An Extremely Stable,Highly Soluble Monosubstituted Anthraquinone for Aqueous Redox Flow Batteries

An extremely stable, energy-dense (53.6 Ah L⁻¹, 2 m transferrable electrons), low crossover (permeability of <1 × 10⁻¹³ cm² s⁻¹ using Nafion 212 (Nafion is a trademark polymer from DuPont)), and potentially inexpensive anthraquinone with 2-2-propionate ether anthraquinone structure (abbreviated 2-2PEAQ) is synthesized and extensively evaluated under practically relevant conditions for use in the negolyte of an aqueous redox flow battery. 2-2PEAQ shows a high stability with a fade rate of 0.03–0.05% per day at different applied current densities, cut-off voltage windows, and concentrations (0.1 and 1.0 m ) in both a full cell paired with a ferro/ferricyanide posolyte as well as a symmetric cell. 2-2PEAQ is further shown to have extreme long-term stability, losing only ≈0.01% per day when an electrochemical rejuvenation strategy is employed. From post-mortem analysis (nuclear magnetic resonance (NMR), liquid chromatography–mass spectrometry (LC-MS), and cyclic voltammetry (CV)) two degradation mechanisms are deduced: side chain loss and anthrone formation. 2-2PEAQ with the ether linkages attached on carbons non-adjacent to the central ring is found to have three times lower fade rate compared to its isomer with ether linkages on the carbon adjacent to the central quinone ring. The present study introduces a viable negolyte candidate for grid-scale aqueous organic redox flow batteries.     

Five-Membered Ring Nitroxide Radical: A New Class of High-Potential,Stable Catholytes for Neutral Aqueous Organic Redox Flow Batteries

The utilization of redox-active and stable cyclic nitroxide radicals (CNRs) holds a great promise in neutral aqueous organic redox flow batteries (AORFBs) for large-scale energy storage. Herein, a new class of CNRs with five-membered ring pyrrolidine and pyrroline motifs for AORFBs is reported. By rational molecular engineering of introducing CC double bond into the pyrrolidine-based molecule, 3-carbamoyl-2,2,5,5-tetramethylpyrroline-1-oxyl (CPL) with a high redox potential of 0.76 V (vs Ag/AgCl) is demonstrated, which is 160 mV higher than the common 2,2,6,6-tetramethylpiperidine 1-oxyl derivatives with a six-membered ring as the core structure. Density functional theory calculations reveal that the much enhanced redox potential for CPL is largely contributed by lowered standard free energy in reduction reaction and charge population sum of N O radical head. When paired with the BTMAP-viologen anolyte, the CPL-based AORFB delivers constant capacity retention of up to 99.96%/cycle over 500 cycles.     

Engineering Transition Metal Layers for Long Lasting Anionic Redox in Layered Sodium Manganese Oxide

Oxygen-redox-based-layered cathode materials are of great importance in realizing high-energy-density sodium-ion batteries (SIBs) that can satisfy the demands of next-generation energy storage technologies. However, Mn-based-layered materials (P2-type Na-poor Na_y[A_xMn_1−x]O₂, where A = alkali ions) still suffer from poor reversibility during oxygen-redox reactions and low conductivity. In this work, the dual Li and Co replacement is investigated in P2-type-layered Na_xMnO₂. Experimentally and theoretically, it is demonstrated that the efficacy of the dual Li and Co replacement in Na_0.6[Li_0.15Co_0.15Mn_0.7]O₂ is that it improves the structural and cycling stability despite the reversible Li migration from the transition metal layer during de-/sodiation. Operando X-ray diffraction and ex situ neutron diffraction analysis prove that the material maintains a P2-type structure during the entire range of Na⁺ extraction and insertion with a small volume change of ≈4.3%. In Na_0.6[Li_0.15Co_0.15Mn_0.7]O₂, the reversible electrochemical activity of Co³⁺/Co⁴⁺, Mn³⁺/Mn⁴⁺, and O^2-/(O₂)^n- redox is identified as a reliable mechanism for the remarkable stable electrochemical performance. From a broader perspective, this study highlights a possible design roadmap for developing cathode materials with optimized cationic and anionic activities and excellent structural stabilities for SIBs.     

Boosting Kinetics of Ce3+/Ce4+ Redox Reaction by Constructing TiC/TiO2 Heterojunction for Cerium-Based Flow Batteries

Cerium, a unique rare earth element, possesses a relatively high abundance, low cost, and high redox voltage, making it an attractive candidate for redox flow batteries. However, the sluggish kinetics and corrosion nature of the Ce³⁺/Ce⁴⁺ electrolyte result in overpotential and degradation of carbon felt (CF) electrodes, which hinders the development of cerium-based flow batteries. Therefore, it is essential to develop an electrode with high catalytic activity and corrosion resistance to the Ce³⁺/Ce⁴⁺ electrolyte. Herein, a TiC/TiO₂ coated carbon felt (TiC/TiO₂-CF) electrode is proposed. Remarkably, the TiC/TiO₂ coating effectively minimizes the exposure of the CF to the highly corrosive cerium electrolyte, consequently enhancing the electrode's corrosion resistance. Additionally, X-ray photoelectron spectroscopy and high-resolution transmission electron microscopy characterizations reveal the formation of a heterojunction between TiC and TiO₂, which significantly enhances the redox reaction kinetics of the Ce³⁺/Ce⁴⁺ redox couple. Eventually, the practical application of TiC/TiO₂-CF catalytic electrode in a Ce–Fe flow battery is demonstrated. This study sheds light on the synthesis conditions of the TiC/TiO₂-CF electrode, elucidates its heterojunction structure, and presents a novel Ce–Fe flow battery system.     

Carbon-Supported High-Entropy Oxide Nanoparticles as Stable Electrocatalysts for Oxygen Reduction Reactions

Nanoparticles supported on carbonaceous substrates are promising electrocatalysts. However, achieving good stability for the electrocatalysts during long-term operations while maintaining high activity remains a grand challenge. Herein, a highly stable and active electrocatalyst featuring high-entropy oxide (HEO) nanoparticles uniformly dispersed on commercial carbon black is reported, which is synthesized via rapid high-temperature heating (≈1 s, 1400 K). Notably, the HEO nanoparticles with a record-high entropy are composed of ten metal elements (i.e., Hf, Zr, La, V, Ce, Ti, Nd, Gd, Y, and Pd). The rapid high-temperature synthesis can tailor structural stability and avoid nanoparticle detachment or agglomeration. Meanwhile, the high-entropy design can enhance chemical stability to prevent elemental segregation. Using oxygen reduction reaction as a model, the 10-element HEO exhibits good activity and greatly enhances stability (i.e., 92% and 86% retention after 12 and 100 h, respectively) compared to the commercial Pd/C electrocatalyst (i.e., 76% retention after 12 h). This superior performance is attributed to the high-entropy compositional design and synthetic approach, which offers an entropy stabilization effect and strong interfacial bonding between the nanoparticles and carbon substrate. The approach promises a viable route toward synthesizing carbon-supported high-entropy electrocatalysts with good stability and high activity for various applications.     

Reactivating the Dead Lithium by Redox Shuttle to Promote the Efficient Utilization of Lithium for Anode Free Lithium Metal Batteries

Anode free lithium metal batteries (AFLMBs), as a kind of novel battery configuration with zero excess lithium, can improve the energy density to the limit compared with lithium metal batteries and effectively ensure the safety. However, the lifespan of AFLMBs is a tricky problem because there is no extra lithium source to compensate for the irreversible loss of active lithium, which is mainly caused by the continuous decomposition of electrolyte and the formation of dead lithium. Herein, a redox shuttle additive, which can be oxidized in the cathode and reduced in the electrolyte reversibly, is introduced to improve the lithium utilization and lifespan of AFLMBs by reactivating the dead lithium. During the charging process, the redox shuttle additive can be oxidized on the cathode surface and serve as electron acceptor toward dead lithium. The electrically isolated dead lithium in the electrolyte can be re-activated into active lithium ions when captured by oxidized redox shuttle additive.As a result, electrolyte with redox shuttle achieves average higher coulombic efficiency of 99.13% than electrolyte without redox shuttle (97.71%). In addition, the AFLMB with redox shuttle exhibits improved cycling performance with extended lifespan.     

Unveiling the Anionic Redox Chemistry in Phosphate Cathodes for Sodium-Ion Batteries

Anionic redox chemistry has aroused increasing attention in sodium-ion batteries (SIBs) by virtue of the appealing additional capacity. However, up to now, anionic redox reaction has not been reported in the mainstream phosphate cathodes for SIBs. Herein, the ultrathin VOPO₄ nanosheets are fabricated as promising cathodes for SIBs, where the oxygen redox reaction is first activated accompanied by reversible ClO₄⁻ (from the electrolyte) insertion/extraction. As a result, the VOPO₄ cathode harvests a record-high capacity (168 mAh g⁻¹ at 0.1 C) among its counterparts ever reported. Moreover, the ClO₄⁻ insertion efficiently expands the interlayer spacing of VOPO₄ and accelerates the ion diffusion, enabling an unprecedentedly high rate performance (69 mAh g⁻¹ at 30 C). Via systematic ex situ characterizations and theoretical computations, the anionic redox chemistry and charge storage mechanism upon cycling are thoroughly elucidated. This study opens up a new avenue toward high-energy phosphate cathodes for SIBs by triggering anionic redox reactions.     

Nanoflake Arrays of Lithiophilic Metal Oxides for the Ultra‐Stable Anodes of Lithium‐Metal Batteries

A molten lithium infusion strategy has been proposed to prepare stable Li‐metal anodes to overcome the serious issues associated with dendrite formation and infinite volume change during cycling of lithium‐metal batteries. Stable host materials with superior wettability of molten Li are the prerequisite. Here, it is demonstrated that a series of strong oxidizing metal oxides, including MnO₂, Co₃O₄, and SnO₂, show superior lithiophilicity due to their high chemical reactivity with Li. Composite lithium‐metal anodes fabricated via melt infusion of lithium into graphene foams decorated by these metal oxide nanoflake arrays successfully control the formation and growth of Li dendrites and alleviate volume change during cycling. A resulting Li‐Mn/graphene composite anode demonstrates a super‐long and stable lifetime for repeated Li plating/stripping of 800 cycles at 1 mA cm^?2 without voltage fluctuation, which is eight times longer than the normal lifespan of a bare Li foil under the same conditions. Furthermore, excellent rate capability and cyclability are realized in full‐cell batteries with Li‐Mn/graphene composite anodes and LiCoO₂ cathodes. These results show a major advancement in developing a stable Li anode for lithium‐metal batteries.     

Integrated Saltwater Desalination and Energy Storage through a pH Neutral Aqueous Organic Redox Flow Battery

Here, a pH neutral aqueous organic redox flow battery (AORFB) consisting of three electrolytes channels (i.e., an anolyte channel, a catholyte channel, and a central salt water channel) to achieve integrated energy storage and desalination is reported. Employing a low cost, chemically stable methyl viologen (MV) anolyte, and sodium ferrocyanide catholyte, this desalination AORFB is capable of desalinating simulated seawater (0.56 m NaCl) down to 0.023 m salt concentration at an energy cost of 2.4 W h L^?1 of fresh water—competitive with current reverse osmosis technologies. Simultaneously, the cell delivers stored energy at 79.7% efficiency with a cell voltage of 0.85 V. Furthermore, the cell is also capable of higher current operation up to 15 mA cm^?2, providing 4.55 mL of fresh water per hour. Combining energy storage and water desalination into such a bifunctional device offers the opportunity to address two growing global issues from one hardware installation.     

Metal Catalyst to Construct Carbon Nanotubes Networks on Metal Oxide Microparticles towards Designing High-Performance Electrode for High-Voltage Lithium-Ion Batteries

Designing carbon nanotubes (CNTs)-based materials are attracting great attention due to their fantastic properties and greater performance. Herein, a new CNTs network triggered by metal catalysts (e.g., Co, Ni, or Cu) is constructed on metal oxide (e.g., MnO) microparticles, giving rise to a high-performance Co-MnO@C-CNTs anode in lithium-ion batteries (LIBs). An extremely high capacity of 1050 mAh g⁻¹, extraordinary rate capacities over 10 A g⁻¹, and a long lifespan over 500 cycles are demonstrated. The great features of Co-MnO@C-CNTs anode are further confirmed in LIBs when the nickel-rich cathode (e.g., LiNi_0.8Co_0.1Mn_0.1O₂) is used and charged at a high voltage over 4.5 V. A high-capacity retention of 71.5% can be maintained at 1 C over 150 cycles. The superior performance relates to the CNTs network, which not only acts as an “expressway network” for fast ion/electron transportation but also buffers structural variation. Moreover, the metal nanoparticles can also enhance the electrical conductivity and catalyze the (de-)lithiation of metal oxide, resulting in higher reversibility and long-term cyclability. This study opens a new avenue to prepare CNTs-based functional materials and also explores the potential applications of metal oxide-based anode for high-performance batteries.     

In Situ Formation of Conductive Metal Sulfide Domain in Metal Oxide Matrix: An Efficient Way to Improve the Electrochemical Activity of Semiconducting Metal Oxide

A new effective way to improve the electrochemical activity of semiconducting metal oxide is developed by the in situ formation of conductive metal sulfide domain in the metal oxide matrix. The Li_0.96Ti_1.08S₂?Li₄Ti₅O₁₂ nanocomposites with tunable compositions and electrical properties are synthesized by the reaction of Li₄Ti₅O₁₂ with CS₂ at elevated temperature. The resulting incorporation of conductive Li_0.96Ti_1.08S₂ domain in the Li₄Ti₅O₁₂ matrix is effective in enhancing the electrical conductivity and electrode activity of semiconducting lithium titanate. As anode materials for lithium ion batteries, the obtained Li_0.96Ti_1.08S₂?Li₄Ti₅O₁₂ nanocomposites show much greater discharge capacity and better rate characteristics than does the pristine Li₄Ti₅O₁₂. The usefulness of the present method is further evidenced from the improvement of the electrochemical activity of semiconducting CsTi₂NbO₇ after the reaction with CS₂. The present study clearly demonstrates the in situ formation of conductive metal sulfide domain using CS₂ liquid can provide an efficient and universal way to improve the electrode functionality of semiconducting metal oxide.     

Low‐Temperature‐Grown Transition Metal Oxide Based Storage Materials and Oxide Transistors for High‐Density Non‐volatile Memory

An effective stacked memory concept utilizing all‐oxide‐based device components for future high‐density nonvolatile stacked structure data storage is developed. GaInZnO (GIZO) thin‐film transistors, grown at room temperature, are integrated with one‐diode (CuO/InZnO)–one‐resistor (NiO) (1D–1R) structure oxide storage node elements, fabricated at room temperature. The low growth temperatures and fabrication methods introduced in this paper allow the demonstration of a stackable memory array as well as integrated device characteristics. Benefits provided by low‐temperature processes are demonstrated by fabrication of working devices over glass substrates. Here, the device characteristics of each individual component as well as the characteristics of a combined select transistor with a 1D–1R cell are reported. X‐ray photoelectron spectroscopy analysis of a NiO resistance layer deposited by sputter and atomic layer deposition confirms the importance of metallic Ni content in NiO for bi‐stable resistance switching. The GIZO transistor shows a field‐effect mobility of 30 cm² V⁻¹ s⁻¹, a V_th of +1.2 V, and a drain current on/off ratio of up to 10⁸, while the CuO/InZnO heterojunction oxide diode has forward current densities of 2 × 10⁴ A cm⁻². Both of these materials show the performance of state‐of‐the‐art oxide devices.     

Energy Storage Mechanism,Challenge and Design Strategies of Metal Sulfides for Rechargeable Sodium/Potassium-Ion Batteries

Rechargeable sodium/potassium-ion batteries (SIBs/PIBs) with abundant reserves of Na/K and low cost have been a promising substitution to commercial lithium-ion batteries. As for pivotal anode materials, metal sulfides (MSx) exhibit an inspiring potential due to the multitudinous redox storage mechanisms for SIBs/PIBs applications. Nevertheless, they still confront several bottlenecks, such as the low electrical conductivity, poor ionic diffusivity, sluggish interfacial/surface reaction kinetics, and severe volume expansion, which distinctly restrain the battery performance. Meanwhile, the systematic insights into the design strategies of MSx for SIBs/PIBs have been seldom elaborated. In this review, the energy storage mechanism, challenge, and design strategies of MSx for SIBs/PIBs are expounded to address the above predicaments. In particular, design strategies of MSx are highlighted from the aspects of morphology modifications involving 1D/2D/3D configurations, atomic-level engineering containing heteroatom doping, vacancy creation, and interlayer spacing expansion, and MSx composites with other MSx, metal oxides, carbonaceous, and graphite materials to boost the comprehensive electrochemical performance of SIBs/PIBs. Furthermore, prospects are presented for the further advance of MSx to surmount imminent challenges, hoping to forecast feasible future orientations in this field.     

Cobalt Single-Atom Electrocatalysts Enhanced by Hydrogen-Bonded Organic Frameworks for Long-Lasting Zinc-Iodine Batteries

Herein, a hydrogen-bonded cobalt porphyrin framework is presented that can efficiently host iodine and serve as an electrocatalyst for aqueous zinc-iodine (Zn-I₂) organic batteries. The Fourier Transform infrared spectroscopy (FT-IR), X-ray Photoelectron Spectroscopy (XPS), and Density functional theory (DFT) results demonstrate that hydrogen-bonded organic frameworks (HOFs) possess excellent adsorption properties for iodine species. In situ Raman spectroscopy illustrates that the redox mechanism of Zn-I₂ battery depends on the redox reaction of I/I⁻, with I₃⁻/I₅⁻ serving as intermediary products. The in situ Ultraviolet-visible (UV–vis) spectroscopy further reveals that HOFs restrict polyiodide solubilization. The aqueous Zn-I₂ organic batteries with I₂@PFC-72-Co cathodes exhibit excellent rate capability, achieving 134.9 mAh g⁻¹ at 20 C. Additionally, these batteries demonstrate long-term cycle stability, enduring > 5000 cycles at 20 C. The impressive electrochemical performance of I₂@PFC-72-Co can be attributed to the cooperative Co single-atom (CoSA) electrocatalyst in the HOF-Co structure. Moreover, the benzene ring structure and the carboxyl functional group of HOFs possess a strong ability to adsorb iodine and iodide. Owing to these synergistic effects, the aqueous Zn-I₂ batteries with the I₂@PFC-72-Co cathode exhibit excellent electrochemical performance.     

Metal Ions versus Protons: Tracking of Charge-Carrier Insertion into a Cathode Oxide in Aqueous Rechargeable Batteries

Protons in aqueous electrolytes can perform as an additional type of charge carrier for insertion/extraction in addition to the primary carrier cations in aqueous rechargeable batteries. Despite many diverse claims regarding the effect of protons, mutually conflicting experimental results and their interpretations without direct evidence have been reported over the last decade. Systematic examinations and analyses are thus imperative to clarify the conditions of proton insertion in aqueous rechargeable batteries. Utilizing V₂O₅ as a model cathode and beaker-type cells with a sufficient amount of ZnSO₄ aqueous electrolytes in this work, it is demonstrated that protons are inserted into the cathode prior to Zn-ions in low-pH conditions (pH ≤ 3.0). In stark contrast, the influence of protons on the discharge voltage and capacity is insignificant, when either the pH becomes higher (pH ≥ 4.0) or the electrolyte volume is considerably low in coin-type cells. Similar behavior of pH-dependent proton insertion is also verified in Na–, Mg–, and Al-ion electrolytes. Providing a resolution to the controversy regarding proton insertion, the present study emphasizes that the influence of protons substantially varies depending on the pH and relative volume of electrolytes in aqueous batteries.     

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.     

Electrochemical Overview: A Summary of ACoxMnyNizO2 and Metal Oxides as Versatile Cathode Materials for Metal-Ion Batteries

Early LiCoO₂ research provided the basis for the tremendous commercial success of Li⁺ batteries since their invention in the early 1990s. Today, LiNiMnCoO₂ (Li-NMC) is one of the most widely used batteries in the rapidly evolving electronic vehicle industry. Li-NMC batteries continue to receive significant interest as research efforts aim to partially, or entirely, replace the use of scarcely available and toxic Co with elemental doping to form binary, ternary, and quaternary layered oxides. Furthermore, safety concerns and rising uncertainty for the future of Li supplies have resulted in growing curiosity toward non-Li⁺ rechargeable batteries such as Na⁺ and K⁺. Unfortunately, the success of Li⁺ host materials does not always directly transfer to Na⁺ and K⁺ batteries due to the difficulty of reversibly intercalating larger ions without irreparably distorting the host structure. Consequently, this report provides an overview of the Li-based materials surrounding the success of commercial Li-NMC and the subsequent progress of their lesser studied Na and K counterparts. The challenges for current cathode materials are highlighted, and the opportunities for progression are suggested. The summary presented in this review can be consulted to steer new and unique research avenues for layered oxide materials as metal-ion battery cathodes.     

Rational Design of Transition Metal Phosphide-Based Electrocatalysts for Hydrogen Evolution

Developing efficient and inexpensive electrocatalysts for the hydrogen evolution reaction (HER) is critical to the commercial viability of electrochemical clean energy technologies. Transition metal phosphides (TMPs), with the merits of abundant reserves, unique structure, tunable composition, and high electronic conductivity, are recognized as attractive HER catalytic materials. Nevertheless, the HER electrocatalytic activity of TMPs is still limited by various thorough issues and inherent performance bottlenecks. In this review, these issues are carefully sorted, and the corresponding reasonable explanations and solutions are elucidated on the basis of the HER catalytic activity origins of TMPs. Subsequently, highly targeted multiscale strategies to improve the HER performance of TMPs are comprehensively presented. Additionally, critical scientific issues for constructing high-efficiency TMP-based electrocatalysts are proposed. Finally, the HER reaction process, catalytic mechanism research, TMP-based catalyst construction, and their application expansion are mentioned as challenges and future directions for this research field. Expectedly, this review offers professional and targeted guidelines for the rational design and practical application of TMP-based HER catalysts.     

全钒液流电池泵损耗对电池的性能和效率影响分析

摘要: 建立一个全钒液流电池系统模型,通过对全钒液流电池系统模型在不同管径和流速下的泵损耗进行理论分析和研究,得出全钒电池泵损耗的规律。运用Fluent模拟仿真半电池在不同流速下的电解液分布,不同充电电流和流速下对全钒液流电池性能的影响。结果表明：根据钒电池结构优化控制泵的损耗和电解液流速,对于提高钒电池储能系统的效率和改善电池系统稳定性至关重要。在大规模应用储能技术时,泵损和流速的影响将更为明显。