Li-ion half-cells studied operando during cycling by small-angle neutron scattering

Abstract

Small-angle neutron scattering (SANS) was recently applied to the in situ and operando study of the charge/discharge process in Li-ion battery full-cells based on a pouch cell design. Here, this work is continued in a half-cell with a graphite electrode cycled versus a metallic lithium counter electrode, in a study conducted on the SANS-1 instrument of the neutron source FRM II at the Heinz Maier-Leibnitz Zentrum in Garching, Germany. It is confirmed that the SANS integrated intensity signal varies as a function of graphite lithiation, and this variation can be explained by changes in the squared difference in scattering length density between graphite and the electrolyte. The scattering contrast change upon graphite lithiation/delithiation calculated from a multi-phase neutron scattering model is in good agreement with the experimentally measured values. Due to the finite coherence length, the observed SANS contrast, which mostly stems from scattering between the (lithiated) graphite and the electrolyte phase, contains local information on the mesoscopic scale, which allows the development of lithiated phases in the graphite to be followed. The shape of the SANS signal curve can be explained by a core-shell model with step-wise (de)lithiation from the surface. Here, for the first time, X-ray diffraction, SANS and theory are combined to give a full picture of graphite lithiation in a half-cell. The goal of this contribution is to confirm the correlation between the integrated SANS data obtained during operando measurements of an Li-ion half-cell and the electrochemical processes of lithiation/delithiation in micro-scaled graphite particles. For a deeper understanding of this correlation, modelling and experimental data for SANS and results from X-ray diffraction were taken into account. research papers J. Appl. Cryst. (2020). 53, 210-221 Johannes Hattendorff et al. SANS operando study of Li-ion half-cells 211 research papers 212 Johannes Hattendorff et al. SANS operando study of Li-ion half-cells J. Appl. Cryst. (2020). 53, 210-221 Figure 2An operando X-ray diffractogram recorded from the Li/graphite half-cell cycled at C/5, showing the presence of well defined lithiation stages, which indicates good homogeneity across the electrode. J. Appl. Cryst. (2020). 53, 210-221 Johannes Hattendorff et al. SANS operando study of Li-ion half-cells 219 Figure 9An illustration of the calculation mesh and the coherence volumes centred at each mesh element k, (a) for small particles and (b) for a large particle with two phases, e.g. active material and electrolyte or solvent. One square is of the order of 30 nm.

Strategies towards enabling lithium metal in batteries: interphases and electrodes

“…Microscopic techniques include transmission electron microscopy (TEM), 14,15 scanning electron microscopy (SEM), 9 laser scanning microscopy (LSM), 16 micro computed tomography (micro-CT), 17 atomic force microscopy (AFM), 18,19 and optical microscopy. 20 Spectroscopic & scattering techniques include grazing-incidence small angle X-ray scattering (GISAXS), 21 small-angle neutron scattering (SANS), 22 Fourier-transformed infrared (FTIR), 8,23 nuclear magnetic resonance (NMR), 24,25 and electron paramagnetic resonance (EPR) 24 Spectroscopy. Within the classifications and individual rows, the spatial resolution becomes higher the more left the method is depicted.…”

“…((Grazing-Incidence) small-angle X-ray scattering (GI)SAXS), 21 or neutrons (small-angle neutron scattering, SANS). 22 While in the case of X-rays, the photons interact with the electrons, i.e. heavier atoms typically exhibit a larger signal, neutrons are elastically scattered by the nucleus and, thus, can be very sensitive even for light elements.…”

Solid electrolyte interphase layer formation on mesophase graphite electrodes with different electrolytes studied by small‐angle neutron scattering

“…The SANS intensity at q < 0.01 Å −1 study is mainly contributed by the lithiation zone within the large‐scale carbon grains, 34 which is not in the scope of this work. The curves in Figure 1 are the scattering intensity profiles at different states, which is proportional to the difference in the material‐specific scatting length densities of graphite and SEI matrix from the anode surface, which is used to determine the SEI relative thickness of MGP anode.…”

Soft Matter Sample Environments for Time-Resolved Small Angle Neutron Scattering Experiments: A Review

“…Here again there is a lack of electron density contrast between the Carbon and the Li compared to the pores, which indicates that neutron scattering is better suited to gain insights into the effects of the use of different Li-salts and concentrations during the duty cycle for in-operando cycling/discharging [133]. Similar experiments, but with greater emphasis on the analysis of the scattering results and the role of the scattering contrast in the analysis of the data, were also published [134].…”