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Charge-Discharge Mechanism of High-Entropy Co-Free Spinel Oxide Toward Li⁺ Storage Examined Using Operando Quick-Scanning X-Ray Absorption Spectroscopy.

ABSTRACT: Transition metal high-entropy oxides (HEOs) are an attractive class of anode materials for high-performance lithium-ion batteries (LIBs). However, owing to the multiple electroactive centers of HEOs, the Li⁺ storage mechanism is complex and debated in the literature. In this work, operando quick-scanning X-ray absorption spectroscopy (XAS) is used to study the lithiation/delithiation mechanism of the Cobalt-free spinel (CrMnFeNiCu)₃ O₄ HEO. A monochromator oscillation frequency of 2 Hz is used and 240 spectra are integrated to achieve a 2 min time resolution. High-photon-flux synchrotron radiation is employed to increase the XAS sensitivity. The results indicate that the Cu²⁺ and Ni²⁺ cations are reduced to their metallic states during lithiation but their oxidation reactions are less favorable compared to the other elements upon delithiation. The Mn^2+/3+ and Fe^2+/3+ cations undergo two-step conversion reactions to form metallic phases, with MnO and FeO as the intermediate species, respectively. During delithiation, the oxidation of Mn occurs prior to that of Fe. The Cr³⁺ cations are reduced to CrO and then Cr⁰ during lithiation. A relatively large overpotential is required to activate the Cr reoxidation reaction. The Cr³⁺ cations are found after delithiation. These results can guide the material design of HEOs for improving LIB performance.

SUBMITTER: Luo XF

PROVIDER: S-EPMC9313486 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Here, we report that the trimetallic nanosized oxide NiFeMnO4 consists of a mixture of NiO and a strained cubic spinel phase, which is clearly demonstrated by analysis of the pair distribution function (PDF) and synchrotron X-ray data. Such a finding can easily be overlooked by using only inhouse X-ray powder diffraction, leading to inaccurate assumption of the stoichiometry and oxidation states. Such advanced characterization is essential because a homogeneous distribution of the elements is observed in energy-dispersive X-ray spectroscopy maps, giving no hints for a phase separation. Cycling of the sample against Li delivers a high reversible capacity of ≈840 mAh/g in the 50th cycle. Operando X-ray absorption spectroscopy (XAS) experiments indicate that ≈0.8 Li/fu is consumed without detectable changes of the electronic structure. Increasing amounts of Li, Mn3+, and Fe3+ are simultaneously reduced. The disappearance of the pre-edge features in X-ray absorption near-edge spectroscopy indicates movement of these cations from tetrahedral sites to octahedral sites. PDF analysis of the pattern after an uptake of 2 Li/fu evidences that the principal structure can be sufficiently well modeled assuming coexisting NiO, a mixed monoxide, and a small amount of residual spinel phase. Thus, the majority of cations is located on octahedral sites. Furthermore, an improvement of the PDF model is achieved taking into account small amounts of LiOH. The 7Li MAS NMR spectrum of this sample clearly shows the signal of Li in a diamagnetic environment, excluding Li-O-TM bonds. A further increase of the Li content leads to a successive conversion of the cations to nanosized metal particles embedded in a LiOH/Li2O matrix. Ex situ XAS results indicate that Fe can be reversibly reoxidized to Fe3+ during charge whereas Mn does not reach the oxidation state observed in the pristine material. After excessive cycling, reoxidation of metallic Ni is suppressed and contributes to a capacity loss compared with the early discharge/charge cycles.

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Charge-Discharge Mechanism of High-Entropy Co-Free Spinel Oxide Toward Li⁺ Storage Examined Using Operando Quick-Scanning X-Ray Absorption Spectroscopy.

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Charge-Discharge Mechanism of High-Entropy Co-Free Spinel Oxide Toward Li+ Storage Examined Using Operando Quick-Scanning X-Ray Absorption Spectroscopy.

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OmicsDI is part of the ELIXIR infrastructure

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Charge-Discharge Mechanism of High-Entropy Co-Free Spinel Oxide Toward Li⁺ Storage Examined Using Operando Quick-Scanning X-Ray Absorption Spectroscopy.