The Effect of Electrolyte Composition and Additives on Lithium Plating during Low Temperature Charging

Abstract

There is considerable international interest in the exploration of the icy moons of Jupiter and Saturn, particularly Europa, Enceladus, Ganymede, Titan and Calisto. NASA is currently considering a mission to the surface of Europa, where the average temperature is approximately -170 °C (for comparison, Mars has an average surface temperature of -63 °C). Such extreme temperatures pose serious challenges for batteries which are used either as the primary power source or to store energy from photovoltaics (PVs) or radioisotope thermoelectric generators (RTGs). Additionally, low temperature rechargeable battery operation is of considerable interest to the automotive and aviation industries, where low temperature performance and decreased lifetime still remain as significant hurdles to overcome. To enable these potential missions to icy moons, the Electrochemical Technologies Group (ETG) at the Jet Propulsion Laboratory (JPL) has engaged in development of long-life rechargeable batteries for continuous operation at low temperatures. All-carbonate based lithium-ion electrolytes, as well as solutions containing ester co-solvents, were evaluated after drawing from experience of developing cell chemistries for past and present missions, including the Mars Exploration Rovers (MER) and the Mars InSight program. One major issue to overcome for long life low temperature battery is to prevent lithium plating during charging. Here, we study the effects of electrolyte composition and electrolyte additives on the low temperature charging in three-electrode laboratory cells. Additives, such as vinylene carbonate (VC), are generally added to the electrolyte to form protective films on the electrodes which prolong life at ambient temperatures, however, these protective films can impede lithium intercalation kinetics and cause significant problems during charging at low temperatures. Most additives that were studied lowered cathode film resistance but increased anode SEI resistance, leading to an imbalance between the electrodes. This led to a substantial increase in lithium plating at low temperatures. Electrolyte compositions were investigated using three-electrode experimental cells consisting of MCMB carbon anodes, LiNiCoAlO2 cathodes (electrodes fabricated by Enersys-Quallion, LLC), and lithium reference electrodes, at different temperatures using a combination of tests, including electrochemical impedance spectroscopy (EIS), linear micro-polarization and Tafel polarization. Low temperature cycling was carefully studied using differential analysis (dQ(mAh)/dV) as a means to estimate the amount of lithium that was plated during the charge. The effect of charge rate and charge voltage upon this behavior, pulse discharging, and low temperature discharge after room temperature charging were also investigated. Using a methyl propionate-based electrolyte formulation containing a beneficial additive, we did not observe the presence of lithium plating during charging at -30 °C using C/5 rates and were able to suppress lithium plating to an estimated 11% of the total capacity at -50 °C. ACKNOWLEDGEMENT 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 supported by the NASA Game Changing Development Program.