9 research outputs found

    Analysis of the Deterioration Mechanism of Si Electrode as a Li-Ion Battery Anode Using Raman Microspectroscopy

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    Propylene carbonate (PC) and an ionic liquid consisting of 1-[(2-methoxyethoxy)­methyl]-1-methylpiperidinium (PP1MEM) and bis­(trifluoromethanesulfonyl)­amide (TFSA) were used as electrolyte solvents for Li-ion batteries, and the anode properties of Si electrodes were investigated using a thick film prepared by gas deposition without any binder or conductive additive. The Si electrode in PP1MEM-TFSA exhibited good cycle performance with a reversible capacity of 1050 mA h g<sup>–1</sup> even at the 100th cycle, whereas the Si electrode in PC showed a capacity of only 110 mA h g<sup>–1</sup>. It is noteworthy that the electrode performance was significantly enhanced just by changing the electrolyte solvent to an ionic liquid even with the same Si used as the active material. Raman mapping analyses of the Si anodes after cycling were conducted to clarify the deterioration mechanisms of the electrodes. It was revealed that, in the case of PC, crystalline Si locally remained in the electrode after cycling, and Li–Si alloying and dealloying reactions occurred in limited regions. This led to the generation of intensive stress accumulation due to the extreme volume changes of Si in the regions inside the electrode, causing severe disintegration of the Si electrode. Consequently, the anode property of the Si electrode in PC resulted in very poor performance. In contrast to the behavior in the organic electrolyte, Li–Si reactions uniformly took place over the entire electrode in PP1MEM-TFSA, which relatively avoided any stress accumulation that could lead to electrode disintegration. This is considered to be the reason for the significant improvement in the cycle performance of the Si electrode using the ionic liquid instead of the conventional electrolyte

    Nb-Doped Rutile TiO<sub>2</sub>: a Potential Anode Material for Na-Ion Battery

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    The electrochemical properties of the rutile-type TiO<sub>2</sub> and Nb-doped TiO<sub>2</sub> were investigated for the first time as Na-ion battery anodes. Ti<sub>1–<i>x</i></sub>Nb<sub><i>x</i></sub>O<sub>2</sub> thick-film electrodes without a binder and a conductive additive were prepared using a sol–gel method followed by a gas-deposition method. The TiO<sub>2</sub> electrode showed reversible reactions of Na insertion/extraction accompanied by expansion/contraction of the TiO<sub>2</sub> lattice. Among the Ti<sub>1–<i>x</i></sub>Nb<sub><i>x</i></sub>O<sub>2</sub> electrodes with <i>x</i> = 0–0.18, the Ti<sub>0.94</sub>Nb<sub>0.06</sub>O<sub>2</sub> electrode exhibited the best cycling performance, with a reversible capacity of 160 mA h g<sup>–1</sup> at the 50th cycle. As the Li-ion battery anode, this electrode also attained an excellent rate capability, with a capacity of 120 mA h g<sup>–1</sup> even at the high current density of 16.75 A g<sup>–1</sup> (50<i>C</i>). The improvements in the performances are attributed to a 3 orders of magnitude higher electronic conductivity of Ti<sub>0.94</sub>Nb<sub>0.06</sub>O<sub>2</sub> compared to that of TiO<sub>2</sub>. This offers the possibility of Nb-doped rutile TiO<sub>2</sub> as a Na-ion battery anode as well as a Li-ion battery anode

    Electrochemical Lithiation and Sodiation of Nb-Doped Rutile TiO<sub>2</sub>

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    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 TiO<sub>2</sub> synthesized by a sol–gel method. We changed the particle and crystallite sizes of the Nb-doped rutile TiO<sub>2</sub> 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 TiO<sub>2</sub> showing better high-rate performances exhibited a larger ratio of crystallite size to particle size. The size-dependent enhancement in the performance of rutile TiO<sub>2</sub> was much more drastic than that of anatase TiO<sub>2</sub>. 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

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    The effect of nickel substitution on the electrochemical performance of a lanthanum silicide (LaSi<sub>2</sub>)/silicon (Si) composite electrode for lithium-ion batteries was studied. The results of X-ray diffraction analysis showed that LaSi<sub>2</sub> forms a substitutional solid solution with Ni, and that only the Si site in LaSi<sub>2</sub> is substituted by Ni, whereas elemental Si in the crystal structure is not substituted. Although the charge–discharge capacity of a LaNi<sub><i>x</i></sub>Si<sub>2–<i>x</i></sub> electrode (<i>x</i> = 0.06 and 0.12) was lower than that of a LaSi<sub>2</sub> electrode, the LaNi<sub><i>x</i></sub>Si<sub>2–<i>x</i></sub> electrode exhibited a high-rate performance. A LaNi<sub>0.10</sub>Si<sub>1.90</sub>/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 LaSi<sub>2</sub>/Si composite, and suppressed the decrease in the initial Coulombic efficiency of the Si electrode. The LaNi<sub>0.10</sub>Si<sub>1.90</sub>/Si electrode also exhibited an excellent high-rate performance with a reversible capacity of 2240 mA h g­(Si)<sup>−1</sup> at a rate of 10 C. The results of computational chemistry demonstrated that LaNi<sub>0.25</sub>Si<sub>1.75</sub> favors Li migration in the pathway compared to LaSi<sub>2</sub>. These results indicate that Ni substitution in a LaSi<sub>2</sub>/Si composite negative electrode significantly improves its electrochemical performance

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

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    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

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    Sodiation–desodiation behaviors were investigated for electrodes composed of various binary phosphides, InP, CuP<sub>2</sub>, 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 CuP<sub>2</sub>, 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

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    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

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    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

    Discovery of DF-461, a Potent Squalene Synthase Inhibitor

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    We report the development of a new trifluoromethyltriazolobenzoxazepine series of squalene synthase inhibitors. Structure–activity studies and pharmacokinetics optimization on this series led to the identification of compound <b>23</b> (<b>DF-461</b>), which exhibited potent squalene synthase inhibitory activity, high hepatic selectivity, excellent rat hepatic cholesterol synthesis inhibitory activity, and plasma lipid lowering efficacy in nonrodent repeated dose studies
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