Step 1: Ingredients
The materials are stirred in a high-vacuum, fully automated system for 10 hours to ensure uniform dispersion of the materials required for lithium batteries, thereby improving battery consistency and overall performance. Why is this done? Because material preparation is a core aspect of lithium battery manufacturing; poor material preparation directly impacts battery performance.
Step 2: Coating
An automated feeding system, an automated blade adjustment system, and an online thickness measurement system are used to ensure uniform coating of the positive and negative electrode sheets. Why is this necessary? Because coating is fundamental to lithium battery manufacturing; it determines the battery's consistency.
Step 3: Adjusting the rollers
After the positive and negative electrode sheets are coated, the positive and negative materials are relatively loose, so a certain amount of pressure needs to be applied to the electrode sheets to compact the positive and negative electrode materials to a certain range.
Step 4: Slice into strips
Depending on the battery model, the positive and negative electrode plates need to be cut to the required width. For example, for 18650 lithium batteries, the electrode plate width is within 56-58mm.
Step 5: Film preparation and winding
A fully automated sheet-making machine is used to weld the positive and negative tabs onto the positive and negative electrode sheets. A fully automated winding machine is then used to wind the positive and negative electrode sheets and the separator together into a cylindrical shape.
Step 6: Bottom grooving and vacuum drying
The core is placed inside the steel casing, and the negative electrode tab is automatically welded and automatically grooved. In addition, it undergoes high-vacuum, high-temperature baking to dry out any remaining moisture, thus ensuring the performance of the lithium battery.
Step 7: Dissolve in water
Lithium batteries need to undergo charge and discharge tests before being shipped; the batteries are charged before leaving the factory.
Step 8: Assemble the lithium battery
The fully automatic welding machine welds multiple batteries together using connecting pieces, then mounts them onto a circuit board, performs aging tests, and inspects them before shipping.
The manufacturing of lithium batteries for electric vehicles mainly involves two steps: the production of lithium-ion cells and the assembly of these cells through series or parallel connections to achieve the desired voltage, capacity, and charge/discharge requirements for the electric vehicle's lithium-ion battery pack. Let's take a look at these steps:
I. Lithium-ion Cell Manufacturing for Electric Vehicle Lithium Batteries
This mainly describes the manufacturing method of lithium battery cells, and the basic steps are as follows:
1. Mixing and blending of raw materials: Mix the electrode active material, binder, solvent, etc. together, stir and disperse thoroughly to form a slurry.
2. Coating of positive and negative electrode sheets: The slurry is intermittently and evenly coated on the surface of the conveying current collector and dried to form positive and negative electrode sheet rolls respectively.
3. Cold pressing of positive and negative electrode sheets: After the positive and negative electrode sheets are coated, the positive and negative materials are relatively loose. It is necessary to apply a certain pressure to the electrode sheets to compact the positive and negative electrode materials to a certain range.
4. Cutting and slitting: According to the battery model, the positive and negative electrode sheets need to be cut into the corresponding widths.
5. Stacking of positive and negative electrode plates: Small positive and negative electrode plates and separators are stacked together to form a bare cell.
6. Casing, Spot Welding, and Vacuum Drying: The bare battery cells are wrapped in packaging aluminum foil, and the top and sides are heat-sealed. Additionally, they undergo high-vacuum, high-temperature baking to dry out any remaining moisture, ensuring the performance of the lithium battery.
7. Electrolyte injection: Add electrolyte into the battery cell and completely seal the battery cell.
8. Formation: After assembly, the battery is given a certain current to activate the positive and negative electrode materials inside. The battery can only be used as a power source after it has been formed.
9. Capacity Classification: During the manufacturing process, the actual capacity of batteries may vary due to process differences. Through certain charge and discharge tests, the batteries are classified according to their capacity.
10. Molding: Final processing of the battery cell shape.
After the above steps, a lithium battery cell is successfully manufactured. The next step is to assemble the cells into a battery pack.
II. The desired electric vehicle lithium battery pack is achieved by connecting individual lithium cells in series or parallel.
Electric vehicle lithium battery assembly: For example, if you want to make your own 48V 20Ah battery pack, you can buy lithium iron phosphate batteries. Using 3Ah 26650 batteries, a 16-cell series 7-parallel configuration can achieve 48V 20Ah. Then, buy a 16-cell lithium iron phosphate protection board to control the current to 6A normally, 12A maximum, and 18A instantaneously. A single 26650 battery costs 24 yuan, the protection board costs 160 yuan, totaling approximately 2848 yuan. A charger costs 50 yuan. You can assemble it yourself. Lithium iron phosphate batteries are the safest lithium batteries with the highest cycle life.
1. Prepare materials, including a stainless steel battery box and a 60V 24AH lithium battery for assembling the electric vehicle. The lithium battery must be an electric vehicle power battery.
2. Connect 20 lithium batteries in a string, for a total of 8 strings.
3. Connect 8 lithium batteries in parallel and insulate them with separators and tape.
4. Secure with adhesive tape and connect in series with a protective welding wire.
5. Wrap the series-welded lithium batteries with heat-shrink film for insulation, connect the protection board, and ensure proper insulation to prevent short circuits.
6. Short circuits in lithium batteries are very dangerous. Once the lithium battery is wrapped in heat-shrink film, the assembly of the electric vehicle's lithium battery is complete. Simply place it into the electric vehicle.
Issues to be aware of when assembling lithium batteries for electric vehicles:
1. Inspection of lithium batteries during electric vehicle assembly
During battery removal, check the quality of all connections, including the fuse holder, charging socket, and the lithium battery lead wires for proper and reliable contact. Tighten all connections. Replace any components that need replacing, and thoroughly examine their reliability; replace any unreliable components.
2. Installation of lithium batteries for electric vehicles
Install the electric vehicle lithium battery according to the instructions inside the battery packaging. In most battery boxes, each battery cell is connected in series. Use copper wire of at least one square millimeter to solder each cell together with a soldering iron. Finally, solder the two remaining output terminals (positive and negative) to the two ends of the output socket. Be careful not to reverse them; they must correspond to the positive and negative terminals on the charger. Otherwise, the consequences can be serious.
4. Trial use of assembled electric vehicle lithium batteries
After installing the lithium battery for the electric vehicle, use a multimeter to measure the voltage at the battery's output port. The actual battery voltage should be 2-5V higher than the rated voltage. Only after this is confirmed can the battery be put into normal operation.
Lithium-ion batteries mainly consist of several parts, including the positive electrode, negative electrode, electrolyte, and separator. Currently, commercially available lithium-ion battery positive electrode materials primarily include lithium iron phosphate, lithium cobalt oxide, lithium manganese oxide, and ternary materials; the negative electrode is composed of carbon materials, such as MCMB and natural graphite; the separator uses microporous organic polymer separators, such as Celgard separators from the United States; the electrolyte consists of an organic solvent and a conductive salt, with organic solvents such as ethylene carbonate and dimethyl carbonate, and conductive salts such as LiClO4, LiPF6, LiAsF6, and LiBF4. The current collector for the negative electrode is copper foil, and the current collector for the positive electrode is aluminum foil. Commonly used binders include polyvinylidene fluoride (PVDF). A thin film is formed by adhering negative electrode materials such as graphite and lithium titanate to copper foil using a binder. Because the positive electrode material has poor conductivity, conductive carbon black must be added. The active material, carbon black, and PVDF are mixed evenly according to a certain ratio, and an appropriate amount of solvent is added to form a gel-like mixture with a certain fluidity. This mixture is then evenly coated onto aluminum foil and vacuum dried to serve as the positive electrode. Both the positive and negative electrodes must use active materials that allow Li+ to be inserted/extracted. A schematic diagram of their structure is shown in Figure 1.
Schematic diagram of a secondary lithium-ion battery
Due to their light weight and small size, button-cell lithium-ion batteries (CLIBs) better meet the miniaturization and weight reduction requirements of modern electrical devices. CLIBs are now commercially available and primarily used as power sources for small electronic products such as computer motherboards, MP3 players, watches, calculators, gifts, clocks, toys, Bluetooth headsets, PDAs, electronic keys, IC cards, and hand-cranked rechargeable flashlights, with a lifespan of 5-10 years. Furthermore, CLIBs are less expensive than cylindrical and prismatic lithium-ion batteries, easier to seal, and require simpler equipment. Therefore, in recent years, many battery companies, universities, and research institutions have increasingly focused on developing CLIBs.
Experimental equipment and materials:
1. Experimental equipment: weighing bottles, magnetic rotors, magnetic stirrers, coating machines, electric thermostatic drying ovens, vacuum drying ovens, electrode die punches, glove boxes, electrochemical testing instruments (Land), electrochemical workstations; scanning electron microscopes, X-ray diffractometers.
2. Experimental materials: positive and negative electrode material powder, copper foil, aluminum foil, electrolyte, conductive agent (Super P), binder (PVDF), button cell casing (positive and negative electrode casing), springs, gaskets, etc.
Manufacturing process of button cells
1. Selection of positive and negative electrode active materials, conductive agents, binders, and current collectors
The electrode active materials are selected from positive electrode materials (lithium iron phosphate, lithium manganese oxide, lithium cobalt oxide, or ternary materials; the selection needs to be based on the material's physical and electrochemical properties). The negative electrode materials are selected from hard carbon, silicon carbide, natural graphite, or artificial graphite; the selection needs to be based on the material's physical and electrochemical properties. The binder is polyvinylidene fluoride (PVDF). The positive electrode current collector is aluminum foil, the negative electrode current collector is copper foil, the conductive agent is acetylene black, and the simulated half-cell is lithium foil.
2. Fabrication of positive and negative electrode plates
Active material: conductive additive: binder = 80:10:10 (mass ratio). Weigh each material to a total of 1000mg. First, place the active material (800mg) and conductive additive acetylene black (100mg) in a weighing bottle. Then add 100mg of binder (PVDF), dry mix and stir for 30min to make the powder uniformly mixed. Then add N-methylpyrrolidone (NMP) dropwise to adjust the viscosity and magnetically stir to form a slurry. The final slurry should be just flowing.
After magnetic stirring for 4 hours, the stirred slurry was evenly coated onto the current collector using a manual coating machine (the opening of the coating machine was set to 150 μm). Aluminum foil was used for the positive electrode material and copper foil was used for the negative electrode material. The coating thickness was 20 micrometers.
The coated copper or aluminum foil is placed in a vacuum oven and dried at 110°C for 12 hours. Then, the electrode sheet is punched into positive and negative electrode sheets with a diameter of 15 mm using a punching machine. At the same time, blank copper or aluminum foil is punched to accurately weigh the amount of active material. The punched electrode sheets are then placed in a vacuum oven and dried at 60°C for 4 hours.
Select diaphragms or several diaphragms (intact and undamaged) of equivalent weight to the electrode, clean them with anhydrous ethanol, place them in lint-free paper, dry them with a hair dryer, and put them, along with a 1mL syringe and several lint-free papers, into a 60℃ vacuum oven to dry for 4 hours.
