Papers by Keyword: High Rate

Abstract: A nanocrystalline LiFePO₄/graphene-carbon nanotubes (LFP-G-CNT) composite has been successfully synthesized by a hydrothermal method followed by heat-treatment. The microstructure and morphology of the LFP-G-CNTs composite were comparatively investigated with LiFePO₄/graphene (LFP-G) and LiFePO₄/carbon nanotubes (LFP-CNT) by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The LFP-G-CNTs nanoparticles were wrapped homogeneously and loosely within a 3D conducting network of graphene-carbon nanotubes. The conducting networks provided highly conductive pathways for electron transfer during the intercalation/deintercalation process, facilitated electron migration throughout the secondary particles, accelerated the penetration of the liquid electrolyte into the LFP-G-CNT composite in all directions and enhanced the diffusion of Li ions. The results indicate that the electrochemical activity of LFP-G-CNT composite may be enhanced significantly. The charge-discharge curves, cyclic voltammograms (CV) and electrochemical impedance spectroscopy (EIS) results demonstrate that LFP-G-CNT composite performes better than LFP-G and LFP-CNT composites. In particular, LFP-G-CNT composite with a low content of graphene and carbon nanotubes exhibites a high initial discharge capacity of 168.4 mAh g⁻¹ at 0.1 C and 103.7 mAh g⁻¹ at 40 C and an excellent cycling stability.

Abstract: A hybrid battery-supercapacitor (LiFePO₄+AC)/Li₄Ti₅O₁₂ using a Li₄Ti₅O₁₂ anode and a LiFePO₄/activated carbon (AC) composite cathode was built. The electrochemical performances of the hybrid battery-supercapacitor (LiFePO₄+AC)/Li₄Ti₅O₁₂ were characterized by constant current charge-discharge, rate charge-discharge, electrochemical impedance spectra, internal resistance, leakage current, self-discharge and cycle performance testing. The results show that (LiFePO₄+AC)/Li₄Ti₅O₁₂ hybrid battery-supercapacitors have rapid charge-discharge performance, high energy density, long cycle life, low resistance, low leakage current and self-discharge rate, which meet the requirements of practical power supply and can be applied in auxiliary power supplies for hybrid electric vehicles. At 4C rate, the capacity loss of (LiFePO₄+AC)/Li₄Ti₅O₁₂ hybrid battery-supercapacitors in constant current mode is no more than 7.71% after 2000 cycles, and the capacity loss in constant current-constant voltage mode is no more than 4.51% after 1500 cycles.

Abstract: The tractive lithium ion batteries were gradually become the main energy provider for the Electric vehicles (EVs) and hybrid electric vehicles (HEVs) in recent years. However, it was urgent and important to remove the heat generated from the tractive lithium ion batteries during charge-discharge processes for its future application in EVs and HEVs. In this study, the heat release and indirect liquid cooling of tractive lithium ion batteries was investigated. The temperatures of batteries at different positions were recorded under different discharge rates and environmental temperatures. The results showed that indirect liquid cooling could effectively decrease the temperatures of battery. The decreasing ratios of temperature at different positions of battery were varied from 1.9% to 8.1%. It presented preferable cooling effects at the positive and negative of battery.

Abstract: A series of ZnO:Al (AZO) thin films was prepared on quartz at different substrate temperature using magnetron sputtering with high deposited rate of 67 nm/min. The structural, electrical and optical properties of these films were investigated as a function of substrate deposition temperature ranging from room temperature to 500 °C. The surface micrograph of AZO film deposited at room temperature was measured by a scanning electron microscope (SEM) and an atomic force microscope (AFM). The results of X-ray diffraction (XRD) test show that all the films have a (002) preferential orientation. The best electrical property was obtained at 500 °C, the resistivity was 9.044×10-4 ohm•cm, and the corresponding carrier concentration and mobility were 3.379×1020 /cm3 and 20.45 m2/Ns, respectively. What's more, all the films show a high optical transmittance.

Abstract: Polycrystalline Cubic Boron Nitride (PCBN) is a super-hard material, which is used in some of the most demanding material removal operations today. PCBN cutting tools are employed in turning of hardened steels as well as machining of other abrasive and aerospace grade alloys. In these applications the tools are subjected to high operating temperatures, abrasive and impact loading. Impact loading can lead to the sudden fracture and hence failure of the tool. Much of the recent developments in this industry have been focused on improving the fracture toughness of the PCBN compact. In this work a hypothesis based on induced thermal stresses at the crack tip has been put forward to explain the observed rate sensitivity of PCBN. The results show that the fracture toughness of PCBN is closely linked to the CBN grain size and that the rate sensitivity can be explained in part by induced thermal stresses at the crack tip at high rates of loading.

Abstract: Polycrystalline Cubic Boron Nitride (PCBN) is a super-hard material used in some of the most demanding material removal operations today. These include turning of hardened steels, as well as the machining of highly abrasive alloys. In these applications the tools are subjected to high operating temperatures, abrasive and impact loading. This can lead to the brittle fracture of the tool. Accurate determination of the fracture toughness and mechanical properties of PCBN under a wide range of operating conditions is therefore essential in order to evaluate the performance of the tool under these highly demanding conditions. For this study, a laboratory scale three point bend test rig has been used for the fracture tests. The fracture toughness of two different grades of PCBN are measured at a range of loading rates and temperatures corresponding to the actual in-service conditions. The results show the measured properties of these materials vary with both loading rate and temperature. The fracture surfaces of the specimens are examined using scanning electron microscopy to determine dominant fracture mechanisms.

Abstract: From the impact experiment for the nonlinear plastic behavior with the dynamically loaded adhesively-bonded TDCB specimens, there is the range of load from 1 to 2 kN or pin displacement from 4 to 10 mm for the most part in case of the impact rates 1, 2.5, 5, 7.5 and 12.5m/s. There is also the range of energy from 5 to 10 J or energy release rate(fracture energy) from 3000 to 6000 J/m2 for the most part in case of all impact rates. The fracture energy on automotive adhesive joints can be estimated by using the fracture toughness, GIC, experimental results under high rates of loading in this study. The key fracture mechanics parameter, namely the fracture energy, GIC, was ascertained as a function of test rate and may be used to assess and model the joint performance.

Abstract: Polycrystalline Cubic Boron Nitride (PCBN) is a superhard material which is used in machining of hardened steels and other abrasive and aerospace grade alloys. In these applications the tools are subjected to high operating temperatures, abrasive and impact loading. Impact loading can lead to the sudden fracture and hence failure of the tool. In this work the static and dynamic fracture toughness of PCBN is determined via a combined experimental-numerical approach. The results show that the fracture toughness of PCBN varies with loading rate.