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Abstract A major obstacle to the development of commercially successful electric vehicles (EV) or hybrid electric vehicles (HEV) is the lack of a suitably sized battery. Lithium ion batteries are viewed as the solution if only they could be “scaled-up safely”, i.e. if thermal management problems could be overcome so the batteries could be designed and manufactured in much larger sizes than the commercially available near-2-Ah cells. Here, we review a novel thermal management system using phase-change material (PCM). A prototype of this PCM-based system is presently being manufactured. A PCM-based system has never been tested before with lithium-ion (Li-ion) batteries and battery packs, although its mode of operation is exceptionally well suited for the cell chemistry of the most common commercially available Li-ion batteries. The thermal management system described here is intended specifically for EV/HEV applications. It has a high potential for providing effective thermal management without introducing moving components. Thereby, the performance of EV/HEV batteries may be improved without complicating the system design and incurring major additional cost, as is the case with “active” cooling systems requiring air or liquid circulation.

Abstract To elucidate the gas generation mechanism due to electrolyte decomposition in commercial lithium-ion cells after long cycling, we developed a device which can accurately determine the volume of generated gas in the cell. Experiments on LixC6/Li1−xCoO2 cells using electrolytes such as 1 M LiPF6 in propylene carbonate (PC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) are presented and discussed. In the nominal voltage range (4.2–2.5 V), compositional change due mainly to ester exchange reaction occurs, and gaseous products in the cell are little. Generated gas volume and compositional change in the electrolyte are detected largely in overcharged cells, and we discussed that gas generation due to electrolyte decomposition involves different decomposition reactions in overcharged and overdischarged cells.

Abstract When a lithium ion polymer battery (LiPB) is being cycled, one major cause for degradations is the irreversible side reactions between ions and solvent of electrolyte taking place at the surface of anode particles. SEM analysis of cycled battery cells has revealed that the deposits from the side reactions are dispersed not only on particles, but also between the composite anode and the separator. Thus, the solid electrolyte interface (SEI) becomes thicker and extra deposit layers are formed between composite anode and separator. Also, XPS analysis showed that the deposits are composed of Li 2 CO 3 , which is ionic conductive and electronic nonconductive. Based on the mechanisms and findings, we identified four degradation parameters, including volume fraction of accessible active anode, SEI resistance, resistance of deposit layer and diffusion coefficient of electrolyte, to describe capacity and power fade caused by the side reactions. These degradation parameters have been incorporated into an electrochemical thermal model that has been previously developed. The terminal voltage and capacity of the integrated model are compared with experimental data obtained for up to 300 cycles. Finally, the resistance of the deposit layer calculated by the model is validated against the thickness of the deposit layer measured by SEM.

Abstract Flexible thermoelectric power generators fabricated by evaporating thin films on flexible fiber substrates are demonstrated to be feasible candidates for waste heat recovery. An open circuit voltage of 19.6 μV K per thermocouple junction is measured for Ni–Ag thin films, and a maximum power of 2 nW for 7 couples at ΔT = 6.6 K is measured. Heat transfer analysis is used to project performance for several other material systems, with a predicted power output of 1 μW per couple for Bi2Te3/Sb2Te3-based fiber coatings with a hot junction temperature of 100 °C. Considering the performance of woven thermoelectric cloths or fiber composites, relevant properties and dimensions of individual thermoelectric fibers are optimized.

Abstract Surface modification of petroleum coke (PC) and those heat-treated at 1860, 2300 and 2800 °C (PC1860, PC2300 and PC2800) has been performed by F 2 , ClF 3 and NF 3 to improve their charge/discharge characteristics in propylene carbonate containing solvents. Surface fluorination by F 2 increased surface disorder of PC1860, PC2300 and PC2800, leading to increase in their first coulombic efficiencies in 1 mol dm −3 LiClO 4 –ethylene carbonate (EC)/diethyl carbonate (DEC)/propylene carbonate (PPC) (1:1:1 in volume) solution. First coulombic efficiencies were the largest in fluorinated PC1860 with the highest surface disorder. However, surface modification by ClF 3 and NF 3 did not increase surface disorder of petroleum cokes, being not as effective as the fluorination with F 2 to increase first coulombic efficiencies of petroleum cokes. The reactions of ClF 3 and NF 3 with carbon materials are radical reactions while the reaction with F 2 is an electrophilic reaction yielding fluorinated layers with high disorder. Surface modification using F 2 , ClF 3 and NF 3 also increased first charge capacities of PC and PC1860.

Abstract The total energy storage system cost is determined by means of a robust performance-based cost model for multiple flow battery chemistries. Systems aspects such as shunt current losses, pumping losses and various flow patterns through electrodes are accounted for. The system cost minimizing objective function determines stack design by optimizing the state of charge operating range, along with current density and current-normalized flow. The model cost estimates are validated using 2-kW stack performance data for the same size electrodes and operating conditions. Using our validated tool, it has been demonstrated that an optimized all-vanadium system has an estimated system cost of -1 for 4-h application. With an anticipated decrease in component costs facilitated by economies of scale from larger production volumes, coupled with performance improvements enabled by technology development, the system cost is expected to decrease to 160 kWh -1 for a 4-h application, and to $100 kWh -1 for a 10-h application. This tool has been shared with the redox flow battery community to enable cost estimation using their stack data and guide future direction.

SOFC composite electrodes of yttria-stabilized zirconia (YSZ) and either LaNi(0.6)GFe(0.4)O(3) (LNF) or La0.91Sr0.09Ni0.6Fe0.4O3 (LSNF) were prepared by infiltration to a loading of 40 wt% of the perovskite into Porous YSZ using aqueous solutions of the nitrate salts. XRD measurements indicated that the perovskite structures were formed following calcination at 850 degrees C, at which temperature the LNF and LSNF form small particles that coat the YSZ pores. Heating to 1100 degrees C causes the particles to form a dense film over the YSZ but caused no solid-state reaction. Calcination of an LNF-YSZ composite to 1200 degrees C led to an expansion of the LNF lattice, suggesting introduction of Zr(IV) into the perovskite; further heating to 1300 degrees C caused the formation of La2Zr2O7. For 850 degrees C calcination, the electrode performance of both LNF-YSZ and LSNF-YSZ composites was similar to that reported for composites of YSZ and La0.8Sr0.2FeO3 (LSF), with a current-independent impedance of approximately 0.1 Omega cm(2) at 700 degrees C in air. For 1100 degrees C calcination, both LNF-YSZ and LSNF-YSZ composites exhibited impedances that decreased strongly under both anodic and cathodic polarization. The implications of these results for preparing electrodes based on LNF and LSNF are discussed.

Abstract A novel dot matrix and sloping baffle flow field plate for proton exchange membrane fuel cell (PEMFC) cathode is designed. The plate consists of dispersive and arrayed blocks with sloping angles as shoulders. Features of the plate include a large fluid domain, and air guidance in two directions is achieved by sloping sides of the block. The cell output performance, internal transport process and liquid water removal process of the PEMFC with the matrix flow field are numerically investigated by three-dimensional two-phase full cell model and volume of fluid (VOF) model. The simulation results show that compared with the parallel and serpentine flow field, the matrix flow field can achieve high cell output performance by both improving oxygen supply to gas diffusion layer (GDL) and uniform distribution. Comparing five matrix flow fields with different block sizes and numbers shows that adequate contact area between the plate and GDL for current conductor is critical. For liquid water removal process in the matrix flow field, liquid water is hardly blocked by arrayed blocks and can leave GDL quickly. In summary, the matrix flow field fits high current density demand of PEMFC well, and some new perspectives on flow field design are presented.