18650 lithium battery cells

　　What should be paid attention to in the winding process of 18650 lithium-ion batteries?

　　1. Humidity control ≤ 1%RH Purpose: To prevent water absorption during the winding process of the positive and negative electrodes, 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 (detection particle size is 0.5um

　　1. Humidity control ≤1%RH Purpose: To prevent positive and negative electrode sheets from absorbing water during the winding process, 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 (detection particle size is 0.5um)

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

　　Method: use a dust tester;

　　3. Abnormal cutting burrs

　　Process requirements: pole piece ≤ 8um; tab burr ≤ 12um; detection method: randomly select 1PCS cell for dissection in the first inspection of each machine in each shift, and detect the front and rear ends of the positive and negative electrodes and the positive and negative electrodes according to the "burr detection operation guide" Ear clipping burrs.

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

　　18650 lithium ion battery winding steps

　　4. Poor coverage of positive and negative electrodes

　　Process requirements: the alignment of positive and negative plates is 0.75~.55mm

　　Negative plate and diaphragm alignment 1?.5mm

　　Detection method: continuous random inspection of 3PCS cells after reel change, detection of alignment according to the "X-RAY Operation Instructions" Adverse effects: 1) The alignment of positive and negative electrodes exceeds the process specification, which may cause the negative electrode to not cover the positive electrode During the charging process, the lithium ions released from the positive electrode cannot find the corresponding graphite to embed, resulting in free lithium ions in the battery cell accumulating on the negative electrode and forming dendrites. The dendrites penetrate the separator and cause an internal short circuit, which poses a safety hazard.

　　2) If the alignment between the negative electrode and the diaphragm exceeds the process standard, the negative electrode may be squeezed and deformed, and the negative material on the electrode may fall off. During the charging process, the battery cell expands, and the powder penetrates the diaphragm, causing the internal short circuit of the positive and negative electrodes to cause safety. Hidden danger;

　　5. Poor coverage of the pole piece in the winding direction (the length of the outer layer negative electrode exceeds the length of the positive electrode material, and the length of the inner layer negative electrode exceeds the length of the positive electrode material) detection method: every 2H each winding machine randomly checks the dissection of 3PCS batteries, and measures the two parts with eyepieces and rulers respectively. A coverage gap size.

　　Adverse effects: It may cause the negative electrode sheet not to enclose the positive electrode sheet. During the charging process of the battery, the lithium ions released from the positive electrode cannot find the corresponding graphite to embed, causing free lithium ions in the battery cell to accumulate on the negative electrode and appear dendrites. Dendrites puncture the separator and cause internal short circuit, which poses a safety hazard.

　　18650 lithium ion battery winding steps

　　6. Short circuit test

　　Parameter setting (100V, 25nF250V,

　　250uA) Detection method: test the machine with a short-circuit sample during the first inspection of each shift; adverse effects: self-discharge, heat, explosion and other short-circuit factors: cutting particles, metal dust, burrs, etc. cause diaphragm holes;