Electrode Thermal Conductivity Research Articles

How the Effective Thermal Conductivity of Lithium-Ion Cell Electrodes Is Impacted By the Compression during Calendering

During the design process of lithium-ion batteries the simultaneous optimization of the mechanical, electrical and thermal properties of the components and their interfaces is crucial. As these are strongly influenced by the production steps, a thorough understanding of their impact on said properties is key to reaching optimized material properties of the cells. While many researchers have already investigated the impact of the calendering process on the electrical and mechanical behavior [1][2][3][4], this study covers the alteration of the thermal material properties due to calendering.In this context, different material coatings consisting of two graphite anodes with different starting thicknesses and two cathodes with NMC622 and NMC811 as active materials were investigated. The electrodes were calendered with different forces to reach a broad spectrum of porosities and layer thicknesses. For each material the specific heat capacity and density of the solid phase were measured with differential scanning calorimetry and gas pycnometry, respectively. The thermal diffusivity was measured with laser flash analysis for different compression rates for each active material. With the derived values, the effective thermal conductivity of the different electrodes was determined and interesting indications were found.Considering those results, the values of the effective thermal conductivity of one-sided coated electrodes, plotted vs. the compression rate do not show a steadily increasing slope as suggested by results of common models for their dependence on a decreasing porosity [5][6]. Instead, the thermal conductivity stays at an almost constant value or even decreases at small to medium compression rates before it increases again for a strong compression. This observation indicates that more complex changes and effects happen within the particulate coating layer and at its interfaces to the substrate during the process of calendering than just a change in the porosity. As an example: In a mechanical context, similar variations of the adhesion strength between coating and current collector have been observed [1][2]. It may thus be assumed that the calendering process affects the thermal connection between coating and substrate. The contribution will discuss this and more potentially happening effects and according modifications and extensions of existing models for the thermal conductivity of electrode stacks.

Thermal transport in lithium-ion batteries: The effect of degradation

In this work, we report thermal conductivities of pristine and degraded electrodes, from commercial lithium-ion batteries. The thermal conductivities were measured with and without electrolyte solvent and at different compaction pressures. The effect of degradation on thermal transport, both internal and external, is assessed. In addition, the overall cell cooling efficiency is reported as a function of the state-of-health, and full cell thermal conductivities are estimated. A reduction of the electrode thermal conductivity of up to 65% is found for degraded material. The reduction appears to be the most extreme for dry graphite anodes. Both mechanical clamping of the cells during cycling, and cold temperatures, appear to mitigate the reduction in thermal conductivity. The cell cooling efficiency is found to decrease by 50% at a state-of-health of 70–75%. Decreased wetting, due to a reduction in the amount of electrolyte and gassing, is believed to be responsible for the discrepancy between cell cooling efficiency and thermal conductivity of the electrodes. The main cause of a reduction in full cell thermal conductivity was found to be due to a reduction in anode thermal conductivity and reduction of electrolyte solvent.

Modeling and Simulation of Hafnium Oxide RRAM Based on Oxygen Vacancy Conduction

The resistive memory has become one of the most promising new memory types because of its excellent performance, and HfO2 resistive material has attracted extensive attention. The conduction mechanism based on oxygen vacancy is widely recognized in the research of new nonvolatile memory. An RRAM electrothermal coupling model based on the oxygen vacancy conduction mechanism was constructed using COMSOL. The resistance process of the device is simulated by solving the coefficient partial differential equation, and the distribution of oxygen vacancy concentration, temperature, electric field, electric potential and other parameters in the dielectric layer at different voltages are obtained. The effects of temperature, dielectric layer thickness, top electrode thermal conductivity and conductive wire size on the resistance characteristics of the device are studied. It has guiding significance to further study the RRAM mechanism.

Heat and mass transfer performance of proton exchange membrane fuel cells with electrode of anisotropic thermal conductivity

Proton exchange membrane fuel cells (PEMFCs) are widely used because they are clean, efficient, and renewable. However, many advanced electrode materials have distinct characteristics in different dimensions, and the anisotropy of thermal conductivity can significantly influences the performance of PEMFCs. In this study, the coupling characteristics of heat transfer and catalysis by a PEMFC are systematically analyzed using an anisotropic electrode thermal conductivity model. The results revealed that the anisotropy in the through-plane direction of the electrode thermal conductivity exhibited a more significant influence than in other directions. Specifically, the heat generated in the cathode electrode during the electrochemical process was the primary heat source in the PEMFC, and the molar concentration distributions of liquid water and oxygen on the electrode surface also varied at different operational temperatures. Moreover, the output performance of the PEMFC could be effectively improved through appropriate anisotropic thermal conductivity in the through-plane direction at a low operational temperature. However, the improvement of the electrochemical reaction is limited under high operational temperature conditions, owing to a decrease in transition region of proton conductivity. Overall, this study shows a new strategy of improving the performance of PEMFCs by reasonably design the electrode materials with anisotropic thermal conductivity.

Influence of Different Tool Electrode Materials on Electrochemical Discharge Machining Performances.

Electrochemical discharge machining (ECDM) is an emerging method for developing micro-channels in conductive or non-conductive materials. In order to machine the materials, it uses a combination of chemical and thermal energy. The tool electrode’s arrangement is crucial for channeling these energies from the tool electrode to the work material. As a consequence, tool electrode optimization and analysis are crucial for efficiently utilizing energies during ECDM and ensuring machining accuracy. The main motive of this study is to experimentally investigate the influence of different electrode materials, namely titanium alloy (TC4), stainless steel (SS304), brass, and copper–tungsten (CuW) alloys (W70Cu30, W80Cu20, W90Cu10), on electrodes’ electrical properties, and to select an appropriate electrode in the ECDM process. The material removal rate (MRR), electrode wear ratio (EWR), overcut (OC), and surface defects are the measurements considered. The electrical conductivity and thermal conductivity of electrodes have been identified as analytical issues for optimal machining efficiency. Moreover, electrical conductivity has been shown to influence the MRR, whereas thermal conductivity has a greater impact on the EWR, as characterized by TC4, SS304, brass, and W80Cu20 electrodes. After that, comparison experiments with three CuW electrodes (W70Cu30, W80Cu20, and W90Cu10) are carried out, with the W70Cu30 electrode appearing to be the best in terms of the ECDM process. After reviewing the research outcomes, it was determined that the W70Cu30 electrode fits best in the ECDM process, with a 70 μg/s MRR, 8.1% EWR, and 0.05 mm OC. Therefore, the W70Cu30 electrode is discovered to have the best operational efficiency and productivity with performance measures in ECDM out of the six electrodes.

THERMAL PROPERTY OF CARBON RESIN ELECTRODES DEVELOPED FOR ELECTROCHEMICAL TREATMENT OF WATER AND WASTEWATERS

In this paper, thermal conductivity of carbon resin electrodes developed for electrochemical treatment of water and wastewater was investigated. Carbon resin electrodes were developed from used dry cells and resin using non-heat treatment processes. Thermal conductivity of the electrodes was measured and effects of particle size, compacting pressure, carbonisation temperature and percentage of the resin used on thermal conductivity of the electrodes were monitored using standard method through RE 890G and ALDA AVD 890G thermocouples at two different points (5cm apart). Effective thermal conductivity of the electrodes was modelled using Okazaki et al model. The study revealed that thermal conductivity of carbon resin electrodes ranged from 1.39 W/K. cm to 2.24 W/K. cm. Thermal conductivity of the material increased with decreased particle size (1.48 to 2.24 W/K. cm with 245 to 45mm) and decreased percentage resin (1.49 to 2.20 W/K. cm with 12 % to 1%), decreased with decreased compacting pressure (2.12 to 1.44 W/K. cm with 110 MN/ m2 to 60 MN/ m2) and carbonization temperature (2.12 to 1.39 W/K. cm with 260 oC to 30o C). Okazaki et al model agreed reasonably with the experimental data with correlation coefficient of 0.3206 and coefficient of determination 0.9917. It was concluded that particle size, compacting pressure, carbonization temperature and percentage resin play important role in thermal conductivity of carbon resin electrodes.

Impact of electrode thermal conductivity on high resistance state level in HfO2-based RRAM

This study examines the influence of different electrode thermal conductivity on switching behavior during the reset process. Electrical analysis methods and an analysis of current conduction mechanism indicate that better thermal conductivity in the electrode will require larger input power in order to induce more active oxygen ions to take part in the reset process. More active oxygen ions result in a more oxidized switching layer, and cause the effective switching gap (dsw) to become larger in the reset process. The effect of the electrode thermal conductivity and input power are explained by our model and clarified by electrical analysis methods.

Thermal Conductivity Study on a Working Li-Ion Battery Cell

Lithium-ion batteries have been popular powering mobile electronics and electric vehicles owing to its high energy density and good electrochemical performance. However, thermal transport performance, especially in cross-plane direction, is not on a par with electrochemical ones. Poor thermal transport may result in overheating and even thermal runaway while there’s still a lack of methods studying battery electrode thermal conductivity under working condition1. Previous efforts provide measurement on either dry battery electrodes or reassembled electrodes with electrolyte but not being able to charge and discharge2, 3. Current study demonstrates a new method measuring thermal conductivity of a working battery cell through flash diffusivity technique. By minimizing contact resistance between electrode sample and holder, the work can contribute to comprehensive study of a working battery cell for better thermal performance.1. V. Vishwakarma, C. Waghela, Z. Wei, R. Prasher, S. C. Nagpure, J. Li, F. Liu, C. Daniel, and A. Jain, Journal of Power Sources, 300 123-131 (2015).2. H. Maleki, S. A. Hallaj, J. R. Selman, R. B. Dinwiddie, and H. Wang, Journal of The Electrochemical Society, 146 (3), 947-954 (1999).3. S. C. Nagpure, R. Dinwiddie, S. S. Babu, G. Rizzoni, B. Bhushan, and T. Frech, Journal of Power Sources, 195 (3), 872-876 (2010).

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

In this paper we report the thermal conductivity of several commercial and non-commercial Li-ion secondary battery electrode materials with and without electrolytesolvents. We also measure the Tafel potential, the ohmic resistance, reaction entropyand external temperature of a commercial pouch cell secondary Li-ion battery. Finallywe combined all the experimentally obtained data in a thermal model and discuss thecorresponding internal temperature effects.The thermal conductivity of dry electrode material was found to range from 0.07to 0.41 WK−1m−1 while the electrode material soaked in electrolyte solvent rangedfrom 0.36 to 1.10 WK−1m−1. For all the different materials it was found that addingthe electrolyte solvent increased the thermal conductivity by at least a factor of three. For one of the anode materials it was found that heat treatment at 3000 K increasedthe thermal conductivity by a factor of almost five.Measuring the electric heat sources of an air cooled commercial pouch cell bat-tery at up to ± 2C and the thermal conductivity of the electrode components madeit possible to estimate internal temperature profiles. Combining the heat sources withtabulated convective heat transfer coefficients of air allowed us to calculate the ambi-ent temperature profiles. At 12C charging rate (corresponding to 5 minutes completecharging) the internal temperature differences was estimated to be in the range of 4-20K, depending on the electrode thermal conductivity. The external temperature dropin air flowing at the battery surface was estimated to nearly 40K. Evaluating thermal management of batteries in the light of our measurement led to the conclusion that ex-ternal cooling is more challenging than internal, though neither should be neglected.

Effect of electrode thermal conductivity in cardiac radiofrequency catheter ablation: A computational modeling study

Purpose: Radiofrequency (RF ablation) is the treatment of choice for certain types of cardiac arrhythmias. Recent studies have suggested that using gold instead of platinum as the electrode material for cardiac catheter ablation leads to larger thermal lesions due to its higher thermal conductivity. In this study we created computer models to compare the effects of different electrode materials on lesion dimensions using different catheters, insertion depths, and flow rates.Materials and methods: Finite element method (FEM) models of two cardiac ablation electrodes (7Fr, length 4 mm and 8Fr, length 10 mm) made of platinum, gold, and copper were created with tissue insertion depths of 0.75, 1.25, and 2.5 mm. Convective cooling was applied to the electrode and tissue based on measurements from previous studies at different flow rates. RF ablations were simulated with both temperature control and constant power control algorithms to determine temperature profiles after 60 s.Results: With the constant power algorithm there was no difference in lesion dimensions between the electrode materials over the range of parameters. With the temperature control algorithm, lesion width and depth were only marginally larger (∼0.1–0.7 mm) with the gold and copper electrodes compared to the platinum electrode for all parameter combinations.Conclusion: Our computer modelling results show only minor increases in thermal lesion dimensions with electrode materials of higher thermal conductivity. These observed differences likely do not provide a significant advantage during clinical procedures.

Ring electrode for radio-frequency heating of the cornea: modelling and in vitro experiments.

Radio-frequency thermokeratoplasty (RF-TKP) is a technique used to reshape the cornea curvature by means of thermal lesions using radio-frequency currents. This curvature change allows refractive disorders such as hyperopia to be corrected. A new electrode with ring geometry is proposed for RF-TKP. It was designed to create a single thermal lesion with a full-circle shape. Finite element models were developed, and the temperature distributions in the cornea were analysed for different ring electrode characteristics. The computer results indicated that the maximum temperature in the cornea was located in the vicinity of the ring electrode outer perimeter, and that the lesions had a semi-torus shape. The results also indicated that the electrode thickness, electrode radius and electrode thermal conductivity had a significant influence on the temperature distributions. In addition, in vitro experiments were performed on rabbit eyes. At 5 W power, the lesions were fully circular. Some lesions showed non-uniform characteristics along their circular path. Lesion depth depended on heating duration (60% of corneal thickness for 20 s, and 30% for 10 s). The results suggest that the critical shrinkage temperature (55-63 degrees C) was reached at the central stroma and along the entire circular path in all the cases.

Dielectric breakdown in high-ε films for ulsi drams

Dielectric breakdown has been studied in several materials intended for high-dielectric DRAMs (dynamic random access memories), emphasizing lead zirconate-titanate (PZT) and barium strontium titanate (BST) ceramics. In this paper recent results from PZT are presented. In order to distinguish among impulse thermal breakdown, dc thermal breakdown, and avalanche breakdown mechanisms, studies have been carried out as functions of temperature, electrode material and shape, frequency and duration of applied fields, and specimen size and shape. Notable in the results is the fact that maximum breakdown field varies directly with electrode work function but is uncorrelated with electrode thermal conductivity; this militates against a purely thermal breakdown interpretation and instead favors an avalanche mechanism in which the initial step is electronic followed by thermal run-away. Thickness dependence also favors avalanche mechanisms, but dependence upon applied field ramp rate favors an impulse thermal mechanism.

Dielectric breakdown in high-ε films for ULSI DRAMs

Abstract Dielectric breakdown has been studied in several materials intended for high-dielectric DRAMs (dynamic random access memories), emphasizing lead zirconate-titanate (PZT) and barium strontium titanate (BST) ceramics. In this paper we present our results on PZT. A second paper will deal with BST. In order to distinguish among impulse thermal breakdown, de thermal breakdown, and avalanche breakdown mechanisms, studies have been carried out as functions of temperature, electrode material and shape, frequency and duration of applied fields, and specimen size and shape. Notable in the results is the fact that maximum breakdown field varies directly with electrode work function but is uncorrelated with electrode thermal conductivity; this militates against a purely thermal breakdown interpretation and instead favors an avalanche mechanism in which the iniation step is impact ionization of Ti ions from electrons emitted from the electrodes, followed by thermal run-away. Thickness dependence also favors avalanche mechanisms, but dependence upon applied field ramp rate favors an impulse thermal mechanism. Taken altogether, the data indicate characteristics of mixed impulse-thermal and avalanche mechanisms: i.e., electron-initiation followed by thermal run-away.

On-state behaviour and degradation effects in thin-film amorphous switching devices

The on-state behaviour of thin-film chalcogenide threshold switches was studied with special reference to the influence of electrode materials and the progressive effects of device degradation. For operations during the forming period, the on-state current-voltage characteristics remain identical for both rising and falling current. The on-state minimum voltage is found to be closely proportional to the square root of the electrode thermal conductivity and, in addition, shows some polarity dependence with dissimilar electrode combinations. This behaviour is interpreted in terms of a model in which the voltage drop across the on-state current channel is dominated by constrictions and associated hot spots near the channel/electrode boundaries. After forming and after a further number of operations depending both on electrode material and ambient temperature, one or more stable intermediate steps or “branches” develop in the I– V characteristic of the transition from off-state to on-state. The exact pattern shows some polarity dependence. Branching is identified with the progressive precipitation of tellurium-rich “islands” in the glass as the number of device operations increases and as a result of which the growth of the on-state channel proceeds via a number of “island-hopping” stages.