Charging Energy Efficiency Research Articles

Enhanced capacitive deionization via modulating local electron of electro-adsorption sites in a Trace-Fe-modified carbon framework

In order to alleviate the crisis of freshwater resources, it is essential to explore a clean, efficient, and low-consumption water treatment technology. As a kind of electro-adsorption water purification technology, capacitive deionization (CDI) has drawn continuously growing attention because of its advantages. The ion adsorption capability of CDI is closely related to the electrodes. Unfortunately, the ion adsorption capacity of common carbon materials is limited and far from reaching the rapidly increasing requirements of fresh water treatment. In this study, Fe-N-HPC electrode materials with trace Fe uniformly dispersed in N-doped hollow carbon polyhedral frameworks were tactfully prepared by a simple in-situ growth and pyrolysis method. The structure and morphology of the heterostructure material were verified by various analysis. Electrochemical tests showed the Fe-N-HPC electrode had an enhanced performance with a higher specific capacitance and fast ions diffusion coefficient. The Fe-N-HPC showed excellent CDI performance, with an enhanced desalinization capacity (34.38 mg/g, 500 mg/L NaCl solution, 1.2 V), and regenerative stability after 100 adsorption–desorption cycles. In addition, it also exhibited higher charge efficiency, energy efficiency and lower specific energy consumption. The removal mechanism of Na+ on the electrode and the participation of trace Fe can modulate the local electron of the electro-adsorption sites were reasonably verified by ex-situ XRD, Raman, and XPS characterizations, which finally facilitated the electro-adsorption property. This work presents a promising scheme for the advance of high efficiency capacitive desalination system.

Performance Analysis of Finned-Tube Heat Exchanger Charged with Phase Change Material for Space Cooling

The performance of a latent heat storage unit comprised of phase change material (PCM) enclosed in a finned-tube heat exchanger was evaluated experimentally and theoretically to determine its viability to condition a space during summer. The internal and external design conditions of a typical building were selected and analyzed to determine the type of PCM, and the phase change temperature required for space cooling. Subsequently, a PCM of Plus-ice A17 was selected and charged into a small-scale finned-tube heat exchanger. Extensive measurements were conducted on the PCM heat exchanger at different operating conditions. Meanwhile, a three-dimensional computational fluid dynamics model for the PCM heat exchanger was developed and validated with the experimental measurements and thus simulated. When the airflow velocity increases from 1.3 m/s to 6 m/s, the phase change periods decrease by 25% and 13% for the PCM charging and discharging processes respectively. When the PCM thermal conductivity increases from 1 W/(m·K) to 8 W/(m·K), the phase change periods reduce by 36.3% and 47.7% for the PCM charging and discharging processes respectively. In addition, for the same increased range of PCM thermal conductivity, the charging energy efficiency increases by 16.3%, and the discharging energy ratio drops by 7.1%.

Multi-objective optimization for multi-stage constant current charging for Li-ion batteries

Fast charging is a key challenge for the widespread adoption of electric vehicles (EVs), as it can make EVs more convenient and appealing to consumers. Therefore, different charging methods are proposed to enhance the performance of lithium-ion batteries (LIBs). Multi-stage constant current (MSCC) charging can improve LIB's performance in several aspects, including charging time, charged capacity, temperature rise, average temperature rise, and charging energy efficiency. However, achieving a multi-objective performance during LIB charging is challenging. In this paper, the Taguchi method is used to determine the multi-objective optimal (MOO) charging profile for the MSCC charging strategy. The Orthogonal experiments are designed and conducted to find the optimal solutions for each performance parameter for a five-stage constant current (5SCC) charging profile. A comparison is conducted among the performance-based selective charging profiles to validate the optimal charging profile. Furthermore, a comparison is made between the obtained MOO charging profile and the classical equivalent constant current constant voltage (CCCV) method. Experimental results demonstrated that the MOO charging profile reduces the charging time with comparable temperature rise to the CCCV, making it promising for the future alternative efficient EV charging. These findings highlight the effectiveness of the MSCC approach in improving LIB performance.

Tuning the Ferroelectric Response of Sandwich-Structured Nanocomposites with the Coordination of Ba0.6Sr0.4TiO3 Nanoparticles and Boron Nitride Nanosheets to Achieve Excellent Discharge Energy Density and Efficiency.

With the rapid development of new electronic products and sustainable energy systems, there is an increasing demand for electrical energy storage devices such as electrostatic capacitors. In order to comprehensively improve the dielectric, insulating, and energy storage properties of PVDF-based composites, sandwich-structured composites were prepared by layer-by-layer solution casting. The outer layers of the sandwich structure composite are both PVDF/boron nitride nanosheet composites, and the middle layer is a PVDF/Ba0.6Sr0.4TiO3 nanoparticles composite. The structural and electrical properties of the sandwich-structured composites were characterized and analyzed. The results show that when the volume percentage of Ba0.6Sr0.4TiO3 nanoparticles in the middle layer of the sandwich structure composite is 1 vol.%, the dielectric properties are significantly improved. Its dielectric constant is 8.99 at 10 kHz, the dielectric loss factor is 0.025, and it has better insulating properties and resistance to electrical breakdown. Benefiting from the high breakdown electric field strength and the large maximum electrical displacement, the sandwich-structured composites with 1 vol.% and Ba0.6Sr0.4TiO3 nanoparticles in the middle layer show a superior discharge energy density of 8.9 J/cm3, and excellent charge and discharge energy efficiency of 76%. The sandwich structure composite achieves the goal of simultaneous improvement in breakdown electric field strength and dielectric constant.

Experimental study on charging energy efficiency of lithium-ion battery under different charging stress

Accurate measurement of the energy efficiency of lithium-ion batteries is critical to the development of efficient charging strategies. Energy efficiency is discussed in published work from the perspective of cell design, more than that, the insufficient probe of stresses influencing the energy efficiency of commercialized batteries while the conclusions coupled with the effect of battery temperature rise have limited engineering guidance value. Few papers specify test profiles for energy efficiency baseline. This paper designs a charging energy efficiency (CEE) test profile to present an offline map of baseline value for commercial ternary lithium-ion batteries. The time-frequency domain impedance characteristics are analyzed based on the distribution of relaxation times, providing a mechanistic explanation of the CEE evolution. The contributions of temperature, capacity-rate (C-rate), and state of charge (SOC) to the CEE are quantified by global sensitivity analysis and range statistics. The findings show that the proposed profile decouples the effect of temperature rise under forced convection conditions, and has an error of less than 0.04 % for 3 cycles compared to the FreedomCAR guidance of at least 10 cycles. The CEE-SOC curve shape is similar to “M”, which is attributed to the impedance curve shape of “W”, breaking the previous inherent experience of “lower impedance in the middle SOC”. The median of the Map is 0.964, concomitantly the outlier points are concentrated below 0.887 at 10 °C. The global sensitivity analysis carried out by the Sobol method and the range statistical indicates that the importance ranked is C-rate > Temperature > SOC, with the range statistical of each stress being 11.8 %, 10.223 %, and 7.51 %, respectively, as well as the total-order Sobol indexes being 0.56, 0.439, and 0.066, which is beneficial for optimizing the operating SOC interval of lithium-ion batteries and guiding the development of fast charging strategies.

Experimental Analysis of Charging and Discharging Characteristics of Sensible Energy Storage System

Abstract: To meet energy needs in the absence of an energy source, practical energy storage devices can be combined with home and industrial systems. The thermal properties of a practical energy storage system with numerous cylindrical channels are investigated in this work experimentally during the charging and discharging cycles. By adjusting the mass flowrate of air from 0.022 to 0.031 kg/s and the input air temperature from 45 to 75 °C, the transient temperature distribution, energy storage, energy release, and charging/discharging energy efficiency are assessed. At an intake temperature of 55 °C and an air mass flowrate of 0.031 kg/s, the maximum charging energy efficiency of 81.3% was discovered. The maximum discharging energy efficiency is discovered to be 74.3%, which corresponds to an air mass flowrate of 0.031 kg/s and an inlet temperature of 45 °C.

Experimental Investigation on the Impact of Various Cooling Conditions for Fast Charging Cylindrical Lithium-ion Cells

Various commercial 18650 and 21700 lithium-ion high-energy cells were investigated experimentally in a wind tunnel for battery cells, regarding their fast-charging performance. Convective cooling with air stream velocities of 1ms−1, 5ms−1, and 10ms−1 were applied at different ambient temperatures ranging from 10°C to 40°C. For each combination of convective air stream velocity and ambient temperature, a constant current (CC) charge rate capability test, controlled by voltage and temperature, as well as a multistep constant current (MCC) protocol were investigated.An improved rate capability was achieved with stronger convective cooling when charging was limited to the risk of overheating. For 3C CC charging, the charged capacity was doubled for the 18650, as well as the 21700 format. Overcooling at low temperature deteriorated the rate capability. In general, the rate capability of the 18650 cells was superior to the 21700.Regarding the MCC protocol tests, the charging time, charging efficiency, maximum surface temperature and specific cooling power were evaluated. To minimize MCC charging time, an air stream velocity of 1ms−1 at 25°C is recommended to achieve 21min and 25min for the 18650 and the 21700 format, respectively. For this, a peak specific thermal cooling power of around 275W, normalized to a 1kWh battery pack for better format comparability, was required. The charging energy efficiency was above 91% for all tests.

Engineering the next generation of photorechargeable zinc-air batteries

Solar energy has been identified as one of the key building blocks of the future energy generation mix required to meet greenhouse gas emissions targets while leading the way to a zero-carbon economy. In our opinion, photorechargeable zinc-air batteries offer a sustainable and affordable option for delivering continuity in electrical energy supply by utilizing solar energy to improve charging performance and energy efficiency while reducing fossil fuel dependence. However, critical issues of low light utilization efficiency, photochemical instability, poor interfacial charge transfer kinetics and energy efficiency surrounding the development of these systems must be addressed to accelerate full-scale implementation. This timely perspective provides a brief overview of current photorechargeable Zn-air batteries while highlighting recent advances, limitations, and emerging opportunities required for this promising technology. • An overview of photorechargeable zinc-air batteries is provided. • Overall performances are highlighted. • Challenges and future perspectives are discussed.

Testing of the oil‐immersed sensible heat storage unit with circular channel solid heat body under charging modes with different heat transfer temperature difference

Heat storage technology can enrich and store dispersed and discontinuous heat and significantly improve energy efficiency. This paper reports a pilot-scale sensible heat storage unit, which uses circular channel solid made of castables as the heat storage bodies and heat transfer oil as the working fluid. When performing, the heat transfer oil passes through the flow channel of the heat storage body and is in direct contact with the heat storage body for heat exchange. The experiment explores the unit's thermal performance, including heat, power, and charge energy efficiency under different charging temperature difference modes. At the same time, the normalized charge energy efficiency is used to evaluate the heat-storage unit's heat absorption capacity during the charging process. The results show that the average heat storage capacity of the heat storage body is about 1.10 × 106 kJ, accounting for 89% of the heat storage capacity of the unit, and the remaining 11% is the heat stored in the oil inside the unit. In addition, the charging mode with step temperature rise used in the experiment can make the heat stored by the regenerator increase linearly with time. The charging mode with a more considerable temperature difference can significantly enhance the charging power and shorten the charging time, but the increase in the temperature difference reduces the efficiency of the charging process. The efficiency in the experimental range is reduced from 64.5% in the minimum temperature difference mode to 34.8% in the maximum temperature difference mode. This paper has a certain supplementary function for the design and application of heat storage and the evaluation of the thermal performance of the heat storage unit.

Numerical investigation on the polarization and thermal characteristics of LiFePO4-based batteries during charging process

• An electrochemical-thermal couple model is developed for pouch lithium-ion batteries. • Effects of charge rate on polarization and heat generation are numerically studied. • Sudden rises in total polarization are mainly linked to solid-phase diffusion polarization. • Over 85% of the heat in the cell core under 8C charging comes from irreversible heat. • Charge energy efficiency of the cell at different current levels is further analyzed. High-current charging exacerbates internal polarization and abnormal heat generation, stymieing the development of fast-charging technology for lithium-ion batteries. Based on battery disassembly and charge test experiments, an electrochemical-thermal coupling model was developed and validated in this paper. The variation patterns of various polarization and heat generation of pouch-type lithium iron phosphate (LFP) batteries at different charge rates and their influence mechanisms were investigated numerically. Results indicate that the changes in charge voltage profiles are strongly linked to total cell polarization, and excessive charge current aggravates internal polarization, with the average polarization voltage reaching 109.2 mV at 8C, which is 471.7% higher than at 1C. The polarization in the electrodes dominates the cell polarization, especially at the negative electrode. Activation polarization accounted for the largest share of electrode polarization, the change in polarization profiles in the initial and final stages depended mainly on the solid-phase diffusion polarization. Besides, the large cell temperature difference at high charge currents is attributed to the order of magnitude difference in heat generation rates between the positive tab and the cell core. The cell temperature rise is primarily due to heat production in the cell core, where the proportion of irreversible heat increases nonlinearly with the charge rate, exceeding 85% of the total heat generation at 8C. The charge energy efficiency reduces gradually with increasing charge rate and is only 0.948 at 8C. These findings will help to develop appropriate charging protection strategy for better battery operation and life.

Energy efficiency optimization for multiple chargers in Wireless Rechargeable Sensor Networks

To guarantee the continuous coverage of the rechargeable sensors, Wireless Rechargeable Sensor Networks (WRSNs) has emerged with the advantages of high charging efficiency and reliable charging timeliness. Charging planning is an important problem in theoretical research and practical applications, and it faces more difficulties and challenges for multiple mobile chargers. In this paper, we introduce a charging planning problem for multiple chargers, namely Charging Energy Efficiency Maximization problem for Multi-Chargers in WRSNs (CEEM-MC Problem), and prove its NP-hardness. The problem aims to maximize the charging energy efficiency of the charging process by assigning the charging amount and planning the charging path. To balance the charging consumption among multiple chargers, we propose two algorithms which are different on the charging path planning, Ring-Wandering Algorithm and Eight-Wandering Algorithm. To evaluate the performance on energy efficiency, we perform a series of simulations and the results verify the effectiveness of the proposed algorithms.

Multi-objective optimization of a concrete thermal energy storage system based on response surface methodology

This paper focusses on the numerical investigation of a concrete thermal energy storage (CTES) system using air as heat transfer fluid (HTF). To reduce the number of simulations and treat complex interactions between parameters, the response surface models for multiple responses are established based on 27 specific design points which are determined by central composite rotation design (CCRD). With the response surface models, the effects of the CTES system’s design parameters on its performance are analyzed. The results indicate that the HTF velocity is the most important factor affecting the charging time and charging energy efficiency. The HTF inlet temperature substantially influences the energy storage. The interactions also have a crucial influence on the performance indices. The optimization is carried out to minimize the charging time, and maximize the energy storage and the charging energy efficiency simultaneously. The optimal parameter combination is optimized by the desirability function. The discharging process is further considered, so that the overall performance of the cycle process is optimal. The geometrical parameter of 22 tubes and 4 fins is considered appropriate under the selected operating conditions. The proposed method provides an efficient means to efficient design of CTES unit.

Enhanced Charging Energy Efficiency via Optimised Phase of Directly Charging an Energy Storage Capacitor by an Energy Harvester

This paper presents a technique to enhance the charging time and efficiency of an energy storage capacitor that is directly charged by an energy harvester from cold start-up based on the open-circuit voltage (VOC) of the energy harvester. The proposed method charges the capacitor from the energy harvester directly until the capacitor voltage reaches 0.75VOC of the energy harvester, which corresponds to an equivalent charging efficiency of over 81% based on theoretical analysis. This charging efficiency is much higher than relying on a boost converter to charge up the capacitor when the energy harvester is low as most of the functioning blocks cannot operate at low voltage. A control circuit based on RC high-pass and low-pass filters, and a comparator was introduced to detect the instance when the capacitor is charged up to 0.75VOC of the energy harvester. A circuit was built to verify the proposed method and tested with a piezoelectric energy harvester. The proposed circuit achieved an enhanced charging time of over 91% faster and a final capacitor voltage of 317% higher than a conventional boosting scheme.

Spindle-shape ferric oxyhydroxides with nano-sized grains for efficient oxygen evolution reaction and supercapacitors

The rational design and development of novel electrode materials with a unique hierarchical nanostructure is crucial for improving their electrochemical activities, charge transfer kinetics, energy efficiency, and energy-storing ability in energy conversion and storage devices. In this study, we synthesized spindle-shaped ferric oxyhydroxide nanoparticles directly grown on carbon cloth (spindle-FON/CC) by a facile and straightforward hydrolysis method. This material is a promising candidate for the fabrication of efficient electrodes used in supercapacitors (SCs) and electrocatalytic cells for the oxygen evolution reaction (OER). The as-prepared spindle-FON/CC exhibits unique structural features with nano-sized grains and pores that provide large electrolyte contact areas (electrochemically active sites) and favorable ion diffusion pathways. These structural properties lead to efficient capacitive behavior and electrochemical catalytic activity. The as-prepared spindle-FON/CC electrode showed a high specific capacitance of 612.5 mF cm−2 and outstanding cycling stability (95.7 % capacitance retention after 4,000 cycles). When used as an OER electrocatalyst, the spindle-FON/CC exhibited improved electrocatalytic activity with a low overpotential of 216 mV at a current density of 10 mA cm−2 and a small Tafel slope of 73.4 mV dec−1.

Charging and Discharging Characteristics of Sensible Energy Storage System With Multiple Cylindrical Passages

Abstract Sensible energy storage systems can be integrated with domestic and industrial systems to fulfill energy needs in the absence of an energy source. The present study experimentally investigates the thermal characteristics of a sensible energy storage system with multiple cylindrical passages during the charging and discharging cycles. Transient temperature distribution, energy storage, energy release, and charging/discharging energy efficiency are evaluated by varying the mass flowrate of air from 0.022 to 0.031 kg/s and inlet air temperature from 45 to 75 °C. The maximum charging energy efficiency of 81.3% was found at 55 °C inlet temperature and 0.031 kg/s of the mass flowrate of air. The maximum discharging energy efficiency is found to be 74.3% corresponding to 45 °C inlet temperature and 0.031 kg/s of the mass flowrate of air.

Thermal performance enhancement of a phase change material (PCM) based portable box for cold chain applications

A phase change material (PCM) based portable box for cold chain transportation applications was studied. A composite containing paraffin-based PCM (RT 5), fumed silica and graphene was used. The chemical compatibility of ingredients, and the thermal properties and cyclability of the composite PCMs were investigated. An in-situ X-ray Diffractometer (XRD) was used to study the solidification behaviour of the PCM composites. An experimental rig was built to compare the charging time, cooling duration and energy efficiency of the portable box containing the composite PCMs. The results showed that the composite PCMs had good cyclability and chemical stability. An addition of 4 wt.% fumed silica was able to eliminate the PCM leakage. By adding 1 wt.% of graphene, the thermal conductivity of composite increased by 55.4%. When using composite PCMs, the charging time of the box was reduced by 6.25%. Besides, the portable box could provided a temperature environment of 2~8 °C for up to 11.5 hours. The charging and overall energy efficiency increased by 6.09% and 12.58%, respectively. The results also show substantial evidence that the use of silica and graphene enhances the nucleation process of phase change kinetics and reduces the PCM supercooling.

High power density near‐neutral pH aqueous redox flow batteries using zinc chloride and 4,5‐dihydroxy‐1,3‐benzenedisulfonate as redox couple with polyethylene glycol additive

Redox flow batteries (RFBs) using zinc chloride (ZnCl2) and 4,5-dihydroxy-1,3-benzenedisulfonate (Tiron) redox couple is introduced. ZnCl2 and Tiron are used as negative and positive active materials, which are dissolved in near-neutral pH, ammonium chloride (NH4Cl) supporting electrolyte. Cell voltage of RFB using ZnCl2 and Tiron is extremely high as 1.8 V, while two cellulose spacers are introduced to prevent the growth of zinc dendrite on the membrane. When the performances of RFBs using ZnCl2 and Tiron are measured, their charge efficiency (CE), voltage efficiency (VE), and energy efficiency (EE) are 95, 79, and 75% at 40 mA cm−2, whereas their capacity fading rate is high as 0.12 Ah L−1 per cycle. This is due to the zinc dendrite formed on the electrode of RFB that is attributed to the aggregation of zinc ions. To suppress the aggregation and to preserve active sites for the redox reaction of zinc ions during cycling, the polyethylene glycol (PEG) additive is suggested. Regarding the optimization of PEG, 5000 ppm PEG induces both high efficiencies (97, 81, and 79% of CE, VE, and EE at 40 mA cm−2) and low capacity loss rate (0.03 Ah L−1 per cycle), which are more enhanced performances than those of RFBs operated without PEG. In terms of power density of RFB using ZnCl2 and Tiron, high power density of 144 mW cm−2 is achieved under 120 mA cm−2, which is far better performance than that of other RFBs operated under near-neutral pH electrolyte.

Design of a Compact and Highly Efficient Energy Harvester System Suitable for Battery-Less Low Cost On-Board Unit Applications

This study addresses the general problem regarding the power supply in specific on-board unit (OBUs) solutions. In detail, this paper refers to a subset of the so-called electronic toll collection (ETC) applications such as assets control and vehicle identification, where simplicity, low costs, and maximum compactness represent the most important features. In this context, the next generation of OBUs, developed specifically with reference to such applications, will involve energy harvester-based battery-less techniques. Previous studies have mainly concentrated on performance optimization by achieving maximum energy transmission to the OBUs. This study discusses a technique suitable for both maximizing performance and minimizing the dimensions of transponder energy harvesters suitable for assets control and vehicle identification operating at 5.8 GHz. The technique assumes that an optimal source impedance exists that maximizes the energy transfer to the transponder, thus enabling its power supply in a battery-less configuration. We discuss a solution based on a compact patch antenna designed to exhibit this optimal source impedance to the RF-to-DC rectifier. This approach avoids the use of a lossy matching network. For the sake of comparison, the same function is compared with an equivalent development, which includes the interstage matching network between the antenna and the RF-to-DC rectifier. We introduce experimental results demonstrating that the ultracompact energy harvester optimized at −5 dBm of impinging power is capable of increasing both the charge current and energy efficiency from 340 to 450 μA and from 37% to 47%, respectively.

An adaptive on‐demand charging scheme for rechargeable wireless sensor networks

AbstractIn view of the stability and reliability of energy supply, distinct from the time‐varying and uncertainty of energy harvesting systems, adopting mobile vehicles to replenish energy of sensors has become a research hotspot. While some existing studies on the mobile recharging problem ignored the limited energy capacity carried by mobile vehicle and the difference in energy consumption rates of sensors, in this work, we propose an adaptive real‐time on‐demand charging scheduling scheme that maximizes energy efficiency (CSS‐MEE) for Rechargeable Wireless Sensor Networks. In CSS‐MEE, we aim to achieve a compromise between maximizing charging energy efficiency and maximizing charging throughput for solving the on‐demand mobile charging problem. Due to the limited energy capacity of the mobile charger, CSS‐MEE uses both full‐charge mode and adaptive charging mode, depending on the number of charging requests. It combines charging node selection with dispatch path feasibility determination, which takes into account the location‐generated charging cost and energy‐driven charging priority, to ensure the charging efficiency. Extensive simulations are conducted to demonstrate the advantages of CSS‐MEE. Compared with existing approaches, simulation results show that CSS‐MEE achieves better performance in terms of charging throughput, average charging latency, charge scheduling times, and charging efficiency.

Electrocatalysis of Lithium (Poly-) Sulfides in Organic Ether-Based Electrolytes

This work aims at identifying an effective electrocatalyst for polysulfide reactions to improve the electrode kinetics of the sulfur half-cell in liquid organic electrolytes for alkali-sulfur cells. To increase the charge and discharge rates and energy efficiency of the cell, functionalized electrocatalytic coatings have been prepared and their electrode kinetics have been measured. To the best of our knowledge, there is no extensive screening of electrocatalysts for the sulfur electrode in dimethoxyethane:1,3-dioxolane (DME:DOL) electrolytes. In order to identify a suitable electrocatalyst, apparent exchange current densities at various materials (Al, Co, Cr, Cu, Fe, Steel, glassy carbon, ITO, Ni, Pt, Ti, TiN, Zn) are evaluated in a polysulfide electrolyte using potentiodynamic measurements with a Butler-Volmer fit. The chemical stability and surface morphology changes after electrochemical measurements are assessed with X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM). The results show that cobalt is a promising candidate with appropriate electrocatalytic properties for polysulfide reactions while being stable in the electrochemical environment, followed by chromium in terms of catalytic activity and stability. Sputtered TiN was found to be a very stable material with very low catalytic activity, a possible current collector for the cell.