Sea Technology

NOV 2017

The industry's recognized authority for design, engineering and application of equipment and services in the global ocean community

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24 st / November 2017 www.sea-technology.com ion batteries are intrinsically unsafe and unsuitable for deployment. But like any high-power-density system, it is necessary to consider appropriate safety measures in their design and use. The Advanced Seal Delivery System (ASDS) fire of 2008 led to significant changes in U.S. Navy testing and safety requirements, and civilian shipping classification agencies have recently released, and continue to develop, test protocols and safety standards for various applications of lithium-ion batteries. Because the U.S. Navy changed their safety requirements after the ASDS fire, GA began developing a system to im- prove safety of a battery assembly by preventing propaga- tion of a single-cell thermal runaway event. The Navy's re- vised testing scheme noted that some individual cells would intentionally be ignited to induce thermal runaway, and manufacturers had to develop ways to prevent that induced failure from cascading to other cells, starting a chain reac- tion and thus destroying the entire battery (and quite pos- sibly the host platform). GA has developed a cell-level fault-tolerant system ar- chitecture that enables safe deployment of lithium-ion bat- teries and passes the required testing. There are several key aspects to the architecture, including the use of smaller cells (limiting the amount of energy initially released), and vari- T he ever-increasing demand for safe subsea energy stor- age and delivery with greater energy densities is clear to those who use and need that energy on a daily basis. New technologies in this area may not only improve performance of existing platforms and operations, but enable new platforms previously considered too energy intensive. Two technologies that are undergoing rapid development and deployment now are lithium-ion bat- teries and fuel cells. Although the core concepts of batteries and fuel cells have been around for many decades, recent advances are proving there is a lot of improvement still to be found. Providing access to the performance of lithium- ion batteries, while ensuring maximum safety, has led Gen- eral Atomics (GA) to develop its Lithium-ion Fault Tolerant (LiFT) system architecture. Advances in fuel cell technology continue to show greater performance; GA researchers have developed safe, robust and high-capacity solid fuels that en- able generation of pure hydrogen and oxygen on demand for optimal system performance. Lithium-Ion Batteries Lithium-based battery chemistries continue to develop and improve in performance and safety, yet their deploy- ment has been hampered by both real accidents and per- ceived shortcomings. There is a perception that tried-and-true lead-acid batter- ies, having been in use for well over a century, are safe and stable. However, noting just two references, a study by the U.S. National Highway Traffic Safety Administration found that lead-acid battery explosions in 1993 alone injured 2,280 people severely enough to have required hospital treatment; and, in 2015, the Australian government noted there had been 37 lead-acid battery accidents related to mining operations since 2004. Finally, as all submariners know, lead-acid batteries emit explosive hydrogen during charging operations. Therefore, safe operations of a lead-ac- id battery system must include ventilation to mitigate com- bustion or even explosion. Lithium-ion batteries have also had high-profile failures in automobiles, aircraft, consumer products and submers- ibles. These failures have led some to believe that lithium- The Future of Subsea Energy Storage Building More Powerful, Safer Batteries and Fuel Cell Systems By Dr. Jerome E. Gormley The LiFT battery system.

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