Today, Wuxi Rihuan Sensing Technology Co., Ltd. will introduce how laser displacement sensors are used in the lithium battery industry? - Three major applications: sheet thickness, roll diameter, and positioning.

The production process of lithium batteries involves more than fifty steps. The core processes mainly include raw material pulping, coating, rolling, winding, assembly, testing, and packaging. In this precise production chain, laser displacement sensors, with their advantages of non-contact measurement, high-speed sampling, and high-precision output, have become indispensable measurement tools for key links such as sheet thickness detection, separator roll diameter monitoring, and battery cell assembly positioning.

1. Sheet Thickness Detection: The Micrometer-level "Gatekeeper" of Coating and Rolling

Core Detection Requirements

The sheet is the core component of the battery cell, composed of copper foil/aluminum foil current collectors and positive/negative electrode active material coatings. The thickness of the current collector is mostly in the range of 8-20 μm, and the coating thickness is usually 50-150 μm. The industry's tolerance for the overall thickness of the sheet is ±1 μm. The uniformity of the sheet thickness directly determines the capacity, weight, energy density, and other performance indicators of the battery. In the coating and rolling processes, uneven sheet thickness may also cause damage. Even extremely small thickness deviations can lead to battery capacity degradation or increased internal resistance.

Selection Points

Laser displacement sensors usually adopt an upper and lower beam reflection installation scheme - the upper probe is fixed above the equipment, and the lower probe is fixed below. The thickness is calculated by combining the distance measurement of the upper and lower sensors and the fixed spacing. The sensor is installed in a C-shaped frame structure with linear reciprocating motion along the width direction of the sheet, scanning the entire width for full-frame detection.

When selecting, the following parameters need to be focused on:

Repeatability Accuracy: Lithium battery sheet thickness detection requires the sensor's repeatability accuracy to reach micrometer-level or even sub-micrometer-level. Some high-precision models can have a repeatability accuracy of 0.25 μm or even 0.01 μm.

Sampling Frequency: The line speed of the coating and rolling processes can reach 3-5 m/s or even higher, requiring the sensor to achieve uninterrupted real-time measurement. High-frequency sampling models can reach 50 kHz or even 160 kHz.

Measurement Range: It needs to be adapted to the sheet thickness fluctuations and installation margin. The typical reference distance is 30 mm, and the measurement range is ±5 mm.

Installation Precautions

Alignment Control: The upper and lower beam reflection installation must ensure that the optical axes of the two sensors are strictly coaxial. Usually, a U-shaped marble bracket is used to ensure coaxiality.

Vibration Isolation: The vibration of the C-shaped frame movement will bring measurement errors. Optimization of the scanning strategy and filtering processing can be used to reduce the impact of vibration.

Calibration: Use a standard sheet thickness measurement calibration module to eliminate measurement errors caused by the coaxiality and measurement inclination of the two sensors.

Surface Reflection Treatment: Copper foil and aluminum foil are high-reflection materials. It is recommended to conduct on-site measurement before installation to confirm the measurement stability of the sensor at different angles and distances. For high-reflection materials, the installation angle can be adjusted or a polarization filter can be used.

2. Roll Diameter Measurement: The "Real-time Monitor" of Separator and Sheet Rolling

Core Detection Requirements

The rolling process of materials such as sheets and separators is the core link determining the quality of the battery cell. The uniformity and consistency of the rolling diameter directly affect the stability of the battery cell's capacity output, the balance of internal stress distribution, and are closely linked to the safety performance of the final product. During the operation of the laminating machine or winding machine, the equipment needs to confirm the condition of the separator leftover material in real time and notify the workers to replace the new material roll when the material is insufficient.

The traditional method counts the rotation circle of the servo motor to determine the condition of the winding material, but due to the floating range of the separator rolling thickness, the accuracy is limited.

Selection Points

The laser displacement sensor is installed above the unwinding device, aligning with the surface of the separator roll material, and using the laser triangulation reflection principle to capture the thickness changes of the roll material in real time. The sensor outputs distance data at high-frequency sampling and converts it into residual material thickness through algorithms.

Key parameters for selection:

Detection range: Needs to be compatible with different specifications of material rolls. Typical models have an effective measurement range of 200-600mm or even 400mm, covering both small-diameter experimental rolls and large-scale production work rolls.

Repeatability accuracy: When the detection distance is between 200-400mm, the repeatability accuracy can reach 0.15mm, which is nearly 10 times higher than that of traditional ultrasonic sensors (1-2mm accuracy).

Sampling frequency: For scenarios with dynamic changes in roll diameter, a 1kHz high-frequency sampling can track the thickness changes of the roll material in real time, and the residual material thickness data is updated in milliseconds.

Installation precautions:

Installation position: The sensor should be installed above the unwinding device, aligned with the surface of the roll material, and ensure that the laser light spot falls within the effective measurement area.

Environmental adaptability: Production sites may have interference factors such as vibration and temperature changes. Therefore, a product with good anti-interference ability and IP67 protection level should be selected.

Compact design: The lithium battery equipment has limited installation space. Compact sensors (such as 44.4×25×20mm) should be preferred to avoid interfering with the existing production line layout.

III. Positioning detection: "Precise ruler" for the height of battery shell and cover plate

Core detection requirements

On the lithium battery cell assembly line, whether the height of the top cover after pressing is within the tolerance range and whether there is a significant difference in the surrounding area of the shell opening are key indicators determining the sealing performance and quality of the cell. Insufficient flatness of the top cover can lead to sealing failure. Additionally, at the welding station, real-time height feedback is required to compensate for the Z-axis of the welding equipment to prevent welding abnormalities.

Traditional contact-type probes face numerical fluctuations on high-speed production lines due to wear, rebound, and slight vibrations of the workpiece. Laser displacement sensors use non-contact measurement, directly reading distance changes, and are more suitable for high-speed assembly lines.

Selection points

Measurement logic: This station truly requires continuous distance measurement, rather than simply a signal presence. The sensor should be able to simultaneously determine the overall height and local segment differences.

Output mode: It should support both switch quantity determination and analog output, facilitating subsequent connection to PLC, industrial computers, or data acquisition modules.

Range selection: For compact stations, a specification with a center distance of around 50mm should be selected. The range should be compatible, ensuring stable signal transmission.

Installation precautions

Angle control: The vertical angle between the sensor installation and the measured object should be controlled within ±5° to avoid deformation of the laser light spot. For high-reflective edges, the emission angle needs to be adjusted to place the measurement point in a more stable reference area.

Reference setting: In conjunction with the teaching mode, set the upper and lower limit windows, and set the reference plane and judgment window. The same station can determine both the overall height and identify local warping or unevenness after pressing.

Multi-sensor collaboration: When measuring the flatness of the lithium battery cover plate, the measurement values from multiple laser displacement sensors should be combined to determine the flatness of the top cover.

Surface condition assessment: Before selecting the measurement scheme, confirm three things - the surface condition of the measurement object, the installation distance, and whether it requires switch quantity or continuous displacement data.

Selection summary

Application scenarios Core detection requirements Key selection parameters Installation points

Sheet thickness μm-level thickness tolerance Repeatability accuracy ≤ 1μm, sampling frequency ≥ 10kHz Up-down beam, coaxial installation, vibration isolation

Roll diameter measurement Real-time residual material monitoring Range ≥ 200mm, repeatability accuracy ≤ 0.2mm Installed above the unwinding device, high-frequency sampling

Positioning detection Height/segment difference/flatness 50mm center distance, analog output Vertical angle ≤ ±5°, multi-sensor collaboration The value of laser displacement sensors in the lithium battery industry lies not merely in pursuing high precision, but in providing a more stable and easier-to-integrate data-based detection method under high-speed, small-size, and complex surface conditions. The thickness tolerance of the electrode sheet is measured in micrometers, and the winding diameter directly affects the safety of the battery cell and the assembly accuracy determines the yield of the finished product - these key indicators ultimately rely on laser displacement sensors to achieve online, real-time, and non-contact precise measurement.

Rihuan Sensing provides a series of high-precision laser displacement sensor products suitable for the lithium battery industry, covering various application scenarios such as electrode sheet thickness detection, winding diameter monitoring, and battery shell cover plate positioning. The products support multiple measurement principles such as the triangulation method and spectral confocal. The products have high-speed sampling, micrometer-level repeatability accuracy, and industrial-level anti-interference capabilities. Please follow Rihuan Sensing to obtain professional measurement solutions for the lithium battery industry.