Effect of Porous Carbon Morphologies and Composite Manufacturing Processes on Long-Cycling Performance in High Sulfur Loading Li-S Batteries

Long-cycling performance of Li-S batteries was studied with the high-sulfur loading composites composed of 86% sulfur and 14% carbon. The composites are made by the physical mixing and S-liquefied pore-filling processes with nano sulfur powder and two kinds of porous carbons. The initial discharge capacities of the composite prepared by the physical mixing and liquefied pore-filling with 1-µm-sized carbon were 1060 mAh/g and 1121 mAh/g, respectively. On the other hand, the capacities of the composite using 5-µm-sized carbon were 705 mAh/g in physical mixing and 845 mAh/g in liquefied pore-filling process. The composite with the 1 µm carbon showed approximately ∼1.4 times higher than that of 5 µm. The reason for this difference is that the surface area of the sulfur wrapping the small particle carbon surface is larger than that of the composite wrapping the large particle carbon surface. Importantly, after 500 cycles, the cycle stability in the physical mixing process is 15∼30% higher than that in the S-liquefied pore filling process in both carbons, due to the decrease of electrolyte resistance by capturing polysulfide into the pores which are not filled by the sulfur during the process. In the case of high-sulfur loading composites, manufacturing process as well as the size and morphologies of the carbon are crucial factors that affect the capacity and cycle stability of the Li-S battery.

Mathematical Heat Transfer Modeling and Experimental Validation of Lithium-Ion Battery Considering: Tab and Surface Temperature, Separator, Electrolyte Resistance, Anode-Cathode Irreversible and Reversible Heat

The temperature and heat produced by lithium-ion (Li-ion) batteries in electric and hybrid vehicles is an important field of investigation as it determines the power, performance, and cycle life of the battery pack. This paper presented both laboratory data and simulation results at C-rates of 1C, 2C, 3C, and 4C at an ambient temperature of approximately 23 °C. During experiment thermocouples were placed on the surface of the battery. The thermal model assumed constant current discharge and was experimentally validated. It was observed that temperature increased with C-rates at both the surface and the tabs. We note that at 4C the battery temperature increased from 22 °C to 47.40 °C and the tab temperature increased from 22 °C to 52.94 °C. Overall, the simulation results showed that more heat was produced in the cathode than the anode, the primary source of heat was the electrolyte resistance, and the battery temperature was the highest near the tabs and in the internal space of the battery. Simulation of the lithium concentration within the battery showed that the lithium concentration was more uniform in the anode than in the cathode. These results can help the accurate thermal design and thermal management of Li-ion batteries.

Laser induced molybdenum sulphide loading on doped graphene cathode for highly stable lithium sulphur battery

Lithium sulphur (Li-S) batteries are known to have much higher charge capacity than the currently widely used lithium-ion batteries with graphite anodes. However, maintaining high charge cycle stability is a key challenge for Li-S batteries due to the shuttle effect. Here we show highly stable characteristics with 100% charge capacity of Li-S batteries with 500 charge/discharge cycles at 0.5 C, 1 C, 2 C and 3 C charge rates. This was made possible by the combination of laser synthesised sulfur (S) and nitrogen (N) doped graphene electrodes (without a binder) with molybdenum sulphide (MoS2) nanoparticle loading. The N/S doped porous graphene structure presented enhanced interface adsorption by the production of –SO2, which suppressed diffusion of polysulfide into the electrolyte through promoting oxygen-containing functional groups chemically bonding with sulfur. A low electrolyte resistance, interphase contact resistance and charge-transfer resistance accelerate electrons and Li+ transport by laser induced N/S doped graphene.

Electrical conductivity of low-temperature sodium-potassium cryolite melts

Electrical conductivity of NaF-KF-AlF3 melts with different ratios of sodium fluoride and potassium fluoride was measured using a pyrolytic boron nitride tube-type cell with constant distance of electrodes. Molar cryolite ratios MR = (n(NaF) + n(KF))/n(AlF3) varied from 1.5 to 1.2 (with a step 0.1) in the temperature range of (675—900) °C. AC-techniques with a sine wave signal with small amplitude in the high frequency range were applied. Electrolyte resistance was obtained from nonlinear regression analysis according to equivalent circuit. Concentration and temperature dependency of electrical conductivity was described and defined. Experimental data were compared with literary sources and regression equations.

SrCe0.9Sm0.1O3-α Compounded with NaCl-KCl as a Composite Electrolyte for Intermediate Temperature Fuel Cell

SrCeO3 and SrCe0.9Sm0.1O3-α were synthesized using a high-temperature solid-state reaction method using Sm2O3, SrCO3, CeO2 as precursors, then the SrCe0.9Sm0.1O3-α-NaCl-KCl composite electrolyte was fabricated by compounding SrCe0.9Sm0.1O3-α with NaCl-KCl and sintering it at a lower temperature (750 °C) than that of a single SrCeO3 material (1540 °C). The phase and microstructure of the samples were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The conductivities of the samples were measured in dry nitrogen atmosphere using electrochemical analyzer. The conductivities of the SrCeO3, SrCe0.9Sm0.1O3-α and SrCe0.9Sm0.1O3-α-NaCl-KCl at 700 °C were 2.09 × 10−5 S·cm−1, 1.82 × 10−3 S·cm−1 and 1.43 × 10−1 S·cm−1 respectively. The conductivities of SrCe0.9Sm0.1O3-α-NaCl-KCl composite electrolyte are four orders of magnitude higher than those of SrCeO3 and two orders of magnitude higher than those of SrCe0.9Sm0.1O3-α. The result of logσ ~ logpO2 plot indicates that SrCe0.9Sm0.1O3-α-NaCl-KCl is almost a pure ionic conductor. The electrolyte resistance and the polarization resistance of the H2/O2 fuel cell based on SrCe0.9Sm0.1O3-α-NaCl-KCl composite electrolyte under open-circuit condition were 1.0 Ω·cm2 and 0.2 Ω·cm2 respectively. Further, the obtained maximum power density at 700 °C was 182 mW·cm−2.

Electrical conductivity of molten fluoride-oxide melts with high addition of aluminium fluoride

Electrical conductivity of NaF-AlF3 melts with an addition of 2 wt % Al2O3 and/or 5 wt % CaF2 was measured using a pyrolytic boron nitride tube-type cell with a constant distance of electrodes. The molar cryolite ratios MR = n(NaF)/n(AlF3) were 1.8 and 1.6, and the temperature was varied from 865 °C to 1005 °C. Ac-techniques with a sine wave signal with small amplitude in the high frequency range were applied. Electrolyte resistance was obtained from nonlinear regression analysis according to equivalent circuit. Experimental data were used to describe the dependence of the electrical conductivity in fluoride melts with lower temperature on the amount of various additions and temperature.