Battery Separator Research Articles

Enhancement in optical, thermal and electrical properties of Polyvinyl pyrrolidone/ polyethylene oxide matrix-based nanocomposites for advanced flexible optoelectronic technologies considering nanoceramic zinc oxide/titanium dioxide filler

Polyvinyl pyrrolidone (PVP) and polyethylene oxide (PEO) hybrid nanocomposites with varying zinc oxide (ZnO) and titanium dioxide (TiO2) concentrations were created using the solution casting process. The influence of ZnO/TiO2 nanoparticles on the optical, thermal, and electrical properties of the pure PVP/PEO composite was investigated and discussed. The results of the XRD analysis show that as ZnO/TiO2 NPs concentrations increases, the crystallinity of the nanocomposite films decreases. The interactions between the ZnO/TiO2 nanoparticles and the PVP/PEO polymeric chain is shown by FT-IR spectra. Peak positions and intensity variations in the FT-IR absorption spectra are observed when the concentration increases from 0.5 to 2 wt.% of ZnO/TiO2 NPs. The optical parameters including energy gap (Eg), refractive index (n), and Urbach energy (Eu) for PVP/PEO/ZnO/TiO2 nanohybrid samples were calculated using UV/Vis analytical spectroscopy. The energy gap narrows when ZnO/TiO2 nanohybrid concentration rises, as shown by the optical absorption spectra. The allowed indirect energy gap of the polymer matrix was reduced from 3.72 to 1.94 eV by the addition of 2 wt.% ZnO/TiO2 NPs. The TGA curve shows that the ZnO/TiO2 nanohybrid enhanced the thermal stability of the samples. As the concentration of metal oxides increased, the activation energy (Ea) decreased. AC conductivity showed that the PVP/PEO -(2 wt.%) ZnO/TiO2 NPs nanocomposites have higher electrical conductivity than PVP/PEO. For samples of -(2 wt.%) ZnO/TiO2, the σdcof nanocomposites reached 4.64×10−5Scm−1. Exponential factor (S) results show that in nanocomposite samples with non-Debye relaxation processes, the correlated barrier hopping mechanism (CBH) is dominant. High values of ε' at low-frequency in the dielectric characteristics demonstrated space charge polarization, whereas higher values of ε" in the composite samples could be associated with an increase in energy loss. These results illustrate the appropriateness of these nanocomposites for variety of uses, including flexible capacitors, battery separators, and energy storage devices.

Study on cellulose nanofibers/aramid fibers lithium-ion battery separators by the heterogeneous preparation method

In this study, a heat-resistant and high-wettability lithium-ion batteries separator (PI-CPM-PI) composed of cellulose nanofibers (CNF) and aramid fibers (PMIA chopped fiber/PPTA pulp) with the reinforced concrete structure was fabricated via a traditional heterogeneous paper-making process. CNF played crucial roles in optimizing the pore structure and improving the wettability of PI-CPM-PI separator. The effects of composition on separator properties were investigated and the results indicated that the optimal compositions were 0.5 wt% CNF, 0.5 wt% PMIA chopped fiber/PPTA pulp (ratio of 5:5), 0.05 wt% diatomite and 1.5 wt% polyimide. Relevant tests demonstrated that the performance advantages of PI-CPM-PI separators were exhibited at the wettability and thermal stability compared to the commercial separator (PP). Additionally, batteries assembled with PI-CPM-PI separators showed excellent electrochemical and cycling performance (ionic conductivity of 1.041 mS.cm−1, the first discharge capacity of 158.2 mAh.g−1 at 0.2C and capacity retention ratio of 99.76 % after 100 cycles).

Preparation of High Performance Lithium‐Ion Battery Separators by Double‐Needle Electrospinning

AbstractTraditional polyolefin separators suffer from poor heat resistance and wettability with electrolyte, which leads to compromised safety and electrical properties of lithium‐ion batteries. Polyvinylidene fluoride (PVDF) has high thermal stability and good chemical stability, but its high crystallinity leads to low ionic conductivity. In order to solve these problems, polyvinyl alcohol (PVA) resin was introduced in this paper, and the PVDF/PVA composite separator was prepared by double‐needle electrospinning. The introduction of PVA resin improved its mechanical properties and electrolyte wettability, and ionic conductivity after assembly into a battery. Double‐needle electrospinning process is simple and can preserve the surface properties of fibers, and the prepared composite separator had a high porosity and electrolyte uptake. The composite separator has an ionic conductivity of 2.454 mS ⋅ cm−1, a high capacity retention rate of 97.5 % after 100 charge and discharge cycles, and a capacity retention rate of 86.8 % under 2 C high‐rate discharge. The results show that the battery assembled with PVDF/PVA composite separator has high safety performance and electrical performance, and has application prospects.

Engineering high transport plastic separators for next-generation Li-ion batteries

Engineering high transport plastic separators for next-generation Li-ion batteries

Advances in Surface Functionalization of Lithium Battery Separators and Their In-Service Process Damage Behavior

In recent years, with the rapid development of the lithium battery and energy storage industry, lithium-ion/lithium batteries have received extensive attention and have applications in high-power, portable household and power energy storage [...]

High electrolyte uptake of MXene integrated membrane separators for Zn-ion batteries

The recent development of separators with high flexibility, high electrolyte uptake, and ionic conductivity for batteries have gained considerable attention. However, studies on composite separators with the aforementioned properties for aqueous electrolytes in Zn-ion batteries are limited. In this research, a polyacrylonitrile (PAN)/bio-based polyurethane (PU)/Ti3C2Tx MXene composite membrane was fabricated using an electrospinning technique. Ti3C2 MXene was embedded in fibers and formed a spindle-like structure. With Ti3C2Tx MXene, the electrolyte uptake and ionic conductivity reached the superior values of 2214% and 3.35 × 10−3 S cm−1, respectively. The composite membrane presented an excellent charge–discharge stability when assembled in a Zn//Zn symmetrical battery. Moreover, the developed separator exhibited a high flexibility and no dimensional and structural changes after heat treatment, which resulted in the high-performance separator for the Zn-ion battery. Overall, the PAN/bio-based PU/Ti3C2Tx MXene composite membrane can be potentially used as a high-performance separator for Zn-ion batteries.

Poly(ether imide) Porous Membrane Developed by a Scalable Method for High-Performance Lithium-Sulfur Batteries: Combined Theoretical and Experimental Study.

Lithium-sulfur (Li-S) batteries are one of the emerging candidates for energy storage systems due to their high theoretical energy density and the abundance/nontoxicity/low cost of sulfur. Compared with conventional lithium-ion batteries, multiple new challenges have been brought into this advanced battery system, such as polysulfide shuttling in conventional polyolefin separators and undesired lithium dendrite formation of the Li metal anode. These issues severely affect the cell performance and impede their practical applications. Herein, we develop a poly(ether imide) (PEI)-based membrane with a sponge-like pore morphology as the separator for the Li-S battery by a simplified phase inversion method. This new separator can not only alleviate the new challenges in Li-S batteries but also exhibit excellent ion conductivity, better thermal stability, and higher mechanical strength compared to those of the conventional polypropylene (PP) separator. A combined experimental and theoretical study indicates that the sponge-like morphology of the PEI membrane and its good wettability toward the electrolyte can facilitate uniform ion transportation and suppress dendrite growth. Meanwhile, the PEI molecules exhibit a strong interaction with polysulfides and avoid their shuttling effectively. As a result, the PEI-based Li-S battery shows a much better performance from various aspects (capacity, rate capability, and cycling stability) than that of the PP-based Li-S battery, especially at high charge/discharge current densities and high sulfur loadings. Since the developed PEI membrane can be easily scaled up, this work may accelerate the practical applications of Li-S batteries from the point of separators.

Scalable fabrication of Ni(OH)2/carbon/polypropylene separators for high-performance Li-S batteries

Lithium-sulfur (Li-S) batteries are one of the most promising energy storage systems due to their attractive features of high energy density, low cost, and environmental friendliness. However, the shuttle effect of lithium polysulfides stays an obstacle for the further advancement of Li-S batteries. Herein, a novel Ni(OH)2/carbon/ Polypropylene(Ni(OH)2/C/PP) separator was prepared and applied in Li-S batteries to alleviate the shuttle issue. The Ni(OH)2/C/PP separator was constructed through vacuum filtration coating a super thin layer of super P(0.007 mg cm–2) on the Celgard 2325 followed by decorating the carbon layer with Ni(OH)2 nanosheets film formed by a scalable gas-liquid diffusion method. Influence of Ni(OH)2/C on surface hydrophilicity, polysulfide permeability and catalytic effect on polysulfide conversion have been investigated. The results of contact angle, permeation test of Li2S6, XPS S2p spectra, symmetric Li2S6 cells, Li+ ion diffusion coefficient and Tafel slope confirmed that the Ni(OH)2/C/PP greatly improved the wettability for better penetration of electrolyte, lowered polysulfide permeability to retard its diffusion, and enhanced catalytic effect for the polysulfide conversion to boost the electrochemical kinetics. Thus, compared with the bare PP separator, the Ni(OH)2/C/PP separator enabled significantly increased capacity (1153 vs. 703 mAh g−1 at 0.2 C), greatly enhanced rate performance (816 vs. 381 mAh g−1 at 2 C) and satisfactory cyclability ( 0.10% decay rate after 500 cycles). This study provides a feasible separator modification approach for advanced Li-S batteries.

Fabrication of electrospun bilayer separators for lithium-sulfur batteries: A surface and structure dual modification strategy

Fabrication of electrospun bilayer separators for lithium-sulfur batteries: A surface and structure dual modification strategy

Replacement of commercial glass fiber separator in zinc ion batteries by wet forming of waste ZrO2 fibers

In this work, a novel flexible separator-based waste ZrO2 fibers was fabricated via wet net forming technology for aqueous zinc-ion batteries (AZIBs) to replace commercial glass fibers (GF) separators. ZrO2 separator shows ultra-high wettability and heat resistance. The button cell composed of zinc sheet anode, ammonium vanadate cathode, and ZrO2 separators possesses a high specific capacity of 390 mAh·g−1 at a current density 0.15 A·g−1 and outstanding long-term durability of 102 mAh·g−1 after 500 cycles at 5 A·g−1, higher than GF separator at the same condition. Therefore, this work provides a novel perspective for replacing commercial GF separators.

Separator modification of lithium-sulfur batteries based on Ni-Zn bimetallic MOF derived magnetic porous Ni-C composites

Because of its high theoretical specific capacity, lithium-sulfur batteries are regarded as one of the most promising secondary batteries. However, there are still a series of problems, which seriously affect the commercial application of lithium-sulfur batteries. Therefore, a magnetic porous carbon material was developed in this work for the modification of lithium-sulfur battery separators, which may reduce the shuttle effect of polysulfides and increase its electrochemical performances. The solvothermal preparation of Ni-Zn bimetallic MOF precursors was followed by a high-temperature carbonization in nitrogen environment to sublimate Zn ions and produce porous structures, achieving Ni@C(Zn) composite. In order to improve the electrochemical performances of lithium-sulfur batteries, the Ni@C(Zn) composite was coated on one side of the polyethylene (PE) separator. Ni@C(Zn) composite displays good physisorption and chemisorption properties, and it can also operate as a secondary current collector to promote the usage of active materials as well as inhibiting shuttle effect of polysulfides. By using Ni@C(Zn) coated PE separator, the initial discharge specific capacity of lithium sulfur battery is as high as 1278.6 mAh g−1 at a current density of 0.05 C when the S cathode is loaded with 3 mg cm−2 active materials. Furthermore, the discharge specific capacity in the first cycle at 0.5 C is 749.4 mAh g−1, which remains at 461 mAh g−1 after 500 long cycles, and the capacity retention rate is as high as 61.5%. Even when the S loading is as high as 5 mg cm−2, it can still experience a stable cycle of 100 cycles at 0.2 C.

Modification of Battery Separators via Electrospinning to Enable Lamination in Cell Assembly

To meet the requirements of today’s fast-growing Li-ion battery market, cell production depends on cheap, fast and reliable methods. Lamination of electrodes and separators can accelerate the time-consuming stacking step in pouch cell assembly, reduce scrap rate and enhance battery performance. However, few laminable separators are available on the market so far. This study introduces electrospinning as a well-suited technique to apply thin functional polymer layers to common battery separator types, enabling lamination. The method is shown to be particularly appropriate for temperature resistant ceramic separators, for which stable interfaces between separator and electrodes were formed and capacity fading during 600 fast charging cycles was reduced by 44%. In addition, a straightforward approach to apply the method to other types of separators is presented, including separator characterization, coating polymer selection, mechanical tests on intermediates and electrochemical validation in pouch cells. The concept was successfully used for the modification of a polyethylene separator, to which a novel fluoroelastomer was applied. The stability of the electrode/separator interface depends on the polymer mass loading, lamination temperature and lamination pressure, whereas poorly selected lamination conditions may cause damage on the separator. Appropriate adhesion force of 8.3 N/m could be achieved using a polymer loading as low as 0.25 g/m2. In case separator properties, coating polymer, morphology of the fibrous coating and lamination conditions are well adjusted to each other, the implementation of electrospinning and lamination allows for faster, more flexible and robust pouch cell production at comparable or better electrochemical cell behaviour.

Behaviour of battery separator under different charge rates according to poroelastodynamic model

A separator can influence the performance of a battery in several ways, and determining the mechanical response of the separator can allow to unveil the underlying reasons. We use quasi-static and fully dynamic poroelastic governing equations to simulate the separator of a lithium-ion battery under different charge/compression rates to characterise the displacements and pore pressure. The viscoelastic effect is also considered by adjusting the separator Young's modulus. Error analysis and independent mesh tests are used to validate the simulations. The numerical results show a wave pattern in the stress–strain curve of the separator when using the fully dynamic model, whereas this phenomenon cannot be observed when using the quasi-static model. The distribution of properties in the separator shows that the maximum displacement and pore pressure in the separator increase with the compression rate, and the pore pressure fluctuates during compression when using the fully dynamic model. The two variables in the poroelastodynamic model, namely, displacement and pore pressure, can establish an alternative for analysing battery separators. The simulation results provide a new insight into the separator behaviours and help one understand the battery performance degradation caused by separators better.

Repurposing of spent lithium-ion battery separator as a green reductant for efficiently refining the cathode metals

Developing green and high-efficient pyrometallurgy processes to recycle precious metals from spent lithium-ion batteries (LIBs) is of great importance for resource sustainability and environmental protection. Herein, a novel reduction roasting approach relying on spent LIB separator to refine the spent cathode is proposed. The efficiency of repurposing separator as a reductant for roasting the spent LiCoO2 cathode and the underlying mechanisms were investigated. After the separator-mediated roasting at 500 °C for 2 h, Li+ leaching efficiency of the cathode reached 93.2 %, >2.6 times higher than those after roasting without reductant (25.2 %) or with benchmark reductant graphite (26.1 %). Under the separator-added roasting condition, the cathode was converted to the desired products, CoO and Li2CO3. Based on the analysis of in-situ reaction using thermogravimetric/differential scanning calorimetry and pyrolysis gas species identification, the separator-mediated reduction roasting of cathode was composed of two stages, i.e., reducing gas generation due to separator pyrolysis, followed by the reducing gas mediated LiCoO2 reduction. During the process, the generated C2H4 and CO dominated the reduction. The use of co-existing separator to recover precious metals from spent LIBs is an effective and sustainable strategy to maximize the utilization of spent LIBs.

Boosting the cycle stability and safety of lithium-sulfur batteries via a bilayer, heat-treated electrospun separator

A multifunctional lithium–sulfur–battery separator, the heat-treated PAN/CB/VOOH-PAN/PVDF(HFP) (HPCVPP), was synthesized using a single-step electrospinning technique and heat treatment. The HPCVPP separator has two layers for its functions. (i) The PAN/CB/VOOH, close to the Li–S battery cathode, acts as the conductive blocking layer. The conductive blocking layer provides a site for the electrochemical reaction of LIPS species. In addition, the polar VOOH of this layer can adsorb and catalyze LIPS species, slowing down the ‘shuttle effect’. The batteries using the HPCVPP separator exhibited a close-to-theoretical-maximum capacity of 1391 mAh/g at 0.1C and maintained a high capacity (644 mAh/g) even after 500 cycles at 2C. (ii) The second layer is PAN/PVDF(HFP). In particular, the PAN/PVDF(HFP) helps achieve good thermal stability of the HPCVPP separator. The HPCVPP contour can still be maintained at 250 °C, which can ensure the high-temperature safety of the battery. Moreover, the PVDF(HFP) was heat-treated and generated a crosslinked structure between the nanofibers, enhancing the mechanical strength of the separator from 10.6 to 20.8 MPa, which can further improve battery safety. The HPCVPP separator exhibited outstanding performance, including high level of porosity (70.7%), high electrolyte uptake (510.4%), good ionic conductivity (2.81 mS/cm), and excellent electrochemical performance.

Regulating zinc deposition behaviors by functional cotton textiles as separators for aqueous zinc-metal batteries

Rechargeable aqueous zinc batteries (AZBs) have been regarded as promising large-scale energy storage technologies, due to their low cost and high safety. However, the dendrite growth and side reactions on the Zn metal anode hinder their practical application. Herein, the cotton textiles-based separators with easily-fabricated and cost-effective features are demonstrated for AZBs. By complexing inorganic fluoperovskite NaZnF3 and organic Nafion layers, the as-fabricated separator (CT@NZF@N) can regulate the zinc plating/stripping behavior, which will reduce the zinc nucleation overpotential and lower the charge transfer resistance, thus achieving a highly reversible Zn plating/stripping process with corrosion-free and dendrite-free behavior. Consequently, the zinc symmetric cell with CT@NZF@N separator exhibits prolonged cycle life up to 300 h (0.5 mA cm−2, 0.5 mAh cm−2) in a mild ZnSO4 electrolyte. Moreover, the functional separator also enables V2O5//Zn battery significantly improved rate capability and cyclability. This work provides an appealing strategy for designing reliable, efficient, and cost-effective separators for high-performance AZBs.

Lithium-ion battery separators based-on nanolayer co-extrusion prepared polypropylene nanobelts reinforced cellulose

Low-dimensional nanomaterial separators are considered prime candidates for next-generation lithium-ion battery separators due to their higher porosity and thinner thickness. For polyolefin materials, there is no suitable solvent for solution electrospinning, the low yield of melt electrospinning, and the large size of melt-blown fibers make it challenging to efficiently prepare polyolefin low-dimensional nanomaterials. Moreover, polyolefin materials have been criticized for poor electrolyte wettability and insufficient thermal stability. Herein, polypropylene (PP) nanobelts (NBs) are prepared via a high-efficient nanolayer co-extrusion technique as supporting skeleton to suppress the shrinkage of natural cellulose separators during dehydration effectively, and the cellulose fibers have optimized pore size to prevent internal short circuits. The results indicate that the as-prepared PPNBs/cellulose composite separator (PPNBs/CS) with sandwich structure has superior porosity (78.4%) and ionic conductivity (1.04 mS cm−1). Meanwhile, the thermal stability, electrolyte uptake, and tensile strength are all significantly improved due to the synergies between PPNBs and cellulose fibers. More importantly, the LiFePO4||PPNBs/CSs||LM half cells exhibit better rate-performance and cycling durability than Celgard® 2400. Similarly, the NCM811||LM half cells and NCM811||graphite full cells assembled from PPNBs/CS-1/2 also exhibit good electrochemical performance. This work opens a new approach for easy batch preparation of high-performance lithium-ion battery separators.

Porous Activated Carbons Derived from Coffee Waste for Use as Functional Separators in Lithium-Sulfur Batteries

A novel approach has been proposed for improving the performance of lithium-sulfur batteries (LSBs) with a carbon-based material as an interlayer between the cathode and separator. With this method, the cross-over of lithium polysulfides (LiPS) to the anode is suppressed, increasing reutilization of the sulfur cathode. In this study, activated carbons (ACs) were prepared using coffee waste as a carbon source and potassium hydroxide (KOH) as an activation agent at various reaction temperatures ranging from 500 to 800 °C. With the rise in heating temperature, the specific surface areas, micro-surface areas, and micro-pore volumes of the AC samples gradually increased. In particular, the AC sample prepared at 800 °C and used as a functional separator for LSB exhibited improved capacity and cycling performance while suppressing the LiPS shuttle effect.

A PEGylated Chitosan as Gel Polymer Electrolyte for Lithium Ion Batteries.

Due to their safety and sustainability, polysaccharides such as cellulose and chitosan have great potential to be the matrix of gel polymer electrolytes (GPE) for lithium-based batteries. However, they easily form hydrogels due to the large numbers of hydrophilic hydroxyl or amino functional groups within their macromolecules. Therefore, a polysaccharide-based amphiphilic gel, or organogel, is urgently necessary to satisfy the anhydrous requirement of lithium ion batteries. In this study, a PEGylated chitosan was initially designed using a chemical grafting method to make an GPE for lithium ion batteries. The significantly improved affinity of PEGylated chitosan to organic liquid electrolyte makes chitosan as a GPE for lithium ion batteries possible. A reasonable ionic conductivity (1.12 × 10-3 S cm-1) and high lithium ion transport number (0.816) at room temperature were obtained by replacing commercial battery separator with PEG-grafted chitosan gel film. The assembled Li/GPE/LiFePO4 coin cell also displayed a high initial discharge capacity of 150.8 mA h g-1. The PEGylated chitosan-based GPE exhibits great potential in the field of energy storage.

Understanding the Advantageous Features of Bacterial Cellulose‐Based Separator in Li–S Battery

AbstractSeparator is a critical component of lithium–sulfur (Li–S) battery, and the property of separator influences the battery performance significantly. Cellulose‐based separator is emerging as a promising alternative to the traditional polyolefin separator used in Li–S battery. Although the excellent battery performance of various cellulose‐based separators is shown, a comprehensive understanding of the advantageous features of bacterial cellulose (BC)‐based separator in Li–S battery still is lacking. In this work, models of BC separators with different thicknesses are prepared and compared with polypropylene separators in terms of their electrochemical performance. The results show that the BC separator exhibits favorable electrolyte affinity, improved lithium‐ion transport, suppressed shuttling of soluble polysulfides, and inhibited the formation of lithium dendrites. The combination of these unique characters of BC separator endows it with excellent battery performance. These results provide insight into the use and design of functional cellulose‐based separators in advanced secondary batteries.