In Situ X‑ray Diffraction and X‑ray Absorption Spectroscopic Studies of a Lithium-Rich Layered Positive Electrode Material: Comparison of Composite and Core–Shell Structures

In Situ X‑ray Diffraction and X‑ray Absorption Spectroscopic Studies of a Lithium-Rich Layered Positive Electrode Material: Comparison of Composite and Core–Shell Structures

Lithium- and manganese-rich transition-metal oxide (LMR-NMC) electrodes have been designed either as heterostructures of the primary components (“composite”) or as core–shell structures with improved electrochemistry reported for both configurations when compared with their primary components. A det...

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Published in:ACS applied materials & interfaces Vol. 12; no. 12; pp. 13852 - 13868
Main Authors: Ehi-Eromosele, Cyril Osereme, Indris, Sylvio, Bramnik, Natalia N, Sarapulova, Angelina, Trouillet, Vanessa, Pfaffman, Lukas, Melinte, Georgian, Mangold, Stefan, Darma, Mariyam Susana Dewi, Knapp, Michael, Ehrenberg, Helmut
Format: Journal Article
Language:English
Published: United States American Chemical Society 25-03-2020
Subjects:
core−shell structured cathode
composite cathode
lithium-ion battery
in situ XRD
in situ XAS
LMR-NMC
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Summary:Lithium- and manganese-rich transition-metal oxide (LMR-NMC) electrodes have been designed either as heterostructures of the primary components (“composite”) or as core–shell structures with improved electrochemistry reported for both configurations when compared with their primary components. A detailed electrochemical and structural investigation of the 0.5Li2MnO3–0.5LiNi0.5Mn0.3Co0.2O2 composite and core–shell structured positive electrode materials is reported. The core–shell material shows better overall electrochemical performance compared to its corresponding composite material. While both configurations gave the same initial charge capacity of ∼300 mAh/g when cycled at a rate of 10 mA/g at 25 °C, the core–shell sample gives a discharge capacity of 232 mAh/g compared to 208 mAh/g delivered by the composite sample. Also, the core–shell sample gave better rate capability and a smaller first-cycle irreversible capacity loss than the composite sample. The improved performance of the core–shell material is attributed to its lower surface reactivity and limited structural change since the more stable Li2MnO3 shell screens the more reactive Ni-rich core material from interacting with either air or electrolyte at high potentials, thereby preventing electrode surface modification. In situ X-ray diffraction correlated with electrochemical data revealed that the composite sample shows stronger volumetric changes in the lattice parameters during charging to 4.8 V. In addition, X-ray absorption spectroscopy showed an incomplete Ni reduction process after the first discharge for the composite sample. From these results, it was shown that this leads to a more severe degradation in the composite material that affects Li+ intercalation in the subsequent discharge, thereby resulting in its poorer performance. Furthermore, to confirm these results, another LMR-NMC material with a different composition (having a Ni-poor core)0.5Li2MnO3-0.5LiNi0.33Mn0.33Co0.33O2was investigated. The core–shell structured positive electrode material also gave an improved electrochemical performance compared to the corresponding composite positive electrode material. These results show that the core–shell configuration could effectively be used to improve the performance of the LMR-NMC materials to enable future high-energy applications.
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ISSN:1944-8244
1944-8252
DOI:10.1021/acsami.9b21061