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The surface of polypropylene film was modified by cold plasma treatment for alkali secondary battery separator, which is polypropylene (PP) separator, in this paper. The surface treatment was carried out using three different methods, such as plasma initiate concentrated sulfuric acid sulfonation, plasma initiate fuming sulfuric acid sulfonation and plasma initiate mixture sulfonation, and the treatment effects in battery separator were studied.The related performance of original PP separator, direct sulfonation PP separator and plasma initiating sulfonation PP separator was tested, and the involved treatment parameters of three methods above, including sulfonation temperature, sulfonation time, sulfonation concentration etc, were studied systematically. Equally, IR, XPS and SEM were used to characterize the surface properties of the samples such as chemical composition and morphological structure of material surface.Results reveal that sulfonic acid groups were successfully introduced onto the surface of PP separator using those three methods mentioned above, then separator’s hydrophilicity, alkali absorption and membrane surface resistance have been improved. The membrane contact angle changed from 90°to 25°when original PP separator was treated using plasma initiating concentrated sulfuric acid sulfonation. When using plasma initiating fuming sulfuric acid sulfonation, the alkali absorption velocity and quantity of reached 7.2 cm (5min) and 272%, respectively. However, the alkali absorption velocity and quantity could attain 7.6 cm (5min) and 266%, respectively, when plasma initiating mixture acid sulfonation method was used. Meanwhile separator surface resistance in those three conditions decreased 32, 80 and 65 times when compared with that of original PP separator, but there were unobvious influence on the separator’s mechanical properties. The influence of reaction temperature, reaction time and sulfonation concentration on separator was analysized. When the reaction temperature was 90℃, the reaction time was 3 min, and sulfonation concentration was 16.6%, there are not only significant improvement in the PP separator properties, but also a good balance between production costs.
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