Research Summary
Due to the exponential spread of mobile terminal devices and the rising awareness of environmental protection, social needs for more sophisticated batteries are stronger than ever before. Lithium batteries and solid electrolyte fuel cells are the essential tools for the people in the 21st century and have become highly functional. Our research group vigorously promotes to create functional materials and to develop their physical properties, which lead us to develop electro-chemical energy conversion devices with a new functional mechanism.
Designing and Developing Functional Materials for Energy Storage and Conversion
We first research on required functions of materials to examine what chemical element combinations and crystal structures are needed to create the actual materials. Then we widely examine their feasibilities from an inorganic solid chemistry point of view. We also develop the routes for synthesizing the needed materials with various synthesizing techniques such as pressurization, electrochemistry, and softchemistry. When new inorganic solid materials are synthesized, their crystal structures, electromagnetisms, and electrochemical features are investigated in detail and all the information is given as feedback to our material synthetic experiments. By utilizing these methods, we have successfully developed a quite few new materials with required functions.
Mechanistic Study on Host-Guest Reaction
As guest elements, light elements such as lithium and hydrogen that play roles of storage and transporters of energy, reversibly go in and out of the host, a strong crystalized lattice. This intercalation reaction is widely used as electric reaction. A new battery system, lithium-ion battery, has been built by skillfully combining these reactions, and has been successfully validated as a high functional battery.
The phenomena of the changes of crystal structures and physical properties during the intercalation of the guest elements involve various factors. Revealing these factors is one of the best parts of being a solid-state chemist. Because these phenomena greatly affect the charging-discharging feature of battery system, understanding these factors are critically important when they are implemented in practical use. From different perspectives including mean structure, local structure, regularly arrayed guest elements, modulation, fluctuation, and aggregation, we are trying to correctly grasp the information of the light elements such as lithium and hydrogen. We even use highly brilliant synchrotron radiation and neutron to precisely determine the reaction mechanisms. Since we have discovered some novel phase transition phenomena in layered rock salt LiNiO2, spinel LiMn2O4, olivine LiFePO4 and other related materials, we have been conducting in-depth discussions on the essence of material features including lattice instability, electronic transportation, magnetic interaction, and electronic lattice interaction to find out their relevance to the electrode features.
Electrode Materials for Fuel Cells
Material science plays the important role not only in lithium ion batteries, but also in fuel cells, another next generation energy exchange device. We promote the development of new pyrochlore electrode materials, the optimization of electrode structures for the low-temperature operation of solid-state oxide fuel cells, and the elucidation of their electric reactions from various points of view.
Development of Super Ionic Conductors and the Related Material Science
While they are in solid state, super ionic conductors (solid electrolytes) allow ions to selectively move around inside the structure in high speed. Our research lab has been researching the mechanism of high-speed ionic diffusion and the development of new materials based on the mechanism of super ionic conductors. These studies have led us to discover a new solid-state material group, LGPS (Li10GeP2S12 type compounds), which has the highest lithium ion conductivity. It has been expected that replacing organic electrolytes to solid materials can broaden the possibility of lithium batteries. We also work on the demonstrations of the principles of various high functional devices with new materials as cores. One of our themes is the exploratory research of proton conductors believing that they will be developed to the next generation fuel cells.
Analysis of Electrode Interface Reaction for the Realization of High-Speed Charge Exchange Reaction
All electrical energy conversion devices have electrode/electrolyte interfaces where charge exchange reaction occurs. This reaction often regulates the features of the devices. We research to reveal systemically the mechanisms of anisotropy, ultrastructural changes, and electronic state changes during the interface reaction that progress in only a few nanometers region by using a new nanometer direct analysis technique. This technique is being established as a technique to build three-dimensional nano-interfaces with self-organization reaction and ideal interfaces of simple crystal thin films with pulse laser synthetic method, and to provide the reaction field for the elucidation of the interface reaction mechanism.
Development to All-Solid-State Battery
All-solid-state battery, which only be realized with the comprehensive optimization of combining electrode materials and electrolyte materials and their interface forming technology, is considered as an ideal chemical-electrical conversion device, and is believed to be a great future technology. For its realization, the development of all-solid-state batteries is taken place by examining their optimized mechanism based on LGPS, making prototype devices to find out their issues, and going through the underlying technologies to solve the issues.