High-Voltage, Lithium-Ion Research for Transportation Applications

An obvious way to increase the energy output of current lithium-ion chemistries is to increase the upper cutoff voltage to which cells are charged. Typical, layered NMC-based cathodes can generally cycle about ~60% of their theoretical capacity, leaving substantial stores of lithium, and energy, untapped. This limit (~60%) is due in part to the demanding cycle-life requirements of certain applications (e.g., transportation) where degradation mechanisms can prove too severe at high voltages and high states of delithiation for acceptable cell ageing. Argonne National Laboratory is conducting an extensive study into the degradation mechanisms at play when lithium-ion cells are operated at high voltages (e.g., ≥4.4 V vs. graphite). Key questions of interest focus on the role of surface vs. bulk effects, cycle-performance in full-cell systems, and the proper analysis of data to ensure meaningful and reliable results. This presentation will discuss the process and protocols of the project, some initial results, and future directions of research.