A report presents results of research on carbonate-based electrolytes to improve the low-temperature-performances of lithium-ion rechargeable electrochemical cells. The loss of performance with decreasing temperature is attributable largely to a decrease of ionic conductivity and the increase in viscosity of the electrolyte. What is needed to extend the minimum operating temperature from 20 °C down to –40 °C is a stable electrolyte solution with relatively large low-temperature conductivity, relatively small low-temperature viscosity, a large electric permittivity, adequate coordination behavior, and appropriate ranges of solubilities of liquid and salt constituents.
This work was done by Marshall Smart, Ratnakumar Bugga, Chen-Kuo Huang, and Subbarao Surampudi of Caltech for NASA's Jet Propulsion Laboratory. To obtain a copy of the report, "Rechargeable Lithium-Ion Cells with Improved Low-Temperature Performance with Novel Carbonate-Based Electrolyte," access the Technical Support Package (TSP) free on-line at www.nasatech.com/tsp under the Materials category. NPO-20407
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Update on electrolytes for low-temperature lithium cells
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Overview
The document is a technical report detailing advancements in electrolytes for low-temperature lithium-ion cells, authored by a team from the Jet Propulsion Laboratory (JPL) under NASA. The focus is on developing novel carbonate-based electrolytes that enhance the performance of lithium-ion batteries in cold environments, which is crucial for applications in space and other extreme conditions.
The report outlines the challenges associated with traditional electrolytes, such as ethylene carbonate (EC) and dimethyl carbonate (DMC), which tend to become highly viscous and lose ionic conductivity at low temperatures. To address these issues, the authors emphasize the importance of optimizing several parameters, including the dielectric constant, viscosity, and salt solubility of the electrolyte solutions. A viable electrolyte must not only exhibit high conductivity at low temperatures but also possess good electrochemical stability across a wide voltage range (0 to 4.5V), form stable passivating films on electrodes, and maintain thermal and chemical stability.
The research involved evaluating various electrolyte formulations, leading to the selection of six promising candidates for further testing in prototype lithium-ion cells. The report highlights the successful demonstration of these electrolytes in experimental cells, showcasing their improved low-temperature performance and cycle life. Notably, a specific formulation containing 1.0 M LiPF6 in a ternary mixture of EC, DEC, and DMC was found to deliver approximately 60% of its room temperature capacity at -30°C, indicating significant advancements in low-temperature battery performance.
The document also includes a disclaimer regarding the endorsement of specific commercial products and emphasizes that the work was conducted under NASA's contract, ensuring that the findings are rooted in rigorous scientific research. Overall, the report presents a comprehensive overview of the innovative approaches taken to enhance the functionality of lithium-ion cells in low-temperature environments, which could have far-reaching implications for both space exploration and terrestrial applications. The advancements in electrolyte technology are positioned to improve the reliability and efficiency of lithium-ion batteries, making them more suitable for a variety of demanding conditions.
