Lithium-ion batteries have had a profound impact on our daily life, but inherent limitations make it difficult for Li-ion chemistries to meet the growing demands for portable electronics, electric vehicles and grid-scale energy storage. Therefore, chemistries beyond Li-ion are currently being investigated and need to be made viable for commercial applications. The use of metallic Li is one of the most favoured choices for next-generation Li batteries, especially Li-S and Li-air systems. After falling into oblivion for several decades because of safety concerns, metallic Li is now ready for a revival, thanks to the development of investigative tools and nanotechnology-based solutions. In this Review, we first summarize the current understanding on Li anodes, then highlight the recent key progress in materials design and advanced characterization techniques, and finally discuss the opportunities and possible directions for future development of Li anodes in applications.

Reviving the lithium metal anode for high-energy batteries

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).

A lithium superionic conductor

Solid-state electrolytes are attracting increasing interest for electrochemical energy storage technologies. In this Review, we provide a background overview and discuss the state of the art, ion-transport mechanisms and fundamental properties of solid-state electrolyte materials of interest for energy storage applications. We focus on recent advances in various classes of battery chemistries and systems that are enabled by solid electrolytes, including all-solid-state lithium-ion batteries and emerging solid-electrolyte lithium batteries that feature cathodes with liquid or gaseous active materials (for example, lithium–air, lithium–sulfur and lithium–bromine systems). A low-cost, safe, aqueous electrochemical energy storage concept with a ‘mediator-ion’ solid electrolyte is also discussed. Advanced battery systems based on solid electrolytes would revitalize the rechargeable battery field because of their safety, excellent stability, long cycle lives and low cost. However, great effort will be needed to implement solid-electrolyte batteries as viable energy storage systems. In this context, we discuss the main issues that must be addressed, such as achieving acceptable ionic conductivity, electrochemical stability and mechanical properties of the solid electrolytes, as well as a compatible electrolyte/electrode interface. This Review details recent advances in battery chemistries and systems enabled by solid electrolytes, including all-solid-state lithium-ion, lithium–air, lithium–sulfur and lithium–bromine batteries, as well as an aqueous battery concept with a mediator-ion solid electrolyte.

Lithium battery chemistries enabled by solid-state electrolytes

Fast Lithium Ion Conduction in Garnet‐Type Li7La3Zr2O12

Colossal magnetoresistance—a huge decrease in resistance in response to a magnetic field—has recently been observed in manganese oxides with perovskite structure. This effect is attracting considerable interest from both fundamental and practical points of view1. In the context of using this effect in practical devices, a noteworthy feature of these materials is the high degree of spin polarization of the charge carriers, caused by the half-metallic nature of these materials20,21; this in principle allows spin-dependent carrier scattering processes, and hence the resistance, to be strongly influenced by low magnetic fields. This type of field control has been demonstrated for charge-carrier scattering at tunnelling junctions2,3 and at crystal-twin or ceramic grain boundaries4,5, although the operating temperature of such structures is still too low (⩽150 K) for most applications. Here we report a material—Sr2FeMoO6, an ordered double perovskite6—exhibiting intrinsic tunnelling-type magnetoresistance at room temperature. We explain the origin of this behaviour with electronic-structure calculations that indicate the material to be half-metallic. Our results show promise for the development of ordered perovskite magnetoresistive devices that are operable at room temperature.

Room-temperature magnetoresistance in an oxide material with an ordered double-perovskite structure

High ionic conductivity in lithium lanthanum titanate

Ferroelectricity was induced in $\mathrm{SrTiO}{}_{3}$ by the isotope exchange of ${}^{18}\mathrm{O}$ for ${}^{16}\mathrm{O}$. Dielectric measurements confirmed the ferroelectricity of $\mathrm{SrTi}{}^{18}\mathrm{O}{}_{3}$, showing a peak at 23 K. A hysteresis loop in the $D$ vs $E$ measurement and TO phonon observed in the Raman spectra supported the evolution of ferroelectricity in $\mathrm{SrTi}{}^{18}\mathrm{O}{}_{3}$. This is the first demonstration of $\mathrm{SrTi}\mathrm{O}{}_{3}$ becoming ferroelectric without the application of external fields or the introduction of a random field through cation substitution.

Ferroelectricity Induced by Oxygen Isotope Exchange in Strontium Titanate Perovskite

Candidate compounds with perovskite structure for high lithium ionic conductivity

A polar oxide ZnSnO3 was synthesized by a solid-state reaction under a pressure of 7 GPa and a temperature of 1000 degrees C. The crystal structure was determined by Rietveld analysis of the X-ray powder diffraction data. ZnSnO3 has a rhombohedral LiNbO3-type structure with unit cell parameters, a = 0.52622(1) nm, c = 1.40026(2) nm (space group: R3c). The polar structure is characterized by the large displacement of Zn along the c-axis in the ZnO6 octahedron based on the strong chemical bonding between Zn and three O. ZnSnO3 is a candidate piezoelectric and pyroelectric material as well as nonlinear optical material.

Yoshiyuki Inaguma

Papers

High ionic conductivity in lithium lanthanum titanate

Ferroelectricity Induced by Oxygen Isotope Exchange in Strontium Titanate Perovskite

Candidate compounds with perovskite structure for high lithium ionic conductivity

A polar oxide ZnSnO3 with a LiNbO3-type structure.

High lithium ion conductivity in the perovskite-type compounds Ln12Li12TiO3(Ln=La,Pr,Nd,Sm)