Designing High-Temperature Stable Electrolytes: Insights from the Degradation Mechanisms of Boron-Containing Additives

With the increasing energy density and expanding applications of lithium-ion batteries, the demand for enhanced high-temperature performance has grown significantly. Although previous studies have attempted to improve the high-temperature stability through electrolyte modifications, the underlying failure mechanisms and the rational design principles for suitable electrolyte systems remain insufficiently understood. This study focuses on electrolytes containing boron-based additives, particularly lithium tetraborate, which exhibits excellent rate capability and impressive low-temperature performance but suffers from instability at elevated temperatures. Our investigation reveals that high-temperature battery failure is not solely attributed to aluminum current collector corrosion and the thermal instability of the bulk electrolyte but also to interphasial instability. These include detrimental side reactions catalyzed by Ni-rich cathodes and compromised electron-blocking capabilities of interphasial films. Based on these findings, we propose a new design guideline for high-temperature-stable electrolyte solutions, which is validated by the successful application of tris(2,2,2-trifluoroethyl) borate and 1,3,5-trimethyl-1,3,5-tris(3,3,3-trifluoropropyl) cyclotrisiloxane as functional additives. These additives effectively address the identified degradation pathways, resulting in significantly enhanced high-temperature performance. This comprehensive framework provides valuable insights into the rational design of advanced electrolyte systems for lithium-ion batteries that can be operated across a broad temperature range.