Polyethylene battery separator with auto-shutdown ability, thermal stability of 220°C, and hydrophilic surface via solid-state ultraviolet irradiation

To assure the safety of the lithium-ion battery, the separator is required to have good thermal stability. Because the single-layer polyethylene (PE) separator can only tolerate a temperature of 130°C, it is seldom employed currently by lithium-ion battery manufacturers although its cost is low. In this article, we modified PE separator chain structure through solid-state ultraviolet (UV) irradiation method to achieve a separator with composite structure of ∼40% crystallized PE and ∼70% gel content. Approximately 40% crystallized PE chains fulfill the task of auto-shutdown at 130°C through melting and filling the pores. At the same time, the PE separator can maintain integrity till 220°C because of its highly cross-linked chain structure. Besides, the modified PE separator is hydrophilic with a water contact angle of 33° after UV treatment and is able to absorb more electrolyte. However, the tensile strength and elongation at the break decreased because the cross-linking network increased the rigidity. Nevertheless, these values still meet the requirements as the separator for lithium-ion battery. Considering the low cost and easy preparation, current cross-linked PE separator has potential to be used in lithium-ion batteries for various applications, including electric vehicles and energy storage purpose. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132 , 42169.