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Abstract
In recent years, high-entropy oxides are receiving increasing attention for electrochemical energy-storage applications. Among them, the rocksalt (Co0.2Cu0.2Mg0.2Ni0.2Zn0.2)O (HEO) has been shown to be a promising high-capacity anode material. Because high-entropy oxides constitute a new class of electrode materials, systematic understanding of their behavior during ion insertion and extraction is yet to be established. Here, we probe the conversion-type HEO material in lithium half-cells by acoustic emission (AE) monitoring. Especially the clustering of AE signals allows for correlations of acoustic events with various processes. The initial cycle was found to be the most acoustically active because of solid-electrolyte interphase formation and chemo-mechanical degradation. In the subsequent cycles, AE was mainly detected during delithiation, a finding we attribute to the progressive crack formation and propagation. Overall, the data confirm that the AE technology as a non-destructive operando technique holds promise for gaining insight into the degradation processes occurring in battery cells during cycling.
Highlights
In recent years, high-entropy oxides are receiving increasing attention for electrochemical energystorage applications
Previous investigations using X-ray diffraction (XRD), selected-area electron diffraction (SAED) and transmission electron microscopy (TEM) have shown that the lithiation/delithiation processes rely on a partial conversion mechanism
Even if the outgassing can be excluded as a source of significant acoustic activity, the evolution of C 2H4 is a clear indication of the formation of a solid-electrolyte interphase (SEI) on the anode[13,35,36]
Summary
High-entropy oxides are receiving increasing attention for electrochemical energystorage applications. Recent X-ray absorption spectroscopy (XAS) studies have shown that the initial lithiation/delithiation processes are incomplete and irreversible[16], leading to the formation of a mixture of metals and metal oxides, and that alloying and dealloying reactions with Li are involved in the charge-storage mechanism in the subsequent cycles (typical of ZnO and MgO anodes). Overall, this somewhat limits the possibility of operando investigations beyond the first cycle and, in particular, hinders further understanding of the reaction and degradation mechanisms under realistic conditions. This work aims at improving knowledge of AE monitoring in the field of operando characterization of battery materials
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