9 research outputs found
Analysis of the Deterioration Mechanism of Si Electrode as a Li-Ion Battery Anode Using Raman Microspectroscopy
Propylene carbonate (PC) and an ionic
liquid consisting of 1-[(2-methoxyethoxy)Âmethyl]-1-methylpiperidinium
(PP1MEM) and bisÂ(trifluoromethanesulfonyl)Âamide (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
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>
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
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 gÂ(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
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, 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
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
Discovery of DF-461, a Potent Squalene Synthase Inhibitor
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