Detailed interpretation of lithium ion battery process
The manufacturing process of lithium batteries can be "handy" for all practitioners in the field of new energy. However, can the simple process express the difficulties of lithium battery manufacturing process technology? The following Shenzhen Max Power Co., Ltd. will introduce the key points of the main lithium battery process control. (throwing a brick to attract jade)
Part 1 The positive electrode ingredients (the positive electrode is composed of active material, conductive agent, and binder)
1. The first thing is to confirm and bake the incoming materials. Generally, the conductive agent needs to be baked at ≈120°C for 8 hours, and the binder PVDF needs to be baked at ≈80°C for 8 hours. The active materials (LFP, NCM, etc.) depend on the state and process of the incoming materials Determine whether it needs to be baked and dried. The current workshop requires temperature: ≤40°C, humidity: ≤25%RH.
2. After drying, (wet process) needs to prepare PVDF glue (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 glue will turn yellow, which will affect the cohesiveness; if the stirring speed is too high, the glue will be broken easily. The specific speed depends on the size of the dispersing disc. Generally, the linear speed of the dispersing disc is 10-15m /s (higher device dependency). At this time, it is required that the stirring tank needs to open the circulating water, the temperature: ≤30°C.
3. The next step is to mix the positive electrode slurry. At this time, it is necessary to pay attention to the order of feeding (add active substance and conductive agent and mix slowly, and then add glue), feeding time, feeding ratio, and strictly follow the process. Secondly, it is necessary to strictly control the revolution and rotation speed of the equipment (generally, the dispersion line speed should be above 17m/s, depending on the performance of the equipment, which varies greatly among different manufacturers), the vacuum degree and temperature of the 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°C, humidity: ≤25%RH, vacuum degree ≤-0.085mpa.
4. After the slurry is prepared, it is necessary to transfer the slurry to the transfer tank or coating workshop. When the slurry is transferred out, it needs to be screened to filter large particles, precipitate and remove ferromagnetic substances. Large particles affect the coating until the end, which may lead to the risk of excessive battery self-discharge or short circuit; too much ferromagnetic material in the slurry will lead to excessive battery self-discharge and other defects. The process requirements at this time are temperature: ≤40°C, humidity: ≤25%RH, screen ≤100 mesh, particle size ≤15um (parameters are for reference only).
Part 2 Negative electrode ingredients (the 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 need to be dried. This process requires the conductivity of deionized water to be ≤1us/cm. Workshop requirements temperature: ≤40°C, humidity: ≤25%RH.
The schematic diagram of the process is as follows
2. After confirming the incoming materials, first prepare the glue (composed of CMC and water). At this time, graphite C and conductive agent are poured into the mixer for dry mixing. It is recommended not to evacuate and turn on the circulating water (during dry mixing, the friction and friction of particles will generate serious heat). . Next, pour the glue into the mixer and start vacuuming (≤-0.09mpa), scrape the material twice at a low speed of 15~20rpm, then adjust the speed (35rpm at a low speed, 1200~1500rpm at a high speed), and run for 15min~60min (depending on each The manufacturer's own wet process depends). Finally, pour the SBR into the blender. It is recommended to stir quickly at this time (SBR is a long-chain polymer, and the molecular chain is easily broken and loses activity if the speed is too high and the time is too long). 10-20min.
3. Finally measure viscosity (2000-4000 mPa.s), particle size (35um≤), solid content (40-70%), and vacuum sieve (≤100 mesh). The specific process value needs to be different according to the influence of material properties and mixing process. Workshop requirements temperature: ≤30°C, humidity: ≤25%RH.
Part 3 Coating
1. Positive electrode coating means that the positive electrode slurry is extruded or sprayed on the AB surface of the aluminum current collector, the density on one side is ≈20-40 mg/cm2 (NCM power type), and the temperature of the coating oven is usually 4-8 knots (or higher More), the baking temperature of each section is 95 ℃ ~ 120 ℃ adjusted according to actual needs, to avoid transverse cracks and solvent dripping in baking cracking. The speed ratio of the transfer coating roller is 1.1-1.2, the gap position is thinned by 20-30um (to avoid tailing and cause excessive compaction at the tab position, and lithium is precipitated during the battery cycle), and the coating water content is ≤2000-3000ppm (specifically according to materials and workmanship). The temperature of the positive electrode in the workshop is ≤30°C, and the humidity is ≤25%. The schematic diagram is as follows
Schematic diagram of coating transport
Positive and negative coated pole piece diagram
2. Negative electrode coating is to extrude or spray the negative electrode slurry on the AB surface of the copper current collector. The density on one side is ≈10-15 mg/cm2. The temperature of the coating oven is usually 4-8 sections (or more), each section Baking temperature 80℃～105℃ should be adjusted according to actual needs to avoid transverse cracks in baking cracks. The transfer roller speed ratio is 1.2-1.3, the gap position is thinned by 10-15um, the coating moisture is ≤3000ppm, the negative electrode temperature in the workshop is ≤30°C, and the humidity is ≤25%.
Part 4 Positive Electrode Production
1. After the positive electrode is coated and dried, it is necessary to carry out roll alignment within the process time. The rollers are used to compact the pole pieces. At present, there are two processes of hot pressing and cold pressing. Compared with cold pressing, hot pressing has higher compaction rate and lower rebound rate; however, cold pressing process is relatively simple and easy to operate and control. The main equipment of the pair of rolls reaches the following process values, compaction density, rebound rate, and elongation. At the same time, it should be noted that there are no brittle chips, hard blocks, falling materials, wavy edges, etc. on the surface of the pole piece, and no breakage is allowed in the gap. At this time, the ambient temperature of the workshop: ≤23°C, humidity: ≤25%.
Compaction: the mass of the dressing per unit volume, the true density data of the current conventional materials
Commonly used compaction table
Rebound rate: general rebound 2-3um
Elongation: Positive pole piece is generally ≈1.002
Schematic diagram of pole piece to roll
3. After the positive electrode is rolled, the next step is to divide the whole pole piece into small strips with the same width (corresponding to the height of the battery). Pay attention to the burrs of the pole piece when dividing the strips. It is necessary to fully check the X and Y directions of the pole piece. Burrs (with the help of secondary equipment), the longitudinal length of the burr process Y≤1/2 H diaphragm thickness. Workshop ambient temperature ≤23°C dew point ≤-30°C
Part 5 Negative electrode production
1. Negative electrode production is the same operation as positive electrode, but the process design is different. Workshop ambient temperature: ≤23℃, humidity: ≤25%. True Density of Common Anode Materials
Common negative compaction table
Rebound rate: generally 4-8um
Elongation: generally ≈1.0012
2. Negative electrode slitting is similar to positive electrode slitting process, both X and Y direction burrs need to be controlled. Workshop ambient temperature ≤23°C dew point ≤-30°C
Part 6 Positive electrode sheet preparation
After the slitting is completed, the positive electrode sheet needs to be dried (at 120°C), and then the aluminum tab and the tab wrapping process are performed. At this time, the length of the tab and the width of the shaping need to be considered.Taking the design of 18650 as an example, the design of the exposed tab mainly considers the reasonable fit when the positive tab needs to be welded to the cap and the rolling groove. If the tab is exposed too long, it is easy to short-circuit the tab and the steel shell during grooving; if the tab is too short, the cap cannot be welded. At present, the ultrasonic welding head has a linear shape and a point shape, and the domestic process mostly uses a linear shape (overcurrent, welding strength considerations). In addition, high temperature glue is used to cover the tabs, mainly considering the risk of short circuit caused by metal burrs and metal debris. The ambient temperature of this workshop is ≤23°C, the dew point is ≤-30°C, and the moisture content of the cathode is ≤500-1000ppm.
Simple Welding Process of 18650 Type Positive Tab
Schematic diagram of coiled positive tab welding
Schematic diagram of winding positive ear wrap
Part 7 Negative Electrode Preparation
It is necessary to dry the negative plate (105-110°C), and then to weld the nickel tab and the tab wrapping process. Tab length and shaping width also need to be considered. The ambient temperature of this workshop is ≤23°C, the dew point is ≤-30°C, and the moisture content of the negative electrode is ≤500-1000ppm.
Simple Welding Process of 18650 Type Negative Tab
Part 8 Winding
Winding is to pass the separator, positive electrode sheet, and negative electrode sheet into a single winding core through a winding machine. The principle is to use the negative electrode to wrap the positive electrode, and then separate the positive and negative electrodes through the diaphragm. Because the negative electrode of the conventional system is used as the control electrode of the battery design, the capacity design is 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 formation and charging. Winding requires special attention to winding tension and pole piece alignment.
Small winding tension will affect the internal resistance and shell penetration rate; excessive tension will easily cause short circuit or fragmentation risk. Alignment refers to the relative position 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 play to avoid the risk of 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 upper diaphragm, and 0.08-0.15Mpa for lower diaphragm, which should be adjusted according to equipment and process. The ambient temperature of this workshop is ≤23°C, the dew point is ≤-30°C, and the moisture content is ≤500-1000ppm.
Schematic diagram of stacking sequence of wound pole piece diaphragm
Schematic diagram of winding into a core
Part 9 Into the Shell
Before the winding core is put into the shell, Hi-Pot test voltage of 200~500V is required (to test whether there is a high-voltage short circuit), and vacuum treatment (to further control the dust before entering the shell). Here we need to emphasize the three major control points of lithium batteries: moisture, burrs, and dust. After the previous process is completed, put the lower pad into the bottom of the core and bend the negative tab so that the tab face faces the pinhole of the core roll, and finally insert the steel or aluminum shell vertically (take the 18650 model as an example, the outer diameter ≈18mm+ height ≈71.5mm). Of course, the cross-sectional area of the winding core is < the internal cross-sectional area of the steel shell, and the shell penetration rate is about 97% to 98.5%, because the rebound value of the pole piece and the degree of liquid injection during the later injection should be considered. In the same process as the surface pad, the top pad is also assembled. The ambient temperature of this workshop is ≤23°C, and the dew point is ≤-40°C.
Schematic diagram of entering the shell
Part 10 Roll groove
1. Insert the welding pin (usually made of copper or alloy) into the middle hole of the core. Commonly used welding needle specifications are Φ2.5*1.6mm, and the welding strength of the negative electrode lug is ≥12N. There are hidden dangers such as rust and dew.
2. The simple understanding of rolling groove is to fix the winding 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 cutting the shell when the horizontal speed is too high, and the nickel layer of the notch falling off or affecting the height of the groove to affect the sealing if the longitudinal speed is too fast. It is necessary to check whether the process values of groove depth, flare, and groove height are up to standard (through 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 debris, the vacuum degree is ≤-0.065Mpa, and the vacuuming time is 1~2s. The ambient temperature of this workshop is ≤23°C, and the dew point is ≤-40°C.
Schematic diagram of spot welding and rolling
Part 11 Battery Baking
After the cylindrical cells have been rolled, 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, and the cells to be baked are placed neatly, the desiccant is placed in the oven, the parameters are set, and the temperature is raised to 85°C (taking lithium iron phosphate cells as an example), it takes several vacuum drying cycles to complete the process. Up to standard.
Baking standards for several different sizes of batteries:
Part 12 Injection
Conduct the moisture test on the baked battery cells, and only after meeting the previous baking standards can the next step: inject electrolyte. Quickly put the battery cell that has passed the baking into the vacuum glove box, weigh it, record the weight, put on the liquid injection cup, and add the electrolyte with the designed weight into the cup (generally, a bubble test will be carried out: put the battery Put the cell into the electrolyte, soak for a period of time, test the maximum liquid absorption of the cell, generally inject liquid according to the experimental amount), put it in a vacuum box to vacuum (vacuum degree ≤ -0.09Mpa), accelerate the electrolyte to infiltrate the electrode After a few cycles, take out the cell and weigh it, and calculate whether the liquid injection volume meets the design value. If it is less, it needs to be replenished, and if it exceeds, it needs to pour out the excess until it meets the design requirements. Glove box environment: temperature ≤23°C, dew point ≤-45°C.
Part 13 Super Weld Caps
Put the cap into the glove box in advance, fasten the cap on the mold under the super welding machine with one hand, hold the battery with the other hand, align the positive ear of the battery with the ear of the cap, confirm that the positive ear and the ear of the cap are aligned OK, step on Welder foot pedal switch. After that, it is necessary to fully inspect the battery cells: self-check the welding effect of the tabs ①Observe whether the tabs are aligned ②Pull the tabs lightly to see if the tabs are loose. The battery core with the over-soldered cap that has been soldered needs to be re-soldered.
Experience value of super welding equipment parameters:
.jpg)
.jpg)
.jpg)
.jpg)
.jpg)
.jpg)
.jpg)
.jpg)
