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. 2023 Feb 2;8(2):1273-1280.
doi: 10.1021/acsenergylett.2c02699. eCollection 2023 Feb 10.

Lithiation Gradients and Tortuosity Factors in Thick NMC111-Argyrodite Solid-State Cathodes

Alyssa M Stavola  1 , Xiao Sun  2 , Dominick P Guida  1 , Andrea M Bruck  1 , Daxian Cao  2 , John S Okasinski  3 , Andrew C Chuang  3 , Hongli Zhu  2 , Joshua W Gallaway  1
Affiliations

Lithiation Gradients and Tortuosity Factors in Thick NMC111-Argyrodite Solid-State Cathodes

Alyssa M Stavola et al. ACS Energy Lett. .

Abstract

Achieving high energy density in all-solid-state lithium batteries will require the design of thick cathodes, and these will need to operate reversibly under normal use conditions. We use high-energy depth-profiling X-ray diffraction to measure the localized lithium content of Li1-xNi1/3Mn1/3Co1/3O2 (NMC111) through the thickness of 110 μm thick composite cathodes. The composite cathodes consisted of NMC111 of varying mass loadings mixed with argyrodite solid electrolyte Li6PS5Cl (LPSC). During cycling at C/10, substantial lithiation gradients developed, and varying the NMC111 loading altered the nature of these gradients. Microstructural analysis and cathode modeling showed this was due to high tortuosities in the cathodes. This was particularly true in the solid electrolyte phase, which experienced a marked increase in tortuosity factor during the initial charge. Our results demonstrate that current distributions are observed in sulfide-based composites and that these will be an important consideration for practical design of all-solid-state batteries.

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Conflict of interest statement

The authors declare no competing financial interest.

Figures

Figure 1
Figure 1
(a) The concept of an ASLB with a thick 110 μm cathode, with EDXRD data taken in six 20 μm slices to observe nonuniformity through the cathode thickness. (b) The structure of NMC111. (c) Operando EDXRD for a cell with a 50 μm thick cathode at C/10. Composition was 70% CAM with a coating.
Figure 2
Figure 2
Operando EDXRD data for initial cycling of NMC111-LPSC cathodes as a function of cathode composition. (a) 80% cathode active material (CAM); (b) 70% CAM; (c) 40% CAM; (d) 70% CAM with an LLSTO-coated NMC. For each cell, local Li content (1 – x) is shown correlated to the voltage profile.
Figure 3
Figure 3
(a) Lithiation profiles for each cell at the midpoint of charge 1. These profiles are marked by note 1 and dashed lines in Figure 2. (b–e) Spatially resolved total reaction amounts in Δx during each cycling stage for (b) 80% CAM; (c) 70% CAM; (d) 70% CAM with a cathode coating; and (e) 40% CAM.
Figure 4
Figure 4
(a) Effective electronic conductivity σel,eff and ionic conductivity σion,eff of composite cathodes as a function of mass% CAM. Open markers at 70 mass% are coated CAM data. (b) Fitted tortuosity factor of each phase as a function of phase fraction.
Figure 5
Figure 5
COMSOL simulations during initial charge showing local Li content (1 – x) as a function of cathode depth: (a–c) 70% CAM cell with greater reaction at the current collector. (d–f) 80% CAM cell with greater reaction at the separator.
Figure 6
Figure 6
Peak bifurcation of the NMC111 (003) reflection during charge 1, as a function of time and depth in the cathode. (a) 70% CAM with a coating. (b) Uncoated 70% CAM. Photon energies of the bifurcated peaks are shown, with the right and left peaks given by circles and squares. Peak magnitude is indicated by the marker size. Color-shaded regions show the weighted standard deviations of the photon energies. Dashed lines correspond to the times of the data in Figure S16. The conclusion is that peak bifurcation was more significant in the uncoated cell.
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