The Research On Self-Activating Overcharge Safety Protection Of Lithium-ion Battery

Lithium-ion batteries are one of the most promising next generation high density energy storage devices due to their high energy density, environmentally-friendly energy and other advantages. The safety issues of lithium-ion batteries are from liquid electrolytes. consist of volatile organic solvents and strong active electrolyte components. A complex series of decomposition reactions occur with generation of gas and heat along with the overcharge of lithium-ion cells, which can lead to thermal runaway and possible explosion.. Therefore, it is very important that the lithium-ion battery voltage remains in the stable range to prevent voltage runaway when the overcharge occurs. Utilization of redox shuttles provides an economic and efficient solution to avoid the overcharge hazard without addition of extra weight or volume to the battery system.It is an effective and convenient way to prevent the voltage run away by adding in the electrolyte with overcharge protection additive. The battery safety is improved by establishing an overcharge protection mechanism inside the battery so as not to result burning and other accidents caused by overcharge. This dissertation studied the overcharge protection effect of the battery when the redox shuttle electrolyte additives is added in the electrolyte.In the first chapter, the lithium-ion battery safety issues and the methods to improve battery performance is summarized. It is found from the analysis and comparison that the overcharge protection additive is a low cost security protection with good effect. Progress in overcharge protection additives is reviewed and the main features and applications of overcharge protection additive is also summarized.The second chapter describes the experimental method. The main research methods are described from the experimental principle, laboratory equipment and other aspects. The condition of the parameter settings is also described.In the third chapter, 4-iodoanisole as an overcharge protection additive is investigated. 4-iodoanisole can play the role of barrier to hinder the voltage from rising rapid during overcharge, which can prevent the uncontrolled voltage from causing security problems. Additives added to the battery do not significantly influence the cycling ability. Adding 5% mass fraction of 4-iodoanisole provides the best overcharge protection.In fourth Chapter, the co-use of additives to improve battery overcharge protection effect is explored. Two kinds of different types of additives in combination are better able to protect the battery by playing each other's performance advantages. The study shows that two additives that can react together make the oxidation potential down so that it can work more timely. The oxidation potential of two mixed additives of 4-iodoanisole and biphenyl moves from 4.5-4.7 V to 4.3 V(vs. Li/Li+). The polymerization reaction of 4IA and BP makes 4IA more easily lose electrons to oxidation so that oxidation potential is reduced. Due to combined effect of two different classes of additives, the implementation of multi-guard for the battery is built to improve the safety performance of the battery. The influence of the additives to the battery cycle performance is also weakened because the amount of additives is reduced.In summary, the redox shuttle electrolyte additives added in the electrolyte is studied in this paper from setting out to enhance the security of the electrolyte. The additives used in the battery can hinder voltage rising fast during overcharge and play good buffer role in maintaining electrolyte voltage stability, which improve the safety performance of the battery and is conducive to promoting the use of power lithium-ion batteries.