(Invited) Systematic Study of Electrolyte Components and Their Effects on the Fast Charging of High Energy Density Li-Ion Cells

Energy density, cost and safety are, more than ever, the most significant barriers to overcome in order to increase the wide acceptance of Li-ion batteries (LIBs) in electric vehicles (EVs). 1 The U.S. Department of Energy (DOE) has set ultimate goals for battery electric vehicles (BEVs), which include reducing the production cost of the battery pack to $150/kWh, increasing the electrical range of the battery to 300 miles, and decreasing the charging time to 15 minutes or less. 2 Increasing electrode thickness, and hence increasing active material loading, is an effective way to achieve these energy density and cost targets. 3 The caveat, however, is that thicker electrodes fail during fast charging. One of the solutions for enabling extreme fast charging while retaining most of the battery energy can be achieved through the significant enhancement of the Li-ion mass-transport in electrolytes such that enough Li ions are available for intercalation in graphite. The mass transport of Li-ions can be evaluated by two macroscopic characteristic values: 1) the Liions ionic conductivity that is related to the total flux of charge carriers, 2) the Liion transference number that is related to the fraction of the total current that is carried by Liions. An electrolyte with both higher Liions conductivity and transference numbers is ideal for higher Liions transport, and hence would be a step toward realizing cells with higher charging rates. The fast charging performance of high-energy density (NMC811/graphite) Li-ion cells is studied when different electrolytes were used. The effect of electrolyte components and their effect of the electrode materials, electrolytes and electrolyte/electrode interfaces were studied and will be presented. (1) Needell, Z. A.; et al. Potential for Widespread Electrification of Personal Vehicle Travel in the United States. Nat. Energy 2016 , 1 (9). (2) Howell, D.; et al. Enabling Fast Charging: Enabling Fast Charging: A Technology Gap Assessment. 2017 , No. October. (3) Du, Z.; et al. Understanding Limiting Factors in Thick Electrode Performance as Applied to High Energy Density Li-Ion Batteries. J. Appl. Electrochem. 2017 , 47 (3), 405–415.