Weakening of mechanical properties of cellulose separator caused by electrolyte immersion and elevated temperature

The separator is an important component of the lithium‐ion batteries (LIBs). Considering the influence of temperature and hygroexpansion effect of cellulose materials, the mechanical properties of cellulose separators in air (dry), electrolyte immersion (wet), and elevated temperature (heated) environments are studied. Firstly, orthogonal experiments were designed and conducted to investigate the effects of various factors on the tensile properties of cellulose separators. Based on the results of the orthogonal test, the cellulose separator and the polypropylene (PP) separator were then subjected to tensile and puncture test under dry and wet condition, respectively. The results show that temperature has slight effect on cellulose separator, while it is known that PP separator has weak thermal stability. The mechanical property of PP separator is not sensitive to the immersion of electrolyte. However, the mechanical strength of cellulose separator is greatly reduced when immersed in electrolyte or exposed to high temperature. The tensile property and puncture property of the cellulose separator are severely decreased in the electrolyte. The mechanical properties of the cellulose separator in the electrolyte are insufficient to ensure battery safety. The hydro‐thermal properties of cellulose separator need enhancement in the future research. POLYM. COMPOS., 40:3857–3865, 2019. © 2019 Society of Plastics Engineers