A vanadium pentoxide electrode is prepared in the amorphous form (a-V2O5), and its electrode performances are compared to those for its crystalline counterpart (c-V2O5). The a-V2O5 electrode ...outperforms c-V2O5 in several ways. First, it is free from irreversible phase transitions and Li trapping, which evolve in c-V2O5, probably due to the lack of interactions between the inserted Li+ ions/electrons and V2O5 matrix. Second, the absence of Li trapping allows a reversible capacity amounting to >600 mA h g–1, which is larger than that given by c-V2O5. Third, it shows an excellent rate property. The notably high reversible capacity and rate capability seem to be due to Li storage at vacant sites that are ill-defined but numerous in a-V2O5, which Li+ ions can easily access. However, irreversible capacity of a-V2O5 is appreciable in the first cycle due to a parasitic Li reaction with surface hydroxyl groups. Treatment with n-butyllithium can suppress the irreversible capacity by removing the surface hydroxyl groups.
Extensive studies to develop high-capacity electrodes have been conducted worldwide to meet the urgent demand for next-generation lithium-ion batteries. In this work, we demonstrated a novel strategy ...to alter the lithiation mechanism of the transition metal oxide to increase the reversible capacity of the electrode material. A representative insertion-type negative electrode material, MoO2, was modified by introducing a heterogeneous element (Co) to synthesize the solid solution of CoO and MoO2 (CoMoO3). CoMoO3 exhibited a notably improved reversible capacity of 860 mA h g–1, attributed to the conversion reaction, in contrast to MoO2 that delivers 310 mA h g–1, as it is limited by the insertion reaction. X-ray absorption spectroscopy and X-ray diffraction demonstrated that CoO is converted to Co and Li2O, amorphizing the host structure, whereas the conversion of MoO2 takes place subsequently. Furthermore, the superior initial Coulombic efficiency of CoMoO3 (84.4%) to that of typical conversion materials is attributed to the highly conductive Co and MoO2, which reinforce the electronic conductivity of the active particles. The results obtained from this study provide significant insights to explore high capacity metal oxides for the advanced lithium-ion batteries.
Extensive studies to develop high-capacity electrodes have been conducted worldwide to meet the urgent demand for next-generation lithium-ion batteries. In this work, we demonstrated a novel strategy ...to alter the lithiation mechanism of the transition metal oxide to increase the reversible capacity of the electrode material. A representative insertion-type negative electrode material, MoO
, was modified by introducing a heterogeneous element (Co) to synthesize the solid solution of CoO and MoO
(CoMoO
). CoMoO
exhibited a notably improved reversible capacity of 860 mA h g
, attributed to the conversion reaction, in contrast to MoO
that delivers 310 mA h g
, as it is limited by the insertion reaction. X-ray absorption spectroscopy and X-ray diffraction demonstrated that CoO is converted to Co and Li
O, amorphizing the host structure, whereas the conversion of MoO
takes place subsequently. Furthermore, the superior initial Coulombic efficiency of CoMoO
(84.4%) to that of typical conversion materials is attributed to the highly conductive Co and MoO
, which reinforce the electronic conductivity of the active particles. The results obtained from this study provide significant insights to explore high capacity metal oxides for the advanced lithium-ion batteries.
This work demonstrates that structural defects in amorphous metal oxide electrodes can serve as a reversible Li+ storage site for lithium secondary batteries. For instance, molybdenum dioxide ...electrode in amorphous form (a‐MoO2) exhibits an unexpectedly high Li+ storage capacity (up to four Li per MoO2 unit), which is larger by a factor of four than that for the crystalline counterpart. The conversion‐type lithiation is discarded for this electrode from the absence of Mo metal and lithium oxide (Li2O) in the lithiated a‐MoO2 electrode and the retention of local structural framework. The sloping voltage profile in a wide potential range suggests that Li+ ions are inserted into the structural defects that are electrochemically nonequivalent. This electrode also shows an excellent cycle stability and rate capability. The latter feature is seemingly due to a rather opened Li+ diffusion pathway provided by the structural defects. A high Li+ mobility is confirmed from nuclear magnetic resonance study.
An amorphous MoO2 (a‐Mo2)electrode exhibits an unexpectedly high Li+ storage capacity (up to 810 mA h g−1), which is larger by a factor of four than that of its crystalline counterpart. Li+ ions are hosted by the structural defects in a‐MoO2 and opened vacancies and void spaces give a much faster charge/discharge rate as compared with the crystalline counterpart.
Sodium meta-arsenite (SA) is an orally available arsenic compound. We investigated the effects of SA on the development of autoimmune type 1 diabetes. Female non-obese diabetic (NOD) mice were orally ...intubated with SA (5mg/kg/day) from 8weeks of age for 8weeks. The cumulative incidence of diabetes was monitored until 30weeks of age, islet histology was examined, and lymphocytes including T cells, B cells, CD4+ IFN-γ+ cells, CD8+ IFN-γ+ cells, CD4+ IL-4+ cells, and regulatory T cells were analyzed. We also investigated the diabetogenic ability of splenocytes using an adoptive transfer model and the effect of SA on the proliferation, activation, and expression of glucose transporter 1 (Glut1) in splenocytes treated with SA in vitro and splenocytes isolated from SA-treated mice. SA treatment decreased the incidence of diabetes and delayed disease onset. SA treatment reduced the infiltration of immunocytes in islets, and splenocytes from SA-treated mice showed a reduced ability to transfer diabetes. The number of total splenocytes and T cells and both the number and the proportion of CD4+ IFN-γ+ and CD8+ IFN-γ+ T cells in the spleen were significantly reduced in SA-treated NOD mice compared with controls. The number, but not the proportion, of regulatory T cells was decreased in SA-treated NOD mice. Treatment with SA either in vitro or in vivo inhibited proliferation of splenocytes. In addition, the expression of Glut1 and phosphorylated ERK1/2 was decreased by SA treatment. These results suggest that SA reduces proliferation and activation of T cells, thus preventing autoimmune diabetes in NOD mice.
•SA prevents the development of diabetes and delays the age of onset in NOD mice.•SA decreases the number but not the proportion of T lymphocytes in NOD mice.•SA reduces IFN-γ-producing T lymphocytes in NOD mice.•SA reduces proliferation and activation of T lymphocytes in vitro and in vivo.•SA reduces the expression of glucose transporter 1 (Glut1) in splenocytes.
Amorphous molybdenum oxides are prepared by a reduction of Mo6+ aqueous solution with KBH4. Two molybdenum oxides that differ in the average Mo valence are obtained by changing the solution pH, and ...their electrode performance is compared with each other. The X‐ray absorption spectroscopy and thermogravimetric analysis illustrate that the sample prepared at the higher pH (4.0) shows an Mo valence of +5.5, which is close to that for MoO3, whereas the Mo valence (+4.4) for the other sample, prepared at the lower pH (0.8), is close to that for MoO2. The latter electrode outperforms the former with respect to cycle retention. The former electrode is lithiated by a conversion reaction, which is the case for MoO3. This electrode exhibits a larger initial capacity, but poorer cycle performance, due to massive volume change and repeated metal‐oxygen bond breaking/formation with cycling. The other electrode, the Mo valence, which is +4.4, is lithiated by an addition reaction, in which Li+ ions are stored in structural defects, such as vacancies and void spaces. The superior cycle performance of this electrode can be ascribed to the absence of massive volume change and bond breaking/formation.
To improve the coulombic efficiency of GeO
2 electrode, a Cu-containing ternary metal oxide (CuGeO
3) was prepared and the electrochemical behavior of Cu component was studied. The GeO
2 electrode ...shows a low coulombic efficiency in the first cycle (43%), which is mainly caused by a poor Ge oxidation kinetics (Ge
+
2Li
2O
→
GeO
2
+
2Li
+
+
2e
−). The X-ray absorption spectroscopy (XAS) data illustrate that the Cu component in CuGeO
3 is converted to nano-sized metallic Cu in the earlier stage of lithiation but idles thereafter. In contrast, the Ge component in CuGeO
3 behaves like the GeO
2 electrode. It is converted to nano-sized Ge by a conversion reaction and further lithiated by alloying reaction. The de-lithiation proceeds in the reverse order. The CuGeO
3 electrode shows a much improved coulombic efficiency (74%) in the first cycle, which is indebted to a facilitated Ge oxidation with a much reduced electrode polarization. This feature has been explained by the favorable roles provided by the
in situ generated nano-sized metallic Cu particles that make such an intimate contact with the nano-sized Ge and Li
2O that they can catalyze Li
2O decomposition and provide an electronic conductive network for Ge oxidation. A similar favorable effect was observed with the other ternary oxides (FeGeO
3 and CoGeO
3), wherein the formation of nano-sized metallic Fe and Co can be assumed.
