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Mapping Electrochemical Heterogeneity in Li[Ni0.6Mn0.2Co0.2]O2 Cathodes Using Operando X-Ray Techniques

Tuesday, 31 May 2022: 17:20
West Meeting Room 109 (Vancouver Convention Center)
L. A. Middlemiss (University of Sheffield), A. Morrison (Electrochemical Innovation Lab, UCL), J. Entwistle (University of Sheffield), J. Li, Y. Zhang, A. Boyce (Electrochemical Innovation Lab, UCL), A. James, S. Ahmed (Diamond Light Source), D. J. Cumming (University of Sheffield), P. R. Shearing (Electrochemical Innovation Lab, UCL), and S. A. Cussen (University of Sheffield)
Nickel-rich layered oxides, such as Li[Ni0.6Mn0.2Co0.2]O2 (NMC-622), present nearest-stage opportunities for high energy density lithium-ion batteries due to their high practical capacities and market maturity [1]. However, the interplay of electrochemistry, particle mechanical properties and electrical contacts in these layered oxides is often complex and requires a variety of characterisation techniques to deconvolute. Ni-rich materials suffer from surface instabilities and anisotropic lattice distortions at high states of charge, which are detrimental to their performance [2]. Particle arrangement within Li-ion electrodes is often heterogeneous, resulting in regions of ‘trapped capacity’ from which lithium cannot be extracted [3]. Better understanding how the particles of these electrodes are arranged, particularly in thicker electrodes, and how this affects electrochemical performance is key in designing optimal microstructures for Ni-rich electrodes, in the pursuit of better performing batteries.

Here, we have applied operando XRD to map electrochemical heterogeneity as a function of cross-section of ~ 200 μm Li[Ni0.6Mn0.2Co0.2]O2 electrodes. We observe that the NMC unit cell changes differently in the centre of the electrode, compared to at the edges, during cycling. To investigate this further, we use synchrotron sources to monitor peak splitting and shifting as a function of electrode depth. These experiments reveal changes in lattice parameters from the top of the electrode (near the separator) to the bottom (closer to the current collector). This indicates an alteration in extent of lithiation for these NMC-622 materials at different depths of the electrode (Fig. 1). These are important insights for better understanding performance limitations of nickel rich cathodes.

References:

[1] A. Manthiram, B. Song and W. Li, Energy Storage Materials, 2017, 6, 125.

[2] Y. Kim, W. M. Seong and A. Manthiram, Energy Storage Materials, 2021, 34, 250.

[3] H. Gao, Q. Wu, Y. Hu, J. P. Zheng and K. Amine, J. Phys. Chem. Lett., 2018, 9, 5100.

See more of: A02 - Advanced Characterization 2
See more of: A02: Lithium Ion Batteries
See more of: Batteries and Energy Storage
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