The accumulation of solid electrolyte interphases (SEI) in graphite anodes related to elevated formation rates (0.1C, 1C and 2C), cycling rates (1C and 2C), and electrode-separator lamination is investigated. As shown previously, the lamination technique is beneficial for the capacity aging in graphite-LiNi_1/3Mn_1/3Co_1/3O₂ cells. Here, surface resistance growth phenomena are quantified using electrochemical impedance spectroscopy (EIS). The graphite anodes were extracted from the graphite NMC cells in their fully discharged state and irreversible accumulations of lithium in the SEI are revealed using neutron depth profiling (NDP). In this post-mortem study, NDP reveals uniform lithium accumulations as a function of depth with lithium situated at the surface of the graphite particles thus forming the SEI. The SEI was found to grow logarithmically with cycle number starting with the main formation in the initial cycles. Furthermore, the EIS measurements indicate that benefits from lamination arise from surface resistance growth phenomena aside from SEI growth in superior anode fractions.

Multimethod study reveals distinct Na⁺ diffusion mechanisms and structural transitions in NASICON solid-state electrolytes for next-generation solid-state batteries.

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.

LiFePO₄ (LFP) primary particles and secondary agglomerates have been processed into water- and solvent-based cathodes. By means of neutron and X-ray diffraction it was found that no structural changes of LiFePO₄ occurred upon water- and solvent-based slurry preparation. Electrochemical characterization was carried out with full-cells and a distinct influence of particle morphology was observable. Water-based processing of primary particles leads to deficits in electrochemical performance while secondary agglomerates are non-sensitive to water during processing. In the presence of water, high mechanical stress during slurry preparation causes a partial detachment of carbon coating. However, this effect is negligible for secondary agglomerates since only surface particles are exposed to mechanical stress. Due to longer diffusion paths and the fact that secondary agglomerates represent a micro-heterogeneity in the cathode, the C-rate capability of secondary agglomerates is slightly lower than that of primary particles. This paper demonstrates that for any high energy application with moderate C-rates, secondary agglomerates hold a great potential for environmentally friendly and cost-efficient water-based cathode production.

LiFeMnPO₄ secondary agglomerates have been aged under different temperature and moisture conditions. The aged and pristine powder samples were then processed to water- and solvent-based cathodes. Structural studies by means of neutron and X-ray diffraction revealed that neither ageing nor water-based processing significantly modified the crystal structure of LiFeMnPO₄ secondary agglomerates. Electrochemical characterization was carried out with full-cells. It was found that long-term cycling is similar independent of the solvent used for slurry preparation. Full-cells assembled with water-based cathodes show a better C-rate capability due to a more homogeneous distribution of cathode constituents compared to solvent-based ones. In no case was any negative effect of initial active material ageing on the electrochemical performance found. During ageing and processing, LiFeMnPO₄ is effectively protected by carbon coating and water can be completely removed by drying since it is only reversibly bound. This contribution shows that LiFeMnPO₄ secondary agglomerates allow simplified active material handling and have a high potential for sustainable water-based electrode manufacturing.

Li-substituted P-type layered oxides with different morphologies and polymorphisms are investigated as positive electrode materials for sodium-ion batteries. In situ temperature-resolved X-ray diffraction (XRD) and spatially resolved synchrotron micro-XRD revealed the phase evolution during synthesis. For the first time, a P2 shell is shown to nucleate at the P3 particle surface, consistent with Na concentration gradients. The intermediate Li₂MnO₃, formed in the presence of Na₂CO₃, can be suppressed by using Na₂O₂ as Na source. Ni_1/4Mn_3/4(OH)₂ is also tested as a precursor, allowing for faster P2 crystallization from P3. Three samples with different polymorphisms and morphologies are then synthesized and compared in terms of evolution of crystal and electronic structure during cycling. Galvanostatic intermittent titration technique (GITT) measurements are further employed to investigate the kinetics of the samples. A P2-polycrystalline material retains ≈90% capacity after 150 cycles and offers the best rate capability up to 10C, appearing as the most promising candidate for further development of high-performance layered oxides.