Nickel-hydrogen batteries for large-scale energy storage

Integrating hydrogen utilization in CO2 electrolysis with reduced energy loss

Electrochemical carbon dioxide reduction reaction using sustainable energy is a promising approach of synthesizing chemicals and fuels, yet is highly energy intensive. The oxygen evolution reaction is particularly problematic, which is kinetically sluggish and causes anodic carbon loss. In this context, we couple CO2 electrolysis with hydrogen oxidation reaction in a single electrochemical cell. A Ni(OH)2/NiOOH mediator is used to fully suppress the anodic carbon loss and hydrogen oxidation catalyst poisoning by migrated reaction products. This cell is highly flexible in producing either gaseous (CO) or soluble (formate) products with high selectivity (up to 95.3%) and stability (>100 h) at voltages below 0.9 V (50 mA cm-2). Importantly, thanks to the "transferred" oxygen evolution reaction to a water electrolyzer with thermodynamically and kinetically favored reaction conditions, the total polarization loss and energy consumption of our H2-integrated CO2 reduction reaction, including those for hydrogen generation, are reduced up to 22% and 42%, respectively. This work demonstrates the opportunity of combining CO2 electrolysis with the hydrogen economy, paving the way to the possible integration of various emerging energy conversion and storage approaches for improved energy/cost effectiveness.

An All-Climate Nonaqueous Hydrogen Gas-Proton Battery

Rechargeable hydrogen gas batteries, driven by hydrogen evolution and oxidation reactions (HER/HOR), are emerging grid-scale energy storage technologies owing to their low cost and superb cycle life. However, compared with aqueous electrolytes, the HER/HOR activities in nonaqueous electrolytes have rarely been studied. Here, for the first time, we develop a nonaqueous proton electrolyte (NAPE) for a high-performance hydrogen gas-proton battery for all-climate energy storage applications. The advanced nonaqueous hydrogen gas-proton battery (NAHPB) assembled with a representative V2(PO4)3 cathode and H2 anode in a NAPE exhibits a high discharge capacity of 165 mAh g-1 at 1 C at room temperature. It also efficiently operates under all-climate conditions (from -30 to +70 °C) with an excellent electrochemical performance. Our findings offer a new direction for designing nonaqueous proton batteries in a wide temperature range.

Non-Noble Metal High-Entropy Alloy-Based Catalytic Electrode for Long-Life Hydrogen Gas Batteries

The development of efficient, stable, and low-cost bifunctional catalysts for the hydrogen evolution/oxidation reaction (HER/HOR) is critical to promote the application of hydrogen gas batteries in large scale energy storage systems. Here we demonstrate a non-noble metal high-entropy alloy grown on Cu foam (NNM-HEA@CF) as a self-supported catalytic electrode for nickel-hydrogen gas (Ni-H2) batteries. Experimental and theoretical calculation results reveal that the NNM-HEA catalyst greatly facilitates the HER/HOR catalytic process through the optimized electronic structures of the active sites. The assembled Ni-H2 battery with NNM-HEA@CF as the anode shows excellent rate capability and exceptional cycling performance of over 1800 h without capacity decay at an areal capacity of 15 mAh cm-2. Furthermore, a scaled-up Ni-H2 battery fabricated with an extended capacity of 0.45 Ah exhibits a high cell-level energy density of ∼109.3 Wh kg-1. Moreover, its estimated cost reaches as low as ∼107.8 $ kWh-1 based on all key components of electrodes, separator and electrolyte, which is reduced by more than 6 times compared to that of the commercial Pt/C-based Ni-H2 battery. This work provides an approach to develop high-efficiency non-noble metal-based bifunctional catalysts for hydrogen batteries in large-scale energy storage applications.

Zn-ion Batteries: Charge Storing Mechanism and Development Challenges

Improving the energy share of renewable energy technologies is the only solution to reduce greenhouse gas emissions and air pollution. The high-performing green battery energy storage technologies are critical for storing energy to address the intermittent nature of renewable energy resources. In recent years, aqueous batteries, particularly Zn-ion batteries (ZIBs), have achieved and shown great potential for stationary energy storage systems owing to their low cost and safer operation. However, the practical applications of the ZIBs have significantly been impeded due to the gap between the breakthroughs achieved in academic research and industrial developments. The present review discusses the ZIB's advantages, possibilities, and shortcomings for stationary energy storage systems. The Review begins with a brief introduction to the ZIBs and their charge storage mechanisms based on the structural properties of cathode materials. The scientific and technical challenges that obstruct the commercialization of the ZIBs are discussed in detail concerning their impact on accelerating the utilization of the ZIBs for real-life applications. The final section highlights the outlook on research in this flourishing field.

Ion Tunnel Matrix Initiated Oriented Attachment for Highly Utilized Zn Anodes

Metallic zinc is an ideal anode for aqueous energy storage; however, Zn anodes suffer from nonhomogeneous deposition, low reversibility, and dendrite formation; these lead to an overprovision of zinc metal in full cells. Herein, oriented-attachment-regulated Zn stacking initiated through a trapping-then-planting process with a high zinc utilization rate (ZUR) is reported. Due to the isometric topology features of cubic-type Prussian blue analog (PBA), the initial Zn plating occurs at specific sites with equal spacing of ≈5 Å in the direction perpendicular to the substrate; the trace amount of zinc ions trapped in tunnel matrix provides nuclei for the oriented attachment of Zn (002) deposits. As a result, the PBA-decorated substrate delivers high reversibility of dendrite-free zinc plating/stripping for more than 6600 cycles (1320 h) and achieves an average Coulombic efficiency (CE) of 99.5% at 5 mA cm-2 with 100% ZUR. Moreover, the anode-limited full cell with a low negative-positive electrode ratio (N/P) of 1.2 can be operated stably for 360 cycles, displaying an energy density of 214 Wh kg-1 ; this greatly exceeds commercial aqueous batteries. This work provides a proof of concept design of metal anodes with a high utilization ratio and a practical method for developing high-energy-density batteries.

Ultrafast Electrical Pulse Synthesis of Highly Active Electrocatalysts for Beyond-Industrial-Level Hydrogen Gas Batteries

The high reliability and proven ultra-longevity make aqueous hydrogen gas (H2 ) batteries ideal for large-scale energy storage. However, the low alkaline hydrogen evolution and oxidation reaction (HER/HOR) activities of expensive platinum catalysts severely hamper their widespread applications in H2 batteries. Here, cost-effective, highly active electrocatalysts, with a model of ruthenium-nickel alloy nanoparticles in ≈3 nm anchored on carbon black (RuNi/C) as an example, are developed by an ultrafast electrical pulse approach for nickel-hydrogen gas (NiH2 ) batteries. Having a competitive low cost of about one fifth of Pt/C benckmark, this ultrafine RuNi/C catalyst displays an ultrahigh HOR mass activity of 2.34 A mg-1 at 50 mV (vs RHE) and an ultralow HER overpotential of 19.5 mV at a current density of 10 mA cm-2 . As a result, the advanced NiH2 battery can efficiently operate under all-climate conditions (from -25 to +50 °C) with excellent durability. Notably, the NiH2 cell stack achieves an energy density up to 183 Wh kg-1 and an estimated cost of ≈49 $ kWh-1 under an ultrahigh cathode Ni(OH)2 loading of 280 mg cm-2 and a low anode Ru loading of ≈62.5 µg cm-2 . The advanced beyond-industrial-level hydrogen gas batteries provide great opportunities for practical grid-scale energy storage applications.

Solid-Liquid-Gas Management for Low-Cost Hydrogen Gas Batteries

Aqueous nickel-hydrogen gas (Ni-H₂) batteries with excellent durability (>10,000 cycles) are important candidates for grid-scale energy storage but are hampered by the high-cost Pt electrode with limited performance. Herein, we report a low-cost nickel-molybdenum (NiMo) alloy as an efficient bifunctional hydrogen evolution and oxidation reaction (HER/HOR) catalyst for Ni-H₂ batteries in alkaline electrolytes. The NiMo alloy demonstrates a high HOR mass-specific kinetic current of 28.8 mA mg^-1 at 50 mV as well as a low HER overpotential of 45 mV at a current density of 10 mA cm^-2, which is better than most nonprecious metal catalysts. Furthermore, we apply a solid-liquid-gas management strategy to constitute a conductive, hydrophobic network of NiMo using multiwalled carbon nanotubes (NiMo-hydrophobic MWCNT) in the electrode to accelerate HER/HOR activities for much improved Ni-H₂ battery performance. As a result, Ni-H₂ cells based on the NiMo-hydrophobic MWCNT electrode show a high energy density of 118 Wh kg^-1 and a low cost of only 67.5 $ kWh^-1. With the low cost, high energy density, excellent durability, and improved energy efficiency, the Ni-H₂ cells show great potential for practical grid-scale energy storage.

Ultralow-Temperature Aqueous Conductive Polymer-Hydrogen Gas Battery

Hydrogen gas batteries are regarded as one of the most promising rechargeable battery systems for large-scale energy storage applications due to their advantages of high rates and long-term cycle lives. However, the development of cost-effective and low-temperature-tolerant hydrogen gas batteries is highly desirable yet very challenging. Herein, we report a novel conductive polymer-hydrogen gas battery that is suitable for ultralow-temperature energy storage applications and consists of a hydrogen gas anode, a conductive polymer cathode using polyaniline (PANI) or polypyrrole as examples, and protonic acidic electrolytes. The PANI-H₂ battery using 1 M H₂SO₄ as the electrolyte exhibits a capacity of 67 mA h/g, a remarkable rate up to 15 A/g, a Coulombic efficiency around 100%, and an ultra-long life of 10,000 cycles. Using the anti-freezing 9 M H₃PO₄ electrolyte, the PANI-H₂ battery can operate well at temperatures down to -70 °C, which maintains ∼70% of the capacity at room temperature and shows an excellent cycle stability under -60 °C. Benefiting from the fast redox kinetics of both electrodes, this work demonstrates excellent rate performance and low-temperature feasibility of conductive polymer-H₂ batteries, providing a new avenue for further development of low-cost and reliable polymer-H₂ batteries for large-scale energy storage.

Descriptor-Driven Computational Design of Bifunctional Double-Atom Hydrogen Evolution and Oxidation Reaction Electrocatalysts for Rechargeable Hydrogen Gas Batteries

Rechargeable hydrogen gas batteries (RHGBs) have been attracting much attention as promising all-climate large-scale energy storage devices, which calls for low-cost and high-activity hydrogen evolution/oxidation reaction (HER/HOR) bifunctional electrocatalysts to replace the costly platinum-based catalysts. Based on density functional theory (DFT) computations, herein we report an effective descriptor-driven design principle to govern the HER/HOR electrocatalytic activity of double-atom catalysts (DACs) for RHGBs. We systematically investigate the d-band center variation of DACs and their correlations with HER/HOR free energies. We construct activity maps with the d-band center of DACs as a descriptor, which demonstrate that high HER/HOR electrocatalytic activity can be achieved with an appropriate d-band center of DACs. This work not only broadens the applicability of d-band center theory to the prediction of bifunctional HER/HOR electrocatalysts but also paves the way to fast screening and design of efficient and low-cost DACs to promote practical applications of RHGBs.

Rechargeable Batteries for Grid Scale Energy Storage

Ever-increasing global energy consumption has driven the development of renewable energy technologies to reduce greenhouse gas emissions and air pollution. Battery energy storage systems (BESS) with high electrochemical performance are critical for enabling renewable yet intermittent sources of energy such as solar and wind. In recent years, numerous new battery technologies have been achieved and showed great potential for grid scale energy storage (GSES) applications. However, their practical applications have been greatly impeded due to the gap between the breakthroughs achieved in research laboratories and the industrial applications. In addition, various complex applications call for different battery performances. Matching of diverse batteries to various applications is required to promote practical energy storage research achievement. This review provides in-depth discussion and comprehensive consideration in the battery research field for GSES. The overall requirements of battery technologies for practical applications with key parameters are systematically analyzed by generating standards and measures for GSES. We also discuss recent progress and existing challenges for some representative battery technologies with great promise for GSES, including metal-ion batteries, lead-acid batteries, molten-salt batteries, alkaline batteries, redox-flow batteries, metal-air batteries, and hydrogen-gas batteries. Moreover, we emphasize the importance of bringing emerging battery technologies from academia to industry. Our perspectives on the future development of batteries for GSES applications are provided.

Chasing protons in lithium-ion batteries

Parasitic reactions between delithiated cathode materials and non-aqueous electrolytes have been a major barrier that limits the upper cutoff potential of cathode materials. It is of great importance to suppress such parasitic reactions to unleash the high-energy-density potential of high voltage cathode materials. Although major effort has been made to identify the chemical composition of the cathode electrolyte interface using various cutting edge characterization tools, the chemical nature of parasitic reactions remains a puzzle. This severely hinders the rational development of stable high voltage cathode/electrolyte pairs for high-energy density lithium-ion batteries. This feature article highlights our latest effort in understanding the chemical/electrochemical role of the cathode electrolyte interface using protons as a chemical tracer for parasitic reactions.

Production of a hybrid capacitive storage device via hydrogen gas and carbon electrodes coupling

Conventional electric double-layer capacitors are energy storage devices with a high specific power and extended cycle life. However, the low energy content of this class of devices acts as a stumbling block to widespread adoption in the energy storage field. To circumvent the low-energy drawback of electric double-layer capacitors, here we report the assembly and testing of a hybrid device called electrocatalytic hydrogen gas capacitor containing a hydrogen gas negative electrode and a carbon-based positive electrode. This device operates using pH-universal aqueous electrolyte solutions (i.e., from 0 to 14) in a wide temperature range (i.e., from - 70 °C to 60 °C). In particular, we report specific energy and power of 45 Wh kg^-1 and 458 W kg^-1 (both values based on the electrodes' active materials mass), respectively, at 1 A g^-1 and 25 °C with 9 M H₃PO₄ electrolyte solution. The device also enables capacitance retention of 85% (final capacitance of about 114 F g^-1) after 100,000 cycles at 10 A g^-1 and 25 °C with 1 M phosphate buffer electrolyte solution.

Facile Fabrication of Bifunctional Hydrogen Catalytic Electrodes for Long-Life Nickel-Hydrogen Gas Batteries

The renaissance of long-lasting nickel-hydrogen gas (Ni-H₂) battery by developing efficient, robust, and affordable hydrogen anode to replace Pt is particularly attractive for large-scale energy storage applications. Here, we demonstrate an extremely facile corrosion induced fabrication approach to achieve a self-supporting hydrogen evolution/oxidation reaction (HER/HOR) bifunctional nanosheet array electrode for Ni-H₂ battery. The electrode is constituted by ultrafine Ru nanoparticles on Ni(OH)₂ nanosheets grown on nickel foam. Experimental and theoretical calculation results reveal that the electrode with optimized geometric and electronic structures ensures the efficient and robust catalytic hydrogen activities. The fabricated Ni-H₂ battery using the Ru-Ni(OH)₂/NF anode with an industrial scale areal capacity of 16 mAh cm^-2 demonstrates a high energy density, good rate capability and excellent durability without capacity decay over 1800 h. This study casts light on the development of low manufacturing cost and high performance bifunctional hydrogen catalytic electrodes for future hydrogen energy applications.

Laser-induced breakdown spectroscopy to obtain quantitative three-dimensional hydrogen mapping in a nickel–metal-hydride battery cathode for interpreting its reaction distribution

A three-dimensional quantitative hydrogen distribution and state-of-charge distribution in a Ni–MH battery cathode can be acquired using laser-induced breakdown spectroscopy.

An Ultrafast and Ultra-Low-Temperature Hydrogen Gas-Proton Battery

Aqueous proton batteries are regarded as one of the most promising energy technologies for next-generation grid storage due to the distinctive merits of H⁺ charge carriers with small ionic radius and light weight. Various materials have been explored for aqueous proton batteries; however, their full batteries show undesirable electrochemical performance with limited rate capability and cycling stability. Here we introduce a novel aqueous proton full battery that shows remarkable rate capability, cycling stability, and ultralow temperature performance, which is driven by a hydrogen gas anode and a Prussian blue analogue cathode in a concentrated phosphoric acid electrolyte. Its operation involves hydrogen evolution/oxidation redox reactions on the anode and H⁺ insertion/extraction reactions on the cathode, in parallel with the ideal transfer of only H⁺ between these two electrodes. The fabricated aqueous hydrogen gas-proton battery exhibits an unprecedented charge/discharge capability of up to 960 C with a superior power density of 36.5 kW kg^-1, along with an ultralong cycle life of over 0.35 million cycles. Furthermore, this hydrogen gas-proton battery is able to work well at an ultralow temperature of -80 °C with 54% of its room-temperature capacity and under -60 °C with a stable cycle life of 1150 cycles. This work provides new opportunities to construct aqueous proton batteries with high performance in extreme conditions for large-scale energy storage.

A Review on Drive Train Technologies for Passenger Electric Vehicles

Transportation is the second-largest sector contributing to greenhouse gas emissions due to CO2 gas generation from the combustion of fossil fuels. Electric vehicles (EVs) are believed to be a great solution to overcome this issue. EVs can reduce CO2 emissions because the vehicles use an electric motor as a propeller instead of an internal combustion engine. Combined with sustainable energy resources, EVs may become zero-emission transportation. This paper presents an overview of the EV drive train types, including their architecture with the benefits and drawbacks of each type. The aim is to summarize the recent progress of EV technology that always continues to be updated. Furthermore, a comparative investigation on energy density and efficiency, specific energy and power, cost, and application is carried out for batteries as the main energy storage. This discussion provides an understanding of the current development of battery technology, especially the batteries used in EVs. Moreover, the electric motor efficiency, power density, fault tolerance, reliability, and cost are also presented, including the most effective electric motor to use in EVs. The challenges and opportunities of EV deployment in the future are then discussed comprehensively. The government regulation for EVs is still a major non-technical challenge, whereas the charging time and battery performance are the challenges for the technical aspect.

Scalable synthesis of 3D porous germanium encapsulated in nitrogen-doped carbon matrix as an ultra-long-cycle life anode for lithium-ion batteries

Germanium-based materials attract more interest as anodes for lithium-ion batteries, stemming from their physical and chemical advantages. However, these materials inevitably undergo capacity attenuation caused by significant volumetric variation in repeated electrochemical processes. Herein, we designed 3D porous Ge/N-doped carbon nanocomposites by the encapsulation of 3D porous Ge in a nitrogen-doped carbon matrix (denoted as 3D porous Ge/NC). The 3D porous structure can accommodate the volume change during alloying/dealloying processes and improve the penetration of the electrolyte. Furthermore, the doping of N in the carbon framework could introduce more defects and active sites, which can also contribute to electron transportation and lithium-ion diffusion. The half-cell test found that at a current density of 1 C (1 C = 1600 mA h g^-1), the specific capacity stabilized at 917.9 mA h g^-1 after 800 cycles; and the specific capacity remained at 542.4 mA h g^-1 at 10 C. When assembled into a 3D porous Ge/NC//LiFePO₄ full cell, the specific capacity was stabilized at 101.3 mA h g^-1 for 100 cycles at a current density of 1 C (1 C = 170 mA h g^-1), and the cycle specific capacity was maintained at 72.6 mA h g^-1 at a high current density of 5 C. This work develops a low-cost, scalable and simple strategy to improve the electrochemical performance of these alloying type anode materials with huge volume change in the energy storage area.

Promoting Pore-Level Mass Transport/Reaction in Flow Batteries: Bi Nanodot/Vertically Standing Carbon Nanosheet Composites on Carbon Fibers

Elaborate nanoarchitectured solid/liquid interface design of felt electrodes is arguably the most effective pathway to promote the pore-level transport-reaction processes of redox flow batteries. Herein, we conceive a new type of nanocatalytic-layer-architectured graphite felt via introducing the vertically standing carbon nanosheet-confined Bi nanodots onto carbon fiber surfaces. The vertically standing carbon nanosheets construct a nanoporous layer with straight channels for vanadium ion shuttling, where highly dispersed Bi nanodots are stiffly confined to afford abundant active sites. The vanadium redox flow battery utilizing the rationally designed electrodes achieves an energy efficiency of 89% at 150 mA cm^-2, which is substantially higher than those of raw felt (61%) and oxidized felt (77%). Also, the battery with the present electrode maintains an energy efficiency of over 73% even at 400 mA cm^-2, showing the excellent capability of withstanding fast charging and discharging. The multiphysics simulation shows that the vertically standing architecture optimizes the vanadium ion accessibility to the solid/liquid interfaces and thus maximizes the catalytic activity. Moreover, the battery can sustain more than 1000 cycles without obvious efficiency decay, confirming the superb stability of the present electrode. These encouraging results indicate that engineering vertically standing structures with tailored compositions may open up new avenues for advancing the flow battery technology.

Future directions of material chemistry and energy chemistry

Energy is an important substantial foundation for the survival and development of humans. However, the over-consumption of resources and environmental pollution have become more prominent. The key factors for solving energy problems are to increase energy utilization efficiency and optimize energy structure. The development of new materials is the research emphasis in the field of material chemistry all the time. For instance, developing new light-capture materials and catalysts to improve the efficiency of existing photovoltaic cells is one of the most effective approaches to increasing solar power capacity radically. The design of high-performance catalytic materials to make better use of energy from fossil fuels and biomass. In addition, it is an important research direction of material chemistry and energy chemistry to deeply understand the reaction mechanism of energy conversion.

The Survival of Haloferax mediterranei under Stressful Conditions

Haloarchaea can survive and thrive under exposure to a wide range of extreme environmental factors, which represents a potential interest to biotechnology. Growth responses to different stressful conditions were examined in the haloarchaeon Haloferax mediterranei R4. It has been demonstrated that this halophilic archaeon is able to grow between 10 and 32.5% (w/v) of sea water, at 32–52 °C, although it is expected to grow in temperatures lower than 32 °C, and between 5.75 and 8.75 of pH. Moreover, it can also grow under high metal concentrations (nickel, lithium, cobalt, arsenic), which are toxic to most living beings, making it a promising candidate for future biotechnological purposes and industrial applications. Inductively Coupled Plasma Mass Spectrometry (ICP-MS) analysis quantified the intracellular ion concentrations of these four metals in Hfx. mediterranei, concluding that this haloarchaeon can accumulate Li⁺, Co²⁺, As⁵⁺, and Ni²⁺ within the cell. This paper is the first report on Hfx. mediterranei in which multiple stress conditions have been studied to explore the mechanism of stress resistance. It constitutes the most detailed study in Haloarchaea, and, as a consequence, new biotechnological and industrial applications have emerged.

A Comprehensive Review on Energy Storage Systems: Types, Comparison, Current Scenario, Applications, Barriers, and Potential Solutions, Policies, and Future Prospects

Driven by global concerns about the climate and the environment, the world is opting for renewable energy sources (RESs), such as wind and solar. However, RESs suffer from the discredit of intermittency, for which energy storage systems (ESSs) are gaining popularity worldwide. Surplus energy obtained from RESs can be stored in several ways, and later utilized during periods of intermittencies or shortages. The idea of storing excess energy is not new, and numerous researches have been conducted to adorn this idea with innovations and improvements. This review is a humble attempt to assemble all the available knowledge on ESSs to benefit novice researchers in this field. This paper covers all core concepts of ESSs, including its evolution, elaborate classification, their comparison, the current scenario, applications, business models, environmental impacts, policies, barriers and probable solutions, and future prospects. This elaborate discussion on energy storage systems will act as a reliable reference and a framework for future developments in this field. Any future progress regarding ESSs will find this paper a helpful document wherein all necessary information has been assembled.

A High-Rate Lithium Manganese Oxide-Hydrogen Battery

Rechargeable hydrogen gas batteries show promises for the integration of renewable yet intermittent solar and wind electricity into the grid energy storage. Here, we describe a rechargeable, high-rate, and long-life hydrogen gas battery that exploits a nanostructured lithium manganese oxide cathode and a hydrogen gas anode in an aqueous electrolyte. The proposed lithium manganese oxide-hydrogen battery shows a discharge potential of ∼1.3 V, a remarkable rate of 50 C with Coulombic efficiency of ∼99.8%, and a robust cycle life. A systematic electrochemical study demonstrates the significance of the electrocatalytic hydrogen gas anode and reveals the charge storage mechanism of the lithium manganese oxide-hydrogen battery. This work provides opportunities for the development of new rechargeable hydrogen batteries for the future grid-scale energy storage.

Roadmap for advanced aqueous batteries: From design of materials to applications

Safety concerns about organic media-based batteries are the key public arguments against their widespread usage. Aqueous batteries (ABs), based on water which is environmentally benign, provide a promising alternative for safe, cost-effective, and scalable energy storage, with high power density and tolerance against mishandling. Research interests and achievements in ABs have surged globally in the past 5 years. However, their large-scale application is plagued by the limited output voltage and inadequate energy density. We present the challenges in AB fundamental research, focusing on the design of advanced materials and practical applications of whole devices. Potential interactions of the challenges in different AB systems are established. A critical appraisal of recent advances in ABs is presented for addressing the key issues, with special emphasis on the connection between advanced materials and emerging electrochemistry. Last, we provide a roadmap starting with material design and ending with the commercialization of next-generation reliable ABs.

Large-scale Co9S8@C hybrids with tunable carbon thickness for high-rate and long-term performances of an aqueous battery

To realize high-rate and long-term performances of an aqueous rechargeable battery, the most effective approach is to build electrode materials with more reaction active sites and stable structures. Transition metal sulfides have become up-and-coming electrodes due to their high conductivity. Herein, we demonstrated the in situ construction of core-shell Co9S8@C materials with controlled carbon content and thickness. Nanorod-like cobalt-organic chelates were used as the precursors. The cobalt in cobalt-organic chelates reacted with sublimed sulfur to generate the Co9S8 core in situ; meanwhile, the organic chelates were converted into carbon shells, which coated the Co9S8 core and connected with each other to maintain the whole rod shape. Moreover, tunable thickness and content of the carbon shell in the Co9S8@C composite could be achieved by regulating the composition of the reaction solvent. In addition, when 20 mL of dimethylcarbinol was used, the obtained Co9S8@C composite (H1) exhibited the most excellent electrochemical performances, in particular outstanding cycling stability. When assembled with a treated iron powder (TIP) electrode, the Co9S8@C//TIP aqueous rechargeable battery delivered 220.7 mA h g-1 discharge capacity at 1 A g-1, which decreased to 152.8 mA h g-1 even when the current density was increased by a factor of ten (10 A g-1), indicating surprising high-rate performance. Also, after 5000 cycles at 10 A g-1, 74.8% of capacity retention was obtained, further illustrating its excellent long-term cycling stability. Suitable electrode materials with a tunable carbon content have direct impact on the overall performance of an aqueous rechargeable battery, which will guide us for obtaining high-rate and long-term aqueous batteries.