Kaoru Dokko

Innovation in the design of electrolyte materials is crucial for realizing next-generation electrochemical energy storage devices such as Li–S batteries. The theoretical capacity of the S cathode is 10 times higher than that of conventional cathode materials used in current Li–ion batteries. However, Li–S batteries suffer from the dissolution of lithium polysulfides, which are formed by the redox reaction at the S cathode. Herein, we present simple solvate ionic liquids, glyme–Li salt molten com

We demonstrate that Li⁺ hopping conduction, which cannot be explained by conventional models i.e., Onsager's theory and Stokes' law, emerges in highly concentrated liquid electrolytes composed of LiBF₄ and sulfolane (SL). Self-diffusion coefficients of Li⁺ ( D_Li), BF₄^- ( D_BF₄), and SL ( D_SL) were measured with pulsed-field gradient NMR. In the concentrated electrolytes with molar ratios of SL/LiBF<

This is the first report of impedance technique run on single particle electrodes with the aim of clarifying its electronic and ionic transport properties. Measurements were successfully conducted on a particle of 15 μm diam resulting in impedance magnitude on the order of MΩ. The impedance spectra exhibited (i) one semicircle in the high frequency region, (ii) Warburg impedance in low frequencies, and finally, (iii) a limiting capacitance in the very low frequencies. The spectra were analyzed u

LiFePO4 (space group: Pnma) was synthesized by the hydrothermal method at 443 K. The pH of the precursor solution was systematically changed between 2.5 and 9.5. The particle morphology, crystal orientation, and electrochemical reactivity of the prepared LiFePO4 particles changed depending on the concentration of the Li source and pH of the precursor. The particles obtained from acidic solutions (pH ≈ 3.5) were needle-like particles. On the other hand, plate-like crystals were obtained from weak

The kinetics of Li-ion extraction and insertion at single particles (8-21 μm diam) were investigated by cyclic voltammetry, potential step chronoamperometry (PSCA), and electrochemical impedance spectroscopy (EIS) methods using a microelectrode technique. The EIS measurements in a frequency range from 110 kHz to 11 mHz were conducted successfully on a single particle resulting in the magnitude of MΩ orders. The impedance spectra exhibited (i) a single semicircle in the high frequency region, (ii

Chemical states and structural changes accompanying the electrochemical Li extraction and insertion of LiNixMn2 − xO4 (0 < x < 0.5) thin films in LiBF4–EC–DMC solutions, studied by in situ Raman spectroscopy, are reported for the first time. Ex situ Raman measurements for the virgin electrodes revealed that the oxidation state of Ni in the pristine thin films was Ni2+. In situ Raman spectra of the thin films collected in the organic electrolyte during Li ion extraction and insertion in the poten

Li+ ion hopping conduction in highly concentrated solutions of lithium bis(fluorosulfonyl)amide (LiFSA) dissolved in dinitrile solvents, namely succinonitrile, glutaronitrile, and adiponitrile, was investigated. Phase behaviors of the LiFSA/dinitrile binary mixtures assessed by differential scanning calorimetry suggested that LiFSA and the dinitriles form stable solvates in a molar ratio of 1 : 2. For succinonitrile, a glass forming room temperature liquid is formed when [LiFSA]/[succinonitrile]

Electrochemical lithium‐ion extraction/insertion properties of single particles were investigated by attaching a filament microelectrode to the particle in carbonate + propylene carbonate electrolyte. High‐resolution cyclic voltammograms and galvanostatic chronopotentiograms were recorded. In addition, we observed in situ particle fracture during charge‐discharge using an optical microscope equipped with a charge‐coupled device camera. We found that the particle fractures when it is polarized ab

The electrochemical behavior of a lithiated graphite single-particle electrode during high-rate Li deintercalation in an organic electrolyte was investigated using a microelectrode technique. A Ni-plated metal filament (diameter: 10 μm) was attached to a mesocarbon microbead (MCMB) in the electrolyte under optical microscope observation, and galvanostatic charge−discharge tests were carried out. The discharge capacity of a lithiated MCMB particle (diameter: 18 μm) was 2.02 nA h in the potential