Showing papers in "Journal of energy storage in 2018"

Lead batteries for utility energy storage: A review

Abstract: Energy storage using batteries is accepted as one of the most important and efficient ways of stabilising electricity networks and there are a variety of different battery chemistries that may be used. Lead batteries are very well established both for automotive and industrial applications and have been successfully applied for utility energy storage but there are a range of competing technologies including Li-ion, sodium-sulfur and flow batteries that are used for energy storage. The technology for lead batteries and how they can be better adapted for energy storage applications is described. Lead batteries are capable of long cycle and calendar lives and have been developed in recent years to have much longer cycle lives compared to 20 years ago in conditions where the battery is not routinely returned to a fully charged condition. Li-ion batteries have advantages in terms of energy density and specific energy but this is less important for static installations. The other technical features of Li-ion and other types of battery are discussed in relation to lead batteries. A selection of larger lead battery energy storage installations are analysed and lessons learned identified. Lead is the most efficiently recycled commodity metal and lead batteries are the only battery energy storage system that is almost completely recycled, with over 99% of lead batteries being collected and recycled in Europe and USA. The sustainability of lead batteries is compared with other chemistries.

Supercapacitors: Properties and applications

Abstract: Energy accumulation and storage is one of the most important topics in our times. This paper presents the topic of supercapacitors (SC) as energy storage devices. Supercapacitors represent the alternative to common electrochemical batteries, mainly to widely spread lithium-ion batteries. By physical mechanism and operation principle, supercapacitors are closer to batteries than to capacitors. Their properties are somewhere between batteries and capacitors. They are able to quickly accommodate large amounts of energy (smaller than in the case of batteries – lower energy density from weight and volume point of view) and their charging response is slower than in the case of ceramic capacitors. The most common type of supercapacitors is electrical double layer capacitor (EDLC). Other types of supercapacitors are lithium-ion hybrid supercapacitors and pseudo-supercapacitors. The EDLC type is using a dielectric layer on the electrode − electrolyte interphase to storage of the energy. It uses an electrostatic mechanism of energy storage. The other two types of supercapacitors operate with electrochemical redox reactions and the energy is stored in chemical bonds of chemical materials. This paper provides a brief introduction to the supercapacitor field of knowledge.

An overview of progress in electrolytes for secondary zinc-air batteries and other storage systems based on zinc

Abstract: The revived interest and research on the development of novel energy storage systems with exceptional inherent safety, environmentally benign and low cost for integration in large scale electricity grid and electric vehicles is now driven by the global energy policies. Within various technical challenges yet to be resolved and despite extensive studies, the low cycle life of the zinc anode is still hindering the implementation of rechargeable zinc batteries at industrial scale. This review presents an extensive overview of electrolytes for rechargeable zinc batteries in relation to the anode issues which are closely affected by the electrolyte nature. Widely studied aqueous electrolytes, from alkaline to acidic pH, as well as non-aqueous systems including polymeric and room temperature ionic liquids are reported. References from early rechargeable Zn-air research to recent results on novel Zn hybrid systems have been analyzed. The ambition is to identify the challenges of the electrolyte system and to compile the proposed improvements and solutions. Ultimately, all the technologies based on zinc, including the more recently proposed novel zinc hybrid batteries combining the strong points of lithium-ion, redox-flow and metal-air systems, can benefit from this compilation in order to improve secondary zinc based batteries performance.

Materials for energy storage: Review of electrode materials and methods of increasing capacitance for supercapacitors

Abstract: Supercapacitors (SCs) have shown great promise as a possible solution to the increasing world demand for efficient energy storage Two types of mechanisms for SCs exist (double-layer and pseudocapacitive), and each type utilizes a wide variety of materials In this review, a detailed overview of the mechanisms employed by SCs is provided in the introduction, and many studies are compared in order to determine which materials produce electrodes with high capacitance and cyclability in SCs, and to summarize and gauge the state of such research The types of materials looked at include graphene and graphene nanocomposites, activated carbons from renewable materials, conducting polymers, and transition metal dichalcogenides Additionally, different methods of activation that are meant to increase specific capacitance are examined Among the dozens of materials found in the literature during this study, the ones that exhibited the highest specific capacitances are rGO/PANI (Reduced Graphene Oxide/Polyaniline), and PANI-NFS/GF (Polyaniline Nanofiber Sponge Filled Graphene Foam) demonstrated impressive performances These materials all exceeded the current expectations of SCs by remarkable amounts, and more research into similar materials is highly encouraged As more fundamental studies carried out for understanding the mechanisms of SCs, energy density and specific capacitance values continue to improve Production of SCs from renewable materials encourage optimism for environmentally friendly options soon becoming feasible for use on larger scales

Review of latent heat thermal energy storage for improved material stability and effective load management

Abstract: Thermal energy storage is important to counter balance demand and supply of energy and maintain balance in the system and boost the use of intermittent renewable energy source. Phase change material-based thermal energy storage has massive potential to substitute large-scale energy demand and assist both economic and environmental benefits. This paper reviews functional principle, thermophysical properties and other material characteristics of different phase change materials for thermal energy storage system. Long-term stability of phase change material and its interaction with storage container have been discussed. Various heat transfer and thermal conductivity enhancement technique to enhance latent thermal energy storage system have been discussed. The paper also examines the schematics of some of the proposed & tested systems and describes the results of prototype setup for thermal load management and application in water heating system and buildings. The paper also summarizes energy and exergy analysis of some thermal energy storage systems.

Detecting the internal short circuit in large-format lithium-ion battery using model-based fault-diagnosis algorithm

Abstract: The spontaneous internal short circuit that sporadically occurs during operation is an unsolved safety problem that hinders the widespread application of lithium ion batteries. An online fault-diagnosis algorithm is an urgent requirement for early detection of the spontaneous internal short circuit of lithium-ion batteries to guarantee safe operation. This paper presents a model-based fault-diagnosis algorithm for online internal-short-circuit detection. Relying on the theory of model-based control, the algorithm transforms the measured voltage and temperature to the intrinsic electrochemical status that can reflect typical internal-short-circuit features, i.e. the excessive depletion of capacity and abnormal heat generation. The estimated status of the suspicious cell deviates from the average value of the battery pack, therefore the algorithm can capture the internal-short-circuit fault by evaluating the levels of deviation. Simultaneously considering the diagnosis result calculated from both the voltage and temperature signal helps enhance the robustness of the algorithm with few false alarms. Substitute internal-short-circuit tests confirm that the algorithm is capable of identifying the internal-short-circuit fault before it develops into a severe hazard, e.g., thermal runaway. The equivalent short resistance, which can reflect the level of the internal short circuit, can be estimated with small error by the online fault-diagnosis algorithm.

Influence of operational and design parameters on the performance of a PCM based heat exchanger for thermal energy storage – A review

Abstract: Thermal energy storage using phase change materials (PCM) proved to be a promising technology because of its relative advantages over the other types of energy storage methods. Along with thermophysical properties of PCM, the performance of latent heat based thermal energy storage system depends on the design of the heat exchanger. Although extensive research is being carried out over the past few years, an integrated study on the design of PCM heat exchanger is scarce. This review presents the in-depth analysis of various operating conditions and design parameters that need to be considered in the design of a PCM based heat exchanger. Shell and tube type, triple concentric tube type heat exchangers are discussed along with the various heat transfer techniques employed in both the types of heat exchangers. In each enhancement technique, the influencing geometric parameters are summarized, and the recommended values of those parameters are provided. The present article is expected to be a helpful reference for the researchers working in the field of thermal energy storage.

Life Cycle Assessment of repurposed electric vehicle batteries: an adapted method based on modelling energy flows

Abstract: After their first use in electric vehicles (EVs), the residual capacity of traction batteries can make them valuable in other applications. Although reusing EV batteries remains an undeveloped market, second-use applications of EV batteries are in line with circular economy principles and the waste management hierarchy. Although substantial environmental benefits are expected from reusing traction batteries, further efforts are needed in data collection, modelling the life-cycle stages and calculating impact indicators to propose a harmonized and adapted life-cycle assessment (LCA) method. To properly assess the environmental benefits and drawbacks of using repurposed EV batteries in second-use applications, in this article an adapted LCA is proposed based on the comparison of different scenarios from a life-cycle perspective. The key issues for the selected life-cycle stages and the aspects and parameters to be assessed in the analysis are identified and discussed for each stage, including manufacturing, repurposing, reusing and recycling. The proposed method is applied to a specific case study concerning the use of repurposed batteries to increase photovoltaic (PV) self-consumption in a given dwelling. Primary data on the dwelling’s energy requirements and PV production were used to properly assess the energy flows in this specific repurposed scenario: both the literature search performed and the results obtained highlighted the relevance of modelling the system energy using real data, combining the characteristics of both the battery and its application. The LCA results confirmed that the environmental benefits of adopting repurposed batteries to increase PV self-consumption in a house occur under specific conditions and that the benefits are more or less considerable depending on the impact category assessed. Higher environmental benefits refer to impact categories dominated by the manufacturing and repurposing stages. Some of the most relevant parameters (e.g. residual capacity and allocation factor) were tested in a sensitivity analysis. The method can be used in other repurposing application cases if parameters for these cases can be determined by experimental tests, modelling or extracting data from the literature.

Revisiting the dual extended Kalman filter for battery state-of-charge and state-of-health estimation: A use-case life cycle analysis

Abstract: One of the most discussed topics in battery research is the state-of-charge (SOC) and state-of-health (SOH) determination of traction batteries. Unfortunately, neither is directly measurable and both must be derived from sensor signals using model-based algorithms. These signals can be noisy and erroneous, leading to an inaccurate estimate and, hence, to a limitation of usable battery capacity. A popular approach tackling these difficulties is the dual extended Kalman filter (DEKF). It consists of two extended Kalman filters (EKFs), that synchronously estimate both the battery states and parameters. An analysis of the reliability of the DEKF estimation against realistically fading battery parameters is still a widely discussed subject. This work investigates the DEKF performance from a high-level perspective, involving different load dynamics and SOH stages. A numerical optimization-based approach for the crucial filter parameterization is employed. We show that the DEKF partly improves the accuracy of the SOC estimation compared to the simple EKF over battery lifetime within the operational limits of an automotive application. However, capacity and internal resistance estimation becomes unreliable and partly diverges from the reference under constant and realistic load scenarios coupled with advanced degradation. As a consequence, a downstream use of both parameters in a SOC or SOH estimation is hampered over the battery lifetime. Extensions are needed to improve reliability and enable employment in real-world applications.

Multiple-segment metal foam application in the shell-and-tube PCM thermal energy storage system

Abstract: This study describes a new approach for heat-transfer enhancement in PCM-based shell-and-tube thermal energy storage systems by employing multiple-segment or cascaded metal foam. The principle is based on the fact that temperature gradient across the PCM during the phase change reduces significantly in the heat flow direction thus affecting the heat transfer rate and resulting in a poor overall storage performance. This study suggests using multiple-segment metal foam with porosity cascading in the heat flow direction so that a state closer to uniform temperature distribution can be achieved. A mathematical model that considers natural convection during charging and discharging of the system in addition to non-Darcy effects of the porous foam was developed and validated. The influence of using different cascading arrangements of the metal-foam on the evolution of the solid-liquid interfaces, distribution of isotherms and profile of the liquid fraction was investigated. The use of non-cascaded single-segment foam versus the use of cascaded multi-segment foam was also investigated and compared for the same system’s volume usage. Results from the study show that energy storage and recovery times can be substantially shortened by foam cascading in the PCM/metal foam composite.

A review on the heterostructure nanomaterials for supercapacitor application

Abstract: The typical physical and chemical properties lead the nanomaterials to breakthrough in the field of energy storage especially, supercapacitor applications. The optimization of electrical conductivity, structural flexibility, band gap and charge carrier mobility are the key point to solve the issues in the electrochemical charge storage mechanism of supercapacitor. The semiconducting heterostructured nanomaterials are the best choice to store energy by near-surface ion adsorption along with additional contribution from fast reversible faradic reactions. The creation of active sites and defects in the grain boundary of the heterostructure materials results in multiple redox activity, superior ionic conductivity and short diffusion path. Therefore, sufficient researches enrooted to the doped and nano heterostructure electrode materials needs to be performed in order to exploit the high power and energy storage applications. This article reviews current trends in the synthesis of heterostructure electrode through hybridization of different electrochemical double layer capacitance (EDLC) and pseudocapacitive materials. This article also emphasize on the effect of doping on the electrode possessing both EDLC as well as the pseudocapacitance. In addition, the advantages of superlattice structure for the superior electrochemical properties are also discussed.

Analysis and modeling of calendar aging of a commercial LiFePO4/graphite cell

Abstract: This paper presents a comprehensive calendar aging study on a lithium-ion battery with a test duration of 29 months. This aging study was realized with a widely used commercial LiFePO4/graphite cell from Sony/Murata, which promises both long calendar and cycle lifetime, which is especially required for stationary battery applications. The development of the cells’ capacity, as well as the resistances, are shown in a static calendar aging study for 17 test points, each with 3 cells, having constant storage conditions of temperature and state of charge. Based on the measurement data, a semi-empirical aging model is presented for the capacity loss and resistance increase, consisting of only 5 parameters which are valid for all storage conditions. An additional dynamic calendar aging study is performed with 9 months test duration for model validation, consisting of 15 test points with varying conditions of temperature and state of charge. The absolute model errors against the validation data points remain below 2.2% for the capacity loss and below 6.9% for the resistance increase for all dynamic validation tests. In conclusion, this calendar aging model allows the prognosis of the calendar lifetime of LiFePO4/graphite batteries in different applications with varying storage conditions over time.

Pilot-scale demonstration of advanced adiabatic compressed air energy storage, Part 1: Plant description and tests with sensible thermal-energy storage

Abstract: Experimental and numerical results from the world's first advanced adiabatic compressed air energy storage (AA-CAES) pilot-scale plant are presented. The plant was built in an unused tunnel with a diameter of 4.9 m in which two concrete plugs delimited a mostly unlined cavern of 120 m length. The sensible thermal-energy storage (TES) with a capacity of 12 MWhth was placed inside the cavern. The pilot plant was operated with charging/discharging cycles of various durations, air temperatures of up to 550 °C, and maximum cavern gauge pressures of 7 bar. Higher pressures could not be reached because of leaks that were traced mainly to the concrete plugs. Simulations using a coupled model of the TES and cavern showed good agreement with measurements. Cycle energy efficiencies of the TES were determined to lie between 76% and 90%. The estimated round-trip efficiency of the pilot plant was based on the measured TES performance and estimated performances of the other components, yielding values of 63–74%, which compares favorably with the usually quoted values of 60–75% for prospective AA-CAES plants.

Experimental investigation of thermal and strain management for lithium-ion battery pack in heat pipe cooling

Abstract: Thermal and strain management is required for a considerate lithium-ion battery management system (BMS) to depress the operating temperature and strain. In this paper, non-destructive temperature equipment and strain gauges are used simultaneously to monitor the temperature and strain of 18650 lithium-ion battery pack with a heat pipe cooling device (HPCD) which is used to depress temperature. At the steady-state and dynamic-state discharge processes, the temperature of pack is dramatically different with cooling device or not, and the optimal operating temperature is kept when HPCD is embedded in the center of pack with forced convection. The strain decreases in discharge progress after the pack is equipped with HPCD and has the same trend of temperature change in charge-discharge cycle process. The battery management system of temperature and strain is also effective during multiple charge-discharge processes. Furthermore, this system has the superiority of low power consumption.

Parameter variations within Li-Ion battery packs – Theoretical investigations and experimental quantification

Abstract: Single lithium-ion cells within electric vehicles’ battery packs generally show variations in capacity and impedance due to the manufacturing process as well as operational conditions. Therefore, cells connected in parallel experience different dynamic loads during vehicle operation, which may potentially result in uneven and accelerated aging behavior. However, in literature only little is mentioned about the different reasons for parameter variations within single cells of parallel connections as well as their magnitude in real-life conditions. In this work, capacity and impedance variations within parallel-connected cells are investigated theoretically and are quantified exemplary by a batch of new cylindrical 18650 cells as well as an retired BEV battery pack with a 2p96s configuration of prismatic cells. Furthermore, the development of existing parameter variations along cycling are analyzed for two modules of the battery pack. It is demonstrated, that the aged cells show a strong increased parameter spread compared to the new cells. During further aging, the existing capacities spread of the block and especially the state of inhomogeneity of parallel couples increases. Hence, the widespread theory of a self-balancing effect inside a parallel connection, which leads to a convergence of the cells’ SOH, is disproved.

Irreversible calendar aging and quantification of the reversible capacity loss caused by anode overhang

Abstract: Calendar aging tests are presented quantifying the reversible capacity loss caused by lithium migration from the active part to the overhang of the anode. Based on these tests, capacity loss at five different SOCs with respect to the anode is evaluated. The remaining capacity shows a non-linear part in the beginning representing the reversible capacity loss caused by the overhang. The subsequent linear part ending after 100–200 days corresponds to the irreversible capacity loss. By extrapolating the linear part to t = 0, the lithium lost to the overhang is measureable for each storage condition. This approach matches well to theoretical values calculated using a simple equation. In later stages of the capacity loss curve, another superposed effect can be observed that decreases capacity fade. The reason is found in an increasing homogeneity of lithium distribution that correlates to the peak height of differential voltage characteristics. In this publication an increasing homogeneity is associated with a higher extractable capacity and vice versa. An especially high increase of homogeneity is observable when a high voltage difference coincides with pressure change due to lithium insertion. Finally, the temperature dependency of the lateral lithium flow is shown for three temperatures at a fixed storage position.

Synthesis and characterization of activated carbon from the biomass of Saccharum bengalense for electrochemical supercapacitors

Abstract: Low cost and very simple activation method (ZnCl2 as activating agent) is used for the synthesis of activated carbon derived from the biomass of Saccharum bengalense (S. bengalense) leaves. The S. bengalense derived activated carbon (SbAC) as the electrode material in Electric Double Layer Capacitors (EDLCs) is reported for the first time. The structural, surface morphological study and vibrational response of the SbAC are characterized by using X-ray diffraction (XRD), Field Emission Scanning Electron Microscopy (FE-SEM), Fourier Transform Infrared Spectroscopy (FTIR), Raman spectroscopy, and Brunauer-Emmett-Teller (BET) surface area. Electrochemical studies indicate that the SbAC delivers the maximum specific capacitance of 102.6 F g−1at scan rate of 2 mV/s in aqueous electrolyte (1 M Li2SO4) for 1.6 V operating voltage. This high value of specific capacitance is credited to its high specific surface area (2090 m2 g−1) and pore volume of 0.281 cm3 g−1. The SbAC exhibits good rate capability with an excellent charging/discharging cycle stability in aqueous electrolyte (1 M Li2SO4) during 120,000 cycles. The results indicate that SbAC shows good electrochemical properties to be used for energy storage applications in future.

Equivalent circuit model parameters extraction for lithium ion batteries using electrochemical impedance spectroscopy

Abstract: Numerical modelling is the method by virtually testing and verifying the functionality of a specific product or component. The primary goal is to get approximate results of how the system behaves in a given time and environment. We are able to accept a certain numerical error from a real experiment, thus significantly speeding up part of the development of the device. In the field of electrochemistry of lithium-ion accumulators, several variants of numerical models have been proposed that yield satisfactory results in modelling certain physical fields of these batteries (electric field, temperature field, current field).

Evaluation of battery inconsistency based on information entropy

Abstract: The power battery system is the core for electric vehicles, which is composed by hundreds or thousands of cells in series and parallel generally. Cells have inherent inconsistency because of slight deviations and uncertain factors in their production process. And they work in the complicated charge and discharge environment for a long time, so their inconsistency will be further aggravated to greatly reduce the available capacity and shorten the service life. There is an urgent need to establish an evaluation mechanism for the inconsistency of batteries to provide the gist for the high-efficiency and reliable management. The test platform and scheme are built to obtain accurate data. And a comprehensive evaluation method for battery inconsistency is proposed based on the information entropy. Taking the capacity, internal resistance and the ratio of constant current charge capacity to constant voltage charge capacity as evaluation factors, the inconsistency of the battery pack composed of twelve cells is analyzed comprehensively. Experimental results show that the method can scientifically evaluate the inconsistency of the battery pack in different life and has wide adaptability.

Preparation and Enhanced Thermal Performance of Novel (Solid to Gel) Form-Stable Eutectic PCM Modified by Nano-Graphene Platelets

Abstract: This study presents the development of form-stable eutectic mixtures, modified with nanoscale structures for enhanced thermal performance. These additives may result in the next generation of phase change materials (PCMs) for thermal energy storage systems. An appropriate gelling or thickening agent (2-hydroxypropyl ether cellulose) is introduced so that the PCM will lose its fluidity, become form-stable, and the liquid leakage problem will be overcome. Nano-graphene platelets (NGPs) are added in order to enhance the thermal properties and overall heat transfer. Differential scanning calorimetry (DSC) was carried out for the thermal analysis of the PCMs. The paper experimentally studied in detail the enhanced thermo-physical properties required for stimulating and modelling the PCM in energy storage applications such as specific heat, thermal diffusivity, thermal conductivity, enthalpy, and density. The principle of the T-history method was applied using a parallel plate heating/cooling guarded plate apparatus to determine the true phase transition temperatures of bulk PCM. The supercooling of the enhanced shape stable mixture was found to be less than 0.1 °C. The thermal reliability test indicated that the enhanced form-stable eutectic mixture had reliable thermal performance over a postulated lifetime of 80 years. As a result, the developed form stable PCM eutectic mixture is a promising material for thermal energy storage.

Ramp-rate control smoothing methods to control output power fluctuations from solar photovoltaic (PV) sources—A review

Abstract: Solar photovoltaic generator is an intermittent source and mitigating its output power ramp-rate is crucial as they threaten the stability of the utility grid. This paper is aimed at bringing out the latest comprehensive review on different ramp-rate control smoothing methods under three broad classifications: (i) moving average and exponential smoothing based methods, (ii) filter based methods, and (iii) ramp-rate based algorithms. Application of moving average and low pass filter from filter based methods is widely chosen by the researchers for solar photovoltaic ramp-rate control. Therefore, a detailed analysis on these methods supported by simulation results is carried out to analyze the capability of these methods to control the solar photovoltaic ramp-rate. On application of these methods, it was found that there will be an increase in the energy storage’s degradation and size. In addition, reduction in energy storage’s operating life can also be found. Later, a detailed comparison on different techniques are summarized in the discussion section, from which it was found that the ramp-rate based algorithms are advantageous than moving average and filter based method. The advantages of the ramp-rate based algorithms are discussed as well. In addition, the disadvantages of the existing ramp-rate based algorithms are also highlighted. Finally, the necessitate for, (i) improvement in ramp-rate based algorithms, (ii) application of dual energy storage for large solar photovoltaic plant, and (iii) regulation in control of solar photovoltaic ramp-rates is suggested in this paper. These suggestions will contribute to decrease in energy storage’s capacity and degradation, and increase in its operation life.

Critical electrode properties and drying conditions causing component segregation in graphitic anodes for lithium-ion batteries

Abstract: Among others, the performance of lithium-ion batteries is determined by the structure and material distribution of the electrodes. These electrodes are known to develop an inhomogeneous inactive material distribution during drying of the wet-coated film. The segregation of the conductive additive and the binder was found for the graphite anodes studied in this work and was proven by indirect and direct analyses. Segregation reduces the adhesion strength between coating and substrate and increases the electrical resistance as well as the elasticity of the anode. It was found by spectroscopic analysis that binder concentration and by association carbon black concentration increase from bottom to top of the coating. This Segregation increases with drying temperature and the amount of solvent that needs to evaporate. An auxiliary parameter is introduced to determine a combined, critical value for the driving force of the solvent evaporation (drying temperature) and the anodes’ mass loading. Finally, the mass loading and/or the drying temperature to avoid segregation can be estimated with regard to the final product and the existing drying equipment.

Experimental investigation of transient melting and heat transfer behavior of nanoparticle-enriched PCM in a rectangular enclosure

Abstract: An experimental study was conducted to investigate the transient melting and heat transfer behavior of nanoparticle-PCM mixtures in a rectangular enclosure. Four types of nanoparticles, silver, copper oxide, aluminum oxide and multi-walled carbon nanotubes were considered, and paraffin wax was used as the PCM. The results show that all four nanoparticle-enriched PCM mixtures provided better thermal performance as compared to the case with the plain PCM. It has been argued that the addition of surfactant to improve the suspension-ability of nanoparticles in the PCM counteracted the viscosity enhancement due to nanoparticles in the PCM. Among the four tested nanoparticles, silver nanoparticles were found to be the most effective in the heat transfer enhancement, followed by copper oxide nanoparticles. The performances of aluminum oxide and MWCNT were hampered due to their higher settlement rates. The transient heat transfer coefficients for all cases were computed and found to have increased rapidly in the early stages of melting up to the melted fraction of about 0.2, after that they remained almost constant for the rest of the melting process. The heat transfer coefficients for CuO and silver were found to be about 18% and 14% higher than the plain PCM case, while aluminum oxide and MWCNT were lower and closer to the plain PCM case due to higher sinking rates. The thermal behavior of CuO-enriched PCM was further investigated for 1, 3, 6, 8 and 10% mass fractions of CuO. It was found that under given conditions, 6% CuO fraction provides the best thermal performance and highest melting rate. For this case, the melting rate and heat flux were about 25% higher than that for the plain PCM case.

Experimental study of internal and external short circuits of commercial automotive pouch lithium-ion cells

Abstract: In order to develop a deeper understanding of the behaviour of commercial automotive lithium-ion pouch cells under short-circuiting conditions, two scenarios were experimentally investigated and compared. Firstly, experiments were conducted by internally shorting 15 Ah cells by full nail penetration using three different nail materials; copper, steel and plastic. A second set of experiments involved externally shorting the cell tabs using an external circuit with a range of resistance values. In both scenarios the cell electrical and thermal response were determined by the shorting resistance. In the case of nail penetration there was a clear distinction between the outcome of the conducting and non-conducting nails, although the outcome using conducting nails suffered from poor reproducibility. The poor reproducibility was attributed to the variation in the contact resistance between the nail and the cell layers. Correlating the outcome of both tests can be used to estimate the shorting resistance and construct the current profile during nail penetration test.

Evaluation of redox flow batteries goes beyond round-trip efficiency: A technical review

Abstract: The flow battery is a promising technology for large-scale storage of renewable energy owing to its unique advantages such as independence of power and energy capacity, scalability and versatility. The evaluation method is extremely important for the developments of both researches and applications of flow batteries. However, there is a lack of clear and uniform evaluation criteria in the open literature. The round-trip energy efficiency is commonly used to evaluate cell performance, whereas other different evaluating criteria may be suitable for different situations, with respective emphases. This paper reviews the development of performance evaluation criteria for redox flow batteries and clarifies the selection principle of evaluation criteria, stating that the system energy efficiency is the primary criterion, and power density or/and energy density are also vital evaluation criteria on the premise of maintaining high system energy efficiency for diverse types of redox flow batteries. The recent applications of these evaluation criteria on flow batteries are demonstrated afterwards. Finally, some exceptional conditions under what the system energy efficiency criterion is unsuitable are discussed, and emphasis is addressed on the new types of flow batteries. Applying a proper evaluation criterion helps to circumvent the remaining challenges of redox flow batteries, therefore, this review paper will be a useful guideline for the technology development and practical deployment of flow batteries.

Understanding the functions of carbon in the negative active-mass of the lead–acid battery: A review of progress

Abstract: The addition of supplementary carbon to lead–acid batteries that are intended for use in emerging automotive duties can provide improvement in two aspects of performance. (i) In both hybrid electric and battery electric vehicles that are designed to preserve energy through the operation of regenerative-braking, conventional lead–acid batteries exhibit a rapid decline in the efficiency of the recuperative charging (which can involve rates up to 30C1) and fail quickly as a result of an accumulation of lead sulfate on the negative plate. It has been widely reported that supplementary carbon — either intimately mixed with the negative active-material or included as a separate component attached to the plate — can enhance charge-acceptance. (ii) Full-hybrid electric and battery electric vehicles employ high-voltage batteries composed of large numbers of cells connected in series. Consequently, when conventional lead–acid batteries are used in such configurations, the continuous cycling encountered in normal driving will almost certainly lead to divergence in the states-of-charge of the unit cells and thereby demand periodic equalization charges. In this application, it has been demonstrated that lead–acid batteries with supplementary carbon incorporated into the negative plate are rendered immune to the divergence problem and therefore operate without the need for an equalization charge. The inclusion of supplementary carbon does, however, promote hydrogen evolution and failure due to the loss of water from the electrolyte solution. Current research efforts are directed towards methods by which this disadvantage can be mitigated without losing the benefits that the addition of carbon provides. This review covers the extensive research that has been conducted to understand the mechanism by which the additional carbon operates, the additional studies that have sought to identify the best types and optimum amounts of carbon that should be used, together with the most effective manner for their deployment.

Thermodynamic analysis and optimisation of a combined liquid air and pumped thermal energy storage cycle

Abstract: Pumped thermal energy storage (PTES) and liquid air energy storage (LAES) are two large-scale electricity storage technologies that store energy in the form of thermal exergy. This is achieved by operating mechanically-driven thermodynamic cycles between thermally insulated storage tanks. Both technologies are free from geographic restrictions that apply to pumped hydro and most compressed air storage. The present paper describes a novel, combined system in which PTES operates as a topping cycle and LAES as a bottoming cycle. The fundamental advantage is that the cold thermal reservoirs that would be required by the two separate cycles are replaced by a single heat exchanger that acts between them, thereby saving significant amounts of storage media per unit of energy stored. In order to reach cryogenic temperatures, the PTES cycle employs helium as the working fluid, while the LAES cycle uses supercritical air (at around 150 bar) which is cooled sufficiently to be fully liquefied upon expansion, thus avoiding recirculation of leftover vapour. A thermodynamic study of a baseline configuration of the combined cycle is presented and results are compared with those of the separate systems. These indicate that the new cycle has a similar round-trip efficiency to that of the separate systems while providing a significantly larger energy density. Furthermore, three adaptations of the base-case combined cycle are proposed and optimised. The best of these adaptations achieves an increase in thermodynamic efficiency of about 10 percent points (from 60% to 70%), therefore significantly exceeding the individual cycles in both energy density and efficiency.

PCM addition inside solar water heaters: Numerical comparative approach

Abstract: The aim of this paper is to highlight the design of solar storage tank integrating PCM modules for solar hot water production. The objective is to simulate working cycle of solar thermal energy storage systems with encapsulated PCM operating under realistic environmental conditions (Marrakech, Morocco) and typical consumption load profile. Thus, two numerical codes were built to predict the temperature evolution in a storage tank simulation filled by PCM. This research aims to compare two numerical procedures: the technique of apparent specific heat capacity ( C p app ) and the Enthalpy method, basically used to simulate the phase change phenomena for latent storage inside a solar tank integrating spherical PCM capsules. Effects, advantages and limits of these numerical methods were examined via various numerical observations as well as a set of system thermal performance indicators. The assumptions, equations used in numerical modeling, the temperature profiles and the PCM liquid fraction evolution are presented and discussed as well. It was found that the time required for a complete melting inside the storage tank for the considered PCMs is 2.5 h and the increase in PCM amount decreases the melting velocity and enhance the heat losses to surrounding in dynamic mode. Results also show that the choice of a numerical method plays an important role in describing efficiently the phase change phenomena and system thermal performance. Based on the design and parameter studies performed, other suggestions and several numerical model improvements for further studies are as well addressed.

Highly densified NCM-cathodes for high energy Li-ion batteries: Microstructural evolution during densification and its influence on the performance of the electrodes

Abstract: For positive electrodes in Lithium ion batteries LiNi1/3Co1/3Mn1/3O2 (NCM) is widely used as an active material. The performance of the electrodes in different applications is mainly influenced through the electrode manufacturing process. This work aims to contribute to a better understanding of the relation between microstructure development caused by the densification of the electrodes and its influence on electrochemical behaviour as well as ageing. Therefore, NCM-based cathodes were compacted in several interstages down to a porosity of 18%. By detailed microscopic analyses and Hg porosimetry we provide important insights concerning the electrodes microstructure, its evolution during densification and the correlation to the electrochemical performance. In doing so it will become obvious that major microstructural changes take place when electrodes are compacted to porosities below 22–25% which goes along with a significant decline of the capacity and energy density at current rates of 2C and more. However, at current rates below 1C the highest energy density is observed for cathodes with even lower porosities. Additionally, the microscopic analyses provide important information about how this problem can be tackled.

Techno-economic analysis of battery storage and curtailment in a distribution grid with high PV penetration

Abstract: Global solar PV capacity continues growing and this technology is a central solution for the global energy transition based on both economic growth and decarbonisation. PV technology is mainly being installed in distribution networks next to the consumption centres but it is an intermittent source which does not offer demand matching capability therefore calling for the redesign of distribution networks. In this study, battery storage and PV curtailment are compared as solutions for a residential area in Zurich (Switzerland) with large PV penetration from a techno-economic perspective. The techno-economic analysis focuses on the implications of the location (and related size) of battery storage and the type of curtailment control (fixed versus dynamic) for relevant stakeholders such as consumers and the distribution network operator. PV energy time-shift, the avoidance of PV curtailment and the upgrade deferral of the distribution transformer are the energy services provided by battery systems. Residential batteries offer more value for PV management than grid-scale solutions despite higher levelized cost but PV curtailment is the most cost-effective solution since only up to 3.2% of total PV electricity generation in energy terms should be curtailed for avoiding the transformer upgrading. We conclude that shared ownership models for PV curtailment could considerably improve its acceptance among consumers.