Electrolytes have been shown to be a major source of poor safety response of Li ion cells. The physical hazards associated with conventional LiPF6 and carbonate-based electrolytes are well documented and include high volume gas decomposition products at elevated temperature, large combustion enthalpy and flammability of solvent vapor. However, the physical and health hazards of the decompositions products can be often overlooked. Electrolyte additives proposed to reduce gas generation and mitigate flammability have not gained much traction, in general, because of the trade-off in cell performance. To maintain cell performance, quantities of additives are generally introduced in fractions <10% which significantly decreases the efficacy of the additive. New additives need to be developed in order to strike the balance between improving abuse tolerance and maintaining performance.
Safety response of Li ion batteries is increasingly recognized as a critical performance requirement for commercial adoption of this chemistry, especially in large scale vehicular applications. The development of increasingly safe battery systems requires continued improvements in cell thermal stability as well as new pack and vehicle designs with rigorous and redundant safety controls. There are many advanced materials being developed and characterized in industry, universities, and national laboratories for Li ion batteries. These materials are often developed primarily for improved performance such as energy density, specific energy, power capability, low temperature response, cycle lifetime, and cost. Safety is often a property determined after the development phase. Safety and thermal stability should become a prime consideration in the initial development and material selection process. There is certainly no need for a “safe” battery that does not perform but also there is no need for a high performance battery that is unsafe.
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