Our lab aims (1) to understand complex phenomena in energy storage systems by the background of Electrochemistry and Materials Science, (2) to issue/elucidate mechanisms to cause problems, and (3) to solve the problems or to devise new concepts and technologies.
 

RESEARCH INTERESTS
  • Lithium-Ion Batteries (LIBs)
  • All-Solid-State Batteries (ASSBs)
  • Atomic Layer Deposition for Batteries
  • Li-Air Batteries
  • Supercapacitor

Overview
  



All-Solid-State Lithium Batteries

  • Thanks to recent developments of superionic conductors (10-2-10-4 S/cm) where Li+-ion conductivity is comparable to that of the conventional liquid electrolyte for lithium-ion batteries (~10-2 S/cm), a proof-of-concept of 'all-solid-state composite batteries' or 'bulk-type all-solid-state batteries' was demonstrated. The all-solid-state batteries do not suffer from any safety concern relating to safety hazards such as solvent leakage and flammability of liquid electrolytes used for commercial lithium–ion batteries (LIBs), still providing high energy density comparable to the LIBs ideally.

  • Several challenging issues - still low conductivity, instability of electrode-electrolyte interface, both electronic and ionic conduction pathways, volume and weight fraction of the solid electrolyte - should be addressed for competitiveness or application of all-solid-state batteries. Conductivity improvement can be achieved by control of crystallinity and composition. Improvement of the performance can be achieved by applying nanostructured electrode materials and selectively chosen solid electrolyte depending on the voltages. Our research efforts will be focusing on development of high performance solid electrolyte and all-solid-state batteries using advanced electrode materials.
  • Prototype "bulk"-type ASSLBs announced recently by several companies attract much attention.  
    •  Aug. 24th, 2012.    Toyota announced Prototypes All-solid-state Battery With 5x Higher Output Density. [Link]

    •  Nov. 18th, 2010.    Toyota announced 4-layer all-solid-state battery that is comprised of LiCoO2/sulfide electrolyte/graphite and exhibits the average potential of 14.4 V. [Link]
    •  Mar. 3rd-5th, 2010.    Idemitsu Idemitsu Showcases A6-size Laminated All-solid Li-ion Battery. The battery is made by using lithium sulfide (solid-state inorganic material) as an electrolyte. [Link]
 

Atomic Layer Deposition (ALD) for Lithium-Ion Batteries (LIBs)
  • Despite their promise, problems with LIBs such as life and safety issues have been bottlenecks for the introduction of these batteries in mass production of advanced electric vehicles (HEVs and PHEVs). Some of the degradation and capacity loss can be traced to corrosion of the electrodes due to electrode dissolution and reactions that occur between the electrodes and the surrounding electrolyte. Establishing long-term durability while operating at realistic temperatures for a battery that does not fail catastrophically remains a significant challenge.

 

  • Atomic layer deposition (ALD) is a gas-phase method of thin-film growth using sequential, self-limiting surface reactions. ALD requires only a minimal amount of precursor, and ALD coatings are conformal and offer atomic thickness control. ALD can be also applied either on powders or on as-fabricated electrodes. The well-known ALD process utilizing trimethylaluminum (TMA) and H2O are  
(A) AlOH* + Al(CH3)3 ® AlO-Al(CH3)2* + CH4  
(B) AlCH3* + H2O ® Al-OH* + CH4                   

ALD was demonstrated to significantly improve the performance of cathode and anode for LIBs in terms of durability, rate capability, and safety. The improvements are explained by protective role of the ALD coatings against undesirable electrode-electrolyte side reactions and enhanced mechanical integrity. An unexpected improvement of performance of LiCoO2/graphite full cell was also studied. Coating the anode appears to reduce the formation of soluble byproducts, mitigating the coupled side reaction that accelerates the degradation of the cathode. Recently, it was demonstrated that the thin Al2O3 ALD coating on polymer separators not only enable wetting by an extremely polar electrolyte but also significantly mitigate thermal shrinkage which is one of the critical factors on safety of LIBs. 
   
  

Study on Structural-Electrochemical Relationship

  • Understanding a relationship between electrochemical behaviors and structural properties in terms of thermodynamics and kinetics is crucial for characterization of the electrode and designing new electrode materials.  One example is a 'thermoelectrochemical activation.' Some materials show no activity toward Li insertion at room temperature even though thermodynamics tells it should react.  After the inactive electrode materials react at elevated temperature, they are converted to be active.  Underlying mechanism is the changed phases or microstructures.  For example, Cu7In3 is inactive at room temperature but can be converted to an active CuIn phase after thermoelectrochemical activation.  Crystalline MoO2 accomodates only one or two Li at room temperature but is converted to an amorphous phase that can uptake four lithium by thermoelectrochemical activation.

Design of New Electrode Architecture