Lithium-ion batteries have gained a significant presence among large-format batteries. They are extensively used in airplanes, electric vehicles, and energy storage systems. However, there are risks of thermal runaway in lithium-ion batteries along with combustion phenomena, just like the other electrochemical systems batteries.
Thermal runaway (TR) is the most dangerous event in a lithium-ion cell. It’s a rapid, self-perpetuating rise in temperature and pressure caused by chain reactions inside the cell.
This can lead to the battery heating violently, potentially triggering combustion phenomena within the cell and, in severe cases, even exploding.
Besides a serious risk to the EV users, this permanently renders the device unserviceable.
Let us dive into thermal runaway in lithium-ion batteries and the number of stages of the entire thermal runaway process.
Thermal Runaway in Lithium-ion Batteries: An Overview
In short, the thermal runaway in Lithium-ion batteries is a dangerous chain reaction within a lithium-ion battery cell. An initial rise in temperature triggers a cascade of self-heating events, ultimately leading to extreme temperatures, fire, or even explosion.
This complex process involves several aspects, such as:
- Breakdown of components: Heat or damage can cause internal battery components to break down, releasing gases and generating more heat.
- Electrolyte Reactions: The electrolyte in the battery reacts with the released gases, further increasing the temperature.
- Short Circuits: These can occur as materials warp and melt, leading to rapid uncontrolled energy release.
Thermal Runaway in Lithium-ion Batteries: Some Examples
Several thermal runaway-caused battery accidents occurred in recent years, such as:
- 787 Boeing Dreamliner batteries: In 2013, the Boeing 787 Dreamliner, designed to be fuel-efficient and innovative, was grounded worldwide due to recurring battery fires.
- Jiangsu Chemical Plant Disaster: A powerful explosion attributed to a thermal runaway devastated the Tianjiayi Chemical Co., Ltd. facility in Jiangsu Province, China, on March 21, 2019.
- Fire of the Tesla Model S electric car: In 2013, a Tesla Model S caught fire in Smyrna, Tennessee, triggering federal investigations.
Latest Studies to Tackle the Thermal Runaway in Lithium-ion Batteries
While extensive research has improved our understanding of thermal runaway, the precise mechanisms and interactions remain complex. This makes it difficult to completely prevent, highlighting the need for continuous safety innovation and improvement in battery technology.
Here are some studies that are pivotal in advancing our understanding of thermal runaway mechanisms and enhancing the safety of battery technologies.
Thermal Runaway Mechanisms in All-Solid-State Batteries
A 2023 study in Energy & Environmental Science delves into thermal runaway in sulfide-based all-solid-state batteries, focusing on reactions such as gas-solid and solid-solid interactions.
In-Situ Monitoring Technologies
The research titled Recent Progress on In-Situ Monitoring and Mechanism Study of Battery Thermal Runaway Process highlights the use of technologies like X-ray CT, SEM, and infrared gas analyzers for early detection of thermal runaway by monitoring internal battery changes.
Fire Suppression and Thermal Runaway in Lithium-Ion Batteries
An MDPI study examines the effectiveness of fire suppression systems, both manual and automatic, in controlling thermal runaway in different lithium-ion battery types through detailed experimental setups.
Thermal Runaway in Lithium-ion Batteries: 4 Stages
According to the generally accepted mechanism of the phenomenon, let us explore the principal stages of thermal runaway in Lithium-ion batteries:
Stage 1: SEI Layer Destruction and Heat Generation
The first stage is considered to be the destruction of the SEI (solid electrolyte interphase), which is the passivating layer at the anode. This stage occurs when a battery is heated to a temperature exceeding 90℃.
The SEI layer comprises meta-stable polymers and stable components such as LiF and Li2CO3. At temperatures above 90℃, the meta-stable components decompose exothermically.
Stage 2: Uncontrolled Heating and Gas Generation
The exothermic decomposition reaction of SEI will increase the temperature inside the battery. The heating up results in exothermic reactions of the interaction between the lithium intercalated in the anode and the organic solvents in the electrolyte.
During this stage, the battery temperature can rapidly rise to exceed 200°C (392°F), producing flammable gasses and potentially resulting in rupture, fire, or explosion if the thermal runaway is not controlled or reduced.
Proper battery design, thermal management, and safety devices are critical for preventing and controlling thermal runaway in lithium-ion battery systems.
Stage 3: Separator Meltdown and Internal Short Circuits
At a temperature higher than 130℃, the separator melts as it is made of polyethylene (PE)/polypropylene (PP). As a result, a series of internal short circuits occur between the electrodes. Also, the voltage at the battery terminals drops to 0 volts.
As a result, the energy accumulated in the battery due to charging is released, increasing the battery’s temperature even more.
Stage 4: Cathode Breakdown, Oxygen Release, and the Risk of Explosion
The active materials of the cathode begin to decompose, and the oxygen release starts with a further rise in the temperature. This stage of thermal runaway is considered the most dangerous and devastating since it involves releasing volatile materials, fire, and maybe explosions.
Thermal Runaway in Lithium-ion Batteries: Combustion Behavior
While thermal analysis is a valuable tool for evaluating the safety of large-scale lithium-ion battery setups, the risk of thermal runaway and combustion still exists. By studying combustion behavior, we can gain the insights needed to improve battery design and ensure safe, widespread implementation. This also informs effective firefighting strategies and shapes safety protocols for large-scale battery use.
The combustion behavior can be divided into three stages:
- Igniting: Initial heat triggers exothermic reactions, releasing flammable gases.
- Stably Combusting: A flammable gas mixture ignites, leading to self-sustaining combustion with visible flames.
- Extinguishing: Combustion ceases as fuel is consumed or external suppression methods are applied.
Fully charged batteries exhibit complex combustion behavior, including a sudden smoke release from the pressure-limiting valve during the stable combustion stage. This smoke release is associated with a sharp surface temperature increase from 198°C to 405°C.
Latest Research to Minimize the Risks of Combustion Behavior
Here are some new developments that can contribute to preventing the combustion behavior:
Understanding LIB Fire Risks: The Role of Electrolyte and Gasses
Researchers investigated the thermochemical and combustion properties of electrolytes and flammable gasses, which regulate ignition and burning behavior.
As a result, the researchers found that combustion enthalpy and vaporization enthalpy are essential to determine the flammability of carbonate solvents.
Warehouse Fire Hazards: Understanding Lithium-Ion Battery Combustion
FM Global evaluated the hazard posed by the bulk stage of LIB in warehouse scenarios. They studied the flammability of battery storage in two series, small-format and large-scale rack storage, and proposed the best protection recommendations.
In this study, the 50 Ah Li (NixCoyMnz)O2/LTO battery, one of the safest composition schemes for large-scale batteries, was selected to study the combustion behavior and fire hazards experimentally.
The dynamical parameters, including mass loss, surface and flame region temperature, and heat release rate, were obtained to characterize the combustion behavior of lithium titanate batteries. The fire hazards under different states of charge (SOC) were compared further.
To Sum It Up
While the ongoing research offers tremendous promise for a sustainable future, the risks of lithium-ion batteries and combustion must be carefully managed. The studies and examples highlighted in this article underscore the importance of continuous research and innovation in battery safety.
By prioritizing safety without hindering innovation, we can leverage the full potential of lithium-ion batteries. Advancements in materials science, cell design, and safety monitoring systems promise a future where these powerful batteries fuel our lives with both efficiency and peace of mind.