Discussion on Pre-testing Procedure of 18650 Cylindrical Cell
The safety problems can be controlled basically when the lithium-ion batteries used alone or in small series and parallel, but when 18650 lithium-ion batteries are used in large groups, especially as the electric vehicle battery pack, the safety problems will be more prominent.When lithium-ion batteries are used in groups, because of the large number of monomers, complicated structures, consistency of the monomer screening and matching management are more difficult to match, which makes the "short board" battery of battery pack more easy to over-aging, which in the course of the more prone to accidents.
Therefore, to solve the safety problems of lithium-ion battery pack, while improving the safety of the battery at the same time, from the battery system point of view to strengthen the group of lithium-ion battery security technology is also very necessary and urgent.
There are many sources of inconsistency, the composition of the battery material itself is not entirely consistent, and the manufacturing process of the battery can not be controlled to each battery in any details are the same. This will lead to inconsistent capacity, terminal voltage inconsistencies, internal resistance inconsistencies, life inconsistencies.It is very difficult to solve fundamentally,It is necessary to select and test the cells before assembly battery pack.
In addition to the electrical properties need to be screened, 18650 lithium ion battery appearance also need to be tested. Such as battery surface scratches, damage, stains, pits, bumps and other defects, will affect the battery module assembly and security after built battery pack .
Such as the package plastic damage of cell surface , there will be short-circuit security risks;
The stains, pits / bumps, etc., of end surface will also affect the circuit's welding stability;
Plastic coated smoothness will also affect module assembly efficiency;
The length of the batteries and end face diameter uniformity also affects the production efficiency of module assembly.
So the appearance test is necessary before PACK process .