Polymer Li-ion battery, also called Li-polymer battery, is compact and light-weighted. It has long life span of more than 1000 times and no memory effect, that is, it can be recharged anytime without influencing its performance. The battery is widely applied in mobile phone, tablet computer, lap-top, portable camera, DVD player and portable military equipments, etc. Now, polymer Li-ion battery is being developed for electric vehicles, including electric bikes, electric motors and electric automotives. Battery shell of polymer Li-ion battery is an integrated part of polymer Li-ion battery. Its barrier property against water vapor would influence electrochemical property and life span of the battery. Therefore, water vapor transmission quantity of battery shell is an important index for manufacturers. Taking Labthink W3/330 Water Vapor Permeability Tester as a example, a brief introduction is made for water vapor transmission quantity testing of polymer Li-ion battery shell.
1. Significance for Testing Water Vapor Transmission Quantity of Polymer Li-ion Battery Shell
Lithium salt exists inside polymer Li-ion battery, which can instantly produce strongly corrosive hydrofluoric acid when meets water vapor in the battery shell. If the shell material is improper for barrier performance against water vapor, the atmospheric water vapor would permeate into the battery, and when meets lithium salt, would produce hydrofluoric acid. The aluminum foil would be seriously corroded. Aluminum foil would be separated with the internal membrane, and would be corrosively perforated. The whole shell is ruined. Thus, water vapor transmission quantity must be tested.
2. Testing Methods for Water Vapor Transmission Quantity of Polymer Li-ion Battery Shell
Battery shell of polymer Li-ion Battery has high barrier property against water vapor. As to such high barrier material, electrolytic method is usually applied to test water vapor transmission rate. The detailed method is as follows: prepared sample is clamped in between the testing chambers. Nitrogen gas with a certain humidity flows at one side of the sample; dry nitrogen flows at the other side of the sample. Owing to the humidity differences, water vapor would permeate from the high humidity side into the low humidity side. At the low humidity side, the permeated water vapor would be carried to the electrolytic sensor by the dry nitrogen gas flow, and produce corresponding electronic signals when entering into the sensor. Through analysis and calculation of the electronic signals, water vapor transmission rate of the sample can be obtained. Labthink W3/330 Water Vapor Transmission Rate Testing System applies computer monitoring with simple operations and human friendly interface. The instrument has a patent design of 3 testing cells integrated in one. The master-satellite mode is applied, that is, a master base can connect up to 9 satellite modules. In other words, 30 samples can be tested at the same time. Its high precision and excellent repetition guarantees perfect testing for water vapor transmission quantity through polymer Li-ion battery.
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| Water Vapor Transmission Rate Testing System |
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