Hot Box Test Research Articles

In Situ Polymerization Facilitating Practical High-Safety Quasi-Solid-State Batteries.

Quasi-solid-state batteries (QSSBs) are gaining widespread attention as a promising solution to improve battery safety performance. However, the safety improvement and the underlying mechanisms of QSSBs remain elusive. Herein, a novel strategy combining high-safety ethylene carbonate-free liquid electrolyte and in situ polymerization technique is proposed to prepare practical QSSBs. The Ah-level QSSBs with LiNi0.83Co0.11Mn0.06O2 cathode and graphite-silicon anode demonstrate significantly improved safety features without sacrificing electrochemical performance. As evidenced by accelerating rate calorimetry tests, the QSSBs exhibit increased self-heating temperature and onset temperature (T2), and decreased temperature rise rate during thermal runaway (TR). The T2 has a maximum increase of 48.4°C compared to the conventional liquid batteries. Moreover, the QSSBs do not undergo TR until 180°C (even 200°C) during the hot-box tests, presenting significant improvement compared to the liquid batteries that run into TR at 130°C. Systematic investigations show that the in situ formed polymer skeleton effectively mitigates the exothermic reactions between lithium salts and lithiated anode, retards the oxygen release from cathode, and inhibits crosstalk reactions between cathode and anode at elevated temperatures. The findings offer an innovative solution for practical high-safety QSSBs and open up a new sight for building safer high-energy-density batteries.

Battery Venting Caused By Fast Charging

Lithium-ion batteries (LIBs) experience high risks of failure during unreasonable fast charging. Various degradation mechanisms inside the LIBs such as lithium (Li) plating, solid electrolyte interphase growth and electrolyte dry-out can undermine the electrochemical performance and induce massive gas generation alongside the operation. As a typical failure behaviour, venting occurs when the internal pressure of battery cell exceeds the safety threshold, releasing the gaseous products as well as depressurizing the cell. Recent studies1–3 of thermal runaway (TR) tests after fast charging have found that accumulated plated Li can react with electrolyte at elevated external temperatures, decreasing both self-heating and onset temperatures of TR. Yet, how fast-charging degradation will affect battery venting behaviours remains unclear.To answer this question, in this study, a series of fast charging experiments under controlled cooling as well as adiabatic TR tests were conducted with 51 Ah LiNi0.6Mn0.2Co0.2O2/graphite prismatic LIBs. The results showed that the prismatic battery underwent severe Li plating with over 30% capacity fade after 10 cycles of 4C charging. In the adiabatic TR tests, the aged batteries after 4C charging exhibited lower self-heating temperature and venting temperature as compared to the fresh batteries, by 51 ℃ and 34.4 ℃ respectively. This can be explained by the additional gas generation from the reaction between plated Li and electrolyte in the fast-charged batteries. Gas analyses of 120 ℃ hot-box tests for the degraded anodes with the electrolyte showed that the vented gas at the early venting stage primarily consisted of carbon dioxide, carbon monoxide and ethylene. The same charging protocols were then conducted in a natural convection thermal chamber with poor heat dissipation, where the temperature rise was much higher than those under forced convection as expected. Excessive cycling operations with off-limit charge rates (5C and 5.6C) were observed to directly cause battery swelling and venting without TR, and the temperature decreasing rates during rest after each charging process tend to slow down and even remain stable during a certain period of time. This indicates that the exothermic reaction between plated Li and electrolyte can be directly triggered by fast charging if heat removal is not effective enough. The findings provide useful insights into battery venting induced by fast charging, which can shed light on battery safety evaluation for fast charging techniques.Acknowledgements:This work is supported by the Faraday Institution BESAFE project (FIRG038), the Imperial College President’s PhD Scholarship Scheme (funded by EPSRC), the National Natural Science Foundation of China (Grant No. 52207241), China National Postdoctoral Program for Innovative Talents (grant no. BX20220171), China Postdoctoral Science Foundation (grant no. 2022M711760), and Shuimu Tsinghua Scholar Program (grant no. 2021SM130).

Experimental Thermal Conductivity Measurement of Hollow-Structured Polypropylene Material by DTC-25 and Hot Box Test

In this study, experimental measurements of porous polypropylene (PP) using the DTC-25 TA laboratory equipment and a hot box test are compared. The thermal conductivity of building materials indicates their insulation capability. Excellent building materials will have a lower thermal conductivity value as well as other building insulator performance metrics. While results show that increasing the volume fraction of fluid in porous PP has an inverse association with the thermal conductivity of the material, as predicted by porous media theories, there is a marked difference in the measured values of thermal conductivity using the two methods. The thermal conductivity values of porous PP from the DTC-25 and the hot box test were 0.21 and 0.0033 W/mK, respectively. The difference in the thermal conductivity values was due to the misapplication of the Fourier’s guarded heat flow model in the DTC-25 device to a convective fluid porous medium.

Direct venting during fast charging of lithium-ion batteries

Lithium-ion batteries pose high risks of failure when subjected to fast charging due to accumulated degradation from side reactions. Venting is a common failure behaviour that results in the release of gases and depressurization. However, the connection between fast-charging degradation and venting characteristics remains unclear. In this study, fast-charging experiments are conducted on LiNi0.6Mn0.2Co0.2O2 (NMC622)/graphite prismatic cells (51 Ah) with controlled cooling, followed by adiabatic thermal runaway tests. The degraded cell, after 4C charging, shows venting at a temperature 34.4 °C lower than a fresh cell. Gas analysis of the degraded anode-electrolyte partially reactive system in hot-box tests reveals that the reaction between plated lithium and electrolyte was a primary contributor to the additional gases. The fast-charging protocols are conducted under natural convection with less heat dissipation, causing battery swelling and venting without thermal runaway when subjected to excessive cycling at off-limit charge rates (5C and 5.6C). The temperature decreasing rates during rest after each charging process slow down or stabilize for a certain period, highlighting the role of exothermic side reactions. This experimentally demonstrates that venting failures can be directly triggered by the exothermic, gas generating reaction during fast charging. These findings inform future designs for safe and rapid battery charging.

Printing thermal performance: an experimental exploration of 3DP polymers for facade applications

The decarbonisation of the building sector requires the development of building components that provide energy efficiency while producing minimal environmental impact. We investigate the potential of polymer 3D printing (3DP) for the fabrication of mono-material translucent facade components, whose properties can be tailored according to climatic conditions and functional requirements. These components bear the potential to reduce energy consumption in buildings and, at the same time, can be fabricated with minimal environmental impact thanks to the recyclability of the feedstock material. In this study, we explore the effect of component geometry on the thermal insulation properties of 3DP objects with bespoke internal structures. Different prototypes are fabricated using a robotic polymer extruder, and their thermal properties are measured following a hot-box test method. The experimental results are then used to calibrate a heat transfer simulation model describing the joint effects of conduction, natural convection and infrared radiation through the components. We show that it is possible to fabricate insulating polymer components providing thermal transmittance ranging from 1.7 to 1 W/m2 K only by changing the internal cavity distribution and size. This proves the possibility of designing 3DP thermally-insulating components for different climatic conditions and requirements. This study provides the first insights into the thermal behaviour of polymer 3DP facades on a large scale. The results suggest that this innovative manufacturing technique is promising for application in facades and encourages further research toward performant and low-embodied energy 3DP building components.

Influence of 3D Microstructure Pattern and Infill Density on the Mechanical and Thermal Properties of PET-G Filaments.

This study aims to evaluate the thermal and mechanical performances of PET-G thermoplastics with different 3D microstructure patterns and infill densities. The production costs were also estimated to identify the most cost-effective solution. A total of 12 infill patterns were analysed, including Gyroid, Grid, Hilbert curve, Line, Rectilinear, Stars, Triangles, 3D Honeycomb, Honeycomb, Concentric, Cubic, and Octagram spiral with a fixed infill density of 25%. Different infill densities ranging from 5% to 20% were also tested to determine the best geometries. Thermal tests were conducted in a hotbox test chamber and mechanical properties were evaluated using a series of three-point bending tests. The study used printing parameters to meet the construction sector's specific needs, including a larger nozzle diameter and printing speed. The internal microstructures led to variations of up to 70% in thermal performance and up to 300% in mechanical performance. For each geometry, the mechanical and thermal performance was highly correlated with the infill pattern, where higher infill improved thermal and mechanical performances. The economic performance showed that, in most cases, except for the Honeycomb and 3D Honeycomb, there were no significant cost differences between infill geometries. These findings can provide valuable insights for selecting the optimal 3D printing parameters in the construction industry.

Assessment of the thermal properties for the geothermal use of a permeable pavement structure for pedestrian and cycle paths

Sustainable Drainage Systems (SuDS) have positioned themselves as one of the most widely applied Green Infrastructure (GI) techniques for sustainable stormwater management. In recent decades, new lines of research have emerged leading to the geothermal use of SuDS. The aim is to optimise available space in cities and minimise dependence on non-renewable energy sources. Previous research has focused on determining the feasibility of combining the two technologies, both in laboratory and field studies. Other aspects such as the influence of the surface geothermal system on the quality of the water present in the SuDS were also studied. This previous research has focused mainly on permeable pavements, positioning them as one of the SuDS techniques of reference in this line of research. This article attempts to give continuity to what has been established by other authors. It studies in depth the thermal properties of a complete section of permeable pavement under different hydraulic operating conditions. To this end, a complete section of a permeable pavement has been simulated in the laboratory using Hot-Box tests as set out in different international standards. With these tests, the values of thermal transmittance and equivalent thermal conductivity were determined. The aim of this research is to establish a test procedure for the thermal properties of permeable floorings, based on standardised equipment. The aim is to better understand the heat transfer procedures inside SuDS. In this way, it will be possible to optimise the design of these in combination with surface geothermal elements.

Democratized innovation & accessible thermal testing: The approachable hot box

To meet the goals established by the 2015 Paris Accord, scientists say that we will need to achieve zero emissions between 2030 and 2050, which will require a drastic departure from current practices in the building industry, as buildings are a primary contributor of carbon emissions and a major consumer of natural resources. However, building technology research is often driven by disciplinary ‘experts’ and end-users have little opportunity for involvement in the design process. As buildings become more technologically complex, users must rely on industry professionals with specialized knowledge to design, manufacture and manage these increasingly complex environments Instead, this paper provides an alternative attitude to approachable research methods that open up building technology innovation opportunities to untraditional innovators. When the user has control of the design/innovation process, it opens up a new realm of possibilities rich with lived experience.Understanding the movement of heat, or thermal transmittance, through materials and assemblies is critical in controlling energy consumption in buildings. Despite recent advances in computational technologies, physical testing is still the industry standard to determine a material’s thermal properties. However, this process can require expensive equipment, a controlled environment for testing and deep technical knowledge to create a degree of accuracy that is not necessary for all phases of the innovation process and can even act as a barrier to the early stages of design. In this paper we propose the Approachable Hot Box (AHB), a low-cost, low-tech and accessible testing apparatus that can quickly and easily evaluate the impact of simple building materials and assemblies on ambient environmental conditions. By reducing unnecessary complexity for early-level design decisions, the AHB is consistent and reliable at an affordable price. Not only does the AHB rapidly and affordably test small material samples, it helps to articulate potentially complex concepts in a tangible and understandable way, which helps to lower the barrier to innovation. By creating a non-disciplinary, iterative design approach that uses conventional materials and accessible concepts, this work demonstrates that rapid experimentation can be used as a tool to study building assemblies or systems by non-traditional innovators.

Thermal performance of cross-laminated timber (CLT) and cross-laminated bamboo and timber (CLBT) panels

ABSTRACT Cross-laminated timber (CLT) is increasingly being utilized in Europe, North America and elsewhere due to its superior mechanical properties and environmental-friendly performance. Considering regions and countries, such as China, those are scarce in structural wood resource but rich in bamboo forest, an idea of introducing bamboo into CLT system has been proposed to form a novel composite material, named as cross-laminated bamboo and timber (CLBT). This paper focuses on the comparison of thermal insulation performance of CLBT and CLT panels. The thermal resistance and transmittance of CLT and CLBT wall specimens were measured by the Guarded Hot Box test. A calculation method provided by ISO standard and a finite element (FE) model were also used to evaluate the thermal resistance of CLT and CLBT panels. Based on the proposed FE model, some parametric analysis was performed through 11 CLBT panels with different compositions, including the layer number of glubam and timber, the thickness of extruded polystyrene and the use of gypsum board and screws. Moreover, the feasibilities of these CLBT panels were evaluated for the application in different climate regions of China and the United States in accordance with the corresponding Chinese and American building energy efficiency standards, respectively. It can be finally concluded that, the development and application of CLBT contributes to achieving the low carbon sustainable features of structures, which is due to the good carbon sequestration ability of its component materials (i.e., timber and bamboo) as well as the good insulation performance of CLBT panels.

Comparison of the Experimental Measurement Methods for Building Envelope Thermal Transmittance

Building energy consumption and ways to reduce it have drawn increasing attention in recent decades. Thermal transmittance is not only a code-enforced parameter during the design and retrofit phase of building assemblies, but also strongly related to the accuracy of whole-building energy modeling. There are several existing methods to measure the building envelope thermal transmittance, and with the development of new techniques, more practical and precise measurement methods have been explored. The study discussed here focused on comparing methods to measure the building envelope thermal transmittance, both in laboratory and for in-situ measurement. Typical research studies related to the Hot Box Test Method, the Heat Flow Meter Method and the Infrared Thermography Method are described and compared. This paper provides a state-of-the-art review of the up-to-date measurement methods for building envelope thermal transmittance and provides alternatives for engineers, architects and researchers to practically measure the building envelope thermal transmittance.

Thermal resistance of the ventilated air-spaces behind external claddings; theoretical definition and a parametric study

The presence of a ventilated air cavity between the external cladding and the wall core of a wall assembly can have a varying contribution to the thermal performance of the building envelope. In particular, the thermal resistance of a ventilated air-space is a dynamic parameter that is influenced by various thermo-physical parameters. In this study, a theoretical definition of the thermal resistance of a ventilated air-space behind an external cladding is introduced, employing a non-linear network of thermal resistances in the air-space. A numerical code is developed for the steady-state condition and verified with data from hot box tests available in the literature. Thereafter, a parametric analysis is performed based on the air change rate in the cavity (0 to 1000 1/h), type of the external cladding (brick and vinyl siding), seasonal variation (summer and winter conditions), and presence of the reflective insulation. The results are compared with a closed cavity to see the efficiency of the ventilation in the air-space. The results confirm that the theoretical thermal resistance of the ventilated air-space is a function of multiple factors, and its magnitude varies under different conditions.

Thermal Resistance of Insulated Precast Concrete Sandwich Panels

Many nations are already working toward full implementation of energy efficiency in buildings known as Green Building. In line with this perspective, this paper aims to develop a thermally efficient precast concrete sandwich panels (PCSP) for structural applications. Therefore, an experimental investigation was carried out to determine the thermal resistance of the proposed PCSP using Hotbox method and the results were validated using finite element method (FEM) in COMSOL Multiphysics Software. The PCSP were designed with staggered shear connectors to avoid thermal bridges between the successive layers. The staggered connectors are spaced at 200 mm, 300 mm and 400 mm on each concrete layer, while the control panel is designed with 200 mm direct shear connection. In the experimental test, four (4) panels of 500 mm × 500 mm and 150 mm thick were subjected to Hotbox Test to determine the thermal resistance. The result shows that thermal resistance of the PCSP with staggered shear connection increases with increase in spacing. The PCSP with 400 mm staggered shear connectors indicates the best thermal efficiency with a thermal resistance (R value) of 2.48 m2K/W. The thermal performance was verified by FEA which shows less than 5% error coupled with a precise prediction of surface temperature gradient. This indicates that, with conventional materials, thermal path approach can be used to develop a precast concrete building with better thermal resistant properties. Hopefully, stakeholders in the green building industry would find this proposed PCSP as an alternative energy efficient load bearing panel towards sustainable and greener buildings.

Battery eruption triggered by plated lithium on an anode during thermal runaway after fast charging

Lithium-ion batteries (LIBs) are suffering from severe thermal runaway risks in the use of their whole lifespans. The heat release characteristics of thermal runaway after fast charging have been proven to be highly related to lithium plating, yet whose impacts on the eruption behaviors are rarely investigated. In this study, the changes in the battery eruption temperature during thermal runaway after fast charging are thoroughly analyzed, and the effects of lithium plating on gas production are revealed. Accelerating Rate Calorimetry tests of pouch cells and prismatic cells are performed to investigate the eruption temperature of LIBs charged at different rates, confirming the advanced eruption of thermal runaway on batteries with plated lithium. To reveal the root cause of early eruptions, reactions between plated lithium and electrolytes are characterized by Synchronous Thermogravimetry Analysis and Mass Spectrometry, observing the fierce gas production process. Afterwards, and the gas and solid products of the reaction are further obtained using partially reactive systems in hot-box tests, and their compositions are analyzed. Overall, this study contributes to a more profound understanding of the characteristics of thermal runaway after fast charging, providing valuable insights on the rational design and management for LIB safety.

Evaluating dynamic thermal performance of building envelope components using small-scale calibrated hot box tests

The hot box test method has been applied to evaluate both the steady-state (U-value) and dynamic thermal properties of building envelopes. However, the high construction cost of full-scale hot box apparatus and the testing time required (usually several days) may prevent its wider adoption. To overcome the limitations of full-scale hot box tests, this paper proposes a novel method to evaluate the dynamic thermal performance of building envelope components using a small-scale calibrated hot box and scaled-down specimen. In this paper, the scaling relationships of thermal properties evaluated using a full-size specimen and a scaled-down specimen are established based on the Laplace transform of the heat transfer equations. In addition, dynamic thermal properties obtained from scaled-down experimental tests are compared to the values calculated by the EN ISO13768 (ISO) method. A small-scale hot box with a 355 mm × 355 mm metering area was constructed and calibrated to validate the correlations. Three scaled-down concrete sandwich wall panels were then tested and the scaling relationship was cross-validated using the experimental results, finite difference (FD) simulations, and the ISO method. The results indicate that the dynamic thermal properties obtained from a scaled-down hot box test can be correlated to its full-size counterpart when certain conditions are met. The scaled-down hot box test is demonstrated to be an effective yet economical alternative to a full-scale test with significantly reduced experimentation cost and turn-around time.

Determining the thermal resistance of a highly insulated wall containing vacuum insulation panels through experimental, calculation and numerical simulation methods

The purpose of this paper is to investigate the potential for calculation methods to determine the thermal resistance of a wall system containing vacuum insulation panels (VIPs) that has been experimentally characterised using a guarded hot box (GHB) apparatus. The VIPs used in the wall assembly have not been characterised separately to the wall assembly, and therefore exact knowledge of the thermal performance of the VIP including edge effect is not known. The calculations and simulations are completed using methods found in literature as well as manufacturer published values for the VIPs to determine the potential for calculation and simulation methods to predict the thermal resistance of the wall assembly without the exact characterisation of the VIP edge effect. The results demonstrate that disregarding the effect of VIP thermal bridges results in overestimating the thermal resistance of the wall assembly in all calculation and simulation methods, ranging from overestimates of 21% to 58%. Accounting for the VIP thermal bridges using the manufacturer advertised effective thermal conductivity of the VIPs resulted in three methods predicting the thermal resistance of the wall assembly within the uncertainty of the GHB results: the isothermal planes method, modified zone method and the 3D simulation. Of these methods only the 3D simulation can be considered a potential valid method for energy code compliance, as the isothermal planes method requires too drastic an assumption to be valid and the modified zone method requires extrapolating the zone factor beyond values which have been validated. The results of this work demonstrate that 3D simulations do show potential for use in lieu of guarded hot box testing for predicting the thermal resistance of wall assemblies containing both VIPs and steel studs. However, knowledge of the VIP effective thermal conductivity is imperative to achieve reasonable results.

Progress in Thermal Management and Safety of Cells and Packs By Testing in Battery Calorimeters

With increasing energy density the safety and the thermal management of Li-ion batteries is becoming more and more important, because the thermal runaway can cause an ignition or even explosion of the battery with simultaneous release of toxic gases. In the last nine years we have established battery calorimetry as a powerful and versatile electrochemical-thermal characterization technique, which allows both advancements for the thermal management and the safety of batteries. With six adiabatic Accelerating Rate Calorimeters (ARC) of different sizes and two sensitive Tian-Calvet calorimeters, all of them combined with cyclers, the IAM-AWP now operates Europe’s largest battery calorimeter center, which enables the evaluation of thermodynamic, thermal and safety data on material, cell and pack level under quasiadiabatic and isoperibolic environments for both normal and abuse conditions (thermal, electrical, mechanical). It will be shown how sophisticated battery calorimetry allows finding new and quantitative correlations between different critical thermally and safety related parameters that will help to design safer systems. For an optimized design with regard to safety cells and packs have to be characterized not only for their temperature behavior but also for the heat dissipation and the pressure development in a quantitative manner.Calorimetry allows the collection of quantitative data required for optimum battery performance and safety. This information can then be used to define the requirements for cooling and thermal management and adapt them accordingly. The battery calorimeters can be used for studies on heat generation and dissipation of Li-ion cells and are coupled to a battery cycler in order to perform the measurements during charging and discharging of the cells under defined thermal conditions. Isoperibolic (constant temperature of the calorimeter) or quasiadiabatic (no heat exchange with the calorimeter) ambient conditions are adjusted by heaters and thermocouples that are located in lid, bottom and side walls of the calorimeter chamber, in which the cell is inserted. For improving the thermal management system, the measured temperature data are converted into generated and dissipated heat data [1] by determination of specific heat capacity and heat transfer coefficient using heat flux sensors.Concerning safety aspects it will be presented how battery calorimeters provide thermal stability data on materials level, e.g. of anodes, cathodes or electrolytes or there combinations and to perform safety tests on cell and pack level by applying thermal [2], mechanical or electrical [3] abuse conditions. The studies on materials level are especially important for Post-Li cells, which make use of more abundant materials, such as sodium or magnesium instead of Li, nickel and cobalt, because these data help to develop safe cells from the beginning all along the value chain. For the advanced Li-ion technology, a holistic safety assessment is in the focus, because the thermal runaway can have multiple interacting causes and effects. A test in the calorimeter is much more sensitive than a hotbox test and reveals the entire process of the thermal runaway with the different stages of exothermic reactions. Self-heating, thermal stability and thermal runaway are characterized and the critical parameters and their thresholds for safe cell operation are determined. As a result of the different tests quantitative and system relevant data for temperature, heat and pressure development of materials and cells are provided. In addition it will be explained how calorimeters allow studying the thermal runaway propagation in order to develop and qualify suitable countermeasures, such as heat protection barriers, which is currently becoming a very hot topic, because a global technical regulation (GTR) on electric vehicle safety is being developed, which includes thermal propagation. There is still the open question, which is the best initialization method to become a standard. We hope that the research in the Calorimeter Center will help to make progress in this field as well. Reference s : [1] C. Ziebert et al., in: L.M. Rodriguez, N. Omar, eds., EMERGING NANOTECHNOLOGIES IN RECHARGABLE ENERGY STORAGE SYSTEMS, Elsevier Inc., ISBN 978032342977, 195-229. 2017.[2] B. Lei, W. Zhao, C. Ziebert, et al., Experimental analysis of thermal runaway in 18650 cylindrical cells using an accelerating rate calorimeter, Batteries 3 (2017) 14, doi:10.3390/batteries3020014.[3] A. Hofmann, N. Uhlmann, C. Ziebert, O. Wiegand, A. Schmidt, Th. Hanemann, Preventing Li-ion cell explosion during thermal runaway with reduced pressure, Appl. Thermal Eng. 124 (2017) 539-544. Figure Caption: Different sizes of accelerating rate calorimeters at the IAM-AWP Calorimeter Center (upper part) and X-Ray tomography image of 18650 cell showing position of pressure line and pressure vs. temperature curves for external and internal pressure measurement during thermal abuse test in an ARC (lower part). Figure 1

Co-creation of local eco-rehabilitation strategies for energy improvement of historic urban areas

Energy performance and thermal comfort in historic and traditional urban environments are important because of the social and cultural requirement to conserve these areas as living entities, but also for the environmental obligation to decrease the impact of existing buildings globally. The objective of ENERPAT approach is to address this global challenge from the local perspective, through the co-creation of efficient solutions that improve the energy performance of historic areas considering local techniques and skills, taking into account the whole life cycle of the solutions, and supporting local economy and business. The objective is to test the efficiency and suitability of eco-renovation strategies that have been co-created with local stakeholders and are based on traditional energy conservation measures, as a way to work with locally-based business models that can safeguard cultural aspects and enable economic development. Two living labs have been established in the cities of Vitoria-Gasteiz (Spain) and Cahors (France) in two representative buildings of the historic urban area of each city. The living labs operate as inclusive multi-agent discussion arenas with a long-term vision, where multi-criteria co-creation processes are implemented to select conservation-friendly solutions based on local materials including criteria such as operational energy, impact on heritage values, quality of life, socio-economic development and easy logistics. The energy behaviour of the buildings and the hygrothermal performance of the external walls have been studied using on-site and laboratory experiments, through an efficient partnership between local authorities and universities. Likewise, local-based refurbishment solutions that were designed in the co-creation processes have been thermally characterised in the laboratory, through thermal conductivity and guarded hot box tests. Finally, the energy improvement of the whole renovation strategy has been simulated showing the enhancement of the two buildings.

A pore-controllable polyamine (PAI) layer-coated polyolefin (PE) separator for pouch lithium-ion batteries with enhanced safety

A series of pore-controllable polyamine (PAI) layer-coated polyolefin (PE) separators (PAI-PE-1, PAI-PE-2, and PAI-PE-3) are prepared by using a phase-transfer and gravure-printing method and used to improve the safety of pouch lithium-ion batteries (LIBs) based on a PAI “guest-host transition” and PE “pore on-off” cooperative strategy. And the safety mechanism for the LIBs using PAI-PE-1, PAI-PE-2, and PAI-PE-3 separators with pore sizes of approximately 0.02, 0.17, and 0.85 μm is discussed. In the overcharge, nail, and hot box tests, the LIBs with PAI-PE separators all meet safety requirements, while the LIBs with PE separators exhibit either fire or smoke issues. The LIBs with PAI-PE-1 separators have the lowest temperature of 102 °C and the highest residual voltage of 3.97 V in the nail and hot box tests, respectively, and the LIBs with PAI-PE-3 separators have the lowest temperature of 129 °C in the overcharge test. The mechanism for the enhanced safety of LIBs with PAI-PE separators is ascribed to a PAI “guest-host transition” and PE “pore on-off” cooperative process. These results indicate that this pore-controllable PAI-PE separator has promising prospects in the application of LIBs with enhanced safety requirements.

EVALUATION OF SELECTED DYNAMIC MODELS IN COMPARISON WITH HOT BOX TEST RESULTS FOR MEASUREMENT OF BUILDING ENVELOPE THERMAL PROPERTIES

ABSTRACT This research is mainly focused on the experimental measurement of R-value by several different models. Building energy consumption accounts for about 40% of the total energy use in the U.S, and therefore accurate energy simulation is desired. The R-value is one of the key parameters that can influence the energy simulation results and therefore is of great importance. The Average Model has long been the most widely accepted method to measure the thermal properties of building components. However, its steady-state assumption and dependence on temperature difference limit its use especially for in-situ measurement. In this study, several dynamic models, including the Pentaur Model and R-C Network Models, are studied with test data obtained from a series of hot box tests performed in the Building Enclosure Testing Laboratory. The results show that the 3R2C model has the best performance and a desirable stability of accuracy with respect to different levels of temperature difference, and therefore is recommended for practical measurement. The results also indicate that unlike the Average Model, the accuracy of dynamic models does not necessarily depend on the level of temperature difference.

A Four-Layers Hamburger-Structure PVDF-HFP/Al2O3/PE/PVDF-HFP Composite Separator for Pouch Lithium-Ion Batteries with Enhanced Safety and Reliability

A unique composite separator with four-layers hamburger-structure is prepared and demonstrated to be promising application in lithium-ion batteries (LIBs) with enhanced safety and reliability. Using polyolefin (PE) as substrate, Al2O3 as heat resistance layer, and 2 layers of polyvinylidene difluoride hexafluoropropylene (PVDF-HFP) on the upper and lower, this PVDF-HFP/Al2O3/PE/PVDF-HFP (PH/Al/PE/PH) separator is constructed through a gravure printing and phase transfer process. Compared with PE substrate coating with the mixture of Al2O3 and PVDF-HFP (PH-Al/PE) separator, the as-prepared separator can further enhance the safety performance of LIBs. In external short and nail tests, the maximum temperatures of LIBs with PH/Al/PE/PH separators (100 °C and 103 °C) are lower than LIBs with PH-Al/PE separators (132 °C and 115 °C). And after hot-box test, the voltage of former (4.13 V) is more stable than later (3.78 V). Meanwhile, compared with PE substrate coated by Al2O3 (Al/PE), the cycle performance of LIBs with PH/Al/PE/PH separator is significantly improved, and the deformation of LIBs is effectively controlled. Furthermore, the mechanism for the enhancement of safety and reliability of LIBs is elucidated. The results indicate that this separator exhibits promising prospects in the application of LIBs with enhanced safety and reliability.