With the continuous development of technology, a variety of new manufacturing processes and technologies for batteries are emerging, and today we will take a look at the detailed production process of lithium batteries.
First of all, lithium battery manufacturing can be divided into 13 major steps, including positive pole batching, negative pole batching, coating, positive pole slicing, negative pole slicing, positive pole chip preparation, negative pole chip preparation, winding, shelling, rolling groove, core baking, liquid injection, and over-welding cap.
1 Positive electrode material
The positive electrode material of lithium battery is composed of active material, conductive agent and binder, and its specific production process is as follows:
Incoming material confirmation & baking
Generally, the conductive agent needs to be baked at about 120℃ for 8 hours, the binder PVDF needs to be baked at about 80℃ for 8 hours, and the active material (LFP, NCM, etc.) needs to be baked and dried depending on the incoming material status and process. The current workshop requires temperature ≤ 40 ℃, humidity ≤ 25% RH.
Configuration of PVDF glue
If wet process is used, PVDF glue (solute PVDF, solution NMP) needs to be prepared in advance.
Good or bad PVDF glue is crucial to the internal resistance and electrical performance of the battery.
Factors affecting the glue are temperature, stirring speed. The higher the temperature, the glue is easy to dispense yellowing, affecting the adhesion; stirring speed is too high, easy to break the glue, the specific speed needs to depend on the size of the dispersion disk, generally dispersing disk line speed in 10-15m / s (high dependence on equipment). At this time, the stirring tank needs to open circulating water, and the temperature is ≤30℃.
Positive electrode slurry
At this time, it is necessary to pay attention to the order of charging (first add the active substance and conductive agent mixed by slow stirring, and then add the glue), charging time, charging ratio, and it is necessary to strictly implement according to the process.
Secondly, it is necessary to strictly control the equipment rotation and rotation speed (generally dispersing line speed should be more than 17m/s depending on the performance of the equipment, which varies a lot from manufacturer to manufacturer), stirring vacuum and temperature.
At this stage requires regular testing of the slurry particle size and viscosity, and particle size and viscosity with the solid content, material properties, charging order and process technology is closely related. At this time, the conventional process requires temperature ≤ 30 ℃, humidity ≤ 25% RH, vacuum ≤ -0.085MPa.
After the slurry is finished, it is necessary to transfer the slurry to the transfer tank or coating workshop, the slurry needs to be sifted when it is transferred out, the purpose is to filter large particles, precipitation and removal of ferromagnetic and other substances.
Large particles affect the coating to the end may lead to the risk of battery self-discharge or short circuit; slurry ferromagnetic material is too high will lead to battery self-discharge is too large and other bad. At this time, the process requirements are temperature ≤ 40 ℃, humidity ≤ 25% RH, screen ≤ 100 mesh, particle size ≤ 15um (parameters for reference only).
2 Negative electrode dosage
Negative electrode is similar to positive electrode, in addition to active material, conductive agent, adhesive, but also need dispersant.
Confirmation of incoming materials
Conventional negative electrode system is aqueous mixing process (solvent is deionized water), so there is no need to dry the incoming material. This process requires the conductivity of deionized water to be ≤1us/cm, and the workshop requires the temperature to be ≤40℃ and humidity to be ≤25%RH.
The specific process diagram is as follows:
Negative electrode dosage flow chart
Preparation of glue
After confirming the material, firstly prepare the glue. At this time, graphite C and conductive agent are poured into the mixer for dry mixing, it is recommended not to pump vacuum, turn on the circulating water (dry mixing particles extrusion friction heat production is serious), low-speed 15-20rpm, intervals of 15 minutes to scrape the material cycle 2-3 times.
Next, pour the glue into the mixer to open the vacuum (≤ -0.09mpa), low-speed 15-20rpm scraping cycle 2 times, and then adjust the speed (low-speed 35rpm, high-speed 1200-1500rpm), running 15-60 minutes (depending on each manufacturer's own wet process).
Finally, SBR will be poured into the mixer, it is recommended that this time fast low-time mixing (SBR belongs to the long-chain polymer, the speed is too high for too long molecular chain is easy to interrupt the loss of activity), it is recommended that the low-speed 35-40rpm, high-speed 1200-1800rpm, 10-20 minutes.
Viscosity measurement
Reference values are as follows: viscosity 2000-4000m Pa.s, particle size ≤ 35μm, solid content 40-70%, vacuum sieve ≤ 100 mesh.
Specific process values need to be based on the material properties, mixing process and other influences have some differences. Workshop temperature ≤ 30 ℃, humidity ≤ 25% RH.
3 Coating
Positive pole coating
Extrusion coating or spraying of anode slurry on the AB surface of aluminum collector, single-side density 20-40 mg/cm2 (NCM power type), coating oven temperature conventional 4-8 sections or more, baking temperature of 95-120 ℃ in each section, adjusted according to the actual needs, to avoid baking cracks appearing transverse cracks and solvent dripping phenomenon.
Transfer coating roller speed ratio of 1.1-1.2, gap position playing thin 20-30um (to avoid dragging the tail lead to too much compaction in the lug position, lithium precipitation in the battery cycle process), coating water ≤ 2000-3000ppm (depending on the material and process). Workshop anode temperature ≤ 30 ℃, humidity ≤ 25%. The schematic diagram is as follows:
Schematic diagram of coating tape
Negative electrode coating
Negative electrode slurry extrusion coating or spraying on the AB surface of copper collector, one-sided density of about 10-15mg/cm2, coating oven temperature conventional 4-8 sections or more, each section baking temperature 80-105 ℃, adjusted according to the actual needs, to avoid baking cracks appear transverse cracks.
Transfer roller speed ratio 1.2-1.3, gap position playing thin 10-15um, coating moisture ≤ 3000ppm, workshop negative temperature ≤ 30 ℃, humidity ≤ 25%.
4 Positive pole filming
After the anode coating is dried, it needs to be rolled within the process time. Rolling is the compaction of the pole piece, and there are two kinds of processes: hot pressing and cold pressing.
Hot pressing compaction is relatively high compared with cold pressing, and the rebound rate is low; cold pressing process is relatively simple and easy to operate and control.
Roller main equipment to the following process values: compaction density, rebound rate, elongation. At the same time, it should be noted that the surface of the pole piece is not brittle, hard, drop material, wavy edges and other phenomena and the gap does not allow fracture. At this time, the ambient temperature of the workshop ≤ 23 ℃, humidity ≤ 25%.
Compaction: mass per unit volume of dressing, the current true density data of conventional materials:
Bounce rate: generally bounce 2-3μm;
Elongation: positive pole piece is generally around 1.002.
Schematic diagram of roll pairing of pole piece
The next step is slitting, which is to cut small strips of the same width (corresponding to the height of the battery), the slitting should pay attention to the burrs of the pole piece, and it is necessary to fully inspect the X and Y burrs of the pole piece (with the help of quadratic element equipment), and the longitudinal burr length of the process is Y ≤ 1/2 H thickness of the diaphragm. Workshop ambient temperature ≤ 23 ℃, dew point ≤ -30 ℃.
Schematic diagram of slitting
5 Negative electrode slicing
Negative electrode slicing is operated in the same way as positive electrode, but the process design is different, the ambient temperature of the workshop is ≤23℃ and humidity is ≤25%. True density of common negative material:
Commonly used negative compaction table
Elasticity: generally around 4-8μm;
Elongation: generally around 1.0012.
Negative pole slitting is similar to positive pole slitting process, both X and Y direction burrs need to be controlled. The ambient temperature of the workshop is ≤23℃ and the dew point is ≤-30℃.
6 Preparation of positive electrode sheet
After the slitting is finished, the positive electrode sheet needs to be dried (120℃), and then the aluminum lugs are welded and the lugs are covered with adhesive. At this time, it is necessary to consider the length and shaping width of the lugs.
Taking a lithium battery design as an example, the design of the lugs exposed mainly takes into account the positive lugs to be welded caps and rolling grooves with a reasonable fit.
Ear exposed too long, rolling groove is easy to make the ear and steel shell short circuit; too short ear can not weld the cap. Pole at present ultrasonic welding head has line and point, the domestic process more line (overcurrent, welding strong consideration).
Another high-temperature adhesive is used to cover the pole ear, mainly considering the risk of short circuit caused by metal burrs and metal deb ris. The ambient temperature of this workshop is ≤23℃, dew point is ≤-30℃, and the moisture content of positive pole is ≤500-1000ppm.
Simple welding process for a certain type of positive lug
Lug welding schematic
Schematic diagram of coiled positive lug wrapping glue
7 Negative Electrode Preparation
The negative electrode sheet needs to be dried (105-110°C), and then there is the process of soldering nickel lugs and lug wrapping. The lug length and shaping width also need to be considered. The ambient temperature of this workshop is ≤23℃, dew point is ≤-30℃, moisture content of negative electrode is ≤500-1000ppm.
Simple process for welding a certain type of negative lug
8 Winding
Winding is the process of forming the diaphragm, positive pole piece, and negative pole piece into a single core by means of a winding machine. The principle is that the negative electrode is wrapped around the positive electrode, and then the positive and negative electrode sheets are separated by the diaphragm.
Because the negative electrode of the conventional system is designed as the control electrode of the battery, 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 negative electrode in the "empty space" during the chemical charging. Winding requires special attention to the winding tension and the alignment of the pole pieces.
A small winding tension will affect the internal resistance and shell-in rate; too much tension will easily cause a short-circuit or chip breakage risk. Alignment refers to the relative position of negative pole, positive pole and diaphragm, negative pole width 59.5mm, positive pole 58mm, diaphragm 61mm, the three are centered and aligned to avoid the risk of short circuit.
The winding tension is generally 0.08-0.15Mpa for positive tension and 0.08-0.15Mpa for negative tension; the upper diaphragm tension is 0.08-0.15Mpa and the lower diaphragm tension is 0.08-0.15Mpa, which should be adjusted according to the equipment and process. The ambient temperature of the workshop is ≤23℃, dew point is ≤-30℃, moisture content is ≤500-1000ppm.
Schematic diagram of the stacking sequence of wound pole piece diaphragm
Schematic diagram of winding into cores
9 Shelling
Before the core is put into the shell, Hi-Pot test voltage 200-500V (to test whether there is a high-voltage short-circuit), vacuuming treatment (to further control dust before shelling).
Here we need to emphasize the three major control points of lithium-ion moisture, burrs, dust.
After the completion of the previous process, the following pad pad into the bottom of the core after bending the negative lugs, so that the surface of the lugs is facing the core needle hole, and finally inserted vertically into the steel shell or aluminum shell (a model, for example, the outer diameter of about 18mm, height of about 71.5mm).
Of course, the cross-sectional area of the core should be smaller than the inner cross-sectional area of the steel shell, about 97-98.5% of the shell rate, because we have to take into account the rebound value of the pole piece and the degree of liquid injection in the later stage of the liquid under the liquid. The same as into the surface pad process, the upper pad will also be assembled to complete. The ambient temperature of this workshop is ≤23℃, dew point ≤-40℃.
Schematic diagram of shell insertion
10 Roll groove
Insert the welding pin (usually made of copper or alloy) into the center hole of the core. The common specification of the welding pin is Φ2.5*1.6mm, and the welding strength of the negative pole ear ≥12N is qualified, too low is easy to weld falsely and the internal resistance is big; too high is easy to weld off the nickel layer on the surface of the steel shell, which will lead to rust and liquid dew at the welded joints and other hidden dangers.
Rolling groove is simply understood as fixing the core in the shell without shaking. This process requires special attention to the transverse extrusion speed and longitudinal downward speed matching, to avoid transverse speed is too large to cut the shell, longitudinal speed is too fast groove nickel layer off or affect the groove height to affect the sealing.
Need to test the groove depth, flaring, groove height process value is up to standard (through practical and theoretical calculations). Common hob specifications are 1.0, 1.2, 1.5mm, after the completion of rolling groove need to be again on the overall vacuum treatment, to avoid metal debris, vacuum ≤ -0.065Mpa, vacuum time 1-2s. The ambient temperature of this workshop is ≤23℃, dew point ≤-40℃.
Schematic diagram of spot bottom welding and groove rolling
11 Baking
After the cylindrical cell is rolled and grooved, the next step is very important: baking. During the manufacturing process, the battery cell will bring in a certain amount of moisture, if the moisture is not controlled within the standard in time, it will seriously affect the performance of the battery and the safety performance.
The general use of automatic vacuum oven for baking, neatly placed in the core to be baked, inside the oven set the desiccant, set the parameters, heating temperature to 85 ℃ (lithium iron phosphate core, for example), need to go through a few vacuum drying cycle in order to reach the standard.
Several different sizes of electric core baking standards:
Note: Setting temperature 85℃, actual temperature 85±3℃.
12 Liquid injection
The baked core is tested for moisture and meets the previous baking standards before the next step: injection of electrolyte.
Baking qualified core quickly into the vacuum glove box, weighing, recording the weight, set on the liquid injection cup, the design of the weight of the electrolyte into the set of cups (generally will be soaking experiment: the core into the electrolyte, soak for a period of time, test the maximum amount of liquid absorption of the core, generally according to the experimental amount of liquid injection), put into a vacuum box vacuum (vacuum ≤ -0.09Mpa), to accelerate electrolyte Infiltrate the pole piece.
After several cycles, take out the core for weighing, calculate whether the liquid injection is in line with the design value, less need to make up the liquid, over the need to pour out the excess, until it meets the design requirements. Glove box environment: temperature ≤ 23 ℃, dew point ≤ -45 ℃.
13 Super welding cap
Put the cap into the glove box in advance, one hand will fasten the cap in the mold under the super welder, one hand take the electric core, the positive pole ear of the electric core and the polar ear of the cap are aligned, make sure that the positive pole ear and the polar ear of the cap are aligned with the OK, then step on the pedal switch of the super welder.
After that, you need to check the whole core: self-check the welding effect of the lugs, the first is to observe whether the lugs are aligned; the second is to lightly pull the lugs to see whether the lugs are loosened. If the over-welding cap is not welded, you need to over-weld again.
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