01. What is the power battery

The basic agreement of the global electric vehicle industry: the batteries that provide driving power for electric vehicles are called power batteries, including traditional lead-acid batteries, nickel-metal hydride batteries and emerging lithium-ion power batteries, which are divided into power type power batteries (hybrid electric vehicles) And energy-based power batteries (pure electric vehicles).

As we all know, power battery is the "heart" of new energy vehicles. The power lithium batteries are mainly ternary material batteries and lithium iron phosphate batteries, and the downstream is the installed application of new energy vehicles, which has higher discharge power than ordinary batteries.

As a supporting industry for new energy vehicles, driven by the new energy vehicle industry in recent years, the power battery industry has also ushered in explosive growth.

02. Relationship between power battery and laser industry

The power battery accounts for 30%-40% of the total cost of new energy vehicles, and it is the largest part of the cost of new energy vehicles. It is very important for key indicators such as the cruising range, vehicle life, and safety of new energy vehicles. Therefore, improving the performance of power batteries is the key to improving the overall performance of new energy vehicles.

In the production process of power batteries, welding is a very important manufacturing process from cell manufacturing to PACK assembly. In particular, the power battery structure contains a variety of materials, such as steel, aluminum, copper, nickel, etc.

These metals may be made into electrodes, wires or casings. Therefore, whether it is welding between one material or between multiple materials, higher requirements are placed on the welding process.

Laser welding is to use the excellent directionality and high power density of the laser beam to work. The laser beam is focused in a small area through the optical system, and a heat source with high energy concentration is formed at the welded part in a very short time. zone, so that the welded material melts and forms a solid welding spot and seam.

In the entire power battery industry chain, laser welding is mainly used in the midstream production of power lithium batteries. As a high-precision welding method, it is extremely flexible, accurate and efficient, and can meet the performance requirements of the power battery production process. It is the first choice in the power battery manufacturing process and has become the standard equipment of the power battery production line.

03. Common welding applications of power batteries

Power batteries are divided into square, cylindrical and soft pack batteries. At present, in the production of power batteries, the use of laser welding mainly includes:

Middle process: welding of pole ears (including pre-welding), spot welding of pole strips, pre-welding of battery cells into the shell, sealing welding of the top cover of the shell, sealing welding of liquid injection ports, etc.;

Back-end process: including the welding of the connecting piece when the battery packs the module, and the welding of the explosion-proof valve on the cover behind the module, etc.

1. Battery explosion-proof valve welding

The explosion-proof valve is a thin-walled valve body on the battery sealing plate. When the internal pressure of the battery exceeds the specified value, the explosion-proof valve body first ruptures and deflates, releasing the pressure to prevent the battery from bursting. The explosion-proof valve has an ingenious structure, and two aluminum metal sheets of a certain shape are fixed by laser welding.

When the internal pressure of the battery rises to a certain value, the aluminum sheet ruptures from the designed groove position, preventing the battery from expanding further and causing an explosion.

Therefore, this process has extremely strict requirements on the laser welding process. It requires the welding seam to be sealed, and the heat input is strictly controlled to ensure that the damage pressure value of the welding seam is stable within a certain range. If it is too large or too small, it will cause great harm to the safety of the battery influences.

Therefore, the explosion-proof valve generally adopts butt welding. After a lot of practice, it has been proved that high-speed and high-quality welding can be achieved by using HGLASER hybrid welding laser, and the welding stability, welding efficiency and yield rate can be guaranteed.

2. Pole welding

The poles on the battery cover are divided into internal and external connections of the battery. The internal connection of the battery is the welding of the electrode lugs of the battery core and the poles of the cover plate; the external connection of the battery is the welding of the battery poles through the connecting piece to form a series and parallel circuit to form a battery module.

The poles of the battery are the positive and negative electrodes of the battery. Generally, the positive electrode is made of aluminum, and the negative electrode is made of copper. The commonly used structure is the riveting structure, which is fully welded after the riveting is completed, and its size is generally a circle with a diameter of. When welding, in the case of meeting the tensile force and electrical conductivity required by the design, the fiber laser or compound welding laser with good beam quality and uniform energy distribution is preferred. Aluminum structure welding, copper-copper structure welding stability, reduce spatter, and improve welding yield.

3. Adapter welding

The adapter and soft connection are the key components to connect the battery cover and the cell. It must also take into account the requirements of overcurrent, strength and low spatter of the battery, so during the welding process with the cover plate, there needs to be enough welding seam width, and it is necessary to ensure that there is no part falling on the cell to avoid the occurrence of battery short circuit.

 Copper, which is used as a negative electrode material, is a high-reflection material with low absorption rate, and requires higher energy density to weld during welding.

4. Shell sealing welding

The shell materials of the power battery are aluminum alloy and stainless steel, among which aluminum alloy is the most used, and a few use pure aluminum. Stainless steel is the best material for laser weldability, especially 304 stainless steel, whether pulsed or continuous laser can obtain welds with good appearance and performance.

5. Welding of sealing nails (electrolyte injection port)

There are also many forms of sealing nails (liquid injection hole caps). The shape is usually a circular cap with a diameter of 8mm and a thickness of about 0.9mm. The basic requirements for its welding are that the pressure resistance value reaches 1.1MPa, and it is sealed without pinholes. , the presence of cracks and bursts.

As the last process of cell welding, the yield of sealing nail welding is particularly important. Due to the existence of residual electrolyte during the welding of sealing nails, there are defects such as explosion points and pinholes, and the key way to suppress these defects is to reduce the heat input.

6. Power battery module and PACK welding

The battery module can be understood as the combination of lithium-ion cells in series and parallel, and the addition of a single battery monitoring and management device. The structural design of the battery module can often determine the performance and safety of a battery pack.

Its structure must support, fix and protect the cell. At the same time, how to meet the overcurrent requirements, current uniformity, how to meet the control of the temperature of the battery cells, and whether it can be powered off when there is a serious abnormality, to avoid chain reactions, etc., will all be the criteria for judging the quality of battery modules.

Because the brittle compound is easily formed after laser welding between copper and aluminum, which cannot meet the requirements of use, usually copper and copper, aluminum and aluminum are generally laser welded, except for ultrasonic welding. At the same time, due to the fast heat transfer of copper and aluminum, and the high reflectivity to the laser, the thickness of the connecting piece is relatively large, so it is necessary to use a higher power laser to achieve welding.