The battery cell is the smallest unit of a battery system. Multiple cells form a module, and multiple modules form a battery pack. This is the basic structure of a vehicle power battery. A battery is like a container that stores electrical energy. The capacity it can store is determined by the amount of active material covered by the positive and negative electrodes. The design of the positive and negative electrode pieces needs to be tailored according to different models. The gram capacity of positive and negative electrode materials, the ratio of active materials, electrode piece thickness, compaction density, etc. also have a crucial impact on capacity.

　　Pulping of active materials - mixing process

　　Mixing is to mix the active materials 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 the battery and the finished product qualification rate. Moreover, the process flow of this process is complex and has high requirements on raw material ratio, mixing steps, mixing time, etc.

　　Battery production-how the battery core is processed

　　Mixed here are the active materials of the battery.

　　Low temperature lithium iron phosphate battery 3.2V 20A -20℃ charging, -40℃ 3C discharge capacity ≥70%

　　Charging temperature: -20~45℃ -Discharge temperature: -40~+55℃ -40℃ Support maximum discharge rate: 3C -40℃ 3C discharge capacity retention rate ≥70%

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　　In addition, dust needs to be strictly controlled during the mixing process to prevent dust from affecting battery consistency. The level of dust control in CATL's production workshops is equivalent to pharmaceutical levels.

　　Apply the mixed slurry to the copper foil - coating process

　　This process is to evenly apply the slurry that has been mixed after the previous process to the top and bottom of the 4,000-meter-long copper foil at a speed of 80 meters per minute. The copper foil before coating is only 6 microns thick, which can be described as "as thin as a silkworm's wing".

　　Coating is very important to ensure that the thickness and weight of the electrode pieces are consistent, otherwise it will affect the consistency of the battery. Coating must also ensure that no particles, debris, dust, etc. are mixed into the pole piece. Otherwise, the battery will discharge too quickly and may even cause safety hazards.

　　Press the negative electrode material on the copper foil and then cut it - cold pressing and pre-cutting

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　　Charging temperature: 0~45℃ Discharge temperature: -40~+55℃ Specific energy: 240Wh/kg -40℃ Discharge capacity retention rate: 0.5C Discharge capacity ≥ 60%

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　　In the rolling workshop, the pole pieces with positive and negative electrode materials attached are rolled by rollers. On the one hand, the coated materials are made denser, the energy density is increased, and the thickness is ensured. On the other hand, dust will be further controlled. and humidity.

　　Cut the cold-pressed pole pieces according to the size of the battery to be produced, and fully control the generation of burrs (the burrs here can only be seen clearly under a microscope). The purpose of this is to prevent the burrs from piercing the separator and causing Serious safety hazard.

　　Cut out the small ears of the positive and negative terminals on the battery - die cutting and striping of the terminal ears

　　The tab die-cutting process is to use a die-cutting machine to form conductive tabs for the battery core. We know that the battery is divided into positive and negative poles. The tabs are the metal conductors that lead the positive and negative poles out of the battery core. Generally speaking, the tabs on the positive and negative poles of the battery are the contact points during charging and discharging.

　　Battery production-how the battery core is processed

　　The next slitting process is to slit the battery pole pieces with a cutter.

　　Complete the prototype of the battery core - the winding process

　　Here, the positive electrode sheet, negative electrode sheet, and separator film of the battery are combined into a bare cell in a rolling method. Advanced CCD visual inspection equipment can complete active detection and active correction to ensure that the battery pole pieces are not in position.

　　With the assistance of CCD visual inspection equipment, the battery production workshop of CATL Ningde era is one of the most automated battery production workshops in the world.

　　Removal of water and injection of electrolyte - baking and injection

　　Moisture is the enemy of the battery system. The battery baking process is to ensure that the internal moisture content of the battery reaches the standard and ensure that the battery has good performance throughout its life cycle.

　　Liquid injection is to inject electrolyte into the battery core. The electrolyte is like the blood flowing in the body of the battery 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 amount of electrolyte injected is the key. If the amount of electrolyte injected is too large, it will cause the battery to heat up or even directly fail. If the amount of electrolyte injected is too small, it will affect the cycleability of the battery.

　　The process of battery activation - formation

　　Formation is the process of activating the battery core after liquid injection. Through charging and discharging, a chemical reaction occurs inside the battery core to form an SEI film (SEI film: When the lithium battery is first cycled, the electrolyte and negative electrode material are at the solid-liquid phase level. Reaction occurs, so a layer of passivation film is formed, just like coating the battery core with a film.), ensuring the safety, reliability and long cycle life of subsequent battery cells during the charge and discharge cycle. To activate the function of the battery core, a series of "physical examination processes" such as X-ray monitoring, insulation monitoring, welding monitoring, and capacity testing are also required.

　　The formation process also includes the second injection of electrolyte after "activating" the battery core, weighing, welding of the liquid injection port, and air tightness testing; self-discharge testing, high-temperature aging and standing to ensure product performance.

　　Each cell cell after production has a separate QR code, recording the date of birth, production environment, functional parameters, etc. A powerful traceability system can record any information. If an abnormality occurs, production information can be retrieved at any time; at the same time, these big data can provide targeted data support for subsequent improvement designs.

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