lithium battery winding machine is used to wind lithium battery cells. It is a machine that assembles the positive electrode sheet, negative electrode sheet and separator of the battery into a core pack (JR: JellyRoll) in a continuous rotating manner.
Domestic winding manufacturing equipment began in 2006, starting with semi-automatic circular, semi-automatic square winding, and automated film production, followed by combined automation, film and winding integrated machines, laser die-cutting and winding integrated machines, anode continuous winding machines, separator continuous winding machines, etc.
Principle of winding
(1) Principle of winding machine
The winding machine has positive and negative electrode feeding units. The mechanism that winds the positive electrode, negative electrode and separator together is called a rolling needle.
According to the shape of the battery core, it is mainly divided into square and cylindrical battery cell winding machines. Generally, the winding equipment adopts the structure of two or more sets of winding needles and single-sided needle withdrawal. The main mechanisms of the winding machine include: active unwinding of positive and negative pole pieces and separators, roll changing of pole pieces and separators, automatic correction, and automatic tension detection and control. The pole piece is introduced into the winding needle part by the nip roller driving mechanism, and is wound together with the diaphragm according to the process requirements. After the winding is completed, the workstation is automatically changed, the diaphragm is cut and the termination tape is applied. After the finished bare battery core is automatically unloaded, after pre-pressing and code scanning, the good finished bare battery core is automatically transferred to the tray and then transferred to the subsequent process. Defective bare battery cells are automatically discharged to the collection point for defective bare battery cells. The winding process flow is as follows:
Winding equipment process flow chart
(2) Winding mechanism description
① Pre-winding: The initial feeding process of positive and negative electrode plates. In this process, the positive and negative electrode plates are clamped by the pole plate feeding mechanism and fed into the coiling needle at a certain speed. The rotation angle and speed of the coiling needle need to be controlled to match the pole piece feeding mechanism. This process involves two synchronizations: the unwinding speed of the diaphragm is synchronized with the speed of the winding needle, and the speed of the pole piece is synchronized with the speed of the winding needle.
② Winding process: After completing the initial feeding process of the positive and negative electrode sheets, the positive and negative electrode sheets are tightly wrapped by the separator and wound around the winding needle. Continuous winding can be achieved by subsequent rotation of the winding needle. In this process, the tension of the material roll is detected and the discharge speed of the pole piece discharge motor is adjusted to ensure the constant tension of the material roll during the winding process.
Schematic diagram of the winding process
The control problem in pre-winding is an open-loop control problem. Whether the winding needle, separator and pole piece are truly synchronized cannot be accurately measured. This requires us to establish an accurate winding control model, especially for larger batteries, which require higher winding requirements. The tension of the material belt during winding can be controlled using closed-loop feedback control technology.
In addition, during the winding process, what we actually control is the rotation speed of the winding motor, and the actual speed is a function of the actual radius of each material roll and the winding needle, and the radius changes dynamically. At present, in the absence of actual sensor measurement, we assume that the core gradually increases after the material roll is loaded once, and the change pattern of the intermediate radius is completely consistent with Archimedes' spiral law. The initial roll radius is preset through the program.
③ Dynamic control model of the winding process: Since the pre-winding process is an open-loop control, an accurate mathematical model is the key to the success or failure of the winding control system. Especially when the linear speed of the pole piece is greater than 1m/s, an accurate winding model is the key to controlling the stability of the winding tension and is the key to winding quality control.
④ High-quality winding of battery cells: The core issue of high-quality winding of battery cells is that the separator and pole pieces of the wound cell are evenly adhered, showing that there is no gap, and the contact stress between the separator and pole pieces is maintained uniformly in all directions during the use of the battery.
This puts forward two requirements for the winding machine. The first is that the fit stress should be consistent after the winding core is drawn out. This is very important for the design of the outline shape of the winding needle. Especially for square winding batteries, it is necessary to ensure that the fit stress between the pole piece and the separator is uniform after the winding needle is drawn out. The winding contour curve must be a closed curve with continuous first-order derivatives. The judgment principle is that the curve is continuous and smooth without sharp corners.Secondly, when the diaphragm and pole pieces enter the winding needle, the tension of and is consistent in the direction of the bus line of the winding needle tangent. This requires that the correction amplitude of the diaphragm pole piece should not be too large, and should ensure a limit within the elastic range of the diaphragm and pole piece.
⑤ GAP problem of square wound battery
Even if the winding needle curve of the square battery is a closed curve with continuous first-order derivative, there will be no gap between the electrode piece and the separator after flattening, but during the charging and discharging of the battery During the charging process, due to the inconsistent expansion and contraction of the pole pieces, the gap between the pole pieces will gradually increase with the charging cycle. When the electrolyte here is not rich, lithium ions cannot be transferred, which will affect the capacity. Long-term use will cause lithium precipitation safety issues. Moreover, with the requirements for increasing energy density, the negative electrode is gradually introduced into the silicon negative electrode system. Due to the large expansion of the silicon negative electrode sheet, the wound electrode assembly is prone to fracture of the inner ring electrode sheet, which affects the service life of the battery and limits the amount of silicon material added. The recommended method is to appropriately add rich electrolyte when injecting the liquid.
Characteristics of winding
According to the degree of automation of the winding machine, it can be divided into manual, semi-automatic, fully automatic and all-in-one types. According to the size of the core package produced, it can be divided into small, medium, large, super large, etc. The following are schematic diagrams of several winding machines. The characteristics of
winding core are as follows:
♦ pole piece and diaphragm are continuous and integrated, with high manufacturing efficiency;
♦ winding has only two sides, few edges, complete pole piece, easy to control burrs;
♦ simple production control, operation Easy and easy to control;
♦ should not be rolled too thickly, as the layers interact with each other and are easily deformed;
♦ pole pieces require high flexibility;
♦ The transverse tension of the pole pieces is inconsistent, and gaps may occur inside, making it difficult to make the bonding stress uniform;
♦ The expansion of the pole pieces causes GAP problems and makes it difficult to achieve high quality. The key structure of
winding machine
The main modules of the equipment include: pole piece/diaphragm automatic unwinding module, pole piece/diaphragm roll changing module, automatic correction module, guide roller module, pole guide smoothing module, main drive module, tension control module, tension measurement /Display and storage module, pole piece feeding module, diaphragm static elimination device, pole tab discount/folding and pole piece damage detection module, CCD online detection module, pole piece cutting module, dust removal system, pole piece and diaphragm defective single roll and rejection module, winding head assembly, diaphragm cutting module, diaphragm adsorption module, termination tape module, automatic unloading module, bare cell pre-pressure module, blanking module, equipment frame and large board module.
Winding machine layout diagram
Development trend of winding machine
① High speed and high precision: The linear speed of the winding pole piece has developed from the existing 2-3m/s to 4-5m/s, and the alignment accuracy of the winding pole piece has been improved from the existing ±0.3mm to ±(0.1-0.2) mm.
② High pass rate: CPK increased from 1.33 to 1.67, and finally developed to above 2.0, reaching the inspection-free level.
③Stability: improves the mean time between failures from the existing tens or hundreds of hours to the level of thousands or thousands of hours.
④ equipment realizes digital and intelligent control: winding tension, the alignment of pole pieces and separators are monitored online, winding parameters and final battery performance parameters are optimized in a closed loop, and the winding qualification rate is improved.
⑤ Laser die-cutting and winding integration: laser die-cutting and winding processes are combined to achieve equipment integration.
⑥ High-speed winding machine: achieves doubling of winding efficiency through a breakthrough in diaphragm continuous winding technology.
Conclusion
Based on years of technology accumulation and accumulation, the winding process has obvious advantages in terms of production equipment, technical processes, efficiency, cost, etc. However, under the trend of demand for standardization, large capacity and large size of automotive grade power batteries , the winding process has begun to "be unable to meet its expectations". How to improve the quality of winding is the core issue facing the industry.
