Effects of 2,4-difluorobiphenyl as an Electrolyte Additive to Enhance the Overcharge Protection of Cylindrical LiCoO₂/graphite Batteries

摘要

Combined with the use of a pressure-sensitive cap, 2,4-difluorobiphenyl (DFBP) is investigated as anovercharge safety additive for the protection of 4.4 V commercial cylindrical LiCoO2/graphitebatteries. DFBP can be electrochemically polymerized when the LiCoO2 is charged to approximately4.60 V (vs. Li+/Li), resulting in the release of large amounts of gases; this release can be utilized toactivate the current interrupt device (CID) and solve overcharge risk issues. With the addition of DFBPto the electrolyte from 0–6% (wt.%), the CID activation status of charge (SOC)% of LiCoO2/graphitebatteries decreases from 175% to 140.5%, and quite noteworthy the DFBP amounts of 2% to 4% in theelectrolyte can be used to prevent the overcharge explosions. In addition, it is also demonstrated thatthe DFBP additive has no obvious negative influences on the cycle and temperature performances ofLiCoO2/graphite batteries under normal conditions, indicating the promising prospect of DFBP as anovercharge safety additive for the protection of commercial cylindrical LiCoO2/graphite batteries.