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The single largest barrier to adoption of electrochemical storage in the grid is often stated to be the value of a battery over the life of the system. To ensure long-term system safety and reliability, batteries must be selected based on application specific requirements and performance characteristics. Our approach to addressing the uncertainty in the performance and cycle life of commercially viable lithium ion batteries for grid storage has been to design studies with multiple chemistries, and conduct long term life cycle evaluations with systematically varied cycling conditions. Namely, we initiated a large-scale, multi-year cycling study of commercial LiFePO4/LFP, LiNixCoyAl1-x-yO2/NCA, and LiNixMnyCo1-x-yO2/NMC cells. This study looks at chemistry specific influences on efficiency and cycle life under variables that include discharge rate, depth of discharge (DoD) and temperature, and is complemented by a calendar aging study. The source of differences in aging behavior was investigated through electrochemical impedance spectroscopy and differential capacity analysis. We compare results to literature to identify the degree to which variations may be expected with manufacturer and version, as products can see manufacturing changes year to year. Understanding variations is critical for lifetime assessment and economic evaluation that is meaningful for installed systems. We further look at how these best-case scenario results from single cell studies may be used as a baseline in moving toward understanding aging in module and system configurations. The overarching goal is to begin to effectively understand laboratory cell studies in a context applicable to grid storage systems. Sandia National Laboratories is a multi-mission laboratory managed and operated by National Technology & Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525. |
