Part of the positive electrode ingredients (the positive electrode is composed of active material, conductive agent, and binder)
1. First, confirm and bake the incoming materials. Generally, the conductive agent needs to be baked at ≈120℃ for 8h, and the binder PVDF needs to be baked at ≈80℃ for 8h. The active material (LFP, NCM, etc.) depends on the state and process of the incoming material. Determine whether you need to bake and dry. The current workshop requires temperature: ≤40℃, humidity: ≤25%RH.
2. After the drying is completed, (wet process) it is necessary to prepare PVDF glue solution (solute PVDF, solution NMP) in advance. The quality of PVDF glue is very important to the internal resistance and electrical performance of the battery. The factors that affect glue making are temperature and stirring speed. The higher the temperature, the yellowing of the glue will affect the adhesion; the high stirring speed will easily break the glue. The specific rotation speed depends on the size of the dispersing disc. Generally, the linear speed of the dispersing disc is 10-15m /s (higher dependence on equipment). At this time, it is required to open the circulating water in the stirring tank, and the temperature: ≤30℃.
3. The next step is to prepare the positive electrode slurry. At this time, it is necessary to pay attention to the order of feeding (first add the active material and the conductive agent, slowly stir and mix, and then add the glue), the feeding time, and the feeding ratio, which must be strictly implemented in accordance with the process. Secondly, it is necessary to strictly control the revolution and rotation speed of the equipment (generally, the linear speed of dispersion should be above 17m/s, depending on the equipment performance, which varies greatly from manufacturer to manufacturer), the vacuum degree and temperature of stirring. At this stage, the particle size and viscosity of the slurry need to be checked regularly, and the particle size and viscosity are closely related to the solid content, material properties, feeding sequence, and process technology (not described this time, welcome to discuss). At this time, the conventional process requires temperature: ≤30℃, humidity: ≤25%RH, and vacuum degree ≤-0.085mpa.
4. After the slurry is prepared, the slurry should be transferred out to the transfer tank or coating workshop. When the slurry is transferred out, it needs to be screened, the purpose is to filter large particles, precipitate, and remove ferromagnetic substances. Large particles affect the application to the end, which may lead to the risk of excessive battery self-discharge or short circuit; excessively high slurry ferromagnetic substance will cause excessive battery self-discharge and other defects. The process requirements at this time are temperature: ≤40℃, humidity: ≤25%RH, screen ≤100 mesh, particle size ≤15um (parameters are for reference only).
Part two: negative electrode ingredients (negative electrode is composed of active material, conductive agent, binder, and dispersant)
1. The conventional negative electrode system is a water-based mixing process (the solvent is deionized water), so the incoming material does not require drying. This process requires the conductivity of deionized water to be ≤1us/cm. Workshop temperature: ≤40℃, humidity: ≤25%RH.
2. After the incoming materials are confirmed, the glue solution (composed of CMC and water) is prepared first. At this time, graphite C and conductive agent are poured into the mixer for dry mixing. It is recommended not to vacuum, turn on the circulating water (the particles are extruded and frictionally generate severe heat during dry mixing), low-speed 15-20rpm, interval ≈15min, scraping 2-3 times. Next, pour the glue into the mixer and start vacuuming (≤-0.09mpa), scraping at a low speed of 15-20 rpm for 2 times, then adjust the speed (low-speed 35rpm, high speed 1200～1500rpm), and run for 15min～60min (depending on each Depending on the manufacturer’s own wet process). Finally, pour the SBR into the mixer, and it is recommended to stir at a low speed at this time (SBR is a long-chain polymer, and the molecular chain is easy to break and lose its activity if the speed is too high and the time is too long). It is recommended that the low speed is 35-40rpm and the high speed is 1200～1800rpm. 10-20min.
3. Finally, measure the viscosity (2000～4000 mPa.s), particle size (35um≤), solid content (40-70%), and then vacuum and sieve (≤100 mesh). The specific process value needs to be different according to the influence of material properties and mixing process. Workshop temperature: ≤30℃, humidity: ≤25%RH.
Part Three：Coating
1. Cathode coating is to squeeze or spray the anode slurry on the AB surface of the aluminum current collector, with a single-sided density ≈20～40 mg/cm2 (NCM power type), and the coating oven temperature is usually 4-8 knots (or more Many), the baking temperature of each section is 95℃～120℃ adjusted according to actual needs to avoid the phenomenon of horizontal cracks and solvent dripping caused by baking cracking. The transfer coating roller speed ratio is 1.1-1.2, the gap position is thinned by 20-30um (to avoid excessive compaction at the tab position caused by tailing, and lithium evolution during battery cycle), and the coating water content is less than or equal to 2000-3000ppm (specifically based on Material and craftsmanship). The temperature of the anode in the workshop is ≤30℃, and the humidity is ≤25%
2. Negative electrode coating is to squeeze or spray the negative electrode slurry on the AB surface of the copper current collector, the single-sided density ≈10-15 mg/cm2, the coating oven temperature is usually 4-8 knots (or more), each section The baking temperature is 80℃～105℃ according to actual needs to avoid horizontal cracks caused by baking cracking. The transfer roller speed ratio is 1.2-1.3, the gap is 10-15um thinner, the coating water content is ≤3000ppm, the temperature of the negative electrode in the workshop is ≤30℃, and the humidity is ≤25%.
Part four: positive electrode production
1. After the positive electrode is coated and dried, the roller needs to be aligned within the processing time. The rollers are used to compact the pole pieces. Currently, there are two processes: hot pressing and cold pressing. Compared with cold pressing, hot pressing is higher, and the rebound rate is lower; however, the cold pressing process is relatively simple and easy to operate and control. Roll the main equipment to the following process values, compaction density, rebound rate, and elongation. At the same time, pay attention to the fact that there are no chips, lumps, material drop, wavy edges, etc. on the surface of the pole piece, and no cracks are allowed in the gap. At this time, the workshop environment temperature: ≤23℃, humidity: ≤25%.
Compaction: the mass of the dressing per unit volume, the current true density data of conventional materials
Rebound rate: generally rebound 2-3um
Elongation: the positive pole piece is generally ≈1.002
2. After the positive pole pair is finished, the next step is slitting, that is, the entire pole piece is cut into small strips of the same width (corresponding to the battery height). When slitting, pay attention to the burrs of the pole piece, and you need to check the X and Y directions of the pole piece. Burr (with the aid of two-dimensional equipment), longitudinal burr length process Y≤1/2 H diaphragm thickness. Workshop ambient temperature≤23℃, dew point≤-30℃
Part five: negative electrode production
1. The negative electrode production is the same as the positive electrode, but the process design is different. The workshop environment temperature: ≤23℃, humidity: ≤25%. The true density of common negative materials
Rebound rate: generally 4-8um
Elongation rate: generally ≈1.0012
2. The negative slitting process is similar to the positive slitting process, and both X and Y burrs need to be controlled. Workshop ambient temperature≤23℃, dew point≤-30℃
Part six: of positive electrode preparation
After the slitting is completed, the positive electrode sheet needs to be dried (120°C), and then the welding aluminum tab and the tab encapsulation process. At this time, the length of the tab and the width of the shaping need to be considered.
Take the **650 types design as an example, the design of the exposed tabs mainly takes into account the reasonable cooperation when the positive tabs are welded with caps and roll grooves. If the lugs are exposed too long, it is easy to short-circuit the lugs and the steel shell when rolling grooves; if the lugs are too short, the caps cannot be welded. At present, the ultrasonic welding head is linear and point-shaped, and the domestic process is mostly linear (considering overcurrent and welding strength). In addition, high-temperature glue is used to cover the tabs, mainly considering the risk of short circuits caused by metal burrs and metal debris. The ambient temperature of this workshop is ≤23℃, the dew point is ≤-30℃, and the positive electrode moisture content is ≤500-1000ppm.
Part seven: preparation of negative electrode sheet
The negative electrode sheet needs to be dried (105-110°C), and then the nickel electrode lug and the lug encapsulation process are required. It is also necessary to consider the length of the tab and the width of the shaping. The ambient temperature of this workshop is ≤23℃, the dew point is ≤-30℃, and the moisture content of the negative electrode is ≤500-1000ppm.
Part eight: winding
Winding is to pass the separator, positive electrode sheet, and negative electrode sheet through a winding machine into a single core. The principle is to wrap the positive electrode with the negative electrode and then separate the positive and negative plates with a separator. Because the negative electrode of the conventional system is used as the control electrode of the battery design, the capacity is designed to be higher than that of the positive electrode, so that the Li+ of the positive electrode can be stored in the "vacancy" of the negative electrode during the formation charge. Winding requires special attention to winding tension and pole piece alignment.
The winding tension is small, which will affect the internal resistance and the shelling rate; excessive tension may cause short circuits or broken pieces. Alignment refers to the relative positions of the negative electrode, positive electrode, and separator. The width of the negative electrode is 59.5mm, the positive electrode is 58mm, and the separator is 61mm. The three are aligned in the drama to avoid the risk of a short circuit. The winding tension is generally 0.08-0.15Mpa for positive tension, 0.08-0.15Mpa for negative tension, 0.08-0.15Mpa for the upper diaphragm, and 0.08-0.15Mpa for lower diaphragm depending on the equipment and process. The ambient temperature of this workshop is ≤23℃, the dew point is ≤-30℃, and the moisture content is ≤500-1000ppm.
Part nine: into the shell
Before the core is put into the shell, a Hi-Pot test voltage of 200~500V (test for high-voltage short-circuit) is required, and dust collection treatment (further control of dust before entering the shell). Here we need to emphasize the three major control points of lithium battery, moisture, burr, and dust. After the previous process is completed, put the lower pad into the bottom of the winding core and bend the negative ear, so that the surface of the ear is facing the pinhole of the winding core, and finally insert the steel shell or aluminum shell vertically (take the 18650 model as an example, the outer diameter is ≈18mm+ Height ≈ 71.5mm). Of course, the cross-sectional area of the core is smaller than the inner cross-sectional area of the steel shell, and the shell penetration rate is approximately 97% to 98.5% because of the rebound value of the pole piece and the degree of liquid injection during later injection must be considered. In the same process as the surface pad, the upper pad is also assembled. The ambient temperature of this workshop is ≤23℃, and the dew point is ≤-40℃.
Part ten: roll groove
1. Insert the solder pin (usually made of copper or alloy) into the middle hole of the core. The commonly used welding pin specification is Φ2.5*1.6mm, and the welding strength of the negative pole lug is ≥12N to be qualified. If it is too low, it is easy to weld and the internal resistance is too large; if it is too high, it is easy to weld off the nickel layer on the surface of the steel shell, resulting in solder joints Hidden dangers such as rust and dew.
2. A simple understanding of the rolling groove is to fix the core in the shell without shaking. In this process, special attention should be paid to the matching of the horizontal extrusion speed and the vertical pressing speed, so as to avoid excessively high horizontal speed from cutting the shell, and excessively high vertical speed and the nickel layer of the notch will fall off or affect the height of the groove to affect the sealing. It is necessary to check whether the process values of groove depth, flaring, and groove height meet the standards (by actual and theoretical calculations). Common hob specifications are 1.0, 1.2, 1.5mm. After the rolling groove is completed, it is necessary to vacuum the whole again to avoid metal chips, the vacuum degree is ≤-0.065Mpa, and the vacuum time: 1~2s. The ambient temperature of this workshop is ≤23℃, and the dew point is ≤-40℃.
Part eleven: Battery baking
After the cylindrical cell passes through the rolling groove, the next step is very important: baking. During the production process of the battery cell, a certain amount of moisture will be brought in. If the moisture is not controlled within the standard in time, it will seriously affect the performance and safety of the battery. Generally, an automatic vacuum oven is used for baking, neatly put the batteries to be baked, put the desiccant in the oven, set the parameters, and heat to 85°C (taking lithium iron phosphate batteries as an example), and need to go through several vacuum drying cycles. Up to standard.
Part twelve: Injection
Test the moisture of the baked cells, and only after they meet the previous baking standards, can we proceed to the next step: inject electrolyte. Quickly put the baked cells into the vacuum glove box, weigh them, record the weight, put on the liquid injection cup, and add the electrolyte with the designed weight into the cup (usually conduct a bubble test: Put the core in the electrolyte, soak for a period of time, test the maximum liquid absorption of the cell, generally inject the liquid according to the experimental volume), put it in a vacuum box and vacuum (vacuum ≤-0.09Mpa) to accelerate the electrolyte infiltration After a few cycles, take out the battery cell and weigh it to calculate whether the injection volume meets the design value. If it is less, it needs to be refilled. If it exceeds, the excess part needs to be discarded until it meets the design requirements. Glove box environment: temperature≤23℃, melting point≤-45℃.
Part thirteen: super welding cap
Put the cap into the glove box in advance, buckle the cap tightly on the lower mold of the super welding machine with one hand, hold the battery cell in the other hand, and align the positive ear of the battery with the cap lug. After confirming that the positive lug is aligned with the cap lug, step on the super welder. Foot pedal switch for welding machine. Afterward, you need to check the battery cell completely: self-check the welding effect of the tabs ① observe whether the tabs are aligned ② pull the tabs lightly to see if the tabs are loose. Cells with over-welded caps and virtual welds need to be over-welded again.
