7 conditions that lithium battery separators must have!
Important raw materials for batteries:
The separator, one of the key inner layer components in the structure of lithium batteries, is located between the positive and negative electrodes.
The main role of the diaphragm
The main function of the diaphragm is to separate the positive and negative active materials to prevent the two poles from being short-circuited due to contact; in addition, during the electrochemical reaction, it can maintain the necessary electrolyte to form a channel for ion movement; the positive and negative electrodes of the battery are separated. It can prevent the two poles from contacting and short-circuit, and also has the function of allowing electrolyte ions to pass through.
It should be known that the performance of the separator determines the interface structure and internal resistance of the battery, which directly affects the capacity, cycle and safety performance of the battery. The separator with excellent performance plays an important role in improving the overall performance of the battery.
Therefore, the diaphragm must meet the following seven conditions
(1) It has electronic insulation to ensure the mechanical isolation of positive and negative electrodes.
(2) It has a certain pore size and porosity to ensure low resistance and high ionic conductivity, and has good permeability to lithium ions.
(3) Since the solvent of the electrolyte is an organic compound with strong polarity, the separator must be resistant to corrosion by the electrolyte and have sufficient chemical and electrochemical stability.
(4) Good wettability to electrolyte and sufficient liquid absorption and moisturizing ability.
(5) It has sufficient mechanical properties, including puncture strength, tensile strength, etc., but the thickness is as small as possible.
(6) Good spatial stability and flatness.
(7) Good thermal stability and automatic shutdown protection performance. Power batteries have higher requirements for separators, and composite membranes are usually used.
At present, the diaphragm materials on the market are mainly polyolefin (Polyolefin) diaphragms mainly composed of polyethylene (PE) and polypropylene (PP). Among them, PE products are mainly made by wet process, and PP products are mainly made by dry process. As for the properties of the two materials, PE and PP.
In general, PP is relatively more resistant to high temperature, and PE is relatively resistant to low temperature; PP has a lower density than PE; PP has a higher melting point and closed cell temperature than PE; PP products are brittle than PE; PE is more sensitive to environmental stress.