Dissertations / Theses on the topic 'Battery separators'

Ce travail s'est concentré sur la compréhension de l'influence de la formulation et plus spécifiquement de la silice précipitée sur la résistivité électrique de séparateurs en polyéthylène destinés à des batteries au plomb. Les séparateurs de batteries en polyéthylène sont composés de silice précipitée, de polyéthylène ultra haute masse molaire (UHMWPE) et d'huile organique. La première partie de ce travail a été d'élaborer à l'échelle du laboratoire, des membranes modèles en polyéthylène. La seconde a été de comprendre l'influence de certains facteurs sur les propriétés structurales et physicochimiques des membranes. Ces facteurs sont principalement la quantité d'huile, la quantité et le grade de silice précipitée, les conditions de température lors de la cristallisation de la membrane et le mode de mise en œuvre utilisé. Les influences des quantités d'huile et de silice sur la cristallisation du polyéthylène sont méticuleusement étudiées, montrant que l'huile aide à augmenter la cristallinité finale de l'UHMWPE et que la silice joue un rôle de réservoir d'huile. Il a également été mis en évidence que la quantité ainsi que le grade de silice influencent la quantité de porosité de la membrane mouillable par l'électrolyte. La présence de silice en surface des pores est responsable de la mouillabilité de la membrane. Un paramètre empirique a donc été proposé dans le but de pouvoir quantifier l'efficacité de l'état de dispersion/distribution de la silice précipitée dans la membrane. Pour terminer, pour une formulation et un même mode de mise en œuvre, il est possible de discriminer l'efficacité des grades de silice précipitée pour l'application séparateur de batterie
This work is devoted to understand the effect of the formulation and more specifically of the precipitated silica on the resistivity of the PE-separators. The PE-separators are designed for the lead-acid batteries. PE-separators are composed of precipitated silica, ultrahigh molecular weight polyethylene (UHMW-PE) and organic oil. The first part of this work was to elaborate PE-separator models at a laboratory scale. Then, the factors impacting the structural and physico-chemicals properties of PE-separators were investigated. These factors are mainly the amounts of oil, precipitated silica, the grade of the precipitated silica, the temperature conditions of crystallization and the device used to elaborate the membrane. The influence of the amounts of oil and precipitated silica on the crystallization of the polyethylene wasthoroughly described showing that the oil helps to increase the final crystallinity of UHMWPE and that the silica plays a role of oil reservoir. Moreover, it was shown that the amount and the grade of precipitated silica have an influence on the wettable part of the porosity of the PE-separators. The coating of the pores by the precipitated silica is responsible of the wettability of the membranes by the electrolyte. Thus, an empirical parameter has been proposed in order to quantify the efficiency of the dispersion and distribution of the precipitated silica in the membrane. The more the membranes are wettable by the electrolyte the more the resistivity of the membranes is decreased. To finish, for a same amount of components and a same method of processing, it is possible to discriminate the efficiency of each grade of precipitated silica for the battery separator application

Lithium-ion battery (LIB) is widely utilized in many modern applications as energy sources. Numerous efforts have been dedicated to increasing electrochemical performances, but improvement on battery safety remains a visible challenge. While new electrode materials have been developed, advancement in new separator for LIB has remained relatively slow. Separator is the polymeric porous material that physically separates electrodes and allows free flow of ions through its structure. It is electrochemically inactive but essential for avoiding thermal runaway conditions. Besides its crucial functions, separator has been known as the mechanically weakest component. Structural battery is a new approach that employs multifunctional material concept to use LIB as load-bearing material to minimize the weight of the complete system and maximize the efficiency. Separator materials are required to have good thermal stability, battery chemistry, and mechanical performance. This work aims at creating electrospun membranes with improved thermal resistance, structural integrity and moderate ionic conductivity as the next generation LIB separators. Electrospinning process is known as a versatile and straightforward technique to fabricate continuous fibers at nano- and micro- scales. The electrospinning process employs an electrostatic force to control the production of fibers from polymer solutions. Solution and process parameters, including type of polymer and solvent system, concentration of polymer solution, acceleration voltage, and solution feed rate, have been studied to achieve the desirable membrane properties. In this report, the electrospinning parameters affecting morphology and corresponding properties of electrospun membranes, electrospun polymer composite and polymer-metal oxide composite membranes for structural battery applications will be discussed.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2017.
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 135-143).
With the rapid growth of electric vehicle (EV) market, the mechanical safety of lithium-ion batteries has become a critical concern for car and battery manufacturers as well as the public. Lithium-ion battery cells consist of cathode, anode, separator and shell casing or aluminum plastic cover. Among them, the shell casing provides substantial strength and fracture resistance under mechanical loading, and the failure of the separator determines onset of internal short circuit of the cell. In the first part of this thesis, a plasticity and fracture model of the battery shell casing by taking the anisotropic plasticity and stress-state dependent fracture into account was developed. The shell casing model is calibrated and validated at both specimen and component levels. This shell casing model, together with homogenized jellyroll model could predict mechanical behavior of single cylindrical 18650 cell well and could serve for battery pack crash simulation purposes. Another part of this thesis is mechanical test, characterization and modeling of battery separators since the mechanical properties of separators are crucial to internal shorts of lithium-ion batteries. Mechanical properties of commercially available four typical separators that including polypropylene (PP), trilayer (PP-PE-PP), ceramic-coated and nonwoven separators were compared, such as in-plane tensile strength, out-of-plane compression strength and puncture strength. Two distinct failure modes of dry-processed separators under biaxial loading were observed in the tests and used to explain the differences in short circuit characteristics of same cells. A conservative defection-based failure criterion for predicting of onset of short from experimental data was proposed. Numerical model of separator was developed and it succeeded in predicting the response of PP separator under biaxial loading. Owing to the micro porous semi-crystalline nature of widely used PP separator, interrupted tests of PP separator under different in-plane tension including machine direction, transverse direction and diagonal direction were conducted in order to reveal deformation mechanism at the micrometer level. Through scanning electric microscopy (SEM) observation and X-ray diffraction of deformed regions from interrupted test specimens, deformation sequences of micro fibrils and lamellae blocks of PP separator are reported. Lastly, significant mechanical degradation of separator due to charge-discharge cycling was described.
by Xiaowei Zhang.
Ph. D.

The battery separator is a component of the conventional battery that for long has been overlooked. Just because it’s the only inactive component, doesn’t mean it’s any less important for the battery cell. Recent trends point to an immense growth of the electrical vehicle-industry, and by so, also the lithium-ion battery separators market. This is because the lithium-ion battery is the most common battery type in commercial electrical vehicles. In one of the major manufacturing processes of the separator, mineral oil is used, to achieve a porous film. This study aims to evaluate different oils interaction with the polymer resin in the manufacturing process. Since most oils used in the battery separator industry today use paraffin rich oils, oils with different naphthenic content is tested to find correlations between the oils properties and the crystallinity or the porosity. No correlations for either the porosity or the crystallinity could be made to the oil’s properties. The images taken with the SEM was not enhanced enough to study the pores themselves or the pore structure of the films. For future studies it is recommended to collect more data to identify outliers so more accurate values are obtained. The methodology needs to be verified to ensure the procedure is reproducible. For the study of the pores and the pore structure, an FE-SEM should be used to achieve greater quality enhancement images on the surface of the films.
Batteri separatorn är en komponent i det konventionella batteriet som länge har förbisetts. Bara för att den är en inaktiv komponent, betyder inte att den är mindre viktig för battericellens prestation. Trender idag pekar mot en enorm tillväxt inom elbils-industrin, och med det även litium-jon batteriseparatorns marknad. Det är för att litium-jon batteriet är det batteriet som vanligen används kommersiellt idag i elbilar. I en av de två stora industriella tillverkningsprocesserna används olja för att åstadkomma en porös film. Denna studie syftar på att utvärdera olika oljors interaktion med polymeren i denna tillverkningsprocess. Eftersom de flesta batteriseparator-industrier idag använder paraffinrik olja så testas oljor med olika mycket naftalensikt innehåll för att hitta korrelationer mellan oljornas egenskaper och kristalliniteten eller porositeten hos filmerna. Inga korrelationer för porositeten eller kristalliniteten kunde göras till oljornas egenskaper. Bilderna tagna med SEM var ej tillräckligt förstorade för att kunna studera vare sig porstorleken eller porstrukturen hos filmerna. För framtida studier rekommenderas att samla in mer data för att kunna utskilja ”outliers” i datan, för att erhålla mer korrekta värden. Metodiken måste även verifieras för att säkerställa att proceduren är reproducerbar. För att studera porerna och porstrukturen, borde en FE-SEM användas för att få mer förstorade bilder med bättre kvalité på filmernas yta.

This thesis deals with the development and current issues of Li-ion and Li-S accumulators, especially the separators. In the theoretical part is described history of Li-ion batteries, their properties and materials for the positive electrode. Li-S batteries and their problems are also described in this diploma thesis. In the practical part, electrochemical methods were described, and several separator samples with various modifications were created. These samples were then photographed using an SEM electron microscope and evaluated using electrochemical methods.

Nanofibrous separators use in lithium-ion batteries brings many advantages. In contrast to contemporary used commercial separators, nanofibrous ones exhibit higher temperature resistance,ionic conductivity and higher electrolyte uptake. Better ionic conductivity is ensured by porous structure and large specific surface. Fibers creates channels for the ionic species motion. Amorphous texture of nanofibers allows quick lithium ionic species motion within the polymeric matrix of separator. Furthermore, these separators exhibit higher volume of uptaken electrolyte. Further advantage of electrospinned nanofibrous separators are both high porosity and chemical stability.

Le polymère poreux (PM) associe les avantages double des matériaux poreux et des polymères, ayant la structure unique de pore, la porosité supérieure et la densité inférieure, ce qui possède une valeur d’application importante dans les domaines de l'adsorption, le soutien de catalyseur, le séparateur de batterie, la filtration, etc. Actuellement, il existe plusieurs façons de préparer le PM, comme la méthode de gabarit, la méthode de séparation de phase, la méthode d'imagerie respiratoire, etc. Chacune des méthodes ci-dessus existe ses propres avantages, mais la préparation à grande échelle de PM à structure de pore contrôlable et aux fonctions spécifiques est toujours un objectif à long terme sur le domaine et l'un des principaux objectifs de ce mémoire. La co-extrusion de microcouche est une méthode pour produire de façon efficace et successive des polymères avec des structures de couches alternées, ayant les avantages de haute efficacité et faible coût. Par conséquent, sur les exigences structurelles de PM de l’application spécifique, ce mémoire a conçu le PM avec une structure spécifique et une co-extrusion de microcouche de manière créative combinée avec la méthode traditionnelle de préparation de PM (méthode de gabarit, méthode de séparation de phase), en combinant les avantages des deux méthodes, les PM avec une structure de pore idéale peuvent être préparés en grande quantité et l’on peut également explorer son application dans les séparateurs de batteries au lithium-ion et l'adsorption d'hydrocarbures aromatiques polycycliques.Le plus important, dans la deuxième partie de cet essai, se trouve que la simulation micro-numérique est utilisée pour étudier le transport et le dépôt de particules dans des milieux poreux pour explorer le mécanisme des matériaux poreux dans les domaines de l'adsorption et du séparateur de batterie. Le code de 3D-PTPO (un modèle tridimensionnel de suivi des particules combinant Python® et OpenFOAM®) est utilisé pour étudier le transport et le dépôt de particules colloïdales dans des milieux poreux, l’on adopte trois modèles (colonne, venturi et tube conique) pour représenter différentes formes de matériaux poreux. Les particules sont considérées comme des points matériaux pendant le transport, le volume des particules sera reconstitué et déposé comme partie de la surface du matériau poreux pendant le dépôt, la caractéristique principale de ce code est de considérer l'influence du volume des particules déposées sur la structure des pores, les lignes d'écoulement et le processus du dépôt des autres particules. Les simulations numériques sont d'abord conduites dans des capillaires simples, le travail de chercheurs de Lopez et d’autres est réexaminé en établissant un modèle géométrique tridimensionnel plus réaliste et il explore les mécanismes cachés derrière les règles de transmission et de dépôt. Par la suite, des simulations numériques sont effectuées dans des capillaires convergents-divergents pour étudier la structure des pores et l'effet de nombre Peclet sur le dépôt de particules. Enfin, l’on étudie l’effet double de l'hétérogénéité de surface et de l'hydrodynamique sur le comportement de dépôt de particules
Due to the combination of the advantages of porous media and polymer materials, polymeric porous media possess the properties of controllable porous structure, easily modifiable surface properties, good chemical stability, etc., which make them applicable in a wide range of industrial fields, including adsorption, battery separator, catalyst carrier, filter, energy storage, etc. Although there exist various preparation methods, such as template technique, emulsion method, phase separation method, foaming process, electrospinning, top-down lithographic techniques, breath figure method, etc., the large-scale preparation of polymeric porous media with controllable pore structures and specified functions is still a long-term goal in this field, which is one of the core objectives of this thesis. Therefore, in the first part of the thesis, polymeric porous media are firstly designed based on the specific application requirements. Then the designed polymeric porous media are prepared by the combination of multilayer coextrusion and traditional preparation methods (template technique, phase separation method). This combined preparation method has integrated the advantages of the multilayer coextrusion (continuous process, economic pathway for large-scale fabrication, flexibility of the polymer species, and tunable layer structures) and the template/phase separation method (simple preparation process and tunable pore structure). Afterwards, the applications of the polymeric porous media in polycyclic aromatic hydrocarbons adsorption and lithium-ion battery separator have been investigated.More importantly, in the second part of the thesis, numerical simulations of particle transport and deposition in porous media are carried out to explore the mechanisms that form the theoretical basis for the above applications (adsorption, separation, etc.). Transport and deposition of colloidal particles in porous media are of vital important in other applications such as aquifer remediation, fouling of surfaces, and therapeutic drug delivery. Therefore, it is quite worthy to have a thorough understanding of these processes as well as the dominant mechanisms involved. In this part, the microscale simulations of colloidal particle transport and deposition in porous media are achieved by a novel colloidal particle tracking model, called 3D-PTPO (Three-Dimensional Particle Tracking model by Python® and OpenFOAM®) code. The particles are considered as a mass point during transport in the flow and their volume is reconstructed when they are deposited. The main feature of the code is to take into account the modification of the pore structure and thus the flow streamlines due to deposit. Numerical simulations were firstly carried out in a capillary tube considered as an element of an idealized porous medium composed of capillaries of circular cross sections to revisit the work of Lopez and co-authors by considering a more realistic 3D geometry and also to get the most relevant quantities by capturing the physics underlying the process. Then microscale simulation is approached by representing the elementary pore structure as a capillary tube with converging/diverging geometries (tapered pipe and venturi tube) to explore the influence of the pore geometry and the particle Péclet number (Pe) on particle deposition. Finally, the coupled effects of surface chemical heterogeneity and hydrodynamics on particle deposition in porous media were investigated in a three-dimensional capillary with periodically repeating chemically heterogeneous surfaces

This thesis is completion of whole stage of researches and it is a result of existing need of increase efficiency, utilization rate and service life of lead acid batteries VRLA planned for utilization in hybrid electric vehicles in mode of partial state-of-charge PSoC. During the application of mode PSoC at lead acid battery occurs irreversible sulfation of negative electrodes and thus to loss their charging capability. This phenomenon, according to the latest trend called PCL3, isn´t connected with subsequently referred effects PCL1, PCL2, show up on positive electrodes. Result of this thesis is finding a new types of additives, determine their optimum amount and size in such a way that innovated composition of negative active materials be able to resist sulfation of negative electrode during operation in mode PSoC. Part of the effort to clarify actions ongoing on negative active material and causes non-returnable sulfation electrodes is also monitoring of structural changes electrode active material by using environmental scanning electron microscope, which helped to clarify processes related with loss of capacity in mode PSoC. Special attention during reserches was focused on study of the properties contact layers between collector and electrodes active material and itself active materials lead-acid battery druring exploitation. There were gain new information about influence repeated cycling of (charging, discharging) the critical area of the electrodes. Measurements was carried out on specially prepared experimental electrodes DC Difference Method, this enabled obtain data in situ.

The lead-acid batteries used in hybrid electronic vehicles HEV operate in high-rate mode in a state of partial charge PSoC. It occurs when the degradation mechanisms related to irreversible sulphation and negative electrodes are a limiting factor in the life of lead-acid batteries. The electrode system was applied to experimental pressure cells of different sizes. Exp. cells were subjected to measurement and evaluation of potential negative electrode, a negative active mass resistance, contact resistance of transition collector - the active mass with the evaluation and measurement of pressure fluctuations within four PSoC runs.

Presented work investigates the problem of secondary lithium-ion cells and the different available cathode materials. We have prepared samples of LiFePO4 with the addition of different kinds of carbon materials such as Super P, Vulcan and expanded graphite. We have always created the sample with and without surfactant. Developed samples were compared by measuring electrochemical methods (cyclic voltammetry, charge and discharge cycles and impedance spectroscopy). We also modeled the three-point cell for measuring electrochemical electrode materials.

Three mathematical models, two of primary alkaline battery cathode discharge, and one of primary alkaline battery discharge, are developed, presented, solved and investigated in this thesis. The primary aim of this work is to improve our understanding of the complex, interrelated and nonlinear processes that occur within primary alkaline batteries during discharge. We use perturbation techniques and Laplace transforms to analyse and simplify an existing model of primary alkaline battery cathode under galvanostatic discharge. The process highlights key phenomena, and removes those phenomena that have very little effect on discharge from the model. We find that electrolyte variation within Electrolytic Manganese Dioxide (EMD) particles is negligible, but proton diffusion within EMD crystals is important. The simplification process results in a significant reduction in the number of model equations, and greatly decreases the computational overhead of the numerical simulation software. In addition, the model results based on this simplified framework compare well with available experimental data. The second model of the primary alkaline battery cathode discharge simulates step potential electrochemical spectroscopy discharges, and is used to improve our understanding of the multi-reaction nature of the reduction of EMD. We find that a single-reaction framework is able to simulate multi-reaction behaviour through the use of a nonlinear ion-ion interaction term. The third model simulates the full primary alkaline battery system, and accounts for the precipitation of zinc oxide within the separator (and other regions), and subsequent internal short circuit through this phase. It was found that an internal short circuit is created at the beginning of discharge, and this self-discharge may be exacerbated by discharging the cell intermittently. We find that using a thicker separator paper is a very effective way of minimising self-discharge behaviour. The equations describing the three models are solved numerically in MATLABR, using three pieces of numerical simulation software. They provide a flexible and powerful set of primary alkaline battery discharge prediction tools, that leverage the simplified model framework, allowing them to be easily run on a desktop PC.

Three mathematical models, two of primary alkaline battery cathode discharge, and one of primary alkaline battery discharge, are developed, presented, solved and investigated in this thesis. The primary aim of this work is to improve our understanding of the complex, interrelated and nonlinear processes that occur within primary alkaline batteries during discharge. We use perturbation techniques and Laplace transforms to analyse and simplify an existing model of primary alkaline battery cathode under galvanostatic discharge. The process highlights key phenomena, and removes those phenomena that have very little effect on discharge from the model. We find that electrolyte variation within Electrolytic Manganese Dioxide (EMD) particles is negligible, but proton diffusion within EMD crystals is important. The simplification process results in a significant reduction in the number of model equations, and greatly decreases the computational overhead of the numerical simulation software. In addition, the model results based on this simplified framework compare well with available experimental data. The second model of the primary alkaline battery cathode discharge simulates step potential electrochemical spectroscopy discharges, and is used to improve our understanding of the multi-reaction nature of the reduction of EMD. We find that a single-reaction framework is able to simulate multi-reaction behaviour through the use of a nonlinear ion-ion interaction term. The third model simulates the full primary alkaline battery system, and accounts for the precipitation of zinc oxide within the separator (and other regions), and subsequent internal short circuit through this phase. It was found that an internal short circuit is created at the beginning of discharge, and this self-discharge may be exacerbated by discharging the cell intermittently. We find that using a thicker separator paper is a very effective way of minimising self-discharge behaviour. The equations describing the three models are solved numerically in MATLABR, using three pieces of numerical simulation software. They provide a flexible and powerful set of primary alkaline battery discharge prediction tools, that leverage the simplified model framework, allowing them to be easily run on a desktop PC.

The shortage of energy sources and the global climate change crisis have become critical issues. Solving these problems with clean and sustainable energy sources (solar, wind, tidal, and so on) is a promising solution. In this regard, energy storage techniques need to be implemented to tackle with the intermittent nature of the sustainable energies. Among the next-generation energy storage systems, lithium sulfur batteries has gained prominence due to the low cost, high theoretical specific-capacity of sulfur. Extensive research has been conducted on this battery system. Nevertheless, several issues including the “shuttle effect” and the growth of lithium dendrites still exist, which could cause rapid capacity loss and safety hazards. Several methods are proposed to tackle the challenges in this dissertation, including cathode engineering, interlayer design, and lithium metal anode protection. An asymmetric cathode structure is first developed by a non-solvent induced phase separation (NIPS) method. The asymmetric cathode comprises a nanoporous matrix and ultrathin and dense top layer. The top-layer is a desired barrier to block polysulfides transport, while the sublayer threaded with cationic networks facilitate Li-ions transport and sulfur conversions. In addition, a conformal and ultrathin microporous membrane is electrodeposited on the whole surface of the cathode by an electropolymerization method. This strategy creates a close system, which greatly blocks the LiPS leakage and improves the sulfur utilization. A polycarbazole-type interlayer is deposited on the polypropylene (PP) separator via an electropolymerization method. This interlayer is ultrathin, continuous, and microporous, which defines the critical properties of an ideal interlayer that is required for advanced Li–S batteries. Meanwhile, a self-assembled 2D MXene based interlayer was prepared to offer abundant porosity, dual absorption sites, and desirable electrical conductivity for Li-ions transport and polysulfides conversions. A new 2D COF-on-MXene heterostructures is prepared as the lithium anode host. The 2D heterostructures has hierarchical porosity, conductive frameworks, and lithiophilic sites. When utilized as a lithium host, the MXene@COF host can efficiently regulate the Li+ diffusion, and reduce the nucleation and deposition overpotential, which results in a dendrite-free and safer Li–S battery.

碩士
國立成功大學
化學工程學系
106
We utilized the fluoro-based polymer, PVdF-co-HFP to prepare the separators for ion batteries by casting-film and electrospinning membrane. In the part of casting-film, we tried to mix the PVdF-co-HFP and ionic liquid with different ratios. According to the SEM analysis, it would be found that the addition of ionic liquid could increase the porous structure; on the other side, we added the cross-linker 1,3-Diaminopropane(DAP) into the solution of polymer, and then prepare the separators by the casting-film and electrospinning membrane. We tested the physical properties of our separators by SEM、FT-IR、TGA、DSC analysis, and the electrochemical properties by AC impedance analysis. From the SEM analysis, the electrospinning membrane of PVdF-co-HFP could helpfully increase the mobility since the porous structure. It also could be observed the microphase separation after soaked in the ionic liquid. According to the TGA、DSC analysis, we found that after the addition of cross-linker, the mechanical properties promote with the increasing of the ratio of cross-linker without obvious difference of thermal properties. In the electrochemical property analysis, the uptake of electrolyte decreased with the increasing of the ratio of cross-linker after the membrane soaked in the ionic liquid; in the AC impedance analysis, it also shows the same tendency of the ionic conductivity. It explained the influence of the cross-linker for the membrane structure, but the ionic conductivities were still lower than the PVdF-co-HFP separators in lithium-ion batteries. As for the compatibility of aluminum-ion battery, there was a concern about the reactivity for the electrolyte which is wildly used in aluminum-ion battery. It is inferred that if we would like to apply our PVdF-co-HFP electrospinning membrane to aluminum-ion batteries, it is necessary to modify the surface structure of polymer in order to improve the compatibility of aluminum-ion battery.

The energy source shortage has become a severe issue, and solving the problem with renewable and sustainable energy is the primary trend. Among the new generation energy storage, lithium-sulfur (Li-S) battery stands out for its low cost, high theoretical capacity (1,675 mAh g-1), and environmentally friendly properties. Intensive researches have been focusing on this system and significant improvement has been achieved. However, several problems still need to be resolved for its practical application, especially for the “shuttle effect” issue coming from the dissolved intermediate polysulfides, which could cause rapid capacity decay and low Coulombic efficiency (CE). Several methods are proposed to eliminate this issue, including using interlayers, modifying separators, and protecting the lithium anode. A carbon interlayer is first introduced to compare the function of the graphene and carbon nanotubes (CNTs), while the CNTs performs better with its higher conductivity and 3D network structure. The following study is conducted based on this finding. A more efficient method is to modify the separator with functional materials. 1) The dissolved polysulfide (Sn2-) could be repelled by electrostatic forces. With the Poly (styrene sulfonate) (PSS), the separator could function as an anion barrier to the intermediate polysulfides. 2D ultra-thin zinc benzimidazolate coordination polymer has the OH- functional groups and works with the same mechanism. 2) A novel covalent organic framework (COF) has a relatively small pore size, which can block the polysulfide and restrain them at the cathode side. 3) Metal-organic framework (MOF) materials have the adjustable pore size and structure, which can absorb and trap polysulfides within their cavities. Moreover, the dense stacking of the MOF particles creates a physical blocking for the polysulfides, which efficiently suppresses the diffusion process. Protection of the lithium surface directly with an artificial layer or a solid electrolyte interphase (SEI) can inhibit the polysulfide deposition and suppress the lithium dendrite. A polyvinylidene difluoride (PVDF) membrane is used as an artificial film on lithium anode, which could greatly enhance the battery cyclability and CE. Future work will be conducted based on this concept, especially building an artificial SEI.

碩士
中國文化大學
化學工程與材料工程學系奈米材料碩士班
103
A separator is an important element in a lithium-ion battery, which is used for determining the battery performance. The demand for lithium-ion batteries has significantly increased due to the rapid development of electronic products, thus triggering more research on the material applications of separators. This experiment used five basis weights of separator paper (12〖g/m^2〗, 14〖g/m^2〗, 16〖g/m^2〗, 18〖g/m^2〗, and 20〖g/m^2〗) in four different ratios of long to short fibers at 100:0, 10:90, 20:80, and 30:70 with a freeness of 300 ml using northern bleached kraft pulp (NBKP) together with laubhǒlxer bleached kraft pulp (LBKP). Using the handsheet (wet laid non-woven) technique with steps such as beating, screening, pressing, and drying, separators made of polyethylene were compared to those previously mentioned to explore their advantages and disadvantages. The study found that the fiber separator with a basis weight of 16 g or more, made from natural fiber NBKP mixed with LBKP, has excellent mechanical strength, well interwoven pores, and a unique nanopore due to its excellent resistance, electrolyte wettability, thermal properties (pyrolysis and heat shrink), smoothness, etc. Compared with commercially available polyethylene separators, natural fibers can become lithium-ion battery separators if the pores are slightly reduced.

碩士
亞東技術學院
纖維與材料應用產業研發碩士專班
103
As technology has advanced, miniaturized electronic products have become dominant in the market. Although battery sizes have been reduced, the demand for large battery capacity increases. Battery explosions have frequently occurred in recent years, primarily because thermal runaway can occur on the battery separator, causing short circuits and explosions. Such explosions occur during the power generation process, and are caused by the mechanical failure of separators that have undergone nanocoating and surface treatment; thus, examining this phenomenon is crucial. Relevant studies were reviewed that detailed the explosions resulting from static electricity or friction in batteries in which various nanomaterials were integrated with nonwoven fabrics. Common metal powders such as Ag, Au, Pt, Cu, Fe, and Zn were investigated in this study in addition to the novel nanomaterial graphene and its derivatives, which have been prevalently applied in recently developed battery electrodes. Moreover, because the upper and lower explosive limits of the evaluated materials are influenced by humidity, various humidity levels were applied to examine the explosions in batteries after nanomaterials were integrated with nonwoven fabrics. The findings should serve as a crucial reference regarding industrial safety in nanopractical production plants.

碩士
國立屏東科技大學
材料工程研究所
106
In recent years, there has been a growing demand for batteries for power supply due to the booming development of portable electronic products and electric transport equipment. , Lithium secondary battery which has the advantages of high energy, high power, light weight, long life and good environmental protection, is currently the best mobile power supply. The key issue of lithium battery technology lies in the safety of lithium batteries, but also the highest proportion of the cost component is the separator. The main function of the separator is when the battery abnormal temperature rises, the battery can stop the charge-discharge reaction to avoid the battery explosion caused by overheating. In this dissertation, the coating method was used to coat different BX-100, BX-500 and BX-900 solutions on different substrates. After heat treatment at different temperatures, surface structure analysis and characterization were carried out as the evaluation of a separator. And then, the above-mentioned separators, using button-type lithium battery assembly, assembled into a button-type lithium battery to measure its electrical properties. The results show that BX-100, BX-500 and BX-900 solution after heat treatment at different temperatures have different ability of pores filling, which will affect the performance of button-type lithium battery.

碩士
長庚大學
化工與材料工程學系
106
Lithium oxygen battery change the cathode into a air-breathing structure, and use the oxygen as the reactor in the cathode. The operation leads that Lithium air battery provides higher theoretical voltage. Also the theoretical specific energy reaches up to 12 kWh/kg, which is close to the specific energy of the fossil oil, 13 kWh/kg. Among the components in the Lithium oxygen battery, the separator and structure of the cathode have tremendous effect on the efficiency of charging/discharging, impedance and max power rate. The cathode usually decides the charge/discharge efficiency of the whole battery, while separator affects the impedance. On the cathode side, this research will focus on how adding microporous layer and Pt catalyst onto the cathode will effect the cycle life, impedance and max power rate. After adding the microporous layer and Pt catalyst, the max power rate rise from 2.91 mW/cm2 to 4.52 mW/cm2, the ohm impedance reduced due the good conductivity of the Pt particles, while the electrical chemical impedance raised a little bit. The cycle life extended from 40 hours to 250 hours, also the over potential on the first cycle reduce from 1.4V to 1.0V. In order to improve the moisture prevention of the battery, this research changed the test model from the bottle cell to the MTI model. MTI model has 1/16 stainless steel gas tube and is also made of stainless steel, these advantages can stop the moisture from going into the battery’s materials. Under the circumstances that cathode has microporous layer and Pt catalyst on different side of it, the cycle life extended from 250 hours to 1240 hours. On the separator side, the research hopes improve the over potential, cycle life, impedance, open circuit voltage and max power rate via changing the separators into glass fibers or Celgrad polymer commercial separators. The result showed that after changing the separator from glass fiber into Celgard separator, the ohm impedance decreased a little bit, while the electrical chemical impedance was large at first but still decreased as time goes by. The cycle life increase from 1240 hours to 1330 hours due to the smaller pores on the Celgard membrane comparing to the glass fiber, which prevents moisture from penetrating to the lithium metal also allowing lithium ion flows. But the over potential and max power rate didn’t change a lot.

碩士
南臺科技大學
工業管理研究所
105
Lithium battery has been widely used in industry and 3C commercial devices owning to its remarkable properties such as high energy, high power efficiency, long cycle life, no memory effect, low electrical self-discharge, and good to the environment. In addition, lithium ionic battery research has been recently attracted to great attention in renewable energy techniques to energy crisis and environmental issues. Among the relative studies, separator acted as a key material of the lithium battery is also drawn great concern. In this study, Causes & Effects Chart was applied to find out the key factors that affecting the quality characteristics of the gurley and the thickness of the membrane which are the in the middle process of separator manufacture. Moreover, Central Composite Design (CCD), one method of Response Surface Methodology (RSM), was employed to optimize the process parameters in order to improve the production yield and lower the cost. The results showed that the average of membrane gurley (in second) is improved from 10.8s to 9.27s where its target is 9s, and its standard deviation is reduced from 0.66s to 0.56s. The average of membrane thickness (in μm) is improved from 20.43μm to 20.02μm with the target of 20μm, and its standard deviation is also shrank from 0.18μm to 0.12μm.

The development of the new cathode and anode materials of Lithium-Ion Batteries (LIBs) with high energy density and outstanding electrochemical performance is of substantial technological importance due to the ever-increasing demand for economic and efficient energy storage system. Because of the abundance of element sulfur and high theoretical energy density, Lithium-Sulfur (Li-S) batteries have become one of the most promising candidates for the next-generation energy storage system. However, the shuttling effect of electrolyte-soluble polysulfides severely impedes the cell performance and commercialization of Li-S batteries, and significant progress have been made to mitigate this shuttle effect in the past two decades. Coordination polymers (CPs) or Metal-organic Frameworks (MOFs) have been attracted much attention by virtue of their controllable porosity, nanometer cavity sizes and high surface areas, which supposed to be an available material in suppressing polysulfide migration. In this thesis, we investigate different mechanisms of mitigating polysulfide diffusion by applying a layer of MOFs (including Y-FTZB, ZIF-7, ZIF-8, and HKUST-1) on a separator. We also fabricate a new free-standing 2D coordination polymer Zn2(Benzimidazolate)2(OH)2 with rich hydroxyl (OH-) groups by using a simple, scalable and low cost method at air/water surface. Our results suggest that the chemical stability, the cluster morphology and the surface function groups of MOFs shows a greater impact on minimizing the shuttling effect in Li-S batteries, other than the internal cavity size in MOFs. Meanwhile, the new design of 2D coordination polymer efficiently mitigate the shuttling effect in Li-S battery resulting in a largely promotion of the battery capacity to 1407 mAh g-1 at 0.1 C and excellent cycling performance (capacity retention of 98% after 200 cycles at 0.25C). Such excellent cell performance is mainly owing to the fancying physical and chemical structure controllability of MOFs or CPs, which has substantial potential for future commercial utilizations.