The manufacturing process of Lifepo4 battery.What processes have been done to produce a lithium battery.
Active material stirring
Mixing is to stir the active material into a slurry through a vacuum mixer. This is the first process of battery production. The quality control of this process will directly affect the quality of batteries and the qualified rate of finished products. Moreover, the process flow of this process is complex, and there are high requirements for raw material proportioning, mixing steps, mixing time, etc.
The main cathode materials are lithium cobaltate, lithium manganate, lithium nickel oxide and lithium iron phosphate.
negative electrode homogenate
Graphite is the most widely used cathode material
▲Active material stirring of battery
During the mixing process, the dust needs to be strictly controlled to prevent the dust from affecting the consistency of the battery.
Apply the stirred slurry on the copper foil - coating process
This process is to evenly apply the slurry that has been stirred after the previous process to the 4000 meter long copper foil at the speed of 80 meters per minute. The copper foil before coating is only 6 microns thick.
▲The most important thing in the coating process is the consistency of thickness and weight
Coating is very important. It is necessary to ensure that the thickness and weight of the electrode are consistent, otherwise the consistency of the battery will be affected. Coating must also ensure that no particles, debris, dust, etc. are mixed into the electrode. Otherwise, the battery will discharge too fast, and even there will be potential safety hazards.
Compress the negative material on the copper foil and then cut
In the rolling workshop, the pole pieces attached with positive and negative materials are rolled by rollers. On the one hand, the coated materials are tighter, the energy density is improved, and the consistency of thickness is ensured. On the other hand, dust and humidity will be further controlled.
▲Cold pressing is to compress and compact the positive and negative materials on the aluminum foil, which is also important to improve the energy density
Cut the cold pressed pole piece according to the size of the production battery, and fully control the generation of burrs (the burrs here can only be seen clearly under the microscope). The purpose of this is to avoid burrs penetrating the diaphragm, resulting in serious safety hazards.
Die cutting and slitting of electrode tab
The die-cutting process of the electrode lug is to use the die-cutting machine to form the conductive electrode lug for the electric core. We know that the battery is divided into positive and negative poles. The pole ear is the metal conductor that leads the positive and negative poles out of the cell. Generally speaking, the ears of the positive and negative poles of the battery are the contact points during charging and discharging.
▲electrode tab cutting
the prototype of the cell - winding process
the positive sheet, negative sheet and isolation film of the battery are combined into a bare cell in a winding manner. The advanced CCD visual inspection equipment can realize automatic detection and automatic deviation correction to ensure that the electrode pieces of the electric core are not misaligned.
▲After the winding process, the prototype of the electric core is basically formed
Moisture removal and electrolyte injection - baking and liquid injection
Moisture is the enemy of the battery system. The battery baking process is to make the internal moisture of the battery meet the standard and ensure that the battery has good performance in the whole life cycle.
▲In order to remove moisture, the cell needs to be baked
Liquid injection is to inject electrolyte into the cell. Electrolyte is like the blood flowing in the body of the cell, and the exchange of energy is the exchange of charged ions. These charged ions are transported from the electrolyte to the other electrode to complete the charge and discharge process. The injection amount of electrolyte is the key among the keys. If the injection amount of electrolyte is too large, the battery will heat up or even fail directly. If the injection amount is too small, it will affect the cycling of the battery.
Process of cell activation - formation
Formation is the process of activating the cell after liquid injection. Chemical reaction takes place inside the cell through charge and discharge to form SEI film (SEI film: it is the reaction between electrolyte and negative electrode material on the solid-liquid interface during the first cycle of lithium battery, so a passivation film will be formed, just like plating a facial mask on the cell.), Ensure the safety, reliability and long cycle life of subsequent cells in the process of charge and discharge cycle. To activate the performance of the cell, we have to go through a series of "physical examination processes" such as X-ray monitoring, insulation monitoring, welding monitoring, capacity testing, etc.
The formation process also includes the second filling of electrolyte after the "activation" of the cell, weighing, welding of the injection port, and air tightness testing; Self discharge test, high temperature aging and standing ensure the product performance.
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