The new energy industry is experiencing explosive growth, but this rapid expansion brings a critical focus to battery safety. Frequent spontaneous combustion incidents in electric vehicles and growing concerns over fire hazards in large-scale energy storage power stations have highlighted a significant challenge: battery thermal runaway . This uncontrolled chain reaction within a battery is a key bottleneck hindering the full potential of clean energy. At its core, thermal runaway is a vicious cycle where the energy released from internal chemical reactions overwhelms the battery’s ability to dissipate heat. Research, including experimental work by Academician Ouyang Minggao’s team, reveals that thermal runaway is intricately linked to critical internal events like positive electrode oxygen release, negative electrode lithium plating, and diaphragm collapse.
To ensure the safe development of the new energy sector, we need a deep dive into the scientific principles, common causes, and proactive prevention strategies for battery thermal runaway.
The Core Causes of Battery Thermal Runaway
Battery thermal runaway rarely has a single cause; it’s often a complex interplay of internal flaws, external stresses, and system malfunctions. Understanding these triggers is paramount for effective prevention and mitigation.
1. Internal Defects: The Ignition Point
The most insidious triggers of thermal runaway often originate from within the battery itself, stemming from manufacturing imperfections or material limitations.
- Internal Short Circuit: This is a direct and rapid initiator of heat. Impurities during manufacturing, microscopic burrs on electrode materials, or mechanical damage (like extrusion or puncture during assembly or use) can cause the positive and negative electrodes to come into direct contact. This immediately releases a tremendous amount of heat. For instance, in a controlled needle puncture test, the temperature in the short-circuit area can surge past 500∘C, directly setting off thermal runaway.
- Lithium Plating Phenomenon: When lithium-ion batteries are charged at low temperatures or discharged with excessively high currents, lithium ions fail to properly insert into the negative electrode. Instead, they deposit as metallic lithium on the negative electrode surface, forming dendrites (tree-like structures). These dendrites can grow and eventually pierce the diaphragm, causing an internal short circuit. This process not only generates heat but also releases flammable gases, further aggravating the temperature rise.
- Material Defects: The intrinsic properties of battery materials also play a significant role. Some positive electrode materials, particularly certain ternary materials, exhibit poor thermal stability and can decompose at high temperatures, releasing oxygen. When combined with a flammable electrolyte, these material characteristics create a highly volatile internal environment susceptible to thermal runaway.
2. External Abuse: The Catalyst for Catastrophe
Beyond inherent flaws, external conditions and improper usage can act as powerful catalysts, pushing even well-designed batteries towards thermal runaway.
- Overcharge and Over-discharge: Pushing a battery’s voltage beyond its rated limits through overcharging or deep discharging can cause irreversible chemical reactions. Overcharging can lead to the oxidation and decomposition of the electrolyte, generating oxygen and heat, thereby creating a dangerous feedback loop. Similarly, extreme over-discharging can lead to internal structural damage and subsequent short-circuiting. Unstable voltage sources, like those seen with improvised charging methods such as “flying wire charging,” can easily lead to dangerous overcharging.
- High Temperature Environment: Batteries are engineered to operate within specific temperature ranges. When the ambient temperature consistently exceeds, for example, 45∘C, the battery’s natural heat dissipation efficiency significantly decreases. Concurrently, internal side reactions within the battery accelerate, rapidly accumulating heat and accelerating the thermal runaway process.
- Mechanical Shock: External forces such as severe collisions, accidental drops, or strong vibrations can physically damage the battery’s intricate internal structure. This damage might rupture the delicate diaphragm that separates the electrodes or cause immediate internal short circuits, directly triggering thermal runaway.
3. System Failure: The Amplifier of Danger
Even with robust batteries and careful handling, malfunctions within the broader battery management ecosystem can amplify risks and turn a minor issue into a major incident.
- BMS (Battery Management System) Failure: The BMS is the battery’s guardian, constantly monitoring critical parameters like voltage, current, and temperature. If the BMS malfunctions, provides inaccurate readings, or fails to respond effectively to detected abnormalities in real time, it can significantly delay or completely miss crucial early warnings of an impending thermal runaway event. This can render other safety measures ineffective.
- Circuit Aging: Over prolonged periods of use, electrical circuits within the battery pack can degrade. Damage to the line insulation layer or poor electrical contacts can lead to increased electrical resistance, causing localized overheating. These “hot spots” can then act as an external heat source, initiating thermal runaway in adjacent battery cells.
Conclusion
Battery thermal runaway presents a complex challenge, requiring a dual focus on both advanced technical solutions and meticulous human management. The journey towards safer new energy systems necessitates building a comprehensive, full-chain safety system that encompasses “prevention – monitoring – emergency response.
From a technological standpoint, continuous innovation is essential. This includes ongoing research into new material solutions, such as solid electrolyte development, which promises inherent improvements in thermal stability. Equally important are advancements in system-level protection, including highly intelligent BMS platforms capable of precise thermal runaway prediction and sophisticated heat spread suppression technologies designed to contain and mitigate incidents.
For users, adopting standardized charging practices and diligently avoiding battery use in extreme environments are fundamental steps in reducing risks. Ultimately, only by giving equal importance to both cutting-edge technology and rigorous operational management can we build a truly solid safety line for energy storage, thereby fostering the steady and sustainable development of the new energy industry.