Lithium-Rich NMC Cathodes and Si-C Anodes in Low Flammability Li-Ion Battery Electrolytes

Li-ion batteries were successfully employed in our Mars planetary surface missions, e.g., robotic Mars Rovers, Spirit, Opportunity and Curiosity.  However, the future space missions involve human exploration and demand further advances both in energy densities and safety. For example, astronaut Extra Vehicular Activity requires safer batteries with a specific energy in excess of 300 Wh/kg, albeit with moderate cycle life. We have therefore been developing advanced cell components, i.e., high specific capacity cathodes and anodes for improving the specific energy and also low-flammability electrolytes for enhancing safety.

         Our cathode materials belong to the class of Li-rich, layered-layered composites (of Li₂MnO₃ and LiMO₂)¹.  Over the last few years, we have: i) optimized their compositions and modified synthesis to maximize specific capacities and tap densities, ii) identified new simpler synthetic methods, based on high energy ball–milling² and molten salt fluxes iii) and developed new surface coatings, e.g., AlPO₄to improve interfacial and cyclic stability.  To augment the in-house development, we have also evaluated materials from commercial materials suppliers.

         A critical component to the performance of the high-energy cathode and anode materials is electrolyte, especially due to the high cathode potentials resulting in electrolyte oxidation and the need to passivate anode for kinetic stability.  Further, to improve safety, we adopted low-flammability electrolytes with suitable non-flammable co-solvents, and/or flame retardant additives, e.g., triphenyl phosphate.³ Also, to improve the interfacial stability, especially both cathode and anode, various electrolyte additives, such as vinylene carbonate and lithium bis(oxalate) borate were studied in addition to the surface coatings on cathode particles.  We will present the performance of the AlPO₄-coated Li-rich NMC cathode against MPG111 anode in different low-flammability electrolytes .  Some of these electrolytes have also shown excellent performance in 4V systems, giving comparable cycle life in prototype cells .

         In this paper, we will present the performance of some of our recent Li-rich NMC cathode materials and Si-C anode composite anodes in conjunction with various low flammability electrolytes.  The effect of electrolyte, as well surface coating, on the cathode activation process as well as the (transition) metal leaching from the cathode will be examined.  Finally, the performance of the low flammability electrolyte in large-format prototype cells will be presented.

Acknowledgments

The work described here was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration (NASA) and was supported by the Office of Chief Technologist’s Advanced Space Power Systems project.

References 

1. J. R. Dahn et al, J. Electrochem. Soc., 149, A778, 2002; K. Amine et al, Electrochem. Solid-State Lett., 6, A183, 2003; M. M. Thackeray et al,  Electrochem. Comm., 9, 787 (2007); A. Manthiram et al, J. Electrochem. Soc., 155, A635 (2008).
2. W. C. West, J. Soler, and B. V. Ratnakumar^, J. Power Sources (in press).
3. M.C. Smart, F. C. Krause, C. Hwang, W. C. West, J. Soler, G. K. S. Prakash, and B. V. Ratnakumar, 220^th ECS Fall Meeting, Boston, MA, Oct. 2012; 222^nd ECS Fall Meeting, San Francisco, CA , Oct 24-30 (2013).