Thermal modelling of commercial lithium-ion batteries

The accelerating adoption of electrical technologies in vehicles over the recent years has led to an increase in the research on electrochemical energy storage systems, which are among the key elements in these technologies. The application of electrochemical energy storage systems for instance in hybrid electrical vehicles (HEVs) or hybrid mobile working machines allows tolerating high power peaks, leading to an opportunity to downsize the internal combustion engine and reduce fuel consumption, and therefore, CO2 and other emissions. Further, the application of electrochemical energy storage systems provides an option of kinetic and potential energy recuperation. Presently, the lithium-ion (Li-ion) battery is considered the most suitable electrochemical energy storage type in HEVs and hybrid mobile working machines. However, the intensive operating cycle produces high heat losses in the Li-ion battery, which increase its operating temperature. The Li-ion battery operation at high temperatures accelerates the ageing of the battery, and in the worst case, may lead to a thermal runaway and fire. Therefore, an appropriate Li-ion battery cooling system should be provided for the temperature control in applications such as HEVs and mobile working machines. In this doctoral dissertation, methods are presented to set up a thermal model of a single Li-ion cell and a more complex battery module, which can be used if full information about the battery chemistry is not available. In addition, a non-destructive method is developed for the cell thermal characterization, which allows to measure the thermal parameters at different states of charge and in different points of cell surface. The proposed models and the cell thermal characterization method have been verified by experimental measurements. The minimization of high thermal non-uniformity, which was detected in the pouch cell during its operation with a high C-rate current, was analysed by applying a simplified pouch cell 3D thermal model. In the analysis, heat pipes were incorporated into the pouch cell cooling system, and an optimization algorithm was generated for the estimation of the optimalplacement of heat pipes in the pouch cell cooling system. An analysis of the application of heat pipes to the pouch cell cooling system shows that heat pipes significantly decrease the temperature non-uniformity on the cell surface, and therefore, heat pipes were recommended for the enhancement of the pouch cell cooling system.

Novel approaches to the synthesis and treatment of cathode materials for lithium-ion batteries

Nous avons mis au point une approche novatrice pour la synthèse d’un matériau de cathode pour les piles lithium-ion basée sur la décomposition thermique de l’urée. Les hydroxydes de métal mixte (NixMnxCo(1-2x)(OH)2) ont été préparés (x = 0.00 à 0.50) et subséquemment utilisés comme précurseurs à la préparation de l’oxyde de métal mixte (LiNixMnxCo(1-2x)O2). Ces matériaux, ainsi que le phosphate de fer lithié (LiFePO4), sont pressentis comme matériaux de cathode commerciaux pour la prochaine génération de piles lithium-ion. Nous avons également développé un nouveau traitement post-synthèse afin d’améliorer la morphologie des hydroxydes. L’originalité de l’approche basée sur la décomposition thermique de l’urée réside dans l’utilisation inédite des hydroxydes comme précurseurs à la préparation d’oxydes de lithium mixtes par l’intermédiaire d’une technique de précipitation uniforme. De plus, nous proposons de nouvelles techniques de traitement s’adressant aux méthodes de synthèses traditionnelles. Les résultats obtenus par ces deux méthodes sont résumés dans deux articles soumis à des revues scientifiques. Tous les matériaux produits lors de cette recherche ont été analysés par diffraction des rayons X (DRX), microscope électronique à balayage (MEB), analyse thermique gravimétrique (ATG) et ont été caractérisés électrochimiquement. La performance électrochimique (nombre de cycles vs capacité) des matériaux de cathode a été conduite en mode galvanostatique.

A detailed study of the lithiation of iron phosphate as well as the development of a novel synthesis of lithium iron silicate as cathode material for lithium-ion batteries

Dans cette thèse nous démontrons le travail fait sur deux matériaux de cathodes pour les piles lithium-ion. Dans la première partie, nous avons préparé du phosphate de fer lithié (LiFePO4) par deux méthodes de lithiation présentées dans la littérature qui utilisent du phosphate de fer (FePO4) amorphe comme précurseur. Pour les deux méthodes, le produit obtenu à chaque étape de la synthèse a été analysé par la spectroscopie Mössbauer ainsi que par diffraction des rayons X (DRX) pour mieux comprendre le mécanisme de la réaction. Les résultats de ces analyses ont été publiés dans Journal of Power Sources. Le deuxième matériau de cathode qui a été étudié est le silicate de fer lithié (Li2FeSiO4). Une nouvelle méthode de synthèse a été développée pour obtenir le silicate de fer lithié en utilisant des produits chimiques peu couteux ainsi que de l’équipement de laboratoire de base. Le matériau a été obtenu par une synthèse à l’état solide. Les performances électrochimiques ont été obtenues après une étape de broyage et un dépôt d’une couche de carbone. Un essai a été fait pour synthétiser une version substituée du silicate de fer lithié dans le but d’augmenter les performances électrochimiques de ce matériau.

Low cost synthesis of cathode and anode materials for lithium-ion batteries

Dans cette thèse, nous démontrons des travaux sur la synthèse à faible coût des matériaux de cathode et l'anode pour les piles lithium-ion. Pour les cathodes, nous avons utilisé des précurseurs à faible coût pour préparer LiFePO4 et LiFe0.3Mn0.7PO4 en utilisant une méthode hydrothermale. Tout d'abord, des matériaux composites (LiFePO4/C) ont été synthétisés à partir d'un précurseur de Fe2O3 par une procédé hydrothermique pour faire LiFePO4(OH) dans une première étape suivie d'une calcination rapide pour le revêtement de carbone. Deuxièmement, LiFePO4 avec une bonne cristallinité et une grande pureté a été synthétisé en une seule étape, avec Fe2O3 par voie hydrothermale. Troisièmement, LiFe0.3Mn0.7PO4 a été préparé en utilisant Fe2O3 et MnO comme des précurseurs de bas coûts au sein d'une méthode hydrothermale synthétique. Pour les matériaux d'anode, nous avons nos efforts concentré sur un matériau d'anode à faible coût α-Fe2O3 avec deux types de synthèse hydrothermales, une a base de micro-ondes (MAH) l’autre plus conventionnelles (CH). La nouveauté de cette thèse est que pour la première fois le LiFePO4 a été préparé par une méthode hydrothermale en utilisant un précurseur Fe3+ (Fe2O3). Le Fe2O3 est un précurseur à faible coût et en combinant ses coûts avec les conditions de synthèse à basse température nous avons réalisé une réduction considérable des coûts de production pour le LiFePO4, menant ainsi à une meilleure commercialisation du LiFePO4 comme matériaux de cathode dans les piles lithium-ion. Par cette méthode de préparation, le LiFePO4/C procure une capacité de décharge et une stabilité de cycle accrue par rapport une synthétisation par la méthode à l'état solide pour les mêmes précurseurs Les résultats sont résumés dans deux articles qui ont été récemment soumis dans des revues scientifiques.

Microwave-assisted hydrothermal synthesis of magnetite nanoparticles with potential use as anode in lithium ion batteries

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

On the well-posedness of a mathematical model for lithium-ion batteries.

We discuss the well-posedness of a mathematical model that is used in the literature for the simulation of lithium-ion batteries. First, a mathematical model based on a macrohomogeneous approach is presented, following previous work. Then it is shown, from a physical and a mathematical point of view, that a boundary condition widely used in the literature is not correct. Although the errors could be just sign typos (which can be explained as carelessness in the use of d/dx versus d/dn, with n the outward unit vector) and authors using this model probably use the correct boundary condition when they solve it in order to do simulations, readers should be aware of the right choice. Therefore, the deduction of the correct boundary condition is done here, and a mathematical study of the well-posedness of the corresponding problem is presented.

Co3O4 nanostructures with a high rate performance as anode materials for lithium-ion batteries, prepared via book-like cobalt-organic frameworks

The self-assembly of cobalt coordination frameworks (Co-CPs) with a two-dimensional morphology is demonstrated by a solvothermal method. The morphology of the Co-CPs has been controlled by various solvothermal conditions. The two-dimensional nanostructures agglomerated by Co3O4 nanoparticles remained after the pyrolysis of the Co-CPs. The as-synthesized Co3O4 anode material is characterized by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and galvanostatic charge-discharge measurements. The morphology of Co3O4 plays a crucial role in the high performance anode materials for lithium batteries. The Co3O4 nanoparticles with opened-book morphology deliver a high capacity of 597 mA h g-1 after 50 cycles at a current rate of 800 mA g-1. The opened-book morphology of Co3O4 provides efficient lithium ion diffusion tunnels and increases the electrolyte/Co3O4 contact/interfacial area. At a relatively high current rate of 1200 mA g-1, Co3O4 with opened-book morphology delivers an excellent rate capability of 574 mA h g-1.

Porous tin film synthesized by electrodeposition and the electrochemical performance for lithium-ion batteries

Porous tin films as anode for lithium-ion batteries are electrodeposited on graphite paper. Homogeneous tin films with significant void space accommodate the volume change during tin lithiation/delithiation. Through adjusting the electrodeposition currents and time, the morphologies and void space of tin films on graphite paper are controllable. At fixed electrodeposition current densities, the prolonged electrodeposition time plays the role in growing big tin particles and resulting the disappearance of void space among tin particles. The increased electrodeposition current plays the role to increase the quantity of tin seeds in thickness of tin film, and the void space among tin particles remains but the thick film limits its electrochemical performance. The tin films electrodeposited at an optimized current densities and for an optimized electrodeposition time, present the best electrochemical performance, because the tin nanoparticles are well dispersed on graphite substrate including void space. The tin film electrodeposited at 0.2 A cm-2 for 2 min shows the capacity of 1.0 mAh cm-2 after 50 charge/discharge cycles. The void space of tin film is very important for the best capacity and cyclic ability. The metallic tin film produced at 0.4 A cm-2 for 3 min remains the uniform and microporous structure after charge/discharge for 50 cycles.

Tin oxide based composites derived using electrostatic spray deposition technique as anodes for lithium-ion batteries

Recent advances in the electric & hybrid electric vehicles and rapid developments in the electronic devices have increased the demand for high power and high energy density lithium ion batteries. Graphite (theoretical specific capacity: 372 mAh/g) used in commercial anodes cannot meet these demands. Amorphous SnO2 anodes (theoretical specific capacity: 781 mAh/g) have been proposed as alternative anode materials. But these materials have poor conductivity, undergo a large volume change during charging and discharging, large irreversible capacity loss leading to poor cycle performances. To solve the issues related to SnO2 anodes, we propose to synthesize porous SnO2 composites using electrostatic spray deposition technique. First, porous SnO2/CNT composites were fabricated and the effects of the deposition temperature (200, 250, 300 °C) & CNT content (10, 20, 30, 40 wt %) on the electrochemical performance of the anodes were studied. Compared to pure SnO2 and pure CNT, the composite materials as anodes showed better discharge capacity and cyclability. 30 wt% CNT content and 250 °C deposition temperature were found to be the optimal conditions with regard to energy capacity whereas the sample with 20% CNT deposited at 250 °C exhibited good capacity retention. This can be ascribed to the porous nature of the anodes and the improvement in the conductivity by the addition of CNT. Electrochemical impedance spectroscopy studies were carried out to study in detail the change in the surface film resistance with cycling. By fitting EIS data to an equivalent circuit model, the values of the circuit components, which represent surface film resistance, were obtained. The higher the CNT content in the composite, lower the change in surface film resistance at certain voltage upon cycling. The surface resistance increased with the depth of discharge and decreased slightly at fully lithiated state. Graphene was also added to improve the performance of pure SnO2 anodes. The composites heated at 280 °C showed better energy capacity and energy density. The specific capacities of as deposited and post heat-treated samples were 534 and 737 mAh/g after 70 cycles. At the 70th cycle, the energy density of the composites at 195 °C and 280 °C were 1240 and 1760 Wh/kg, respectively, which are much higher than the commercially used graphite electrodes (37.2–74.4 Wh/kg). Both SnO2/CNTand SnO2/grapheme based composites with improved energy densities and capacities than pure SnO2 can make a significant impact on the development of new batteries for electric vehicles and portable electronics applications.

Facile synthesis of copper-manganese spinel anodes with high capacity and cycling performance for lithium-ion batteries

Copper-manganese spinel containing anodes were synthesized by a facile sol-gel method and evaluated in lithium-ion battery applications for the first time. The synergistic effects between copper-manganese and the aqueous binder (sodium carboxymethyl cellulose) provided a high specific capacity and excellent cycling performance. It was found that the specific capacity of the copper-manganese spinel remained at 608 mAh g⁻¹ after 100 cycles at a current density of 200 mA g⁻¹. Furthermore, a relatively high reversible capacity of 278 mAh g⁻¹ could be obtained at a current density of 2000 mA g⁻¹, indicating a good rate capability. These studies suggest that copper-manganese spinel is a promising material for lithium-ion battery applications due to a combination of good electrochemical performance and low cost.

A NOVEL MODELING AND STATE OF CHARGE ESTIMATION SCHEME FOR LITHIUM-ION BATTERIES

Lithium Ion (Li-Ion) batteries have got attention in recent decades because of their undisputable advantages over other types of batteries. They are used in so many our devices which we need in our daily life such as cell phones, lap top computers, cameras, and so many electronic devices. They also are being used in smart grids technology, stand-alone wind and solar systems, Hybrid Electric Vehicles (HEV), and Plug in Hybrid Electric Vehicles (PHEV). Despite the rapid increase in the use of Lit-ion batteries, the existence of limited battery models also inadequate and very complex models developed by chemists is the lack of useful models a significant matter. A battery management system (BMS) aims to optimize the use of the battery, making the whole system more reliable, durable and cost effective. Perhaps the most important function of the BMS is to provide an estimate of the State of Charge (SOC). SOC is the ratio of available ampere-hour (Ah) in the battery to the total Ah of a fully charged battery. The Open Circuit Voltage (OCV) of a fully relaxed battery has an approximate one-to-one relationship with the SOC. Therefore, if this voltage is known, the SOC can be found. However, the relaxed OCV can only be measured when the battery is relaxed and the internal battery chemistry has reached equilibrium. This thesis focuses on Li-ion battery cell modelling and SOC estimation. In particular, the thesis, introduces a simple but comprehensive model for the battery and a novel on-line, accurate and fast SOC estimation algorithm for the primary purpose of use in electric and hybrid-electric vehicles, and microgrid systems. The thesis aims to (i) form a baseline characterization for dynamic modeling; (ii) provide a tool for use in state-of-charge estimation. The proposed modelling and SOC estimation schemes are validated through comprehensive simulation and experimental results.

Graphite for lithium-ion batteries: mineral analysis and global Material Flow Analysis

Graphite is a mineral commodity used as anode for lithium-ion batteries (LIBs), and its global demand is doomed to increase significantly in the future due to the forecasted global market demand of electric vehicles. Currently, the graphite used to produce LIBs is a mix of synthetic and natural graphite. The first one is produced by the crystallization of petroleum by-products and the second comes from mining, which causes threats related to pollution, social acceptance, and health. This MSc work has the objective of determining compositional and textural characteristics of natural, synthetic, and recycled graphite by using SEM-EDS, XRF, XRD, and TEM analytical techniques and couple these data with dynamic Material Flow Analysis (MFA) models, which have the objective of predicting the future global use of graphite in order to test the hypothesis that natural graphite will no longer be used in the LIB market globally. The mineral analyses reveal that the synthetic graphite samples contain less impurities than the natural graphite, which has a rolled internal structure similar to the recycled one. However, recycled graphite shows fractures and discontinuities of the graphene layers caused by the recycling process, but its rolled internal structure can help the Li-ions’ migration through the fractures. Three dynamic MFA studies have been conducted to test distinct scenarios that include graphite recycling in the period 2022-2050 and it emerges that - irrespective of any considered scenario - there will be an increase of synthetic graphite demand, caused by the limited stocks of battery scrap available. Hence, I conclude that both natural and recycled graphite is doomed to be used in the LIB market in the future, at least until the year 2050 when the stock of recycled graphite production will be enough to supersede natural graphite. In addition, some new improvement in the dismantling and recycling processes are necessary to improve the quality of recycled graphite.

Lithium ion rechargeable batteries: State of the art and future needs of microscopic theoretical models and simulations

This review deals with the recent developments and present status of the theoretical models for the simulation of the performance of lithium ion batteries. Preceded by a description of the main materials used for each of the components of a battery -anode, cathode and separator- and how material characteristics affect battery performance, a description of the main theoretical models describing the operation and performance of a battery are presented. The influence of the most relevant parameters of the models, such as boundary conditions, geometry and material characteristics are discussed. Finally, suggestions for future work are proposed.

Cellulose based Lithium ion polymer electrolytes for Lithium batteries

The separator membrane in batteries and fuel cells is of crucial importance for the function of these devices. In lithium ion batteries the separator membrane as well as the polymer matrix of the electrodes consists of polymer electrolytes which are lithium ion conductors. To overcome the disadvantage of currently used polymer electrolytes which are highly swollen with liquids and thus mechanically and electrochemically unstable, the goal of this work is a new generation of solid polymer electrolytes with a rigid backbone and a soft side chain structure. Moreover the novel material should be based on cheap substrates and its synthesis should not be complicated aiming at low overall costs. The new materials are based on hydroxypropylcellulose and oligoethyleneoxide derivatives as starting materials. The grafting of the oligoethyleneoxide side chains onto the cellulose was carried out following two synthetic methods. One is based on a bromide derivative and another based on p-toluolsulfonyl as a leaving group. The side chain reagents were prepared form tri(ethylene glycol) monoethyl ether. In order to improve the mechanical properties the materials were crosslinked. Two different conceptions have been engaged based on either urethane chemistry or photosensitive dimethyl-maleinimide derivatives. PEO - graft - cellulose derivatives with a high degree of substitution between 2,9 and 3,0 were blended with lithium trifluoromethane-sulfonate, lithium bis(trifluorosulfone)imide and lithium tetrafluoroborate. The molar ratios were in the range from 0,02 to 0,2 [Li]/[O]. The products have been characterized with nuclear magnetic resonance (NMR), gel permeation chromatography (GPC) and laserlight scattering (LS) with respect to their degree of substitution and molecular weight. The effect of salt concentration on ionic conductivity, thermal behaviour and morphology has been investiga-ted with impedance spectroscopy, differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA). The crosslinking reactions were controlled with dynamic mechanical analysis (DMS). The degree of substitution of our products is varying between 2,8 and 3,0 as determined by NMR. PEO - graft - cellulose derivatives are highly viscous liquids at room temperature with glass transition temperatures around 215 K. The glass transition temperature for the Lithium salt complexes of PEO - graft - cellulose deri-vatives increase with increasing salt content. The maximum conductivity at room temperature is about 10-4 and at 100°C around 10-3 Scm-1. The presence of lithium salt decreases the thermal stability of the complexes in comparison to pure PEO - graft - cellulose derivatives. Complexes heated over 140 – 150°C completely lose their ionic conductivity. The temperature dependence of the conductivity presented as Arrhenius-type plots for all samples is similar in shape and follows a VTF behaviour. This proofs that the ionic transport is closely related to the segmental motions of the polymer chains. Novel cellulose derivatives with grafted oligoethylen-oxide side chains with well-defined chemical structure and high side chain grafting density have been synthesized. Cellulose was chosen as stiff, rod like macromolecule for the backbone while oligoethylen-oxides are chosen as flexible side chains. A maximum grafting density of 3.0 have been obtained. The best conductivity reaches 10-3 Scm-1 at 100°C for a Li-triflate salt complex with a [Li]/[O] ratio of 0.8. The cross-linked complexes containing the lithium salts form elastomeric films with convenient mechanical stability. Our method of cellulose modification is based on relatively cheap and commercially available substrates and as such appears to be a promising alternative for industrial applications.