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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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The Electrochemical Society Interface • Fall 2010 49 L arge-scale stationary battery energy storage has been under development for several decades with the successful use of pumped hydroelectric storage as a model. Several large battery demonstration projects have been built and tested under a variety of electric utility grid applications. In addition, renewable energy sources such as wind and photovoltaics may require energy storage systems. While these applications are new and expanding, the shift toward an expanded role for battery energy storage in the de-regulated electricity market became evident by the late 1980s and early 1990s. Studies by Sandia National Laboratories identified opportunities for battery energy storage in the generation as well as on the transmission and distribution segments of the electric grid. Reports 1,2 from these studies describe battery storage application requirements and provide a preliminary estimate of potential costs and benefits of these applications for the U.S. electric grid. Applications fall into two broad categories: energy applications and power applications. Energy applications involve storage system discharge over periods of hours (typically one discharge cycle per day) with correspondingly long charging periods. Power applications involve comparatively short periods of discharge (seconds to minutes), short recharging periods, and often require many cycles per day.Detailed performance criteria for applications such as peak shaving and load leveling (energy applications) as well as frequency and voltage regulation, power quality, renewable generation smoothing and ramp rate control (power applications) are described elsewhere.2 Generally, the most important requirements have been the need for low cost, flexible designs, proven battery technologies, and reliable performance.While many battery technologies have been proposed and developed for electrical energy storage applications, only a handful have actually been used in fielded systems. Technologies that are used in fielded systems include leadacid, nickel/cadmium, sodium/sulfur, and vanadium-redox flow batteries. Cost effective energy storage systems have been identified 3 for utility, enduser, and renewable applications. Other battery technologies, such as the many lithium-ion batteries, are less matureand not yet well-developed for these applications.

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