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 ℃.
