LITHIUM-ION BATTERIES SUSTAINABLE ENERGY NEW SCIENCE JOURNAL ISSUE IV UL.COM/NEWSCIENCE

Transcription

1 NEW SCIENCE SUSTAINABLE ENERGY LITHIUM-ION BATTERIES COMPUTATIONAL MODELING OF LITHIUM-ION BATTERIES SAFEGUARDING LITHIUM-ION BATTERY SEPARATORS THERMAL ANALYSIS OF LITHIUM-ION BATTERIES JOURNAL ISSUE IV UL.COM/NEWSCIENCE

2 NEW CHALLENGES CALL FOR NEW SCIENCE Progress is an unstoppable, transformative force. New technologies, product advances and globalization are arriving one on top of another at a dizzying pace. Innovation makes us more efficient, more productive and more connected. But there is a cost, and that cost is risk. To help mitigate the emerging risks, UL is developing New Science. Through fundamental discovery, testing methodologies and equipment, procedures, software and standards, UL is creating new and important ways to make the world a safer place. NEW SCIENCE: SUSTAINABLE ENERGY 2

3 SUSTAINABLE ENERGY LITHIUM-ION BATTERIES OVERVIEW Our Lithium-ion Batteries journal covers three key subjects that further demonstrate how UL is working to enhance the safety of this sustainable energy source. Computational Modeling is a critical tool we use to complement laboratory experiments and field data. We are able to mathematically reproduce and examine what happens in a lithium-ion battery when an internal short circuit (ISC) occurs. This work is critical because the vast majority of field failures can be attributed to ISCs. Lithiumion Battery Separators are also a focus of our research because of their central role in facilitating battery performance and in helping to prevent ISCs. We applied materials science to develop a robust set of tests to identify potential safety risks of today s increasingly thinner and lighter separators. Additionally, we have developed an in-depth Thermal Analysis capability that allows us to exhaustively study heat generation, which is related to the most significant safety issues in lithium-ion batteries. COMPUTATIONAL MODELING OF LITHIUM-ION BATTERIES, PG.4 We developed a unique thermal model of the common lithium-ion battery cell that enhances our ability to mathematically simulate, explore and understand the causes and severity of internal short circuits. SAFEGUARDING LITHIUM-ION BATTERY SEPARATORS, PG.9 UL applied materials science to develop a testing approach that establishes a more robust evaluation of lithium-ion battery separators. These tests help ensure that lithium-ion battery design is safe for its intended use. THERMAL ANALYSIS OF LITHIUM-ION BATTERIES, PG.13 We established a comprehensive thermal analysis capability that enables us to identify and measure exothermic and endothermic reactions within a lithium-ion battery cell. NEW SCIENCE: SUSTAINABLE ENERGY 3

4 COMPUTATIONAL MODELING OF LITHIUM-ION BATTERIES SAFEGUARDING LITHIUM-ION BATTERY SEPARATORS THERMAL ANALYSIS OF LITHIUM-ION BATTERIES NEW SCIENCE: SUSTAINABLE ENERGY 4

5 WHY COMPUTATIONAL MODELING OF LITHIUM-ION BATTERIES MATTERS Lithium-ion batteries are a vital source of sustainable energy and are being used across an expanding array of applications from portable electronic devices to electric vehicles to stationary energy storage. Importantly, the high energy density that contributes to the performance and popularity of these batteries also makes a small percentage of them vulnerable to internal short circuits (ISCs) that can result in fires or explosions. Computational modeling is a method UL is using to better understand ISCs, along with the mechanisms of heat generation that occur due to the electrochemical reactions within a lithium-ion battery and the primary causes of thermal runaway, which represents the worst-case and most hazardous scenario of possible lithium-ion battery failure modes. CONTEXT The energy density of lithium-ion batteries has tripled since their commercial introduction in Energy density or a battery s energy delivery capability relative to its weight or volume is one of the advantages of lithium-ion batteries, which have the highest energy density and the highest voltage of any commercially available rechargeable battery. 2 This was largely accomplished by packing more active material into the cell and making the electrodes and separators thinner. 3 Ultimately, this means that lithium-ion batteries are smaller and lighter than other batteries; this is one of the primary reasons for their growing popularity. Thermal modeling is a method UL is using to better understand ISCs, along with the mechanisms of heat generation that occur due to the electrochemical reactions within a lithium-ion battery and the primary causes of thermal runaway. The power that a lithium-ion battery packs into its volume is largely achieved by the use of an electrolyte composed of lithium salts in flammable organic solvents such as ethylene carbonate and ethyl methyl carbonate. This differs from the electrolytes in other common types of batteries, which are composed of acid or base aqueous solutions that are nonflammable. 4 The flammable electrolyte, coupled with increasingly thin and light separators, increases the risk of failure. Currently, lithiumion batteries have a failure rate of approximately one in 10 million cells. 5 Although this may seem relatively low, in the context of the 4.4 billion lithium-ion battery cells manufactured in 2012, 6 the failure rate equates to 440 potential battery failures in one year, a figure that could increase as the lithium-ion battery market doubles over the next four years. 7 Lithium-ion batteries have been involved in several highly publicized incidents over the past several years. 8 In many cases the battery failures were linked to ISCs that led to thermal runaway, resulting in the explosive release of energy along with fire. 9 Thus, it became imperative for UL to gain a better understanding of ISCs to identify the factors that cause the most heat generation within the shortest time, leading to catastrophic battery failure. SUSTAINABLE ENERGY JOURNAL/COMPUTATIONAL MODELING OF LITHIUM-ION BATTERIES 5

6 WHAT DID UL DO? We developed a unique computational thermal modeling capability to enable us to mathematically simulate, explore and understand the causes and severity of ISCs. Our thermal model was developed using SC/Tetra computational fluid dynamic (CFD) software and built on a complex geometric representation of the type or other cylindrical lithium-ion battery, making it especially suitable for these cells. The model provides a robust simulation of lithium-ion battery characteristics because all of the thermal and physical properties of each component are based on information from investigated literature or real experimental data. 10 This gives us the ability to investigate all the factors involved with an ISC. UL s thermal model takes into account different sources of heat generation electrical, electrochemical and chemical and encompasses the factors related to material and construction design that are the dominant elements in determining the capability of a cell to dissipate excess heat. This enables UL scientists and engineers to investigate the components and/or ISC conditions that are the critical factors in determining the temperature rise distribution within the whole cell as well as outcomes involved with an ISC under steady and pseudo-steady state conditions. 11 Our key findings include: KEY CHARACTERISTICS OF AN ISC EVENT Our model showed that other than in a case caused by mechanical abuse, most ISC events begin on a small scale in a localized area within a single lithium-ion battery cell, which results in localized heating at the very beginning of the event. Further, once the ISC is triggered, all safety designs outside of cells have no effect, and most of the safety devices within the cells will also be bypassed (e.g., the fuse that is designed to open to vent excess voltage or heat). 12 UL developed a unique computational thermal modeling capability to enable us to mathematically simulate, explore and understand the causes and severity of ISCs. ISC BEHAVIORS Three principal findings relative to ISC behaviors were observed from our Indentation Induced ISC Test (for more information, refer to the article Indentation Induced ISC Test ). The worst-case scenario of an ISC can occur when the resistance at the point of the ISC is similar to the resistance level of the whole cell. This leads to the maximum generation of Joule heat from the ISC point to the surrounding area in the battery. In addition, our model showed that the location of an ISC is directly related to its severity. An ISC SUSTAINABLE ENERGY JOURNAL/COMPUTATIONAL MODELING OF LITHIUM-ION BATTERIES 6

7 located in the center of the bottom side of a cylindrical lithium-ion battery exhibits the highest rise in temperature, reaching 1,066 F. Our third key finding about ISC behaviors is counterintuitive. Assuming the same electrochemistry energy and constant resistance at the ISC point and within the whole cell, we found that the smaller the initial ISC, the greater its severity and the more likely it is to lead to thermal runaway (i.e., the rapid buildup of heat inside the battery that can lead to fire or explosion). 13 FAILURE MECHANISMS IN AN ISC Using our thermal model, we were able to assess the impact of materials, product design, battery construction and electrochemistry on ISCs. We identified the heat-generation profiles through three different heating sources. One common heat source in a lithium-ion battery is the result of localized overheating by the Joule effect, which means the current flows through the ISC point in the battery, generating localized overheating due to the impedance at the ISC bridging point. The second heat source is when an ISC triggers an electrochemical reaction in the battery material via electron transfer that leads to globalized overheating of the battery. The final heat source we detected involves an ISC that creates a localized overheating condition that consequently causes material decomposition around the point of the ISC. The profiles of all three heat sources can be simulated using different material properties, which can be flexibly set by the simulation tool. We also developed a geometry model, composed of a detailed spiral jelly roll structure that includes all the components within the cell with appropriate thermal property settings. This enables us to create a virtual heatconducting medium that can simulate the heat dissipation capability of a real battery. This simulation is important because the heat-generation rate and a battery s ability to dissipate heat are the two critical factors involved with thermal runaway and potentially significant fire and explosion hazards. We observed that the faster the heat builds within the battery, the less likely the battery s fail-safe devices will be able to effectively vent the excess heat quickly enough, and the more likely the ISC will lead to thermal runaway. 14 Using our thermal model, we were able to assess the impact of materials, product design, battery construction and electrochemistry on ISCs. SUSTAINABLE ENERGY JOURNAL/COMPUTATIONAL MODELING OF LITHIUM-ION BATTERIES 7

8 IMPACT Computational modeling is an important tool we use to gain insight into how a product functions, how it malfunctions and the risks involved. For lithium-ion batteries, UL applied this tool to develop a thermal model to help us proactively gain a better understanding of how ISCs work and why some lithium-ion battery cells fail while others do not. With new insights about the characteristics and behaviors of ISCs as well as their failure mechanisms, we are better able to help manufacturers safeguard the batteries they make across the design, materials specification, manufacturing and quality assurance processes. RELATED ARTICLE Since you were interested in reading Computational Modeling of Lithium-Ion Batteries, we thought you might find the following related article of interest. INDENTATION INDUCED ISC TESTING SUSTAINABLE ENERGY JOURNAL/COMPUTATIONAL MODELING OF LITHIUM-ION BATTERIES 8

9 COMPUTATIONAL MODELING OF LITHIUM-ION BATTERIES SAFEGUARDING LITHIUM-ION BATTERY SEPARATORS THERMAL ANALYSIS OF LITHIUM-ION BATTERIES NEW SCIENCE: SUSTAINABLE ENERGY 9

10 WHY THE LITHIUM-ION BATTERY SEPARATOR RECOGNITION PROGRAM MATTERS The separator is a critical component within a lithium-ion battery that supports its overall performance while facilitating its safe operation. As demand for lithium-ion batteries has grown across a broad array of consumer, industrial and infrastructure applications, so has the push to improve their energy density and battery life. To help improve battery performance, separators have been made progressively thinner and lighter, which has diminished the capability of some to perform critical functions such as preventing electrode contact or shutting the battery down when overheating occurs. The resultant safety risks could hinder the continued advancement of lithium-ion battery performance as well as the expansion of this sustainable energy source. CONTEXT The reduction of the separator thickness to 18μm or less means that some lithium-ion batteries may now be more susceptible to manufacturing defects and external damage. Research has shown that a thinner separator is critical to achieving higher energy and power density in a lithium-ion battery. 1 Over the past two decades, the ongoing reduction of separator thickness and addition of active materials have contributed to a threefold increase in the energy density of lithium-ion batteries. 2 These batteries now offer unmatched performance, which has helped lithium-ion become the battery chemistry of choice for a range of applications first for consumer electronics, but more and more for automobiles and the electric power grid. 3 Evidence of the growing role of lithium-ion batteries can be seen in the size of the market, which reached $11.7 billion in 2012 and is projected by Frost & Sullivan to double by One of the primary contributors to the safety risks of lithium-ion batteries is their use of flammable electrolyte solutions. 5 This underscores the critical role the separator plays in preventing electronic contact of the electrodes while enabling free ionic transport and isolating the electronic flow within the battery. 6 The reduction of the separator thickness to 18µm or less means that some lithium-ion batteries are now more susceptible to manufacturing defects and external damage. 7 Specifically, this translates to a potentially increased risk of internal short circuits, which can lead to thermal runaway the rapid buildup of heat inside the battery that ignites the flammable electrolyte or raises the vapor pressure until the cell bursts. 8 SUSTAINABLE ENERGY JOURNAL/ SAFEGUARDING LITHIUM-ION BATTERY SEPARATORS 10

11 WHAT DID UL DO? UL applied materials science to develop a comprehensive testing approach that establishes a more robust evaluation of lithium-ion battery separators. The key characteristics of the separator as it relates to potential safety risks and performance were identified. We then developed a Separator Recognition Program comprising a suite of tests some of which already existed while others were developed specifically for the program including permeability, thickness, material composition, tensile strength, puncture strength, dimensional stability, shutdown temperature and melting temperature. 9 Component Recognition is a service UL offers that covers the evaluation of components or materials intended for incorporation and use in other end-use products or systems. 10 UL s Separator Recognition Program was designed to identify the key properties of a separator to help ensure that it is appropriate and safe for the scope of its intended use. We developed the program to help drive some consistency in the evaluation of all the important separator parameters. 11 Our recognition program outlines eight specific parameters of a lithium-ion battery separator that our research and experience show to be critical to both battery safety and performance. 12 For five of the parameters, existing test protocols are ideal. For separator thickness, dimensional stability and shutdown temperature, we needed to create new test protocols. 13 KEY PARAMETERS AND TESTS IN THE UL SEPARATOR RECOGNITION PROGRAM 14 UL applied materials science to develop a comprehensive testing approach that establishes a more robust evaluation of lithium-ion battery separators. TYPE OF TEST CRITICAL PARAMETER TEST PROTOCOL Identification Tests Permeability ASTM D726 Thickness Material ID modified UL 746A Mechanical Strength Tests Tensile Strength ASTM D882 Puncture Strength ASTM D3763 Thermal Tests Dimensional Stability modified Shutdown Temperature Melt Temperature modified UL 746A With this comprehensive set of parameters and corresponding test protocols, our Separator Recognition Program is intended to help manufacturers establish tighter controls on critical battery safety components. SUSTAINABLE ENERGY JOURNAL/ SAFEGUARDING LITHIUM-ION BATTERY SEPARATORS 11

12 IMPACT The Separator Recognition Program extends UL s commitment to ensure the safety of lithium-ion batteries, focusing on one specific and vital component. To implement the program, we are conducting and witnessing tests, and we also publish parameters in the UL online directory. Still in its early stages, the program is not yet fully utilized by the industry. However, today, lithium-ion battery and separator manufacturers can submit separators to UL for safety testing and certification. Importantly, there are no pass/fail criteria; instead, our program is focused on identifying the properties of tested separators. In this way, we can help manufacturers advance the performance of lithium-ion batteries while enhancing their safety. RELATED ARTICLES Since you were interested in reading Safeguarding Lithium-Ion Battery Separators, we thought you might find the following related articles of interest. INDENTATION INDUCED ISC TESTING AGING EFFECTS OF LITHIUM-ION BATTERIES SUSTAINABLE ENERGY JOURNAL/ SAFEGUARDING LITHIUM-ION BATTERY SEPARATORS 12

13 COMPUTATIONAL MODELING OF LITHIUM-ION BATTERIES SAFEGUARDING LITHIUM-ION BATTERY SEPARATORS THERMAL ANALYSIS OF LITHIUM-ION BATTERIES NEW SCIENCE: SUSTAINABLE ENERGY 13

14 WHY THERMAL ANALYSIS OF LITHIUM-ION BATTERIES MATTERS The use of lithium-ion batteries is undergoing dramatic growth, primarily due to their industry-leading energy density and comparatively long battery life. 1 As the leading rechargeable battery for consumer electronics and electric vehicles (EVs), and a rapidly growing source for energy storage, lithium-ion batteries are playing an increasingly critical role in facilitating energy sustainability. 2 One critical concern, however, is that a small percentage of lithium-ion batteries experience internal short circuits (ISCs) that result in thermal runaway, the rapid buildup of heat within the battery that leads to the explosive release of energy or fire. 3 Because the most significant safety issues for lithium-ion batteries are related to heat generation, thermal analysis examining the impact of temperature on lithium-ion battery performance and safety provides a critically important way to pinpoint, understand and mitigate the risks. 4 CONTEXT As the leading rechargeable battery for consumer electronics and EVs, and a rapidly growing source for energy storage, lithium-ion batteries are playing an increasingly critical role in facilitating energy sustainability. There are three potential causes of heat generation that can make lithium-ion batteries unsafe: 1. An improper load (i.e., flow of electric energy) between the positive and negative poles in a battery can generate heat. This can be caused, for example, by an external short circuit (e.g., a DC charger is connected with the polarity reversed) or by high-rate charging/discharging. In addition, more heat can be generated by overcharging or over-discharging the battery. Improper load will usually heat the entire cell uniformly, as the electrochemical reaction occurs along both the electrodes. 2. Heat can also be generated from inside the battery cell by an ISC caused by contamination that occurred on the production line (e.g., introducing metal particles into the cell) or by dendrite formation (i.e., lithium metal deposits that occur due to a polarization effect or after overcharge conditioning). An ISC can generate a substantial amount of heat that will accumulate locally inside the cell within seconds. 3. Unsafe heat generation in a lithium-ion battery can also occur when the ambient (or surrounding) environment overheats the battery. This external overheating of a lithium-ion battery will sometimes trigger exothermic (i.e., heat-releasing) reactions inside the battery. The generated heat may then induce additional heat-generating reactions, eventually resulting in thermal runaway. 5 Even if the external overheating is minor and causes only a very SUSTAINABLE ENERGY JOURNAL/THERMAL ANALYSIS OF LITHIUM-ION BATTERIES 14

15 preliminary self-heating in the battery (i.e., the initial self-heating can be triggered between C), there may be safety issues in further use of the battery because the protective layer (i.e., solid electrolyte interface or SEI) between electrode and electrolyte may have been destroyed. In all three cases, when the heat generation inside the battery exceeds the battery s dissipation capacity, the result will be thermal runaway, in which an initial heat event in the battery triggers additional exothermic reactions very rapidly in a chain reaction. When this happens, the battery will typically catch fire, rupture or explode. 6 WHAT DID UL DO? We established a comprehensive thermal analysis capability that includes all existing techniques, which enables us to measure exothermic (heat-emitting) and endothermic (heat-absorbing) reactions within a lithium-ion battery on a constituent material level or to measure the reactions in a cell as a whole. 7 This allows us to examine and better understand the potential safety risks of different materials and components in a battery, as well as their complex electrochemical and functional interactions and how these are affected by heating conditions. 8 We use five core methods to conduct thermal property analysis of lithium-ion batteries: 9 TEST METHODOLOGY LEVEL OF TEST SAMPLE PURPOSE Differential Scanning Calorimetry (DSC) Material/Component To study interaction effects between different battery materials and components and to examine the thermal stability of electrode materials under different state-of-charge conditions. Accelerating Rate Calorimetry (ARC) Component/Cell/Module To provide an adiabatic (i.e., isolated) environment that eliminates measurement inaccuracies, enabling us to demonstrate chemical reactions and thermodynamic models within the battery, and helping us identify the point at which a battery becomes self-heating. Thermogravimetric Analysis-Mass (TGA-Mass) Material/Component To characterize materials based on how their mass changes as a function of temperature or time. The outcome of a TGA-Mass analysis is often compared with the results of DSC to determine the thermal decomposition of chemical materials in a lithium-ion battery. Thermal Ramp Cell To study the behavior of lithium-ion batteries primarily heat generation and gas buildup under thermal abuse conditions. Thermal Imaging Cell/Module/Battery To identify the uniformity of heat distribution in a lithium-ion battery while it is charging and discharging and to help predict the failure modes of batteries typically used under rapid charge/discharge conditions. SUSTAINABLE ENERGY JOURNAL/THERMAL ANALYSIS OF LITHIUM-ION BATTERIES 15

16 Our research has produced several key findings about the types of fundamental thermal reactions caused by the overheating of lithium-ion batteries (with a standard LiCoO 2 chemistry). Separator Melting Lithium-ion battery separators have a porous structure and are made of polyethylene (PE) or polypropylene (PP). Under normal conditions, PE will melt at approximately 130 C and PP at around 160 C in endothermic reactions, helping block ion transfer and shut down the inner circuit of an overheating battery. Decomposition of Electrolyte Lithium-ion battery electrolytes are organic solvents that decompose under overheating conditions. The decomposition of the solvent will sometimes produce active products as well as gaseous substances that pressurize the cell. Generally, electrolyte decomposition does not result in significant heat generation by itself, but the side products will sometimes react with the battery electrodes at higher temperatures. Reduction Reaction of the Anode (i.e., negative electrode) with the Electrolyte the SEI, a thin film that has the same chemistry as a liquid electrolyte but is in a different form, is easily formed on the anode-electrolyte interface. Even mild heating of a lithium-ion battery will stimulate SEI formation, but the SEI film will melt if the battery is further heated to C, and it will release a small amount of heat. Under an ARC test, the initial SEI decomposition within a cell can be triggered as early as C under the simulated adiabatic condition. The Oxidation Reaction of the Cathode (i.e., positive electrode) with the Electrolyte When the temperature of a lithium-ion battery goes beyond 180 C, the cathode and the electrolyte will interact in a way that releases significant heat. If this heat cannot be dissipated effectively, it will finally lead to material decomposition of the cathode, releasing more heat and causing thermal runaway. UL s research has produced several key findings about the types of fundamental thermal reactions caused by the overheating of lithium-ion batteries (with a standard LiCoO 2 chemistry). Decomposition of Electrode Materials At higher temperatures, typically C, the electrode material will decompose. Once this reaction is initiated, a substantial amount of heat is generally released, causing the battery to explode or catch fire. In addition, the decomposition of the cathode will produce oxygen gas, which further increases the potential for thermal runaway. 10 SUSTAINABLE ENERGY JOURNAL/THERMAL ANALYSIS OF LITHIUM-ION BATTERIES 16

17 IMPACT Safeguarding lithium-ion batteries is made more difficult by the complex interactions of more than 10 types of materials and components. With a comprehensive set of thermal analysis tools and methods, UL is able to holistically examine and better understand how these batteries react to heat conditions, which is important because all lithium-ion battery safety issues involve heat generation. Our thermal analysis is especially critical today, as the industry pushes to advance lithium-ion battery performance through the use of new materials and battery designs. With thermal analysis, we are continuing to help pinpoint safety risks, identify safe performance envelopes and develop effective risk-mitigation approaches. 11 RELATED ARTICLES Because you were interested in reading Thermal Analysis of Lithium-Ion Batteries, we thought you might find the following related articles of interest. THERMAL MODELING OF LED LIGHTS ADVANCED COMPUTER MODELING BASEMENT FIRE COMPUTER MODELING SUSTAINABLE ENERGY JOURNAL/THERMAL ANALYSIS OF LITHIUM-ION BATTERIES 17

18 SOURCES COMPUTATIONAL MODELING OF LITHIUM-ION BATTERIES SAFEGUARDING LITHIUM-ION BATTERY SEPARATORS THERMAL ANALYSIS OF LITHIUM-ION BATTERIES 1 Savitz, E., Apple: What Lithium-Ion Battery Limits Could Mean for iphone 5, Forbes, 18 July Web: 20 July com/sites/ericsavitz/2012/07/18/apple-whatlithium-ion-battery-limits-could-mean-foriphone-5/. 2 About Rechargeable Batteries, AA Portable Power Corp., Web: 18 Nov batteryknowledge.aspx. 3 Orendorff, C.J., The Role of Separators in Lithium-Ion Cell Safety, The Electrochemical Society Interface, Summer Web: 29 July interface/sum/sum12/sum12_p061_065.pdf. 4 Jacoby, M., Assessing the Safety of Lithium- Ion Batteries, Chemical & Engineering News, Volume 91, Issue 6, 11 Feb Web: 10 July Assessing-Safety-Lithium-Ion-Batteries.html. 5 6 Standards Are Tightened for Lithium-Ion Batteries, New York Times, 12 June Web: 19 Nov com/2013/06/13/business/lithium-ion-batterystandards-are-tightened.html?_r=0. 7 Global Lithium-Ion Battery Market to Double Despite Recent Issues, Frost & Sullivan, 21 Feb Web: 18 Nov thefreelibrary.com/frost+%26+sullivan,+global+ Lithium-ion+Market+to+Double+Despite+Recent...-a Wu, A., et al., Simulation of Internal Short Circuits in Lithium-Ion Cells, UL Corporate Research and NASA Johnson Space Center, White paper, 29 May Wu, A., Brief Introduction of Thermal Modeling of ISC in LIB, UL, Presentation, 4 Sept Wu, A., Personal Interview, 30 Sept Li-ion Battery Separators, UL, Presentation, 3 Sept Savitz, E., Apple: What Lithium-Ion Battery Limits Could Mean for iphone 5, Forbes, 18 July Web: 20 July sites/ericsavitz/2012/07/18/apple-what-lithiumion-battery-limits-could-mean-for-iphone-5/. 3 Jaffe, S., The Lithium Ion Inflection Point, Battery Power, 9 Oct Web: 21 Nov articles/the-lithium-ion-inflection-point/. 4 Global Lithium-ion Battery Market to Double Despite Recent Issues, Frost & Sullivan, 21 Feb Web: 18 Nov thefreelibrary.com/frost+%26+sullivan,+global+ Lithium-ion+Market+to+Double+Despite+Recen t...-a Jacoby, M., Assessing the Safety of Lithium- Ion Batteries, Chemical & Engineering News, Volume 91, Issue 6, 11 Feb Web: 10 July Safety-Lithium-Ion-Batteries.html. 6 Li-ion Battery Separators, UL, Presentation, 3 Sept Orendorff, C.J., The Role of Separators in Lithium-Ion Cell Safety, The Electrochemical Society Interface, Summer Web: 29 July sum/sum12/sum12_p061_065.pdf. 8 Jacoby, M., Assessing the Safety of Lithium- Ion Batteries, Chemical & Engineering News, Volume 91, Issue 6, 11 Feb Web: 10 July Safety-Lithium-Ion-Batteries.html. 9 Wang, E., Personal Interview, 25 Sept UL Component Recognition, UL, Web: 2 Dec aboutul/ulmarks/promotional/mark3/#comp_ recog. 11 Li-ion Battery Separators, UL, Presentation, 3 Sept Wu, A., et al., Polarization and Thermal Stability Effects on Aged Lithium-ion Batteries, UL, Presentation: 30 May Jaffe, S., The Lithium Ion Inflection Point, Battery Power, 9 Oct Web: 21 Nov articles/the-lithium-ion-inflection-point/. 3 Jacoby, M., Assessing the Safety of Lithium- Ion Batteries, Chemical & Engineering News, Volume 91, Issue 6, 11 Feb Web: 10 July Safety-Lithium-Ion-Batteries.html. 4 Wu, A., Thermal Runaway Mechanism and Thermal Analysis Technologies for Lithium-ion Batteries, UL, Aug Report (draft): 8 Oct Wu, A., Personal Interview, 4 Dec Wu, A., Thermal Runaway Mechanism and Thermal Analysis Technologies for Lithium-ion Batteries, UL, Aug Report (draft): 8 Oct Wu, A., Personal Interview, 4 Dec Wu, A., Brief Introduction of Thermal Modeling of ISC in LIB, UL, Presentation, 4 Sept SUSTAINABLE ENERGY JOURNAL/SOURCES 18

19 NEW CHALLENGES. NEW RISKS. NEW SCIENCE. WANT TO LEARN MORE? DOWNLOAD THE OTHER JOURNALS IN OUR NEW SCIENCE SERIES AT UL.COM/NEWSCIENCE New Science Sustainable Energy cannot be copied, reproduced, distributed or displayed without UL s express written permission. V.5. UL and the UL logo are trademarks of UL LLC 2014