Sodium layered oxides NaxCoO2 form one of the most fascinating low-dimensional and strongly correlated systems; in particular P2–NaxCoO2 exhibits various single-phase domains with different ...Na+/vacancy patterns depending on the sodium concentration. Here we used sodium batteries to clearly depict the P2–NaxCoO2 phase diagram for x≥0.50. By coupling the electrochemical process with an in situ X-ray diffraction experiment, we identified the succession of single-phase or two-phase domains appearing on sodium intercalation with a rather good accuracy compared with previous studies. We reported new single-phase domains and we underlined the thermal instability of some ordered phases from an electrochemical study at various temperatures. As each phase is characterized by the position of its Fermi level versus the Na+/Na couple, we showed that the synthesis of each material, even in large amounts, can be carried out electrochemically. The physical properties of the as-prepared Na1/2CoO2 and Na2/3CoO2 ordered phases were characterized and compared. Electrochemical processes are confirmed to be an accurate route to precisely investigate in a continuous way such a complex system and provide a new way to synthesize materials with a very narrow existence range.
Lithium iron phosphate is one of the most promising positive-electrode materials for the next generation of lithium-ion batteries that will be used in electric and plug-in hybrid vehicles. Lithium ...deintercalation (intercalation) proceeds through a two-phase reaction between compositions very close to LiFePO(4) and FePO(4). As both endmember phases are very poor ionic and electronic conductors, it is difficult to understand the intercalation mechanism at the microscopic scale. Here, we report a characterization of electrochemically deintercalated nanomaterials by X-ray diffraction and electron microscopy that shows the coexistence of fully intercalated and fully deintercalated individual particles. This result indicates that the growth reaction is considerably faster than its nucleation. The reaction mechanism is described by a 'domino-cascade model' and is explained by the existence of structural constraints occurring just at the reaction interface: the minimization of the elastic energy enhances the deintercalation (intercalation) process that occurs as a wave moving through the entire crystal. This model opens new perspectives in the search for new electrode materials even with poor ionic and electronic conductivities.
Operando X-ray absorption spectroscopy investigations have been carried out to follow changes in the atomic and electronic local structures of all three transition metals for the ...Li1.20Mn0.54Co0.13Ni0.13O2 layered oxide during the first and second charges and discharges of lithium batteries. The experiments were performed using a Quick-XAS monochromator on the SAMBA beamline at Synchrotron SOLEIL to record the three K-edges by edge-jumping between two energy ranges (Mn, Co and Co, Ni) every 3 min during the cycling of the battery. The results obtained especially at the Mn K-edge fully support the participation of oxygen in the reversible charge–discharge reaction of this Li- and Mn-rich layered material as a redox center and not only with oxygen loss, as was proposed previously.
The structure of Li2MnO3 was investigated by the means of X-ray and electron diffraction as well as high resolution transmission electron microscopy experiments. Extra spots are present in the ...Li2MnO3 electron diffraction patterns, and their origin is fully understood and explained here. They result from the existence of diffuse scattering lines observed along the c* monoclinic axis, intercepted by the Ewald’s sphere, and not from double diffraction phenomenon nor from superstructure. Furthermore, the origin of these scattering lines is due to stacking faults of the ordered lithium/manganese layers along the c-axis that were observed in images obtained using high resolution transmission electron microscopy.
Lithium deintercalation of Li x CoO2 from x = 1 to x ≈ 0 has been carried out electrochemically. The changes in the electronic structure from LiCoO2 to CoO2 have been investigated by X-ray ...photoelectron spectroscopy (XPS) to bring some new developments about the electron transfer mechanisms upon lithium deintercalation. All available XPS core peaks (Co 2p, Co 3p, Co 3s, O 1s, F 1s, P 2p, C 1s) and valence spectra have been analyzed. The contributions of the electrode material and of the electrode/electrolyte interface have been clearly distinguished. We show that cobalt and oxygen simultaneously undergo a partial oxidation process and that the sole participation of oxygen atoms to the charge transfer process, as it is sometimes assumed, can be excluded. The surface film consists of organic and inorganic species resulting from degradation of the electrolyte.
Sodium intercalation in P2-Na2/3Co2/3Mn1/3O2 (obtained by a coprecipitation method) was investigated by ex situ and in situ X-ray absorption spectroscopy. The electronic transitions at the O K-edge ...and the charge compensation mechanism, during the sodium intercalation process, were elucidated by combining Density Function Theory (DFT) calculations and X-ray absorption spectroscopy (XAS) data. The pre-edge of the oxygen K-edge moves to higher energy while the integrated intensity dramatically decreases, indicating that the population of holes in O 2p states is reduced with increasing numbers of sodium ions. From the K-edge and L-edge observations, the oxidation states of pristine Co and Mn were determined to be +III and +IV, respectively. The absorption energy shifts to lower positions during the discharging process for both the Co and the Mn edges, suggesting that the redox pairs, that is, Co3+/Co2+ and Mn4+/Mn3+, are both involved in the reaction.
Glioblastomas (GBM) are some bad prognosis brain tumors despite a conventional treatment associating surgical resection and subsequent radio-chemotherapy. Among these heterogeneous tumors, a ...subpopulation of chemo- and radioresistant GBM stem-like cells appears to be involved in the systematic GBM recurrence. Moreover, recent studies showed that differentiated tumor cells may have the ability to dedifferentiate and acquire a stem-like phenotype, a phenomenon also called plasticity, in response to microenvironment stresses such as hypoxia. We hypothesized that GBM cells could be subjected to a similar dedifferentiation process after ionizing radiations (IRs), then supporting the GBM rapid recurrence after radiotherapy. In the present study we demonstrated that subtoxic IR exposure of differentiated GBM cells isolated from patient resections potentiated the long-term reacquisition of stem-associated properties such as the ability to generate primary and secondary neurospheres, the expression of stemness markers and an increased tumorigenicity. We also identified during this process an upregulation of the anti-apoptotic protein survivin and we showed that its specific downregulation led to the blockade of the IR-induced plasticity. Altogether, these results demonstrated that irradiation could regulate GBM cell dedifferentiation via a survivin-dependent pathway. Targeting the mechanisms associated with IR-induced plasticity will likely contribute to the development of some innovating pharmacological strategies for an improved radiosensitization of these aggressive brain cancers.
Liy(Ni0.425Mn0.425Co0.15)0.88O2 materials were synthesized by a slow rate electrochemical deintercalation from Li1.12(Ni0.425Mn0.425Co0.15)0.88O2 during the first charge and the first discharge in ...order to study the structural modifications occurring during the first cycle and especially during the irreversible “plateau” observed in charge at 4.5 V vs Li+/Li. Chemical Li titrations showed that the lithium ions are actually deintercalated from the material during the entire first charge process, excluding the possibility that electrolyte decomposition causes the “plateau”. Redox titrations revealed that the average transition metal oxidation state is almost constant during the “plateau”, despite further lithium ion deintercalation. 1H MAS NMR data showed that no Li+/H+ exchange was associated to the “plateau” itself. Rietveld refinement of the XRD pattern for a material reintercalated after being deintercalated at the end of the “plateau”, as well as redox titrations, revealed an M/O ratio larger than that of the pristine material, which is consistent with the oxygen loss proposed by Dahn and coauthors for the LiNi x Li(1/3−2x/3)Mn(2/3−x/3)O2 materials to explain the irreversible overcapacity phenomenon observed upon overcharge. X-ray and electron diffraction showed that the transition metal ordering initially present within the slabs is lost during the “plateau” due to a cation redistribution. To explain this behavior a cation migration to the vacancies formed by the lithium deintercalation from the transition metal sites (3a) is assumed, leading to a material densification.
Trends in the evolution of antimicrobial resistance and mechanisms of resistance of
Haemophilus influenzae
to β-lactam antibiotics in France were assessed through a retrospective database review. The ...antimicrobial resistance of 2,206
H. influenzae
strains from children aged ≤5 years was studied between 2001 and 2008. Strains were isolated from blood or cerebrospinal fluid (
n
= 170), bronchial secretions (
n
= 188), middle ear fluid, and nasopharynx or conjunctiva (
n
= 1,848). A proportion of 95.1 % (
n
= 2,097) were non-typeable
H. influenzae
(NTHi). β-lactamase production was identified in 27.5 % of NTHi isolates (all TEM-1), while β-lactamase-negative ampicillin resistance and β-lactamase-negative amoxicillin–clavulanate resistance among NTHi was 16.9 and 6.4 %, respectively. Over time, a statistically significant decrease in β-lactamase-producing strain prevalence (
p
< 0.0001) and a statistically significant increase in β-lactamase-negative ampicillin-resistant (BLNAR) strains (
p
< 0.0001) were observed in NTHi isolates from 2001 to 2008. The largest changes coincided with a campaign to reduce antibiotic use in France. An increasing diversity of amino acid substitution patterns was observed, with the emergence of group III/‘III-like’ patterns linked to high-level resistance. In France, amino acid substitution patterns are increasingly diverse, and strains with high-level antibiotic resistance are emerging. This study highlights the complexity of resistance dynamics within a given country. These results have implications on antibiotic guidelines and illustrate the importance of continued surveillance.
The remarkable electrochemical behavior of complete activated carbon/cobalt oxide cells is reported in the present work. Among the various weight ratios between the positive and negative electrodes ...evaluated, the best features are obtained with an overcapacitive cobalt oxide electrode. The energy densities obtained by this system (20 Wh kg−1 for a power density of 209 W kg−1) are twice higher than those measured for a activated carbon/activated carbon symmetric cell, in the same operating conditions. With discharge capacities around 62 F g−1, this system is among the best ones reported in the literature for this category.
•Original conductive nano cobalt oxide is used in hybrid C/Co supercap.•The positive/negative ratio was optimized.•Best performances for a positive/negative weight ratio of 1.25.•This system is among the best ones of its category (61.6 F g−1).•The system exhibits excellent electrochemical ageing over 3000 cycles.
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