Sou Taminato

Real-time observations of lithium battery reactions—operando neutron diffraction analysis during practical operation

Among the energy storage devices for applications in electric vehicles and stationary uses, lithium batteries typically deliver high performance. However, there is still a missing link between the engineering developments for large-scale batteries and the fundamental science of each battery component. Elucidating reaction mechanisms under practical operation is crucial for future battery technology. Here, we report an operando diffraction technique that uses high-intensity neutrons to detect reactions in non-equilibrium states driven by high-current operation in commercial 18650 cells. The experimental system comprising a time-of-flight diffractometer with automated Rietveld analysis was developed to collect and analyse diffraction data produced by sequential charge and discharge processes. Furthermore, observations under high current drain revealed inhomogeneous reactions, a structural relaxation after discharge, and a shift in the lithium concentration ranges with cycling in the electrode matrix. The technique provides valuable information required for the development of advanced batteries.

Mechanistic studies on lithium intercalation in a lithium-rich layered material using Li2RuO3 epitaxial film electrodes and in situ surface X-ray analysis

The surface structure of a lithium-rich layered material and its relation to intercalation properties were investigated by synchrotron X-ray surface structural analyses using Li2RuO3 epitaxial-film model electrodes with different lattice planes of (010) and (001). Electrochemical charge–discharge measurements confirmed reversible lithium intercalation activity through both planes, corresponding to three-dimensional lithium diffusion within the Li2RuO3. The (001) plane exhibited higher discharge capacities compared to the (010) plane under high rate operation (over 5 C). Direct observations of surface structural changes by in situ surface X-ray diffraction (XRD) and surface X-ray absorption near edge structure (XANES) established that an irreversible phase change occurs at the (010) surface during the first (de)intercalation process, whereas reversible structural changes take place at the (001) surface. These experimental findings suggest that the surface reconstructed phase limits lithium intercalation between the electrode and the electrolyte, leading to the poor rate capability of the (010) film. Surface structural changes at the initial cycling therefore have a pronounced effect on the power characteristics and stability of lithium-rich layered materials during battery operation.

Structure–property relationships in lithium superionic conductors having a Li10GeP2S12-type structure

The crystal structures of the superionic conductors Li9.81Sn0.81P2.19S12 and Li10.35Si1.35P1.65S12, both having a Li10GeP2S12 (LGPS)-type structure, were determined by neutron diffraction analysis over the temperature range 12-800 K. The maximum entropy method was also employed to clarify the lithium distribution in these materials. The Sn system showed one-dimensional diffusion in the c direction over a wide temperature range, even though the Ge-based system typically exhibits three-dimensional conduction at higher temperatures. The ionic conduction mechanisms of analogous Si, Ge and Sn phases with LGPS-type structures are discussed on the basis of the observed structural parameter changes.

Lithium intercalation in the surface region of an LiNi1/3Mn1/3Co1/3O2 cathode through different crystal planes

Epitaxial LiNi1/3Co1/3Mn1/3O2 film electrodes with orientations of (104), (1−18) and (003) were fabricated on SrRuO3/SrTiO3 by pulsed laser deposition. The films have a thickness of 23.8 to 25.0 nm and a flat surface with a roughness of approximately 2 nm, which offered a model system for clarifying the reaction plane dependencies of lithium intercalation at the LiNi1/3Co1/3Mn1/3O2 surface. All reaction planes delivered reversible lithium intercalation for electrochemical charging–discharging between 3.0 V and 4.3 V (vs. Li/Li+). The (104) surface exhibited reversible behavior at a higher operation voltage between 3.0 V and 4.5 V, but the (1−18) and (003) planes showed fading of the discharge capacity and average discharge voltage. The anisotropic stability of the surface region indicates the importance of crystallographic facet control for the development of an LiNi1/3Co1/3Mn1/3O2 cathode with high cycle stability.