Polyanthraquinone as a Reliable Organic Electrode for Stable and Fast Lithium Storage

In spite of recent progress, there is still a lack of reliable organic electrodes for Li storage with high comprehensive performance, especially in terms of long‐term cycling stability. Herein, we report an ideal polymer electrode based on anthraquinone, namely, polyanthraquinone (PAQ), or specifically, poly(1,4‐anthraquinone) (P14AQ) and poly(1,5‐anthraquinone) (P15AQ). As a lithium‐storage cathode, P14AQ showed exceptional performance, including reversible capacity almost equal to the theoretical value (260 mA h g^?1; >257 mA h g^?1 for AQ), a very small voltage gap between the charge and discharge curves (2.18–2.14=0.04 V), stable cycling performance (99.4 % capacity retention after 1000 cycles), and fast‐discharge/charge ability (release of 69 % of the low‐rate capacity or 64 % of the energy in just 2 min). Exploration of the structure–performance relationship between P14AQ and related materials also provided us with deeper understanding for the design of organic electrodes.     

Charge Storage Mechanism and Structural Evolution of Viologen Crystals as the Cathode of Lithium Batteries

Although organic ionic crystals represent an attractive class of active materials for rechargeable batteries owing to their high capacity and low solubility in electrolytes, they generally suffer from limited electronic conductivity and moderate voltage. Furthermore, the charge storage mechanism and structural evolution during the redox processes are still not clearly understood. Here we describe ethyl viologen iodide (EVI₂) and ethyl viologen diperchlorate (EV(ClO₄)₂) as cathode materials of lithium batteries which crystallize in a monoclinic system with alternating organic EV²⁺ layers and inorganic I^?/ClO₄^? layers. The EVI₂ electrode exhibits a high initial discharge plateau of 3.7 V (vs. Li⁺/Li) because of its anion storage ability. When I^? is replaced by ClO₄^?, the obtained EV(ClO₄)₂ electrode displays excellent rate performance with a theoretical capacity of 78 % even at 5 C owing to the good electron conductivity of ClO₄^? layers. EVI₂ and EV(ClO₄)₂ also show excellent cycling stability (capacity retention >96 % after 200 cycles).     

Synthesis and characterization of submicron size particles of LiMn<Subscript>2</Subscript>O<Subscript>4</Subscript> by microemulsion route

Among the various positive electrode materials investigated for Li-ion batteries, spinel LiMn₂O₄ is one of the most important materials. Small particles of the active materials facilitate high-rate capability due to large surface to mass ratio and small diffusion path length. The present work involves the synthesis of submicron size particles of LiMn₂O₄ in a quaternary microemulsion medium. The precursor obtained from the reaction is heated at different temperatures in the range from 400 to 900 °C. The samples heated at 800 and 900 °C are found to possess pure spinel phase with particle size <200 nm, as evidenced from XRD, SEM, and TEM studies. The electrochemical characterization studies provide discharge capacity values of about 100 mAh g⁻¹ at C/5 rate, and there is a moderate decrease in capacity by increasing the rate of charge–discharge cycling. Studies also include charge–discharge cycling and ac impedance studies in temperature range from −10 to 40 °C. Impedance data are analyzed with the help of an equivalent circuit and a nonlinear least squares fitting program. From temperature dependence of charge-transfer resistance, a value of 0.62 eV is obtained for the activation energy of Mn³⁺/Mn⁴⁺ redox process, which accompanies the intercalation/deintercalation of the Li⁺ ion in LiMn₂O₄.     

Electrochemically activated MnO as a cathode material for sodium-ion batteries

Besides classical electrode materials pertaining to Li-ion batteries, recent interest has been devoted to pairs of active redox composites having a redox center and an intercalant source. Taking advantage of the NaPF₆ salt decomposition above 4.2 V, we extrapolate this concept to the electrochemical in situ preparation of F-based MnO composite electrodes for Na-ion batteries. Such electrodes exhibit a reversible discharge capacity of 145 mAh g^− 1 at room temperature. The amorphization of pristine MnO electrode after activation is attributed to the electrochemical grinding effect caused by substantial atomic migration and lattice strain build-up upon cycling.     

A Multi-Wall Sn/SnO2@Carbon Hollow Nanofiber Anode Material for High-Rate and Long-Life Lithium-Ion Batteries

Multi-wall Sn/SnO₂@carbon hollow nanofibers evolved from SnO₂ nanofibers are designed and programable synthesized by electrospinning, polypyrrole coating, and annealing reduction. The synthesized hollow nanofibers have a special wire-in-double-wall-tube structure with larger specific surface area and abundant inner spaces, which can provide effective contacting area of electrolyte with electrode materials and more active sites for redox reaction. It shows excellent cycling stability by virtue of effectively alleviating pulverization of tin-based electrode materials caused by volume expansion. Even after 2000 cycles, the wire-in-double-wall-tube Sn/SnO₂@carbon nanofibers exhibit a high specific capacity of 986.3 mAh g⁻¹ (1 A g⁻¹) and still maintains 508.2 mAh g⁻¹ at high current density of 5 A g⁻¹. This outstanding electrochemical performance suggests the multi-wall Sn/SnO₂@ carbon hollow nanofibers are great promising for high performance energy storage systems.     

A Redox‐Active 2D Metal–Organic Framework for Efficient Lithium Storage with Extraordinary High Capacity

Metal–organic framework cathodes usually exhibit low capacity and poor electrochemical performance for Li‐ion storage owing to intrinsic low conductivity and inferior redox activity. Now a redox‐active 2D copper–benzoquinoid (Cu‐THQ) MOF has been synthesized by a simple solvothermal method. The abundant porosity and intrinsic redox character endow the 2D Cu‐THQ MOF with promising electrochemical activity. Superior performance is achieved as a Li‐ion battery cathode with a high reversible capacity (387 mA h g^?1), large specific energy density (775 Wh kg^?1), and good cycling stability. The reaction mechanism is unveiled by comprehensive spectroscopic techniques: a three‐electron redox reaction per coordination unit and one‐electron redox reaction per copper ion mechanism is demonstrated. This elucidatory understanding sheds new light on future rational design of high‐performance MOF‐based cathode materials for efficient energy storage and conversion.     

Synthesis and properties of polyenic oligosulfides derived from acetylene and elemental sulfur

Oligosulfides derived from ethyne-1,2-dithiol were synthesized in up to 96% yield via insertion of elemental sulfur into the Na-C_sp bond of sodium acetylides (HC≡CNa, NaC≡CSNa) in liquid ammonia, followed by hydrolysis and spontaneous oligomerization of ethynethiols, ethynedithiols, and mono-and bis-(polysulfanyl)ethynes (HC≡CSH, HSC≡CSH, HC≡CS_xH, HS_xC≡CS_yH). The resulting polyenic oligosulfides were isolated as brown powders melting in the temperature range from 122 to 203°C and containing up to 77% of sulfur; they are sparingly soluble in organic solvents and are high-resistance semiconductors (10^?13–10^?14 S cm^?1) possessing paramagnetic (10¹⁷–10¹⁸ spin g^?1) and redox properties. According to the data of IR and ESR spectroscopy and cyclic voltammetry, the oligomers obtained consist mainly of different oligosulfide units, including oligothienothiophene structures. They also ensure a high discharge capacity (345–720 mA h g^?1) of lithium sulfur rechargeable batteries.     

Micro‐MoS2 with Excellent Reversible Sodium‐Ion Storage

Low storage capacity and poor cycling stability are the main drawbacks of the electrode materials for sodium‐ion (Na‐ion) batteries, due to the large radius of the Na ion. Here we show that micro‐structured molybdenum disulfide (MoS₂) can exhibit high storage capacity and excellent cycling and rate performances as an anode material for Na‐ion batteries by controlling its intercalation depth and optimizing the binder. The former method is to preserve the layered structure of MoS₂, whereas the latter maintains the integrity of the electrode during cycling. A reversible capacity of 90 mAh g^?1 is obtained on a potential plateau feature when less than 0.5 Na per formula unit is intercalated into micro‐MoS₂. The fully discharged electrode with sodium alginate (NaAlg) binder delivers a high reversible capacity of 420 mAh g^?1. Both cells show excellent cycling performance. These findings indicate that metal chalcogenides, for example, MoS₂, can be promising Na‐storage materials if their operation potential range and the binder can be appropriately optimized.     

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.     

A Truxenone-based Covalent Organic Framework as an All-Solid-State Lithium-Ion Battery Cathode with High Capacity

All-solid-state lithium ion batteries (LIBs) are ideal for energy storage given their safety and long-term stability. However, there is a limited availability of viable electrode active materials. Herein, we report a truxenone-based covalent organic framework (COF-TRO) as cathode materials for all-solid-state LIBs. The high-density carbonyl groups combined with the ordered crystalline COF structure greatly facilitate lithium ion storage via reversible redox reactions. As a result, a high specific capacity of 268 mAh g⁻¹, almost 97.5 % of the calculated theoretical capacity was achieved. To the best of our knowledge, this is the highest capacity among all COF-based cathode materials for all-solid-state LIBs reported so far. Moreover, the excellent cycling stability (99.9 % capacity retention after 100 cycles at 0.1 C rate) shown by COF-TRO suggests such truxenone-based COFs have great potential in energy storage applications.     

Cyclotetrabenzil Derivatives for Electrochemical Lithium-Ion Storage

Organic electrode materials could revolutionize batteries because of their high energy densities, the use of Earth-abundant elements, and structural diversity which allows fine-tuning of electrochemical properties. However, small organic molecules and intermediates formed during their redox cycling in lithium-ion batteries (LIBs) have high solubility in organic electrolytes, leading to rapid decay of cycling performance. We report the use of three cyclotetrabenzil octaketone macrocycles as cathode materials for LIBs. The rigid and insoluble naphthalene-based cyclotetrabenzil reversibly accepts eight electrons in a two-step process with a specific capacity of 279 mAh g⁻¹ and a stable cycling performance with ≈65 % capacity retention after 135 cycles. DFT calculations indicate that its reduction increases both ring strain and ring rigidity, as demonstrated by computed high distortion energies, repulsive regions in NCI plots, and close [C⋅⋅⋅C] contacts between the naphthalenes. This work highlights the importance of shape-persistency and ring strain in the design of redox-active macrocycles that maintain very low solubility in various redox states.     

An Aqueous Conducting Redox‐Polymer‐Based Proton Battery that Can Withstand Rapid Constant‐Voltage Charging and Sub‐Zero Temperatures

Electrodes based on organic matter operating in aqueous electrolytes enable new approaches and technologies for assembling and utilizing batteries that are difficult to achieve with traditional electrode materials. Here, we report how thiophene‐based trimeric structures with naphthoquinone or hydroquinone redox‐active pendent groups can be processed in solution, deposited, dried and subsequently polymerized in solid state to form conductive (redox) polymer layers without any additives. Such post‐deposition polymerization offers efficient use of material, high mass loading (up to 10 mg cm^?2) and good flexibility in the choice of substrate and coating method. By employing these materials as anode and cathode in an acidic aqueous electrolyte a rocking‐chair proton battery is built. The battery shows good cycling stability (85 % after 500 cycles), withstands rapid charging, with full capacity (60 mAh g^?1) reached within 100 seconds, allows for direct integration with photovoltaics, and retains its favorable characteristics even at ?24 °C.     

长循环高电压钠离子电池正极材料P2-Na2/3Mn1/3Bi1/3Ni1/3O2的合成及性能

镍基层状氧化物NaNiO₂钠离子电池材料具有高电压和高容量的特性,且制备方法较为简单,但姜-泰勒(Jahn-Teller)效应使其在高倍率循环下容量较低以及在高电压(4.5 V)下无法稳定循环。通过调节溶胶-凝胶工艺的条件,设计、合成了Na_2/3Mn_1/3Bi_1/3Ni_1/3O₂片层状金属氧化物,并将其作为正极活性材料,在空气环境中组装成钠离子电池,进行电化学测试,考察Bi、Mn掺入量对电池电化学影响。研究结果表明:当金属Mn和Bi共掺时,在1.2~4.5 V宽电压范围内,电池在循环50周后容量为90.39 mAh·g^-1。在2.0~4.0 V电压范围内1.0C (115 mA·g^-1)倍率下恒流充放电50周后的容量保持率为96.96%,循环850周后的保持率为80.15%,具有良好的循环稳定性和安全性。     

Reaction of (diacetoxyiodo)benzene with excess of trifluoromethanesulfonic acid. A convenient route to para-phenylene type hypervalent iodine oligomers

Reaction of (diacetoxyiodo)benzene [PhI(OAc)₂] in trifluoromethanesulfonic acid (TfOH) resulted in oligomerization of PhI(OAc)₂. Quenching with NaBr gave the bromide salts of hypervalent iodine oligomers that were determined by thermolysis with KI to be a para phenylene type of oligomers. Neutralization of the reaction mixture of PhI(OAc)₂ and TfOH with aqueous NaHCO₃ yielded the triflate salts of iodine oligomers. Furthermore, quenching the reaction mixture with aromatic substrates afforded arylated iodine oligomers. These iodine oligomers were found to be 3-4 of the number average degree of polymerization (P_n) by GC analysis of the thermolysis products and ¹H NMR analysis. The major products, trimer and tetramer, were synthesized independently.     

长循环高电压钠离子电池正极材料P2-Na2/3Mn1/3Bi1/3Ni1/3O2的合成及性能

镍基层状氧化物NaNiO₂钠离子电池材料具有高电压和高容量的特性,且制备方法较为简单,但姜-泰勒(Jahn-Teller)效应使其在高倍率循环下容量较低以及在高电压(4.5 V)下无法稳定循环。通过调节溶胶-凝胶工艺的条件,设计、合成了Na_2/3Mn_1/3Bi_1/3Ni_1/3O₂片层状金属氧化物,并将其作为正极活性材料,在空气环境中组装成钠离子电池,进行电化学测试,考察Bi、Mn掺入量对电池电化学影响。研究结果表明：当金属Mn和Bi共掺时,在1.2~4.5 V宽电压范围内,电池在循环50周后容量为90.39 mAh·g^-1。在2.0~4.0 V电压范围内1.0C (115 mA·g^-1)倍率下恒流充放电50周后的容量保持率为96.96%,循环850周后的保持率为80.15%,具有良好的循环稳定性和安全性。     

长循环高电压钠离子电池正极材料P2-Na2/3Mn1/3Bi1/3Ni1/3O2的合成及性能

镍基层状氧化物NaNiO₂钠离子电池材料具有高电压和高容量的特性,且制备方法较为简单,但姜-泰勒(Jahn-Teller)效应使其在高倍率循环下容量较低以及在高电压(4.5 V)下无法稳定循环。通过调节溶胶-凝胶工艺的条件,设计、合成了Na_2/3Mn_1/3Bi_1/3Ni_1/3O₂片层状金属氧化物,并将其作为正极活性材料,在空气环境中组装成钠离子电池,进行电化学测试,考察Bi、Mn掺入量对电池电化学影响。研究结果表明：当金属Mn和Bi共掺时,在1.2~4.5 V宽电压范围内,电池在循环50周后容量为90.39 mAh·g^-1。在2.0~4.0 V电压范围内1.0C (115 mA·g^-1)倍率下恒流充放电50周后的容量保持率为96.96%,循环850周后的保持率为80.15%,具有良好的循环稳定性和安全性。     

A Multi‐Wall Sn/SnO2@Carbon Hollow Nanofiber Anode Material for High‐Rate and Long‐Life Lithium‐Ion Batteries

Multi‐wall Sn/SnO₂@carbon hollow nanofibers evolved from SnO₂ nanofibers are designed and programable synthesized by electrospinning, polypyrrole coating, and annealing reduction. The synthesized hollow nanofibers have a special wire‐in‐double‐wall‐tube structure with larger specific surface area and abundant inner spaces, which can provide effective contacting area of electrolyte with electrode materials and more active sites for redox reaction. It shows excellent cycling stability by virtue of effectively alleviating pulverization of tin‐based electrode materials caused by volume expansion. Even after 2000 cycles, the wire‐in‐double‐wall‐tube Sn/SnO₂@carbon nanofibers exhibit a high specific capacity of 986.3 mAh g^?1 (1 A g^?1) and still maintains 508.2 mAh g^?1 at high current density of 5 A g^?1. This outstanding electrochemical performance suggests the multi‐wall Sn/SnO₂@ carbon hollow nanofibers are great promising for high performance energy storage systems.     

Catalytically Active CoSe2 Supported on Nitrogen-Doped Three Dimensional Porous Carbon as a Cathode for Highly Stable Lithium-Sulfur Battery

Lithium-sulfur batteries are promising secondary energy storage devices that are mainly limited by its unsatisfactory cyclability owing to inefficient reversible conversion of sulfur and lithium sulfide on the cathode during the discharge/charging process. In this study, nitrogen-doped three-dimensional porous carbon material loaded with CoSe₂ nanoparticles (CoSe₂-PNC) is developed as a cathode for lithium-sulfur battery. A combination of CoSe₂ and nitrogen-doped porous carbon can efficiently improve the cathode activity and its conductivity, resulting in enhanced redox kinetics of the charge/discharge process. The obtained electrode exhibits a high discharge specific capacity of 1139.6 mAh g⁻¹ at a current density of 0.2 C. After 100 cycles, its capacity remained at 865.7 mAh g⁻¹ thus corresponding to a capacity retention of 75.97 %. In a long-term cycling test, discharge specific capacity of 546.7 mAh g⁻¹ was observed after 300 cycles performed at a current density of 1 C.     

A hybrid nonaqueous electrochemical supercapacitor using nano-sized iron oxyhydroxide and activated carbon

A beta-iron oxyhydroxide (FeOOH) was synthesized via a hydrolyzing route and investigated as a lithium intercalation host. It delivers a capacity of about 170 mAh/g and exhibits good cycling performance when charged/discharged in the voltage range from 1.6 V to 3.3 V. For the first time we have confirmed that FeOOH is suitable for using it as a negative electrode for hybrid electrochemical supercapacitor assembled with an activated carbon positive electrode in 1.0 M LiPF₆ ethylene carbonate/dimethyl carbonate (EC/DMC, 1:2 in volume) solution. The cell reveals a slightly sloping voltage profile from 0 V to 2.8 V and gives an estimated specific energy of 45 Wh/kg based on the total weight of two electrode materials, approximately two times of carbon/carbon electrochemical double layer capacitors. The hybrid supercapacitor shows a good cycling performance, it remains approximately 96% of initial capacity after 800 cycles at a charge/discharge rate of 4 C. The capacitor also shows a desirable rate capability, even at 10 C discharge rate, it holds 80% of capacity compared with that at 1 C discharge rate.     

Hierarchical SnO2/Carbon Nanofibrous Composite Derived from Cellulose Substance as Anode Material for Lithium‐Ion Batteries

A hierarchical fibrous SnO₂/carbon nanocomposite composed of fine SnO₂ nanocrystallites immobilized as a thin layer on a carbon nanofiber surface was synthesized employing natural cellulose substance as both scaffold and carbon source. It was achieved by calcination/carbonization of the as‐deposited SnO₂‐gel/cellulose hybrid in an argon atmosphere. As being employed as an anode material for lithium‐ion batteries, the porous structures, small SnO₂ crystallite sizes, and the carbon buffering matrix possessed by the nanocomposite facilitate the electrode–electrolyte contact, promote the electron transfer and Li⁺ diffusion, and relieve the severe volume change and aggregation of the active particles during the charge/discharge cycles. Hence, the nanocomposite showed high reversible capacity, significant cycling stability, and rate capability that are superior to the nanotubular SnO₂ and SnO₂ sol–gel powder counter materials. For such a composite with 27.8 wt % SnO₂ content and 346.4 m² g^?1 specific surface area, a capacity of 623 mAh g^?1 was delivered after 120 cycles at 0.2 C. Further coating of the SnO₂/carbon nanofibers with an additional carbon layer resulted in an improved cycling stability and rate performance.