18650 lithium battery cells.What should we pay attention to in the winding process of 18650 lithium battery?

　　1. Humidity control <1% RH Purpose: To prevent water absorption during the winding process of positive and negative electrode sheets, resulting in zero voltage, self-discharge, and poor cycle performance;

　　Method: Calculate the dew point value and temperature value to obtain the temperature and humidity value;

　　2. Dust control ≤100,000pc/ft3 (detected particle size is 0.5um)

　　Purpose: To prevent dust from being involved in the pole assembly during winding, causing battery core short circuit, overheating, fire, self-discharge and other defects;

　　Low temperature lithium iron phosphate battery 3.2V 20A -20℃ charging, -40℃ 3C discharge capacity ≥70%

　　Charging temperature: -20~45℃ -Discharge temperature: -40~+55℃ -40℃ Support maximum discharge rate: 3C -40℃ 3C discharge capacity retention rate ≥70%

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　　Method: Use dust tester;

　　3. Abnormal cutting burrs

　　Process requirements: pole piece ≤8um; pole lug burr ≤12um; detection method: randomly select 1 PCS battery cells for dissection during the first inspection of each machine in each shift, and detect the front and rear ends of the positive and negative pole pieces and the anode according to the "Burr Detection Work Instructions" , Negative tab cutting burrs.

　　Adverse effects: The burrs on the pole pieces or tabs exceeding the process requirements may cause the burrs to pierce the diaphragm, short-circuit the positive and negative poles, cause the battery core to overheat, and may explode in severe cases, posing serious safety hazards.

　　18650 lithium ion battery winding steps

　　Low temperature and high energy density 18650 3350mAh-40℃ 0.5C discharge capacity ≥60%

　　Charging temperature: 0~45℃ Discharge temperature: -40~+55℃ Specific energy: 240Wh/kg -40℃ Discharge capacity retention rate: 0.5C Discharge capacity ≥ 60%

　　4. Poor coverage of positive and negative electrodes

　　Process requirements: The alignment of positive and negative electrode plates is 0.75?.55mm

　　The alignment between the negative electrode sheet and the separator is 1?.5mm

　　Detection method: Randomly inspect 3 PCS cells continuously after changing the roll. Check the alignment according to the "X-RAY Operation Instructions". Adverse effects: 1) The alignment of the positive and negative electrode sheets exceeds the process specifications, which may cause the negative electrode sheet not to wrap the positive electrode sheet. During the charging process, the lithium ions released from the positive electrode cannot find the corresponding graphite to embed, causing free lithium ions in the battery core to accumulate on the negative electrode and form dendrites. The dendrites pierce the separator, causing an internal short circuit and posing a safety hazard.

　　2) If the alignment between the negative electrode sheet and the separator exceeds the process standard, the negative electrode sheet may be squeezed and deformed, and the negative electrode material on the electrode sheet may partially fall off. During the charging process, the battery core will expand, and the powder will pierce the separator, causing an internal short circuit of the positive and negative electrodes, causing safety hazards. hidden danger;

　　5. Poor pole piece coverage in the winding direction (the length of the outer layer of negative electrode and super positive electrode material, the length of the inner layer of negative electrode and super positive electrode material) detection method: every 2 hours, each winding machine randomly inspects the dissection of 3 PCS cells, and uses an eyepiece and a ruler to measure the two Different coverage sizes.

　　Adverse effects: It may cause the negative electrode sheet not to wrap the positive electrode sheet. During the charging process of the battery cell, the lithium ions released from the positive electrode cannot find the corresponding graphite to embed, causing free lithium ions in the battery core to accumulate on the negative electrode and form dendrites. Dendrites pierce the diaphragm and cause an internal short circuit, posing a safety hazard.

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