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

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–x Ni1/3Mn1/3Co1/3O2 (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.

Detection of a Cobalt-Containing Interphase at the Li6PS5Cl-NMC111 Interface by In Situ μXANES and EIS

“…Instead, point contacts between the solid electrolyte and active material particles are the locations of electrochemical activity. 17,30 Evidence of an interphase region containing reduced Co 2+ was observed above. From the EIS, a high initial impedance was observed for uncoated ASLBs.…”

“…We have previously reported spatially-resolved non-uniformity in the electrochemical reaction during ASLB cycling in 120 μm thick cathodes. 17 In such a thick cathode with 70% CAM, the maximum gradient in 1-x was measured to be 29% of the total cyclable cathode capacity.…”

“…This was important for our system, which we previously found to be transport-limited, making kinetics difficult to characterize using EDXRD data alone. 17 However, they are usually more simplistic than physics-based models, sacrificing some accuracy for ease of interpretation. For example, current flow in liquid electrolyte is not solely a conduction phenomenon.…”

“…We have previously reported an operando analysis of Li + and e − conduction across a composite cathode based on Li-Ni 1/3 Mn 1/3 Co 1/3 O 2 (NMC111) and Li 6 PS 5 Cl (LPSC) during initial cycling. 17 This analysis indicated that conduction during initial cycling was subject to high tortuosity factors (τ 2 ) for both the LPSC and NMC phases. Because cathode performance was limited by conduction, we were unable to infer information about kinetic phenomena or the active surface area between the NMC and LPSC.…”

Methods for Tomographic Segmentation in Pseudo-Cylindrical Coordinates for Bobbin-Type Batteries

“…Within batteries, it is well established that the relative ease of ionic and electronic conductions in an electrode is highly relevant. Specifically, inhomogeneity in electrode utilization is largely dependent on the effective ionic and electronic conductivities. , As a result, it is important to consider the ion and electron sources and sinks when analyzing an electrode. In the case of commercial Zn–MnO 2 batteries, this complicates radial analyses if the current collecting pin is off-center.…”