A one (single) particle measurement was employed to estimate electrochemical parameters of active materials for lithium ion batteries in order to design porous electrodes and cells. A micro electrode was used as a current collector for LiCoO2 and graphite particles. In the cases of materials with large expansion and shrinkage during discharge and charge process, a tweezers-type current collector was developed and applied to the measurement. Si particle as an anode material for post lithium ion batteries was measured by using a tweezers-type current collector to stabilize a contact between active material and current collector. Successfully, the tweezers-type current collector provided a stable contact to the active material particle. The electrochemical parameters for various active materials were obtained from the one (single) particle measurement. Based on these parameters, the porous electrode and lithium ion cell can be designed.
Oxygen reduction reaction (ORR) rate constants (k) on Pt and Pt–M (M = Fe, Co, Ni) electrodes were evaluated in N-ethyl-N-methylpyrrolidinium fluorohydrogenate (EMPyr(FH)1.7F) ionic liquid at 298–333 K. The Pt–Fe electrode exhibited the best catalytic activity in EMPyr(FH)1.7F, because of the large surface area of its nanoporous structure after Fe dissolution. X-ray photoelectron spectroscopy and field-emission scanning electron microscopy showed that Co and Ni barely dissolved in EMPyr(FH)1.7F. The observed ORR activities of Pt–Co and Pt–Ni alloys were lower than that of Pt in EMPyr(FH)1.7F.
In-situ atomic force microscopy (AFM) was applied to the investigation of surface film formation processes on a nongraphitizable carbon electrode. A glassy carbon (GC) plate with heat-treatment at 500°C was used as a model electrode of the nongraphitizable carbon. The in-situ AFM was combined with a cyclic voltammetry measurement. Based on the results, the effect of different electrolyte solutions was investigated and the thickness of the surface film on GC was found to be thinner than that on highly oriented pyrolytic graphite.
To elucidate effective species and their quantitative requirements for reversible magnesium deposition, a triglyme solution of ethylmagnesium bromide (EtMgBr) complex was mixed with magnesium bis(trifluoromethanesulfonyl) amide/triglyme solution in various ratios. The mixed electrolyte characteristics have been assessed using electrochemical magnesium deposition tests, titration of methanol, and Raman spectroscopy. The existence of EtMgBr reduces the overpotential of magnesium deposition. The Coulombic efficiency of this process varies linearly with the EtMgBr content, although the active EtMgBr decreases more than expected from the mixing ratio. Raman spectra for the mixed electrolyte suggest a change in the structure of magnesium bromide species and coordination mode of magnesium by mixing of EtMgBr with magnesium sulfonylamide salt.
Dialkyl ethers show high relative permittivities and low viscosities as compared to the corresponding linear carbonates. We have synthesized 1-(2-fluoroethoxy)-2-(2,2,2-trifluoroethoxy)ethane (FETFEE). The relative permittivity and viscosity of FETFEE were higher than those of 1,2-diethoxyethane (DEE, ethylene glycol diethyl ether). The conductivity of 1 mol dm−3 LiPF6 solution in FETFEE was higher than that in 1-ethoxy-2-(2,2,2-trifluoroethoxy)ethane (ETFEE). The use of FETFEE as a co-solvent improved the discharge capacity of a Li | LiCoO2 coin cell.
The differing activities of cobalt-phosphate (Co-Pi) and cobalt-borate (Co-Bi) oxygen evolution cocatalysts photodeposited on SrTiO3 photoelectrodes under the same conditions for use in water splitting were investigated using in situ X-ray absorption fine structure (XAFS) spectroscopy. Prior to XAFS analyses, the photoelectrochemical water oxidation activities of both cocatalysts were assessed by linear sweep voltammetry, with results demonstrating that the Co-Bi cocatalyst enhances oxygen evolution to a greater degree than the Co-Pi. Co K-edge XAFS spectra were acquired for both cocatalysts on SrTiO3 photoelectrodes during photoelectrochemical water splitting. The XAFS spectrum of the Co-Bi was significantly more intense than that of the Co-Pi, indicating that a greater concentration of the Co-Bi cocatalyst was present on the photoelectrode compared with the Co-Pi. The results of this study demonstrate that both the Co-Pi and Co-Bi cocatalysts are able to efficiently promote water oxidation, and that the Co-Bi functions more effectively than the Co-Pi because it generates a greater abundance of reaction sites.
In this paper, we studied platinum (Pt)- and cobalt oxide (CoOx)-loaded silver tantalate (AgTaO3) for photocatalytic overall water splitting. Pt and CoOx were loaded on AgTaO3 by photodeposition, and the obtained photocatalysts were characterized by using powder X-ray diffraction (XRD), UV-visible (UV-vis) absorption spectroscopy, X-ray photoelectron spectroscopy (XPS), inductively coupled plasma atomic emission spectroscopy (ICP-AES), and microscope inspection. By the scanning transmission electron microscope (STEM) inspection, the diameters of Pt and CoOx particles were found to be approximately 30 and 50 nm, respectively. When AgTaO3 photocatalyst loaded with Pt and CoOx nanoparticles was employed for water splitting, the activity was demonstrated to be 80 times higher compared with the bare AgTaO3, indicating that the photodeposited Pt and CoOx effectively functioned as the hydrogen (H2) and oxygen (O2) evolution cocatalysts, respectively. While the use of photodeposited CoOx is often limited in photoelectrochemical water oxidation and photocatalytic half-reaction of water, CoOx deposited on AgTaO3 could be demonstrated to enhance the photocatalytic overall water splitting activity.
An atomic configuration of LiNi0.5Mn0.5O2 with the layered rock-salt structure was investigated by means of the reverse Monte Carlo simulation using neuron Faber-Ziman type structure factor, reduced pair distribution function and Bragg profile simultaneously. From the obtained atomic-configuration snapshot, it is indicated that a bond length of Ni-O is longer than that of Mn-O and is almost the same as that of Li-O. The tendency reflects the different ionic radii of the cations, and should be one of the reasons for a position exchange between Li and Ni in the layered structure, i.e., a cation mixing. It is also demonstrated that a significant correlation of Ni-Ni can be found around 4 Å. Since the correlation corresponds to the second-nearest distance between the Li and transition-metal layers, the analytical result suggests a partial formation of a Ni-O rock-salt domain which can be considered as inactive for Li diffusion. In order to study distributions of Ni and Mn in the transition-metal layer, we analyzed bond-angle distributions of the transition metals. As a result, it is indicated that Ni-Ni-Ni and Mn-Mn-Mn bond angles have the highest probability at 120°, suggesting a local ordering of the transition metals.
In-situ simultaneous measurement technique of soft X-ray absorption and X-ray emission spectroscopy, which was available for atmospheric pressure and high temperature, was developed. This technique is expected to provide direct information about electronic structures, both occupied and unoccupied pDOS, of functional materials under controlled atmospheric and temperature conditions. In this work, this technique was applied to simultaneously measure O K-edge X-ray absorption and X-ray emission spectra of LaCoO3-based oxides under various oxygen partial pressure and temperatures. Clear O K-edge spectra could be obtained even in 1 bar of 100 ppm O2-He, 0.1%O2-He and 1%O2-He atmospheres below 873 K. The changes of the O K-edge X-ray absorption and X-ray emission spectra due to the changes of oxygen partial pressure and temperature were discussed in terms of changes of defect concentrations and spin states of the oxides. Availability of the developed in-situ simultaneous spectroscopic technique was successfully demonstrated.
A binary system, x Li4MoO5–(1 − x) LiFeO2, is studied as electrode materials for rechargeable lithium batteries. A sample of single phase is obtained at x = 0.5, and it is found that Li1.42Mo0.29Fe0.29O2 (x = 0.5) crystalizes into Li5ReO6-type structure. Although an initial charge capacity of Li1.42Mo0.29Fe0.29O2 reaches 350 mAh g−1, irreversible phase transition associated with oxygen loss and molybdenum migration on charge is evidenced by X-ray diffraction and X-ray absorption spectroscopy. The irreversible phase transition inevitably results in large polarization on discharge as electrode materials in Li cells. These findings provide the basis for the development of high-capacity electrode materials with solid-state redox reaction of oxide ions.
The LiNi0.8Co0.2O2 was synthesized by the coprecipitation method, and then measured using powder neutron diffractions of electrochemically cycled cathodes. Crystal and electronic structure analyses were conducted using the Rietveld and maximum entropy methods (MEM). Based on those results, we tried to reveal the charge and discharge mechanism of this material, and to clarify the influence of the crystal structure on the several charge or discharge depths. We analysed the crystal structures of the electrodes after second discharge process as well as the pristine electrode by the Rietveld analysis which used neutron diffraction and synchrotron X-ray diffraction data. As a result, it was demonstrated that the crystal structure analysis by ex-situ measurement could be successfully performed even for the electrode with a weight of about 10 mg. Furthermore, we examined the average structure of the electrode accompanying with charge depths. The electrodes were prepared about 2.50 V, 3.65 V, 3.85 V, and 4.30 V which corresponded to the plateau portions of a 10th charging curve. In the analysis of the electrode accompanying charge depths, it was suggested that there was almost no participation to cation mixing accompanying charge depth.
After electrochemically extracting lithium ions from LiNi0.5Mn1.5O4, we have investigated the structural variation during the relaxation process by means of X-ray diffraction coupled with the Rietveld analysis, assuming Li-rich and Li-lean spinel phases with symmetry coexistence. For both x = 0.1 and 0.2 of LixNi0.5Mn1.5O4, mole fraction of Li-lean phase decreases with the relaxation time, although any apparent change in lattice parameter does not occur for both phases. This indicates that Li-lean phase with larger oxygen tetrahedron size, presumably favorable for lithium diffusion, is formed with excess amount during the lithium extraction, and then it transforms into Li-rich and Li-lean phases with smaller lithium concentration during the relaxation process. Slight increase in the size of oxygen tetrahedron and decrease in that of octahedron during relaxation for Li-lean phase of x = 0.1 are also consistent with above phase change.
Raman spectroscopy was conducted for LiNi1/3Mn1/3Co1/3O2 (NMC) composite positive electrodes in all-solid-state batteries using Li2S-P2S5 solid electrolytes. Raman spectral changes attributable to structural changes of NMC were observed during the initial charge-discharge test. To evaluate state-of-charge (SOC) distributions in the NMC electrodes, Raman mapping was carried out for the electrodes of charged and discharged cells. The mapping images indicated that most NMC particles were uniformly delithiated and lithiated by the charge-discharge process. It is noteworthy that uniform charge-discharge reactions proceeded in the NMC electrodes.