Thermal Runaway.pptx, THERMAL RUNWAY PROBLEM IN EVS BATTERY

THERMAL RUNWAY PROBLEM IN ELECTRIC VEHICLE BATTERY

1. Th ermal Runaway In Electric Vehicles Team Name – Failsafe Forwards

2. Introduction The Paradigm Shift: The global shift to Electric Vehicles (EVs) is powered by high-energy-density lithium-ion batteries . The Inherent Risk : These batteries, however, carry the risk of thermal runaway —a self-propagating cycle of extreme, uncontrollable overheating. The Consequence Spectrum: This event can lead to catastrophic failure , including intense fires and the violent ejection of toxic gases, posing severe safety risks. The Strategic Imperative : Preventing thermal runaway is therefore essential for public safety , building consumer confidence, and securing the future of electric mobility.

3. Lithium-ion batteries (LIBs) are the preeminent power source for portable electronics and electric vehicles, owing to their superior energy density , extended operational lifespan , and ecological advantages. However, a paramount safety challenge is their propensity for thermal runaway —a catastrophic failure mode culminating in deflagration or explosion. To counteract this vulnerability, a multi-faceted approach to safety is employed. At the cell and package level , manufacturers embed intrinsic safety features —such as Positive Temperature Coefficient (PTC) thermistors, Current Interrupt Devices (CIDs) , and safety vents—to preemptively thwart the onset of thermal runaway. Externally, at the system level , a Battery Thermal Management System (BTMS) is indispensable for active thermal regulation, maintaining the battery within its optimal thermal window. The efficacy of these mitigation strategies is quantified by critical metrics, including the heating rate , total heat generation , and the temporal delay to thermal runaway onset. Li-ion Battery

4. Safety Device for Thermal Runaway Positive Temperature Coefficient (PTC): Core Concept: A Positive Temperature Coefficient (PTC) device is an advanced, thermally-sensitive polymer that functions as a smart, resettable fuse . Under normal conditions, it maintains an extremely low electrical resistance, but its resistance increases exponentially when heated past a specific threshold temperature , effectively blocking current flow. Operational Principle: The mechanism is rooted in a phase transition within its conductive polymer matrix. During an overheating event, this matrix undergoes a rapid volumetric expansion , which forces the embedded conductive particles (e.g., carbon black) apart. This action breaks the electrical pathways, causing the dramatic, nonlinear increase in resistance that impedes the fault current.

5. Application in Battery Safety: Integrated directly into a battery cell's structure, a PTC acts as a crucial intrinsic safety feature . When a fault like an internal short circuit or overcurrent generates intense localized heat (Joule heating), the PTC is automatically triggered. Its swift transition to a high-resistance state suppresses the fault current at its source, preventing the escalation into a full thermal runaway event. Validated Efficacy: The effectiveness of this technology has been extensively validated. Modern innovations include PTC-integrated electrodes , where a PTC layer is coated within the cell itself. These designs have proven to effectively suppress internal short circuits and cease discharging at elevated temperatures (typically 120-150 °C), providing a reliable, built-in defense mechanism for enhancing battery safety.

6. Current Interrupt Devices (CIDs): Current interrupt devices are a protective device that cuts off the electrical connection of equipment when the internal pressure or current exceeds its predetermined level. Thus, CIDs can be roughly classified into pressure-responsive CIDs and temperature responsive CIDs. Pressure-Responsive CIDs : Operational Principle: A pressure-responsive CID is a safety device that irreversibly breaks the circuit when internal cell pressure exceeds a set threshold, primarily to prevent overcharge-induced thermal runaway . Activation Conditions: These devices are typically validated to activate around 100 °C , which corresponds to internal pressures of approximately 1.8 MPa . Critical Failure Mode: A significant vulnerability, especially in high-voltage systems , is the generation of a destructive electrical arc during circuit interruption. Critical Failure Mode: A significant vulnerability, especially in high-voltage systems , is the generation of a destructive electrical arc during circuit interruption.

7. Temperature-Responsive CIDs : Operational Mandate: A thermal fuse is a single-use safety device that irreversibly interrupts the current pathway when the battery's temperature surpasses a predefined activation threshold, preventing thermal runaway. Preventative Strategy: Engineered from low-melting-point alloys , their preemptive strategy is to activate between 85-120 °C , cutting off the circuit before the more critical temperatures that cause internal short circuits are reached. Critical Disadvantage: The primary limitation of a thermal fuse is that its operation causes permanent, non-resettable battery failure . When the alloy melts to break the circuit, it can simultaneously reduce the insulation distance between adjacent terminals, compromising the cell's insulating capacity and rendering it permanently inoperable.

8. Thermal Management Methods

9. Introduction Commercial battery packs, like those in EVs, consist of thousands of individual cells stacked in a high-density, confined space. While intrinsic safety devices like PTCs and CIDs are effective for a single cell, their ability to prevent a pack-level event is severely limited in these configurations. The failure of one protected cell can still release an enormous amount of heat that transfers to adjacent cells, raising their temperature beyond a critical point. This can trigger a dangerous chain reaction known as thermal runaway propagation , where the failure cascades through the pack, leading to widespread fires or explosions. That’s why we need some specific methods like: Air-Cooled Thermal Management. PCM Thermal Management Spray/Jet Method for Mitigating THERMAL RUNAWAY

10. Air-Cooled Thermal Management Air-cooled thermal management has many advantages such as simple structure, light weight, easy maintenance, low cost, and easy battery replacement, and is one of the more traditional methods of battery thermal management systems (BTMSs) . Air cooling is shown in diagram e.g., Honda’s Insight electric vehicle.

11. Designed a forced cooling of air thermal management system for cylindrical battery cooling. It was found that the arrangement of the cells affects the airflow lines, resulting in a large temperature difference within the pack and reducing the cooling effect. Forced-air cooling can significantly reduce the temperature of the entire cell module, depending on many factors, such as cell module layout, ambient temperature, cooling air-temperature flow rate, flow area, and airflow path length. The parallel ventilation method, and the maximum temperature difference of the battery pack can be reduced by 29% by increasing the spacing around the battery where the highest temperature is located, while decreasing the spacing around the battery where the lowest temperature is located for a constant heat production rate of the battery. Optimization of the duct shape can enhance cooling effectiveness Learn Some More About This: 29%

12. PCM Thermal Management 02

13. PCM Thermal Management A Phase Change Material (PCM) is a substance used for passive thermal management within battery packs. Its core principle is the absorption of large amounts of latent heat at a constant temperature as it undergoes a phase transition (e.g., melting). PCMs are primarily classified as organic (like paraffins), inorganic (salt hydrates), or eutectic mixtures .

14. Learn Some More About This: Organic paraffins are often the preferred choice due to their high specific heat capacity and stable chemical properties. The main goal of using PCMs in batteries is to delay the onset of thermal runaway and inhibit its propagation to adjacent cells. It achieves this first by acting as a thermal barrier , physically slowing the conduction of heat from a failing cell to its neighbors. The main goal of using PCMs in batteries is to delay the onset of thermal runaway and inhibit its propagation to adjacent cells. It achieves this first by acting as a thermal barrier , physically slowing the conduction of heat from a failing cell to its neighbors. Second, it directly absorbs the immense heat energy released during a thermal runaway event, buffering the temperature spike. Finally, during normal operation, it helps reduce temperature differences across the pack, preventing the formation of localized hot spots.

15. Jet Method for Mitigating THERMAL RUNAWAY 03

16. Spray/Jet Method for Mitigation ## Fundamental Strategy: Active Thermal Suppression The primary method for combating battery thermal runaway is active thermal suppression , most commonly achieved through spray or jet cooling. The core strategy is to aggressively interrupt the positive feedback loop, where heat generation triggers further exothermic reactions. By applying an extinguishing agent, the system leverages forced heat exchange to extract thermal energy from the failing cell and its surroundings at a rate faster than it is being generated, thereby preventing the escalation to catastrophic failure.

17. Learn Some More About This: ## Comparative Analysis of Extinguishing Agents The choice of agent is critical, as different substances have vastly different levels of effectiveness. ### Inert Gases and Powders (Limited Efficacy) While common in traditional fire suppression, agents like dry powder, Carbon Dioxide (CO₂), and halogenated alkanes have proven to be inadequate for controlling thermal runaway. Core Limitation: These agents can often extinguish the external flames by displacing oxygen, but they lack the specific heat capacity to absorb enough energy to halt the internal, self-sustaining exothermic reactions within the battery. Performance: Studies show these agents can only sometimes prevent propagation at a very low State of Charge (SOC) and are largely ineffective at stopping the initial event. CO₂ is particularly deficient, failing to suppress either the flame or propagation. ## Synergistic Extinguishing Strategies To overcome the limitations of single-agent systems, a synergistic approach that combines a gaseous extinguishing agent with a water mist has been developed. This dual-agent method demonstrates a significantly better suppression effect than either component used in isolation.

18. Learn Some More About This: ### Water-Based Systems (High Efficacy) Water, particularly in the form of a fine water mist , is demonstrably the most effective agent for thermal runaway suppression. Superior Cooling: Water's effectiveness stems from its exceptionally high specific heat capacity and latent heat of vaporization . It can absorb a massive amount of thermal energy as it heats up and turns to steam, providing unparalleled cooling performance. Proven Results: Experiments confirm that water spray can dissipate significantly more energy than halogenated alkanes (e.g., 459.8 kJ for water vs. 111 kJ for C₆F₁₂O in one study) and can successfully arrest thermal runaway if applied correctly. ## Criteria for an Optimal Extinguishing Agent: The ideal agent must exhibit a combination of properties: rapid extinguishing speed, high thermal conductivity, electrical insulation, and environmental friendliness. Furthermore, it must minimize the generation of toxic gases and particulate matter to ensure the safety of rescue personnel and reduce environmental impact.

19. Thermal runaway in a lithium-ion battery (LIB) is a complex, self-accelerating process driven by a cascade of exothermic chemical reactions. Understanding this step-by-step sequence is critical for designing effective prevention and mitigation strategies. Mechanism Of Thermal Runaway

20. Mechanism: Initial Heat Generation : Trigger: The process begins with an initial internal fault, such as an internal short circuit , overcharging or external abuse. Mechanism: This fault generates localized heat, raising the internal temperature of the cell above its normal operating range. This initial heat is the catalyst for the subsequent destructive reactions. Breakdown of the Solid Electrolyte Interphase (SEI): Threshold: As the temperature inside the cell rises, typically to around 80-120 °C , the Solid Electrolyte Interphase (SEI) layer(imp layer)on the anode surface begins to decompose. Mechanism: The decomposition of the SEI is an exothermic reaction , meaning it releases additional heat, further accelerating the temperature rise. This breakdown also exposes the highly reactive carbon anode to the electrolyte.

21. Anode-Electrolyte Reaction & Gas Generation: With the SEI compromised (around 100-150 °C ), the exposed anode reacts vigorously with the organic electrolyte. Mechanism: exothermic reaction , generating a substantial amount of heat. Crucially, it also produces flammable gases within the sealed cell. Increase in gas volume leads to rise in internal pressure. Separator Melting & Internal Short Circuit Propagation: As temperatures climb further, the polymer separator, which physically separates the anode and cathode, begins to melt and shrink.This melting leads to direct contact between the anode and cathode, causing a massive internal short circuit . This short circuit increases current, producing a drastic increase in internal heat, accelerating the entire process uncontrollably. Electrolyte Decomposition & Venting/Combustion: The electrolyte itself begins to decompose rapidly (around 220-250 °C ), generating more heat and gas. The ever-increasing internal pressure eventually exceeds the cell's structural integrity or activates a safety vent. This leads to venting of hot, flammable gases. If sufficient oxygen is present externally, these gases can auto-ignite, resulting in flame, smoke, and potentially an explosion .

22. Below causes affect the most Mechanical Abuse Thermal Abuse Electrical Abuse Causes Of Thermal Runaway

23. Mechanical Abuse Definition: Mechanical abuse refers to battery damage caused by external forces such as penetration, compression (squeezing), or impact , which can rapidly induce an unsafe, overheated state. Separator Damage: These forces can compromise the integrity of the internal separator , leading to a direct internal short circuit . This fault causes a rapid, uncontrolled discharge of the cell's energy, which generates a significant amount of immediate heat. Casing Rupture: If the battery casing is breached , oxygen from the atmosphere can enter the cell. This ingress of air initiates exothermic oxidation-reduction reactions with the highly reactive electrolyte and active materials, producing additional, intense heat. Escalation to Thermal Runaway: The heat generated from either an internal short circuit or chemical oxidation acts as a catalyst. It triggers a cascade of further internal exothermic reactions that can culminate in a full thermal runaway event. The Danger of Minor Deformation: Even minor casing deformation without a full rupture is hazardous. The compact internal structure means that slight flexing can still cause localized separator failure or direct electrode contact, initiating a dangerous internal short circuit.

24. Thermal Abuse Stage I: Initial Self-Heating & SEI Decomposition: Process begins with the exothermic decomposition of SEI layer on negative electrode (anode). This releases initial heat and initiates a cycle of SEI breakdown and reformation, which consumes lithium ions. Stage II: Separator Failure & Internal Short Circuit As the temperature continues to rise, the polymer separator melts and collapses . This structural failure allows for direct contact between the anode and cathode, initiating a significant internal short circuit. Stage III: Cathode Decomposition & Gas Generation At higher temperatures, the positive electrode (cathode) becomes unstable and begins to decompose. This process releases highly reactive oxygen species which then react exothermically with the electrolyte, generating a large volume of flammable gases and further escalating the battery's temperature. Stage IV: Thermal Runaway Climax & Combustion This is the final, violent stage where oxygen released from the cathode reacts with the anode and the combustible gases. This triggers a massive spike in the heating rate , causing the battery to reach its maximum temperature, often resulting in combustion or explosion .

25. Electrical Abuse Electrical abuse, including external short circuits, overcharging, and over-discharging, subjects a battery to conditions far beyond its safe operating limits. External Short Circuit: This fault induces a massive current flow, leading to rapid Ohmic heating and significant gas generation. The resulting increase in temperature and pressure can cause the battery to swell, rupture, and vent electrolyte.

26. Electrical Abuse Overcharging: This is a multi-stage failure process: Lithium Plating: When the negative electrode becomes saturated, excess lithium begins to deposit as metallic lithium on its surface. Dendrite Formation: This metallic layer can grow into sharp, needle-like lithium dendrites that penetrate the separator, causing a severe internal short circuit. Runaway Reactions: The plated lithium reacts exothermically with the electrolyte, while the positive electrode decomposes, releasing a large amount of heat and oxygen . This oxygen further accelerates the breakdown of the electrolyte, leading to catastrophic failure.

27. Stage 1: Initial Heat Accumulation Period (70-90°C) When a battery is subjected to impact or external heat, its temperature can exceed 70 °C, initiating the degradation of the silicon anode's protective SEI layer. Simultaneously, the massive volume expansion of silicon (>300%) during lithiation creates immense stress, causing a repeated cycle of SEI film fracture and reformation. This process continually exposes fresh silicon, which then undergoes an irreversible chemical reaction with the FEC-based electrolyte. At the same time, the highly oxidized Nr on the positive electrode surface of NCM811 undergoes valence state reduction under thermal disturbance, accompanied by the formation of oxygen vacancies and the precipitation of rock salt phase ( NiO ): Thermal Runaway Process:

28. Thermal Runaway Process The electrolyte system undergoes hydrolysis side reaction. The heat accumulation rate during this stage shows a growth characteristic, dominated by the synergistic effect of SEI decomposition and positive electrode oxygen release . Stage 2: Thermal Acceleration Period (90-260℃) At this stage, the thermal runaway is dominated by the NCM811 positive electrode . Around 200°C, it releases lattice oxygen (O²⁻) , causing a structural phase transition from a layered to a rock salt phase. This oxygen then violently combusts with the FEC electrolyte, releasing immense heat. Simultaneously, the silicon negative electrode undergoes nanoparticle sintering at temperatures above 150°C. This forms new internal conductive pathways, triggering micro short circuits and a rapid accumulation of Joule heat . The combined heat from these reactions causes a sharp acceleration in the temperature rise, leading to electrolyte boiling . This further worsens thermal diffusion and propels the cell towards catastrophic failure.

29. Thermal Runaway Process Stage 3: Thermal runaway outbreak period (>260°C) Irreversible Tipping Point: At approximately 260 °C , system enters a strong exothermic, self-sustaining state . At this juncture, the thermal runaway process becomes irreversible , with a temperature rise rate that accelerates exponentially. Catastrophic Cathode Decomposition: The NCM811 positive electrode undergoes a deep and complete decomposition. Its layered crystal structure collapses and transforms into a mixture of metal oxides ( NiO , CoO , Mn₂O ₃), releasing high-valence metal vapors and residual oxygen. Anode Melting and Eutectic Formation Global Short Circuit Explosive Electrolyte Pyrolysis Violent Climax: Total energy released in this final stage reaches an immense 1600-1800 kJ/kg , over 100% more than in traditional graphite systems. The thermal runaway propagation rate exceeds 500 °C/s , culminating in an intense gas release and pressure wave that causes the battery to explode .

30. Temperature Sensing: A network of sensors (thermistors or thermocouples) is placed throughout the battery pack to directly monitor the temperature of individual cells or modules. A rapid, anomalous temperature rise is a direct indicator of a potential thermal event. Voltage Sensing: BMS continuously monitors cell voltages. A sudden and significant drop in a single cell's voltage is a classic signature of an internal short circuit, often the primary trigger for thermal runaway. Detection & Early Warnings :

31. Detection & Early Warnings Gas Sensors for Electrolyte Vapors (Pre-emptive Method): How it Works: Gas sensors are integrated into battery pack enclosure. These sensors are designed to detect the specific volatile organic compounds (VOCs), hydrogen (H₂), carbon dioxide (CO₂) that are released when electrolyte begins to break down during the initial stages of cell abuse (80-120 °C). Advantages: Acts as a leading indicator , providing a crucial early warning (minutes or even hours) before the thermal event becomes critical. Limitations: Can be prone to false alarms if not calibrated correctly and adds complexity and cost to the pack design. Predictive Analytics & AI-based BMS (Prognostic Method): How it Works: An AI or Machine Learning model, often running in the cloud, analyzes vast amounts of historical and real-time data from the battery. The algorithm learns the subtle, complex patterns that are precursors to cell failure and can predict the probability of a thermal event in the future. This is often referred to as creating a "digital twin" of the battery. Advantages: Offers the earliest possible warning , potentially days or weeks in advance, allowing for scheduled maintenance instead of emergency response.

32. 🔬 Cell-Level Mitigation: Intrinsic Safety Safer Chemistries: The choice of battery chemistry is critical. Lithium Iron Phosphate (LFP) , for example, is significantly more thermally stable than energy-dense chemistries like Nickel Manganese Cobalt (NMC). The strong P-O covalent bond in LFP makes it much harder for oxygen to be released during an abuse event, thus preventing a key driver of thermal runaway. Flame-Retardant Electrolytes: This involves developing advanced electrolytes with additives that are designed to be non-flammable. These additives can scavenge free radicals or form a protective layer on the electrodes at high temperatures, inhibiting the exothermic reactions that lead to a fire. BMS Role: A cts as the guardian, ensuring the cell is never pushed beyond the boundaries of its intrinsic chemical stability. Mitigation & Design Strategies :

33. Solid-State Batteries (SSBs) The Technology: Solid-state batteries replace the flammable liquid organic electrolyte found in conventional lithium-ion cells with a solid, non-flammable electrolyte (typically a ceramic or polymer). This removes a key component—the fuel—from the fire triangle. Impact on Thermal Runaway: By eliminating the flammable electrolyte, the risk of a violent fire or explosion is dramatically reduced. Solid structure can also suppress the growth of lithium dendrites, a primary cause of internal short circuits. The Future of the BMS: will need to manage new challenges, such as maintaining optimal pressure and temperature to ensure good ion conductivity across the solid layers. Future Directions:

34. Conclusion: The Central Challenge: The widespread adoption of high-energy lithium-ion batteries is fundamentally challenged by the severe safety risk of thermal runaway , a catastrophic and self-propagating failure mode that must be comprehensively addressed. The Critical Role of the BMS: The Battery Management System (BMS) acts as the intelligent nerve center of this ecosystem. Its crucial role is to provide active safety by: Detecting anomalies through conventional sensors and advanced off-gas analysis. & Responding decisively by executing isolation protocols, managing emergency cooling, and initiating safe shutdown algorithms. .

35. Our Team Thanking You! Yashodhan Zingade 231030069 Electrical Soham Ambavkar 231030004 Electrical Pushkaraj Chaure 231030028 Electrical Jayesh Kankrej Atharva Naik 231030012 Electrical 231010040 Electrical 1 5 4 3 2