due to their various monomer structures. We synthesize four PIs with different monomers, including 1,2,4,5-pyromellitic dianhydride-4,4′-oxydianiline (PMDA-ODA), 3,3′,4,4′-biphenyltetracarboxylic dianhydride-4,4′-oxydianiline (BPDA-ODA), 3,3′,4,4′-oxydiphthalic dianhydride-4,4′-oxydianiline (ODPA-ODA) and 3,3′,4,4′-benzophenonetetracarboxylic dianhydride-4,4′-oxydianiline (BTDA-ODA), and electrospin them into nanofiber films. Those PI films are then thoroughly evaluated as the separator of LIB. Results show that the electrochemical window of those four PI films is up to 5.1 V (vs. Li+/Li), their wettability and electrolyte uptake are all related to the surface polarity and porosity. Among the four PI separators, BPDA-ODA shows the best cycle performance (95.8% @0.2C, 25 °C) and rate performance in the NCM811|Li battery system, while the BTDA-ODA is the worst in battery applications due to its surface polarity, low electrolyte uptake and the lithiation reaction occurred on the carbonyl groups between two benzene rings, and therefore is not suitable for usage in manufacturing separators.

Porosity variation of lithium-ion battery separators under uniaxial tension

Separators in lithium-ion batteries are susceptible to uneven distributions of deformation, which may lead to inhomogeneous porosity distribution when batteries are subject to complex external loadings. In this study, uniaxial tensile tests were performed for four types of commercial separators and the in-situ 3D Digital Image Correlation (DIC) technique was used to measure the strain fields. In order to minimise the adverse effect caused by the wrinkling in strip-shaped specimens, dogbone-shaped specimens were designed to improve the measurement consistency by avoiding the occurrences of wrinkles in wet-processed separators whose deformation response has weak anisotropy. Homogeneous strain distributions were observed in both wet- and dry-processed separators orientated in the machine direction, but two deformation mechanisms of necking were found for dry-processed separators in the transverse direction. In the range of strain between 0 and 0.5, no thickness change was found in all separators, and large in-plane Poisson's ratio (up to 1.4) was found in wet-processed separators. The relationship between longitudinal and transverse strains was determined experimentally, based on which the in-plane Poisson's ratio is expressed as a polynomial function of longitudinal strain. Finally, relationship between material porosity and longitudinal strain were determined which can provide additional information in multi-physics simulations.

Poly(vinylidene fluoride)/SiO2 composite membrane separators for high-performance lithium-ion batteries to provide battery capacity with improved separator properties

LIBs with improved specific capacity even more than theoretical capacity that is provided by poly (vinylidene fluoride) and silicon dioxide (PVDF/SiO2) nanofiber composite membrane separator is presented in our study. The experiment results are in agreement with simulation analysis that Si can substitute P in the LiFePO4 during the charge-discharge process and lead a great electrochemical performance. It provides a new approach to significantly improve the overall electrochemical performance. This can be described as the capacity of 175 mAh/g at 0.1 C; 160.7 mAh/g at 0.5 C and subsequent residual capacity is 168.6 mAh/g at 0.2 C after long-term cycles of 300 times and the coulombic efficiency is 98.22%. Meanwhile, the PVDF/SiO2 separators are exhibited higher porosity (131.33%) and electrolyte uptake (1514.79%) than commercial PP separator, and also evaluated reduced interfacial resistance and higher thermal property that the initial decomposition temperature is 389.05 °C. The PVDF/SiO2 separators with better performance than commercial separator apply to conventional lithium-ion batteries leads to improved electrochemical performance obviously, and can be more prospective for LIBs after multiple modified preparations.

Ultrathin inorganic-nanoshell encapsulation: TiO2 coated polyimide nanofiber membrane enabled by layer-by-layer deposition for advanced and safe high-power LIB separator

Separators with superior thermal stability, excellent electrolyte uptake and high ionic conductivity are imperative for developing high-power lithium ion batteries (LIBs). Yet it is not easy to build a separator possessing excellent performances in every aspect. For addressing this issue, herein, a novel in-situ growth-bonded titania (TiO2) nanolayer is coated on the polyimide (PI) nanofiber membrane via a novel layer-by-layer deposition (LBLD) strategy. Despite the tiny TiO2 content (2.2%), the resulting hybrid nano-fabric demonstrates improved performance and great potential for high-power LIBs. Benefited from the advantages of LBLD, the TiO2 nanolayer coated on PI nanofibers is ultrathin with neither sacrificing the porosity nor increasing the total thickness, which indicates that the strategy reported herein is a tremendous progress in comparison with conventional coating methods. After coated by the TiO2 nanolayer, the nanofibrous PI membranes exhibit superb heating-endurance, great flame-retardance, excellent wettability and high Li ion transmission, which would enhance the security of LIBs. More importantly, a unique bonding nanostructure is introduced into the nanofibrous PI membrane accompanied by TiO2 nanolayer, leading to strong interactions among PI nanofibers and promoted mechanical performance, which would improve the operability of the separators in LIBs assembly. The electrochemical tests show that cells assembled with the TiO2 coated PI separators have better high-rates performance, higher discharge capacity and great long-term running stability even at 120 °C. These characters suggest that the TiO2 coated PI membrane might play an important role in the forthcoming advanced power LIBs.

Electrospun High-Thermal-Resistant Inorganic Composite Nonwoven as Lithium-Ion Battery Separator

Separators are key materials to ensure the safety of lithium-ion batteries and improve their performance. Currently, commercial lithium-ion battery separators are mainly polyolefin organic diaphragms, but their temperature instability leads to battery short circuit and fire risk. A flexible SiO2 nanofiber membrane combined with a poly(vinylidene fluoride-hexafluoropropylene) (PVDF-HFP) nanofiber membrane is prepared by an electrospinning method. The mechanical strength of the SiO2/PVDF-HFP composite nanofiber membrane (SPF) is twice as high as the pure SiO2 nanofiber membrane and at 200°C, there are almost no dimensional changes of the SPF separators. Compared to commercial polyethylene (PE) separators, SPF shows excellent thermal stability and large-area closed cells at 180°C when used in lithium-ion battery separators. The porosity of SPF is 89.7%, which is more than twice than that of an ordinary PE separator. The liquid absorption rate of SPF is much higher than an ordinary PE separator and has reached 483%. Furthermore, the cycle and rate performance of lithium-ion batteries prepared by SPF has been improved significantly. These excellent properties, as well as the potential for large-scale production of electrospinning technology, make SPF an ideal choice for high-power battery separators.

Three-dimensional cathode with periodically aligned microchannels for improving volumetric energy density of lithium-ion batteries

Increasing the thickness of electrodes of lithium-ion batteries (LIBs) is an effective method for improving the volumetric energy density by reducing the inactive materials (e.g., current collector and separator) in LIBs. However, the thickening of conventional electrodes results in poor capacity due to inefficient transport of Li ions through the irregular microstructure of the electrode. To solve this problem, herein, a new three-dimensional (3D) LiCoO2 (LCO) cathode with periodically aligned microchannels is presented to improve the volumetric energy density of LIBs. The sub-millimeter-thick 3D LCO is fabricated successfully by the ceramics process, which includes lamination of LCO/graphite sheets followed by co-sintering. The 3D LCO demonstrates an excellent areal capacity and rate capability at high rates (31 and 12.1 mAh cm−2 at 0.1 and 1 C, respectively) because of the constant intervals of the microchannels and a low tortuosity value of 1. Moreover, the electrode density of the 3D LCO is similar to that of a conventional LCO, which enables the improvement of the volumetric energy density. A 3D LCO-Li cell achieves a volumetric energy density of up to 1.8 kW h L−1, which is 50% higher than that of a conventional LCO-Li cell.

Electrospun cellulose polymer nanofiber membrane with flame resistance properties for lithium-ion batteries

Current developments of lithium-ion batteries (LIBs) are mainly focused on improving security and cycle performance. Herein, a novel polyvinylidene fluoride (PVDF)/triphenyl phosphate (TPP)/cellulose acetate (CA) nanofiber membrane was fabricated by one-step electrospinning and used as separator in lithium-ion batteries. Compared to traditional polyethylene membrane, the obtained composite showed higher porosity, elevated thermal stability, superior electrolyte wettability, and improved flame resistance. In addition, batteries assembled with PVDF/TPP/CA membrane exhibited excellent electrochemical properties and cycle stability. The enhanced performances were attributed to the porous structure and presence of CA and TPP. Overall, the proposed hybrid organic cellulose-based composite polymer membranes look promising as separators for advanced LIBs.

Detailed Layered Nonlinear Finite Element Analysis for Lithium-Ion Battery Cells to Predict Internal Short Circuits Due to Separator Fractures under Hemisphere Indentation

A numerical analysis method for predicting separator fracture and internal short circuit due to mechanical abuse of lithium-ion batteries (LIBs) is essential for the design of a safe LIB system. In this study, a nonlinear mechanical detailed layered (NDL) model is developed to accurately predict an internal short circuit due to the nonlinear behavior of LIB cells and separator fractures. Each component layer is modeled as a detailed layer, considering the actual thickness and number of layers. The separator fracture is predicted by considering material nonlinearity due to the strain-rate effect and material anisotropy. In comparison with the quasi-static indentation test using three different diameters of indenters, the NDL model accurately predicts the load–displacement and the onset of an internal short circuit. In addition, the separator fracture concentrated in the transverse direction is clearly predicted, and the cross-section of the fracture shape according to the diameter of the indenter is predicted. In contrast, under the same test conditions, the representative-volume-element (RVE) model cannot predict the onset and location of the internal short circuit. The NDL model can more accurately predict the internal short-circuit mechanism caused by a mechanical deformation and separator fracture, compared to the RVE model.

Thermosensitive Polyacrylonitrile/Polyethylene Oxide/Polyacrylonitrile Membrane Separators for Prompt and Safer Thermal Lithium-Ion Battery Shutdown

With the rapid development of high-power and high-energy density lithium-ion batteries, thermal safety has become a critical issue. Due to the fast microstructure change triggered by heat, thermosensitive polymers have aroused increasing attention as thermal shutdown material candidates to prevent the thermal runaway of lithium-ion batteries. In this work, a sandwich-structured polyacrylonitrile/polyethylene oxide/polyacrylonitrile (PAN/PEO/PAN) fibrous membrane with prompt thermal shutdown properties and high thermal stability is prepared using electrospinning technique. The inner layer of the fusible PEO fibrous membrane impart the composite separator with a prompt thermal shutdown function at 80 °C. Meanwhile, the outer layer of the heat-resistant PAN membrane remains thermally stable, even at 200 °C. The large buffering temperature difference (120 °C) between the thermal shutdown temperature and the thermally stable temperature of the composite separator is wider than most of the reported separators and effectively enhances the thermal safety of the lithium-ion batteries. In addition, the PAN/PEO/PAN separator exhibits a higher porosity, better electrolyte wettability, larger ionic conductivity, and lower interfacial resistance compared with a commercial polypropylene/polyethylene/ polypropylene (PP/PE/PP) separator. Moreover, the coin cells assembled by the PAN/PEO/PAN separator presents stable cycle performance and excellent rate capability. Therefore, the novel PAN/PEO/PAN membrane shows great potential as a promising candidate for much safer lithium-ion battery separators.

Correction: Performance of electrode-supported silica membrane separators in lithium-ion batteries

Correction for ‘Performance of electrode-supported silica membrane separators in lithium-ion batteries’ by Kishen Rafiz et al., Sustainable Energy Fuels, 2020, 4, 1254–1264.

Performance of electrode-supported silica membrane separators in lithium-ion batteries

A fully inorganic electrode-supported silica separator for Li-ion batteries.

Development of flexible PVDF/PAMPS polyelectrolyte proton conductive membrane

Progresses in the field of proton conducting polymers have grown very rapidly. A summary of technological growth involving proton conducting polymers indicates that this research area expands at unexpected rates. The paper first introduces the proton conducting polymers and introduces its applications such as used in fabrication of electronic device, thin film transistor (TFT), solar energy conversion, artificial muscles, rechargeable batteries, and solar energy conversion. In this paper, we present and analyse the conductivity of Polyvinylidene fluoride (PVDF)/poly (2-acrylamido-2-methyl-1-propane sulfonic acid) (PAMPS) in frequency range 20 Hz–10 MHz for lithium-ion batteries and battery separator applications. Membrane showing high conductivity has been synthesized by blending PVDF and PAMPS together. Initially the conductivity of pure PVDF membrane was low, but it increased with the addition of PAMPS. The impedance analyser was used to measure dielectric constant, AC conductivity and dissipation factor. In this research paper we have concluded that on adding 60% wt of PAMPs to PVDF; we have got the best result in terms of dielectric constant and conductivity.

Strain rate effect and micro-buckling behavior of anisotropy macromolecular separator for lithium-ion battery

Strain rate effect and micro-buckling behavior of anisotropy macromolecular separator for lithium-ion battery