The effect of pre-roasting on leaching of the gamierite laterite ore, obtained from Yunnan province, China, was investigated in this study. The phase transformation of laterite minerals roasted at ...different temperatures was investigated with X-ray powder diffraction (XRD). The roasting experiment results show that there are two phase transformation processes of dehydroxylation of goethite and lizardite at roasting temperatures of 277 °C and 610 °C, respectively, which accord with the result of DTA–TG analysis. Pre-roasting of the laterite not only alters its mineralogical composition but also increases its porosity and surface area, thus making it more amenable to leaching. Compared to the leaching result of raw ore and ores roasted at different temperatures, it indicates that increasing roasting temperature up to 300 °C appears to provide the optimum nickel recovery and further heating appears to be detrimental to the nickel recovery.
Traditional directional relays of AC transmission lines are usually based on 50 Hz information in frequency domain in China. However, this conventional approach cannot provide the correct fault ...direction for the lines connected to wind farm because of the fault characteristics of the wind power system, that is, frequency deviation, variation of system impedance, weak feed feature, and so on. Then, the conventional approach of finding the phase angle between the fault current and a voltage signal will not identify the correct fault direction. To solve this problem, this paper proposes a novel fault direction identification method in time domain. Based on the RL model of transmission lines, opposite-side voltages of the line can be derived with the measuring current and voltage at wind farm terminal after the fault. Then, the adjusted cosine similarity between the calculation voltage based on the RL model and the memory voltage can be acquired. If the correlation between the calculation voltage and the memory voltage is close to 1, it is a reverse fault. Otherwise, it is a forward fault. Finally, the proposed novel fault direction identification criterion is verified by the PSCAD/EMTDC-based simulation results.
Although the high energy density and environmental benignancy of LiNi0.8Co0.15Al0.05O2 (NCA) holds promise for use as cathode material in Li‐ion batteries, present low rate capabilities, and fast ...capacity fade limit its broad commercial applications. Here, it is reported that surface modification of NCA cathode (R‐3m) with 5 nm‐thick nanopillar layers and Fm‐3m structures significantly improves electrode structure, morphology, and electrochemical performance. The formation of nanopillar layers increases cycling and working voltage stability of NCA by shielding the host material from hydrofluoric acid and improves structural stability with the electrolyte. The modified NCA cathode exhibits an enhanced 89% capacity retention at a rate of 1 C over that of pristine NCA (75.2%) after 150 cycles and effectively suppresses working voltage fade (a drop of 0.025 V after 300 cycles) during repeated charge–discharge cycles. In addition, the diffusion barrier of Li ions in NCA crystals at 0.80 V is noticeably smaller than that of Li ions in pristine NCA (0.87 eV). These findings demonstrate that this unique surface structure design considerably enhances cycle and rate performance of NCA, which has potential applications in other Ni‐rich layered cathode materials.
A surface design to induce the transformation of Ni3+ to Ni2+ and form a newly observed NiO phase in LiNi0.8Co0.15Al0.05O2 cathode is proposed. This surface layer formed NiO phase with Fm‐3m structure is stable and has a lower Li‐ion diffusion barrier, which produces excellent structural stability and cycle stability. It considerably improves cycle stability, rate performance, and effectively supresses voltage decay.
•A novel differential protection scheme for HVDC transmission lines is proposed.•The application of ETPTL solve the calculation problem of voltage distribution.•The capacitive current is calculated ...by integrating the linear distributed voltage.
Based on the compensation of the distributed capacitive current, a novel differential protection scheme for HVDC transmission lines was proposed in this study. According to the analysis, after voltage and current signals at both sides of the line are processed by the same low-pass filter the cut-off frequency of which is low enough, then the voltage distribution along the line can be regarded as linear distribution. The distributed capacitive current can be calculated by integrating the linear distributed voltage. After removing this current, the new differential criterion can be implemented. A ±800kV HVDC transmission system was built in EMTDC to test the performance of the new protection. Comprehensive test studies show that the proposed method not only can detect internal faults correctly and quickly, but also can respond to internal faults with high ground resistance.
High-Entropy Oxides (HEOs) are a novel type of perspective anode materials for lithium ion batteries (LIBs), owing to their stable crystal structure and high theoretical capacity. However, the ...understanding of their intrinsic crystal structure and lithium storage mechanism is relatively shallow, hindering their further development and application. In this work, (FeCoNiCrMn)3O4 HEO was prepared successfully by the oxidation of high-entropy FeCoNiCrMn alloy powders, and was applied as a new advanced anode material for LIBs. The as-prepared (FeCoNiCrMn)3O4 HEO exhibited excellent cycle stability, and achieved a high reversible capacity of 596.5 mA h g−1 and a good capacity retention of 86.2% after 1200 cycles at 2.0 A g−1. Such long cycle stability can be ascribed to its special crystal structure and narrow band gap, which was verified by density functional theory (DFT) calculations. During the first cycle of lithium insertion, (FeCoNiCrMn)3O4 HEO gradually transformed into fine crystals below the XRD detection threshold, which was confirmed by in situ XRD. Our results demonstrate that high-entropy makes (FeCoNiCrMn)3O4 HEO possess a stable structure and narrow band gap, and three-dimensional spinel structure provides a channel for ion transport. This points out the direction for the preparation of HEOs with stable structure and excellent performance, and provides a promising candidate for anode materials of LIBs.
Display omitted
•(FeCoNiCrMn)3O4 HEO was fabricated successfully by the oxidation of FeCoNiCrMn HEA powder for the first time.•Ultra-long cycling life over 1200 cycles at 2.0 A g-1 was obtained, the best cyclic stability displayed so far for HEOs.•The special crystal structure and narrow band gap of HEO was calculated and verified by DFT calculations.
Among many promising cathode materials for SIBs, the transition metal oxides have attracted especially extensive attention for uncostly and environmental-friendly. In this paper, the ...Na0·44Mn2/3Co1/6Ni1/6O2 tunnel cathode material with a hollow porous spherical structure is successfully prepared. Short distance for Na+ diffusion leads to good Na+ diffusion kinetics, so it has excellent rate performance, with the specific discharge capacity of 133 mAh g−1, 127 mAh g−1, 116 mAh g−1, 95 mAh g−1, and 72 mAh g−1 at charge and discharge rates of 0.1 C, 0.2 C, 0.5 C, 1 C, and 2 C (1 C = 120 mA g−1), respectively. The unique hollow porous structure ensures its excellent cycle stability. Therefore, designing a hollow and porous three-dimensional spherical structure is an effective method. Furthermore, it provides a reliable way for the modification of the cathode material for SIBs in the future.
Display omitted
•The novel micron hollow porous spherical NaMCNO-P cathode was synthesized.•NaMCNO-P hollow porous sphere reveals superior cycle stability and rate capability.•NaMCNO-P shortens the diffusion path of Na+ to obtain higher diffusion coefficient.
A cathode material LiNi0.8Co0.1Mn0.1O2 coated with ionic conductor Li3VO4 was prepared through a wet-chemical method. The crystalline phase, chemical valence state and the microstructure of ...Li3VO4-coated material were investigated by X-ray diffraction, energy dispersive spectroscopy, X-ray photoelectron spectroscopy and transmission electron microscopy. The existence of the Li3VO4 coating layer on the surface of sphere particle was validated, and the electrochemical performances of the samples were investigated. The 3 wt% Li3VO4-coated sample exhibited the most remarkable cycling capability at 1 C after 100 cycles, with a retention value of 83.54%. Moreover, the rate performances of all Li3VO4-coated samples were significantly enhanced at high rates (2, 5 and 10 C). Electrochemical impedance spectroscopy and cyclic voltammetry performance analyses revealed that the excellent electrochemical performance of the Li3VO4-coated sample is ascribed to the improved lithium ion conductivity and the suppression of the chemical reaction between the electrode material and electrolyte.
•LiNi0.8Co0.1Mn0.1O2 coated with Li3VO4 was prepared by a facile wet-chemical method.•Side reactions were suppressed by using Li3VO4 as the protecting layer.•Lithium ion diffusion coefficient was increased obviously by Li3VO4 coating.•Cycling and rate performances were greatly improved by Li3VO4 coating.
In this report, Co3O4 nanowires on nickel foam substrate are synthesized by a facile chemical bath deposition route under a mild condition. The prepared Co3O4 is tightly anchored with Ni foam with a ...large BET surface area of 20.7m2g−1, providing good contact between electrode and electrolyte and thus improving the electron and Li+ transmission. As a result, the fabricated Co3O4 nanowires on nickel foam directly as conductive agent- and binder-free electrode for lithium ion batteries show superior electrochemical performance. When cycled at the current density of 0.2Ag−1, it delivers an initial reversible specific capacity of 944mAhg−1 with a coulombic efficiency of 71.7%, and shows almost no capacity fading during 100 cycles. As performed at 4.0Ag−1, it can also show 663mAhg−1 capacity.
The reasonable design of the cathode host material is of great significance for achieving high-efficiency sulfur electrochemistry and increasing the energy density of lithium-sulfur (Li-S) batteries. ...Herein, a uniformly CeO2 doped three-dimensional porous nitrogen-rich carbon nanofiber (CeO2@CNF) is prepared as an advanced sulfur electrode matrix. Carbon nanofibers with good electrical conductivity and abundant pores can effectively store sulfur and inhibit the shuttle of polysulfides by double physicochemical sulfur coordination. In addition, electrocatalytically active CeO2 nanocrystals significantly promote stable redox activity. The prepared sulfur electrode achieves a high area capacity of 8.4 mAh cm−2, a high rate capacity of up to 2 C and an excellent cycle capacity of over 400 cycles.
Display omitted
•Nanofibers with high electrical and ion conductivity are synthesized.•The doped CeO2 nanocrystals have high electrocatalytic activity.•The CeO2@CNF electrodes exhibits good electrochemical performance.
PDF
