Large Energy Storage Research Articles

Large energy storage density and electrocaloric strength of Pb0.97La0.02(Zr0.46-xSn0.54Tix)O3 antiferroelectric thick film ceramics

Pb0.97La0.02(Zr0.46-xSn0.54Tix)O3 (PLZST, x = 0.04, 0.06, 0.08, 0.15, and 0.18) antiferroelectric thick film ceramics were fabricated via a tape-casting approach. The energy storage performance and electrocaloric effect (ECE) were investigated in terms of the measurements on the hysteresis loops and Maxwell relation. The maximum value of energy storage density of 5.2 J/cm3 and efficiency of 78.2% were procured at 600 kV/cm in Pb0.97La0.02(Zr0.42Sn0.54Ti0.04)O3 thick film ceramics at room temperature. In addition, the ECE was indirectly calculated using the Maxwell relation and the polarizations extracted from the P-E loops as a function of temperature and electric field, an adiabatic temperature change of ΔT = 2.47 °C was procured in Pb0.97La0.02(Zr0.42Sn0.54Ti0.04)O3 thick film ceramics at 500 kV/cm, corresponding to the calculated electrocaloric strength of 0.48 K(MV/m)−1. These results indicate that the PLZST thick film ceramics are promising for practical applications in high-power energy storage capacitors and solid-state refrigeration devices.

Unlocking the energy storage potential of polypyrrole via electrochemical graphene oxide for high performance zinc-ion hybrid supercapacitors

Safe and low-cost zinc-ion hybrid supercapacitors using neutral aqueous electrolytes are promising for large scale and high power energy storage. A key challenge for Zn-ion hybrid supercapacitors is to increase their energy density without sacrificing the high power performance. Herein, we report a Zn-ion hybrid supercapacitor using a polypyrrole/electrochemical graphene oxide (PPy/EGO) composite cathode and aqueous 1 M ZnCl 2 or ZnBr 2 electrolytes. The Zn-PPy/EGO system with an operating cell voltage from 0.5 to 1.5 V exhibited high energy and high power densities of 117.7 and 72.1 Wh kg −1 at 0.34 and 12.4 kW kg −1 , respectively, outperforming the Zn-ion hybrid supercapacitors using carbon cathodes. This high performance is because of the facilitated electronic and ionic transport in the PPy/EGO composite. In brief, the EGO prepared via the electrochemical method we recently reported has good structure integrity and is easily reduced; the porous PPy/EGO composite from co-electrodeposition benefits fast ion diffusion in pores; the small, monovalent halides anions in the zinc halides electrolytes are highly mobile in bulk PPy for fast solid-phase anion insertion/de-insertion. Electrochemical characterization and ex-situ X-ray photoelectron spectroscopy confirmed the anion-dominated charge storage mechanism of PPy/EGO cathode in Zn-PPy/EGO system. • PPy/EGO composite electrodes were prepared by one-step co-electrodeposition. • Mildly oxidized EGO with less disrupted structure benefits electron conduction. • Porous structure of PPy/EGO composite electrode facilitate ion diffusion. • Zn-PPy/EGO system using ZnCl 2 or ZnBr 2 electrolyte show record high performance.

In-situ exfoliation and integration of vertically aligned graphene for high-frequency response on-chip microsupercapacitors

Fast response on-chip micro-supercapacitors (MSCs) with large energy storage capabilities are highly in demand for high-frequency circuits and systems such as alternating current (AC) line filters. Devices with vertically aligned graphene thin-film electrodes were shown to be promising in maintaining close-to-ideal capacitive behavior at high frequencies due to low ionic and electric resistances. This study investigates a novel in-situ integration of vertically aligned graphene layers with micro-sized gold current collectors in which a modified bipolar electrochemistry method has been applied. The electrochemical analysis revealed a high average capacitance of 640 μF cm−2 (C.V−1cm−2) at a scan rate of 2 mV s−1 for the fabricated MSCs and their excellent stability even after 50000 successive charge-discharge cycles by constant current. Most notably, the electrochemical impedance spectroscopy results revealed that the MSCs exhibited very fast response and close-to-ideal capacitive behavior even at around 1000 Hz. Specifically, the phase angle and specific capacitance measured at 120 Hz were −81.2 deg and 65.2 μF cm−2, respectively, in addition to a cut-off frequency of 3486 Hz at which the impedance angle is −45 deg. The device was tested as the capacitive energy storage component in a standard AC line filter, and its performance was found comparable to a commercial off-the-shelf aluminum electrolytic capacitor.

Elaborate Control of Inkjet Printer for Fabrication of Chip-based Supercapacitors.

There are tremendous efforts in various fields to apply the inkjet printing method for the fabrication of wearable devices, displays, and energy storage devices. To get high-quality products, however, sophisticated operation skills are required depending on the physical properties of the ink materials. In this regard, optimizing the inkjet printing parameters is as important as developing the physical properties of the ink materials. In this study, optimization of the inkjet printing software parameters is presented for fabricating a supercapacitor. Supercapacitors are attractive energy storage systems because of their high power density, long lifespan, and various applications as power sources. Supercapacitors can be used in the Internet of Things (IoT), smartphones, wearable devices, electrical vehicles (EVs), large energy storage systems, etc. The wide range of applications demands a new method that can fabricate devices in various scales. The inkjet printing method can break through the conventional fixed-sizefabrication method.

Surface modification and in situ carbon intercalation of two-dimensional niobium carbide as promising electrode materials for potassium-ion batteries

Potassium ion batteries (KIBs) have a great potential in large scale energy storage because of their cost advantages and similar working mechanism to lithium ion batteries (LIBs). However, the larger ionic radius of K+ presents great challenges to find suitable electrode materials for K+ insertion/extraction. Herein, the surface-modified and in-situ carbon-intercalated Nb2CTx MXene is rationally designed and synthesized as electrode for KIBs. The as-prepared Nb2C/C has larger effective interlayer distance (i.e. gallery height), higher specific surface area and electrical conductivity, and lower concentration of surface functional groups. As a result, Nb2C/C exhibits a significantly increased coulombic efficiency (67.6% for Nb2C/C, 28.5% for Nb2CTx) and its specific capacity is two times higher than that of Nb2CTx at 0.02 A·g−1, three times at 0.1 A·g−1. The Nb2C/C delivers an initial specific capacity of 397.9 mAh·g−1 at 0.02 A·g−1 and 338.1 mAh·g−1 at 0.1 A·g−1, and maintains 80.0% after 100 cycles at 0.02 A·g−1 and 76.2% after 200 cycles at 0.1 A·g−1, respectively. Notably, Nb2C/C possesses outstanding cyclic stability and rate performance at various current densities, outperforming most of reported MXene-based anodes for KIBs. The excellent potassium storage performance of Nb2C/C can be ascribed to the abundant active sites exposed to electrolyte, rapid diffusion kinetics of K+ and few side reactions at the electrode/electrolyte interface. This work proposes an effective strategy for the MXene-based materials to maximize their potential applications in various fields such as batteries, supercapacitors and catalysts.

Water enables a performance jump of glass anode for lithium-ion batteries

It is known that some oxide glass systems are a promising class of anode materials for lithium-ion Batteries (LIBs). However, the relatively low capacities of glass anodes severely limit their practical application for large energy storage devices. In this work, we establish an unconventional approach, by which the electrochemical performances of glass anodes for LIBs can be considerably enhanced. Specifically, we incorporate water into an electrochemically active glass system, i.e., TeO2-V2O5-P2O5 (TVP) glass powder via humidity treatment, and then mix the hydrated powder with additives to fabricate anode for LIBs. The optimized humidity treatment leads to the structural modification of the TVP glass powder, which boosts the lithium ion storage capacity of the TVP anode by more than 2.4 times, and maintains the reversible capacity for extra-long cycles. The boosted performances are attributed to both the depolymerized structural network for Li+ diffusion and the hydration-induced nanocrystals. These findings help develop superior glass electrodes in an economically effective way.

High performance and long cycle life neutral zinc-iron flow batteries enabled by zinc-bromide complexation

Zinc-based flow batteries have attracted tremendous attention owing to their outstanding advantages of high theoretical gravimetric capacity, low electrochemical potential, rich abundance, and low cost of metallic zinc. Among which, zinc-iron (Zn/Fe) flow batteries show great promise for grid-scale energy storage. However, they still face challenges associated with the corrosive and environmental pollution of acid and alkaline electrolytes, hydrolysis reactions of iron species, poor reversibility and stability of Zn/Zn2+ redox couple. In this work, bromide ions are used to stabilize zinc ions via complexation interactions in the cost-effective and eco-friendly neutral electrolyte. Cyclic voltammetry results reveal that the redox reversibility between Zn and stabilized Zn2+ is greatly improved. The results of spectrum characterizations and density functional theory calculations verify that the formation of Zn[Brn(H2O)6-n]2-n (1 ≤ n ≤4, n is integer.) ions accounts for the increased electrochemical reversibility of Zn/Zn2+pair. Moreover, to overcome the bottleneck of slow kinetics of the coordination interactions between Zn2+ and Br−, ZnBr2 is judiciously selected as the electrolyte additive to promote the complexation process. Adopting K3Fe(CN)6 as the positive redox species to pair with the zinc anode with ZnBr2 modified electrolyte, the proposed neutral Zn/Fe flow batteries deliver excellent efficiencies and superior cycling stability over 2000 cycles (356 h), shedding light on their great potential for large scale energy storage.

High Efficient Ion Selective Membrane Separator for Room Temperature Sodium Polysulfide Redox Flow Batteries

Redox flow batteries (RFBs) have attracted extensive attention in recent years due to their low cost, safe operation, and design flexibility for large scale energy storage applications. Among various types of high-energy-density candidates, lithium-polysulfide (LiPS) and the NaPS equivalent RFBs are especially attractive due to their high energy density and natural abundance of sulfur, which can significantly decrease the capital cost of the RFB system to metrics suitable for deep market penetration. Owing to the lower cost of Na than Li, NaPS RFBs will be able to offer more advantageous for large grid-scale energy storage system applications. Although a molten electrode-based NaS RFB has been successfully developed to support stationary energy storage systems, its high operation temperatures (> 250 °C) and the use of ceramic ion conductors (e.g., beta-alumina solid electrolytes) cause safety and high-cost concerns. To overcome the limitations of high-temperature NaS battery, room temperature NaPS (RT-NaPS) batteries emerged as alternatives. However, the current status of RT-NaPS RFB have to overcome several issues associated with deleterious self-discharge and high rate of capacity-fade. These two macroscopic challenges are fundamentally underpinned by the crossover of polysulfide (PS), so-called shuttle effect, during cycling. Although ceramic conductors (e.g., NASICON) show promising ion selectivity, their fragile mechanical properties and high cost pose major drawbacks for broader application in RFBs. Celgard®, the most widely adopted porous membrane for the LIBs, are highly permeable to PS ions, thus it is not suitable as a separator for NaPS RFBs. The use of Nafion, an ion selective membrane (ISM), in NaPS RFB improved discharge capacity and cycle stability compared to Celgard (350 mAh/g vs. 200 mAh/g at 20 cycles). However, Nafion cannot achieve good performance in organic phase of Na-PS RFBs due to the persistently high crossover of redox couples caused by swelling of the perfluorinated membrane in organic electrolytes.Here we present a multifunctional electrochemical nanocomposite membrane (mECM) with excellent polysulfide blocking properties and chemical stability in organic electrolytes. A biphenyl backbone-based aromatic hydrocarbon membrane reinforced by porous carbon nanotubes layer and boron nitride nanotube layer shows high sodium conductivity as well as sodium selectivity over PS. Our mECM greatly reduce PS crossover which is lower than commercial Celgard 2325 by 4-order of magnitude, while areal resistance is only 3 times higher than Celgard 2325 (25.10 Ω cm2 vs. 7.6 Ω cm2). As a result, the performance of the Na-PS RFB single cell with our composite membranes is superior to that of Celgard and other commercial IEMs (e.g. Nafion 215) under the same condition. The capacity decay rate of the Na-PS RFB cell with the mECM is significantly lower than that of Celgard 2325, which is largely attributed to the excellent capability of mECM to suppress PS crossover. After 200 charge/discharge cycle, the Na-PS cell with Celgard 2325 lost 70% of its initial capacity (initial 1000 mAh/g to 300 mAh/g); in contrast, the Na-PS cell with the mECM achieved 81% capacity retention (initial 900 mAh/g to 750 mAh/g), demonstrating the possibility of our membrane to use in long-term operation of RT-NaPS RFB (Fig. a). Our results show that the performance of our RT-NaPS cell (Fig. b) outperforms other RT-NaS cells reported so far. More detailed descriptions of ion transport properties, electrochemical properties, and battery performance of the membrane separators will be presented. Figure 1

(Invited) Economic Considerations for Low-Temperature Electrochemical Ammonia Production: Ammonia As a Green Energy Vector

As the energy sector shifts from fossil fuels to renewable energy sources, there is a need for robust energy storage solutions to handle the intermittency of renewable electricity. With the rise of the electric vehicle, electrochemical storage in the form of lithium-ion batteries has gained significant attention. Lithium-ion batteries are a good solution for short-term and small-scale energy storage. However, they are not optimal for large-scale energy storage due to their high price and low power density. Green fuels, such as ammonia, are ideal for storing large quantities of energy to tackle renewable electricity intermittency. Ammonia has an energy density comparable to certain fossil fuels, and if produced through renewable methods, it can serve as a zero-emission energy vector. For ammonia to serve as an energy storage solution, it has to be available at low costs and in a decentralized manner. However, the prevalent use of ammonia in the fertilizer industry hinders its use as an energy vector.State-of-the-art ammonia synthesis plants (Haber-Bosch process) achieve high energy efficiencies and low product cost through a high temperature and pressure thermochemical process. The process is responsible for feeding half of the global population, but it also emits 450 million tons of carbon dioxide per year. Thus, while this process is deemed efficient and affordable, there are many environmental concerns regarding the sustainability of the Haber-Bosch process. Furthermore, the scale at which these facilities must operate to achieve these low costs limits the locations where a Haber-Bosch plant can be built. Centralized manufacturing of ammonia indirectly impacts a developing country’s ability to access fertilizers. With the strong correlation between fertilizer usages and agricultural yield, access to fertilizers is essential to mitigate global hunger. This has motivated a strong interest in rethinking how we manufacture fertilizer-based feedstocks such as ammonia.Electrochemical manufacturing of ammonia is one approach being explored for ammonia production, as electrochemical systems can operate at relatively low temperature and pressure. Additionally, electrochemical technologies are scalable and can enable manufacturing at a range of scales to meet large and small agricultural and energy storage demands. However, there are significant challenges associated with electrochemical manufacturing. Electrocatalysts suffer from poor nitrogen reduction selectivity, resulting in low product yield, low energy efficiency, and high capital and operational cost. Since cost ultimately will be the primary driver for technology adoption, it is critical to begin to determine what role system and catalyst design play in reducing the cost of ammonia to meet Haber-Bosch parity.Here, we present a detailed techno-economic study on low-temperature electrochemical ammonia production. Techno-economic analyses are valuable to determine the cost of the performance targets to achieve economic feasibility and identify possible roadblocks that might hinder the implementation of the technology. We discuss the relevant performance parameters that govern the production cost of an electrochemical system. Additionally, we discuss the benefits of electrochemical approaches over the Haber-Bosch process by evaluating the social cost of carbon dioxide emissions associated with producing ammonia. We then highlight challenges and opportunities for electrochemical ammonia production at low temperatures and pressures and set performance targets for future technologies. Lastly, we emphasize the importance air separation plays in intermittent electrochemical ammonia production and highlight a path towards ammonia as an energy vector. This work offers a better understanding of the current state of the use of electrochemical systems for ammonia production. In addition, this work highlights the thresholds that have to be achieved to provide a competitive advantage of the Haber-Bosch process. Figure 1

Energy storage properties in a Bi(Mg1/2Ti1/2)O3 modified BiFeO3-Sr0.7Bi0.2TiO3 film

High-performance dielectric capacitor represents an emerging technological goal for energy storage in modern electrical and electronic systems. In this work, we report a lead-free film capacitor based on the Bi(Mg1/2Ti1/2)O3 modified BiFeO3-Sr0.7Bi0.2TiO3 relaxor. A large recoverable energy storage density of 77.5 J/cm3, together with an efficiency of 56.1% is achieved in the film with 15 mol. % Bi(Mg1/2Ti1/2)O3 in composition. The film also exhibits excellent fatigue endurance with a reduction less than 3% over 1 × 108 cycles in both recoverable energy storage density and efficiency. Such good properties are ascribed to the improved electrical insulation and breakdown strength and the enhanced relaxor behavior by introducing the bismuth-based perovskite-like compound.

Low Power Modular Battery Management System with a Wireless Communication Interface

The paper concerns the design and development of large electric energy storage systems made of lithium cells. Most research advances in the development of lithium-ion battery management systems focus solely on safety, functionality, and improvement of the procedures for assessing the performance of systems without considering their energy efficiency. The paper presents an alternative approach to the design and analysis of large modular battery management systems. A modular battery management system and the dedicated wireless communication system were designed to analyze and optimize energy consumption. The algorithms for assembly, reporting, management, and communication procedures described in the paper are a robust design tool for further developing large and scalable battery systems. The conducted analysis of energy efficiency for the exemplary 100S15P system shows that the energy used to power the developed battery management system is comparable to the energy dissipated due to the intrinsic self-discharge of lithium-ion cells.

A novel modified LiCl solution for three-phase absorption thermal energy storage and its thermal and physical properties

• A novel LiCl solution for three-phase absorption thermal energy storage is proposed. • The energy storage density of the solution is enhanced by adding two types of additives. • The LiCl crystal slurry overcomes the fluidity problem caused by crystallization. • Thermal and physical properties of the modified solution are measured by experiments. Absorption thermal energy storage (TES) is gaining increasing attention due to its large energy storage density (ESD), mobility and long-term thermal storage capability. Expanding the working concentration difference of a solution can significantly enhance its ESD; however, this may result in crystallization, influencing fluidity and blocking flow channels in a TES device. Furthermore, bulky crystals are difficult to dissolve during energy discharge. In this paper, a novel modified LiCl solution is proposed for three-phase absorption TES, which allows the growth of fine crystals and the formation of well suspended slurry. For the first time, two types of additives with competing mechanism are introduced into the solution: ethylene glycol as a crystallization inhibitor and SiO 2 nanoparticles (SNPs) as a nucleating agent. Compared with traditional working fluids, the proposed solution has a larger ESD and good fluidity. The expanded concentration difference is determined by experiments on solubility and suspension. The optimal mass ratio of the LiCl solution, ethylene glycol and SiO 2 nanoparticles are obtained considering both ESD and fluidity. Heat and cold storage density using this novel LiCl crystal slurry can be enhanced by 24.8% and 156.0% respectively. Measurements on thermal and physical properties including vapor pressure, density and viscosity are also carried out.

Construction of AlF3 layer to improve Na3.12Fe2.44(P2O7)2 interfacial stability for high temperature stable cycling

Sodium ion batteries (SIBs) are applied to the field of energy storage due to their unique advantages, however, large scale energy storage equipment, also requires low cost, good cycling performance, safety performance and good environmental adaptation performance, in order to cope with various climatic conditions. The polyanionic material Na3.12Fe2.44(P2O7)2(NFPO) is considered to be an excellent cathode material for SIBs due to its unique large frame work structure and good thermal stability, leading to good cycle stability and a wide working temperature. Nevertheless, poor intrinsic conductivity of the material brings about large polarization, resulting in low electrochemical reversibility. Especially in high temperature environment, the electrolyte aggravates the erosion of the material and increases the side reactions, making the cycle stability worse. In this study, nanoscale NFPO composites are synthesized by an optimized sol–gel method, while the interface is modified using AlF3, to achieve resistance to surface oxidation and corrosion. Impressively, these modified materials exhibit high-temperature electrochemical properties due to the thermal stability and interfacial protection of AlF3. At 60 °C, it provides a discharge capacity of 130 mAh g−1 at 0.1C, still has a discharge capacity of 100.4 mAh g−1 at 10C, a capacity retention rate of 96.3% after 400 cycles, and has excellent long-term cycling performance (70% capacity retention rate after 6000 cycles at 50C). This work demonstrates the effectiveness of the interfacial modification and provides an impactful strategy for the design of batteries at high temperatures.

New definition of levelized cost of energy storage and its application to reversible solid oxide fuel-cell

Renewable energy installation capacity has rapidly increased in recent years. Subsequently, developing and commercializing large energy storage systems (ESSs) has become an important research objective. To evaluate development and compare between different ESSs, levelized cost of energy storage (LCOES) has been used. However, current LCOES often includes cost of electricity production in total investment, and neglects off-design characteristic of ESSs. Therefore, we proposed a new definition for the LCOES (LCOES2) to resolve these problems. An ESS using RSOFC coupled with waste steam was investigated for ESS efficiency characterization. The proposed ESSs and LCOES calculations were applied to South Korea case. The hourly average solar power data for each month was used. Hydrogen production and consumption were matched for sizing ESS and estimating electricity demand profile. The results show that, conventional LCOES, which considers charging electricity cost, overestimated the cost by 7.7% and 14.8% compared to the LCOES2, at RSOFC stack cost of $700/kW and $225/kW, respectively. The constant part-load efficiency model resulted in lower LCOES values, by up to 6.3%, due to higher overall round-trip efficiency. The new LCOES definition, considering variable part-load efficiency, was proved to be an efficiency-sensitive and reliable cost indicator.

Arbitrage analysis for different energy storage technologies and strategies

The time-varying mismatch between electricity supply and demand is a growing challenge for the electricity market. This difference will be exacerbated with the fast-growing renewable energy penetration to the grid, due to its inherent volatility. Energy storage systems can offer a solution for this demand-generation imbalance, while generating economic benefits through the arbitrage in terms of electricity prices difference. In the present study, a method to estimate the potential revenues of typical energy storage systems is developed. The revenue is considered as the income from the energy storage plant with various roundtrip efficiencies. Thus, an optimal methodology was developed to determine the largest revenue through the charging and discharging operations based on the price profile. It is then applied to the California market in the United States to investigate the potential economic performance of three primary energy storage technologies: Lithium-Ion Batteries, Compressed Air Energy Storage and Pumped Hydro Storage. In particular, the maximum daily revenue from arbitrage is calculated considering various strategies of charging and discharging times as well as the technology’s roundtrip efficiency. The estimated capacity cost of energy storage for different loan periods is also estimated to determine the breakeven cost of the different energy storage technologies for an arbitrage application scenario. Pumped hydro storage (PHS) is found to be the most cost-effective but is not a good candidate for increased capacity in many countries due to concerns associated with developing new dams. Compressed Air Energy Storage (CAES), was found to be the second most cost-effective but still requires much more technology development before it is ready for widespread usage. Lithium battery is well-developed but is currently much too costly (by a factor of four) for a large scale energy storage application. The proposed method can be applied as these and other technologies and their associated costs evolve.

Achieving high energy storage performance and ultrafast discharge speed in SrTiO3-based ceramics via a synergistic effect of chemical modification and defect chemistry

Environmentally friendly energy storage materials with high energy storage performance and excellent stability for applications in pulse power systems are urgently needed. SrTiO3-based ceramics have a relatively high dielectric constant and a high breakdown strength (BDS). However, a low polarization strength in this system often yields a low energy storage density. In this paper, high energy storage performance of SrTiO3-based ceramics with the composition of (Sr1-x-y-φNayBix□φ)TiO3 (abbreviated as zSNBT, where x = 0.2 + 0.3z, y = 0.5z, φ = 0.1–0.1z, and z = 0.8–0.1; □ represents Sr vacancies) was achieved using a synergistic effect of chemical modification and defect chemistry. With the decrease of z, the ferroelectric macro-domain of zSNBT ceramics vanishes due to the original effect of paraelectric SrTiO3, significantly improving the BDS and energy storage performance. When z = 0.2, the material exhibited a single cubic phase structure with a nearly hysteresis-free P-E loop. The maximum BDS reached 390 kV/cm, and under such electric field, a large recoverable energy storage density (Wrec) of 3.94 J/cm3 and ultrahigh energy efficiency (η) of 94.71% were achieved simultaneously. Meanwhile, the 0.2SNBT ceramic showed good thermal stability and satisfying cycling stability in the temperature range of 20–160 °C. In addition, the 0.3SNBT ceramic demonstrated outstanding thermal stability with an ultrafast discharge speed (t0.9 ≤ 26 ns) in the temperature range of 20–180 °C. Furthermore, a simulation model containing grains and grain boundaries was established to explain the enhanced BDS and the energy storage performance. Fine and uniform grains with many grain boundaries significantly hindered the propagation of breakdown cracks, yielding a higher BDS value. These results indicate that zSNBT ceramics are promising environmentally friendly materials for pulse power capacitor applications.

A comparative study of iron-vanadium and all-vanadium flow battery for large scale energy storage

The flow battery employing soluble redox couples for instance the all-vanadium ions and iron-vanadium ions, is regarded as a promising technology for large scale energy storage, benefited from its numerous advantages of long cycle life, high energy efficiency and independently tunable power and energy. An open-ended question associated with iron-vanadium and all-vanadium flow battery is which one is more suitable and competitive for large scale energy storage applications. This work attempts to answer this question by means of a comprehensively comparative study with respects to the electrochemical properties, charging-discharging tests, cycling performances and capital cost. The results shown that: i) the overall electrochemical properties of the two batteries are similar because of the limitation of the same negative couple; ii) the iron-vanadium flow battery is of lower energy efficiencies especially at high current densities (9% less at 150 mA cm−2), but superior self-discharge property; iii) the efficiencies of the two batteries are both of outstanding stabilities during long-term running, while the capacity of iron-vanadium flow battery is less stable; iv) The capacity of iron-vanadium flow battery can be recovered by renew the positive electrolyte with acceptable expenses; v) the iron-vanadium flow battery is cost-effective for long duration applications.

Recyclable, Self-Healing, and Flame-Retardant Solid-Solid Phase Change Materials Based on Thermally Reversible Cross-Links for Sustainable Thermal Energy Storage.

Conventional polymeric phase change materials (PCMs) exhibit good shape stability, large energy storage density, and satisfactory chemical stability, but they cannot be recycled and self-healed due to their permanent cross-linking structure. Additionally, the high flammability of organic PCMs seriously restricts their applications for thermal energy storage (TES). Therefore, it is urgently required to explore PCM composites exhibiting superior recyclability, good self-healing capability, and excellent flame retardancy simultaneously. Herein, tri-maleimide end-capped cyclotriphosphazene flame retardant (TMCTP) was synthesized via the nucleophilic substitution between 1,3,5,2,4,6-triazatriphosphorine-2,2,4,4,6,6-hexachloride and N-(2-hydroxyethyl)maleimide. Then, novel dynamically cross-linked PCM composites (FPCMs) with superior recyclability, good self-healing capability, and excellent flame retardancy were fabricated by bonding PEG and TMCTP to polymeric skeleton via reversible furan/maleimide Diels-Alder (DA) reaction. TMCTP, which covalently and dynamically binding in the polymeric FPCMs, acted not only as an efficient flame retardant for reducing the flammability of PCM composites but also as dynamic cross-linking skeletons for thermally induced self-healing and recycling. Differential scanning calorimetry (DSC) analysis confirmed the reversible energy storage and release ability of FPCMs. Due to its reversible DA covalent bonds, the introduction of TMCTP endowed the FPCMs with considerably increased self-healing efficiency (up to 93.1%) and recyclability efficiency (94.6%). Moreover, with the introduction of TMCTP into FPCMs, the heat release rate (HRR) and total heat release (THR) significantly decreased, while the char residue and limiting oxygen index (LOI) value increased, confirming that the flame retardancy of FPCMs greatly improved. Hence, the synthesized FPCMs show enormous potential in TES applications.

Thermochemical energy storage system development utilising limestone

For renewable energy sources to replace fossil fuels, large scale energy storage is required and thermal batteries have been identified as a commercially viable option. In this study, a 3.2 kg prototype (0.82 kWhth) of the limestone-based CaCO3-Al2O3 (16.7 wt%) thermochemical energy storage system was investigated near 900 °C in three different configurations: (i) CaCO3 was thermally cycled between 850 °C during carbonation and 950 °C during calcination whilst activated carbon was utilised as a CO2 gas storage material. (ii) The CaCO3 temperature was kept constant at 900 °C while utilising the activated carbon gas storage method to drive the thermochemical reaction. (iii) A mechanical gas compressor was used to compress CO2 into volumetric gas bottles to achieve a significant under/overpressure upon calcination/carbonation, i.e. ≤ 0.8 bar and > 5 bar, respectively, compared to the ∼1 bar thermodynamic equilibrium pressure at 900 °C. Scenarios (i) and (iii) showed a 64% energy capacity retention at the end of the 10th cycle. The decrease in capacity was partly assigned to the formation of mayenite, Ca12Al14O33, and thus the absence of the beneficial properties of the expected Ca5Al6O14 while sintering was also observed. The 316L stainless-steel reactor was investigated in regards to corrosion issues after being under CO2 atmosphere above 850 °C for approximately 1400 h, and showed no significant degradation. This study illustrates the potential for industrial scale up of catalysed CaCO3 as a thermal battery and provides a viable alternative to the calcium-looping process.

Thermodynamic and economic performance analysis of heat and power cogeneration system based on advanced adiabatic compressed air energy storage coupled with solar auxiliary heat

The advanced adiabatic compressed air energy storage system coupled with other systems not only has a high efficiency but also has the ability to produce heat and power simultaneously, which has great application potential. Reasonable allocation of heat generated by the system can improve the performance of the system. Therefore, a model of a cogeneration system based on advanced adiabatic compressed air energy storage coupled with solar auxiliary heat is proposed and five schemes of heat distribution are established. From the perspective of thermodynamics and economics, the performance of five heat distribution schemes (100%, 75%, 50%, 25%, 0%) is analysed and discussed. The effects of effectiveness of three types of heat exchangers, off-peak electricity and product prices on system performance are studied. In addition, the grey wolf algorithm is used for multi-objective optimization. The results show that the smaller the heat distribution ratio is, the greater the exergy efficiency and net present value. The large heat distribution ratio leads to a large energy storage density. The effect of the heat exchanger effectiveness on the system performance is different across different positions of the system. With the increase in on-peak electricity and hot water prices and the decline in low peak electricity price, the net present value increases. Under the optimal conditions, the ranges of the energy storage densities and the net present values of the five heat distribution schemes are 15.109∼17.466 MJ•m−3 and 13.992 × 107∼22.616 × 107$, respectively.