A number of experimental lithium-ion cells, consisting of MCMB (meso-carbon microbeads) carbon anodes and LiNi0.8Co0.2O2 cathodes, have been fabricated with increased safety and expanded capability. These cells serve to verify and demonstrate the reversibility, low-temperature performance, and electrochemical aspects of each electrode as determined from a number of electrochemical characterization techniques. A number of Li-ion electrolytes possessing fluorinated ester co-solvents, namely trifluoroethyl butyrate (TFEB) and trifluoroethyl propionate (TFEP), were demonstrated to deliver good performance over a wide temperature range in experimental lithium-ion cells.
The general approach taken in the development of these electrolyte formulations is to optimize the type and composition of the co-solvents in ternary and quaternary solutions, focusing upon adequate stability [i.e., EC (ethylene carbonate) content needed for anode passivation, and EMC (ethyl methyl carbonate) content needed for lowering the viscosity and widening the temperature range, while still providing good stability], enhancing the inherent safety characteristics (incorporation of fluorinated esters), and widening the temperature range of operation (the use of both fluorinated and non-fluorinated esters). Furthermore, the use of electrolyte additives, such as VC (vinylene carbonate) [solid electrolyte interface (SEI) promoter] and DMAc (thermal stabilizing additive), provide enhanced high-temperature life characteristics.
Multi-component electrolyte formulations enhance performance over a temperature range of –60 to +60 ºC. With the need for more safety with the use of these batteries, flammability was a consideration. One of the solvents investigated, TFEB, had the best performance with improved low-temperature capability and high-temperature resilience. This work optimized the use of TFEB as a co-solvent by developing the multi-component electrolytes, which also contain non-halogenated esters, film forming additives, thermal stabilizing additives, and flame retardant additives.
Further optimization of these electrolyte formulations is anticipated to yield improved performance. It is also anticipated that much improved performance will be demonstrated once these electrolyte solutions are incorporated into hermetically sealed, large capacity prototype cells, especially if effort is devoted to ensure that all electrolyte components are highly pure.
This work was done by G. K. Surya Prakash of the University of Southern California and Marshall Smart, Kiah Smith, and Ratnakumar Bugga of Caltech for NASA’s Jet Propulsion Laboratory. For more information, download the Technical Support Package (free white paper) at www.techbriefs.com/tsp under the Materials category.
In accordance with Public Law 96-517, the contractor has elected to retain title to this invention. Inquiries concerning rights for its commercial use should be addressed to:
Innovative Technology Assets Management
JPL Mail Stop 202-233 4800 Oak Grove Drive Pasadena, CA 91109-8099 E-mail:
Refer to NPO-45824, volume and number of this NASA Tech Briefs issue, and the page number.
This Brief includes a Technical Support Package (TSP).
Optimized Li-Ion Electrolytes Containing Fluorinated Ester Co-Solvents
(reference NPO-45824) is currently available for download from the TSP library.
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Overview
The document is a technical support package from NASA's Jet Propulsion Laboratory (JPL) detailing advancements in lithium-ion (Li-ion) electrolytes that incorporate fluorinated ester co-solvents, particularly trifluoroethyl butyrate (TFEB). The primary goal of this research is to enhance the safety and performance of Li-ion batteries, especially for future NASA missions to Mars, the Moon, and outer planets, which require batteries capable of operating over a wide temperature range (-60 to +60 °C).
The document outlines the development of multi-component electrolyte formulations that optimize the type and composition of co-solvents. These formulations aim to improve stability, enhance safety characteristics, and widen the operational temperature range. The use of fluorinated esters is emphasized due to their low flammability and favorable properties, which contribute to better performance in extreme conditions. The research also explores the incorporation of electrolyte additives, such as vinylene carbonate (VC) and dimethylacetamide (DMAc), to further enhance thermal stability and high-temperature life characteristics.
Experimental lithium-ion cells were fabricated using MCMB carbon anodes and LiNi0.8Co0.2O2 cathodes to evaluate the performance of these new electrolyte formulations. The results indicated that the fluoroester-based solutions exhibited good reversibility at room temperature and minimal reactivity during formation cycling. Notably, the trifluoroethyl butyrate solutions produced more desirable surface films compared to trifluoroethyl propionate, leading to lower cumulative irreversible capacity losses and higher efficiency values.
The document highlights the promising potential of these optimized electrolyte formulations, suggesting that further refinement could yield even better performance, particularly when used in hermetically sealed large-capacity prototype cells. The research underscores the importance of ensuring high purity in all electrolyte components to maximize performance.
In summary, this technical report presents significant advancements in the development of Li-ion electrolytes with fluorinated esters, showcasing their potential to improve battery performance and safety in extreme environments. The findings are expected to have broader implications for various technological applications beyond aerospace, contributing to the ongoing evolution of rechargeable battery technology.
