Low-Cost,Safe, and Ultra-Long Cycle Life Zn–K Hybrid Ion Batteries

Zinc-ion batteries (ZIBs) are viewed as a promising energy storage system for large-scale applications thanks to the low cost and wide accessibility of Zn-based materials, the high theoretical capacity of Zn anode, and their high level of safety. However, the practical application of ZIBs is hindered by the rapid performance degradation. Herein, a Zn–K hybrid ion battery design is proposed using a high-quality Prussian blue cathode and a nonflammable Zn–K hybrid ion electrolyte. The electrochemical process is divided into two parts, with K⁺ insertion/extraction occurring at the cathode side and Zn²⁺ plating/stripping occurring at the anode side, which avoids structure destruction caused by Zn²⁺ insertion in the cathode. The non-flammable electrolyte not only ensures high safety but also effectively suppresses dendrite growth on the Zn anode. The hybrid cells demonstrate a high capacity of 151.0 mAh g⁻¹, a high voltage of 1.74 V (vs Zn²⁺/Zn), and an ultra-long cycle life of 15 000 cycles. Combining the nonflammable nature of the electrolyte, the abundance of raw materials, and good electrochemical performance, the Zn–K hybrid ion battery system promises a promising future for renewable energy storage applications.     

Recently advances in flexible zinc ion batteries

Flexible batteries are key component of wearable electronic devices.Based on the requirements of medical and primary safety of wearable energy storage devices,rechargeable aqueous zinc ion batteries (ZIBs) are promising portable candid-ates in virtue of its intrinsic safety,abundant storage and low cost.However,many inherent challenges have greatly hindered the development in flexible Zn-based energy storage devices,such as rigid current collector and/or metal anode,easily de-tached cathode materials and a relatively narrow voltage window of flexible electrolyte.Thus,overcoming these challenges and further developing flexible ZIBs are inevitable and imperative.This review summarizes the most advanced progress in designs and discusses of flexible electrode,electrolyte and the practical application of flexible ZIBs in different environments.We also exhibit the heart of the matter that current flexible ZIBs faces.Finally,some prospective approaches are proposed to ad-dress these key issues and point out the direction for the future development of flexible ZIBs.     

Ultrafast Rechargeable Aqueous Zinc-Ion Batteries Based on Stable Radical Chemistry

Aqueous zinc-ion batteries (ZIBs) are a promising candidate for fast-charging energy-storage systems due to its attractive ionic conductivity of water-based electrolyte, high theoretical energy density, and low cost. Current strategies toward high-rate ZIBs mainly focus on the improvement of ionic or electron conductivity within cathodes. However, enhancing intrinsic electrochemical reaction kinetics of active materials to achieve fast Zn²⁺ storage has been greatly omitted. Herein, for the first time, stable radical intermediate generation is demonstrated in a typical organic electrode material (methylene blue [MB]), which effectively decreases the reaction energy barrier and enhances the intrinsic kinetics of MB cathode, enabling ultrafast Zn²⁺ storage. Meanwhile, anionic co-intercalation essentially avoids MB molecules rearranging their configuration and sharing Zn²⁺ with adjacent functional groups, thus keeps the structure stable. As a result, Zn–MB batteries exhibit an excellent rate capability up to 500C and ultralong life of 20 000 cycles with a negligible 0.07% capacity decay per cycle at 100C, which is superior to that of most reported aqueous ZIBs batteries. This work provides a novel strategy of stable radical chemistry for ultrafast-charging aqueous ZIBs, which can be introduced to other appropriate organic materials and multivalent ion battery systems.     

Liquid-State Cathode Enabling a High-Voltage and Air-Stable Fe-Al Hybrid Battery

Aluminum (Al) is an ideal anode material in low-cost battery system for energy storage, with high theoretical capacities. However, the sluggish Al³⁺-involved kinetics challenges the selection of common cathode materials (Al³⁺ intercalation or conversion). Herein, a redox-active Fe–Cl complex serves as the liquid-state cathode to couple with a low-cost Al anode, which synergizes the advantages of redox flow batteries and Al rechargeable batteries. The interplay of Fe-Cl coordinated formula and electrochemical properties are revealed for the first time. It is found that [Fe₂Cl₇]⁻ molecule has a high voltage versus Al anode (1.3 V), and the novel Fe-Al hybrid battery fulfills a capacity of 1.6 mAh cm⁻² (20 Ah L⁻¹) record high in a coin cell among Al-based batteries. Furthermore, the energy efficiency, which is a vital parameter to evaluate the energy cost of the energy storage technology, reaches 85% (superior to most Al-based batteries) and an average of 70% over ≈900 h cycling. Particularly, the unique air-stable character enables normal operation of the battery assembled in ambient air. This work establishes a new application scenario for Al anode toward low-cost large-scale energy storage.     

Ultrathin and Ultralight Zn Micromesh-Induced Spatial-Selection Deposition for Flexible High-Specific-Energy Zn-Ion Batteries

Ultraflexible and ultralight rechargeable aqueous Zn-ion batteries (ZIBs) with the merits of environmental benignity and high security arise as promising candidates for flexible electronic systems. Nowadays, the energy density and cyclical stability of ZIBs on metal-based rigid substrates reach a satisfactory level, while the inflexible substrates severely prevent them from widespread commercial adoption in portable electronics. Although flexible substrates-engineered devices burgeon, the development of flexible ZIBs with high specific energy still faces great challenges. Herein, a flexible ultrathin and ultralight Zn micromesh (thickness of 8 µm and areal density of 4.9 mg cm⁻²) with regularly aligned microholes is fabricated via combining photolithography with electrochemical machining. The unique microholes-engineered Zn micromesh presents excellent flexibility, enhanced mechanical strength, and better wettability. Moreover, numerical simulations in COMSOL and in situ microscopic observation system certify the induced spatial-selection deposition of Zn micromesh. Accordingly, aqueous ZIBs constructed with polyaniline-intercalated vanadium oxide cathode and Zn micromesh anode demonstrate exceptional high-rate capability (67.6% retention with 100 times current density expansion) and cyclical stability (maintaining 87.6% after 1000 cycles at 10.0 A g⁻¹). Furthermore, the assembled pouch cell displays superb flexibility and durability under different scenarios, indicating great prospects in high-energy ZIBs and flexible electronics.     

Pencil Drawing Stable Interface for Reversible and Durable Aqueous Zinc-Ion Batteries

Zinc-ion batteries (ZIBs) have been regarded as one of the most promising aqueous energy storage devices due to their low-cost, high capacity, and intrinsic safety. However, the relatively low Coulombic efficiency caused by the dendrite formation and side reactions greatly hinders the rejuvenation of ZIBs. Here, an utterly simple approach by pencil drawing is employed to improve the poor performance of normal Zn anode and hinders the formation of passivated byproduct as well as serious dendrite growth. Significantly, the functional graphite layer can not only act as ions buffer, but also guide the uniform nucleation of Zn²⁺ in graphite voids. With such synergy effect, the graphite-coated Zn anode (Zn–G) displays low overpotential, high reversibility, and dendrite-free durability compared with the pristine Zn. Consequently, a low voltage hysteresis of ≈ 28 mV can be achieved and maintained over 200 h. Furthermore, the Zn–G anode is paired with a V₂O₅·xH₂O cathode to construct a rechargeable ZIB. As-assembled device can output high energy/power density of 324.3 Wh kg⁻¹/3269.8 W kg⁻¹ (based on the active mass loading in cathode) together with a capacity retention of ≈ 84% over 1500 cycles at a current density of 5 A g⁻¹.     

Integrated Configuration Design Strategy Via Cathode-Gel Electrolyte With Forged Solid Electrolyte Interface Toward Advanced Lithium-Sulfurized Polyacrylonitrile Batteries

Li-SPAN batteries are a promising energy storage system, providing remarkable energy density and high Coulomb efficiency. However, the inherent sluggishness of the cathode's electrochemical kinetics and the instability of the Li anode hamper their cycle lifespan. In this study, a novel design of integrated configuration between cathode and electrolyte that addresses the challenges and promises to reshape the landscape of Li-SPAN, significantly enhancing the cycling stability, is presented. An artificial solid electrolyte interface (ASEI) is forged to simultaneously stabilize the Li anode and improve the interfacial compatibility, enabling an all-in-one battery system. A vertically aligned cathode structure is achieved using directional ice templating, enabling efficient Li-ion diffusion and enhancing electrochemical kinetics. The Li metal anode is coated with a MOF-on-COF ASEI, ensuring uniform Li⁺ deposition and high Li-ion transference number (0.86). Dual surface engineering further enhances the Li-SPAN cell, exhibiting a low capacity decay rate of 0.037% per cycle after 1000 cycles and superior C-rate performance. This study introduces promising strategies for effectively overcoming the challenges associated with the SPAN cathode and Li anode and paves the way for the design of high-performance Li-SPAN batteries, unlocking their full potential in the field of advanced energy storage systems.     

Voltage Hysteresis in Transition Metal Oxide Cathodes for Li/Na-Ion Batteries

The pursuit of rechargeable batteries with high energy density has triggered enormous efforts in developing cathode materials for lithium/sodium (Li/Na)-ion batteries considering their extremely high specific capacity. Many materials are being researched for battery applications, and transition metal oxide materials with remarkable electrochemical performance stand out among numerous cathode candidates for next-generation battery. Notwithstanding the merits, daunting challenges persist in the quest for further battery developments targeting lower cost, longer lifespan, improved energy density and enhanced safety. This is, in part, because the voltage hysteresis between the charge and discharge cycles, is historically avoided in intercalation electrodes because of its association with structural disorder and electrochemical irreversibility. Given the great potential of these materials for next-generation batteries, a review of the recent understanding of voltage hysteresis is timely. This review presents the origin of their undesirable behaviors and materials design criteria to mitigate them by integrating various schools of thought. A large amount of progressive characterization techniques related to voltage hysteresis are summarized from the literature, along with the corresponding measurable range used in their determination. Finally, promising design trends with eliminated voltage hysteresis are tentatively proposed to revive these important cathode materials toward practical applications.     

An Ultrastable Aqueous Iodine-Hydrogen Gas Battery

Rechargeable hydrogen gas batteries are highly desirable for large-scale energy storage because of their long life cycle, high round trip efficiency, fast reaction kinetics, and hydrogen gas profusion. Coupling advanced cathode chemistries with hydrogen gas anode is an emerging and exciting area of research. Here, a novel high-performance aqueous iodine-hydrogen gas (I₂-H₂) battery using iodine as cathode and hydrogen gas as the electrocatalytic anode in environmentally benign aqueous electrolytes is reported. The working chemistry of the battery involves I₂/I⁻ solid-liquid reactions occurring over the cathode along with H₂/H₂O gas-liquid reactions at the anode, achieving a high rate performance of 100 C and long-lasting stability of over 60 000 cycles. Additionally, the static aqueous I₂-H₂ battery displays a volumetric capacity of 15.5 Ah L⁻¹ along with good self-healing capability towards cell overcharge. The current battery design exhibits robust electrochemical performance irrespective of acidic, neutral, and alkaline electrolyte systems. This study paves the way towards the industrialization of economically effective, high-power density, and long-term I₂-H₂ batteries for large-scale energy storage applications.     

High Voltage,Transition Metal Complex Enables Efficient Electrochemical Energy Storage in a Li‐Ion Battery Full Cell

Efficient energy storage systems impact profoundly the renewable energy future. The performance of current electrical energy storage technologies falls well short of requirements for using electrical energy efficiently in transportation, commercial, and residential applications. This paper explores the possibility by using transition‐metal‐based complexes as active materials in a Li‐ion battery full cell that synergizes the concept of both lithium‐ion batteries and redox flow batteries. A cathode made from transition metal complex, [Fe(bpy)₃](BF₄)₂, exhibits high discharge voltage approaching 4 V (vs Li/Li⁺). When coupled with a Li₄Ti₅O₁₂ anode, the Li‐ion full battery exhibits a cell voltage exceeding 2.2 V and decent cycling efficiencies with Coulombic efficiency and energy/voltage efficiencies above 99% and 92%/93%, respectively. Such a Li‐ion battery full cell offers distinct features such as low cost and flexibility in molecular structure design. The result reveals a generic design route toward iron‐based complexes as cathode materials with good electrochemical performances.     

A Hybrid Supercapacitor Fabricated with a Carbon Nanotube Cathode and a TiO2–B Nanowire Anode

Recently, a new hybrid supercapacitor, integrating both the advantages of supercapacitors and lithium‐ion batteries, was proposed and rapidly turned into state‐of‐the‐art energy‐storage devices with a high energy density, fast power capability, and a long cycle life. In this paper, a new hybrid supercapacitor is fabricated by making use of the benefits of 1D nanomaterials consisting of a carbon nanotube (CNT) cathode and a TiO₂–B nanowire (TNW) anode, and the preliminary results for such an energy‐storage device operating over a wide voltage range (0–2.8 V) are presented. The CNT–TNW supercapacitor is compared to a CNT–CNT supercapacitor, and discussed with regards to available energy densities, power capabilities, voltage profiles, and cycle life. On the basis of the total weight of both active materials, the CNT–TNW supercapacitor delivers an energy density of 12.5 W h kg^–1 at a rate of 10 C, double the value of the CNT–CNT supercapacitor, while maintaining desirable cycling stability. The combination of a CNT cathode and a TNW anode in a non‐aqueous electrolyte is proven to be suitable for high‐performance hybrid supercapacitor applications; this can reasonably be assigned to the interesting synergistic effects of the two nanomaterials. It is hoped that the results presented in this study might renew interest in the design of nanomaterials that are applicable not only to hybrid supercapacitors, but also to energy conversion and storage applications of the future.     

Engineering Polymer Glue towards 90% Zinc Utilization for 1000 Hours to Make High-Performance Zn-Ion Batteries

Zinc (Zn) metal is considered the promising anode for “post-lithium” energy storage due to its high volumetric capacity, low redox potential, abundant reserve, and low cost. However, extravagant Zn is required in present Zn batteries, featuring low Zn utilization rate and device-scale energy/power densities far below theoretical values. The limited reversibility of Zn metal is attributed to the spontaneous parasitic reactions of Zn with aqueous electrolytes, that is, corrosion with water, passive by-product formation, and dendrite growth. Here, a new ion-selective polymer glue coated on Zn anode is designed, isolating the Zn anode from the electrolyte by blocking water diffusion while allowing rapid Zn²⁺ ion migration and facilitating uniform electrodeposition. Hence, a record-high Zn utilization of 90% is realized for 1000 h at high current densities, in sharp contrast to much poorer cyclability (usually < 200 h) at lower Zn utilization (50–85%) reported to date. When matched with the vanadium-based cathode, the resulting Zn-ion battery exhibited an ultrahigh device-scale energy density of 228 Wh kg⁻¹, comparable to commercial lithium-ion batteries.     

Finely Crafted 3D Electrodes for Dendrite‐Free and High‐Performance Flexible Fiber‐Shaped Zn–Co Batteries

Rechargeable aqueous Zn‐based batteries, benefiting from their good reliability, low cost, high energy/power densities, and ecofriendliness, show great potential in energy storage systems. However, the poor cycling performance due to the formation of Zn dendrites greatly hinders their practical applications. In this work, a trilayer 3D CC‐ZnO@C‐Zn anode is obtained by in situ growing ZIFs (zeolitic‐imidazolate frameworks) derived ZnO@C core–shell nanorods on carbon cloth followed by Zn deposition, which exhibits excellent antidendrite performance. Using CC‐ZnO@C‐Zn as the anode and a branch‐like Co(CO₃)_0.5(OH)_x·0.11H₂O@CoMoO₄ (CC‐CCH@CMO) as the cathode, a Zn–Co battery is rationally designed, displaying excellent energy/power densities (235 Wh kg^?1, 12.6 kW kg^?1) and remarkable cycling performance (71.1% after 5000 cycles). Impressively, when using a gel electrolyte, a highly customizable, fiber‐shaped flexible all‐solid‐state Zn–Co battery is assembled for the first time, which presents a high energy density of 4.6 mWh cm^?3, peak power density of 0.42 W cm^?3, and long durability (82% capacity retention after 1600 cycles) as well as excellent flexibility. The unique 3D electrode design in this study provides a novel approach to achieve high‐performance Zn‐based batteries, showing promising applications in flexible and portable energy‐storage systems.     

A Universal Strategy Toward Low-Cost Aqueous Sulfur–Iodine Batteries

Rechargeable aqueous batteries with non-toxic and non-flammable features are promising candidates for large-scale energy storage. However, their practical applications are impeded by the insufficient electrochemical stability windows of aqueous electrolytes and intrinsic drawbacks of current electrodes. Herein, an aqueous sulfur–iodine chemistry that can be deployed in aqueous battery systems by employing water-in-bisalt (WiBS) electrolyte, sulfur composite anode, and iodine composite cathode is demonstrated. The freestanding iodine/carbon cloth cathode and halide-containing WiBS electrolyte can support the continuous I⁺/I⁰ reaction by forming interhalogen. Meanwhile, the highly-concentrated electrolyte and inorganic-based solid electrolyte interphase can effectively suppress the dissolution/diffusion of polysulfides, thus realizing S/S_x²⁻ conversion reactions on the anode. Therefore, the as-assembled aqueous sulfur–iodine batteries based on S/S_x²⁻ and I⁺/I⁰ redox couples can deliver a high energy density of 158.7 Wh kg⁻¹ with a considerable cycling performance and safety. Furthermore, this chemistry can be further extended to multivalent ion-based battery systems. As demonstration models, Ca-based and Al-based aqueous sulfur–iodine batteries are also fabricated, which provide a new avenue towards the development of aqueous batteries for low-cost and highly safe energy storage.     

Stabilizing Solid Electrolyte Interphases on Both Anode and Cathode for High Areal Capacity,High‐Voltage Lithium Metal Batteries with High Li Utilization and Lean Electrolyte

High‐energy‐density lithium metal batteries are considered the most promising candidates for the next‐generation energy storage systems. However, conventional electrolytes used in lithium‐ion batteries can hardly meet the demand of the lithium metal batteries due to their intrinsic instability for Li metal anodes and high‐voltage cathodes. Herein, an ester‐based electrolyte with tris(trimethylsilyl)phosphate additive that can form stable solid electrolyte interphases on the anode and cathode is reported. The additive decomposes before the ester solvent and enables the formation of P‐ and Si‐rich interphases on both electrodes that are ion conductive and robust. Thus, lithium metal batteries with a high‐specific‐energy of 373 Wh kg^?1 can exhibit a long lifespan of over 80 cycles under practical conditions, including a low negative/positive capacity ratio of 2.3, high areal capacity of 4.5 mAh cm^?2 for cathode, high‐voltage of 4.5 V, and lean electrolyte of 2.8 µL mAh^?1. A 4.5 V pouch cell is further assembled to demonstrate the practical application of the tris(trimethylsilyl)phosphate additive with an areal capacity of 10.2 and 9.4 mAh cm^?2 for the anode and cathode, respectively. This work is expected to provide an effective electrolyte optimizing strategy compatible with current lithium ion battery manufacturing systems and pave the way for the next‐generation Li metal batteries with high specific energy and energy density.     

Suppressing Manganese Dissolution in Potassium Manganate with Rich Oxygen Defects Engaged High‐Energy‐Density and Durable Aqueous Zinc‐Ion Battery

The manganese dissolution leading to sharp capacity decline as well as the sluggish reaction kinetic are still major issues for manganese‐based materials as aqueous zinc‐ion batteries (ZIBs) cathodes. Here, a potassium‐ion‐stabilized and oxygen‐defect K_0.8Mn₈O₁₆ is reported as a high‐energy‐density and durable cathode for neutral aqueous ZIBs. A new insight into suppressing manganese dissolution via incorporation of K⁺ ions to intrinsically stabilize the Mn‐based cathodes is provided. A comprehensive study suggests that oxygen defects improve electrical conductivity and open the MnO₆ polyhedron walls for ion diffusion, which plays a critical role in the fast reaction kinetics and capacity improvement of K_0.8Mn₈O₁₆. In addition, direct evidence for the mechanistic details of simultaneous insertion and conversion reaction based on H⁺‐storage mechanism is demonstrated. As expected, a significant energy output of 398 W h kg^?1 (based on the mass of cathode) and an impressive durability over 1000 cycles with no obvious capacity fading are obtained. Such a high‐energy Zn‐K_0.8Mn₈O₁₆ battery, as well as the basic understanding of manganese dissolution and oxygen defects may open new opportunities toward high‐performance aqueous ZIBs.     

A Review of Emerging Dual-Ion Batteries: Fundamentals and Recent Advances

Dual-ion batteries (DIBs), based on the working mechanism involving the storage of cations and anions separately in the anode and cathode during the charging/discharging process, are of great interest beyond lithium-ion batteries (LIBs) in high-efficiency energy storage due to the merits of high working voltage, material availability, as well as low cost and excellent safety. Despite the progress achieved, the practical applications of DIBs are still hindered by negative issues, such as limited capacity and cyclic stability, which triggers the development of suitable electrode materials with highly reversible capacities, and corresponding electrolytes with high oxidative stability as well as sufficient reaction kinetics of active ions. Herein, in this article, a systematic and comprehensive review of fundamentals and recent advances in current DIBs with subcategories of cathode materials, anode materials, and electrolytes are presented. In particular, their energy storage mechanisms, as well as their respective features, are dissected. Furthermore, some strategies and perspectives are proposed for facilitating the further development of DIBs in the future.     

Biomimetic Honeycomb Zn Anode Enabled Multi-Field Regulation toward Highly Stable Flexible Zn-Ion Batteries

Flexible Zn-ion batteries (ZIBs) emerge as a promising entrant for flexible and safe energy systems in the post-Li era, while the instability of Zn anode including inferior flexibility, uncontrollable plating, and dendrite growth remains a challenge. Naturally inspired, a topology-optimized biomimetic honeycomb Zn (BH-Zn) anode through mechanical-electrochemical processing is demonstrated. Numerical simulations and experimental observations reveal the BH-Zn engenders smooth current–stress–thermal field distributions, concurrently realizing the multi-field regulation effect and boosted stability. After in situ alloying, the BH-Zn enables half-diminished voltage polarization, superior electrochemical stability of 2000 h cycling, and thermal stability even at 30 mA cm⁻². Moreover, the assembled ZIBs manifest over 20 times enhanced capacity retention and are integrated as a self-powered wearable system for real-time health monitoring. This strategy can be extended to customizable metal anodes and promises to be applied in stable flexible batteries.     

Rechargeable Magnesium–Sulfur Battery Technology: State of the Art and Key Challenges

Inspired by the first rechargeable Mg battery about 20 years ago, based on a Chevrel phase cathode, a Mg foil anode, and a magnesium organo‐aluminate electrolyte, research on rechargeable batteries using sulfur as the cathode together with Mg as the anode has gained substantial and increasing interest. In particular, the safety characteristics of magnesium–sulfur (Mg–S) batteries, the high abundance of both magnesium and sulfur, and the high theoretical volumetric energy density of magnesium render this system specifically interesting for mobile applications that require high volumetric energy densities, i.e., the automotive and aviation sector. While the development of Mg–S batteries is still at a nascent stage, some breakthroughs have already been accomplished. Consequently, it appears necessary to provide a comprehensive up‐to‐date review about the current achievements to facilitate further improvements in this field. In this review, the state of the art in Mg–S batteries is summarized, focusing on sulfur conversion cathodes, magnesium anode materials, currently employed electrolyte systems, as well as on current collectors and separator design. In addition, the challenges and some possible future work to realize a practically applicable and technically viable Mg–S battery are highlighted.     

Nanocellulose-Carboxymethylcellulose Electrolyte for Stable,High-Rate Zinc-Ion Batteries

Aqueous Zn ion batteries (ZIBs) are one of the most promising battery chemistries for grid-scale renewable energy storage. However, their application is limited by issues such as Zn dendrite formation and undesirable side reactions that can occur in the presence of excess free water molecules and ions. In this study, a nanocellulose-carboxymethylcellulose (CMC) hydrogel electrolyte is demonstrated that features stable cycling performance and high Zn²⁺ conductivity (26 mS cm⁻¹), which is attributed to the material's strong mechanical strength (≈70 MPa) and water-bonding ability. With this electrolyte, the Zn-metal anode shows exceptional cycling stability at an ultra-high rate, with the ability to sustain a current density as high as 80 mA cm⁻² for more than 3500 cycles and a cumulative capacity of 17.6 Ah cm⁻² (40 mA cm⁻²). Additionally, side reactions, such as hydrogen evolution and surface passivation, are substantially reduced due to the strong water-bonding capacity of the CMC. Full Zn||MnO₂ batteries fabricated with this electrolyte demonstrate excellent high-rate performance and long-term cycling stability (>500 cycles at 8C). These results suggest the cellulose-CMC electrolyte as a promising low-cost, easy-to-fabricate, and sustainable aqueous-based electrolyte for ZIBs with excellent electrochemical performance that can help pave the way toward grid-scale energy storage for renewable energy sources.