To rationalize and improve the performance of newly developed high-rate battery electrode materials, it is crucial to understand the ion intercalation and degradation mechanisms occurring during realistic battery operation. Here we apply a laboratory-based operando optical scattering microscopy method to study micrometre-sized rod-like particles of the anode material Nb14W3O44 during high-rate cycling. We directly visualize elongation of the particles, which, by comparison with ensemble X-ray diffraction, allows us to determine changes in the state of charge of individual particles. A continuous change in scattering intensity with state of charge enables the observation of non-equilibrium kinetic phase separations within individual particles. Phase field modelling (informed by pulsed-field-gradient nuclear magnetic resonance and electrochemical experiments) supports the kinetic origin of this separation, which arises from the state-of-charge dependence of the Li-ion diffusion coefficient. The non-equilibrium phase separations lead to particle cracking at high rates of delithiation, particularly in longer particles, with some of the resulting fragments becoming electrically disconnected on subsequent cycling. These results demonstrate the power of optical scattering microscopy to track rapid non-equilibrium processes that would be inaccessible with established characterization techniques.
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The data underlying the figures in the main text are publicly available from the University of Cambridge repository at https://doi.org/10.17863/CAM.85438.
The code used to perform phase field modelling is publicly available from the University of Cambridge repository at https://doi.org/10.17863/CAM.85438.
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This work was supported by the Faraday Institution, FIRG012 and FIRG024. A.J.M. acknowledges support from the Engineering and Physical Sciences Research Council (EPSRC) Cambridge NanoDTC, EP/L015978/1. C.S. acknowledges financial support by the Royal Commission of the Exhibition of 1851. We acknowledge financial support from the EPSRC and the Winton Program for the Physics of Sustainability. This project has received funding from the European Research Council under the European Union’s Horizon 2020 research and innovation programme (grant agreement no. 758826). C.P.G., S.P.E. and A.J.M. were supported by a European Research Council Advanced Investigator Grant for C.P.G. (EC H2020 835073). Use of the Advanced Photon Source at Argonne National Laboratory was supported by the US Department of Energy, Office of Science, Office of Basic Energy Sciences, under contract no. DE-AC02-06CH11357. We thank S. Nagendran and J. Thuillier for their help with synthesizing the materials and with the PFG-NMR measurements, P. Magusin for advice regarding the PFG-NMR measurements, B. Mockus for help with the code development and F. Alford for useful discussions regarding analysis of optical data.
C.P.G. is a major shareholder and cofounder of Nyobolt, a start-up company developing fast-charging batteries based on high-rate anode materials. The remaining authors declare no competing interests.
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Nature Materials thanks Sanli Faez, Justin Sambur and Venkatasubramanian Viswanathan for their contribution to the peer review of this work.
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Supplementary Figs. 1–21, Tables 1–5 and Discussions.
Optical response of active NWO particles during one galvanostatic cycle at 5C.
Differential images of the active NWO particles at the start of 5C lithiation, with and without a preceding 2.8 V hold.
Intensity and differential images of an active NWO particle during 5C delithiation from high Li content, including particle cracking.
Intensity and differential images of an active NWO particle during 20C delithiation from high Li content.
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Merryweather, A.J., Jacquet, Q., Emge, S.P. et al. Operando monitoring of single-particle kinetic state-of-charge heterogeneities and cracking in high-rate Li-ion anodes. Nat. Mater. (2022). https://doi.org/10.1038/s41563-022-01324-z