Secrets of Lithium Battery Cell Production Process

China’s lithium-ion batteries have claimed the top spot in the world in sales of lithium-ion power batteries. This proves that Chinese lithium battery has also broken through Japan and South Korea, is emerging as a global leader in the lithium-ion power battery industry. Why China’s lithium battery can catch up with the rest of the world, has gained considerable development and international market recognition. Today, let Smart Propel take you to understand the production workshop of the lithium battery and check out how the high-quality cells produced.

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The cell is the smallest unit of a battery system. A plurality of battery cells form a module, and then a plurality of modules form a battery pack, which is the basic structure of the vehicle power battery. A battery is like a container for storing electrical energy. How much of its capacity can be stored depends on how much active material is contained in the positive and negative plates. The design of positive and negative electrode plates needs to be tailored to different vehicle models. The molar capacity of positive and negative electrode materials, the ratio of active materials, the thickness of the electrode plate, and the density of compaction are also important.

Preparation of active materials —— Agitation process

Mixing is the active material through a vacuum mixer mixing slurry. This is the first process of battery production, this process quality control will directly affect the quality of batteries. And the process flow is complex, raw material ratio, mixing steps, mixing time, and so on have higher requirements.

This is the active material from the battery

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In addition, dust must be strictly controlled in the mixing plant to prevent the dust from affecting the consistency of the battery. The level of dust control in our cell manufacturing plant is equivalent to the level of medicine.

Apply the beaten material paste to copper foil ——coating process

This process is applied the last process has been mixing the slurry at the rate of 80 meters per minute is evenly coated with 4000 meters of copper foil above and below. Before the coating of copper foil only 6 microns thick, can be described as “thin as silkworm wings”.

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The most important aspect of the coating process is consistency in thickness and weight

The coating is essential to ensure that the thickness and weight of the electrodes are the same, otherwise, it will affect the consistency of the battery. The coating must also ensure that no particles, sundries, dust, and others are mixed into the pole piece. Otherwise, it will lead to the battery discharge too fast, and even there will be security risks.

Press the anode material on the copper foil and cut it into pieces —— cold pressing and pre-cutting

In the rolling workshop, the polar plates with positive and negative electrode materials are rolled by rollers. On the one hand, the coated materials are made more compact, the energy density is increased, and the thickness consistency is ensured. On the other hand, dust and humidity are further controlled.

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Cold pressing, which compacts the positive and negative materials on the foil, is also important for increasing energy density

The cold-pressed electrodes are cut to the size needed to produce the battery, and the burrs (which can only be seen clearly under a microscope) are adequately controlled to prevent the burrs from penetrating the diaphragm, to avoid a serious security risk.

Cut off the positive and negative little earbuds of the battery —— Tab cutting and striping

The tab cutting process is the use of a die-cutting machine to form a conductive electrode tab for the cell.

The next step is to slice the battery electrode through a knife.

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Die-cutting tab simply means making small ears with positive and negative poles

Complete the initial stage of the cell —— Winding Process

Here, the positive plate, the negative plate, the isolation film of the battery are wound together to form a bare cell. The advanced CCD vision detection equipment can realize automatic detection and automatic correction to ensure that the electrode of the chip is not out of place.

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After the winding process, the rudiment of the cell is basically formed.

Water is removed and injected into the electrolyte —— Baking and Filling

Moisture is the enemy of the battery system, the battery baking process is to make the battery internal moisture up to standard, to ensure that the battery has a good performance throughout its life cycle.

To remove moisture, the cells need to be baked.

And the injection is injecting the electrolyte into the cell. Electrolytes are like the blood that flows through the body of a battery cell. The exchange of energy is the exchange of charged ions. These charged ions are transported from the electrolyte to another electrode to complete the charging and discharging process. If the amount of electrolyte injected is too large, it will cause the cell to heat up or even to fail directly. If the amount of electrolyte injected is too small, it will affect the cycle of the cell.

The process of cell activation —— Formation

Transformation is the process of activating the cell after the injection, a chemical reaction takes place inside the cell during charge and discharge to form an SEI (Sei film: A passive film formed when the Electrolyte reacts with the anode material at the solid-liquid level during the first cycle of a lithium-ion battery, much like a mask is applied to the cell), to ensure the safety, reliability and long cycle life of the follow-up cell during the charging and discharging cycle. The performance of the core will be activated, but also through X-ray Monitoring, insulation monitoring, welding monitoring, capacity testing, and a series of “physical examination process. ”.

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In addition, after “activation” of the cell, the electrolyte is poured into the cell for the second time, the cell is weighed, the injection port is welded, and the gas tightness is tested.

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Each cell has a separate Qr Code that records the date of birth, manufacturing environment, performance parameters, and so on. A powerful traceability system allows any information to be recorded. If there is an exception, production information can be accessed at any time; at the same time, these big data can be targeted to improve the design of subsequent data support.

A single cell can not be used, only the combination of many cells together, together with a protective board and protective shell, can be used directly. This is called the battery module.

A battery module is composed of a number of cells. Through strict screening, the cells with good consistency are assembled into modular battery modules according to precise design, and a unit battery monitoring and management device is installed. In addition, each module has its own fixed identification code, problems can achieve the whole process of tracing.

The process from a single cell to the E-bike battery pack or EV battery pack is also complex, requiring multiple steps, no simpler than the cell manufacturing process.

An important pre-offline phase —— Offline test

Check the full performance of the module before off-line, including module voltage/resistance, battery unit voltage, withstand voltage test, insulation resistance test, impact test, short current test,high & low-temperature test. Standardized modular design principle can be customized to match different models, each module can also be installed in the car to best fit the space and predetermined location.

Take 72V 100Ah Electric Vehicle Lithium Battery Pack for example, each EV battery pack contains a number of battery cells, integrated with connectors, controllers, and cooling systems, and is encased in aluminum. Through the automatic tightening bolt, connected by an electrical connector, even if there is a failure, only need to replace a separate module, do not have to replace the whole battery, maintenance workload and risk is greatly reduced, replace the module just need to dismantle the cooling system, there are no other components involved.

Lithium Battery Product stability and good word-of-mouth is the key to win, the future needs to continue to launch products with market competitiveness, in order to always stand at the top of the industry.

SmartPropel Writer: Nancy Liu

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