The coupling of solid-state electrolytes with a Li-metal anode and state-of-the-art (SOA) cathode materials is a promising path to develop inherently safe batteries with high energy density (>1000 Wh L−1). However, integrating metallic Li with solid-electrolytes using scalable processes is not only challenging, but also adds extraneous volume since SOA cathodes are fully lithiated. Here we show the potential for “Li-free” battery manufacturing using the Li7La3Zr2O12 (LLZO) electrolyte. We demonstrate that Li-metal anodes >20 μm can be electroplated onto a current collector in situ without LLZO degradation and we propose a model to relate electrochemical and nucleation behavior. A full cell consisting of in situ formed Li, LLZO, and NCA is demonstrated, which exhibits stable cycling over 50 cycles with high Coulombic efficiencies. These findings demonstrate the viability of “Li-free” configurations using LLZO which may guide the design and manufacturing of high energy density solid-state batteries.

A highly resistive Polyethylene oxide-LiTFSI(PEO-LiTFSI)/ Lithium Lanthanum Zirconium Oxide (LLZO) interface, with a resistivity of 95 kOhms.cm2 (30°C) is believed to limit the total conductivity of ceramic-polymer composite electrolyte (CPE). To achieve higher ionic conductivity, the interfacial impedance (Rinterface) must be reduced to <~100 Ohms.cm2 to enable cell impedances comparable to Li-ion technology. The goal of this study was to investigate the origin of this high Rinterface. It was hypothesized that LLZO surface impurities and abrupt changes in Li-ion concentration between the PEO-LiTFSI/LLZO electrolytes contribute to the high impedance. By removing surface impurities through heat-treatment, the Rinterface was reduced to 180 Ohms.cm2 at 30°C. Optimization of Li-salt concentration in PEO to 15:1, resulted in reduction of Rinterface from 1.6 kOhms.cm2 to 421 Ohms.cm2. By understanding the underpinning mechanisms that govern the ceramic-polymer interface impedance, we believe it is possible to develop high conductivity CPE that are easy to fabricate and integrate into solid-state batteries.

We hypothesized that pressure and temperature affect Li metal solid-state battery (LMSB) resistance and susceptibility to Li metal penetration during cycling. To validate this, the kinetics and stability of the Li-solid electrolyte interface was studied using the model polymer electrolyte system: Li/Polyethylene oxide-LiTFSI (PEO-LiTFSI). It was determined that the interface impedance decreased with increasing pressure and was invariant above 400 and 200 kPa at 60 and 80 • C, respectively. In tests to determine susceptibility to Li metal penetration as a function of current density, it was determined that the current density at which Li metal penetrates PEO-LiTFSI, was consistently 0.5 mA/cm 2 for all temperatures tested (60, 80, and 100 • C). To gain a mechanistic understanding of how Li metal penetrates a solid electrolyte at and above the current density for onset of Li metal penetration, an operando optical visual cell was used. A clear correlation between erratic DC polarization behavior and the onset and propagation of Li metal penetration was made. The empirical observations in this study could help better understand the factors that affect the kinetics and stability of the Li-solid electrolyte interface. We believe these findings could help to advance the maturity of LMSB.

The crystal structure of synthetic BI3C 2 has been investigated by X-ray diffraction. Atomic parameters were determined from both conventional refinement techniques, with the spherical-atom model, and multi-0567-7408/79/051052-08501.00 pole expansion refinement. The analysis of the results shows the scale factor and some of the vibrational parameters to be considerably biased by bonding effects. Bias could be reduced by high-order refinements leading to parameters which agree with the results of the multipole expansion refinement within the

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IntroduetionThe crystal structure of rhombohedral B13C 2 is composed of two structural units, the linear C-B-C chain and the B~2 icosahedron. Based on high-order (HO) refinement results, X-X maps of dynamic deformation densities and valence densities have been calculated for sections in both units. The influence of the scale factor and the local distribution of the variance of difference densities were investigated for the density distribution in the B-C bond of C-B-C, which lies in the hexagonal c axis and shows the largest deviations from the spherical free-atom model. Integrations of residual densities in the C-B-C unit yield experimental evidence for a theoretically postulated charge transfer of one electron towards the B~2 icosahedron, providing a 10-electron closed-shell configuration for C-B-C. The charge distribution in and around the somewhat distorted B~2 icosahedron is discussed in terms of a simple covalent-bond model. 0567-7408/79/102291-10501.00In a previous paper (Kirfel, Gupta & Will, 1979; hereafter called part I) the crystal structure of B13C 2 was studied by refinements of X-ray diffraction data. Both the conventional spherical free-atom model and the multipole expansion model (Hirshfeld, 1971; Harel & Hirshfeld, 1975) were used. This preceding paper contains the results from the various refinements and first conclusions concerning the bond character in B13C 2. As a preliminary result no indication could be found that a charge transfer takes place from the C-B-C chain towards the B12 icosahedron. This had been demanded by Longuet-Higgins & Roberts (1955) in a theoretical paper on the bonding features in boron icosahedra. The extreme stability of the refractory borides, including boron carbide, is supposed to be based on such an electron transfer. In a second part of the analysis we have now studied the dynamic deformation densities and valence den-

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