High-Energy Lateral Mapping (HELM) Studies of Inhomogeneity and Failure Mechanisms in NMC622/Li Pouch Cells

Abstract

While it is expected that inhomogeneity negatively affects battery performance, a quantitative understanding of the influence of inhomogeneity has remained elusive due to the difficulty of measuring it in a precise and rapid manner. Here, the ability of high-energy synchrotron X-rays to effectively probe the inhomogeneity in battery cathode films is demonstrated both for fundamental studies of single-layer cathode films and for improving manufacturing processes for industrially relevant multilayer stacks. High-energy lateral mapping studies were performed for very high energy density batteries (∼300 Wh/kg) made from NMC622 cathodes and Li metal anodes, where NMC622 denotes Li-(Ni 0.6 Mn 0.2 Co 0.2 )O 2 . It was first demonstrated for a multilayer pouch cell (7 layers, ∼3 mm thick) that both local and long-range variations in the NMC loading can be precisely quantified, allowing the quality of the coating process to be assessed. Next, it was shown that for a single cathode layer extracted from a pouch cell battery cycled to failure that local variations in the cathode state-of-charge (SOC) can be mapped with a sensitivity of about 0.1%. In this manner it was possible to identify three hot spots in which the local performance was much worse than for the rest of the cell as well as to gain insights into the specific failure mechanisms affecting both these local regions and the cell as a whole.

Enabling Extreme Fast‐Charging: Challenges at the Cathode and Mitigation Strategies

“…heterogeneities are due to heterogeneous cell build geometry, [64,111] active material loading, [112] carbon and binder additives, [113] and electrolyte wetting effects. [114] The through-plane heterogeneous utilization is due to electrolyte transport resistances.…”

Multimodal quantification of degradation pathways during extreme fast charging of lithium-ion batteries

“…HEXRD is an in situ, quantitative method used to obtain the amount of dead Li and Li x C 6 species in cells, as well as cathode and anode SOCs over XFC cycling. [6][7][8]27,[45][46][47] By rastering a millimeter-sized X-ray beam over the entire pouch cell (∼14 cm 2 cross-sectional area) in the discharged state, one can obtain both local (mm-scale) and global (electrode-scale) information about LLI from irreversibly plated Li and dead lithiated graphite, 8,29,30 along with the cathode SOC. 45 The high X-ray energy, ux, and area detectors available at synchrotron sources allowed for such non-destructive analyses in a reasonable amount of time (under 3 hours).…”

“…[6][7][8]27,[45][46][47] By rastering a millimeter-sized X-ray beam over the entire pouch cell (∼14 cm 2 cross-sectional area) in the discharged state, one can obtain both local (mm-scale) and global (electrode-scale) information about LLI from irreversibly plated Li and dead lithiated graphite, 8,29,30 along with the cathode SOC. 45 The high X-ray energy, ux, and area detectors available at synchrotron sources allowed for such non-destructive analyses in a reasonable amount of time (under 3 hours). We have previously used HEXRD to quantify the amount of irreversibly plated Li, dead LiC 6 , and dead LiC 12 over the entire cell 8 and examined the spatial collocation of plated Li, dead Li x C 6 species, and the loss of Li in the cathode in the same cells studied in this work.…”

Expansion-Tolerant Lithium Anode with Built-In LiF-Rich Interface for Stable 400 Wh kg–1 Lithium Metal Pouch Cells

“…The overall battery performance is one of the best among the recently reported Ah level Li metal pouch cells using a high nickel cathode (Figure d, Table S3 and Figure S9). ,,− …”