At the length scale of electrode particles, interfacial reaction and/or bulk diffusion may determine rate-performance of lithium ion batteries (LIBs). In a conventional cell, in which electrodes are composed of active materials, binders, conductive agents, and current collectors, the mixtures of different materials result in a complex architecture, posing a great challenge to extract the intrinsic kinetic parameters of the electrode materials. In this work, we conduct single-particle experiments to directly measure the particle-level kinetics, and elucidate the rate-performance determining factors in LIBs. The scheme of our single-particle measurements is shown in Figure 1 [1]

Li_1-xNi_0.8Co_0.15Al_0.05O₂ (NCA) is chosen as the model electrode material because of its extensive commercial utilization in LIB cathodes [2]. Here, for the first time, NCA single-particle kinetic parameters, including bulk diffusivity and exchange current density, at different states of charge (SOC) and particle sizes are systematically investigated using electrochemical impedance spectroscopy (EIS) and potentiostatic intermittent titration technique (PITT). Based on these obtained particle-level kinetic parameters, we will directly evaluate the relative kinetic contributions to overpotential at the particle level as a function of SOC and particle size, using Biot number analysis [3,4]. In coordination with the experiments, single-particle electrochemical simulations that take particle geometry, interface transport, and surface reactions into account are performed with EIS and PITT conditions. The synergic integration of experiments and simulations will examine and interpret the bulk and interfacial kinetics of NCA single particles. The dependence of these particle-level characteristics on other variables such as cathode composition, primary crystallite size, temperature, cycling history, and electrolyte composition will be discussed.

Acknowledgments

This work was supported as part of the North East 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 # DE-SC0012583. P-cT thanks the Ministry of Science and Technology, Taiwan (MOST 104-2917-I-006-006), for financial support.

References

[1] I. Uchida et al., J. Power Sources, 68, 139 (1997).

[2] R. Amin et al., J. Electrochem. Soc., 162, A1163 (2015).

[3] Juchuan, Li et al., J. Phys. Chem. C, 116, 1472 (2012).

[4] C. Montella et al., J. Electroanal. Chem., 518, 61 (2002).