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By increasing the charging voltage, a cell specific energy of >400 W h kg−1 is achievable with LiNi0.8Mn0.1Co0.1O2 in Li metal batteries. However, stable cycling of high-nickel cathodes at ultra-high voltages is extremely challenging. Here we report that a rationally designed sulfonamide-based electrolyte enables stable cycling of commercial LiNi0.8Co0.1Mn0.1O2 with a cut-off voltage up to 4.7 V in Li metal batteries. In contrast to commercial carbonate electrolytes, the electrolyte not only suppresses side reactions, stress-corrosion cracking, transition-metal dissolution and impedance growth on the cathode side, but also enables highly reversible Li metal stripping and plating leading to a compact morphology and low pulverization. Our lithium-metal battery delivers a specific capacity >230 mA h g−1 and an average Coulombic efficiency >99.65% over 100 cycles. Even under harsh testing conditions, the 4.7 V lithium-metal battery can retain >88% capacity for 90 cycles, advancing practical lithium-metal batteries. Charging at high voltages in principle makes batteries energy dense, but this is often achieved at the cost of the cycling stability. Here the authors design a sulfonamide-based electrolyte to enable a Li metal battery with a state-of-the-art cathode at an ultra-high voltage of 4.7 V while maintaining cyclability.

Critical factors that govern the composition and morphology of discharge products are largely unknown for Na-O2 battery. Here we report a reversible ORR and OER process in a sodium-oxygen battery o...

We present the discovery of a novel radical cation formed through one-electron oxidation of an N-heterocyclic carbene-carbodiimide (NHC-CDI) zwitterionic adduct. This compound possesses a distonic electronic structure (spatially separate spin and charge regions) and displays persistence under ambient conditions. We demonstrate its application in a redox-flow battery exhibiting minimal voltage hysteresis, a flat voltage plateau, high Coulombic efficiency, and no performance decay for at least 100 cycles. The chemical tunability of NHCs and CDIs suggests that this approach could provide a general entry to redox-active NHC-CDI adducts and their persistent radical ions for various applications.

Flow battery technology offers a promising low-cost option for stationary energy storage applications. Aqueous zinc–nickel battery chemistry is intrinsically safer than non-aqueous battery chemistry (e.g. lithium-based batteries) and offers comparable energy density. In this work, we show how combining high power density and low-yield stress electrodes can minimize energy loss due to pumping, and have demonstrate methods to achieve high energy and power density for ZnO/Ni(OH)2 electrodes by changing composition and optimizing testing protocols. Firstly, mechanically stable and homogeneous Ni(OH)2/carbon and ZnO/Zn flowable electrodes in 7 M KOH electrolyte were designed using a microgel dispersion as the suspending matrix. By determining the critical volume fractions for conductivity percolation, colloidal suspensions with 6.2 vol% of carbon and 23.1 vol% of Zn were selected for preparing catholytes and anolytes to ensure that these semi-solid electrodes possess high voltage and high coulombic efficiencies. The resulting flowable electrodes exhibited non-Newtonian rheology with a yield stress of approximately ∼200 Pa, which assists in maintaining mechanical stability of the suspensions. An energy density of up to 134 W h Lcatholyte−1 and power density up to ∼159 mW cmgeo.−2 was demonstrated for semi-solid ZnO/Ni(OH)2 electrodes, and coulombic efficiency of 94% was achieved during cycling by optimizing the charging protocol to 60% SOC of Ni(OH)2. Lastly, semi-solid ZnO and Ni(OH)2 flow cells were built and tested using an intermittent mode of operation. The high energy and power densities, high coulombic efficiency, and negligible pumping loss of the Zn–Ni semi-solid electrodes developed in the present work present a promising system for further development.

Summary Redox flow batteries have great system scalability and operational flexibility but relatively low energy density because of the limited solubility of redox molecules in the electrolytes. By storing energy in solid materials while producing power from redox fluids, the redox-targeting concept provides an effective way to significantly increase the energy density of flow batteries. Redox targeting generally involves multiple redox reactions between the molecules and materials, which inevitably brings about additional complexity in electrolyte composition and low voltage efficiency. The Nernstian-potential-driven redox-targeting reaction reported here considerably eliminates the voltage loss of a LiFePO 4 -based redox flow lithium battery. Driven by the Nernstian potential difference, the redox molecule, a ferrocene-grafted ionic liquid with standard potential identical to that of LiFePO 4 , reacts with the solid material both anodically and cathodically and exhibits near-unity material utilization, a voltage efficiency of 95%, and an energy density of 330 Wh/L (up to 942 Wh/L).

Redox flow batteries, despite great operation flexibility and scalability for large-scale energy storage, suffer from low energy density and relatively high cost as compared to the state-of-the-art Li-ion batteries. Here we report a redox flow lithium battery, which operates via the redox targeting reactions of LiFePO4 with a bifunctional redox mediator, 2,3,5,6-tetramethyl-p-phenylenediamine, and presents superb energy density as the Li-ion battery and system flexibility as the redox flow battery. The battery has achieved a tank energy density as high as 1023 Wh/L, power density of 61 mW/cm2, and voltage efficiency of 91%. Operando X-ray absorption near-edge structure measurements were conducted to monitor the evolution of LiFePO4, which provides insightful information on the redox targeting process, critical to the device operation and optimization.

The ever-increasing penetration of solar energy demands high energy density, safe and affordable energy storage systems. We demonstrated a redox flow battery on the basis of the redox targeting reactions of a bifunctional redox mediator – ethyl viologen diiodide (EVI2) with a low-cost pigment material – Prussian blue (PB). Sharing the same I–/I3– based electrolyte, this new battery system can be feasibly integrated with a dye-sensitized TiO2 photoelectrode for photoassisted charging process. The introduction of PB not only increases the energy density up to 117 Wh/L with good cycling performance and capacity retention, also instantaneously regenerates I– ensuring a stable I–/I3– concentration which is crucial to the operation of the photoelectrode. We anticipate that the work presented here may open an intriguing and credible way for the development of integrated all-in-one solar energy conversion and storage devices for large-scale applications.

Water contamination is generally considered to be detrimental to the performance of aprotic lithium–air batteries, whereas this view is challenged by recent contrasting observations. This has provoked a range of discussions on the role of water and its impact on batteries. In this work, a distinct battery chemistry that prevails in water-contaminated aprotic lithium–oxygen batteries is revealed. Both lithium ions and protons are found to be involved in the oxygen reduction and evolution reactions, and lithium hydroperoxide and lithium hydroxide are identified as predominant discharge products. The crystallographic and spectroscopic characteristics of lithium hydroperoxide monohydrate are scrutinized both experimentally and theoretically. Intriguingly, the reaction of lithium hydroperoxide with triiodide exhibits a faster kinetics, which enables a considerably lower overpotential during the charging process. The battery chemistry unveiled in this mechanistic study could provide important insights into the understanding of nominally aprotic lithium–oxygen batteries and help to tackle the critical issues confronted., Water is believed to undermine the performance of aprotic lithium–air batteries. However, the authors here disclose different battery chemistry, showing that both lithium ions and protons are involved in the battery reactions in the presence of water, leading to an unprecedented dynamic product.

We demonstrate a redox flow lithium oxygen battery (RFLOB) using a pair of soluble redox catalysts, 2,5-di-tert-butyl-p-benzoquinone (DTBBQ) and tris{4-[2-(2-methoxyethoxy)ethoxy]phenyl}amine (TMPPA). The catalytic effects of DTBBQ on the oxygen reduction reaction (ORR) and TMPPA on the oxygen evolution reaction (OER) were investigated and unambiguously substantiated with various electrochemical, morphological, and spectroscopic characterization methods. It is observed that, upon discharging, oxygen is rapidly reduced by DTBBQ•– and Li2O2 is formed in the presence of Li+; upon charging, Li2O2 is oxidized by TMPPA•+, releasing oxygen. Such redox-mediated ORR and OER reactions enable the formation and oxidation of Li2O2 in a separate gas diffusion tank (GDT) other than on the cathode of the cell, thus obviating surface passivation and pore clogging of the electrode. The cell presents a high energy density with DTBBQ as the ORR redox catalyst and good rechargeability when paired with TMPPA as the OER redox c...

The development of rechargeable Li–air batteries has been confronted by the critical challenges of large overpotential loss, low achievable capacity, and prohibitively poor cycling and power performance. Surface passivation and pore clogging of the cathode due to the formation of Li2O2 during discharge result in sluggish interfacial charge transfer and have an impact on the mass transport of Li+ ions and O2 in the electrode, consequently giving rise to large voltage hysteresis and premature termination of discharge with low power performance. Here we report a redox flow lithium–oxygen cell with a modified redox electrolyte to tackle these issues. With the assistance of redox mediators, the cell presents substantially enhanced power performance in O2 and dry air during discharge. Through in situ spectroelectrochemical measurements and theoretical calculations, an oxygen reduction intermediate was unequivocally identified. By judiciously optimizing the redox electrolyte, the cell operates at near complete utilization of Li metal upon multiple refueling. The redox flow lithium–oxygen cell demonstrated here is envisaged to provide a pragmatic approach for the implementation of lithium–oxygen battery chemistry and to pave the way for advanced large-scale energy storage.

A TCO (transparent conductive oxide)-free redox-flow electrochromic window (RFEW) with considerably improved performance is demonstrated. The new RFEW employs Prussian blue (PB)/Prussian white (PW) as the electrochromic (EC) material, in which the decoloration/coloration is achieved by the redox targeting reactions of anthraquinone-2,6-disulfonate (AQDS) and FeCl3 with PB/PW, respectively. These redox molecules are electrochemically oxidized/reduced in an external stack cell and circulated through the window cavity. Hence, the costly TCO glass, indispensable in conventional EC windows, becomes redundant in RFEWs. Owing to the fast charge transfer kinetics of AQDS and Fe3+, the RFEW design investigated in this study presents substantially reduced response time. For a window with a size exceeding 100 cm2, coloration/decoloration switching with a change in absorbance by more than 80% is achieved within approximately 2 min. The static and dynamic optical characteristics of the window pane and the electrochemical behavior of the stack cell were examined in detail to understand the operation of the RFEW.