Electrode powder shedding is currently minimal in lithium cobalt oxide production processes. The possibility of powder shedding during production is influenced by factors such as:
1. Improper formulation ratio, such as too little binder or solvent, resulting in uneven mixing.
2. The adhesive baking temperature is too high, which damages the adhesive structure.
3. The slurry was not mixed for a sufficient time and was not fully mixed.
4. The coating temperature was too low, and the electrode was not dried.
5. Uneven coating amount, with too large a difference in thickness.
6. The electrode sheets were not baked before rolling, and thus absorbed a large amount of moisture from the air.
7. Excessive pressure during roller pressing causes the electrode powder to separate from the current collector.
8. Incorrect feeding method of the electrode sheet during rolling results in uneven force on the electrode sheet.
9. Using an oil-based positive electrode and a water-based negative electrode, how can it prevent powder from falling off?
III. Battery Defects and Their Causes:
1. Low capacity
Causes:
a. Insufficient material content; b. Significant difference in material content between the two sides of the electrode; c. Electrode breakage;
d. Insufficient electrolyte; e. Low electrolyte conductivity; f. Positive and negative electrode plates not properly matched;
g. Low membrane porosity; h. Adhesive aging → material detachment; i. Overly thick core (not dried or electrolyte not penetrated); j. Not fully charged during capacity testing; k. Low specific capacity of positive and negative electrode materials.
2. High internal resistance
Causes:
a. Poor soldering between the negative electrode and the tab; b. Poor soldering between the positive electrode and the tab; c. Poor soldering between the positive tab and the cap; d. Poor soldering between the negative tab and the casing; e. High internal resistance between the rivet and the pressure plate; f. No conductive agent added to the positive electrode; g. No lithium salt in the electrolyte; h. The battery has experienced a short circuit; i. Low porosity of the separator paper.
3. Low voltage
Causes:
a. Side reactions (electrolyte decomposition; impurities at the positive electrode; presence of water); b. Incomplete formation (SEI film not formed safely); c. Leakage on the customer's circuit board (referring to the battery cells returned after customer processing); d. Customer did not spot weld as required (battery cells after customer processing);
e. Burrs; f. Micro-short circuit; g. Dendrite formation at the negative electrode.
4. The reasons for excessive thickness are as follows:
a. Weld leakage; b. Electrolyte decomposition; c. Incomplete drying of moisture; d. Poor sealing of the cap; e. Shell wall too thick; f. Shell too thick; g. Core too thick (too much material attached; electrode not compacted; diaphragm too thick).
5. The causes are as follows:
a. Incomplete or incomplete SEI film formation; b. Baking temperature too high → adhesive aging → material detachment; c. Low specific capacity of negative electrode; d. Excessive positive electrode material attachment but insufficient negative electrode material attachment; e. Leaking cap or weld; f. Electrolyte decomposition, reduced conductivity.
6. Explosion
a. The capacity divider is faulty (causing overcharging); b. The diaphragm has poor closure; c. Internal short circuit.
7. Short circuit
a. Dust; b. Tear during packaging; c. Scratches (small diaphragm paper too small or not properly padded); d. Uneven winding; e. Not properly packaged; f. Holes in the diaphragm; g. Burrs
8. Circuit break
a) The tab and rivet are not properly welded, or the effective weld area is small;
b) The connecting piece is broken (the connecting piece is too short or it is welded too low when spot-welded to the electrode).
IV. Safety Characteristics of Lithium-ion Batteries
Lithium-ion batteries are widely used in people's daily lives, so their safety performance should absolutely be the primary evaluation criterion. Internationally, very strict standards have been established for evaluating the safety performance of lithium-ion batteries. A qualified lithium-ion battery should meet the following conditions in terms of safety performance.
1) Short circuit: No fire, no explosion;
2) Overcharge: No fire, no explosion;
3) Hot box test: No fire or explosion (150℃ constant temperature for 10 minutes)
4) Needle puncture: No explosion (pierce the battery with a Φ3mm nail);
5) Flat plate impact: No fire, no explosion; (10kg weight dropped on the battery from a height of 1 meter)
6) Incineration: No explosion (gas flame burns the battery)
To ensure the safe and reliable use of lithium-ion batteries, experts have conducted very rigorous and meticulous battery safety designs to meet battery safety assessment indicators.
1. Automatic shut-off protection at 135℃: The membrane adopts the internationally advanced Celgard2300PE-PP-PE three-layer composite membrane.
2. When the battery temperature reaches 120℃, the PE membrane pores on both sides of the composite membrane close, the internal resistance of the battery increases, a large-area open circuit is formed inside the battery, and the battery stops heating up.
3. Composite structure of battery cover: The battery cover adopts a grooved explosion-proof structure. When the battery heats up and the pressure reaches a certain level, the groove will crack and release gas.
4. Various environmental abuse tests: Various abuse tests are conducted, such as external short circuit, overcharge, needle penetration, flat plate impact, and burning, to assess the battery's safety performance. Simultaneously, temperature shock tests and mechanical performance tests such as vibration, drop, and impact are performed to examine the battery's performance under real-world usage conditions.
