Investigation of Transport and Kinetic Nonideality in Solid Li-Ion Electrodes through Deconvolution of Electrochemical Impedance Spectra

Abstract

The development of Li-ion battery management systems (BMSs) is highly dependent on high fidelity computer simulations. In traditional physics-based models (PBMs), Fick’s law coupled with the Butler–Volmer equation has been employed to describe both Li-ion diffusion and solid/liquid interfacial Li-ion intercalation/deintercalation, but this methodology makes the primary assumption that there is no nonideality caused by Li–Li interactions. Such nonideality phenomena are usually described by the activity coefficient (γ) of Li-ions in a solid solution. With the nonideality, the activity of Li-ion species is not equivalent to the concentration of Li-ions. This research has demonstrated, through the deconvolution of electrochemical impedance spectra, that significant nonideality exists in the solid active materials during charge/discharge cycles, and it leads to nonlinear variation of both transport and kinetic parameters of the electrodes. We also show that PBMs with new pre-factors derived from nonequilibrium thermodynamics of concentrated solution theory can make battery-level predictions that are consistent with EIS data. The pre-factors developed in this paper are functions of the activity coefficient of the solid phase. They show a three order-of-magnitude variation for diffusivity in the solid active material and a one-to-two order of magnitude change in the reaction rate constant at the solid/liquid interface. The results presented here could provide baseline parameters for PBMs and improve their accuracy for high-fidelity BMSs.

Low-Temperature Lithium Plating/Corrosion Hazard in Lithium-Ion Batteries: Electrode Rippling, Variable States of Charge, and Thermal and Nonthermal Runaway

“…The discharge profile is also completely devoid of the phase change response for graphite (refer to our previous publication on the same 50Ah cells for delineation). 45,46 As mentioned above, after eight RT cycles, this particular cell underwent catastrophic cell failure by nonthermal runaway and venting. Operationally, this meant that the pressure valve opened and the safety fuse was triggered, which led to the instantaneous drop in voltage.…”

“…When correlating this region with graphite (Figure 5b), a pronounced Raman peak at 1837 cm −1 was observed and was attributed to vibrations from Li carbide (Li− CC−Li) bonds. 46 To form Li 2 C 2 , the Li 0 corrosion reaction can facilitate neighbor−neighbor EC reduction to adsorbed acetylene and further reaction to Li 2 C 2 (refer to Figure S6 in the Supporting Information for more details regarding the reaction mechanism). The same 1837 cm −1 peak can be observed at various locations on the graphite electrode, including regions of high-curvature, ripple peaks near the edge, and the bottom edge.…”

“…Qualitatively, well-resolved A 1g and E g bands are observed for NMC electrodes at high curvature, which indicates higher degrees of lithiation ( I 595 / I 474 ∼ 1.81). When correlating this region with graphite (Figure b), a pronounced Raman peak at 1837 cm –1 was observed and was attributed to vibrations from Li carbide (Li–CC–Li) bonds . To form Li 2 C 2 , the Li 0 corrosion reaction can facilitate neighbor–neighbor EC reduction to adsorbed acetylene and further reaction to Li 2 C 2 (refer to Figure S6 in the Supporting Information for more details regarding the reaction mechanism).…”

Improving the Reaction Kinetics by Annealing MoS2/PVP Nanoflowers for Sodium-Ion Storage

“…At an electrolyte/electrode interface, EIS technology is an efficient technique to determine the kinetics of charge transfer [ 31 , 32 , 33 ]. In the Nyquist plots shown in Figure 4 e, a single depressed semicircle in the high-frequency region indicated the charge transfer resistance (Rct), and the sodium-ions diffusion ability, also known as the Warburg impedance (Zw), was indicated by the inclined line in the low-frequency region [ 34 , 35 , 36 ].…”

Degradation Diagnosis of Li(Ni0.5Mn0.2Co0.3)O2/Li Half-cell by Identifying Physical Parameter Evolution Profile Using Impedance Spectra During Cycling

“…41 The relevant equations are transferred from the time domain into the frequency domain. 43 Each dependent variable is expressed as a sum of a steady-state part plus a small perturbation (concentration is used as an example),…”