Large-scale Energy Storage Systems Research Articles

Improving High-Voltage Cycling Stability and High-Rate Capability of Sodium-Ion Layered Cathode Oxides through Trace Amounts of Low-Valence Metals.

With the increasing demand for clean energy sources, the need for large-scale energy storage systems to ensure the stable output of renewable energy sources, such as wind and solar, has also increased. Sodium-ion batteries have emerged as a potential solution for these storage systems owing to their high energy density, abundance in the Earth's crust, and low cost. However, the larger atomic radius of sodium ions results in higher energy barriers for ion migration in cathode materials, which can affect the cycle life and rate performance of the battery. Therefore, developing a suitable structure that facilitates rapid sodiation and desodiation and maintains good cycling stability remains a significant challenge. This study aimed to reduce the content of trivalent manganese ions and minimize the impact of the Jahn-Teller effect to enhance the capacity retention of manganese-based layered oxides. Additionally, a series of P2-type Na0.78Li0.1ZnxNi0.15-xMn0.75O2 compounds were successfully synthesized through doping with divalent zinc ions. Structural analyses of the doped material indicated that Zn doping did not alter the crystal structure but increased the interlayer distance of the transition metals. Electrochemical performance tests revealed that appropriate Zn2+ doping promoted sodium-ion diffusion and improved the reversible capacity of the battery. This study provides a promising approach for developing sodium-ion batteries with rapid charging and discharging capabilities.

The design of chemisorption and catalysis synergistic defender for efficient room temperature sodium-sulfur batteries

Room temperature sodium-sulfur (RT-Na/S) batteries are a promising candidate for large-scale energy storage systems owing to their low manufacturing cost and high energy density. However, the severe shuttle effects and sluggish reaction kinetics hinder their practical application. Here, a Fe3Se4 nanoparticle anchored three-dimensional nitrogen-doped porous carbon nanosheet was designed as a functional defender to inhibit the shuttle effect and achieve high sulfur utilization. The porous carbon nanosheet builds a fast platform for electron and ion transport and acts as a limiting barrier for polysulfide dissolution and shuttling. Additionally, Fe3Se4 nanoparticles are incorporated to enhance the chemical anchoring and catalytic activity of polysulfides. The ex-situ characterization revealed that the Fe sites can feed electrons to polysulfides, thus facilitating the conversion of long-chain polysulfides to Na2S, resulting in high sulfur availability (323 mAh/g at 2 A/g) and long-term cycle life (72 % capacity retention at 1 A/g for 500 cycles).

Rational design of amorphous vanadium pentoxide and hollow porous carbon spheres hybrid for superior zinc-ion battery

Aqueous zinc-ion batteries (AZIBs) are expected to be a promising large-scale energy storage system owing to their intrinsic safety and low cost. Nevertheless, the development of AZIBs is still plagued by the design and fabrication of advanced cathode materials. Herein, the amorphous vanadium pentoxide and hollow porous carbon spheres (AVO-HPCS) hybrid is elaborately designed as AZIBs cathode material by integrating vacuum drying and annealing strategy. Amorphous vanadium pentoxide provides abundant active sites and isotropic ion diffusion channels. Meanwhile, the hollow porous carbon sphere not only provides a stable conductive network, but also enhances the stability during charging/discharging process. Consequently, the AVO-HPCS exhibits a capacity of 474 mAh/g at 0.5 A/g and long-term cycle stability. Moreover, the corresponding reversible insertion/extraction mechanism is elucidated by ex-situ X-ray diffraction, X-ray photoelectron spectroscopy and transmission electron microscopy. Furthermore, the flexible pouch battery with AVO-HPCS cathode shows high comprehensive performance. Hence, this work provides insights into the development of advanced amorphous cathode materials for AZIBs.

Carbon Cloth Electrodes for Vanadium Redox Flow Batteries

Renewable energy sources such as wind and solar are playing an increasingly important role as the decarbonization of the energy industry moves forward. However, wind and solar-based energy production fluctuates daily and seasonally. For a stable electrical grid, a large-scale energy storage system is required. One promising technology for this is the Vanadium Redox Flow Battery (VRFB), developed in the late 1980s by Maria Skyllas-Kazacos (1), which has been continuously researched and improved over the last decades.VRFBs are already commercially available but must overcome significant lifetime and efficiency challenges. Polarization and pumping losses account for a large part of the efficiency losses due to the high flow-through resistance of the electrolyte in the electrode (2). Therefore, the electrode material must be optimized to achieve high catalytic activity and excellent flow properties to enhance the battery's performance.In a previous study, we identified key factors such as the electrode's structure, wettability, and electrochemical performance. Therefore, we developed a suitable set of characterization techniques (3). This multimodal characterization approach has been applied to evaluate woven and knitted carbon cloths. We designed electrode materials with specific fiber structures and weaving and knitting patterns. The raw material for the fibers is cellulose from hemp. To successfully commercialize VRVBs, the manufacturing process of the material must be low-cost and easy to fabricate on an industrial scale. Here, the electrode materials are fabricated by weaving or knitting, a well-established technique in the textile industry for centuries, and are ideally suited for the large-scale industrial production of electrodes. After weaving or knitting, the cloths are subsequently carbonized.To understand the influence of the fabrication pattern, the flow direction, and the 3D electrode structure on the flow behavior, we used Electrochemical Impedance Spectroscopy (EIS) coupled with the Distribution of Relaxation Times (DRT) analysis (4,5). This method allows simultaneously investigating the electrochemical performance, wettability, and structure in an application-oriented, in-house-designed setup. To develop a deeper understanding of the microscopic structure of the fiber and its influence on the key factors, Scanning Electron Microscopy (SEM) and nano-X-ray computed tomography (nano-CT) were utilized. These results were combined with Dynamic Vapor Sorption measurements (DVS), which are used to investigate the wettability of the material, and Cyclic Voltammetry (CV), which accesses the electrochemical performance. Additionally, we studied the effect of thermal activation on these parameters with EIS and DRT analysis, SEM, nano-CT, DVS, CV, and X-ray photoelectron spectroscopy.The materials presented in this paper exhibited excellent electrode performance, demonstrating good wettability, high catalytic activity, and large electrochemically active surface area. These are promising examples of electrode engineering as a pathway to optimal designs of VRFBs.1. M. Skyllas‐Kazacos, M. Rychcik, R. G. Robins, A. G. Fane and M. A. Green, J. Electrochem. Soc., 133(5), 1057–1058 (1986).2. N. Bevilacqua, L. Eifert, R. Banerjee, K. Köble, T. Faragó, M. Zuber, A. Bazylak and R. Zeis, Journal of Power Sources, 439, 227071 (2019).3. K. Köble, M. Jaugstetter, M. Schilling, M. Braig, T. Diemant, K. Tschulik and R. Zeis, Journal of Power Sources, 569, 233010 (2023).4. M. Schilling, M. Braig, K. Köble and R. Zeis, Electrochimica Acta, 430, 141058 (2022).5. M. Schilling and R. Zeis, submitted. Figure 1

(Invited) Organosilicon Coatings Made By a Cold Plasma Processes at Atmospheric Pressure for Electrochemical Applications

Cell manufacturing is estimated to account for up to 40% of battery-industry and the related market will grow 14.1% in the next five years (108.4 B$ in 2019). In this context, high-power and stationary large-scale energy storage systems, such as lithium-ion batteries (LiBs), will be essential to make electricity quickly accessible to the power grid. This is particularly true when it comes to power plants located in remote areas or the use of renewable energy sources. Despite their advantages, commercial LiBs are today limited by their environmental and safety hazards. These limitations lead researchers around the world to discover and employ new technologies for safe recycling operations and a better control of the cycling processes. Currently, works are focused on the development of new advanced materials, composite design as well as advanced interfacial layers. In this context, surface modification by cold plasma is one of the most promising solutions to control and modify charge transport mechanisms at the interfaces. Although, the synthesis of nano-layers made by plasma at atmospheric pressure has already received a lot of interest, their use to modify electrochemical devices, such as electrochemical cells remain limited. In this work, the synthesis of organosilicon coatings on composite conductive layers by atmospheric pressure DBD is studied in detail. The influence of different organosilicon molecules has been analysed to highlight the effect of the growth mode as well as chemical functionalities on the operation of the final electrochemical device. The physical and chemical modifications of plasma on the conductive layer as well as the water stability of the coatings were investigated by ATR-FTIR, XRD, SEM and contact angle. Figure 1

Concentrated Chloride Electrolyte Enabling SEI for Fe Metal Anode

Iron is one of the most abundant metal elements in the Earth’s crust and has been widely used worldwide since ancient times. Due to this natural abundance and well-established mass production methods, iron is a promising candidate as a battery electrode for cost-effective large-scale energy storage systems. Edison’s Ni-Fe battery, invented in 1900, used an alkaline electrolyte without ferrous or ferric ions that eventually limited its anode design using iron oxide. More recent Fe redox flow batteries and the newly suggested Fe-ion batteries that use an acidic electrolyte containing ferrous ions (Fe2+) can utilize iron foil as an anode. Combining iron foil with Fe2+ electrolyte enables a simple design and faster kinetics on the anode side. However, introducing acidic electrolytes accelerates hydrogen evolution reaction (HER) on the iron surface. Severe HER affects cell performance in various ways, including lower Coulombic efficiency (CE), drying out of the electrolyte by water consumption, and precipitation of Fe2+ ions due to increased pH of the electrolyte. In this work, a concentrated chloride-based electrolyte was introduced to Fe-ion batteries to suppress HER and achieve a high-CE Fe2+/Fe electrode. With the help of nonpolar [ZnCl4]2- which enables low-polarity organic additives to be soluble in the aqueous solution, an organic solid electrolyte interface (SEI) can be formed on top of the electrode while plating iron. Fe anode protected by the SEI shows a noticeable decrease in HER during cycling, which leads to higher CE of more than 98% and twice longer cycle life.

Regulated Interfacial Proton and Water Activity Enhances Mn2+/MnO2 Platform Voltage and Energy Efficiency

Aqueous zinc battery (AZB) is one of the most promising energy storage systems for large-scale applications due to its high safety, low cost, and environmental friendliness. To match the high capacity of zinc metal (~820 mAh g-1), various cathode materials, such as oxides, open structure analogues, chalcogens, and halogens, have been explored for AZBs. Among them, manganese dioxide (MnO2) has been considered to be one of the most attractive candidates due to its high capacity (~308 mAh g-1 for one-electron transfer) and adequate redox potential (~0.70 V vs. SHE). Recently, the MnO2 dissolution/deposition charge storage mechanism has been demonstrated to further increase the voltage and capacity of Mn-based AZBs. The dissolution/deposition (Mn2+/MnO2) is a two-electron transfer process, which doubles the theoretical capacity of MnO2 cathode to ~616 mAh g-1 and considerably increases the redox potential (~1.229 V vs. SHE). The charge storage via the dissolution/deposition mechanism pushes the aqueous-based energy density even higher, to over 1000 Wh kg-1.However, this charge storage mechanism involves liquid-solid transition, as well as the thermodynamics and kinetics of this reaction are highly dependent on the acidity and interfacial environment. Yet, the opposite effect of interfacial H+ on the dissolution/deposition processes and the role of interfacial H2O are rarely discussed. Here we introduce tetrafluoroborate anion (BF4 -) into the sulfate-based electrolyte to regulate the interfacial H+ and H2O activity. First, BF4 - hydrolysis increases the electrolyte’s acidity, promoting MnO2 dissolution. Second, BF4 - forms an H-bond network with interfacial H2O that assists H+ diffusion while retaining sufficient H2O supply to facilitate MnO2 deposition. As a result, the cathode-free Zn//MnO2 electrolytic cell achieves a high plateau of ~1.92 V and energy efficiency of ~84.23 % in the BF4 - containing electrolyte. Significantly, the cell delivers 1000 cycles at 1 C with ~100 % Coulombic efficiency and a high energy efficiency retention of 93.65 %. Our findings disclose a new strategy to promote Mn2+/MnO2 platform voltage and energy efficiency for future large-scale energy storage systems.

Amorphous Cobalt Tin Oxide/Reduced Graphene Oxide Decorated on Graphite Felt as Positive Electrode for Vanadium Redox Flow Battery

The Vanadium Redox Flow Battery (VRFB) stands out as one of the most promising large-scale energy storage systems. Nevertheless, the graphite electrode materials commonly used in VRFBs often exhibit drawbacks such as limited electrochemical activity and insufficient conductivity, ultimately resulting in suboptimal performance for the VRFB. In this study, we utilized highly conductive reduced graphene oxide (rGO) as a carrier for cobalt tin oxide (CoSnO3), aiming to enhance their catalytic capability towards vanadium ions. CoSnO3/rGO composite was confirmed using XRD and TEM, revealing nanoboxes morphology and amorphous structure. XPS and EPR analysis showed an increase in oxygen vacancies after composite formation. In order to further prove the effect of CoSnO3/rGO composite catalyst modified graphite felt, the modified graphite felt electrode was applied to the positive electrodes of VRFB, and the charge and discharge tests at different current densities were carried out. At a current density of 160 mA/cm², the composite demonstrated a voltage efficiency of 74.22%, surpassing the heat treated graphite felt by 2.69%. Noteworthy enhancements in capacitance were also evident at this specific current density. Furthermore, stability testing over 50 cycles revealed no significant degradation, underscoring the superior performance and outstanding durability of the CoSnO3-rGO modified graphite felt throughout charge and discharge cycling. The result of this study highlight the promising potential of CoSnO3-rGO composites as efficient catalysts for vanadium redox flow batteries, providing improvements in electrochemical performance and long-term stability.

Design and Characterization of Porous Electrodes for Redox Flow Batteries

The commercialization of redox flow batteries as large-scale energy storage systems depends on lowering the capital and operating costs which depend on achieving maximum power density. Optimizing electrode design parameters and flow field-electrode combinations is critical to minimize losses and maximize active material utilization. Modeling the current drawn from an electrode offers a means to interpret electrode structure based on the electrolyte distribution driven by internal design. However, direct imaging methods (such as in-situ fluorescence microscopy and X-ray tomography) and numerical methods for current to potential prediction (3D Lattice Boltzmann modeling) are specific to individual electrode structures and possess limited predictable value to obtain an ideal electrode design. In this work, we present an electrode impedance spectroscopy (EIS)-based approach for determining electrode design parameters and devise a general method for determination of effective diffusion layer thickness. Using COMSOL modeling we verified the development of slug flow behavior in highly randomized porous electrode systems, indicating that the mass transport properties are dictated by inter-fiber distance. An analytical model to predict current as a function of applied overpotential is presented which allows us to vary structural parameters of the porous electrodes to study the influence of surface area, inter-fiber distances and diffusion layer thickness on the RFB performance. This model is a highly flexible tool applicable to any electrochemical system using a porous electrode and identifies critical variables affecting electrode design to characterize optimal electrode structure to minimize mass transport losses and optimize operational parameters.

Nature-Derived Sulfur Carbons for Highly-Efficient Room Temperature Sodium-Sulfur Energy Storage

In recent years, a growing interest in “beyond-Li-ion“ batteries has caused a speedy development of alternative battery technologies based on other alkali metals. Room temperature sodium sulfur (RT Na-S) batteries are potential candidate for sustainable large-scale energy storage systems. They offer low cost, nontoxicity and natural abundance of both cathode and anode materials combined with high theoretical energy density. However, rapid capacity fading related to the irreversible shuttling of soluble polysulfides, poor reaction kinetics and low sulfur utilisation in the cathode materials significantly limit their practical application.In this work, a microporous sulfur-carbon complex is produced from sustainable natural precursors in a one-pot synthesis via stepwise thermally-induced inverse vulcanisation and condensation. The material exhibits a unique structure, with sulfur chains covalently anchored to the conductive carbon matrix and physically confined in ultra-micropores. An increase in sulfur content in the sulfur-copolymer alters the morphology and chemical composition of the final sulfur-carbon material, enhancing the amount of long-chain sulfur. The combination of optimal microstructure, good electrical conductivity and high content of electrochemically active sulfur translates to an unprecedented ~99% utilisation of sulfur and the highest reported capacity for a room temperature Na-S cathode, along with high rate capability, coulombic efficiency and long-term stability. This study offers an innovative approach towards the understanding of the key chemico-physical properties of the sulfur-carbon composite materials for the development of high-performance cathodes in RT Na-S batteries with an atom-efficient utilisation of sulfur.

Progress on Copper-Based Anode Materials for Sodium-Ion Batteries.

Fossil fuels have clearly failed to meet people's growing energy needs due to their limited reserves, potential pollution of the environment, and high costs. The development of cleaner, renewable energy sources as well as secondary batteries for energy storage is imminent, in a modern society where energy demand is soaring. Sodium-ion batteries (SIBs) have become the focus of large-scale energy storage systems as a promising alternative to lithium-ion batteries. The development of SIBs relies on the construction of high performance electrode materials. The design of low cost and high performance anode materials is a key link in this regard. Copper-based anodes are characterized by high theoretical capacity, abundant reserves, low cost and environmental friendliness. A variety of copper-based anode materials, which include cobalt oxides, sulfides, selenides and phosphides, have been synthesized and evaluated in the scientific literature for sodium storage. In detail, the preparation methods, response mechanisms, strengths and weaknesses, the relationship between morphology structure and electrochemical performance are discussed, as well as highlighting strategies to improve the electrochemical performance of copper-based anode materials. Finally, we offer our perspective on the challenges and potential for the development of copper-based anodes as a means of developing practical and high performing SIBs.

Optimizing the design of parallel busbars to suppress the Taylor Instability in large-scale liquid metal batteries

Abstract In this study, we utilize the open-source software OpenFOAM to numerically simulate the Tayler instability in liquid metal batteries. The simulation depicts the dynamic evolution of the electrolyte layer, fluid flow, and magnetic field distribution in the battery at different operating times. Special attention is paid to the influence of optimizing the parallel busbar configuration on Tayler instability and battery capacity. It is found that the additional magnetic field generated by the busbars can effectively alter the magnetic field distribution inside the battery, thereby significantly reducing the Lorentz force and suppressing the Tayler instability within the battery. Therefore, by optimizing the parallel busbar configuration, the stable operating time of the battery is prolonged, and the battery capacity is enhanced. This study provides theoretical support and practical guidance for the application of liquid metal batteries in large-scale grid-level energy storage systems and offers new insights into the development of energy storage technology.

Regulation on reacting solvent engineering for scalable synthesis of Na3(VOPO4)2F@carbon nanotubes microsphere cathodes towards high-power and long-lifespan Na-ion batteries

Na3(VOPO4)2F (NVOPF) has emerged as a promising cathode candidate for commercial Na-ion batteries, ascribed to its elevated theoretical energy density and robust structure during the extraction/insertion of two Na+ ions. However, the intrinsic poor electronic conductivity and unscalable materials-preparation technologies make it unexpected to stand out in large-scale energy storage systems. In this study, a spray-drying process technology is implemented to synthesize Na3(VOPO4)2F@carbon nanotubes (NVOPF@CNTs) composite through the reduction of V5+ driven by methanol at room temperature, in which the shortened Na-ion transfer path and the rapid electron mobility are facilitated by the CNTs. The resulting NVOPF@CNTs electrode exhibits exceptional capabilities, including a high discharge capacity (122.1 mA h g−1 at 1 C= 120 mA h g−1), outstanding rate performance (103.1 mA h g−1 at 100 C), and an extended lifespan (71.8 % capacity retention after 6000 cycles at 20 C). Additionally, the Na3(VOPO4)2F//NaTi2(PO4)3 full battery system demonstrates impressive high-power output capabilities (93.3 mA h g−1, 20 C), versatile current switching adaptability, and robust cycling performance (75.3 % of 98.5 mA h g−1 for the initial capacity after 3000 cycles). The study underscores the potential of improving the preparation of vanadium-based phosphate materials to enhance the practical application of Na-ion batteries.

Assessment of carbon dioxide transcritical cycles for electrothermal energy storage with geological storage in salt cavities

Carbon capture, utilisation, and storage (CCUS) technologies are envisaged as critical actors in the energy transition and climate change mitigation framework. Despite the recent advances in CCUS implementation, there is still significant scope for their growth and improvement. On the other hand, developing new large-scale energy storage systems is a key factor for the massive deployment of renewable energy systems. Technologies such as the electrothermal energy storage system based on carbon dioxide transcritical cycles incorporating geological storage (CEEGS) can contribute to both fields. Preliminary studies have shown that the integrated storage system can operate with roundtrip efficiencies exceeding 50%, injecting over 1 million tons of captured carbon dioxide (CO2) annually. It is an early-stage technology with open challenges for successful development, such as an adequate balance between the high- and low-temperature thermal storage reservoirs or the operation definition between the electrothermal system and the carbon dioxide injection and recovery. Underground pressures will oscillate with the charge/discharge process, with operational implications and constraints. Advancing in the concept requires the definition of optimised operation. This work presents a novel analysis of the adaptation of CO2 transcritical cycles to include injection and production processes with the specific scenario of salt cavities. It considers new modifications to adapt the transcritical cycles in closed-mode operation to the conditions required by the salt cavities injection and production processes. Different case studies are evaluated, evaluating the impact of injection and geological storage, production and surface storage, and reinjection into the geological formation. The analyses show roundtrip efficiencies within the range of 49.1–73.0% when the injection, production, and reinjection processes are executed.

Engineering ternary hydrated eutectic electrolytes to realize rechargeable cathode-free aluminum-ion batteries

Aluminum-ion batteries (AIBs) have been highlighted as a promising candidate for large-scale energy storage due to the abundant reserve, low cost, high specific capacity, and good safety of aluminum. However, the development of AIBs is hindered by the usage of expensive, corrosive, and humidity-sensitive AlCl3-based ionic liquid electrolytes. Herein, we develop a low-cost, non-corrosive, and air-stable ternary hydrate eutectic electrolyte (HEE) composed of aluminum nitrate hydrate, manganese nitrate hydrate, and N,N-dimethylacetamide for cathode-free AIBs. The solvation structure of metal cations and water state in the electrolyte are regulated through the coordination of both water and N,N-dimethylacetamide molecules. The unique structural features of the HEE enables reversible deposition/stripping of AlxMnO2 on the cathodic current collector that are confirmed by various in-situ and ex-situ characterizations, ultimately realizing cathode-free AIBs. The architected cathode-free AIB delivers a discharge specific capacity of 361 mAh g−1 and shows good cycling stability and high air stability. This study provides a valuable insight into the design of rechargeable multi-valent metal ion batteries for advanced large-scale energy storage systems.

Origins of High Air Sensitivity and Treatment Strategies in O3-Type NaMn1/3 Fe1/3Ni1/3O2.

Sodium-ion layered oxides are one of the most highly regarded sodium-ion cathode materials and are expected to be used in electric vehicles and large-scale grid-level energy storage systems. However, highly air-sensitive issues limit sodium-ion layered oxide cathode materials to maximize cost advantages. Industrial and scientific researchers have been developing cost-effective air sensitivity treatment strategies with little success because the impurity formation mechanism is still unclear. Using density functional theory calculations and ab initio molecular dynamics simulations, this work shows that the poor air stability of O3-type NaMn1/3Fe1/3Ni1/3O2 (NMFNO) may be as follows: (1) low percentage of nonreactive (003) surface; (2) strong surface adsorption capacity and high surface reactivity; and (3) instability of the surface sodium ions. Our physical images point out that the high reactivity of the NMFNO surface originates from the increase in electron loss and unpaired electrons (magnetic moments) of the surface oxygen active site as well as the enhanced metal coactivation effect due to the large radius of the sodium ion. We also found that the hydrolysis reaction requires a higher reactivity of the surface oxygen active site, while the carbon hybridization mode transformation in carbonate formation depends mainly on metal activation and does not even require the involvement of surface oxygen active sites. Based on the calculation results and our proposed physical images, we discuss the feasibility of these treatment strategies (including surface morphology modulation, cation/anion substitution, and surface configuration design) for air-sensitive issues.

Thermodynamic and Exergoeconomic Analysis of a Novel Compressed Carbon Dioxide Phase-Change Energy Storage System

As an advanced energy storage technology, the compressed CO2 energy storage system (CCES) has been widely studied for its advantages of high efficiency and low investment cost. However, the current literature has been mainly focused on the TC-CCES and SC-CCES, which operate in high-pressure conditions, increasing investment costs and bringing operation risks. Meanwhile, some studies based on the phase-change CO2 energy storage system also have had the disadvantages of low efficiency and the extra necessity of heat or cooling sources. To overcome the above problems, this paper proposes an innovative compressed CO2 phase-change energy storage system. During the energy charge process, molten salt and water are used to store heat with a smaller temperature difference in heat exchangers, and high-pressure CO2 is reserved in liquid form. During the energy discharge process, throttle expansion is applied to realize the evaporation at room temperature, and CO2 absorbs the reserved heat to improve the power capacity in the turbine and the system energy storage efficiency. The thermodynamic and exergoeconomic studies are performed firstly by using MATLAB. Then, the parametric study based on energy storage efficiency, system unit product cost, and exergy destruction is analyzed. The results show that energy storage efficiency can be improved by lifting liquid CO2 pressure as well as compressor and turbine isentropic efficiencies, and CO2 evaporation pressure has the optimal pressure point. The system unit product cost can be reduced by decreasing liquid CO2 pressure and compressor isentropic efficiency, while CO2 evaporation pressure and turbine isentropic efficiency both have optimal points. Finally, the optimization of two performances is performed by NSGA-II, and they can reach 75.30% and 41.17 $/GJ, respectively. Moreover, the optimal energy storage efficiency is obviously higher than that of other energy storage technologies, indicating the great advantage of the proposed system. This study provides an innovative research method for a new type of large-scale energy storage system.

Suppressing Formation of Zn─Mn─O Phases by In Situ Ti Decoration of MnO2 for Long Lifespan MnO2-Zn Battery.

Mildly-acidic MnO2-Zn batteries are considered as a promising alternative for large-scale energy storage systems for their low toxicity, high safety, and low cost. Though, the degradation of MnO2 with cycling still hinders the further development of the batteries. In this study, it is observed that the decrease in available capacity of MnO2 with charge and discharge is accompanied by a structural transformation with the emergence of Zn─Mn─O phases. An electrodeposition test indicates that the Zn─Mn─O phase is formed from a co-precipitation of Zn and Mn during the charge process. Further, the structural change of MnO2 is suppressed and its cycle stability is improved with the addition of TiOSO4 as a facile electrolyte additive. As a result, under a current of 1200mA g-1, the MnO2 electrode still gives a capacity of 230 mAh g-1 for over 1500 cycles. Capacity retention is 75% after 10000 cycles under a current rate of 4800mA g-1. These findings provide fundamental insights on the degradation mechanism of MnO2 and a new strategy to improve the electrochemical performance of aqueous MnO2-Zn batteries.

The zinc ion concentration dynamically regulated by an ionophore in the outer Helmholtz layer for stable Zn anode

The Zn dendrite limits the practical application of aqueous zinc-ion batteries in the large-scale energy storage systems. To suppress the growth of Zn dendrites, a zinc ionophore of hydroxychloroquine (defined as HCQ) applied in vivo treatment is investigated as the electrolyte additive. HCQ dynamically regulates zinc ion concentration in the outer Helmholtz layer, promoting even Zn plating at the anode/electrolyte interface. This is evidenced by the scanning electron microscopy, which delivers planar Zn plating after cycling. It is further supported by the X-ray diffraction spectroscopy, which reveals the growth of Zn (002) plane. Additionally, the reduced production of H2 during Zn plating/stripping is detected by the in-situ differential electrochemical mass spectrometry (DEMS), which shows the resistance of Zn (002) to hydrogen evolution reaction. The mechanism of dynamic regulation for zinc ion concentration is demonstrated by the in-situ optical microscopy. The hydrated zinc ion can be further plated more rapidly to the uneven location than the case in other regions, which is resulted from the dynamic regulation for zinc ion concentration. Therefore, the uniform Zn plating is formed. A cycling life of 1100 h is exhibited in the Zn||Zn symmetric cell at 1.6 mA cm−2 with the capacity of 1.6 mAh cm−2. The Zn||Cu battery exhibits a cycling life of 200 cycles at 4 mA cm−2 with a capacity of 4 mAh cm−2 and the average Coulombic efficiency is larger than 99 %. The Zn||VO2 battery with HCQ modified electrolyte can operate for 1500 cycles at 4 A g−1 with a capacity retention of 90 %. This strategy in the present work is wished to advance the development of zinc-ion batteries for practical application.

CVD Grown CNTs-Modified Electrodes for Vanadium Redox Flow Batteries.

Vanadium redox flow batteries (VRFBs) are of considerable importance in large-scale energy storage systems due to their high efficiency, long cycle life and easy scalability. In this work, chemical vapor deposition (CVD) grown carbon nanotubes (CNTs)-modified electrodes and Nafion 117 membrane are utilised for formulating a vanadium redox flow battery (VRFB). In a CVD chamber, the growth of CNTs is carried out on an acid-treated graphite felt surface. Cyclic voltammetry of CNT-modified electrode and acid-treated electrode revealed that CNTs presence improve the reaction kinetics of V3+/V2+ and VO2+/VO2+ redox pairs. Battery performance is recorded for analysing, the effect of modified electrodes, varying electrolyte flow rates, varying current densities and effect of removing the current collector plates. CNTs presence enhance the battery performance and offered 96.30% of Coulombic efficiency, 79.33% of voltage efficiency and 76.39% of energy efficiency. In comparison with pristine electrodes, a battery consisting CNTs grown electrodes shows a 14% and 15% increase in voltage efficiency and energy efficiency, respectively. Battery configured without current collector plates performs better as compared to with current collector plates which is possibly due to decrease in battery resistance.