The solid lithium-ion electrolyte ''Li 7 La 3 Zr 2 O 12 '' (LLZO) with a garnet-type structure has been prepared in the cubic and tetragonal modification following conventional ceramic syntheses routes. Without aluminium doping tetragonal LLZO was obtained, which shows a two orders of magnitude lower room temperature conductivity than the cubic modification. Small concentrations of Al in the order of 1 wt% were sufficient to stabilize the cubic phase, which is known as a fast lithium-ion conductor. The structure and ion dynamics of Al-doped cubic LLZO were studied by impedance spectroscopy, dc conductivity measurements, 6 Li and 7 Li NMR, XRD, neutron powder diffraction, and TEM precession electron diffraction. From the results we conclude that aluminium is incorporated in the garnet lattice on the tetrahedral 24d Li site, thus stabilizing the cubic LLZO modification. Simulations based on diffraction data show that even at the low temperature of 4 K the Li ions are blurred over various crystallographic sites. This strong Li ion disorder in cubic Al-stabilized LLZO contributes to the high conductivity observed. The Li jump rates and the activation energy probed by NMR are in very good agreement with the transport parameters obtained from electrical conductivity measurements. The activation energy E a characterizing longrange ion transport in the Al-stabilized cubic LLZO amounts to 0.34 eV. Total electric conductivities determined by ac impedance and a four point dc technique also agree very well and range from 1 Â 10 À4 Scm À1 to 4 Â 10 À4 Scm À1 depending on the Al content of the samples. The room temperature conductivity of Al-free tetragonal LLZO is about two orders of magnitude lower (2 Â 10 À6 Scm À1 , E a = 0.49 eV activation energy). The electronic partial conductivity of cubic LLZO was measured using the Hebb-Wagner polarization technique. The electronic transference number t eÀ is of the order of 10 À7. Thus, cubic LLZO is an almost exclusive lithium ion conductor at ambient temperature.

Externally triggered motion of small objects has potential in applications ranging from micromachines, to drug delivery, and self-assembly of superstructures. Here we present a new concept for the controlled propulsion of conducting objects with sizes ranging from centimetres to hundreds of micrometres. It is based on their polarization, induced by an electric field, which triggers spatially separated oxidation and reduction reactions involving asymmetric gas bubble formation. This in turn leads to a directional motion of the objects. Depending on the implied redox chemistry and the device design, the speed can be controlled and the motion can be switched from linear to rotational. This type of chemical locomotion is an alternative to existing approaches based on other principles.

Tetragonal Li 10 GeP 2 S 12 (LGPS) is the best solid Li electrolyte reported in the literature. In this study we present the first in-depth study on the structure and Li ion dynamics of this structure type. We prepared two different tetragonal LGPS samples, Li 10 GeP 2 S 12 and the new compound Li 7 GePS 8 . The Li ion dynamics and the structure of these materials were characterized using a multitude of complementary techniques, including impedance spectroscopy, 7 Li PFG NMR, 7 Li NMR relaxometry, X-ray diffraction, electron diffraction, and 31 P MAS NMR. The exceptionally high ionic conductivity of tetragonal LGPS of $10 À2 S cm À1 is traced back to nearly isotropic Li hopping processes in the bulk lattice of LGPS with E A z 0.22 eV.Lithium-ion batteries are considered to play an important role in future energy storage, especially for mobile applications such as vehicle propulsion. 1 One approach to overcome both safety and durability problems of state-of-the-art Lithium-ion batteries is the use of solid electrolytes, which must satisfy the criteria of having high Li ion conductivity and a wide electrochemical window. The lack of suitable materials triggered intense research efforts in the eld of solid state ionics. During recent years signicant progress has been achieved, such that the materials available now are suitable for commercial applications.2 Hereby, two main classes of solid electrolytes have attracted the attention of both academia and industry, namely (i) oxide-based garnet-type electrolytes such as Li 7 La 3 Zr 2 O 12 , [3][4][5] and (ii) sulde-based electrolytes.6-8 The oxide-based materials generally show a wider electrochemical window, whereas the sulde-based electrolytes usually exhibit a higher Li-ion conductivity. In 2011, a new solid electrolyte Li 10 GeP 2 S 12 (LGPS), a metastable phase occurring in the system xLi 4 GeS 4 : yLi 3 PS 4 , was reported.9 Tetragonal LGPS combines the most important prerequisites for a high-performance Li electrolyte: a room-temperature conductivity of 12 mS cm À1, an activation energy of 0.24 eV, and an electrochemical window of up to 4 V vs. Li/Li + . 9 While tetragonal LGPS has only been studied by means of MD and ab initio calculations since the original publication, 10-13 a fundamental study on the Li ion dynamics occurring in tetragonal LGPS has not been reported to date. Additionally, the fact that tetragonal LGPS is a solid solution with a rather broad range of existence has not been considered in the literature so far.In this study, both Li 10 GeP 2 S 12 and Li 7 GePS 8 , a new member of the solid solution of tetragonal LGPS with a Ge : P ratio of 1 : 1, were prepared and structurally characterized. The Li ion dynamics occurring in the materials was studied by several complementary techniques sensitive to (i) long-range Li diffusion (PFG-NMR), (ii) atomic-scale jumps (NMR relaxometry), and (iii) long-range charge transport (impedance spectroscopy). This combination of techniques allows us to connect diffusion (at the macroscopic scale) to ionic ho...

Bipolar electrochemistry, a phenomenon which generates an asymmetric reactivity on the surface of conductive objects in a wireless manner, is an important concept for many purposes, from analysis to materials science as well as for the generation of motion. Chemists have known the basic concept for a long time, but it has recently attracted additional attention, especially in the context of micro- and nanoscience. In this Account, we introduce the fundamentals of bipolar electrochemistry and illustrate its recent applications, with a particular focus on the fields of materials science and dynamic systems. Janus particles, named after the Roman god depicted with two faces, are currently in the heart of many original investigations. These objects exhibit different physicochemical properties on two opposite sides. This makes them a unique class of materials, showing interesting features. They have received increasing attention from the materials science community, since they can be used for a large variety of applications, ranging from sensing to photosplitting of water. So far the great majority of methods developed for the generation of Janus particles breaks the symmetry by using interfaces or surfaces. The consequence is often a low time-space yield, which limits their large scale production. In this context, chemists have successfully used bipolar electrodeposition to break the symmetry. This provides a single-step technique for the bulk production of Janus particles with a high control over the deposit structure and morphology, as well as a significantly improved yield. In this context, researchers have used the bipolar electrodeposition of molecular layers, metals, semiconductors, and insulators at one or both reactive poles of bipolar electrodes to generate a wide range of Janus particles with different size, composition and shape. In using bipolar electrochemistry as a driving force for generating motion, its intrinsic asymmetric reactivity is again the crucial aspect, as there is no directed motion without symmetry breaking. Controlling the motion of objects at the micro- and nanoscale is of primary importance for many potential applications, ranging from medical diagnosis to nanosurgery, and has generated huge interest in the scientific community in recent years. Several original approaches to design micro- and nanomotors have been explored, with propulsion strategies based on chemical fuelling or on external fields. The first strategy is using the asymmetric particles generated by bipolar electrodeposition and employing them directly as micromotors. We have demonstrated this by using the catalytic and magnetic properties of Janus objects. The second strategy is utilizing bipolar electrochemistry as a direct trigger of motion of isotropic particles. We developed mechanisms based on a simultaneous dissolution and deposition, or on a localized asymmetric production of bubbles. We then used these for the translation, the rotation and the levitation of conducting objects. These examples give insight into two ...

We report on a new ultrafast solid electrolyte of the composition Li11Si2PS12, which exhibits a higher room-temperature Li ion diffusivity than the present record holder Li10GeP2S12. We discuss the high-pressure synthesis and ion dynamics of tetragonal Li11Si2PS12, and comparison is made with our investigations of related members of the LMePS family, i.e. electrolytes of the general formula Li11-xMe2-xP1+xS12 with Me = Ge, Sn : Li10GeP2S12, Li7GePS8, Li10SnP2S12. The structure and dynamics were studied with multiple complementary techniques and the macroscopic diffusion could be traced back to fast Li ion hopping in the crystalline lattice. A clear correlation between the diffusivity and the unit cell volume of the LGPS-type electrolytes was observed.

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Janus particles have different features/chemistry on two opposite sides (see figure). So far, they have been obtained mainly by two‐dimensional synthetic methods, which are able to break the symmetry but limit the amount of produced particles. A true bulk approach, based on bipolar electrochemistry, is presented that allows the straightforward synthesis of such asymmetric micro‐ and nano‐objects.

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