Lithium battery swelling is a critical issue affecting devices ranging from smartphones to electric vehicles. This phenomenon not only compromises battery performance but also raises serious safety concerns, including leakage, fires, or explosions. Understanding the root causes of lithium battery swelling is essential for manufacturers and users to mitigate risks and extend battery life. This article explores the scientific, operational, and environmental factors behind this phenomenon, backed by data and research. For information on how to dispose of swollen lithium batteries, please refer to this article: How to Dispose of Swollen Lithium Batteries？
Common Causes of Lithium Battery Swelling
1. Electrolyte Decomposition and Gas Formation
Electrolyte decomposition is one of the leading contributors to lithium battery swelling. In a lithium-ion cell, the electrolyte is responsible for transporting lithium ions between the cathode and anode during charge and discharge cycles. Under normal operating conditions, this process occurs smoothly. However, when the battery is exposed to stress factors—such as high voltage, overcharging, or elevated temperatures—the organic solvents in the electrolyte (for example, ethylene carbonate) begin to break down.
This degradation results in the formation of various gases, including carbon dioxide (CO₂), hydrogen (H₂), and methane (CH₄). Research indicates that these gases can account for up to 60% of the gas buildup in aged cells, contributing significantly to internal pressure. The buildup of pressure not only causes physical expansion of the cell but also compromises the structural integrity of the battery casing. In severe cases, this may lead to venting, leakage, or even thermal runaway, where the battery generates heat uncontrollably. Additionally, impurities or contaminants in the electrolyte can accelerate these side reactions, further worsening the situation.
2. Lithium Plating and Dendrite Growth
Lithium plating occurs when lithium ions, instead of intercalating uniformly into the anode material (typically graphite), deposit on the anode surface as metallic lithium. This is especially prevalent during overcharging or fast charging at low temperatures, where reduced ion mobility prevents the ions from embedding properly into the electrode structure.
Over time, these metallic deposits can evolve into dendrites—needle-like crystalline structures that can grow long enough to pierce the separator between the anode and cathode. When dendrites penetrate this barrier, they create internal short circuits, which result in localized hotspots and further accelerate unwanted chemical reactions within the cell. These reactions often produce additional gas and heat, both of which contribute to swelling. The safety risks associated with dendrite formation are particularly acute, as they can lead to catastrophic failures including fires or explosions if the internal short circuit is severe enough.
3. Mechanical Stress and Manufacturing Defects
The structural integrity of a lithium-ion battery depends heavily on precision during its manufacturing process. Even minor imperfections—such as slight misalignments of the electrodes, contamination, or inconsistencies in the electrode coating—can serve as weak points within the cell. Over repeated charge and discharge cycles (often referred to as the battery’s “breathing”), these weak spots are subjected to mechanical stress.
This continuous mechanical stress can lead to the development of micro-cracks or delamination of the electrode layers. As these defects propagate, they create channels where gases, produced by electrolyte decomposition or other side reactions, can accumulate. In fact, studies have suggested that microscopic manufacturing defects may account for 15–20% of swelling cases observed in commercial batteries. Improving manufacturing precision and quality control is therefore critical in minimizing these risks and ensuring long-term battery reliability.
4. Overcharging and Over-Discharging
Operating lithium-ion batteries beyond their prescribed voltage limits is a major cause of degradation. Overcharging forces an excess of lithium ions into the anode, which can lead to a host of issues including structural deformation, increased internal resistance, and accelerated chemical breakdown of the electrolyte. This excessive influx of lithium ions stresses the anode material, resulting in higher chances for side reactions that generate gas.
Conversely, over-discharging can be equally damaging. When the battery voltage falls below a critical threshold, the cathode structure may be compromised and irreversible damage to the electrode materials can occur. Both overcharging and over-discharging disturb the delicate balance of the battery’s internal chemistry. Data from the IEEE Power & Energy Society indicates that even a small overcharge—by just 5%—can increase the likelihood of swelling by 40% in standard LiCoO₂ batteries. These abnormal operating conditions also pave the way for thermal runaway, where the battery can overheat and swell uncontrollably, posing serious safety hazards.
5. High Temperatures and Poor Thermal Management
Temperature plays a pivotal role in the health and stability of a lithium-ion battery. When operating at temperatures above approximately 45°C, many of the chemical reactions within the battery are accelerated. One particularly sensitive component is the solid electrolyte interphase (SEI) layer on the anode. This protective layer, which forms naturally during initial cycles, starts to degrade at high temperatures. As the SEI breaks down, it not only exposes the electrode to further degradation but also consumes additional electrolyte in the process, leading to further gas generation.
Devices with poor thermal management—whether due to inadequate cooling systems in electric vehicles, laptops, or other electronics—are especially vulnerable. Without proper heat dissipation, the battery’s temperature can rise quickly, exacerbating degradation processes and leading to swelling. In extreme cases, the combination of high internal temperatures and rapid gas generation may trigger thermal runaway, significantly increasing the risk of fire or explosion.
6. Aging and Capacity Fade
Like all rechargeable systems, lithium-ion batteries undergo gradual degradation as they age. Over hundreds of cycles, the performance of the battery inevitably declines—a phenomenon known as capacity fade. This is largely due to the continuous degradation of the electrodes: the cathode may lose active material over time, while the SEI layer on the anode thickens, reducing the efficiency of lithium-ion transport.
As the battery ages, the internal resistance increases, which leads to additional heat generation during charging and discharging. This heat further accelerates side reactions that produce gas, contributing to swelling. A report by Battery University from 2022 notes that after about 500 cycles, the risk of swelling can increase by 20–30% due to these cumulative degradation effects. The imbalance between the deteriorating electrodes not only reduces the overall capacity of the battery but also makes it more susceptible to safety issues, including swelling and eventual failure if the degradation process is left unchecked.
Conclusion
Lithium battery swelling stems from complex interactions between chemical reactions, operational conditions, and manufacturing quality. Each of these factors—whether chemical, mechanical, or thermal—interacts to influence the longevity and safety of lithium-ion batteries. Understanding these mechanisms is critical for developing improved battery designs, implementing effective thermal management systems, and ensuring the overall safety and reliability of devices that rely on these energy storage systems. By addressing factors like electrolyte stability, thermal management, and voltage control, manufacturers can mitigate risks and enhance safety. For consumers, understanding these causes ensures better battery handling and longevity.
