Research Topics

Our society has been in transition from a fossil-fuel-based economy to a clean/green energy economy. In the past decade, there has been an exciting development in the field of lithium-ion batteries (LIBs) as energy storage devices, resulting in the application of LIBs in areas ranging from small portable devices to large-scale energy storage systems such as electric vehicles. However, the theoretical energy density of the current LIB system is not sufficient to meet the demand for new markets in areas such as electric vehicles. Next-generation LIBs can be defined as batteries with a higher theoretical energy density than existing LIBs containing a graphite anode and a lithium transition metal oxide cathode, or lower-cost/clean-energy battery systems.

Among the various research candidates, we will focus heavily on research topics based on Topic 1, the reaction mechanism of inorganic materials using advanced electrochemical and structural analyses. The additional scope can be (Topic 2) intercalation batteries based on new mono/multivalent chemistries, such as Na+, K+, Mg2+, Zn2+, Ca2+, and Al3+, which are particularly promising and have the potential to meet the aforementioned criteria. (Topic 3) all-solid-state LIBs could be promising candidates owing to their high safety and high energy density.

Topic 1 : Understanding of the Electrochemical & Structural Mechanism for the Energy Materials

The basic understanding of electrochemical intercalation chemistry (intercalation mechanism, diffusion kinetics, migration barriers, and structural evolutions) during charge/discharge is the key to the development of high-performance materials for batteries. One of our strengths is that we have advanced powder X-ray crystallographic techniques to study the details of intercalation chemistry, that is, 3D electron density map analyses, bond valence sum analyses, and ab-initio structure determination. In addition, electrochemical analyses clearly reveal the interfacial reaction, intercalation reaction, migration barriers, and resistance of inorganic materials.

Therefore, the aim of our research is to uncover the unknown reaction mechanism of inorganic/ceramic materials. Our results provide novel scientific insights into the development of new electrode materials for battery systems.

Topic 2 : Mono/Multivalent-Ion Electrode Materials for Post Li-Ion Batteries

Even though LIBs have been the most popular energy-storage systems to date, particularly in terms of energy and power densities, there are increasing concerns regarding safety issues, insufficient energy density, lower cost, and environmental friendliness. As one of the post-LIB candidates, multivalent-ion batteries based on Mg2+, Ca2+, Zn2+, and Al3+ ions could be one of the options because of the expected large volumetric energy density of their metals and their abundance on Earth. In addition, Na+ and K+-ion batteries have particularly promising potential for lower cost (earth-abundant) and high durability for large-scale energy storage system applications.

Therefore, our research aim is to discover unprecedented materials that could deliver higher capacity or lower cost than current LIBs can provide, by developing an inorganic electrode material and understanding its reaction behavior using electrochemical and crystallographic analysis techniques.

Topic 3 : High Energy-Density All-Solid-State Applications

Flammable liquid electrolytes of LIBs suffer from significant performance degradation and are at risk of catching fire or exploding under harsh or abnormal operating conditions. Thus, all-solid-state batteries (ASSBs) have promising potential for safety issues in LIBs. In addition, ASSBs theoretically increase the energy density while reducing the material (separator, liquid electrolyte) and fabrication costs. However, the low ionic conductivity of solid electrolytes is a bottleneck for the commercialization of ASSBs. To overcome these issues, various types of inorganic materials have been studied using structural engineering techniques.

The aim of this research is to discover and develop high-performance and new inorganic ionic conducting solid electrolytes for ASSBs that could deliver higher energy densities and superior safety than those that present LIBs.