Application of Laser Displacement Sensor in Lithium Battery Electrode Edge Warpage and Waviness Detection

Measurement Solution

Industry Background In the manufacturing process of new energy lithium batteries, the quality of the electrodes (positive and negative electrodes) directly affects the performance and safety of the cell. Edge warping and waviness of the electrodes are common defects in coating, rolling, and slitting processes, leading to poor electrode alignment and increased short-circuit risk during subsequent stacking or winding. Therefore, online, non-contact, high-precision detection of electrode edge warping and waviness has become a key aspect of quality control in lithium battery production. Detection Requirements Electrode edge warping detection mainly focuses on the height change of the electrode edge relative to a reference plane, while waviness reflects the periodic undulations of the electrode surface. Typical detection parameters include: warping height (usually required to be ≤±0.5mm), waviness amplitude (usually required to be ≤0.3mm), and period. Detection needs to be completed in real time under high-speed electrode movement (e.g., rolling line speed can reach 50m/min), and the data output should be used for feedback and adjustment. Measurement Challenges Interference from highly reflective materials: The electrode substrate (copper foil, aluminum foil) has strong reflectivity, which easily causes spot distortion or signal saturation during laser triangulation measurement. Dynamic accuracy under high-speed motion: When the electrode moves at high speed, the sensor needs a high sampling frequency to capture minute deformations. Edge effect: Material discontinuities at the electrode edges can easily cause diffraction or edge reflection, affecting measurement stability. Environmental adaptability: Lithium battery workshops are subject to dust and temperature/humidity variations; the sensor needs to have certain protective capabilities. Recommended sensor solution: The ST-P series laser displacement sensor is based on non-contact measurement using laser triangulation and is suitable for detecting warping and waviness of lithium electrode sheets. Based on the detection distance and accuracy requirements, the following models are recommended: Model Reference Distance Measurement Range Repeatability Linear Error ST-P30, Detection range 30mm±5mm, Repeatability 0.15μm, Linear error <±3μm ST-P50, Detection range 50mm±10mm, Repeatability 0.25μm, Linear error <±4μm ST-P80, Detection range 80mm±15mm, Repeatability 0.5μm, Linear error <±6μm ST-P150, Detection... The ST-P400 has a detection range of 150mm ± 40mm, repeatability of 1.2μm, and linear error < ±16μm. The ST-P450 has a detection range of 450mm ± 250mm, repeatability of 8μm, and linear error < ±250μm. For electrode edge warping detection, the ST-P30 or ST-P50 is typically selected, as its high repeatability and low linear error meet the requirements for micron-level warping measurements. If the detection distance is large or waviness needs to be measured simultaneously, the ST-P80 or ST-P150 can be used. The sensor's maximum sampling frequency is 160kHz, supporting high-speed online measurement. Implementation Method: The sensor is vertically mounted above the electrode, with the measurement spot aligned with the electrode edge area. For warping detection, single-point measurement is typically used, with the sensor fixed on an adjustable bracket, ensuring the reference distance is perpendicular to the electrode surface. For waviness detection, multiple sensors (e.g., 3-5) can be arranged along the width of the electrode, or a single sensor can be used in conjunction with a scanning mechanism. Measurement Process: The sensor emits a laser beam onto the electrode surface, receives the reflected light, and calculates the distance value. As the electrode moves, the sensor continuously collects data and uploads it to a host computer via Ethernet or RS485. The host computer software calculates the warp height (difference between the maximum and minimum values) and waviness in real time (through filtering or FFT analysis). When the detected value exceeds the limit, an alarm signal (IO or analog signal) is output, triggering rejection or adjustment of rolling parameters. Signal Output Methods: The ST-P series supports Ethernet, RS485, analog signals (4-20mA or 0-10V), and IO outputs, allowing flexible integration with PLCs, industrial computers, or rolling equipment control systems. Ethernet is recommended for high-speed data acquisition, while analog signals are used for real-time feedback control. Selection Considerations: Detection Distance and Range: Select a reference distance based on the installation space from the electrode surface to the sensor to ensure the warp range is within the measurement range. Accuracy and Repeatability: Warpage detection typically requires repeatability ≤1μm and linearity error <±5μm, which the ST-P30/50 meets. Sampling Frequency: The faster the electrode speed, the higher the required sampling frequency. For example, at a linear speed of 50m/min, if one point needs to be collected every 1mm, a sampling rate of at least 833Hz is required, which the ST-P series can easily handle at 160kHz. Surface Characteristics: For highly reflective materials such as copper foil and aluminum foil, it is necessary to confirm sensor compatibility. The ST-P series uses a special optical design to adapt to certain reflective surfaces, but on-site testing and verification are recommended. Environmental Protection: Lithium battery workshops have high dust levels; it is recommended to select an IP67 protection rating or install an air blowing device. Application Value: Improved Yield: Real-time detection of warpage and waviness allows for timely adjustment of process parameters, reducing defective products. Reduced Labor Costs: Replaces manual sampling inspection, achieving 100% online full inspection. Data Traceability: Measurement data can be uploaded to the MES system, supporting quality traceability and process optimization. Precautions For highly reflective materials such as copper and aluminum foil, on-site testing is recommended before installation to confirm the sensor's measurement stability at different angles and distances. Burs or dust may exist on the electrode edges; the sensor lens needs to be cleaned regularly, or a protective cover should be installed. If using a dual-probe through-beam thickness measurement method (for thickness detection), ensure the coaxiality of the two probes is calibrated. This application uses single-probe warp detection, so through-beam measurement is not required. For waviness detection, the sensor installation spacing needs to be determined based on the wave period; it is generally recommended that the spacing be ≤ half the wave period. The above solutions are based on the ST-P series laser displacement sensor. Specific model parameters need to be confirmed based on actual working conditions. It is recommended to contact the manufacturer for sample testing.