Application of Lithium Battery Expansion Force Testing Fixture
Time:2025-12-06
Views:141
1. Battery Swelling Phenomenon:
The generation of battery swelling force is mainly caused by the negative electrode. During the charge and discharge cycles of the battery, lithium ions intercalate into layered materials, leading to an increase in the thickness of the electrode plate. This type of swelling is reversible. Another type of irreversible swelling is primarily caused by gas generated during the formation of the SEI film in the formation process. Gases are also produced during the charge and discharge process of lithium-ion batteries, resulting in varying degrees of battery swelling. The swelling process exerts an outward force on the battery, i.e., the swelling force!
The occurrence of swelling force can cause harm to both the cell and the module. The swelling force caused by the charge and discharge of lithium-ion batteries affects the deformation of the battery assembly space on one hand, and on the other hand, the accumulation of irreversible swelling can lead to damage to structural materials, thereby accelerating capacity decay. For modules, if the swelling force is not properly addressed, it can cause dimensional deviations in the module and even damage the structural frame. This is because the swelling force of the cell is quite significant, and battery swelling occurs earlier than gas overflow. Therefore, conducting in-depth research on the swelling behavior of lithium-ion batteries, summarizing the causes of lithium-ion battery swelling and deformation, is of great significance for optimizing the structural safety of lithium-ion battery materials and developing lithium-ion battery thermal runaway early warning systems.
2. Battery Swelling Principle:
1）. Reversible deformation
During the charging process, lithium ions generated by the decomposition reaction of the cathode material diffuse to the anode under the influence of the electric field force and intercalate into the anode material
In the reaction process, the following steps are shown:
The intercalation and deintercalation of lithium ions have a more pronounced effect on carbon materials, resulting in greater volume changes in the anode material compared to the cathode material, which leads to
During the charging process, volume expansion occurs, but during the discharging process, lithium ions are deintercalated from the negative electrode material, pass through the separator, and are driven by the electric field force
The lithium ions return to the cathode material, then combine with the electrons on the material and re-embed into the cathode material, reducing the battery‘s thickness.
During the use of lithium batteries, due to this reaction, multiple charge and discharge cycles can be performed, making this expansion a reversible deformation
.
2) Irreversible deformation
Research indicates that the causes of irreversible deformation in batteries can be categorized into two types: the formation and thickening of the SEI film, and internal gas expansion resulting from side reactions during charging and discharging
.
During the initial charge and discharge process, an irreversible reaction occurs between the negative electrode and the electrolyte, forming a SEI film to protect the negative electrode material without affecting
The formation of the SEI film allows lithium ions to pass through, but it cannot completely prevent the reaction between the anode and the electrolyte. As the reaction gradually progresses, the SEI film will thicken over time
This also leads to irreversible deformation of the battery.
During the charging and discharging process of lithium batteries, certain side reactions occur to some extent, including the decomposition of the electrolyte and its reaction with water, producing
The generation of CO2, H2, O2, and hydrocarbon gases caused irreversible deformation of the battery‘s volume
3) The Impact of Pressure on Batteries
In addition, lithium batteries are typically assembled into battery modules by connecting multiple battery cells in series or parallel, requiring a certain amount of pressure to secure them. Appropriate pressure can ensure
The positive and negative electrodes inside the battery must be in close contact with the separator to enhance the interface for charge and discharge reactions, reduce internal resistance and polarization, thereby improving
The cycling stability and high-rate charge-discharge performance of the battery have been improved.
Excessive low pressure can reduce the electrode reaction area, deteriorate the reaction interface, increase the battery internal resistance and polarization, and decrease battery capacity after prolonged cycling
It can also cause the electrode material to detach from the current collector, severely affecting battery lifespan.
Excessive pressure can damage the pore structure of electrode materials and separators, deteriorate the reaction interface, and increase the internal resistance of the battery, leading to a rapid decline in battery capacity
Degradation can lead to severe risks such as internal battery short circuits and thermal runaway.
3. Battery Expansion Force Testing Method
How to directly measure battery expansion force?
The most core and mainstream approach involves integrating high-precision pressure sensors on the battery surface or within test fixtures. There are two common technical routes:
One approach is to directly mount micro piezoresistive or piezoelectric sensor arrays on the surface of the battery cell or between the stacked layers of the electrode core, enabling real-time detection of localized pressure variations;
The second method involves using thin-film pressure sensors (such as FSRs) to closely adhere to the battery casing or arranging sensors on the inner walls of rigid testing fixtures to measure the overall swelling of the battery
The external force applied to the expansion. These methods can directly and continuously capture the dynamic battery expansion force during charge-discharge cycles, with reliable and intuitive data, making them currently
The cornerstone of pre-research and production line verification.
Can alternative methods accurately capture battery expansion forces?
Although direct pressure sensing is the gold standard, researchers have also explored other indirect or supplementary methods. For instance, laser displacement sensors or optical dry
The instrument can perform non-contact, high-precision measurement of battery thickness changes and, in combination with the mechanical model of the cell material (such as Young‘s modulus), calculate the theoretical expansion force
.
Another approach involves attaching resistance strain gauges to specific locations on the battery casing and inferring stress through deformation. However, these methods are constrained by model accuracy
The installation location is highly sensitive, and environmental vibrations significantly impact performance, making it difficult to match the real-time, in-situ accuracy of direct pressure sensing in capturing battery expansion forces
Stability is typically used as a supplementary validation.
How to simulate the battery expansion force under real working conditions?
Understanding the swelling behavior of batteries in real-world complex environments is equally crucial. This requires in-situ measurements conducted within environmental simulation test chambers: integrating pressure
The battery of the force sensor is placed in a fixture with controllable temperature and humidity, charge/discharge rates, and mechanical constraints (such as specific clamping force) to simulate electric vehicle acceleration
Scenarios such as high-temperature storage.
This test can reveal how temperature, SOC (State of Charge), and mechanical boundary conditions collectively influence the evolution of battery expansion forces, providing insights for battery packs
Structural design and thermal management strategies provide direct evidence.
Among various detection methods, the integration of pressure sensors for direct measurement is undoubtedly the most commonly used and reliable core technology for capturing battery expansion forces
Technology, particularly array-type and thin-film sensors, is the most widely applied.
4. Selection of testing fixtures
Taking the battery expansion force testing fixture made by Yide Ren Precision as an example, the experimental platform mainly consists of thin film pressure sensors, battery clamps, and charging and discharging equipment
Composed of an upper computer and a high-precision signal collector.
The equipment mainly consists of servo motor pressure mechanism, high-precision thickness measurement mechanism, pressure testing mechanism, data acquisition system, and data processing software
Composed into parts. By applying pressure to the battery cell through a servo motor and controlling a constant gap, the expansion force of the battery cell during charge and discharge cycles can be measured
Try.
Servo motor pressure mechanism: used to apply constant pressure or clearance to the battery cell, ensuring stability and accuracy during the testing process. High precision measurement
Thick mechanism: used to measure the thickness change of battery cells during charge and discharge cycles, and evaluate the expansion of battery cells. Stress testing agency: Real time monitoring of electricity
The pressure changes of the core during the testing process ensure the accuracy of the test data. Data collection system: Collect data during the testing process, including electricity
The thickness and pressure changes of the core provide a basis for subsequent data analysis. Data processing software: perform preliminary processing on the collected data
Generate charts and tables to generate test data reports.
The battery charging and discharging equipment can charge and discharge the battery through the working conditions written by the upper computer, and can record data such as current, voltage, capacity, etc; pressure transmission
Sensors can detect changes in the compression force applied to the battery, and the data acquisition system of the battery expansion force tool from DeRen Jinggong can read these pressures
The reading of the force sensor is used to record the dynamic changes in the surface pressure of the battery.
Through precise measurement and analysis, the expansion performance of battery cells during charge and discharge cycles can be evaluated, providing insights for optimizing battery design and production processes
Learning basis.
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