Do You Know The Laser Welding Process Of Power Batteries

The blowout development of new energy vehicles in the past two years has attracted more and more attention from the outside world, not only the impact of consumption, but also in the industrial field, the technological trend led by new energy vehicles has also grown into a powerful force that cannot be ignored. Today we are going to talk about the laser welding process applied to the battery, the power core of new energy vehicles.

With the increase in sales of new energy vehicles, the installed capacity of power batteries has also grown rapidly. Data show that in 2021, China's new energy vehicle sales of 3.521 million, an increase of 157.5%; The installed capacity of power batteries reached 154.5GWh, an increase of 142.8%. Battery manufacturers have expanded production capacity, Academician Ouyang Minggao at the electric vehicle 100 experts said that by 2025, China's power battery production capacity will reach 3000GWh. In the process of power battery manufacturing, low cost, high quality and high efficiency are the three major goals pursued by manufacturing enterprises, therefore, the technical process and intelligent equipment that can achieve these three goals are favored by battery manufacturers.

The inside of the power battery is also a whole complex system, from the battery cell, battery module, and battery pack, after a manufacturing process, and finally assembled into a whole power battery system. Among them, the connection between materials and materials, modules and modules, and battery pack structures involves a highly demanding welding process - laser welding.

The reasonable selection of welding methods and processes in the manufacturing process of power batteries will directly affect the cost, quality, safety and consistency of the battery. Next, sort out the content of power battery welding.

The power battery is 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 the pole ear (including pre-welding), point welding of the pole belt, pre-welding of the battery into the shell, sealing welding of the shell top cover, sealing welding of the liquid injection port, etc.

After process: including battery PACK module connection plate welding, as well as the module back cover plate on the explosion-proof valve welding.

The shell and cover plate of the power battery play the role of encapsulating the electrolyte and supporting electrode materials, providing a stable closed environment for the storage and release of electric energy, and the welding quality directly determines the tightness and compressive strength of the battery, thus affecting the life and safety performance of the battery. The battery shell is mainly made of Al3003 aluminum alloy, whose thickness is generally between 0.6 and 0.8mm, and low-power pulsed laser welding is generally used. The connection position of the shell and the cover plate is shown in the figure, where the main quality problems of the laser weld are non-penetration, porosity and bed, which will reduce the tightness of the battery.

The pole of the battery is the positive and negative contact plate of the battery, generally speaking, the positive electrode uses aluminum, and the negative electrode uses copper, and its role is to make the battery pole welded through the connection sheet to form a series and parallel circuit to form a battery module.

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 breaks and deflates first to release the pressure and avoid the battery bursting. The structure of the explosion-proof valve is ingenious, and the two aluminum metal sheets of a certain shape are firmly welded by laser welding. When the pressure inside the battery rises to a certain value, the aluminum sheet breaks from the designed groove position, preventing the battery from further expanding and causing an explosion. Therefore, this process has very strict requirements for laser welding process, requiring the weld to be sealed, strictly controlling the heat input, and ensuring that the damage pressure value of the weld is stable within a certain range (generally 0.4~0.7MPa), too large or too small will have a great impact on the safety of the battery.

The adapter plate and the soft connection are the key components to connect the battery cover plate and the battery cell. It must also take into account the overcurrent, strength and low splash requirements of the battery, so there needs to be enough weld width in the welding process with the cover plate, and there needs to be no particles falling on the battery to avoid battery short circuits. As a negative electrode material, copper is a high inverse material with a low absorption rate, which requires a higher energy density to weld when welding and the latest blue light composite laser can solve the traditional process problems such as high inverse and spatter.

The pole on the battery cover plate is divided into internal battery and external battery connection. The internal connection of the battery is the welding of the cell pole and the cover pole; The external connection of the battery is that the battery pole is welded through the connection sheet to form a series and parallel circuit to form the battery module.

The main problem of battery laser welding is also the hole defect, and the reason is similar to the explosion-proof valve. The pole weld is essentially the mating surface of the aluminum transfer block and the pole, and the diameter of the aluminum block hole is only about 6 mm, which makes it very easy to retain impurities such as stamping oil and cleaning agent. The laser light with high energy density causes the temperature of the weldment to surge, resulting in rapid vaporization of the residual impurities at the pole, and the bubbles escape and overcome the surface tension of the weld pool to leave the weld pool, resulting in hole defects. In this process, the rapid change of pulsed laser power further increases the tendency to form blasting holes. Therefore, in addition to enhancing pre-welding cleaning, hole defects can also be reduced by optimizing the laser power variation.

The battery module can be understood as a combination of lithium-ion cells in series and parallel and is equipped with a single battery monitoring and management device. The structural design of the battery module often determines 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 requirements of overcurrent, current uniformity, how to meet the control of the temperature of the cell, and whether there are serious abnormalities can be cut off, to avoid chain reactions, etc., will be the criteria for judging the merits of the battery module.

At the same time, because the heat transfer of copper and aluminum is very fast, and the reflectivity of the laser is very high, the thickness of the connecting sheet is relatively large, so it is necessary to use a higher-power laser to achieve welding.

At present, the main problems of laser welding in power batteries are welding defects such as pores, cracks, poor forming and blasting holes. These defects lead to reduced battery strength, tightness and conductivity, resulting in a series of safety problems such as battery explosion, leakage and heating. To solve these problems, a large number of studies focus on process optimization, adjusting the laser welding power, pulse width, welding speed, defocusing amount and other parameters can effectively reduce the defects.

It is not difficult to see that the power battery welding process is fine work, and any small problem will affect the performance and safety of the subsequent finished power battery. Therefore, high-quality materials and high-quality laser welding instruments are the basis for ensuring the success of the welding process. Intelligent technology represented by laser welding path planning, weld identification, defect identification, quality monitoring, etc., is also one of the future research hotspots.

Xi'an Guosheng Laser Technology Co., Ltd. is a high-tech enterprise specializing in R&D, manufacturing and sales of automatic laser cladding machine, high-speed laser cladding machine, laser quenching machine, laser welding machine and laser 3D printing equipment. Our products are cost-effective and sold domestically and abroad. If you're interested in our products, please contact us at bob@gshenglaser.com.