Date: 2025-09-19 hits: 103
1. Burrs or chipping on the electrode edges
If the electrode is not cut evenly, leaving tiny burrs on the edges, like tiny needles, can pierce the separator, allowing the positive and negative electrodes to come into direct contact. This "physical short," while not a large current, is enough to cause the voltage to drop gradually. Especially during the lamination process, poor electrode alignment can make burrs on the edges more likely to penetrate.
There's also the issue of chipping during coating. If particles of the negative electrode graphite coating fall off and become lodged between the positive and negative electrodes, they can create a localized conduction, leading to low voltage before formation.
2. Defective separators
The separator acts as a "firewall" between the positive and negative electrodes, but if it has pinholes, thin spots, or is wrinkled or scratched during packaging, it becomes ineffective. These conditions can cause micro-shorts, leading to low voltage before formation.
3. Poor packaging
Battery cell packaging requires airtightness, but uneven pressure and insufficient temperature during heat sealing of the aluminum-plastic film can leave tiny gaps. Moisture from the air takes advantage of this opportunity to infiltrate and react with the lithium salts in the electrolyte, generating impurities such as HF. These impurities trigger side reactions, depleting the battery cell's initial energy and causing a voltage drop.
4. Abnormal Tab Welding
As a crucial current-conducting component in lithium-ion batteries, the quality of the tab welds has a profound impact on battery performance. When the weld between the positive tab and the aluminum-plastic film exhibits false welds or false solder joints, tiny gaps develop in the conductive interface that should be tightly fitted. These gaps hinder the flow of current, significantly increasing contact resistance. Compared to a normal weld, resistance can increase several or even dozens of times.
The sealing quality of the tab glue is also crucial. The tab glue not only secures the tab but also acts as a crucial barrier to isolate the electrolyte from the external environment. If the tab glue is not fully coated or cracks exist, the highly corrosive electrolyte can penetrate through the tiny gaps between the tab and the aluminum-plastic film. Initially, this penetration may only cause localized corrosion, leading to oxidation or dissolution of the metal. However, over time, the corrosion area continues to expand, and the adjacent positive and negative electrode materials are gradually exposed and come into contact with each other, forming a micro-short circuit. Although micro-short circuits do not immediately cause battery failure, they will continuously consume the active materials inside the battery. This can also cause low voltage before formation.
5. Insufficient Electrolyte Injection and Poor Wetting
Insufficient electrolyte injection and poor cell wetting after injection prevent the positive and negative electrode materials from fully contacting the electrolyte, resulting in localized "dry areas." This hinders ionic conduction between the positive and negative electrodes, preventing a stable potential difference from being established, and directly lowering the open-circuit voltage. More critically, air can remain in the unwetted areas, forming tiny bubbles after packaging. These bubbles can easily lead to localized oxidation of the electrode sheet, triggering side reactions that consume the active material and further reduce the voltage.
6. Excessive Magnetic Material in the Electrode Sheet
Excessive magnetic material content can lead to low voltage before formation. This is primarily due to the conductive nature of magnetic particles (such as iron and nickel debris). Once mixed into the battery cell, they can penetrate the separator, forming a conductive bridge, creating a micro-short circuit between the positive and negative electrodes, consuming power and lowering the voltage. These particles can also catalyze electrolyte decomposition, triggering side reactions that consume the active material, further exacerbating the voltage drop.
7. Summary
Low voltage before formation is like a "warning signal" from the battery cell. It is not caused by a single reason, but rather a concentrated manifestation of problems in multiple links such as the electrode, diaphragm, packaging, and materials. Therefore, we need to pay attention to the low voltage situation before formation, do a good job of investigation and prevention to prevent larger problems from occurring later.
