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No pressure: This work demonstrates the working principle of an ionic liquid interlayer to enhance the stripping performance of lithium metal in contact with a garnet solid electrolyte. Detailed analysis, including galvanostatic electrochemical impedance spectroscopy and cryogenic FIB-SEM, shows that pores forming in lithium metal during stripping are compensated to a great extent, which improves the stripping performance up to over 15 mAh cm−2. Solid-state-batteries employing lithium metal anodes promise high theoretical energy and power densities. However, morphological instability occurring at the lithium/solid–electrolyte interface when stripping and plating lithium during cell cycling needs to be mitigated. Vacancy diffusion in lithium metal is not sufficiently fast to prevent pore formation at the interface above a certain current density during stripping. Applied pressure of several MPa can prevent pore formation, but this is not conducive to practical application. This work investigates the concept of ionic liquids as “self-adjusting” interlayers to compensate morphological changes of the lithium anode while avoiding the use of external pressure. A clear improvement of the lithium dissolution process is observed as it is possible to continuously strip more than 70 μm lithium (i. e., 15 mAh cm−2 charge) without the need for external pressure during assembly and electrochemical testing of the system. The impedance of the investigated electrodes is analyzed in detail, and contributions of the different interfaces are evaluated. The conclusions are corroborated with morphology studies using cryo-FIB-SEM and chemical analysis using XPS. This improves the understanding of the impedance response and lithium stripping in electrodes employing liquid interlayers, acting as a stepping-stone for future optimization., publishedVersion

Following the demand for increased energy density of lithium-ion batteries, the Ni content of the Nickel-Cobalt-Manganese oxide (NCM) cathode materials has been increased into the direction of LiNiO$_2$ (LNO), which regained the attention of both industry and academia. To understand the correlations between physicochemical parameters and electrochemical performance of LNO, a calcination study was performed with variation of precursor secondary particle size, maximum calcination temperature and Li stoichiometry. The structural properties of the materials were analyzed by means of powder X-ray diffraction, magnetization measurements and half-cell voltage profiles. All three techniques yield good agreement concerning the quantification of Ni excess in the Li layer (1.6%���3.7%). This study reveals that the number of Li equivalents per Ni is the determining factor concerning the final stoichiometry rather than the calcination temperature within the used calcination parameter space. Contrary to widespread belief, the Ni excess shows no correlation to the 1$^{st}$ cycle capacity loss, which indicates that a formerly overlooked physical property of LNO, namely primary particle morphology, has to be considered.

Recently, a Verwey-type transition in the mixed-valence alkali sesquioxide Cs4O6 was deduced from the charge ordering of molecular peroxide O2−2 and superoxide O−2 anions accompanied by the structural transformation and a dramatic change in electronic conductivity [Adler et al., Sci. Adv. 4, eaap7581 (2018)]. Here, we report that in the sister compound Rb4O6, a similar Verwey-type charge ordering transition is strongly linked to O−2 orbital and spin dynamics. On cooling, a powder neutron diffraction experiment reveals a charge ordering and a cubic-to-tetragonal transition at TCO = 290 K, which is followed by a further structural instability at Ts = 92 K that involves an additional reorientation of magnetic O−2 anions. Magnetic resonance techniques supported by density functional theory computations suggest the emergence of a peculiar type of π*-orbital ordering of the magnetically active O−2 units, which promotes the formation of a quantum spin state composed of weakly coupled spin dimers. These results reveal that as in 3d transition-metal compounds, also in the π* open-shell alkali sesquioxides the interplay between Jahn-Teller-like electron-lattice coupling and Kugel-Khomskii-type superexchange determines the nature of orbital ordering and the magnetic ground state.

Recently, a Verwey type transition in the mixed valence alkali sesquioxide Cs4O6 was deduced from the charge ordering of molecular peroxide O2 amp; 8722;2 and superoxide O amp; 8722;2 anions accompanied by the structural transformation and a dramatic change in electronic conductivity [Adler et al., Sci. Adv. 4, eaap7581 2018 ]. Here, we report that in the sister compound Rb4O6, a similar Verwey type charge ordering transition is strongly linked to O amp; 8722;2 orbital and spin dynamics. On cooling, a powder neutron diffraction experiment reveals a charge ordering anda cubic to tetragonal transition at TCO 290 K, which is followed by a further structural instability at Ts 92 K that involves an additional reorientation of magnetic O amp; 8722;2 anions. Magnetic resonance techniques supported by density functional theory computations suggest the emergence of a peculiar type of amp; 960; amp; 8727; orbital ordering of the magnetically active O amp; 8722;2 units, which promotes the formation of a quantum spin state composed of weakly coupled spin dimers. These results reveal that as in 3d transition metal compounds, also in the amp; 960; amp; 8727; open shell alkali sesquioxides the interplay between Jahn Teller like electron lattice coupling and Kugel Khomskii type superexchange determines the nature of orbital ordering and the magnetic ground state