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

ABSTRACT 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.