What are the basic reasons for the excessive internal resistance of lithium batteries?

Internal resistance is one of the important indicators for evaluating the performance of lithium batteries. The internal resistance test of lithium battery includes AC internal resistance and DC internal resistance. Regarding the single battery, it is generally evaluated by the AC internal resistance, which is usually called the ohmic internal resistance. However, for large-scale lithium battery pack applications, such as power supply systems for electric vehicles, due to the limitations of test equipment, it is impossible or inconvenient to directly test the AC internal resistance. Generally, the characteristics of the battery pack are evaluated by the DC internal resistance. In practical applications, DC internal resistance is also used to evaluate the health of the battery, to predict the life, and to estimate the system SOC, output/input capabilities, etc. Analysis of the reasons for the excessive internal resistance of lithium batteries 1. Process aspects (1) There is too little conductive agent for the positive electrode ingredients (the conductivity between the material and the material is not good, because the conductivity of lithium cobalt itself is very poor) (2) The positive electrode ingredients are sticky Too much binder (binders are generally polymer materials with strong insulation performance) (3) Too much binder for negative electrode ingredients (binders are generally polymer materials with strong insulation performance) (4) Ingredients Uneven dispersion (5) Incomplete binder solvent during compounding (not completely soluble in NMP and water) (6) The surface density of the coating drawing is too large (the ion migration distance is large) (7) The compaction density of the lithium battery is too large Large, the roll is too firm. (Rolling is too dead, and some of the active material structure is destroyed) (8) The positive lug is not welded firmly, and there is a virtual weld (9) The negative lug is not welded or riveted, and the negative electrode is welded or riveted. (10) The winding is not Tight, loose core (increasing the distance between the positive and negative plates) (11) The positive electrode lug and the shell are not welded firmly (12) The negative electrode lug and the pole post are not welded firmly. 2. Material aspects (1) The resistance of the positive electrode material Large (poor conductivity, such as lithium iron phosphate) (2) The influence of diaphragm material (diaphragm thickness, small porosity, small pore size) (3) The influence of lithium battery electrolyte material (small conductivity, high viscosity) (4) Positive PVDF Material influence. (The amount is large or the molecular weight is large) (5) The influence of the positive electrode conductive agent material. (Poor conductivity, high resistance) (6) Influence of positive and negative electrode lug materials (thin thickness, poor conductivity, uneven thickness, poor material purity) (7) Copper foil, aluminum foil material has poor conductivity or oxides on the surface 3. Other aspects (1) Lithium battery internal resistance test instrument deviation statement: Some pictures and content of articles published on this site are from the Internet. If there is any infringement, please contact to delete the previous article: What is the important method of charging the lithium iron phosphate battery pack?