Data for "A composite of Nb2O5 and MoO2 as a high-capacity high-rate anode material for li-ion batteries"

A composite of Nb2O5 and MoO2 was synthesised using a hydrothermal reaction (225 C) followed by a short heat-treatment step (600 C) to achieve a high-capacity, high-rate anode for Li-ion battery applications. The composite was shown via powder X-ray diffraction and electron microscopy to be an intimate mix of individual oxide particles rather than an atomically mixed oxide material. The composite was shown by X-ray fluorescence spectroscopy (XRF) to contain a 45:55 ratio of Nb:Mo. This composite oxide is demonstrated to show notable rate capability in Li half-cell cycling and rate tests. When cycled at 100C this material achieved over 100 mAhg-1 even after 400 cycles and shows a stable reversible capacity of 514 mAhg-1 (at 1C), realising its theoretical capacity. This composite shows electrochemical results comparable to Nb2O5:C composites yet achieves far higher capacities at low-rate due to the MoO2 content

Data for Investigating the influence of synthesis route on the crystallinity and rate capability of niobium pentoxide for energy storage

Orthorhombic niobium pentoxide (T-Nb2O5) is known to be an effective anode material for Li-ion batteries (LIBs) with very high rate capability, but the other Nb2O5 polymorphs and non-crystalline phases have lacked thorough exploration. A simple hydrothermal mechanism is used to produce an anisotropically crystalline ‘as-synthesised material’, which has not previously been characterised electrochemically. The as-synthesised material is heat-treated to produce T-Nb2O5 at 600°C and monoclinic (H-) Nb2O5 at 1000°C. We present electrochemical properties for all of these materials. Collectively we report rate sweeps and demonstrate high current stability (20 C-rate capability) and a long life span, up to 200 cycles. We propose the H-phase as a high rate anode when prepared via an anisotropically crystalline precursor, as it is able to demonstrate 60 % capacity retention after 200 cycles at a notably high current flux of 20 C. Such high rates results are rare for this material without integration with carbon materials. For the anisotropically crystalline Nb2O5 material, we achieve cycling rates up to 100 C with 80% capacity recovery upon current reduction, representing an important discovery in the development of very high rate anode materials

Data for Superacid-derived surface passivation for measurement of ultra-long lifetimes in silicon photovoltaic materials

Accurate measurements of bulk minority carrier lifetime are essential in order to determine the true limit of silicon's performance and to improve solar cell production processes. The thin film which forms when silicon wafers are dipped in solutions containing superacids such as bis(trifluoromethane)sulfonimide (TFSI) has recently been found to be effective at electronically passivating the silicon surface. In this paper we first study the role of the solvent in which TFSI is dissolved for the passivation process. We study ten solvents with a wide range of relative polarities, finding TFSI dissolved in hexane provides improved temporal stability, marginally better passivation and improved solution longevity compared to dichloroethane which has been used previously. Sample storage conditions, particularly humidity, can strongly influence the passivation stability. The optimised TFSI-hexane passivation scheme is then applied to a set of 3 Ω cm n-type wafers cut from the same float-zone ingot to have different thicknesses. This enables the reproducibility of the scheme to be systematically evaluated. At 1015 cm−3 injection the best case effective surface recombination velocity is 0.69 ± 0.04 cm/s, with bulk lifetimes measured up to the intrinsic lifetime limit at high injection and > 43 ms at lower injection. Immersion of silicon in superacid-based ionic solutions therefore provides excellent surface passivation, and, as it is applied at room temperature, the effects on true bulk lifetime are minimal

Superacid-treated silicon surfaces : extending the limit of carrier lifetime for photovoltaic applications

Minimizing carrier recombination at interfaces is of extreme importance in the development of high-efficiency photovoltaic devices and for bulk material characterization. Here, we investigate a temporary room temperature superacid-based passivation scheme, which provides surface recombination velocities below 1 cm/s, thus placing our passivation scheme amongst state-of-the-art dielectric films. Application of the technique to high-quality float-zone silicon allows the currently accepted intrinsic carrier lifetime limit to be reached and calls its current parameterization into doubt for 1 Ω·cm n-type wafers. The passivation also enables lifetimes up to 65 ms to be measured in high-resistivity Czochralski silicon, which, to our knowledge, is the highest ever measured in Czochralski-grown material. The passivation strategies developed in this work will help diagnose bulk lifetime degradation under solar cell processing conditions and also help quantify the electronic quality of new passivation schemes

Data for Exceptional surface passivation arising from bis(trifluoromethanesulfonyl)-based solutions

The surface properties of many inorganic electronic materials (e.g. MoS2, WSe2, Si) can be substantially modified by treatment with the superacid bis(trifluoromethane)sulfonimide (TFSI). Here we find more generally that solutions based on molecules with trifluoromethanesulfonyl groups, including TFSI, give rise to excellent room temperature surface passivation, with the common factor being the presence of CF3SO2 groups and not the solution’s acidity. The mechanism of passivation comprises two effects: (i) chemical passivation; and (ii) field effect passivation from a negatively charged thin film likely to be physically adsorbed by the surface. Degradation of surface passivation is caused by de-adsorption of the thin film from the surface, and occurs slowly in air and rapidly upon vacuum exposure. The passivation’s air stability is enhanced by the presence of droplets at the surface which act to protect the properties of the film. The finding that non-acidic solutions can provide excellent electrical passivation at room temperature opens up the possibility of using them on materials more sensitive to an acidic environment

Data for Superacid-Treated Silicon Surfaces: Extending the Limit of Carrier Lifetime for Photovoltaic Applications

Minimizing carrier recombination at interfaces is of extreme importance in the development of high-efficiency photovoltaic devices and for bulk material characterization. Here, we investigate a temporary room temperature superacid-based passivation scheme, which provides surface recombination velocities below 1 cm/s, thus placing our passivation scheme amongst state-of-the-art dielectric films. Application of the technique to high-quality float-zone silicon allows the currently accepted intrinsic carrier lifetime limit to be reached and calls its current parameterization into doubt for 1 Ω·cm n-type wafers. The passivation also enables lifetimes up to 65 ms to be measured in high-resistivity Czochralski silicon, which, to our knowledge, is the highest ever measured in Czochralski-grown material. The passivation strategies developed in this work will help diagnose bulk lifetime degradation under solar cell processing conditions and also help quantify the electronic quality of new passivation scheme