Prismatic battery cell is also called aluminum shell battery cell, which is a battery packed in aluminum shell, using laser sealing technology, fully sealed, aluminum shell technology is very mature, and the material technology such as inflation rate, expansion rate and other indicators are not high, it is a form of power battery promoted earlier in China. Compared with the other two lithium batteries, prismatic battery cell has more outstanding advantages in market using , which can be summarized as follows:
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&#; The prismatic battery cell packaging has high reliability;
&#; High system energy efficiency;
&#; Relatively light weight and high energy density;
&#; The structure is relatively simple and the capacity expansion is relatively convenient. It is an important option to increase energy density by increasing the single unit capacity.
&#; The single unit capacity is large and the system structure is relatively simple, which makes it possible to monitor each single unit one by one. Another benefit of the simple system is that the stability is relatively good.
Main functions and description of the equipment
1.1 Prismatic lithium battery cell assembly equipment
The prismatic lithium battery cell assembly line is used for the mid-stage assembly of power batteries. It is an important part of the power battery production process and has a significant impact on the performance and precision of the battery. Therefore, the degree of automation and operation accuracy of the assembly line equipment are increasingly attracting market attention. This section will introduce ShinHop a very mature battery cell assembly line that has stood the test of time and is recognized in the market. The assembly line equipment has the following characteristics:
&#; Strong compatibility, it can be compatible with a variety of different series of products according to customer requirements.
&#; Modular design, short changeover time, fewer parts and low cost.
&#; High assembly accuracy, dual positioning methods of vision and mechanical to improve positioning accuracy.
&#; Non-standard customization of fully automatic assembly lines can be achieved according to the battery cells with different process routes of customers .
&#; The layout of process equipment is reasonable, space-saving, the entire line is fully automated, and the labor cost is very low.
&#;High manufacturing quality assurance, full parameter detection and monitoring.
&#;Manufacturing guarantee of battery safety and consistency.
This automatic production line is used to realize the automatic assembly of prismatic lithium- ion power battery cells after winding. The production line is mainly composed of the following parts : heat pressing test machine, X-ray machine, pairing machine, ultrasonic welding machine, adapter welding machine, stack combining machine , mylar wrapping/hot melting/taping machine, cell to can pre-tack welding, laser top cover welding machine, helium inspection machine . It realizes the functions of heat pressing of battery cells, X-ray inspection, pre-welding and pairing of tabs, welding of adapter tabs, back taping, cover laser welding, taping, stacking tabs combining machine, taping, wrapping, cell to can, top cover sealing welding, etc., and realizes full automation in the whole process. The overall layout is reasonable, the structure of each equipment is compact, and it is fully automatically monitored and intelligent throughout the process. Each equipment can realize the traceability function, connect to the MES system, and upload data to the system in real time. The equipment runs stably, and the key components are all imported brands or international first-line brands. This assembly line has been put into production in large quantities in other customer factories and has been fully verified. The technology of each equipment is mature.
1.2 Future development trends of assembly production lines
Prismatic battery cell production lines have been used for a long time, the corresponding technology is very mature, and the existing assembly line equipment is also similar. In the future development trend, in addition to continuing to improve materials and finding high-performance battery cell materials, for battery assembly production lines, high efficiency and low cost are still the future development direction of power lithium batteries. After summarizing the current market development overview, the following points are worth noting:
&#; The performance of the battery itself, such as battery size, energy density, multi- electrode structure , etc.
&#; Assembly production efficiency, continuously improve production efficiency while ensuring that equipment costs do not change much.
&#; he automation level of battery cell assembly lines is constantly improving, and the production yield is easier to control. Reasonable control of the production time of each process can effectively shorten the production time of lithium batteries and greatly improve the problems of high labor intensity and high production costs of workers.
&#; Better compatibility, suitable for a wider range of products.
&#; Modular technology is an important way to improve efficiency.
1.3 Design of prismatic lithium battery cell production assembly line
For the design of prismatic lithium battery cell production line , there will be different designs according to the requirements of customers. According to the problems encountered in the production process and the corresponding practices, the following aspects should be considered:
&#;Product technology: including the size of the battery, the size of the tabs , the thickness of the weld, etc.
&#; Factory space size: Rationally arrange the specific location of production line equipment, as well as the mechanisms to be optimized, and also consider ergonomics, the convenience of manual operation, and the operability of subsequent maintenance.
&#; Equipment design: The simpler the structure, the better, so it is easier to operate.
&#; Distribution of beats in the production line: focus on the efficiency of the bottleneck station. If the efficiency cannot be achieved, consider changing the single station to a double station or even multiple stations. At the same time, high safety performance and straight-through yield are also key points of attention.
&#; Product positioning method: Different product positioning methods are adopted to meet different customer needs, such as side positioning, positioning based on both sides, fixture positioning, etc.
&#;Dust prevention device: Basically, every device that needs dust removal in the cylindrical battery cell assembly line has corresponding dust removal facilities, such as dust collectors, brushes, etc.
&#; Logistics design in equipment: including transportation within the equipment, transportation between equipment, etc.
&#;Quality inspection: CCD inspection, battery cell thickness inspection, insulation inspection, short circuit inspection, etc. will be designed in the whole set of assembly lines.
&#; Maintain the consistency of the appearance of the production line and maintain the beauty of the entire set of equipment.
Equipment composition and key structures
The overall layout of the prismatic lithium battery cell assembly line equipment is as follows:
&#; Dimensions of the entire line: length × width × height = mm × mm × mm (height does not include the alarm light), operating surface height 900mm, equipment spacing 800~mm.
&#; Appearance: The load-bearing chassis adopts a square-tube welded structure, the upper sealing frame adopts an aluminum alloy profile structure, sealed with plexiglass, and the entire equipment cover is covered with sheet metal .
&#; Operation interface: Each device is equipped with an independently operated touch screen, and the touch screens of all devices are embedded.
&#;Whole line layout: The layout of the prismatic battery cell assembly line is shown in Figure 1.
Figure 1 Layout of prismatic battery cell assembly line
This production line is a fully automatic production line, which includes the entire production process of prismatic battery cells from heat press to helium tester , as shown in Figure 2, the overall process of prismatic batteries, namely: winding to heat press conveyor line (including 6 sets of material taking manipulators on the winding machine) &#; heat press &#; ultrasonic welding machine &#; adapter sheet laser welding machine &#; Mylar wrapping machine &#; cell to can and pre-tack welding machine &#; top cover laser welding machine &#; air tightness tester.
Figure 2 Overall process of prismatic battery cell
2.1 Heat Press machine
The heat press equipment is used for heat pressing of wound battery cells. Its main functions include: scanning of incoming battery cell codes, automatic loading of A/B battery cells , heat pressing, Hi-pot testing, and rejection of defective products. The heat pressing temperature, pressure, time, and Hi-pot test parameters and results are associated with the barcode and uploaded to the MES system. The equipment mainly includes battery loading and unloading modules, detection modules, heat pressing modules, etc. This equipment is the first step in assembling prismatic battery cells. The effect of heat pressing and winding battery cells directly affects the quality of subsequent processed products. Therefore, the efficiency, working accuracy, and automation level of the assembly equipment are all key considerations . The equipment layout and process flow are shown in Figures 3 and 4.
Figure 3 Heat press equipment layout
Figure 4 Heat press process flow
Figure 4 clearly shows the operation process of the wound battery cell on the heat press. During the operation, the equipment performs inspections on the wound battery cell after heat pressing, and uploads the inspection results including heat pressing temperature, pressure, time and Hi-pot to the MES system for real-time follow-up feedback, elimination of defective products and ensuring processing quality.
From the equipment layout diagram in Figure 3, it can be seen that the loading and unloading robot components, in-and-out transfer line, transfer robots, displacement mechanism, heat pressing components, etc. in the heat press equipment are relatively critical and play a vital role in the entire assembled semi-finished products. Several of these mechanisms are selected for detailed introduction and description.
&#; Offset material distribution mechanism . As shown in Figure 5, the offset material distribution mechanism is used, in which the flipping and positioning module has the following functions: the flipping mechanism uses a belt servo drive to achieve the flipping of the fixture and the synchronous flipping of the connecting plate. The fixture always remains horizontal, and the flipping is stable and reliable. The positioning fixture uses a clamping cylinder and a double-link cylinder for clamping and positioning; the contact surface with the battery cell is made of POM material.
Figure 5 Offset distribution mechanism
&#; Up and down transfer module . The up and down transfer module is shown in Figure 6. Its main actions are: translation uses a synchronous belt servo module, dual belt drive, to increase the stability of the loading and unloading module ; the loading and unloading module uses a belt servo, independent servo control; the clamping jaws are lifted and lowered using a screw cylinder; the pitch mechanism uses a servo-driven connecting rod mechanism, with the middle connecting rod as the positioning reference to achieve synchronous pitch change. The servo can control the equidistant size of the clamping jaws to achieve synchronous loading and unloading of the translation module at different working positions of the heat press.
Figure 6 Up and down transplanting module
&#;Heat pressing assembly . The heat pressing assembly of the heat pressing machine is shown in Figure 7, and its detailed description is as follows:
Figure 7 Heat pressing components
Main components: booster cylinder (pressure 20t, 6 layers), heating tube, thermostat, pressure sensor, etc.
Action flow: Perform heat pressing and Hi-pot tests on the battery cells.
2.2 Ultrasonic welding machine
The ultrasonic welding machine mainly completes the ultrasonic welding of battery cells through processes such as battery cell scanning , automatic pairing of battery cells by the robot, battery cell correction and polarity detection, polarity detection and correction of the adapter sheet storage , welding fixture on the adapter, welding fixture on the battery cell, placing the protective cover, ultrasonic welding and dust extraction, weld mark shaping , taping and taping detection, and automatic unloading. The equipment realizes battery cell scanning , ultrasonic welding, taping and information binding from battery cell pairing to Mylar warpping. It mainly includes: battery cell entry code scanning, battery cell correction and loading, adapter correction and loading, taping inspection, information binding and uploading (MES system), etc. The equipment layout is shown in Figure 8.
Figure 8 Ultrasonic welding machine equipment layout
The grabber is equipped with a color sensor to identify the positive and negative tabs of the battery cell to ensure that the tabs are not paired incorrectly. The battery cell is grabbed by the robot from the incoming conveyor belt, and after the secondary positioning of the battery cell, it is placed in the pallet to ensure that the misalignment error of the A/B battery cell tabs is &#;±0.2mm. The battery cell is placed in the pallet with center alignment. Before placing the battery cell, the elastic clips around the pallet will open, and then the robot will place the battery cell in the pallet, the clips will close, and the battery cell will be positioned in the center of the pallet. This equipment is an automatic production line, and the detailed process flow chart is shown in Figure 9.
Figure 9 Detailed process flow chart of ultrasonic welding machine
Equipment composition and key structures
From the equipment layout diagram of the ultrasonic welding machine in Figure 8, it can be seen that the battery cell loading module, battery cell ultrasonic welding circulation line and fixture module, adapter, protective sheet loading module, protective sheet cover loading and unloading module, ultrasonic positive and negative electrode welding module, weld marking flattening module, battery cell protective glue upper module, battery cell protective glue lower module, battery cell unloading module, taping detection, etc. are relatively critical and play a vital role in the entire assembled semi-finished product. Several of these mechanisms are selected for detailed introduction and explanation.
&#; Battery cell loading module (Figure 10). It has the functions of automatic battery cell loading, incoming material dust removal, incoming material fool proofing, incoming material buffering, and lack of material alarm, and also has the function of battery cell scanning and binding.
Figure 10 Cell loading module
&#;Battery cell ultrasonic welding circulation line and fixture module .
The schematic diagram of the ultrasonic welding loop is shown in FIG11 .
Figure 11 Schematic diagram of ultrasonic welding loop
&#; Adapter sheet and protective sheet loading module (Figure 12).
Figure 12 Schematic diagram of the adapter sheet and protective sheet loading module
&#; Protective sheet cover loading and unloading module (Figure 13).
Figure 13 Protective sheet cover loading and unloading module
&#;Ultrasonic positive and negative welding module (Figure 14).
Figure 14 Ultrasonic positive and negative welding module
&#; Welding mark flattening module (Figure 15). This module requires that the protective sheet does not warp, the tabs do not bend, and the pressing block uses wear-resistant material PEEK.
Figure 15 Welding and printing flattening module
2.3 Adapter laser welding machine
1) Equipment composition
The main functions of the adapter laser welding machine include automatic loading of the top cover and battery cells, and welding the connecting piece and the top cover together by laser welding, and automatic unloading after dust removal and gluing, as shown in Figure 16.
Figure 16 Adapter laser welding machine
Equipment size: length × width × height = mm × mm × mm.
Appearance: The load-bearing bottom frame adopts square-pass welding structure, and the upper sealing frame adopts aluminum alloy profile structure and is sealed with organic glass.
Operation interface: The equipment is equipped with an independently operated touch screen, and the touch screens of all equipment are embedded.
This equipment is an automatic production line, and the detailed process flow chart is shown in Figure 17.
Figure 17 Adapter laser welding machine equipment process flow
2) Key structures
As can be seen from Figure 16, the cover feeding mechanism, upper cover assembly, laser welding module, dust removal mechanism after laser welding, welding mark taping assembly, etc. are relatively critical and play a vital role in the entire assembled semi-finished product. Several of these mechanisms are selected for detailed introduction and description.
&#; Cover loading mechanism (Figure 18).
Figure 18 Cover loading mechanism
&#; Top cover assembly (Figure 19).
Figure 19 Upper cover assembly
&#; Laser welding module (Figure 20).
Figure 20 Laser welding module
&#; Dust removal mechanism after laser welding (Figure 21). The lifting cylinder descends to cover the welding area, forming a sealed space for dust extraction. The dust suction wind speed is &#;12m/s, and the wind speed is steplessly adjustable within the maximum range.
Figure 21 Dust removal mechanism after laser welding
&#; Welding mark taping components (Figure 22).
Figure 22 Welding mark taping assembly
2.4 Mylar wrapping machine
1) Main functions of the equipment
The main functions of the Mylar wrapping machine include automatic shaping of battery cells, automatic loading of Mylar and bottom trays, Mylar wrapping of battery cells, side taping, bottom taping, CCD testing, etc. The equipment layout is shown in Figure 23.
Figure 23 Mylar wrapping machine equipment layout
&#; Basic indicators of equipment .
The overall dimensions of the equipment are: mm×mm×mm.
Equipment quality rate: &#;99.8% (excluding defective incoming materials).
Equipment utilization rate: &#;98% (refers only to failures caused by equipment reasons).
&#; Equipment process flow is shown in Figure 24.
Figure 24 Process flow chart of Mylar wrapping machine equipment
2) Key structures
From the layout diagram of the Mylar wrapping machine in Figure 23, it can be seen that the bottom taping mechanism, the Mylar and bottom support sheet feeding layout mechanism, the front Mylar wrapping mechanism, the bottom tapping mechanism, the side taping turntable mechanism, etc. are relatively critical and play a vital role in the entire assembled semi-finished product. Several of these mechanisms are selected for detailed introduction and description.
&#; The layout of Mylar and base sheet loading (Figure 25).
Figure 25 Mylar and base sheet loading layout
&#; The Mylar wrapping station for the front side (Figure 26) has its film wrapping and hot melt turntable layout as shown in Figure 27.
Figure 26 Mylar wrapping station
Figure 27 Mylar wrapping and hot melt turntable layout
&#; Bottom surface taping mechanism (Figure 28).
Figure 28 Bottom taping mechanism
&#; Taping the side on the turntable (Figure 29).
Figure 29 Side taping turntable
2.5 Cell to can, pre-tack welding machine
1) Main functions of the equipment
The cell to can pre tack welding machine is shown in Figure 30.
Figure 30 Equipment layout of cell to can pre-tack welding machine
Cell to can pre tack welding machine is used to automatically put prismatic battery cell into the can. The main functions of the equipment include: aluminum can loading, automatic battery cell loading and code scanning, aluminum can and cell dust removal, cell to can , battery unloading, information binding and uploading (MES), etc.
&#; Main technical parameters of the equipment.
&#; The process flow of this equipment (Figure 31).
Figure 31 Process flow chart of cell to can pre-welding machine equipment
2) Key structures
From the equipment layout diagram of the cell to can welding machine in Figure 30, it can be seen that the aluminum can feeding mechanism, aluminum can and battery cell, top cover cleaning mechanism, battery cell can entry mechanism, battery cell feeding mechanism, etc. are relatively critical and play a vital role in the entire assembled semi-finished product. Several of these mechanisms are selected for detailed introduction and description.
&#; Aluminum can feed module (Figure 32).
Figure 32 Aluminum can feeding module
&#; Battery cell and can dust removal mechanism (Figure 33).
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Figure 33 Dust removal mechanism for battery cell and can
&#; Battery cell to can mechanism (Figure 34).
Figure 34 Battery cell to can mechanism
&#; Battery cell loading mechanism (Figure 35).
Figure 35 Battery cell loading mechanism
2.6 Pre-tack welding machine
1) Main functions of the equipment
The equipment layout of the pre-tack welding machine is shown in Figure 36.
Figure 36 Pre-tack welding machine equipment layout
The pre-tack welding machine is used for pre-tack welding of prismatic can and cover plates. The main functions of the equipment include: automatic battery cell loading and code scanning, press-fitting, equal height detection, laser welding, battery unloading, information binding and uploading (MES), etc.
&#; Main technical parameters of the equipment .
&#; Its process flow chart (Figure 37).
Figure 37 Pre-tack welding machine equipment process flow chart
2) Key structures
From the equipment layout diagram of the pre-tack welding machine in Figure 36, it can be seen that the cell shaping pre-pressing mechanism, step and short-circuit test module, clamping mechanism and pre-welding mechanism, cover closing and pressing mechanism, etc. are relatively critical and play a vital role in the entire assembled semi-finished product. Several of these mechanisms are selected for detailed introduction and description.
&#; Battery cell shaping and pre-stressing mechanism (2 sets, Figure 38).
Figure 38 Cell shaping pre-pressing mechanism
&#; Cover closing and pressing mechanism (Figure 39).
Figure 39 Cover closing and pressing mechanism
Specific action flow of the cover closing and pressing mechanism :
&#; Pre-welding mechanism (Figure 40).
Figure 40 Pre-welding mechanism
The pre-welding mechanism is mainly composed of a motion system and pre-welding tooling.
2.7 Top cover laser welding machine
1) Main functions of the equipment
Figure 41 shows the layout of the top cover laser welding machine. This equipment mainly performs laser welding of the top cover of the battery cell after pre-welding into the can, Hi-pot detection, etc. The main functions include automatic loading and unloading of battery cells by scanning barcodes, automatic placement of protective cover plates, clamping and positioning, laser sealing welding, Hi-pot detection, NG buffering, process transmission, etc.
Figure 41 Equipment layout of pre-cover laser welding machine
&#; Main technical parameters of the equipment .
The overall dimensions of the equipment are: mm×mm×mm.
The first-time yield rate of the equipment is &#;98.5%, the second-time yield rate is &#;99.5% (excluding defective incoming materials), and the utilization rate is &#;98%.
Welding speed &#;150mm/s, CMK &#;1.33.
Laser welding pressure strength>10kgf,CMK&#;1.33.
Laser welding machine output power and fixture pressure control accuracy: set value ±5%, CMK&#;1.33.
Welding quality (welding positioning accuracy ±0.1mm, weld width deviation &#;±0.1mm) consistency CMK&#;1.33.
Cavity that contacts the product during the laser welding process is higher than the Class 100,000 requirement.
The equipment functions can meet the requirements of organization and communication and docking with the previous and next process equipment.
&#; Top cover laser welding machine equipment process flow (Figure 42).
Figure 42 Top cover laser welding machine equipment process flow
2) Key structures
From the equipment layout diagram of the top cover laser welding machine in Figure 41, it can be seen that the feeding mechanism, upper positioning assembly, protective cover feeding assembly, NG buffer, mobile detection assembly, CCD detection assembly, NG handling assembly, unloading assembly, welding head assembly, etc. are relatively critical and play a vital role in the entire assembled semi-finished product. Several of these mechanisms are selected for detailed introduction and description.
&#; Loading mechanism of top cover laser welding machine (Figure 43).
Figure 43 Top cover laser welding machine loading mechanism
&#; Upper positioning assembly (Figure 44).
Figure 44 Positioning components on the top cover laser welding machine
The specific action flow is as follows:
&#; Protective cover loading assembly (Figure 45).
Figure 45 Top cover laser welding machine protective cover feeding assembly
The specific action flow is as follows:
Note: The protective cover can be replaced without stopping the machine; the protective cover protects the pole and prevents welding spatter from contaminating the pole, QR code, explosion-proof membrane, and injection hole.
&#; CCD detection component (Figure 46).
Figure 46 CCD detection component of top cover laser welding machine
After welding, the battery cell is moved to the mobile detection assembly by the robot module. The mobile detection assembly is equipped with two sets of grippers, which are divided into three positions, namely the loading position, the detection position, and the unloading position. The CCD detection assembly is equipped with a camera to detect whether there are pits, sand holes, explosion points, broken welds, pores, leaks and other defects in the weld after welding (Figure 47).
Figure 47 Schematic diagram of several defects of the top cover laser welding machine
2.8 Positive pressure helium detector
1) Main functions of the equipment
Figure 48 is a layout diagram of the positive pressure helium inspection equipment , which is mainly used for the sealing test of the prismatic battery cell top cover after laser welding. The vacuum method is used to detect the sealing state of the battery cell top cover after welding. The working process is: the battery cell to be tested after the top cover is laser welded is sent into the machine through the feed pull belt and the top cover QR code is read. The battery cell to be tested is placed in the inspection chamber by the material dividing robot, and the battery cell is evacuated. After the negative pressure value is set, the external vacuum source is turned off, and the air tightness inside the battery is tested with an air tightness tester. This device can be used to determine whether the inspected workpiece is qualified.
Figure 48 Layout of positive pressure helium inspection equipment
The system is designed and manufactured strictly in accordance with the requirements of the customers, adopts a modular design, fully considers the purchaser's leakage detection requirements, and also uses standardized modules and components as much as possible to ensure the reliability and maintainability of the system and meet the technical indicators specified by the manufacturer.
The basic indicators of the equipment are as follows:
Equipment yield: &#;99.8% (excluding defective incoming materials).
Equipment utilization rate: &#;99%; false detection rate: &#;0.3%.
Helium detection standard : &#;9.9×10-7Pa·m3/s.
The equipment process flow is shown in Figure 49.
Figure 49 Equipment process flow
2) Key structures
This equipment is composed of the following devices: workpiece inlet/outlet manipulator device, box slide, vacuum/helium filling device, vacuum box leak detection device, helium filling and removal device, and electrical control device. As can be seen from the layout diagram of the positive pressure helium inspection equipment in Figure 48 , the workpiece inlet/outlet manipulator device, vacuum/helium filling device, etc. are relatively key and play a vital role in the entire assembled semi-finished product. Several of these mechanisms are selected for detailed introduction and explanation.
&#; Inspection turntable . The main function of the inspection turntable is to load and unload battery cells while inspecting them, maximizing the efficiency of the airtightness tester. This module is mainly composed of a turntable, a cam divider and an inspection fixture, as shown in Figure 50.
Figure 50 Detection turntable
&#; Vacuuming mechanism (Figure 51). The vacuuming and helium filling part is mainly composed of a vacuum pump, a solenoid valve, a pressure sensor and a pipeline. It can evacuate and fill the workpiece with helium within the set time.
Figure 51 Vacuum extraction mechanism
Equipment selection and application cases
A customer has the following requirements for the size of the battery cell.
&#; The customer provides technical information . The equipment model plan is shown in Figure 52, and its code and size are shown in Table 1.
Figure 52 Equipment model plan
Table 1 Model code and size
&#;Device compatible product dimensions (Table 2).
Table 2 Device compatible product dimensions
According to customer needs, the specifications of battery cells can be clamped by adjusting the shared gripper. If necessary, the production of battery cells of different specifications can be achieved by replacing necessary pads (such as jigs, fixtures, pallets). The range of variation of battery cell size specifications shall not exceed the maximum size range of this equipment .
This automatic production line is used to realize the automatic assembly of prismatic lithium- ion power battery cells after winding. The production line is mainly composed of the following parts: heat pressing, ultrasonic welding machine, adapter laser welding machine, mylar wrapping machine, cell to can machine, pre-tack welding machine, top cover laser welding machine and logistics conveyor lines between various equipment .
As part of my technical consulting work, I&#;ve had the opportunity to work on every aspect of EV battery manufacturing and design.
The battery is the most expensive part in an electric car, so a reliable manufacturing process is important to prevent costly defects. Electric vehicle batteries are also in high demand, which puts pressure on manufacturers to maximize production without compromising quality. As a result, robot automation is almost everywhere during battery manufacturing.
The production process of electric batteries includes many steps. Before going over each step, let&#;s review the structure of battery cells.
Table of Contents
The most important component in an EV battery is the cell. Cells are where the energy of the battery is stored. While different chemistries exist, lithium-ion batteries are the most common on the market because they offer the best compromise between energy density and cost.
Three types of EV battery cells are manufactured: cylindrical cells, prismatic cells, and pouch cells. Cylindrical cells are by far the most popular, but prismatic cells are also important.
All types of cells include the following components, which are assembled in similar ways.
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A coating called the slurry is applied on current collectors to help produce and conduct electricity. The slurry is a homogeneous paste that is mixed under vacuum to make sure that there are no air bubbles or moisture in it.
Here&#;s what it contains:
The slurry does not contain the same materials for the anode and the cathode. In lithium-ion batteries for example, it contains lithium-metal oxide for the cathode and graphite for the anode.
Before mixing, the properties of raw materials used in the slurry are measured and validated before mixing.
Once the slurry is ready, electrode sheets are coated with it in a machine called the coater. Here are the different operations performed during this process:
The electrode sheets are cut so that they have the exact shape needed. The sheets not only need to fit into the casing, but they need to meet specific form factors.
Laser cutting is the technology typically used for high-volume production. In smaller production lines or R&D labs, die cutters are also used.
Laser marking is used to permanently identify the anode and cathode sheets with 2D codes. This will be used to:
The electrode and separator sheets form what is known as a stack. The stack is a series of sheets that are alternated (anode, separator, cathode, separator, etc.) The stack will later be inserted in the cell casing, whether it&#;s a cylindrical case, and prismatic case, or a pouch.
Different methods are used to create these stacks:
A metal strip is welded to the anode stack of copper foils, and another to the cathode stack of aluminum foils. Both ultrasonic bonding and laser welding can be used to make these connections. These metal strips (or tabs) are then connected to the cell terminals and will later be joined to a busbar to create an electrical circuit.
Electrolyte is poured into the casing and is absorbed by the separator sheets. The choice of the electrolyte chemistry is important for the battery&#;s performance. For example, additives can be used to affect factors like viscosity and improve conductivity.
After the electrolyte is poured and absorbed, air bubbles are removed in a vacuum chamber. This step is called degassing, and it ensures that the electrolyte is uniformly distributed.
The casing is then sealed hermetically using methods such as crimping, laser welding, ultrasonic bonding, or heat sealing.
Forming involves the initial charging and testing of battery cells. During this step, cells are connected and undergo multiple charge and discharge cycles (with resting in between) that help set the cells&#; electrochemical properties.
The final step of cell manufacturing (before module and pack assembly) is cell inspection.
After forming, cells undergo final testing to verify their electrical properties like capacity, voltage, and internal resistance. Mechanical properties are also validated with vision cameras. Cells that do not meet requirements are rejected.
Cells with similar properties are grouped together. They will be assembled in the same modules to ensure the high performance of the module as a whole.
During the assembly of battery modules and packs, sealants and adhesives are applied using a dispenser. Adhesives are used to join components together while providing additional properties like thermal conductivity, electrical conductivity, or insulation.
They are applied on battery housings, cells casings, and other components like cooling tubes. The curing time is controlled with active methods like UV light curing to prevent slowdowns.
To maximize the strength of the adhesive bonds, laser surface preparation is used before adhesives and sealants are applied. This process removes all contaminants and can modify the surface roughness if needed.
The positive and negative tabs of each cell is connected to a busbar to create a complete electrical circuit. The busbar is a metal sheet that connects all cells together, joining them in serial and parallel circuits. The combination of these connections is used to achieve specific voltage and capacity.
These connections used to be made with ultrasonic wire bonders, but they are increasingly made using laser welding machines as they are faster and do not mechanically stress the cells with intense vibrations. For this reason, automotive manufacturers only use laser welders for cylindrical cells.
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When the battery pack is assembled, other components that are essential for the good functioning of the battery need to be integrated.
Laserax provides laser solutions for EV battery manufacturing. You can learn more about our solutions here. Or, contact us if you want to discuss one of the following:
Laser welding of tab-to-busbar connections
Laser cleaning before ultrasonic bonding or welding
Laser surface preparation for thermal and structural adhesives
Laser marking of electrodes and cell casings
Laser cleaning of housings before liquid gasketing
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