Low-temperature Cycle Research Articles

Rigid polyurethane foam with durable hydrophobicity and flame retardancy endowed by novel functional surfactants

Traditional rigid polyurethane foam (RPUF) with flame retardancy might be easily damaged in some moist condition due to its hydrophobicity, which would lead to unsafety. Therefore, novel surfactants with both hydrophobic fluorinated group and flame-retardant phosphorus group were synthesized. With lower surface tension and more hydrogen bonds formed in polyurethane, the mixed surfactants, which were used in the preparation of RPUF, have not only obviously improved the size uniformity and integrity of cells but also enhanced its hydrophobicity, compressive strength and thermal insulating performance. Besides, effective ‘protection’ could be constructed on the surface of RPUF by prepared surfactants, when ammonium polyphosphate (APP) and expandable graphite (EG) were introduced to provide good flame retardancy. As a result, with just 2.8wt% content of those functional surfactants, hydrophobic and flame-retardant RPUF with water contact angle of 126 °, limiting oxygen index of 25%, compressive strength of 1.3MPa and thermal conductivity of 27mW/mK, were finally obtained, which is ahead of other flame-retardant RPUF reported before. It’s worth noting that, this hydrophobic and flame-retardant RPUF exhibits more stable and durable properties when soaking in HCl solution (2mol/L), NaOH solution (2mol/L), NaCl saturated solution and various solvents (THF and EtOH), or under strong fiction for 100 times and high and low temperature cycling test for 20 times. This would provide a novel and effective strategy to endow RPUF with enhanced and durable flame retardancy, hydrophobicity, compressive strength and thermal insulating performance even under extreme conditions.

Enhancement of Low-Temperature Cycling Performance of Lithium-Ion Batteries by use of Dual Cosolvent

Abstract Lithium-ion batteries (LIBs) based on conventional electrolyte suffer from poor cycling performance at low temperatures due to the reduced ionic conductivity of electrolytes, sluggish charge transfer reaction, and Li plating during the charging process. Herein, we propose a dual cosolvent composed of methyl acetate (MA) and ethyl fluoroacetate (EFA). MA effectively reduced the viscosity of the electrolyte, improving the ionic conductivity at low temperatures. EFA facilitated the de-solvation of Li+ ions and formed an anion-derived solvation structure, enabling the formation of an inorganic-rich solid electrolyte interphase on the graphite anode. Due to the synergistic effect of MA and EFA, the graphite/LiFePO4 cell employing a dual cosolvent exhibited good cycling performance at low temperatures, delivering a discharge capacity of 68.7 mAh g-1 at -20 °C and 0.2 C and showing a capacity retention of 99.7% after 100 cycles at -20 °C and 0.33 C. Additionally, the cell exhibited an initial discharge capacity of 131.2 mAh g-1 at 25 °C and 1.0 C, with a capacity retention of 99.4% after 300 cycles. Our results demonstrate that liquid electrolytes containing dual cosolvent with various beneficial roles can be a promising solution for improving the low-temperature cycling performance of LIBs.

Analysis of High and Low Temperature Performance of Titanium Zirconium Molybdenum Alloy and High Temperature Alloy Brazed Joint

Abstract Using niobium as the intermediate layer and gold nickel (Au82-Ni) filler metal, TZM alloy and high-temperature alloy GH3128 were brazed. The brazed specimens were subjected to 400 cycles of high and low temperature cycling tests at temperatures ranging from 650 °C ∼ 680 °C (high temperature) to -196 °C (low temperature) for 10 minutes seperately. Then the microstructure variation before and after the experiment were observed and the shear strength of the specimens were tested at room temperature for 50 cycles of 400 high and low temperature testing.. The results show that the microstructure of the transition zone at the brazing interface after brazing is uniform and dense, with good wettability with the substrate and no defects such as cracks. The solder and substrate undergo diffusion reactions, and the molybdenum alloy, niobium, and niobium, high-temperature alloy had each form diffusion layers, formed intermetallic compounds on the brazing surface. After high and low temperature cycling, cracks exist in the braze seam between molybdenum alloy and niobium alloy. The cracking mode should be thermal fatigue based on the fracture morphology and phase analysis. The reasons of interface cracking are that due to different thermal expansion coefficients, low mutual solid solubility, and the formation of a large number of different types of intermetallic compounds, Mo and Nb materials have poor brazing compatibility and lower interface strength. Under cold and hot cycling conditions, brittle intermetallic compounds are prone to form crack source areas. As the number of cycles increases, the cracks gradually expand, ultimately leading to product leakage. In addition, the shear strength of brazed joints shows a decreasing trend with the increase of high and low temperature cycles in 400 high and low temperature tests.

Optimizing cascade refrigeration systems with low GWP refrigerants for Low-Temperature Applications: A thermodynamic analysis

This study offers a comprehensive thermodynamic analysis of a cascade refrigeration system conducted for low-temperature applications, focusing on the use of low-GWP and zero-ODP refrigerants to improve efficiency and sustainability. The target of this study is to explore the performance of the system using a combination of refrigerants: low-temperature cycle refrigerants such as R744, while high-temperature cycle refrigerants such as R717, R1234yf, R1234ze(E), R1336mzz(E), and R1336mzz(Z), respectively. The ECS model incorporating in REFPROP 10.0a tool was utilized to extract the data through coding for analysis. The assessment of this system involves the examination of various parameters such as its coefficient of performance, total compressor workload, total exergy, and exergy efficiency across various operational conditions. The results are compared with and without superheated and subcooled conditions to understand the impact of these parameters on the system performance. The system with R744 in the low-temperature cycle and R717, R1234yf, R1234ze(E), R1336mzz(E), and R1336mzz(Z) in the high-temperature cycle provides a higher COP and lower total compressor work compared to the conventional cascade refrigeration system. In optimal CRS, the R744-R717 pair attains the highest COP of 2.05 at the lowest possible compressor work from 9.53 to 4.87 kW than other refrigerants pair while evaporator temperature shifting from −55 °C to −20 °C. The exergy efficiency of R744/R717 is found at 26.47 % at an evaporator temperature of −55 °C, but it extends to a peak of 51.73 % at −20 °C. The study also shows that the superheating and sub-cooling of the refrigerants have a significant impact on the performance of the cascade refrigeration system. Superheating and sub-cooling at 10 °C, improves the COP of the system by reducing the compressor work and increasing the heat transfer efficiency. The research offers valuable insights into the system’s thermodynamic performance when employing low GWP refrigerants in low-temperature applications. These findings have the potential to guide the design and optimization of cascade refrigeration systems over the range of low-temperature applications.

Thermodynamic Comparative Analysis of Cascade Refrigeration System Pairing R744 with R404A, R448A and R449A with Internal Heat Exchanger: Part 2—Exergy Characteristics

The cascade refrigeration systems (CRS) used in hypermarkets and supermarkets, which are used by many people, have been employing R744 for the low-temperature cycle (LTC) and R404A for the high-temperature cycle (HTC) due to environmental and public safety issues. However, the use of R404A is limited due to its high GWP, and therefore research on alternative refrigerants is necessary. Nevertheless, there is no detailed study in the literature that compares and analyzes the three refrigerants for practical design by applying R744 for LTC and R404A, R448A, and R449A for HTC in CRS. Therefore, this study aims to provide data for the practical detailed design of an alternative system to R744/R404A CRS. Under standard conditions, we analyzed how the exergy destruction rate (EDR) and exergy efficiency (EE) of the system and the EDR of each component change when the important factors affecting CRS (degree of superheating (DSH), degree of subcooling (DSC), and internal heat exchanger (IHX) efficiency of HTC, DSH of LTC, condensation temperature (CT), evaporation temperature (ET), cascade evaporation temperature (CET), and temperature difference of CHX) are varied over a wide range. The main conclusions are as follows. (1) Under the given constant conditions, the smallest change in system EDR based on R448A is DSH of HTC (decreased by 0.07–0.1 kW), followed by IHX of HTC (decreased by 0.12–0.3 kW), DSH of LTC (increased by 0.19–0.25 kW), DSC of HTC (decreased by 0.59–0.69 kW), temperature difference of CHX (increased by 1.57–1.83 kW), CET (decreased and then increased by 0.67–4.43 kW), CT (increased by 1.49–3.9 kW), ET (decreased by 2.39–4.61 kW). (2) The highest change rate of system EE based on R448A is CET (increased and then decreased by 1.38–8.28%), followed by temperature difference of CHX (decreased by 2.96–3.16%), ET (increased and then decreased by 0.63–2.75%), DSC of HTC (increased by 1.26–1.34%), CT (increased and then decreased by 0.24–1.12%), IHX of HTC (increased by 0.11–1.02%), DSH of LTC (decreased by 0.35–0.49%), and DSH of HTC (increased by 0.14–0.19%).

Study of Interlaminar Fracture Toughness and Flexural Properties of Carbon Fibre Composites Reinforced with Polyethersulfone/Graphene Oxide Films

Unidirectional carbon fibre reinforced plastic (CFRP) composites were prepared by inserting polyethersulfone (PES) films or polyethersulfone/graphene oxide (GO) films into the composites and used to improve the interlaminar fracture toughness as well as the flexural properties. The effect of low-temperature cycling (35, 70, 105, and 140 cycles between −55 °C and room temperature (25 °C)) on the flexural properties of the specimens was also investigated, and the damage caused to the reinforcement layer was directly detected by comparing the interlaminar images. The results of the double cantilever beam (DCB) test and the end notched flexure (ENF) test were used to verify the optimisation of the interlaminar fracture toughness and flexural properties of the new composite film (PES/GO film). The results show that the performance of PES/GO film under both DCB test and ENF test is superior to that of PES film. Regarding the effect of low-temperature cycling on the specimens, the flexural properties of the specimens containing PES/GO films were improved. Finally, the matrix interface and failure mechanism of the interlayer reinforcement were investigated by scanning electron microscopy (SEM).

Experimental study on impact behaviour of normal strength mortar at cryogenic temperatures and after freeze-thaw cycles

Concrete structures employed for the storage of Liquefied Natural Gases (LNG) currently undergo temperature as low as −170 °C. These critical engineering structures may also experience dynamic loads such as impact or explosion during service life. Therefore, it is crucial to explore the mechanical response of concrete at intermediate to high strain rates together with low temperatures or cryogenic freeze-thaw (FT) cycles. This study presents experimental research into the combined effects of low temperatures and strain rate on normal strength mortar, providing a preliminary analysis of the dynamic performance of concrete at low and cryogenic temperatures. A Split Hopkinson Pressure Bar (SHPB) device was used to investigate the characteristics of dynamic compression (at strain rates of 40, 80, 120 and 160 s−1) and dynamic split tension (at strain rates of 20, 40, 60 and 80 s−1) of Normal Strength Mortar (NSM) at different low temperatures. In addition, the dynamic compression (at strain rates of 80, 130 and 180 s−1) after cryogenic FT cycles was also explored. The findings revealed that the failure pattern of NSM samples exposed to coupled low temperature or cryogenic FT cycles and high strain rate loading notably varied from that observed under room temperature condition. Both the dynamic compressive and split tensile strengths of NSM increased with the strain rates at all temperatures. At −160 °C, the dynamic compressive and splitting tensile strengths of NSM specimens were greater than those at room temperature (by 10.94 % and 28.29 %, respectively) and −70 °C (by 3.13 % and 4.12 %, respectively). Cryogenic freeze-thaw cycles evidently impacted the material static and dynamic performance. An empirical model was developed to predict the dynamic increase factors (DIFs) for both dynamic compression and splitting tensile strengths of NSM at low/cryogenic temperatures and after freeze-thaw cycles. Scanning electron microscopy (SEM) technique was performed to study and comprehend the microscopic processes and microstructural changes after FT cycles.

The effect of changing the combustion chamber head structure on turbine blades under thermal shock test

When the high-pressure turbine guide blade works in the aero-engine, it is in the complex gas-heat environment of the combustion chamber and the turbine. The temperature distribution and strength of the blade affect the reliability and life of the aero-engine. In order to more accurately analyze the complex flow field aero-thermal parameters between the aero-engine combustion chamber and the turbine, this paper considers the influence of the non-uniform aero-thermal parameters of the combustion chamber outlet on the turbine. Taking the first-stage guide vane of an aero-engine turbine as the research object, the high and low temperature cycle thermal shock test was carried out to obtain the crack location and strength of the turbine guide vane, which provided a certain reference for improving the design of the turbine guide vane. Through the test, it is found that after 750 thermal shock cycles, fatigue cracks appear in four concentrated areas of the blade, which are distributed in the leading edge and trailing edge of the blade respectively. This shows that the temperature at the leading edge and trailing edge of the blade is higher, the heat load is higher, and the risk of damage and ablation is also the highest. Based on the experiment, the cross-component model of the combustion chamber and the blade is established. On this basis, four kinds of swirler structures at the head of the combustion chamber are designed. ANSYS FLUENT software is used to study the unsteady parameters such as the surface temperature of the guide vane under the influence of strong swirling flow. The numerical results show that when the rotation direction of the cyclone is counterclockwise, the temperature of the guide vane wall is more uniform. Compared with the clockwise rotation of the cyclone, the temperature is reduced by about 5 %, and the installation angle of the 50° cyclone blade is better than the installation angle of the 45° blade.

Impact of fast charging and low-temperature cycling on lithium-ion battery health: A comparative analysis

Fast charging and low temperatures create harsh conditions that promote lithium deposition on graphite anodes, which significantly accelerates the degradation of the battery's state of health (SoH) and eventually could result in safety concerns. In this work, commercial lithium-ion batteries are investigated under fast charging conditions and at low environmental temperatures. The findings are compared with lithium-ion battery cycled under ambient temperature conditions. The fast charging and low temperatures result in dead lithium formation, which is then characterized by electrochemical impedance spectroscopy (EIS) and scanning electron microscope (SEM). The low-temperature cycled battery exhibits significant growth of series resistance by an average of 73 %. In comparison, growth in charge transfer resistance is 16 %, and no significant change was observed in solid electrolyte interface (SEI) resistance due to the formation of dead lithium, compared to the battery cycled at ambient temperature. SEM images also confirm the dead lithium formation. The results provide insight into battery degradation in the case of high current due to low temperature and could lead to a better understanding of the degradation mechanism.

Enhanced low-temperature resistance of lithium-ion batteries based on methyl propionate-fluorinated ethylene carbonate electrolyte

Low temperature has been a major challenge for lithium-ion batteries to maintain satisfied electrochemical performance, as it leads to poor rechargeability and low capacity retention. Traditional carbonate solvents, vinyl carbonate and dimethyl carbonate are indispensable components of commercial electrolytes. However, the higher melting point of these carbonate solvents causes their electrical conductivity to be easily reduced when temperatures drop below zero, limiting their ability to facilitate lithium ion transport. In this work, we demonstrate that the use of methyl propionate (MP) carboxylate and fluorocarbonate vinyl (FEC) electrolytes can overcome the limitations of low temperature cycling. Compared with carbonate electrolyte, MP has the characteristics of low melting point, low viscosity and low binding energy with Li+, which is crucial to improve the low temperature performance of the battery, while FEC is an effective component to inhibit the side reaction between MP and lithium metal. The carefully formulated MP-based electrolyte can generate a solid electrolyte interface with low resistance and rich in inorganic substances, which is conducive to the smooth diffusion of Li+, allowing the battery to successfully cycle at a high rate of 0.5 C at −20 °C, and giving it a reversible capacity retention rate of 65.3% at −40 oC. This work designs a promising advanced electrolyte and holds the potential to overcome limitations of lithium-ion batteries in harsh conditions.

Study on the effect of carbon fiber grid plate layup on substrate-solar cell thermal adaptation

Abstract The differences in the configuration and thermal expansion coefficient of solar cell modules result in thermal stress when solar cells undergo high and low-temperature cycles in orbit, which induces the failure of battery module connections. In this paper, finite element modeling and simulation methods are used to study the thermal compatibility design of four different layers of rigid carbon fiber mesh panels: [0/90]3s, [0/90-45/-45-0/90], [0/90-45-45/-45], and [45/-45]3s. The results show that the substrate configuration with a larger proportion of 0/90 layers has good thermal adaptability for the interconnect-oriented battery array.

Vitrified Metal-Organic Framework Composite Electrolyte Enabling Dendrite-Free and Long-Lifespan Solid-State Lithium Metal Batteries.

Solid-state lithium metal batteries (LMBs) are still plagued with low ionic conductivity and inferior interfacial contact, which hinder their practical implementation. Herein, a quasi-solid-state composite electrolyte, poly(1,3-dioxolane) (PDOL)/glassy ZIF-62 (PGZ) with fast ion transport and intimate interface contact, is fabricated via in situ polymerization. The in situ polymerization of DOL in an electrolyte matrix not only improves the exterior interface between electrolyte/electrode but also optimizes the inner interfaces among glassy particles, rendering PGZ as an uninterrupted ionic conductor. Moreover, PGZ inherits the superior ionic conductivity and the robust dendrite prohibition of glassy MOFs originating from their grain-boundary-free nature, isotropy, and abundant groups containing N species. As expected, our proposed PGZ exhibits a prominent ionic conductivity of 6.3 × 10-4 S cm-1 at 20 °C. Li|PGZ|LiFePO4 delivers an outstanding rate performance (103 mAh g-1 at 4C) and a stable cycling capacity (118 mAh g-1 at 1C over 1000 cycles). PGZ also presents excellent low-temperature cycling performance with 75 mAh g-1 for 480 cycles at -20 °C and excellent flame retardance. Even at a high loading of 12.1 mg cm-2, it can still discharge at 140 mAh g-1 for 100 cycles. Hence, PGZ prepared via in situ polymerization holds enormous prospects as a solid-state electrolyte for high-performance and safe LMBs.

Comparison Study of Cascaded Organic Rankine Cycles with Single and Dual Working Fluids for Waste Heat Recovery

This study compares thermodynamics, economics, and environmental performance of cascaded ORCs operated under a single and dual fluids. In the single fluid cascaded ORC, toluene, benzene, acetone and cyclopentane are run in high and low temperature cycles, whereas in dual fluid cascaded ORC, toluene, benzene, acetone and cyclopentane are run in high temperature cycle and R601a in the low temperature cycle. The analysis compares variations in expander inlet temperature and condensation temperature. Thermodynamic performance involved net power output (Pnet) and thermal efficiency (ηth), while economic indicators included net present value (NPV) and levelized cost of electricity (LCOE). In environmental performance, the annual reduction in carbon dioxide emission (CO2-eq) is assessed. The findings revealed that dual fluid cascaded ORC generated the highest Pnet of 1245.11 kW while single fluid cascaded ORC reached 1170.27 kW. The dual fluid cascaded ORC showed the significant increase in Pnet (%DPnet) for about 43% at the lowest expander inlet temperature (500 K). In terms of ηth, dual fluid cascaded ORC attained 37.23 % while single fluid cascaded ORC reached 33.25%. It is further found that acetone+R601a performed well in dual fluid cascaded ORC, resulting in the highest Pnet and allowing system’s NPV to turn positive sooner than other fluids. Furthermore, cyclopentane+R601a had the lowest LCOE of 0.0158 US$/kWh, which is 1.1% lower compared to the single fluid cascaded ORC and competitive in the Thai electricity market. In environmental saving, dual fluid cascaded ORC reduced about 144.96 tCO2-eq/year, and outperformed single fluid cascaded ORC by roughly 6.39%.

Orthorhombic K3V3(PO4)4: A low-temperature cathode material for potassium-ion batteries

Potassium-ion battery has been considered as a promising energy storage device with low cost and high sustainability. However, its low-temperature performance is always poor due to the large size of K+ ions and poor ion transportation capability under low temperature. In this work, a carbon-coated orthorhombic K3V3(PO4)4/C cathode material for potassium-ion batteries is developed with promising low-temperature cycle performance. At −10 °C, K3V3(PO4)4/C retains a reversible capacity of 52.2 mAh/g for 1400 cycles at a current density of 100 mA g−1. The superior low-temperature performance is attributed to its open framework structure, which provides three-dimension channels for K-ion transportation. It is revealed that V3+/V4+ redox dominates the charge compensation in K3V3(PO4)4/C during charge and discharge processes. Carbon coating can not only reduce the charge transfer resistance of the electrode and prevent electrode cracking, but also helps to the formation of CF3-rich interfaces between the cathode and electrolyte, ensuring high interfacial stability of K3V3(PO4)4/C during cycling.

Evolution mechanism and non-destructive assessment of thermal safety for lithium-ion batteries during the whole lifecycle

The thermal safety variations of lithium-ion batteries during operational usage pose a significant threat to the safe application of electric vehicles. This work initially investigates the battery thermal safety evolution mechanism under different degradation paths. Lithium plating is identified as the critical common degradation mechanism leading to the decline of battery thermal safety through multi-angle characterization analysis. However, lithium plating generated by different formation mechanism has different impact on the battery thermal stability. The most severe degradation of battery thermal safety is caused by lithium plating which is induced by the limited lithium intercalation rate under low-temperature cycling and high-rate cycling. Further, the mechanism of internal degradation on the battery thermal safety is elucidated through multi-scale thermal test analysis. It is indicated that lithium plating and transition metal dissolution are crucial factors leading to the decreased thermal stability of the anode and cathode respectively, which consequently results in a significant reduction of T1 and T2. Furthermore, based on the principle of internal degradation synchronously affecting electrochemical characteristics and thermal stability characteristics, the mapping relationship between the observation indicators of electrochemical characteristics and the characterization parameters of thermal safety is established, realizing the non-destructive assessment of battery thermal safety during the whole lifecycle.

Study on the effect of low-temperature cycling on the thermal and gas production behaviors of Ni0.8Co0.1Al0.1/graphite lithium-ion batteries

With their high energy density and long cycle life, lithium-ion batteries (LIBs) are currently the most promising electrochemical energy storage system for electric vehicles. However, their safety and cycling performance can be significantly compromised in low-temperature environments due to lithium plating and other factors. Therefore, it is essential to study the safety of aging batteries. In this study, we focused on a commercially available high-specific-energy Ni0.8Co0.1Al0.1 cathode system battery and simulated the aging of the battery by long-term cycling at 0 ℃. This study compares and analyzes the samples on the basis of the previous ones in terms of heat production power, thermal runaway (TR) characteristics and gas production characteristics. It reveals the influence of low-temperature aging on the comprehensive performance of lithium batteries in a more comprehensive way. The results show that the charging pattern of all three characteristics is related to the aging degree of the battery. In terms of the thermal characteristics, the relative change in specific heat capacity of the aged battery is only between 0.32 % and 1.08 % compared to that of a fresh battery, so the effect of ageing on the specific heat capacity of the battery is negligible. The average heat generation power of batteries with different state of health (SOH) is not monotonically increasing with the decrease of SOH, the threshold of dramatic increase is SOH = 80 %. In terms of TR characteristics, the onset temperature of exothermic reactions (TOER) of aged batteries is significantly lower than that of fresh batteries. With the decrease of SOH, TOER also decreases gradually. Compared with batteries with different SOHs, the more seriously aged the battery safety valve opens earlier, and the TR occurs earlier. In terms of the TR gas production characteristics, the more severely aged the battery, the earlier the safety valve opens compared to a fresh battery. The most gas is produced when SOH = 70 %, which increases the risk of catastrophic damage.

Failure analysis on the abnormal cracking of Si3N4 ceramic substrates for SiC power modules in new energy vehicles

Si3N4 ceramic with good thermal conductivity, high mechanical strength and low thermal expansion coefficient is an advanced thermal management material which has been applied to new energy vehicles. At present, with the rapid development of the electric driving technology for new energy vehicles, Si3N4 ceramic has been gradually used in SiC power modules so as to efficiently achieve the functions of heat dissipation, insulation and voltage resistance. Due to its important role in the power conversion process, the reliability of Si3N4 ceramic was vital, and any factor that might lead to its premature failure must be attached importance to. In this paper, a case about abnormal cracking of Si3N4 ceramic substrates during the high and low temperature cycling tests was reported. To solve this problem, various characterization methods were conducted to analyze the density, thermal conductivity, flexural strength, phase structure, morphology characteristics. Finally, through comprehensive analysis, the root cause that resulted in abnormal cracking of Si3N4 ceramic substrates was determined and meanwhile corresponding countermeasures were also proposed. Hopefully, the achievements of this paper will have positive significance for upgrading the quality of Si3N4 ceramic substrates and improving the service reliability of power modules.

Thermal runaway of Li-ion battery with different aging histories

Safety issues associated with thermal runaway (TR) in batteries have attracted extensive research attention. However, understanding and predicting TR encounter significant challenges due to the complexities of chemical reactions, venting events, thermal stratification, multiphase interactions, and variable boundary conditions. These challenges are further complicated by intrinsic battery degradation, a phenomenon often insufficiently characterized and governed by multiple mechanisms. These primarily include the depletion of electrolyte and active materials, thickening of the solid-electrolyte-interphase (SEI), and formation of lithium plating and dendrites. Such degradation alters the battery's materials and structure, directly causing electrochemical performance penalties and potentially affecting its TR behavior. This study examines the TR behavior of commercial 18,650 cells with lithium nickel manganese cobalt oxide (NMC) cathodes, focusing on degradation associated typical usage scenarios: long-term cycling, low-temperature cycling, dynamic cycling with calendar aging. We employ Electrochemical Impedance Spectroscopy (EIS) to probe internal changes in the electrochemical properties of aged cells compared to fresh counterparts. The EIS results reveal pronounced SEI impedance and substantially increased charge transfer impedance in long-term cycled cells. TR tests were conducted using an Accelerating Rate Calorimeter (EV+ ARC, Thermal Hazard Technology) following the heat-wait-seek (HWS) strategy. Our findings indicate a significant impact of aging mechanisms on second-life battery safety. Specifically, cells subjected to low-temperature cycling demonstrated a considerably lower onset temperature for exothermic reactions, and shorter TR delay time, despite all aged cells showing similar state of health (SOH). Furthermore, the temperature corresponding to the cell voltage drop is consistently much lower for aged cells with dynamic cycling and calendar aging.

Microstructure and Property Evolution of Diamond/GaInSn Composites under Thermal Load and High Humidity.

As a thermal interface material, diamond/GaInSn composites have wide-ranging application prospects in the thermal management of chips. However, studies on systematic reliability that can guide the practical application of diamond/GaInSn in the high-temperature, high-temperature impact, or high-humidity service environments that are faced by chips remain lacking. In this study, the performance evolution of diamond/GaInSn was studied under high-temperature storage (150 °C), high- and low-temperature cycling (-50 °C to 125 °C), and high temperature and high humidity (85 °C and 85% humidity). The experimental results reveal the failure mechanism of semi-solid composites during high temperature oxidation. It is revealed that core oxidation is the key to the degradation of liquid metal composites' properties under high-temperature storage and high- and low-temperature cycling conditions. Under the conditions of high temperature and high humidity, the failure of Ga-based liquid metal and its composite materials is significant. Therefore, the material should avoid high-temperature and high-humidity environments.

Parametric analysis and performance prediction of an ultra-low temperature cascade refrigeration freezer based on an artificial neural network

A thermodynamic analysis is proposed to improve the designing and operating parameters in an ultra-low temperature cascade refrigeration system (CRS). The expressions for predicted parameters of the CRS are obtained based on an artificial neural network (ANN) method. In the first part, a parametric analysis is carried out to analyze the influences of seven variables on the COP, total compressor input power, discharge temperature of two compressors, total exergy destruction, and exergy efficiency. The results show that the condensation temperature of the low-temperature circuit has an optimal value, which maximizes COP and exergy efficiency but minimizes the total compressor input power and exergy destruction. In the second part, the performance of CRS is predicted by the ANN model. Eighty sets of input-output parameters are applied as both the training and testing data. It is found that the correlation coefficients for training-testing data in the range of 0.9886–0.9994 are estimated. The mean absolute errors obtained in the prediction for COP, total compressor power, total exergy destruction, exergy efficiency, and discharge temperature of high and low-temperature cycles with the testing set are 0.0027, 0.9090, 1.0314, 0.1691, 1.1438, and 1.0230, respectively. The outcome indicates that the ANN model has good advantages in predicting the cascade refrigeration system's performance.