What Is Lithium Battery Cell Formation And Process?
Lithium batteries have become a cornerstone of the electric vehicle industry, offering a clean, efficient, and sustainable power source that has transformed the way we think about transportation. Whether you’re an EV enthusiast, a project manager overseeing lithium battery projects, or just a curious soul seeking to understand the science behind the electrifying drive of the future, this blog is helpful for you.
In the manufacturing process of lithium battery cells, the formation process plays a crucial role. Formation is the initial charge and discharge cycling of the battery cells after its assembly and before it is ready for use. This step is of paramount importance for several reasons, and it significantly impacts various aspects of lithium battery cells performance.
Activation and Capacity: Formation is vital for activating the battery cells and establishing its initial capacity. During this process, lithium ions are intercalated into the cathode and anode materials, allowing the battery to store and release energy effectively. It helps bring the battery to its rated capacity and ensures it can deliver its specified performance.
Stabilization: Formation helps stabilize the lithium-ion battery’s chemistry. It reduces the likelihood of side reactions or unwanted chemical changes that can occur during the battery’s first few charge and discharge cycles. This is essential for ensuring the long-term reliability and safety of the battery.
Balancing: Formation also aids in balancing the cell. It helps ensure that all the individual cells within a battery pack have a similar state of charge. Balanced cells contribute to consistent and optimal battery performance.
Cycling Performance: Proper formation can enhance the cycling performance of lithium battery cells. A well-formed battery is less likely to exhibit capacity fade or suffer from issues like capacity loss, elevated internal resistance, and reduced energy density during its lifetime.
Safety: Formation is critical for identifying and addressing potential safety concerns. It helps reveal any defects or issues that may arise during the early stages of battery use, allowing manufacturers to take corrective actions if necessary.
What is lithium-ion battery cell formation?
Battery cell formation, a crucial process, consists of two stages: pre-formation and main formation. It involves a controlled low-current charge to transition lithium-ion battery cells from raw materials into a stable and efficient electrochemical system. The goal of this process is to achieve a secure and effective transformation.
What changes have occurred inside lithium-ion battery cells during the formation process?
During the formation process, there will be the following reactions inside the lithium-ion battery cells:
1. Activation of Active Materials: The formation process kick-starts the activation of active materials. The positive electrode material begins releasing lithium ions, while the negative electrode material becomes prepared to receive lithium-ion insertion.
2. Lithium Ion Migration: Lithium ions initiate their movement within the battery system. They solvate on the positive electrode’s surface, traverse the separator, and ultimately reach the surface of the negative electrode.
3. Interaction with Negative Electrode: Solvated lithium ions come into direct contact with the negative electrode material. As these lithium ions embed into the surface of the negative electrode material, the Fermi level of the material increases, surpassing the lowest unoccupied molecular orbital (LUMO) of the electrolyte. This leads to the reduction and decomposition of the electrolyte on the anode material’s surface, giving rise to the formation of a solid electrolyte interface (SEI) and by-product gas.
4. Gas Emission: As a consequence of these reactions, gas is generated on the electrode, resulting in a gaseous by-product.
5. Electrode piece expansion: The expansion phenomenon of the electrode and diaphragm during the static and formation process after liquid injection can lead to an increase in the thickness of the battery cells. The expansion of the electrode includes three aspects: the expansion of electrode material particles, the swelling of binders, and the relaxation of stress between particles in the electrode.
The expansion of electrode material particles is caused by the insertion of lithium and the formation of surface SEI film. As the amount of lithium intercalation increases, the interlayer spacing of graphite carbon gradually increases, and the cell volume also gradually increases.
Swelling of the binder: After absorbing the solvent in the electrolyte, the binder in the electrode will self swell, causing an increase in particle gap and resulting in an increase in the thickness of the electrode.
Stress relaxation between particles in the electrode: The stress relaxation and expansion between particles is the process of releasing internal stress between active material particles, conductive agent particles, and active material particles inside the electrode after immersion in electrolyte, causing the structure of the electrode to relax and further increasing the thickness of the electrode.
Understanding these intricate changes occurring during the formation process is essential for gaining insights into the behavior of lithium-ion battery cells and their optimal performance. Stay tuned for more informative content on battery technology and its role in various applications.
During the formation process, what efforts can we make to transform a “pile of materials” into a stable “electrochemical system”?
1. Activate all positive and negative electrode materials
As a lithium-ion container, positive and negative electrode materials need to meet the following two points in order to fully activate them:
Firstly, the material itself is able to remove lithium ions normally. The material structure is not damaged.
Secondly, the material can be integrated into the electrochemical system. The electrolyte can infiltrate every particle, providing channels for the transport of lithium ions.
2. Generate dense SEI film
In order to obtain an excellent SEI film layer, the chemical composition is divided into two stages: pre formation and main formation.
In the pre formation stage, a relatively dense SEI film is first generated through a small current. Avoid excessive current, which can lead to rapid nucleation and loose SEI film structure, resulting in poor adhesion to the particle surface; On the other hand, solvation of lithium ions at the interface of the negative electrode material does not occur in time for film forming reactions, and lithium ions and solvents are embedded together in the negative electrode material, damaging the material structure and causing more electrolyte loss.
The pre formation stage is mainly for film formation, so the charge is relatively low and the voltage only reaches the target film formation potential. In order to complete the cycle of detachment, insertion, and detachment of the active material in lithium-ion batteries, the main formation begins.
In the main formation stage, a current greater than the pre formation current is used for charging and discharging cycles. After the SEI film is generated on the surface of the active material, a large current is used to adapt the internal operation of the battery to the actual working conditions, and at the same time, the defects in the SEI are recombined and repaired.
The purpose of pre normalization and main normalization is different. Pre oxidation is mainly for film formation, while main oxidation is mainly to complete the complete process of de embedding of the active material, so more gas is generated during the pre-oxidation process.
3. Gas discharge
Firstly, in the pre formation process, when the generated gas stays between the electrode and the diaphragm, as the gas is an insulator, it will stop the pre formation reaction on the electrode gas path, resulting in uneven electrode formation.
Secondly, the escape of pre formed gas can also cause electrolyte loss. During the pre-formation process, the generated bubbles will occupy a portion of the electrolyte’s space, causing the electrolyte to expand and overflow, resulting in electrolyte loss.
So in order to reduce the residence of gas in the electrode group and enable it to escape quickly, it is necessary to use a negative pressure formation process.
Understanding these processes and the steps involved is essential to ensure the formation of stable electrochemical systems. For further insights into battery technology and manufacturing, stay tuned for more informative content. If you have any questions or require more information, please don’t hesitate to contact us. Thank you for joining us on this journey of exploration and innovation!
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