Key production process of lithium battery -Lithium - Ion Battery Equipment

Key production process of lithium battery control factors -Lithium - Ion Battery Equipment

1. Mixing

It can also be called mixing, homogenizing, pulping, batching, etc. The process of preparing non-newtonian fluids with certain viscosity requirements and particle size requirements from key components such as positive and negative active substances, conductive agents, adhesives, solvents, etc. through certain feeding sequence, stirring process, vacuum control, temperature control and other conditions. The slurry property to be controlled is good fluidity, viscosity and particle size meet the coating requirements.(Lithium - Ion Battery Equipment)

2. Coating

Some companies call it coating. Coating is a process in which the slurry after stirring is evenly coated on the collector and dried to form a pole piece. The coating methods include continuous coating and intermittent coating. The coating methods of lithium ion battery slurry mainly include scraper direct coating, scraper roller coating and slot extrusion coating. The control parameters of coating products are surface density, cohesiveness, moisture content, etc.

3. Pressing

Rolling refers to the process of compacting the coated products to the specified thickness through two steel rolls under a certain gap and pressure. The influencing factors of rolling include feeding angle, gap value, pressure value, rolling speed, winding tension, pole sheet temperature, etc. The purpose of rolling is to further compact the loose and porous electrode, reduce the contact resistance between materials, improve the battery capacity within a certain battery volume, and at the same time, do not overpressure to ensure the wetting effect of electrolyte on the electrode.

4. Slitting

Slitting is also called slitting. The coated pole piece has a large width, so the pole piece should be divided into several pieces. Slitting products are mainly affected by cutter quality, cutter angle and tension.

5. TabForming

The process of shearing the pole piece by controlling the engagement between the upper and lower tool dies of the equipment, so that the pole piece can form a lug according to the design size requirements.

6. ElectrodeDefects

Electrode defects occur in each stage of electrode sheet production, and are easy to produce thick head, thin tail, thick edge, exposed foil, unstable surface density, horizontal and vertical stripes, dry materials, pinhole shrinkage, white spots, pockmarks, foreign matters, etc. during coating. The specific reasons are analyzed in detail. The defects of rolled electrode sheet mainly include uneven winding, wrinkling, thickness rebound, material falling and roller sticking, particles, unstable thickness, etc. The defects of pole slice slitting include wavy edge, burr, crimping, blanking, etc.

7. Winding

Winding is a form of cell composition, which is suitable for cylindrical batteries, square batteries and flexible batteries. By controlling the speed, tension, size, deviation and other factors of the equipment, the process of rolling the size matched negative pole piece, positive pole piece and diaphragm into a bare core. The key point of winding is that the diaphragm wraps the positive and negative electrodes, and the negative electrode sheet wraps the positive electrode sheet. This requires that the negative pole piece shall not be exposed, which will cause partial lithium precipitation on the pole piece to puncture the diaphragm, causing short circuit.

8. Lamination

Another composition of the laminated cell is suitable for square and soft packed lithium ion batteries. The process of stacking the negative pole piece, positive pole piece and diaphragm after punching into bare electric core through control equipment. It is also required that the diaphragm shall cover the positive and negative electrodes, and the negative electrode sheet shall cover the positive electrode sheet.

9. Hot Pressing

Hot pressing is also called shaping. The wound electric core is in a bulge state, which is not conducive to the penetration of the shell and the wetting of the electrolyte. It needs to be hot pressed to promote the contact between the pole piece and the diaphragm, while reducing the volume and preventing the dislocation of the positive and negative pole pieces. The influencing factors of hot pressing include pressure, temperature, time, etc. Generally, 60~80 ℃ hot pressing is selected.

10. Vacuum Baking

Vacuum baking is divided into electrode baking and cell baking, both of which are used to control the moisture content of the cell. Moisture can be fatal to lithium batteries. After water contacts with electrolyte, hydrofluoric acid formed will cause great damage to the battery, and the generated gas will also cause battery bulge. The baking efficiency is affected by vacuum degree, drying temperature and time. The baking process should be adjusted to achieve high drying efficiency with low energy consumption.

11. TabWelding

Welding between the lug and the collector is required for both winding and laminating. The positive and negative electrode lugs shall be welded at the fluid collecting position to ensure the welding strength and prevent the electrode lugs from falling off. Ultrasonic welding is generally used for lug welding. Its principle is to transmit high-frequency vibration wave to two objects to be welded through welding head and welding base under auxiliary pressure. The two contact surfaces to be welded rub against each other and molecules diffuse to form molecular fusion welding. Ultrasonic welding strength is affected by welding pressure, amplitude, frequency, time, stability of welding machine, welding head quality, tooling, material hardness, etc.

12. Packaging

The packaging forms mainly include metal shell packaging and aluminum plastic film packaging. The metal shell includes steel shell and aluminum shell, which are suitable for cylindrical batteries and square batteries. The aluminum plastic film packaging is suitable for flexible batteries. For 18650 cylindrical battery, the packaging step is to put the winding core into the steel shell after winding, conduct spot welding, groove rolling and liquid injection, and then conduct laser welding cap and mechanical sealing. For the square battery, the packaging step is to conduct laser welding and sealing after entering the shell, and then complete the final sealing after the completion of the liquid injection hole. The difference of soft package battery packaging is that it uses aluminum plastic film packaging. The aluminum plastic film is composed of three layers of materials, PP layer, aluminum layer and nylon layer. The key of packaging is to bond the PP layer together after melting. The heat sealing is mainly affected by temperature, heat sealing time and heat sealing pressure. It is necessary to ensure that there is no poor heat sealing, no unsealing, etc. Special attention shall be paid to the top sealing at the place with lug. It is necessary to ensure that the PP layer of aluminum plastic film is well bonded and sealed with the PP layer on the outer surface of the lug, and that the PP layer of aluminum plastic film in the non lug area is well bonded and sealed face to face. In addition, compared with the battery with metal shell, the aluminum plastic film soft packed battery needs to be covered with a protective film after heat sealing to prevent external substances from scratching the aluminum plastic film.

13. Leakage Test

The process of detecting whether the battery has leakage through negative pressure detection or helium detection. The airtightness test is very necessary. The poorly sealed battery will introduce water, impurities, etc., which will cause the side reaction between the battery and the electrolyte, causing the battery to be scrapped.

14. ElectrolyteInjection

Electrolyte is the channel for lithium ion to move inside the battery, which is mainly composed of solute and solvent. The solute is lithium hexafluorophosphate. Generally, three or more solvents are used together, such as EC/DMC/DEC. The process of liquid injection is to inject electrolyte into the cell, and the control parameters mainly include electrolyte amount, injection pressure, time, etc.

15. Formation

Formation refers to the first charge and discharge of the battery after sealing the liquid injection. There are two main purposes for formation: one is that after the battery is made, the electrode material is not in the best applicable state, or the physical properties are not appropriate (such as too large particles, loose contact, etc.), or the phase itself is not correct (such as the metal oxide negative electrode of some alloy mechanisms), so it needs to be activated by the first charge and discharge. Second, the lithium battery is charged and discharged for the first time. The electrons arrive at the surface of the graphite cathode through an external path and react with the electrolyte solvent and lithium ions to form a solid electrolyte membrane (SEI). SEI has an important impact on the performance of the lithium battery. The formation process has a great impact on the battery performance, because such factors as charging and discharging current and time have a great impact on the formation of high-quality SEI, gas production, resistance and other key parameters of the battery.

16. Aging

Aging generally refers to the placement of the battery after the first charging and formation after the completion of the liquid injection of the battery assembly. It can be either normal temperature aging or high temperature aging. Both functions are to make the nature and composition of the SEI film formed after the initial charging and formation more stable, and ensure the stability of the electrochemical performance of the battery.

After the aging is completed, the final capacity of the battery shall be divided, and the battery can be delivered after passing the resistance, voltage drop and other tests.



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