In today's new energy field, lithium-ion power batteries play a pivotal role. Its production process involves numerous complex procedures. From cell manufacturing to
Battery Pack Assembly, every step is crucial for the performance, safety, and reliability of the battery. Today, let's delve deep together into this mysterious and crucial production process of
Battery Assembly.
Cell Manufacturing: Meticulous Construction
1. Slurry Preparation of Active Materials - Mixing Process
The first step in battery production is mixing. Active materials (powder), binder, and conductive additive are uniformly mixed into a uniform slurry with a solvent in a vacuum mixer. This step requires precision control of raw material ratios, mixing steps with set times, and mixing durations. The production environment and working space require dust control at the level of a medical-grade dust-free and sterile workshop. This ensures the quality of the slurry and the pass rate of the finished product.
2. Coating the Slurry on the Copper Foil - Coating Process
Pole piece coating is a process that involves evenly coating the uniformly mixed slurry onto the current collector while drying the organic solvent in the slurry. This requires extremely high precision and speed. The consistency of the coating directly impacts battery performance; an inconsistent coating will cause the battery performance to drop. Control of the coating drying temperature, coating surface density, coating size, and coating thickness will impact battery quality, capacity, and consistency, as well as potential safety risks. Additionally, while coating the copper foil, it is crucial to ensure that there are no particles, sundries, or dust included in the coating process to avoid safety risks.
3. Fine Rolling to Shape the Foundation of the Cell - Rolling and Cutting
The rolling and cutting processes are extremely important in ultra-fine lithium battery manufacturing. The fundamental concept involved is the application of uniform and controlled pressure through a highly engineered rolling system to create uniform and compacted layers of active materials, conductive additives, etc., on a current collector (for example, aluminum foil or copper foil). At the same time, the cutting mechanism can cleanly cut the pole piece synchronously during the rolling process, abiding by the specified size standards, thus ensuring that every pole piece unit is produced to the same specifications and quality standards.
The key to delivering quality pole pieces during the rolling process is to manage and control the rolling pressure. The quality of the cutting equipment will significantly impact cutting results and edge quality. It should also be noted that a small amount of dust and foreign objects will be produced as part of the rolling and cutting processes. If dust and foreign materials get incorporated into the pole piece materials that make up the electrode sheet(s), performance issues could arise, including the potential for internal series-based shorting in the battery, thus having a drastic and dangerous impact on the overall performance and safety of the battery. Consequently, there will be a need for the equipment of the
Lithium-Ion Battery Pack Assembly Line to include an effective dust collection system, with regulations for cleaning processes, and controlled production environments to ensure charged pole piece sheets, while produced accurately, are produced clean of any foreign material and dust particles.
4. Forming the "Embryo" of the Cell - Winding and Stacking Processes
Winding refers to the process where a combination of separators and pole pieces are rolled into a cylindrical (or any other form) shape, either in series or parallel, with a specific order, to create a bare cell "prototype," while managing and controlling tension, speed of both products, and overall construction. The bare cell's or prototype's major feature is to create a continuous current path which aids in ion movement, as well as allows for the use of the anisotropy of materials to help increase overall energy density. Challenges to winding exist, such as the possibility of edge stress concentration affecting cycle life, and lack of even winding impacting performance consistency and safety.
Stacking refers to the alternating stack of pole pieces and separators in layers, exactly positioned and oriented with high-quality bonding of each layer possible using equipment designed for matching. The two key advantages of stacking are the possibility of a long cycle life and the ability to design the shape and size of the cell to be custom designed if needed. The major challenges of stacking are potentially lower production speed and the potential for more solder points on the tabs.
Winding and stacking are important methods for creating the core structure of the cell, and both significantly impact performance. Both methods have unique characteristics and scenarios for cell production, and both have directions for technical and improved production technology outlooks.
Winding Process:
Within the production chain of lithium-ion batteries, the assembly line for a battery pack operates like an accurately functioning artery, while the winding process serves as a highly skilled craftsman. It undertakes a key role where the positive electrode sheet, negative electrode sheet, and separator membrane are masterfully combined in a critical fashion. In the overall process steps of battery pack assembly, it shapes the embryonic form of the battery cell correctly, thus establishing a solid foundation for the construction of a fully functioning and efficient lithium-ion battery pack.
This process features a key step in the birth of the cell. It winds together the appropriately prepared pole pieces and separator membranes into a specific configuration and sequence, like weaving a tightly wound energy "cocoon house." This establishes the basic framework of the battery for subsequent charging and discharging.
The winding equipment adopts an advanced automation process and can accurately control the winding speed, tension, and alignment. The winding equipment also contains a CCD visual inspection device, which can automatically and ultimately determine the general placement of the pole piece, overlap of the separator membrane, and winding diameter, among multiple other parameters, in real time.
5. Removal of Moisture and Activating Life - Baking and Injecting
The baking process is required to eliminate moisture from the battery cell. The baking process utilizes high temperature to expel moisture. To expel moisture without allowing it to react with the electrolyte and affect battery performance, controlled temperature, time, humidity, and air flow are utilized with an oven acting as the thermal mass, effectively allowing for a stable state to bake and then conduct the other processes. Overall, baking will assist in lowering self-discharge, increasing and promoting cycle life.
The electrolytic injection (formation) process occurs in a clean environment and has a high volume and speed measuring system to be used during the injection process. An organic solvent containing lithium salts is injected into the cell battery, essentially converting the battery cell from a passive unit to an active unit with energy storage and releasing capabilities. The electrolyte is the medium for ion movement; therefore, electrolyte composition will have an impact on the electrochemical performance of the battery. Part of the process is to optimize the SEI film through reactions with electrode material incorporated after the electrolyte material is injected, taking battery performance to the next level.
The baking and injection processes are distinctly working in conjunction with each other at the same time. They are key elements to maintaining high-performance batteries, long life, safety performance, and are key to battery production quality.
6. Opening the Closet of the Battery Cell End and Taking the First Steps to the Battery Energy Journey - Forming Process, and Grading
Forms. Opening the Closet to the Battery Cell End and Beginning the Battery Energy Journey.
Core Objective of the Forming Process.
The formation process is a key link in the production of lithium-ion batteries. Its main objective is to create an SEI film on the surface of the negative electrode during the first charge-discharge cycle. The SEI film has excellent protective abilities. While establishing the SEI film, the undesirable reaction possibly between the electrolyte and negative electrode material is suppressed, while re-establishing electrochemical performance. In addition, the SEI film is also establishing a stable channel for lithium ion insertion and extraction so as to establish stable and effective energy operation during the ensuing charge-discharge cycles.
The Process of Implementation and Important Points of the Formation Process
The formation process is typically performed in dedicated formation equipment, which can accurately control parameters like the charging and discharging current, voltage, and time. During the formation process, the battery cell is charged using a relatively small current in the beginning, which gradually allows lithium ions to move from the positive electrode to the negative electrode. During the migration, the solvent and lithium salt of the electrolyte undergo a reduction reaction on the surface of the negative electrode to produce an SEI film, which gradually matures. It is important to carefully limit the upper voltage limit while charging the battery to prevent internal battery structure damage, as well as safety issues due to overcharging. For example, the upper limit of a lithium-ion battery is typically held between 4.2V and 4.35V during the charging stage. Once charging is complete, the battery cell will undergo a discharging operation. During the discharging operation, the cut-off voltage and discharging current need to be stringently controlled. The discharging process will assist in further stabilizing the structure of the SEI film that was previously formed and allows for establishing the initial performance of the battery cell. The entire formation process might take place over multiple charge-discharge cycles to ensure the SEI film quality and performance is optimized. Additionally, controlling the temperature during formation is also important, typically within the temperature window of 25°C and 45°C. A moderate temperature assists in smooth reactions and improves the quality uniformity of the SEI film.
