A comprehensive guide to battery winders

1.Overview of winding equipment classification

1.1 Classification of mainstream winders

Lithium battery winding machine is used to wind lithium battery cells, is a battery positive plate, negative plate and diaphragm in a continuous rotation of the assembly into a core package machine. The battery winding machinehas a positive and negative feeding unit, and the part that winds the positive and negative membranes together is called the winding needle.

According to the different shape types of the winding core, the winding equipment can be mainly divided into square winding and cylindrical winding two categories. Square winding can be subdivided into square automatic winding machine and square production winding machine two categories, square winding out of the battery cell is mainly used to make power/energy storage square batteries, digital batteries and so on.

According to the degree of automation of the winding machine, it can be divided into manual, semi-automatic, fully automatic and all-in-one machines. According to the size of the core can be divided into small, medium, large, super large and so on.

1.2 Difficulties in the development of winding technology

It is undeniable that based on years of technical precipitation and accumulation, the winding process has obvious advantages in terms of production equipment, technical process, efficiency, cost, etc., but under the demand trend of vehicle gauge power batteries for standardization, large capacity and large size, the winding process has begun to "be powerless".

The figure below shows the standard structural characteristics of the wound cell, with rounded corner areas at both ends. During the charge and discharge process of the battery, because the expansion and contraction are inconsistent, the gap between the pole plate and the diaphragm will become larger, when the electrolyte here is not rich, it will affect the play of the capacity, and the long-term use will bring about the safety problem of lithium analysis. In addition, with the requirement of increasing energy density, the negative electrode is gradually introduced into the silicon negative electrode system.

1.3 Future development direction of winding machine

(1)High speed and high precision: the line speed of the winding pole sheet has been developed from the existing 2 ~ 3m/s to 5m/s, and the alignment accuracy of the winding pole sheet has been increased from the existing ±0.3mm to ±(0.1~0.2)mm.

(2)High pass rate: CPK from 1.33 to 1.67, and finally developed to more than 2.0, reaching the level of exemption from inspection.

(3)Stability: improve the average trouble-free time, from the existing tens and hundreds of hours to the level of thousands and millions of hours.

(4)Equipment to achieve digital, intelligent control: winding tension, pole plate and diaphragm alignment to achieve online monitoring, winding parameters and final battery performance parameters to achieve closed-loop optimization, to achieve a higher winding pass rate.

2.Equipment principle, composition and key structure

2.1 Principles of the winding machine

It is mainly used for automatic winding of square battery or cylindrical battery bare cell, the equipment adopts two or more pairs of winding needles, unilateral needle extraction structure, coil positive and negative pole sheet and diaphragm active unwinding, pole sheet diaphragm rewinding, automatic correction, automatic tension detection and control, pole sheet is introduced into the winding part by the pinch roll driving mechanism, and the diaphragm is automatically wound according to the process requirements. After the winding is completed, the working position is automatically changed, the diaphragm is cut off and the termination tape is affixed. After the finished bare cell is automatically cut off, the good finished bare cell is automatically transferred to the tray and then transferred to the post-process after prepressing and scanning the code. 

2.2 Description of winding mechanism

(1)Pre-winding: the positive and negative electrode plate initial feeding process, the process of the positive and negative electrode plate is the electrode plate motor to control the feeding speed at a constant speed, the need to control the rotation Angle speed of the winding needle and the speed of the pole plate. The process involves six motors. Two kinds of synchronization are involved: the synchronization of the unwinding speed of the diaphragm and the speed of the needle; The speed of the pole feed is synchronized with the speed of the winding needle.

(2)Winding process: After completing the initial feeding process of the positive and negative electrode sheet, the positive and negative electrode sheet is wrapped tightly by the diaphragm and wound around the winding needle for a week. In this process, the discharge speed of the pole plate discharge motor is adjusted by detecting the tension of the coil, so as to ensure the constant tension of the coil during the winding process.

The winding process diagram is shown in the figure. The process involves six motors. Two kinds of synchronization are involved: the synchronization of the unwinding speed of the diaphragm and the speed of the needle; The discharge speed of the pole is synchronized with the speed of the winding needle. The control problem in pre-winding is an open-loop control problem, and there is no calibration of feedback quantity between the two, which requires us to establish an accurate winding speed model. There is tension measurement of the material coil in the winding, and closed-loop feedback control technology can be used in the control.

(3)Dynamic modeling of winding process: Since the pre-winding process belongs to open loop control, accurate mathematical model is the key to determine the success or failure of the system.

2.3 Device composition and key structure

The main module list of the equipment includes: Pole/diaphragm automatic unwinding module, pole/diaphragm rewinding module, automatic correction module, roll guide module, pole lug guide flattening module, main drive module, tension control module, tension measurement/display and storage module, pole plate feeding module, diaphragm electrostatic removal device, pole discounting/folding and pole plate breakage detection module, CCD online detection module, pole plate cutting module, Dust removal system, single roll and removal module for pole and diaphragm defective products, winding head assembly, diaphragm cutting module, diaphragm adsorption module, tape termination module, automatic discharge module, bare cell preloading module, blanking module, equipment frame and large plate module.

The key structure is as follows:

(1)Pole plate/diaphragm automatic unwinding system: consists of pole plate/diaphragm automatic unwinding reel, tape assembly, unwinding correction and so on. It realizes the functions of fixing the coil material of the pole plate/diaphragm, automatic unwinding, automatic changing of the pole plate and so on. The release reel adopts mechanical or pneumatic expansion, auxiliary block gauge, edge detection and other mechanisms to facilitate rapid positioning.

(2)Automatic correction module: composed of multi-stage correction mechanism, the correction method can adopt a variety of correction methods such as hanging shaft movement, guide roller swing, and pinch roller drive. Through real-time detection, control and display of the material walking edge, the material edge can be corrected in real time during the walking process. The sensor position is set to avoid dust accumulation, which affects the accuracy of edge value detection. Main parameters unwinding correction accuracy ±0.2mm, process correction accuracy ±0.1mm.

(3)Tension control system: composed of tension detection sensor, tension actuator and display storage module. Tension actuators include linear motors, low friction cylinders or servo motors. The tension detection mechanism is as close as possible to the winding mechanism. By effectively controlling the tension of the material, the function of setting and regulating the tension by turn can be realized. To achieve accurate control, the naked cell deformation cannot be caused by winding tension problems.

During the winding process, with the gradual increase of the winding diameter, the tension will gradually increase in order to ensure the compactness of the cell. In each circle of the pole plate, the fluctuation of the tension must be controlled within a certain range.

(4)pole sheet feeding module: composed of positive and negative pole pinch roller driving mechanism and feeding mechanism, complete the winding of the front pole sheet feeding. During the winding process, the feeding level and the relative position between the materials do not change, and the free length of the feeding pinch roller and the pole sheet before entanglement is as short as possible under the premise of ensuring the feeding and finishing. The feeding point of the pole plate has the function of feeding blow guiding, and uses the digital display pressure monitoring, the Angle of blowing and guiding direction is adjustable and equipped with an Angle dial. At the same time, the feed is effective, low noise, no pollution, and the tilt Angle is convenient for quantitative adjustment.

(5)electrode cutting module: composed of positive and negative electrode clamping and cutting mechanism, it can automatically detect the mark hole at the end of the electrode plate (laser die cutting production), count to the set number of pole ears, or by identifying the distance between the poles, and then finish the fixed length cutting pole plate, it can also realize the function of counting the length cutting pole plate. The cutting edge is recommended to use tungsten steel and other hard materials, and the moving edge and the fixed edge have Angle requirements. In addition, the cutting position needs to have an isolation protective baffle and warning sign, and do anti-stick treatment.