The most complete battery manufacturing process in history (Part 1. How is a battery cell made?)

A battery cell is the smallest unit of a battery system. Multiple battery cells form a module, and multiple modules form a battery pack. This is the basic structure of a car power battery. A battery is like a container for storing electrical energy. The amount of 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 plates needs to be tailored to different models. The gram capacity of the positive and negative electrode materials, the ratio of active materials, the thickness of the electrode plates, the compaction density, etc. are also crucial to the capacity.

Slurrying of active materials - mixing process

Stirring is to stir the active materials into a slurry through a vacuum mixer. This is the first process in battery production. The quality control of this process will directly affect the quality of the battery and the qualified rate of the finished product. Moreover, this process is complex and has high requirements for the raw material ratio, mixing steps, stirring time, etc.

What is being stirred here is the battery's active materials.

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

Apply the stirred slurry on the copper foil - coating process

This process is to evenly apply the slurry that has been stirred in the previous process to the upper and lower surfaces 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. It is necessary to ensure that the thickness and weight of the pole piece 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, it will cause the battery to discharge too quickly and even cause safety hazards.

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

In the rolling workshop, the pole sheets with positive and negative electrode materials attached are rolled by rollers. On the one hand, this makes the coated materials tighter, improves the energy density, and ensures the consistency of thickness. On the other hand, it will further control dust and humidity.

The cold-pressed electrodes are cut into pieces according to the size of the batteries to be produced, and the generation of burrs (the burrs here can only be seen clearly under a microscope) is fully controlled. This is to prevent the burrs from piercing the diaphragm and causing serious safety hazards.

Cut out the small ears of the positive and negative poles on the battery - ear die cutting and striping

The tab die-cutting process is to use a die-cutting machine to form the conductive tabs for the battery. We know that the battery is divided into positive and negative poles, and the tabs are the metal conductors that lead the positive and negative poles out of the battery. In layman's terms, the tabs at the positive and negative poles of the battery are the contact points during charging and discharging.

The next slitting process is to cut the battery electrodes using a cutting knife.

Completing the prototype of the battery cell - winding process

Here, the positive electrode, negative electrode and separator of the battery are wound together to form a bare cell. Advanced CCD visual inspection equipment can realize automatic inspection and automatic deviation correction to ensure that the cell electrodes are not misaligned.

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

Removing moisture and injecting electrolyte – baking and filling

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 throughout its life cycle.

Injection is to inject electrolyte into the battery cell. The electrolyte is like the blood flowing in the body of the battery cell. 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, it will cause the battery to heat up or even fail directly. If the injection amount is too small, it will affect the battery's cyclability.

The process of battery activation - formation

Formation is the process of activating the battery cell after injection. Through charging and discharging, a chemical reaction occurs inside the battery cell to form a SEI film (SEI film: a passivation film is formed when the electrolyte and the negative electrode material react at the solid-liquid phase level during the first cycle of the lithium battery, just like coating the battery cell with a mask.), ensuring the safety, reliability and long cycle life of the subsequent battery cells during the charge and discharge cycle. To activate the performance of the battery cell, it must also go through a series of "physical examination processes" such as X-ray monitoring, insulation monitoring, welding monitoring, and capacity testing.

The formation process also includes the second filling of electrolyte, weighing, welding of the filling port, and air tightness testing after the battery cell is "activated"; self-discharge testing, high-temperature aging and static standing ensure product performance.

Each manufactured battery cell has a separate QR code that records the date of birth, manufacturing environment, performance parameters, etc. The 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 improved designs.