Bohua Wen1 Ping-Chun Tsai1 Yet-Ming Chiang1

1, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States

Over the past several years, reports have emerged of ultrafast charging algorithms for lithium ion batteries [1,2] that in at least one instance [3] is attributed to megahertz frequency modulation of charging/discharging currents. Such algorithms are claimed to dramatically improve active material utilization as well as cycle life, but no mechanisms have been proposed in published work, nor, to our knowledge, have mechanistic studies have been conducted. In this work, we use a recently developed technique [4] in which single electrode particles having capacities of a few nAh can be interrogated with electrodynamic measurements (EIS, GITT, polarization-depolarization) while varying the state-of-charge. This capability allows clean separation of interfacial vs bulk transport limitations at the individual particle level, without complicating factors from typical composite electrode microstructures. To this capability, we have added AC pulse charging and discharging at ultra-low currents (down to picoA) with high-frequency waveforms (up to ~ MHz).
With this capability, we aim to answer a number of questions such as: Are these effects real? Are they significant? And, what are possible mechanisms by which ion transport kinetics in a lithium ion battery are responsive to megahertz frequency excitation?
This work was supported as part of the NorthEast Center for Chemical Energy Storage (NECCES), an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences under Award # DESC0012583.
3. Sherstyuk et al., Extended life battery, US Patent No. 9,966,780B2, May 2018.
4. P.-C. Tsai, B. Wen, M. Wolfman, M.-J. Choe, M. S. Pan, L. Su, K. Thornton, J. Cabana, Y.-M. Chiang, Single-particle measurements of electrochemical kinetics in NMC and NCA cathodes for Li-ion batteries. Energy Environ. Sci., 2018, 11, 860-871.