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Lithium-ion battery process details

Lithium-ion battery process
Introduction

Lithium-ion batteries consisting of LiCoO2 and graphite are popular worldwide as power sources for mobile phones, laptop computers, and other electronic devices. Graphite and LiCoO2 are called lithium insertion materials. In other words, the lithium-ion battery consists of two lithium insertion materials. The combination of two lithium insertion materials is essential for the basic functionality of the lithium-ion battery. An advantage of the lithium-ion battery concept is that the operating voltage of the battery can be designed by the choice of insertion reaction in terms of operating voltage and its charge-discharge profile. In this article, 1.5 V lithium-ion batteries consisting of V2O5 and Li2Nb2O5 are described, which were developed as power sources for memory backup, digital watches with solar cells or mechanical chargers, and so on.

Part 1 The cathode ingredients (the positive electrode is composed of active substances, conductive agents, and binders)

1. First of all, it is to confirm and bake incoming materials. General conductive agents need to bake at ≈120°C for 8 hours, binder PVDF needs to bake at ≈80°C for 8 hours. Active substances (LFP, NCM, etc.) depend on whether the state and process of the incoming materials need to be baked and dried. The current workshop requires a temperature: of ≤40°C, and humidity: of ≤25% RH.
2. After drying, (wet process) needs to be prepared with PVDF glue (solute PVDF, solution NMP) in advance. The quality of PVDF glue is very important for the internal resistance and electrical performance of the battery. The factors affecting the glue are temperature and stirring speed. The higher the temperature, the glue is yellowed, which affects the bondability; the stirring speed is too high, and easy to break the glue. The specific rotation speed depends on the size of the dispersion disk. Generally speaking, the dispersion disk line speed is 10-15m/s (high dependence on the equipment). At this time, the mixing tank is required to turn on the circulating water. The temperature: ≤30°C.
3. Next is to match the positive slurry. At this time, it is necessary to pay attention to the order of feeding (first add active substances and conducive to mix slowly, and then add glue), feeding time, and feeding proportion, which should be strictly carried out according to the process. Secondly, it is necessary to strictly control the rotation 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 from manufacturer to manufacturer), and the vacuum degree and temperature of stirring. At this stage, it is necessary to regularly test the particle size and viscosity of the slurry, and the particle size and viscosity are closely related to the solid content, material performance, feeding order, and process (not described this time, welcome to discuss). At this time, the conventional process requires temperature: ≤30°C, humidity: ≤25%RH, vacuum ≤-0.085mpa.
4. After the slurry is dispensed, the slurry should be transferred to the transit tank or coated workshop. When the slurry is transferred out, it needs to be screened. The purpose is to filter large particulate matter, precipitate, and remove ferromagnetic substances. Large particles may eventually cause the risk of excessive self-discharge or short circuit of the battery; excessive ferromagnetic material of the slurry will lead to excessive self-discharge of the battery. At this time, the process requirements are temperature: ≤40°C, humidity: ≤25% RH, screen ≤ 100 mesh, and particle size ≤ 15um (parameters are for reference only).

Part 2: Negative ingredients (the anode consists of active substances, conductive agents, adhesives, and dispersants)

1. The conventional negative polar system is a water 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. The temperature required for the workshop: was ≤40°C, and the humidity: was ≤25% RH.
2. After the incoming material is confirmed, the glue (CMC and water composition) will be prepared first. At this time, graphite C and the conductive agent are poured into the mixer for dry mixing. It is recommended not to vacuum, turn on the circulating water (when the dry mixing, the particle extrusion friction is serious to produce heat), with a low speed of 15-20rpm, and the interval is ≈15min scraping circulating 2-3 times. Next, pour the glue into the mixer to open the vacuum (≤-0.09mpa), cycle the scraper at a low speed of 15-20rpm, and then adjust the rotation speed (low-speed 35rpm, high-speed 1200-1500rpm), and run for 15min to 60min (depending on the manufacturer’s own It depends on the wet process). Finally, pour the SBR into the blender. It is recommended to stir at a fast and low time (SBR belongs to a long-chain polymer, and the molecular chain is easy to interrupt and lose activity if the molecular chain is too high at a high speed). It is recommended to be low-speed 35-40rpm, high-speed 1200-1800rpm, 10-20min. 3. Finally measure the viscosity (2000-4000 mPa.s), particle size (35um≤), solid content (40-70%), and vacuum screening (≤100 mesh). The specific process value needs to vary according to the influence of the material physical properties and the mixture process. The required temperature of the workshop: ≤30°C, and the humidity: is ≤25% RH.

 Parts 3: Coating

1. Positive coating is extrusion or spraying of positive electrode slurry on the AB surface of the aluminum collector, with a single-sided density of ≈ 20-40 mg/cm2 (NCM power type), the temperature of the coating oven is conventional 4-8 knots (or more), and the baking temperature of each section is 95°C to 120°C adjusted according to actual needs to avoid baking cracking. Transverse cracks and solvent drops occur. Transfer the coating roller speed ratio 1.1-1.2, the gap level is thinned by 20-30um (avoid dragging the tail leading to excessive compaction in the polar ear position, lithium analysis during the battery cycle process), and the coating moisture is ≤2000-3000 ppm (determined according to the material and process). The positive temperature in the workshop is ≤ 30°C and the humidity is ≤25%.
2. Negative coating is to extrude or spray the negative slurry on the AB surface of the copper collector, with a single-sided density of ≈10-15 mg/cm2, and the temperature of the coating oven is routine 4-8 knots (or more). The baking temperature of each section is 80°C to 105°C according to actual needs to avoid horizontal cracking. The transfer roller speed ratio is 1.2-1.3, the clearance level is thinned by 10-15um, the coated moisture is ≤3000ppm, the negative electrode temperature in the workshop is ≤30°C, and the humidity is ≤25%.

Parts 4: Positive production

1. After the positive coating is dry, the roller needs to be carried out within the processing time. The roller is compacted on the electrode. At present, there are two processes: hot pressing and cold pressing. Hot pressing is relatively cold-pressing and rebounding is low; however, the cold pressing process is relatively simple and easy to operate and control. For the main equipment of the roller to the following process values, the compaction density, rebound rate, and elongation rate. At the same time, it should be noted that there are no brittles, hard blocks, falling materials, wave edges, and other phenomena on the surface of the pole, and fractures are not allowed in the gap. At this time, the ambient temperature of the workshop: was ≤23°C, and the humidity: was ≤25%. Compaction: the quality of dressing per unit volume, the current true density data of conventional materials.Rebound rate: general rebound 2-3um Elongation: The positive electrode is generally at ≈1.002
2. After the positive electrode roller, the next step is the strip, that is, the whole pole is cut into small strips of the same width (corresponding to the battery height). The strip should pay attention to the burrs of the pole. It is necessary to fully check the X and Y-directional burrs of the pole (with the help of two-dimensional equipment), and the longitudinal burr length process Y≤1/2 H diaphragm thickness. Ambient temperature in the workshop ≤23°C Dew point ≤-30°C.

 Parts 5: Negative production

1. The negative film is operated the same as the positive electrode, but the process design is different. The workshop ambient temperature: was ≤23°C, and the humidity: was ≤25%. The true density of common anode substances bound rate: generally, 4-8um Elongation: Generally, at ≈1.0012
2. The negative polarization strip is similar to the positive polarization process, and the X and Y burrs need to be controlled. Ambient temperature in the workshop ≤23°C Dew point ≤-30°C.

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 Parts 6: Preparation of cathode film

 After the strip is completed, the positive electrode needs to be dried (120°C), and then the process of welding aluminum ears and ear cladding. At this time, you need to consider the length of the polar ear and the width of the plastic surgery. Taking the **650 design as an example, the design polar ear exposure mainly takes into account the reasonable matching of the cap and roller when the positive ear should be welded. The polar ear is exposed too long, and it is easy to short circuit the polar ear and the steel shell when rolling; the short ear cannot weld the cap. At present, ultrasonic welding heads are linear and dot-shaped, and the domestic process mostly adopts linear (overcurrent and welding strength consideration). In addition, high-temperature glue is used to cover the polar ears, mainly considering the short circuit risk caused by metal burrs and metal debris. The ambient temperature of this workshop is ≤23°C, the dew point is ≤-30°C, and the positive moisture content is ≤ 500-1000ppm.

Part 7: Preparation of negative electrodes

The negative electrode needs to be dried (105-110°C), and then the welding process of nickel ears and ear cladding. You also need to consider the length of the polar ear and the width of the plastic surgery. The ambient temperature of this workshop is ≤23°C, the dew point is ≤-30°C, and the negative water content is ≤ 500-1000ppm.

Parts 8: Winding

 Winding is to form a single core of the diaphragm, positive electrodes, and negative electrodes through the winding machine. The principle is to use a negative electrode to wrap the positive electrode and then isolate the positive and negative electrodes through the diaphragm. Because the conventional system negative electrode is used as a control electrode designed by the battery, the capacity design is higher than the positive electrode, so that the Li+ of the positive electrode can be stored in the negative “vacant” when it is converted into charging. Winding needs to pay special attention to winding tension and pole alignment. Low winding tension will affect the internal resistance and shelling rate; excessive tension can easily cause short circuits or fragmentation risks. Alignment refers to the relative position of the negative electrode, positive electrode, and diaphragm. The negative pole width is 59.5mm, the positive pole is 58mm, and the diaphragm is 61mm. The three are aligned in the play to avoid short circuit risks. Winding tension is generally at positive tension 0.08-0.15Mpa, negative tension 0.08-0.15Mpa, upper diaphragm tension 0.08-0.15Mpa, lower diaphragm tension 0.08-0.15Mpa, which should be adjusted according to the equipment and process. The ambient temperature of this workshop is ≤23°C, the dew point is ≤-30°C, and the moisture content is ≤ 500- 1000 ppm.

Part 9: Into the shell

 Before the coil core is put into the shell, it is necessary to carry out a Hi-Pot test voltage of 200-500V (test for a high-voltage short circuit) and vacuum treatment (further control the dust before entering the shell). It is necessary to emphasize the three control points of lithium electricity, moisture, burrs, and dust. After the completion of the previous process, the lower cushion is padded into the bottom of the coil core and then bent into the negative ear, so that the polar ear surface is facing the coil core coil pinhole, and finally insert vertically into the steel shell or aluminum shell (in the case of model 18650, the outer diameter is ≈18mm+ height≈71.5mm). Of course, the cross-sectional area of the coil core < The internal cross-sectional area of the steel shell is about 97% to 98.5% because the rebound value of the pole and the degree of liquid in the later injection should be taken into account. With the surface pad process, the upper pad will also be assembled. The ambient temperature of this workshop is ≤23°C, and the dew point is ≤-40°C.

Part 10: Roller

1. Insert the welding needle (usually made of copper or alloy) into the middle hole of the coil core. The commonly used welding needle specifications are Φ2.5*1.6mm, which is qualified to reach the welding strength of negative polar ears ≥12N. If it is too low, it is easy to be virtually welded, and the internal resistance is large. If it is too high, it is easy to weld out the nickel layer on the surface of the steel shell, resulting in hidden dangers such as rust dew at the solder joint. 2. The simple understanding of the roller is to fix the core to the shell without shaking. In this process, special attention should be paid to the matching of lateral extrusion speed and longitudinal downward pressure speed to avoid excessive transverse speed cutting the shell, excessive longitudinal speed excessive velocity nickel layer shedding, or affecting the height of the groove to affect the sealing. It is necessary to test whether the groove depth, expansion, and groove high process values meet the standard (through practical and theoretical calculation). Common hob specifications are 1.0, 1.2, and 1.5mm. After the completion of the groove, the overall vacuuming needs to be treated again to avoid metal debris. The vacuum degree is ≤-0.065Mpa, and the vacuuming time is 1 to 2s. The ambient temperature of this workshop is ≤23°C, and the dew point is ≤-40°C.

Part 11: Teen Cell Baking

After the cylindrical cell passes through the groove, it is a very important step: baking. During the production process, the cell will bring a certain amount of moisture. If the moisture is not controlled within the standard in time, it will seriously affect the performance and safety performance of the battery. Generally, an automatic vacuum oven is used for baking, neatly put into the cell to be baked, a desiccant is placed in the oven, parameters are set, and the heating is heated to 85°C (taking lithium iron phosphate cells as an example). It takes several vacuum drying cycles to reach the standard.

Part 12: Liquid injection

After the moisture test of the baked cell meets the previous baking standards, the next step: inject the electrolyte. Quickly put the baked qualified cells into the vacuum glove box, weigh, record the weight, put them on the injection cup, and add the weighted electrolyte to the cup (generally, bubble experiments will be carried out: put the cell into the electrolyte, soak it for a period of time, test the maximum amount of liquid in the cell, and generally inject liquid according to the experimental amount) Put it in a vacuum box to extract vacuum (vacuum degree ≤-0.09Mpa) to accelerate the electrolyte intrusion plate. After several cycles, take out the cell for weighing, and calculate whether the injection amount meets the design value, and there is less need to replenish the liquid. If you need to pour out the excess, you need to pour out the design requirements. Glove box environment: temperature ≤23°C, dew point ≤-45°C.

 Parts 13: Super welding cap

 Put the cap into the glove box in advance, fasten the cap under the over welder in one hand, hold the cell in the other hand, and align the cell cathode ear with the cap ear. After confirming that the positive ear is aligned with the cap ear, step on the pedal switch of the super welding machine. After that, you need to fully check the cell: self-test polar ear welding effect 1 Observe whether the polar ear is aligned 2 gently pull the polar ear to see if the polar ear is loosened. The virtually welded cells of the over-welded cap need to be over-welded again. Experience points for super welding machine equipment parameters: –

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Part 14: Seal

After the cylindrical lithium battery cap is welded and pressed, the weighing and replenishment will be carried out. Then there is the last process of lithium battery packaging – sealing. The conventional seal adopts a squat seal, that is, it consists of pre-sealing, two steals, and three steals. The sealing process mainly designs the compression ratio of the sealing ring, the expansion size of the steel shell, the height of the rear shoulder of the seal, and the pull-off and opening pressure after sealing. At this time, the ambient temperature is ≤23°C and the dew point is ≤-35°C.
1) Sealing ring Compression ratio: 60% to 80%, which is one of the important factors affecting the sealing pressure.
Temperature resistance: 120°C to 140°C Material: Generally, polyethylene
2)
Break the opening pressure
Pull-off Pressure: During the Use of the Battery, The Internal Pressure Reaches a Certain Value, Disconnecting the Aluminum Chip Welding from the Lower Ring, And the Internal Cutting off the Current Circuit, Breaking the Positive and Negative Poles. The Small Cylindrical Teaching Pressure Is Generally 1.2 To 1.5 M Pa. Opening pressure: If the internal pressure of the battery deteriorates further (electrolyte redox of gas production, moisture exceeds the standard, etc.), resulting in pressure exceeding 1.6-2.0M Pa (the cracking pressure value of the gravure mark on the upper ring of the cap), the gravure seal will break and relieve pressure.
3)
Other parameters need to be designed according to the battery model.

Part 15: Cleaning

Due to the sealing, electrolytes or other organic solvents will remain on the surface of the battery case, and the nickel coating (2µm~5µm) at the seal and bottom welding are easy to fall off and rust. Therefore, it needs to be cleaned and rustproof, and the ambient temperature is about 25°C. General cleaning process.

1) Spray and clean the sodium nitrite solution.
2) Spray and clean deionized water.
3) Blow dry the wind gun and dry it from 40°C to 60°C.
4) Brush with anti-rust oil.

Part 16.  Into

1. After the lithium battery is packaged, the final process is transformed into (also one of the most important processes affecting the performance of the battery). The so-called electrochemical process refers to a certain current, in which the positive and negative active substances of the lithium battery are excited, and finally, the battery has the ability to discharge. The factors affecting the melting include the melting current, SOC, aging time, and temperature, and the battery material system and capacity requirements also need to be considered. Instead of simply charging and discharging, it measures the impact on battery performance. A lot of research and verification are required to match the battery.

2. What electrical properties affect the battery?

1) The sum of the primary effect, secondary discharge capacity/recharge capacity = the first effect %.
2) Discharge capacity, charging constant current ratio, discharge platform time.
3) Multiplier performance.
4) Cycle performance.
5) Self-discharge performance
6) AC internal resistance value … For example, the formation process of the dynamic LFP (lithium ferrous phosphate).

3. Turn it into a summary

1) Excessive aging time of ≥65°C negative correlation of late electrical performance.
2) Recharge SOC has a certain impact on the efficiency of the first charge and discharge, and the first effect is positively correlated with the discharge capacity.
3) High current affects magnification and cycle performance…
4) What are the abnormalities in the process of melting? The abnormal data requires a sampling and testing system of 10ms to 100ms, and the data is analyzed in combination with process and formula.

CC-CV curve

1) Constant current charging stage: U does not rise but fall, the change slope is large, and there may be a micro-short circuit inside; constant voltage charging stage: I does not fall and rise, the change slope is large, and there may be a micro short circuit inside.
2) Will it also be charged or not? Turn into high pressure? Turn into a low pressure? Is internal resistance abnormal?

Part 17: Partial Sepaance

Capacity is to charge and discharge the converted battery and distinguish the battery’s capacity, charging constant current ratio, discharge platform voltage, and internal resistance for classification.
1)
Capacity: refers to the capacity of discharge, which is generally circulating 3 to 5 times to take the intermediate discharge capacity as the rated capacity. Generally, the charging and discharge current of ternary batteries is 0.5C, lithium ferrous phosphate is 0.5C to 1C, lithium titan-ate battery is 1C, lithium cobalt-ate battery is 0.2C to 0.5C, etc.
2)
Charging constant current ratio: during the charging process, constant current charging capacity / (the sum of constant current + constant voltage charging capacity) * 100% 3) Discharge platform time: refers to the duration of the battery discharge.

Conclusion

Because lithium-ion batteries are suitable for storing high-capacity power, they are used in a wide range of applications, including consumer electronics such as smartphones and PCs, industrial robots, production equipment, and automobiles. Because lithium-ion batteries are suitable for storing high-capacity power, they are used in a wide range of applications, including consumer electronics such as smartphones and PCs, industrial robots, production equipment, and automobiles.

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