Batteries are a key technology in modern society. They are used to power electric and hybrid electric vehicles and to store wind and solar energy in smart grids. Electrochemical devices with high energy and power densities can currently be powered only by batteries with organic liquid electrolytes. However, such batteries require relatively stringent safety precautions, making large-scale systems very complicated and expensive. The application of solid electrolytes is currently limited because they attain practically useful conductivities (10(-2) S cm(-1)) only at 50-80 °C, which is one order of magnitude lower than those of organic liquid electrolytes. Here, we report a lithium superionic conductor, Li(10)GeP(2)S(12) that has a new three-dimensional framework structure. It exhibits an extremely high lithium ionic conductivity of 12 mS cm(-1) at room temperature. This represents the highest conductivity achieved in a solid electrolyte, exceeding even those of liquid organic electrolytes. This new solid-state battery electrolyte has many advantages in terms of device fabrication (facile shaping, patterning and integration), stability (non-volatile), safety (non-explosive) and excellent electrochemical properties (high conductivity and wide potential window).

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The motion of atoms in a solid always responds to cooling or heating in a way that is consistent with the symmetry of the given space group of the solid to which they belong. When the atoms move, the electronic structure of the solid changes, leading to different physical properties. Therefore, the determination of where atoms are and what atoms do is a cornerstone of modern solid-state physics. However, experimental observations of atomic displacements measured as a function of temperature are very rare, because those displacements are, in almost all cases, exceedingly small. Here we show, using a combination of diffraction techniques, that the hexagonal manganites RMnO3 (where R is a rare-earth element) undergo an isostructural transition with exceptionally large atomic displacements: two orders of magnitude larger than those seen in any other magnetic material, resulting in an unusually strong magneto-elastic coupling. We follow the exact atomic displacements of all the atoms in the unit cell as a function of temperature and find consistency with theoretical predictions based on group theories. We argue that this gigantic magneto-elastic coupling in RMnO3 holds the key to the recently observed magneto-electric phenomenon in this intriguing class of materials.

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