Electrochemical Lithiation and Sodiation of Nb-Doped Rutile TiO₂

As anode materials of Li-ion and Na-ion batteries, the electrochemical insertion/extraction reactions of Li and Na were investigated for a rutile-type Nb-doped TiO₂ synthesized by a sol–gel method. We changed the particle and crystallite sizes of the Nb-doped rutile TiO₂ powders by annealing at various temperatures between 100 and 1000 °C and prepared thick-film electrodes consisting of the powders. The anode performances were remarkably improved not only in the Li-ion battery but also in the Na-ion battery with a reduced annealing temperature of 400 from 1000 °C. We revealed that the Nb-doped TiO₂ showing better high-rate performances exhibited a larger ratio of crystallite size to particle size. The size-dependent enhancement in the performance of rutile TiO₂ was much more drastic than that of anatase TiO₂. These results suggest that rutile’s potential diffusivity of Li and Na appeared more obviously when increasing the ratio because its diffusion coefficient is anisotropic and significantly high

Improved Electrochemical Performance of Lanthanum Silicide/Silicon Composite Electrode with Nickel Substitution for Lithium-Ion Batteries

The effect of nickel substitution on the electrochemical performance of a lanthanum silicide (LaSi₂)/silicon (Si) composite electrode for lithium-ion batteries was studied. The results of X-ray diffraction analysis showed that LaSi₂ forms a substitutional solid solution with Ni, and that only the Si site in LaSi₂ is substituted by Ni, whereas elemental Si in the crystal structure is not substituted. Although the charge–discharge capacity of a LaNi_<i>x</i>Si_2–<i>x</i> electrode (<i>x</i> = 0.06 and 0.12) was lower than that of a LaSi₂ electrode, the LaNi_<i>x</i>Si_2–<i>x</i> electrode exhibited a high-rate performance. A LaNi_0.10Si_1.90/Si (70:30 wt %) composite electrode showed a large initial discharge capacity and a superior long-term cycle performance compared to electrodes composed of Si alone and LaSi₂/Si composite, and suppressed the decrease in the initial Coulombic efficiency of the Si electrode. The LaNi_0.10Si_1.90/Si electrode also exhibited an excellent high-rate performance with a reversible capacity of 2240 mA h g­(Si)⁻¹ at a rate of 10 C. The results of computational chemistry demonstrated that LaNi_0.25Si_1.75 favors Li migration in the pathway compared to LaSi₂. These results indicate that Ni substitution in a LaSi₂/Si composite negative electrode significantly improves its electrochemical performance

Effect of Phosphorus-Doping on Electrochemical Performance of Silicon Negative Electrodes in Lithium-Ion Batteries

The effect of phosphorus (P)-doping on the electrochemical performance of Si negative electrodes in lithium-ion batteries was investigated. Field-emission scanning electron microscopy was used to observe changes in surface morphology. Surface crystallinity and the phase transition of Si negative electrodes before and after a charge–discharge cycle were investigated by Raman spectroscopy and X-ray diffraction. Li insertion energy into Si was also calculated based on computational chemistry. The results showed that a low P concentration of 124 ppm has a meaningful influence on the electrochemical properties of a Si negative electrode; the cycle performance is improved by P-doping of Si. P-doping suppresses the changes in the surface morphology of a Si negative electrode and the phase transition during a charge–discharge cycle. Li insertion energy increases with an increase in the P concentration; Li insertion into P-doped Si is energetically unfavorable, which indicates that the crystal lattice of Si shrinks as a result of the replacement of some Si atoms with smaller P atoms, and therefore, it is more difficult to insert Li into P-doped Si. These results reveal that suppression of the phase transition reduces the large change in the volume of Si and prevents a Si negative electrode from disintegrating, which helps to improve the otherwise poor cycle performance of a Si electrode

Sodiation–Desodiation Reactions of Various Binary Phosphides as Novel Anode Materials of Na-Ion Battery

Sodiation–desodiation behaviors were investigated for electrodes composed of various binary phosphides, InP, CuP₂, GeP, SiP, and LaP, as anode materials of a Na-ion battery. Although LaP electrode did not react with Na, the other electrodes showed reversible sodiation–desodiation reactions in the initial cycles. Rapid capacity decays were observed for CuP₂, GeP, and SiP electrodes. In contrast, a better cyclability was attained for the InP electrode. These results indicate that binary phosphides (<i>M</i>–P) require four properties for improving cyclability: (i) low thermodynamic stability of <i>M</i>–P, (ii) high electronic conductivity of <i>M</i>, (iii) low hardness of <i>M</i>, and (iv) reactivity of <i>M</i> with Na

Nickel-Doped Titanium Oxide with Layered Rock-Salt Structure for Advanced Li-Storage Materials

As advanced anode materials for Li-ion batteries, single-crystalline particles of Ni-, Cu-, and Zn-doped rutile TiO2 with doping amounts of 1–2 at % were synthesized by a hydrothermal method. The effect of divalent cation (Ni2+, Cu2+, and Zn2+) doping on the Li+ diffusion behavior was clarified after the phase change from a rutile structure to a monoclinic layered rock-salt structure. The larger oxygen vacancy amounts were detected for Ni- and Zn-doped TiO2 particles due to their larger doping amounts. The Ni-doped TiO2 electrode exhibited the best high-rate performance with a high reversible capacity of 115 mA h g–1 even at a very high current rate of 100C (33.5 A g–1). This electrode showed an excellent long-term cycling performance with 170 mA h g–1 even after 24,000 cycles. No significant difference was observed depending on the type of doping element: the Li+ diffusion coefficient ranged from 8.8 × 10–15 to 1.3 × 10–14 cm2 s–1. In contrast, the charge transfer resistance of the Ni-doped TiO2 electrode was lower than those of the other electrodes. The first-principles calculation confirmed that the oxygen vacancy donor levels were formed in the forbidden band of the cation-doped layered rock-salt TiO2 to improve its electronic conductivity and that the activation energy required for Li+ diffusion could be reduced by Ni doping. Therefore, we considered that Li+ transfer was promoted in Ni-doped TiO2 to enhance charge–discharge capacities. These results demonstrate the outstanding effect of Ni doping on high-rate and long-term performances

Anode Properties of Sb-Based Alloy Electrodes for K‑Ion Batteries in an Ionic-Liquid Electrolyte

Maintaining the sustainability of society demands the strategic use of multipurpose rechargeable batteries. One promising option is K-ion batteries (KIBs), which are suitable as large stationary storage batteries and store renewable energy because of their abundant K resources. Herein, the anode properties of different binary antimonide (MSbx; M: metal) electrodes were investigated for KIBs in an ionic-liquid electrolyte. The results indicated that although Sb and SnSb electrodes exhibited a high initial reversible capacity, their cycle stability was poor. In contrast, rare-earth antimonide (LaSb, SmSb, and YSb) electrodes showed extremely long cycle stability over 500 cycles with a capacity approximately one-third that of the Sb electrode. Interestingly, rare-earth antimonides possess seamless alloying and dealloying with K without undergoing phase separation into rare-earth and Sb phases. Additionally, other MSbx electrodes, such as FeSb2, FeSb, and AlSb, exhibited relatively higher reversible capacity and cycle stability when M was K-inactive. These electrodes possessed moderate Mohs hardness and low electrical resistance and caused MSbx phase separation into M and Sb phases. Notably, the stiff M phase effectively withstood the compressive stress produced by Sb and provided a supporting skeleton. Our study will provide insight into the physicochemical properties of M alloyed with Sb to achieve excellent cycle stability in KIBs and reveal that the same active material demonstrated different anode properties than Na-ion batteries

Ultrafine Fiber Raman Probe with High Spatial Resolution and Fluorescence Noise Reduction

Considerable interest has been shown in fiber Raman probes as powerful tools for in situ biomedical diagnosis and monitoring processes in the materials industry. Miniaturization and high spatial resolution are required for less invasive measurements with accurate locations. In analysis of organs, widespread visible excitation light produces problematic fluorescence backgrounds. Here, we report an ultrafine fiber Raman probe that is thinner than the needle of a mosquito (labrum: 50–80 μm in diameter) with high spatial resolution (23 μm) and with a function of fluorescence background reduction. Due to the fineness and resolution, the distribution of ions in an electrolyte solution in narrow spaces could be measured. Backgrounds in spectra of liquid containing fluorescent impurity were reduced by using the probe. The probe has wide applicability for noninvasive in situ molecular diagnosis of organs and small devices