The Impact of Additives upon the Propensity of Lithium Plating at Low Temperatures in Mcmb-LiNiCoAlO2-Based Li-Ion Cells with Methyl Propionate-Based Electrolytes
It is well known that the deposition of metallic lithium can occur on the carbon anode under certain conditions, rather than the preferred intercalation of lithium.7,8 This process can occur when the lithium intercalation kinetics are significantly slowed at low temperature and the lithium plating reaction becomes more facile, due to its favorable kinetics. In our previous studies9,10, we have shown there to be a strong influence of electrolyte type upon the susceptibility towards lithium plating. For example, we have observed that the use of particular electrolyte additives, such as vinylene carbonate (VC), can increase the propensity of lithium plating when charging at high rates at low temperatures. This increased likelihood of plating is due to retarded lithium intercalation kinetics at the anode due to resistive surface films, and, in the case of VC, improved de-intercalation kinetics at the cathode.
In collaboration with Quallion, we have recently demonstrated improved wide operating temperature range performance of MCMB-LiNiCoAlO2-based prototype cells containing electrolytes with methyl propionate (MP) and ethyl butyrate (EB)4, and more recently with MP-based electrolytes with various additives. In summary, excellent performance was obtained with these cells at low temperature, with discharge rates of 5C at -40oC and 20C at -20oC being supporting with various MP-based formulations, significantly out-performing the baseline, all carbonate-based electrolyte. However, much of the initial evaluation involved charging at moderate rates and temperatures, with the intent of avoiding any lithium plating in the cell.
In the continuation of this study, we have investigated the impact of the electrolyte type, and especially the influence of the electrolyte additives, upon the likelihood of lithium plating when charging at low temperatures. In particular, we have investigated the influence that MP-based electrolytes containing various electrolyte additives play upon the charging behavior at low temperatures. The electrolyte additives studied include mono-fluoroethylene carbonate (FEC), lithium oxalate, vinylene carbonate (VC), and lithium bis(oxalato) borate (LiBOB). To understand the impact of the electrolyte upon the electrode kinetics, studies were performed in three-electrode lithium-ion cells, consisting of MCMB carbon anode and LiNiCoAlO2cathodes (fabricated by Quallion, LLC),using various techniques, including EIS, Tafel, and linear micro-polarization. Some electrolyte formulations were also incorporated into prototype 0.30Ah cells for evaluation (manufactured by Quallion), consisting of a cell design optimized for biomedical applications. The charge characteristics of these cells were evaluated over a range of conditions, including different temperatures, charge rates, and charge voltages. In general, we have observed a negative influence of some of these additives, such as VC and LiBOB, upon the charge acceptance characteristics under certain conditions at low temperature.
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 Engineering and Safety Center (NESC) and the DOE BATT-ABR program.
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