A novel non-enzymatic glucose sensor based on hollow-structured copper sulfide/cuprous sulfide (CuS/Cu2S) hybrid was developed by using a facile and one-pot solvothermal method. The crystal structure, morphology and surface property of the prepared CuS/Cu2S hybrid were characterized by X-ray diffraction spectroscopy, scanning electron microscopy, transmission electron microscopy, energy dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy. The electrochemical performances of this hybrid modified glassy carbon electrode for glucose oxidation were monitored by cyclic voltammograms and amperometric technology. Results showed that the novel integrated electrode exhibited excellent electrocatalytic performances to the oxidation of glucose with a wide line range of 3.0–1100.0 µM, high sensitivity of 321.3 µA mM−1 cm−2, low detection limit of 1.1 µM (3δ/S), fast response, good anti-interference ability and excellent stability. The proposed sensor was successfully applied for the determination of glucose in human blood serum sample with satisfactory recoveries.
Neurostimulation is an essential technique to trigger and modulate the spatiotemporal activity of local neuronal circuits. Current stimulation methods have a trade-off relationship among aiming precision, temporal resolution, and noninvasiveness, making it difficult to stimulate and monitor a single target neuron for a long term. Here, we show that a method using two needle electrodes in combination of micropatterning techniques provides new possibilities for targeting and stimulating a single neuron selectively. Results of physiological experiments as well as analog circuit simulation reveal that two needle electrodes can stimulate a target neuron selectively by placing the two needle electrodes in proximity to and to straddle the target neuron, and that the steepness of voltage applied to two needle electrodes is important for the target neuron to fire at a low voltage. The proposed method enables a noninvasive stimulation suitable for measuring long-term activity of local neuronal circuits.
We experimentally evaluated the influence of stress on the Li chemical potential (μLi) and phase equilibrium in the two-phase battery electrode materials through the emf measurements while applying a mechanical load. In our measurements, we prepared an electrochemical cell by depositing a thin film of a two-phase electrode material (LiFePO4 or LiCoO2 in the two-phase region) on each of the solid electrolyte surfaces. Then we applied a mechanical load to the electrochemical cell through four-point bending, and the resulting μLi variation in the electrode material was measured as the emf between the two thin films. Our results indicated that μLi in the two-phase electrode materials immediately changed just after loading and then gradually changed while maintaining a constant mechanical load. Besides, the loading and unloading led to the μLi variation in the opposite direction. Such characteristic μLi variations could be explained by considering the change in the phase equilibrium between the two phases, which led to the Li content variation in the two phases and the stress relaxation due to the volume fraction variation of the two phases. Our results can provide valuable insights regarding the influence of stress on the performances of energy storage devices with two-phase electrode materials.
Chemically-delithiated Li1.2Mn0.54Ni0.13Co0.13O2 is regarded as a potential candidate of cathode active materials for magnesium rechargeable batteries owing to its large deliverable capacity and high operation voltage compared to conventional layered transition metal oxides. Our previous study suggested its chemical composition as Li0.13Mn0.54Ni0.13Co0.13O2−δ by X-ray diffraction combined with XAFS analysis. We herein re-analyzed the substantial composition and crystal structure by employing titration technique and combination of neutron and synchrotron X-ray diffractions. Two topotactic phases both belonging to the space group of R3m were strongly suggested by Rietveld analysis, and the chemical formula was subsequently re-defined as Li0.17Mn0.72Ni0.18Co0.18O2 where oxygen defects were filled by a rearrangement from C2/m structure. Although the battery performance of that active material was poor in the previous study, the discharge capacity greater than 400 mAh g−1, ca. 95 % of the theoretical capacity, was achieved by using certain anodically stable electrolytes and specific cell configuration. This result strongly implies that the R3m structure is particularly suitable as a host material for Mg2+ intercalation.
Five types of micrometer-sized Sn and acetylene black (AB) composite powders were prepared by mechanical milling for 1, 3, 6, 12, and 24 h. The Sn/AB powders obtained, in addition to Sn-only powders were added to a binder and conductive material, and then dried under vacuum to prepare negative electrodes (anodes) for sodium-ion batteries (SIBs). SIBs were fabricated with the anodes in the form of 2032-type coin cells, and were evaluated using charge-discharge tests up to 50 cycles within the cutoff voltage range of 0.005–0.65 V at a constant current of 50 mA g−1 at 25 °C. Maximum discharge capacities of 614 to 651 mAh g−1 were obtained with all the anodes prepared with both the Sn-only and the Sn/AB composites. However, the discharge capacities of the Sn-only and Sn/AB composites milled for 1 and 3 h were significantly decreased as the charge-discharge cycle increased. In contrast, the Sn/AB composites milled for 6 h or more exhibited improved cycle characteristics; capacities of 635, 619, and 584 mAh g−1 were maintained during 50 cycles of testing with the Sn/AB_6h, Sn/AB_12h, and Sn/AB_24h samples, respectively, which were significantly higher than the anode prepared with the Sn-only powder (135 mAh g−1).
We report detailed studies of capacity deterioration mechanism of Li[Ni1/3Co1/3Mn1/3]O2 (NCM) cathode after several numbers of cycling with the voltage range of 3.0–4.1 V/cell at 85 °C and after storage at charged states (3.7, 4.0 and 4.1 V/cell) at 70 °C for 150 days by soft X-ray absorption spectroscopy (XAS) and X-ray powder diffraction (XRD). Morphological changes were also observed by scanning electron microscopy (SEM).
Ni, Co, and Mn L-edge XAS analysis revealed that Ni, a part of Co and no Mn were active for charge/discharge in the above-described voltage range. Only Ni L-edge XAS exhibited significant spectral changes by capacity deterioration. Ni mean valence at discharged state increased with the capacity deterioration rate of each sample either after storage test or after cycling test, which corresponds to the increase of the lattice constant ratio c/a, obtained by the XRD analysis. Chemically decomposed species on the NCM particle surfaces increased with capacity deterioration. Many cracks were observed in the SEM image of the sample after extended cycling. Crack generation, formation of the cubic spinel phase on the surface and deposition of decomposed species on the particles hamper the Li ion insertion to the cathode material at discharge, which is responsible for capacity deterioration. The crack generation is enhanced in case of the cycling test, while the deposition of decomposed species and the formation of the cubic spinel phase on the surface are more enhanced in case of the storage test.