Analysis of the Causes of Excessive Internal Resistance of Lithium Batteries.
Process aspect
1) The positive electrode material has too little conductive agent (the conductivity between the material and the material is not good because the conductivity of lithium cobalt itself is very poor).
2) Too much positive electrode binder (binder is generally a polymer material, strong insulation performance).
3) Too many negative electrode binders (binders are generally polymer materials, strong insulation properties).
4) The ingredients are not evenly dispersed.
5) The binder solvent is not complete when the ingredients are added. (not completely soluble in NMP, water)
6) The coating draw density is too large. (Ion migration distance is large)
7) The compaction density is too large, and the roller pressure is too strong. (Rolling is too much, and the structure of the active material is damaged)
8) The positive ear is not welded well, and there is virtual welding.
9) The negative ear welding or riveting is not strong, there is virtual welding, desoldering.
10) The winding is not tight, and the core is slack. (increasing the distance between the positive and negative sheets)
11) The positive electrode and the housing are not welded firmly.
12) The negative pole and the pole are not welded firmly.
13) The battery baking temperature is too high, the diaphragm shrinks. (The diaphragm aperture is reduced)!
14) The amount of liquid injection is too small (conductivity is reduced, the internal resistance increases after cycling!)
15) The holding time is too short after the injection, the electrolyte is not fully wetted.
16) Not fully activated at the time of formation.
17) The electrolyte leaks too much during the formation process.
18) The moisture control in the production process is not strict and the battery expands.
19) The battery charging voltage is set too high, causing overcharge.
20) The battery storage environment is unreasonable.
Material aspect
1) The positive electrode material has a large electrical resistance. (poor conductivity, such as lithium iron phosphate)
2) Influence of diaphragm material (thickness of diaphragm, small porosity, small aperture)
3) The influence of electrolyte materials. (small conductivity, high viscosity)
4) Positive PVDF material influence. (large amount or large molecular weight)
5) The influence of the positive electrode conductive material. (poor conductivity, high resistance)
6) Positive and negative electrode material impact (thickness, poor conductivity, uneven thickness, poor material purity)
7) Copper foil, aluminum foil material has poor conductivity or oxide on the surface.
8) The inner pole of the cover pole riveting contact is too large.
9) The negative electrode material has a large electrical resistance.
Other aspects
1) Internal resistance test instrument deviation.
2) Human operation.
3) The environment.
