The reasons for abnormal internal resistance of lithium-ion batteries can be analyzed in combination with materials, processes, usage conditions and other aspects:
Material and structural factors
1. Electrode material issues
- Poor conductivity of the positive and negative electrode active materials or excessive or unevenly distributed binder hinders electron conduction.
- Oxidation or poor contact of the copper or aluminum foil current collector increases ohmic internal resistance.
2. Abnormal electrolyte
- Insufficient or aged electrolyte (excessive moisture, solvent decomposition) can hinder ion transport.
- Excessive electrolyte increases internal resistance and affects lithium ion concentration stability.
3. Separator Defects
- Low porosity or excessive thickness of the separator restricts lithium ion migration.
Workmanship and manufacturing defects
1. Electrode and Tab Issues
- Uneven electrode coating thickness, excessive compaction density, or poor tab welding (such as cold welds) can lead to excessive local current density.
- High internal resistance between the rivet and the pressure plate, or insufficient positive electrode conductive additive.
2.Insufficient pre-formation.
- The SEI film is not stably formed, and the internal resistance continues to increase during cycling.
Usage and aging factors
1. Overdischarge Impact
- Overdischarge can damage the negative electrode graphite layer, dissolve copper ions in the positive electrode, clog the separator, and increase ohmic internal resistance and charge transfer impedance.
- Severe overdischarge can cause SEI film decomposition, further increasing internal resistance.
2. Temperature and Cycle Loss
- High temperatures accelerate electrolyte decomposition, while low temperatures reduce ion mobility, both leading to increased internal resistance.
- After long-term cycling, the positive electrode material structure collapses, the negative electrode SEI film thickens, and the charge transfer impedance increases.
3. Poor battery pack consistency
- Variations in capacity or self-discharge rate between battery cells lead to inconsistent voltage and abnormal internal resistance.
Other factors
- Micro-short circuits: Metal impurities or diaphragm damage during the production process can cause localized current increase and abnormal internal resistance.
- Seal failure: Gas/liquid leakage after long-term use triggers internal chemical reactions, increasing internal resistance.
