Researchers have discovered a pyrochlore-like oxyfluoride as a stable lithium-ion conductor with excellent conductivity, suitable for use as solid electrolytes in all-state lithium-ion batteries. Credit: scalespeeder from Openverse
Scientists have identified a stable and highly conductive lithium-ion conductor that can be used as a solid electrolyte in solid-state lithium-ion batteries.
Solid lithium-ion batteries, which use solid electrolytes, are non-flammable and have higher energy density and ion transfer indices than their liquid electrolyte counterparts. These characteristics position them as a potential replacement in markets dominated by traditional wet cell batteries, including electric vehicles. Despite these advantages, solid electrolytes have disadvantages such as lower lithium-ion conductivity and difficulty in maintaining sufficient contact between the electrodes and the solid electrolyte.
Although solid sulfide electrolytes are conductive, they react with moisture to form toxic hydrogen disulfide. Therefore, there is a need for sulfide-free solid electrolytes that are conductive and stable in air to make safe, high-performance, fast-charging lithium-ion batteries.
In a recent study published in the journal Chemistry of materialsresearch team led by Professor Kenjiro Fujimoto, Professor Akihisa Aimi of Tokyo University of Science and Dr. Shuhei Yoshida of DENSO CORPORATION, discovered a stable and highly conductive Li-ion conductor in the form of oxyfluoride pyrochlore type.
According to Professor Fujimoto, “The development of all-solid lithium-ion secondary batteries has been a long-standing dream of many battery researchers. We have discovered a solid oxide electrolyte that is a key component of all-solid lithium-ion batteries, which have both high energy density and safety. In addition to being stable in air, the material exhibits higher ionic conductivity than previously reported solid oxide electrolytes.
Detailed analysis and performance
The pyrochlore-type oxyfluoride studied in this paper can be denoted as Li2-xThere(1+x)/3Mr.2Oh6F (Mr. = Nb,Ta). It has been subjected to structural and compositional analysis using various techniques including X-ray diffraction, Rietveld analysis, inductive coupling plasma optical emission spectrometry and electron diffraction in a selected area. More precisely, Li1.25There0.58Not.2Oh6F was developed, showing a total ionic conductivity of 7.0 mS cm⁻¹ and a total ionic conductivity of 3.9 mS cm⁻¹ at room temperature. It was found to be better than the lithium-ion conductivity of known solid oxide electrolytes. The activation energy of the ionic conductivity of this material is extremely low, and the ionic conductivity of this material at low temperatures is one of the highest among known solid electrolytes, including sulfide materials.
Exactly, even at –10°C, the new material has the same conductivity as classical electrolytes based on solid oxides at room temperature. In addition, since conductivity above 100°C has also been verified, the operating range of this solid electrolyte is from –10°C to 100°C. Conventional lithium-ion batteries cannot be used at temperatures below zero. Therefore, the operating conditions of frequently used lithium-ion batteries for mobile phones range from 0°C to 45°C.
The mechanism of Li-ion conductivity in this material was studied. The conduction path of the pyrochlore-like structure covers the F ions located in the tunnels created Mr.Oh6 octahedra. The conduction mechanism is the sequential movement of Li ions while changing bonds with F ions that move to the nearest Li position always passing through metastable positions. Immobile3+ bound to the F ion inhibits the conduction of Li-ions by blocking the conduction path and causing the disappearance of the surrounding metastable positions.
Unlike existing lithium-ion secondary batteries, all oxide-based batteries do not have the risk of electrolyte leakage due to damage or the risk of toxic gas formation as with sulfide-based batteries. Therefore, this new innovation should guide future research. “The newly discovered material is safe and exhibits higher ionic conductivity than previously published solid oxide electrolytes. The application of this material holds promise for the development of revolutionary batteries that can operate in a wide range of temperatures, from low to high,” predicts Professor Fujimoto. “We believe that the performance requirements for solid electrolyte applications for electric vehicles have been met. »
The new material is extremely stable and will not catch fire if damaged. It is suitable for airplanes and other places where safety is important. It is also suitable for high-capacity applications, such as electric vehicles, as it can be used at high temperatures and allows fast charging. Moreover, it is also a promising material for the miniaturization of batteries, home appliances and medical devices.
In summary, the researchers not only discovered a lithium-ion conductor with high conductivity and stability in air, but also introduced a new type of superionic conductor with a pyrochlore-like oxyfluoride. Exploring the local structure around lithium, its dynamic changes during conduction, and its potential as solid electrolytes for all-solid batteries are important areas for future research!