In Situ Electropolymerization Enables Ultrafast Long Cycle Life and High-Voltage Organic Cathodes for Lithium Batteries

Organic cathode materials have attracted extensive attention because of their diverse structures, facile synthesis, and environmental friendliness. However, they often suffer from insufficient cycling stability caused by the dissolution problem, poor rate performance, and low voltages. An in situ electropolymerization method was developed to stabilize and enhance organic cathodes for lithium batteries. 4,4′,4′′-Tris(carbazol-9-yl)-triphenylamine (TCTA) was employed because carbazole groups can be polymerized under an electric field and they may serve as high-voltage redox-active centers. The electropolymerized TCTA electrodes demonstrated excellent electrochemical performance with a high discharge voltage of 3.95 V, ultrafast rate capability of 20 A g⁻¹, and a long cycle life of 5000 cycles. Our findings provide a new strategy to address the dissolution issue and they explore the molecular design of organic electrode materials for use in rechargeable batteries.     

Non‐Conjugated Dicarboxylate Anode Materials for Electrochemical Cells

Classical organic anode materials for Na‐ion batteries are mostly based on conjugated carboxylate compounds, which can stabilize added electrons by the double‐bond reformation mechanism. Now, 1,4‐cyclohexanedicarboxylic acid (C₈H₁₂O₄, CHDA) with a non‐conjugated ring (?C₆H₁₀?) connected with carboxylates is shown to undergo electrochemical reactions with two Na ions, delivering a high charge specific capacity of 284 mA h g^?1 (249 mA h g^?1 after 100 cycles), and good rate performance. First‐principles calculations indicate that hydrogen‐transfer‐mediated orbital conversion from antibonding π* to bonding σ stabilize two added electrons, and reactive intermediate with unpaired electron is suppressed by localization of σ‐bonds and steric hindrance. An advantage of CHDA as an anode material is good reversibility and relatively constant voltage. A large variety of organic non‐conjugated compounds are predicted to be promising anode materials for sodium‐ion batteries.     

Understanding High‐Rate K+‐Solvent Co‐Intercalation in Natural Graphite for Potassium‐Ion Batteries

Graphite shows great potential as an anode material for rechargeable metal‐ion batteries because of its high abundance and low cost. However, the electrochemical performance of graphite anode materials for rechargeable potassium‐ion batteries needs to be further improved. Reported herein is a natural graphite with superior rate performance and cycling stability obtained through a unique K⁺‐solvent co‐intercalation mechanism in a 1 m KCF₃SO₃ diethylene glycol dimethyl ether electrolyte. The co‐intercalation mechanism was demonstrated by ex situ Fourier transform infrared spectroscopy and in situ X‐ray diffraction. Moreover, the structure of the [K‐solvent]⁺ complexes intercalated with the graphite and the conditions for reversible K⁺‐solvent co‐intercalation into graphite are proposed based on the experimental results and first‐principles calculations. This work provides important insights into the design of natural graphite for high‐performance rechargeable potassium‐ion batteries.     

Proton Insertion Chemistry of a Zinc–Organic Battery

Proton storage in rechargeable aqueous zinc‐ion batteries (ZIBs) is attracting extensive attention owing to the fast kinetics of H⁺ insertion/extraction. However, it has not been achieved in organic materials‐based ZIBs with a mild electrolyte. Now, aqueous ZIBs based on diquinoxalino [2,3‐a:2′,3′‐c] phenazine (HATN) in a mild electrolyte are developed. Electrochemical and structural analysis confirm for the first time that such Zn–HATN batteries experience a H⁺ uptake/removal behavior with highly reversible structural evolution of HATN. The H⁺ uptake/removal endows the Zn–HATN batteries with enhanced electrochemical performance. Proton insertion chemistry will broaden the horizons of aqueous Zn–organic batteries and open up new opportunities to construct high‐performance ZIBs.     

Bismuth Nanoparticles Embedded in Carbon Spheres as Anode Materials for Sodium/Lithium‐Ion Batteries

Sodium‐ion batteries (SIBs) are regarded as an attractive alternative to lithium‐ion batteries (LIBs) for large‐scale commercial applications, because of the abundant terrestrial reserves of sodium. Exporting suitable anode materials is the key to the development of SIBs and LIBs. In this contribution, we report on the fabrication of Bi@C microspheres using aerosol spray pyrolysis technique. When used as SIBs anode materials, the Bi@C microsphere delivered a high capacity of 123.5 mAh g^?1 after 100 cycles at 100 mA g^?1. The rate performance is also impressive (specific capacities of 299, 252, 192, 141, and 90 mAh g^?1 are obtained under current densities of 0.1, 0.2, 0.5, 1, and 2 A g^?1, respectively). Furthermore, the Bi@C microsphere also proved to be suitable LIB anode materials. The excellent electrochemical performance for both SIBs and LIBs can attributed to the Bi@C microsphere structure with Bi nanoparticles uniformly dispersed in carbon spheres.     

A Conjugated Copolymer of N‐Phenyl‐p‐phenylenediamine and Pyrene as Promising Cathode for Rechargeable Lithium–Ion Batteries

A novel conjugated copolymer has been synthesized and employed as an organic cathode material in rechargeable lithium–ion batteries (LIBs). Due to the synergistic effects from conducting aniline and pyrene units, the resultant batteries based on the as‐obtained copolymer can deliver a promising reversible specific capacity of 113 mAh g^?1 with a high voltage output of 3.2 V and a remarkable 75.2 % capacity retention after 180 cycles. Moreover, an excellent rate performance is also achieved with a fast recovery of the capacity at different current densities.     

A Deep‐Cycle Aqueous Zinc‐Ion Battery Containing an Oxygen‐Deficient Vanadium Oxide Cathode

Rechargeable aqueous zinc‐ion batteries are attractive because of their inherent safety, low cost, and high energy density. However, viable cathode materials (such as vanadium oxides) suffer from strong Coulombic ion–lattice interactions with divalent Zn²⁺, thereby limiting stability when cycled at a high charge/discharge depth with high capacity. A synthetic strategy is reported for an oxygen‐deficient vanadium oxide cathode in which facilitated Zn²⁺ reaction kinetic enhance capacity and Zn²⁺ pathways for high reversibility. The benefits for the robust cathode are evident in its performance metrics; the aqueous Zn battery shows an unprecedented stability over 200 cycles with a high specific capacity of approximately 400 mAh g^?1, achieving 95 % utilization of its theoretical capacity, and a long cycle life up to 2 000 cycles at a high cathode utilization efficiency of 67 %. This work opens up a new avenue for synthesis of novel cathode materials with an oxygen‐deficient structure for use in advanced batteries.     

A High‐Voltage and Ultralong‐Life Sodium Full Cell for Stationary Energy Storage

Recently, there has been great interest in developing advanced sodium‐ion batteries for large‐scale application. Most efforts have concentrated on the search for high‐performance electrode materials only in sodium half‐cells. Research on sodium full cells for practical application has encountered many problems, such as insufficient cycles with rapid capacity decay, low safety, and low operating voltage. Herein, we present a layered P2‐Na_0.66Ni_0.17Co_0.17Ti_0.66O₂, as both an anode (ca. 0.69 V versus Na⁺/Na) and as a high‐voltage cathode (ca. 3.74 V versus Na⁺/Na). The full cell based on this bipolar electrode exhibits well‐defined voltage plateaus near 3.10 V, which is the highest average voltage in the symmetric cells. It also shows the longest cycle life (75.9 % capacity retention after 1000 cycles) in all sodium full cells, a usable capacity of 92 mAh g^?1, and superior rate capability (65 mAh g^?1 at a high rate of 2C).     

A Dual‐Ion Organic Symmetric Battery Constructed from Phenazine‐Based Artificial Bipolar Molecules

Symmetric batteries received an increasing research interest in the past few years because of their simplified fabrication process and reduced manufacturing cost. In this study, we propose the first dual‐ion organic symmetric cell based on a molecular anion of 4,4′‐(phenazine‐5,10‐diyl)dibenzoate. The alkali salt of 4,4′‐(phenazine‐5,10‐diyl)dibenzoate allows a facile transport of cations and large anions, and remains stable in both oxidized and reduced states. The large potential difference between phenazine and benzoate results in a high cell voltage of 2.5 V and an energy density of 127 Wh kg^?1 at a current rate of 1 C. The introduction of bipolar organic materials may further consolidate the development of symmetric batteries that are fabricated from abundant elements and environmentally friendly materials.     

Solid‐State Electrolyte Anchored with a Carboxylated Azo Compound for All‐Solid‐State Lithium Batteries

Organic electrode materials are promising for green and sustainable lithium‐ion batteries. However, the high solubility of organic materials in the liquid electrolyte results in the shuttle reaction and fast capacity decay. Herein, azo compounds are firstly applied in all‐solid‐state lithium batteries (ASSLB) to suppress the dissolution challenge. Due to the high compatibility of azobenzene (AB) based compounds to Li₃PS₄ (LPS) solid electrolyte, the LPS solid electrolyte is used to prevent the dissolution and shuttle reaction of AB. To maintain the low interface resistance during the large volume change upon cycling, a carboxylate group is added into AB to provide 4‐(phenylazo) benzoic acid lithium salt (PBALS), which could bond with LPS solid electrolyte via the ionic bonding between oxygen in PBALS and lithium ion in LPS. The ionic bonding between the active material and solid electrolyte stabilizes the contact interface and enables the stable cycle life of PBALS in ASSLB.     

An Antiaromatic Electrode‐Active Material Enabling High Capacity and Stable Performance of Rechargeable Batteries

Although aromatic compounds occupy a central position in organic chemistry, antiaromatic compounds have demonstrated little practical utility. Herein we report the application of an antiaromatic compound as an electrode‐active material in rechargeable batteries. The performance of dimesityl‐substituted norcorrole nickel(II) complex (NiNC) as a cathode‐active material was examined with a Li metal anode. A maximum discharge capacity of about 207 mAhg^?1 was maintained after 100 charge/discharge cycles. Moreover, the bipolar redox property of NiNC enables the construction of a Li metal free rechargeable battery. The high performance of NiNC batteries demonstrates a prospective feature of stable antiaromatic compounds as electrode‐active materials.     

Hierarchical Surface Atomic Structure of a Manganese‐Based Spinel Cathode for Lithium‐Ion Batteries

The increasing use of lithium‐ion batteries (LIBs) in high‐power applications requires improvement of their high‐temperature electrochemical performance, including their cyclability and rate capability. Spinel lithium manganese oxide (LiMn₂O₄) is a promising cathode material because of its high stability and abundance. However, it exhibits poor cycling performance at high temperatures owing to Mn dissolution. Herein we show that when stoichiometric lithium manganese oxide is coated with highly doped spinels, the resulting epitaxial coating has a hierarchical atomic structure consisting of cubic‐spinel, tetragonal‐spinel, and layered structures, and no interfacial phase is formed. In a practical application of the coating to doped spinel, the material retained 90 % of its capacity after 800 cycles at 60 °C. Thus, the formation of an epitaxial coating with a hierarchical atomic structure could enhance the electrochemical performance of LIB cathode materials while preventing large losses in capacity.     

An Ultrastable Anode for Long‐Life Room‐Temperature Sodium‐Ion Batteries

Sodium‐ion batteries are important alternative energy storage devices that have recently come again into focus for the development of large‐scale energy storage devices because sodium is an abundant and low‐cost material. However, the development of electrode materials with long‐term stability has remained a great challenge. A novel negative‐electrode material, a P2‐type layered oxide with the chemical composition Na_2/3Co_1/3Ti_2/3O₂, exhibits outstanding cycle stability (ca. 84.84 % capacity retention for 3000 cycles, very small decrease in the volume (0.046 %) after 500 cycles), good rate capability (ca. 41 % capacity retention at a discharge/charge rate of 10 C), and a usable reversible capacity of about 90 mAh g^?1 with a safe average storage voltage of approximately 0.7 V in the sodium half‐cell. This P2‐type layered oxide is a promising anode material for sodium‐ion batteries with a long cycle life and should greatly promote the development of room‐temperature sodium‐ion batteries.     

Reversible Redox Chemistry of Azo Compounds for Sodium‐Ion Batteries

Sustainable sodium‐ion batteries (SSIBs) using renewable organic electrodes are promising alternatives to lithium‐ion batteries for the large‐scale renewable energy storage. However, the lack of high‐performance anode material impedes the development of SSIBs. Herein, we report a new type of organic anode material based on azo group for SSIBs. Azobenzene‐4,4′‐dicarboxylic acid sodium salt is used as a model to investigate the electrochemical behaviors and reaction mechanism of azo compound. It exhibits a reversible capacity of 170 mAh g^?1 at 0.2C. When current density is increased to 20C, the reversible capacities of 98 mAh g^?1 can be retained for 2000 cycles, demonstrating excellent cycling stability and high rate capability. The detailed characterizations reveal that azo group acts as an electrochemical active site to reversibly bond with Na⁺. The reversible redox chemistry between azo compound and Na ions offer opportunities for developing long‐cycle‐life and high‐rate SSIBs.     

Pushing Up Lithium Storage through Nanostructured Polyazaacene Analogues as Anode

According to the evidence from both theoretical calculations and experimental findings, conjugated ladder polymers containing large π‐conjugated structure, a high number of nitrogen heteroatoms, and a multiring aromatic system, could be an ideal organic anode candidate for lithium‐ion batteries (LIBs). In this report, we demonstrated that the nanostructured polyazaacene analogue poly(1,6‐dihydropyrazino[2,3g]quinoxaline‐2,3,8‐triyl‐7‐(2H)‐ylidene‐7,8‐dimethylidene) (PQL) shows high performance as anode materials in LIBs: high capacity (1750 mAh g^?1, 0.05C), good rate performance (303 mAh g^?1, 5C), and excellent cycle life (1000 cycles), especially at high temperature of 50 °C. Our results suggest nanostructured conjugated ladder polymers could be alternative electrode materials for the practical application of LIBs.     

Radical Compatibility with Nonaqueous Electrolytes and Its Impact on an All‐Organic Redox Flow Battery

Nonaqueous redox flow batteries hold the promise of achieving higher energy density because of the broader voltage window than aqueous systems, but their current performance is limited by low redox material concentration, cell efficiency, cycling stability, and current density. We report a new nonaqueous all‐organic flow battery based on high concentrations of redox materials, which shows significant, comprehensive improvement in flow battery performance. A mechanistic electron spin resonance study reveals that the choice of supporting electrolytes greatly affects the chemical stability of the charged radical species especially the negative side radical anion, which dominates the cycling stability of these flow cells. This finding not only increases our fundamental understanding of performance degradation in flow batteries using radical‐based redox species, but also offers insights toward rational electrolyte optimization for improving the cycling stability of these flow batteries.     

An Insoluble Benzoquinone‐Based Organic Cathode for Use in Rechargeable Lithium‐Ion Batteries

Application of organic electrode materials in rechargeable batteries has attracted great interest because such materials contain abundant carbon, hydrogen, and oxygen elements. However, organic electrodes are highly soluble in organic electrolytes. An organic electrode of 2,3,5,6‐tetraphthalimido‐1,4‐benzoquinone (TPB) is reported in which rigid groups coordinate to a molecular benzoquinone skeleton. The material is insoluble in aprotic electrolyte, and demonstrates a high capacity retention of 91.4 % (204 mA h g⁻¹) over 100 cycles at 0.2 C. The extended π‐conjugation of the material contributes to enhancement of the electrochemical performance (155 mA h g⁻¹ at 10 C). Moreover, density functional theory calculations suggest that favorable synergistic reactions between multiple carbonyl groups and lithium ions can enhance the initial lithium ion intercalation potential. The described approach may provide a novel entry to next‐generation organic electrode materials with relevance to lithium‐ion batteries.     

Size‐Mediated Recurring Spinel Sub‐nanodomains in Li‐ and Mn‐Rich Layered Cathode Materials

Li‐ and Mn‐rich layered oxides are among the most promising cathode materials for Li‐ion batteries with high theoretical energy density. Its practical application is, however, hampered by the capacity and voltage fade after long cycling. Herein, a finite difference method for near‐edge structure (FDMNES) code was combined with in situ X‐ray absorption spectroscopy (XAS) and transmission electron microscopy/electron energy loss spectroscopy (TEM/EELS) to investigate the evolution of transition metals (TMs) in fresh and heavily cycled electrodes. Theoretical modeling reveals a recurring partially reversible LiMn₂O₄‐like sub‐nanodomain formation/dissolution process during each charge/discharge, which accumulates gradually and accounts for the Mn phase transition. From the modeling of spectra and maps of the valence state over large regions of the cathodes, it was found that the phase change is size‐dependent. After prolonged cycling, the TMs displayed different levels of inactivity.     

Free‐Standing Air Cathodes Based on 3D Hierarchically Porous Carbon Membranes: Kinetic Overpotential of Continuous Macropores in Li‐O2 Batteries

Free‐standing macroporous air electrodes with enhanced interfacial contact, rapid mass transport, and tailored deposition space for large amounts of Li₂O₂ are essential for improving the rate performance of Li‐O₂ batteries. An ordered mesoporous carbon membrane with continuous macroporous channels was prepared by inversely topological transformation from ZnO nanorod array. Utilized as a free‐standing air cathode for Li‐O₂ battery, the hierarchically porous carbon membrane shows superior rate performance. However, the increased cross‐sectional area of the continuous macropores on the cathode surface leads to a kinetic overpotential with large voltage hysteresis and linear voltage variation against Butler–Volmer behavior. The kinetics were investigated based on the rate‐determining step of second electron transfer accompanied by migration of Li⁺ in solid or quasi‐solid intermediates. These discoveries shed light on the design of the air cathode for Li‐O₂ batteries with high‐rate performance.     

Mesoporous Prussian Blue Analogues: Template‐Free Synthesis and Sodium‐Ion Battery Applications

The synthesis of mesoporous Prussian blue analogues through a template‐free methodology and the application of these mesoporous materials as high‐performance cathode materials in sodium‐ion batteries is presented. Crystalline mesostructures were produced through a synergistically coupled nanocrystal formation and aggregation mechanism. As cathodes for sodium‐ion batteries, the Prussian blue analogues all show a reversible capacity of 65 mA h g^?1 at low current rate and show excellent cycle stability. The reported method stands as an environmentally friendly and low‐cost alternative to hard or soft templating for the fabrication of mesoporous materials.