The Role of Separator Thermal Stability in Safety Characteristics of Lithium-ion Batteries

Abstract

The thermal instability of polymer separators severely threatens the safety characteristics of lithium-ion (Li-ion) batteries. Separators will melt, shrink, vaporize, and collapse under high temperatures, leading to internal short circuits and thermal runaway catastrophes of the cell. Therefore, the amelioration of battery safety challenges benefits from a fundamental understanding of separator behaviors under thermally abusive scenarios. This work investigates the role of separator thermal stability in modulating Li-ion cell safety performance. Three types of separators made of commercially available cellulose, trilayer polypropylene/polyethylene/polypropylene, standard polypropylene, and an in-house modified graphene-polydopamine coated separator are fabricated in custom single layer pouch cells and subjected to accelerating rate calorimeter (ARC) tests to investigate dynamic thermo-electrochemical interactions. The safety hazards of 18650 cylindrical cells assembled with different types of separators are predicted using a verified ARC computational model to compare the effects of separator heat resistance on cell-level thermal runaway risks. This study reveals the thermally robust mechanisms of diverse separator microstructures, indicating how the in-house modified graphene-polydopamine coated separator significantly enhances the safety limits of Li-ion batteries.

Towards separator safety of lithium-ion batteries: a review

“…14,15 Especially, the overcharge state not only elevates the temperature inside the battery but also causes the destruction of the electrode crystal structure and the decomposition of the electrolyte; these conditions all affect the role of the separators and greatly influence battery safety. 12,16,17 According to the separator failure mechanism, modifying the separators and ensuring the safety of the LIBs under complex conditions are of great necessity. 18 Firstly, the heat resistance temperature of the separator should be improved to prevent uncontrollable thermal conditions.…”

“…14,15 Especially, the overcharge state not only elevates the temperature inside the battery but also causes the destruction of the electrode crystal structure and the decomposition of the electrolyte; these conditions all affect the role of the separators and greatly influence battery safety. 12,16,17…”

Heat-Resistant Lithium-Ion-Battery Separator Using Synchronous Thermal Stabilization/Imidization

“…In addition, the short circuit incident accelerates the uncontrollable chemical reaction, and more heat will be released. 11 Severe thermal bursting will dramatically enhance battery operating temperature, and when the temperature polyolefin separator will further shrink or even melt as a result of the explosion. 12 Therefore, commercial polyolefin separators have thermal safety problems when used.…”

“…The polyolefin separator will shrink in extreme environments and eventually lead to a short circuit. In addition, the short circuit incident accelerates the uncontrollable chemical reaction, and more heat will be released . Severe thermal bursting will dramatically enhance battery operating temperature, and when the temperature exceeds the melting point (PP about 165 °C, PE about 135 °C), the polyolefin separator will further shrink or even melt as a result of the explosion .…”

Enhancing the β Phase of Poly(vinylidene fluoride) Nanofibrous Membranes for Thermostable Separators in Lithium-Ion Batteries

“…Apart from the above properties of the separator, safety performance has always been the most concerning and crucial problem that requires urgent settlement . The ceramic nanoparticle coating has been proven to be an effective technique for improving the thermal stability of membranes. − However, traditional coating-modified strategies have not taken the membrane thickness and weight into consideration, which could lead to reduced LIB energy density .…”