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.