Thermal Conductivity, Heat Sources and Temperature Profiles of Li-ion Secondary Batteries

We measure and report the thermal conductivity of several commercial and non-commercial Li-ion secondary battery electrode materials, with and without electrolyte solvents. We also measure the Tafel potential, the ohmic resistance, reaction entropy and external temperature of a commercial pouch cell secondary Li-ion battery. Finally we combine all the experimentally obtained data in a thermal Fourier model and discuss the corresponding internal and external temperature profiles during charging and discharging. Electrochemical accumulators and power sources can be both very effective and efficient energy converters. However, as one seeks to intensify both volumetric and specific capacity the heat of these is an inevitable topic in engineering. Moreover, in order to increase performance, the electrodes are necessarily made porous, so that the active specific surface can be increased. In doing so, the thermal conductivity can be lowered by several orders of magnitude. Literature describing thermal conductivity of this property of different Li-ion electrodes is scarse, according to recent reviews e.g. [1], although it is very important. For the ex-situ thermal conductivity measurements we chose commercial electrode materials and for the temperature profile measurements and the electrochemical characterisation we chose a commercial Li-ion pouch cell battery. The electrode materials that we investigated with respect to thermal conductivity were a commercial cathode material (LiCoO 3 ) and a commercial anode material (SLP50). These materials were measured with in an already established procedure [2], both as dry pristine electrode and with a surplus of an electrolyte solvent. The commercial battery was characterised by classical charge and discharge cycling at different current rates.. These experiments were performed in a temperature regulated cabinet with a thermocouple on the battery surface and another in the ambient air. Thus all information required to model the battery's internal and external temperature profiles were collected for the modelling part. The thermal conductivity of dry and soaked electrode material was found to be 0.30 ±0.01 and 0.89±0.04 W K -1 m -1 for the anode material and 0.36±0.003 and 1.10±0.06 for the cathode material. For all materials examined it was found that adding electrolyte solvent increased the thermal conductivity by at least a factor of three. Measuring and combining the surface and the ambient temperatures of an air cooled commercial pouch cell battery at ±2°C, the electric heat sources, and the thermal conductivity of the electrode components made it possible to estimate internal and external temperature profiles at any current density. At 12C charging rate (corresponding to 5 minutes complete charging) the internal temperature differences was estimated to be in the range of 3-4 K, depending on the electrode thermal conductivity. The external temperature drop in air flowing (by forced convection) at the battery surface was estimated to nearly 70K. Thus it is clear that though it is the external temperature gradients that need the most attention with respect to engineered cooling, also internal temperatures become significant at large current rates

Caesarean section in four South East Asian countries: reasons for, rates, associated care practices and health outcomes

Background: Caesarean section is a commonly performed operation on women that is globally increasing in prevalence each year. There is a large variation in the rates of caesarean, both in high and low income countries, as well as between different institutions within these countries. This audit aimed to report rates and reasons for caesarean and associated clinical care practices amongst nine hospitals in the four South East Asian countries participating in the South East Asia-Optimising Reproductive and Child Health in Developing countries (SEA-ORCHID) project. Methods: Data on caesarean rates, care practices and health outcomes were collected from the medical records of the 9550 women and their 9665 infants admitted to the nine participating hospitals across South East Asia between January and December 2005. Results: Overall 27% of women had a caesarean section, with rates varying from 19% to 35% between countries and 12% to 39% between hospitals within countries. The most common indications for caesarean were previous caesarean (7.0%), cephalopelvic disproportion (6.3%), malpresentation (4.7%) and fetal distress (3.3%). Neonatal resuscitation rates ranged from 7% to 60% between countries. Prophylactic antibiotics were almost universally given but variations in timing occurred between countries and between hospitals within countries. Conclusion: Rates and reasons for caesarean section and associated clinical care practices and health outcomes varied widely between the four South East Asian countries.Mario R Festin, Malinee Laopaiboon, Porjai Pattanittum, Melissa R Ewens, David J Henderson-Smart and Caroline A Crowther for The SEA-ORCHID Study Grou

Geospatial Semantics: Why, of What, and How?

Abstract. Why are notions like semantics and ontologies suddenly getting so much attention, within and outside geospatial information communities? The main reason lies in the componentization of Geographic Information Systems (GIS) into services, which are supposed to interoperate within and across these communities. Consequently, I look at geospatial semantics in the context of semantic interoperability. The paper clarifies the relevant notion of semantics and shows what parts of geospatial information need to receive semantic speci-fications in order to achieve interoperability. No attempt at a survey of ap-proaches to provide semantics is made, but a framework for solving interopera-bility problems is proposed in the form of semantic reference systems. Particular emphasis is put on the need and possible ways to ground geospatial semantics in physical processes and measurements. 1. Introduction: Wh

Thermal Gradients through Sintered Solid State Electrolytes in Lithium-Ion Batteries

Recent advancements in research have made solid state electrolytes a strong contender for the previously common liquid electrolytes, as it enables fast charging at very high current densities without flammable liquids. High current in combination with higher ohmic resistance lead to much more heat being dissipated than in conventional Li-ion batteries. As a result, large amounts of ohmic heat are produced inside the battery. As dry electrochemical cells have much lower heat conducting capacity than liquid-containing ones, knowing the thermal conductivity of the cell components plays a crucial role in predicting the heat distribution in such a cell. Thermal conductivity was measured for three types of solid state electrolyte, Li7La3Zr2O12 (LLZO), Li1.5Al0.5Ge1.5(PO4)3 (LAGP) and Li1.3Al0.3Ti1.7(PO4)3 (LATP) at different compaction pressures. LAGP and LATP were measured in sintered condition, LLZO was measured before and after sintering the sample material. Thermal conductivity for the sintered electrolytes was measured to 0.470 ± 0.009 WK- 1m- 1, 0.5 ± 0.2 WK- 1m- 1 and 0.49 ± 0.02 WK- 1m- 1 at 3 bar compaction pressure for LLZO, LAGP and LATP respectively. Before sintering LLZO showed a thermal conductivity of 0.22 ± 0.02 WK- 1m- 1 at 3 bar compaction pressure. A simple analytical model of a lithium-ion battery cell stack was constructed to show the impact of the results obtained through the thermal conductivity measurements. It is based on a work by Richter et al. [1]. The resulting temperature profiles are shown in Fig. 1. The temperature gradients inside the cell stacks need to be considered when assessing lifetime and degradation effects as seen in other electrochemical systems [2-4]. Figure 1: Temperature of the stack center compared to the outer boundary for a) a dry separator and b) a solid state electrolyte, each with two thicknesses. References [1] F. Richter, P. J. Vie, S. Kjelstrup, O. S. Burheim, Measurements of ageing and thermal conductivity in a secondary nmc-hard carbon li-ion battery and the impact on internal temperature profiles, Electrochimica Acta 250 (2017) 228 – 237. [2] R. Bock, A.D. Shum, X. Xiao, H. Karoliussen, F. Seland, I.V. Zenyuk, O.S. Burheim, Thermal conductivity and compaction of GDL-MPL interfacial composite material, J. Electrochem. Soc. 2018 165(7): F514-F525 [3] R. Bock, H. Karoliussen, B. G. Pollet, M. Secanell, F. Seland, D. Stanier, O. S. Burheim, The influence of graphitization on the thermal conductivity of catalyst layers and temperature gradients in proton exchange membrane fuel cells, International Journal of Hydrogen Energy, In-press 2018 [4] O.S.Burheim, M.A. Onsrud, J.G. Pharoah, F. Vullum-Bruer, P.J.S. Vie, Thermal conductivity, heat sources and temperature profiles of Li-ion batteries, ECS Trans., 58 (2013) 145-171. Figure 1 <jats:p /

Thermal Conductivity, Heat Sources and Temperature Profiles of Li-Ion Secondary Batteries

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