25-30 August 2019
Henry Ford Building
Europe/Berlin timezone

Solid-state NMR studies of the electrochemical cycling of LiNi$_{0.8}$Mn$_{0.1}$Co$_{0.1}$O$_2$ cathodes

27 Aug 2019, 11:55
35m
Lecture Hall C (Henry Ford Building)

Lecture Hall C

Henry Ford Building

Talk Materials applications Materials

Speaker

Dr Katharina Märker (University of Cambridge; The Faraday Institution)

Description

The layered oxide LiNi$_{0.8}$Mn$_{0.1}$Co$_{0.1}$O$_2$ (NMC811) is a promising future cathode material for lithium-ion batteries in electric vehicles due to its high specific energy density. The practical use of NMC811 cathodes, however, faces difficulties as they suffer from fast capacity fade. Mitigating this performance fade requires detailed knowledge of the changes of structure and dynamics of NMC811 during charge and discharge.

$^7$Li solid-state NMR is a well-suited technique for investigating lithium-ion battery materials as it is sensitive to the local Li environment as well as the Li-ion dynamics. NMC811 is a challenging material for such studies due to the high number of paramagnetic centres (Ni$^{2+}$, Ni$^{3+}$, Mn$^{4+}$), leading to short relaxation times and large hyperfine interactions. The acquisition and interpretation of $^7$Li NMR spectra of NMC811 will be demonstrated in this contribution, including data acquired on ex situ and in situ samples.

Ex situ measurements enable the acquisition of NMR spectra under fast magic-angle spinning which yields considerably improved spectral resolution. The ex situ $^7$Li NMR spectra taken on NMC811 cathodes at different states-of-charge (SOC) reveal a strong increase of Li-ion hopping rates during charge which is confirmed by variable temperature measurements.$^{[1]}$ Modelling of these spectra allows estimating the hopping rates and also reveals that Li mobility decreases drastically at high SOC, which is accompanied by Li/vacancy ordering.$^{[1]}$

In situ $^7$Li NMR measurements on NMC811/graphite full-cells are used to simultaneously monitor Li ions in different parts of the cell such as the cathode, the anode, and the electrolyte. We will show a series of measurements at different charging rates and at different temperatures, providing real-time insights into the processes during electrochemical cycling in the whole cell and their contributions to degradation.

[1] K. Märker, P. J. Reeves, C. Xu, K. J. Griffith, C. P. Grey, Chem. Mater. 2019, 31 (7), 2545–2554.

Primary authors

Dr Katharina Märker (University of Cambridge; The Faraday Institution) Dr Chao Xu (University of Cambridge; The Faraday Institution) Mr Philip J. Reeves (University of Cambridge) Dr Kent J. Griffith (University of Cambridge) Prof. Clare P. Grey (University of Cambridge; The Faraday Institution)

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