1. Explanation of the Relationship between Welding and Terminals
The module CCS (Cell Contact System) is the cell contact assembly, also known as an integrated busbar or wiring harness assembly. It primarily consists of signal acquisition components (such as flexible printed circuit boards (FPCs), printed circuit boards (PCBs), and flexible flat cables (FFCs), plastic structural components, and copper-aluminum busbars. These components play a crucial role. The copper-aluminum busbars connect multiple battery cells in series and parallel through methods such as laser welding, achieving electrical connections between the cells and thus forming the basic architecture of the battery module. The signal acquisition components, connected to the copper-aluminum busbars and plastic structural components, form the electrical connection and signal detection components. These components collect key battery signals, such as temperature and voltage, and transmit them to the battery management system (BMS). The BMS monitors and accurately manages the battery status in real time, ensuring the safe and stable operation of the battery module and the entire battery system.
The terminal, as the key component connecting the battery cell to the external circuit, acts like a "bridge" in the battery. One end connects to the electrodes within the battery cell, while the other end connects to components such as the copper and aluminum busbars within the CCS. During module CCS welding, the quality of the weld between the terminal and the CCS components directly impacts the performance of the entire battery module. A weak weld can increase contact resistance, generating excessive heat during charging and discharging, reducing the battery's energy conversion efficiency and potentially posing safety hazards such as overheating and fire. Poor conductivity at the weld site can affect current distribution within the battery module, further impacting battery charge and discharge performance and shortening its lifespan. Therefore, the importance of the terminal in module CCS welding is self-evident; it is a key component in ensuring the proper functioning of the battery module.
2. Impacts of Not Cleaning the Terminal
Failure to clean the terminal during module CCS welding can lead to a series of serious problems. During production, transportation, and storage, the terminal surface inevitably becomes contaminated with various impurities, such as dust, oil, and oxides. These seemingly insignificant contaminants are actually "invisible killers" during the welding process.
First, they can lead to poor solder joints. Cold solder joints are a common welding defect. While the solder joint appears to be connected, it lacks a reliable metal-metal bond, leaving tiny gaps or unfused areas. Oil and oxides hinder the diffusion and fusion of metal atoms during welding. During welding, these impurities form an isolation layer between the terminal and the CCS, preventing the solder from fully wetting the terminal surface, resulting in insufficient weld strength. Research indicates that the incidence of cold solder joints can be as high as 30% or higher when welding without cleaning the terminal, significantly impacting the electrical connection reliability of the battery module.
Insufficient weld strength is also a common problem associated with uncleaning the terminal. Impurities prevent the weld from forming a uniform, strong seam. During use, battery modules are subject to various external forces, such as vibration and impact. Modules with insufficient weld strength are susceptible to cracking and detachment due to these forces, compromising the structural integrity of the battery module and, in turn, affecting the proper functioning of the entire battery system. Take the battery modules of electric vehicles, for example. During driving, they are constantly subjected to vibrations from bumps and bumps on the road. If the weld strength is insufficient, failure is very likely to occur quickly, endangering driving safety.
Furthermore, compromised conductivity is also a significant issue. Battery modules must efficiently conduct current to achieve rapid charging and discharging. Impurities on the surface of the terminals, particularly oxides and some insulating contaminants, significantly increase contact resistance. Increased resistance means more heat is generated when current flows. Excessive heat not only reduces the battery's energy conversion efficiency and actual usable capacity, but can also lead to serious safety hazards such as thermal runaway. There have been cases where poor conductivity at the battery module terminal welds has led to localized overheating, ultimately causing battery fires and resulting in significant loss of life and property.
3. Benefits of Cleaning the Terminals
Since not cleaning the terminals can cause so many problems, what benefits does cleaning them bring to module CCS welding?
From the perspective of welding quality, cleaning the terminals can significantly improve welding reliability and reduce the risk of cold joints. For example, laser cleaning uses a high-energy-density laser beam to illuminate the terminal surface, causing impurities and oxide layers on the surface to instantly absorb the laser energy, rapidly expand, and vaporize, achieving efficient cleaning of the terminal surface. The laser-cleaned terminal surface is highly clean, allowing it to fully fuse with the solder, forming a strong intermetallic compound. Studies have shown that cleaning before welding can increase the shear strength of the weld by 20%-30%, significantly enhancing weld reliability and effectively reducing the occurrence of cold joints and desoldering.
Cleaning the terminals also plays a key role in battery module stability. When impurities on the terminal surface are removed, the resistance of the weld becomes more stable and uniform. This means that during the battery module's charge and discharge process, current flows more smoothly, reducing local overheating caused by resistance fluctuations. Taking the battery modules in energy storage systems as an example, stable welding and uniform resistance distribution ensure consistent performance under long-term, high-current charge and discharge conditions, preventing capacity fade and shortened lifespan due to localized overheating. This improves the stability and reliability of the entire energy storage system.
From a safety perspective, cleaning the battery terminals reduces the risk of thermal runaway and other safety incidents in the battery modules. As mentioned earlier, uncleaned terminals can generate excessive heat due to poor welding quality and increased resistance. However, cleaning the terminals ensures weld quality, reduces resistance, and significantly reduces heat generation. Especially in applications such as electric vehicles, where battery safety is paramount, terminal cleaning can effectively prevent serious safety incidents such as fires and explosions caused by overheating, effectively safeguarding the lives of drivers and passengers.
4. Introduction to Cleaning Methods
Now that we understand the importance of cleaning the battery terminals, let's take a look at common terminal cleaning methods.
Laser cleaning is currently a widely used cleaning method. This method uses a high-energy-density laser beam to illuminate the battery terminal surface, causing impurities and oxide layers on the surface to instantly absorb the laser energy, rapidly expand, and vaporize, achieving efficient cleaning of the terminal surface. Laser cleaning boasts high precision, enabling precise targeting of battery terminals without damaging surrounding areas. This is crucial for cleaning delicate battery components. For example, in the production of new energy vehicle battery modules, battery terminals are small and surrounded by numerous delicate components. Laser cleaning can precisely remove contaminants from the terminal surface without affecting other components. Furthermore, it is a non-contact cleaning method, eliminating the effects of mechanical wear on the terminals and reducing the risk of damage. It is also environmentally friendly, requiring no chemical reagents and generating no hazardous waste.
ACEY-G100W laser rust removal machine mainly uses fiber laser to remove rust, oxides, paint and other coatings from the surface of metals.
Ultrasonic cleaning is also a common method. Its principle is to generate a high-frequency oscillation signal through an ultrasonic generator. An ultrasonic transducer converts this high-frequency oscillation into high-frequency mechanical vibrations, which are then transmitted into the cleaning fluid. This generates countless tiny bubbles in the cleaning fluid. These bubbles rapidly grow and close under the influence of ultrasound, generating strong impact forces and micro-jets, which remove dirt, grease, and other impurities from the terminal surface. In battery production scenarios with relatively low cleaning precision requirements and large production scales, ultrasonic cleaning can be used to clean terminals in batches, improving production efficiency. However, when using ultrasonic cleaning, care must be taken to control the cleaning time and cleaning solution concentration to avoid unnecessary corrosion on the terminal surface.
Chemical cleaning uses chemical reagents to react with impurities on the terminal surface, dissolving them or converting them into easily cleanable substances. For example, acidic solutions are used to remove metal oxides, and alkaline solutions are used to remove oil stains. The advantage of chemical cleaning is its thorough cleaning effect, effectively removing some stubborn contaminants. However, it also has certain disadvantages, such as the potential for environmental pollution caused by chemical reagents, and the need for thorough rinsing and neutralization of the terminal after cleaning to prevent chemical residues from adversely affecting subsequent welding and battery performance.
