Co~(2+)掺杂石墨烯/LiFePO_4锂离子电池复合正极材料的制备与表征

使用溶胶凝胶原位碳热还原制备了Co2+掺杂石墨烯/LiFePO4锂离子电池复合正极材料(石墨烯/LiCo0.03Fe0.97PO4),以期获得比容量高、充放电速率快和循环性能优良的锂离子电池正极材料。结构和形貌表征结果显示:石墨烯/LiCo0.03Fe0.97PO4复合材料具有三维导电网络结构,颗粒在石墨烯片层间生长均匀,粒径在200nm左右。电化学测试结果显示:石墨烯/LiCo0.03Fe0.97PO4复合材料具有高的可逆比容量和优异的循环倍率性能。2.0~4.0V充放电下0.1C时的首次放电比容量为159mA·h·g-1,在10.0C下首次放电比容量也有74mA·h·g-1;0.5C下循环100次,比容量保持率为99.7%。石墨烯/LiCo0.03Fe0.97PO4复合材料电化学性能提高的原因主要为Co2+掺杂和石墨烯包覆的协同作用。     

Two Birds One Stone: Graphene Assisted Reaction Kinetics and Ionic Conductivity in Phthalocyanine-Based Covalent Organic Framework Anodes for Lithium-ion Batteries

This work reports a covalent organic framework composite structure (PMDA-NiPc-G), incorporating multiple-active carbonyls and graphene on the basis of the combination of phthalocyanine (NiPc(NH₂)₄) containing a large π-conjugated system and pyromellitic dianhydride (PMDA) as the anode of lithium-ion batteries. Meanwhile, graphene is used as a dispersion medium to reduce the accumulation of bulk covalent organic frameworks (COFs) to obtain COFs with small-volume and few-layers, shortening the ion migration path and improving the diffusion rate of lithium ions in the two dimensional (2D) grid layered structure. PMDA-NiPc-G showed a lithium-ion diffusion coefficient (D_Li⁺) of 3.04 × 10⁻¹⁰ cm² s⁻¹ which is 3.6 times to that of its bulk form (0.84 × 10⁻¹⁰ cm² s⁻¹). Remarkably, this enables a large reversible capacity of 1290 mAh g⁻¹ can be achieved after 300 cycles and almost no capacity fading in the next 300 cycles at 100 mA g⁻¹. At a high areal capacity loading of ≈3 mAh cm⁻², full batteries assembled with LiNi_0.8Co_0.1Mn_0.1O₂ (NCM-811) and LiFePO₄ (LFP) cathodes showed 60.2% and 74.7% capacity retention at 1 C for 200 cycles. Astonishingly, the PMDA-NiPc-G/NCM-811 full battery exhibits ≈100% capacity retention after cycling at 0.2 C. Aided by the analysis of kinetic behavior of lithium storage and theoretical calculations, the capacity-enhancing mechanism and lithium storage mechanism of covalent organic frameworks are revealed. This work may lead to more research on designable, multifunctional COFs for electrochemical energy storage.     

Insights into the Ti4+ doping in P2-type Na0.67Ni0.33Mn0.52Ti0.15O2 for enhanced performance of sodium-ion batteries

Due to the sodium abundance and availability,sodium-ion batteries (SIBs) have the potential to meet the worldwide growing demand of electrical energy storage.P2-type sodium transition-metal layer oxides with a high energy density are considered as the most promising cathode materials for SIBs.We present here a detailed study of the enhanced rate capability and cyclic stability of the Ti-doped Na0.67Ni0.33Mn0.67O2 cathode material.The combined analysis of ex-situ X-ray absorption fine structure (XAFS) spectroscopy,aberration-corrected high resolution transmission electron microscopy (AB-HRTEM) and X-ray diffraction (XRD) show that the strong Ti-O bond in the transition metal layers stabilizes the local structure,destroy the Na+-vacancy ordering and arrest the irreversible multiphase transformation that occurs during the intercalation/deintercalation process.Actually,Na0.67Ni0.33Mn0.52Ti0.15O2 exhibits a reversible capacity of 89.6 mA h g-1 even at 5 C,an excellent cyclability with 88.78 ％ capacity retention after 200 cycles at 0.5 C.This study provides a better understanding in optimization of the design of high-energy cathode materials based on titanium doped layered oxides for SIBs.     

Carbon nanotube (CNT)-based composites as electrode material for rechargeable Li-ion batteries: A review

The ever-increasing demands for higher energy density and higher power capacity of Li-ion secondary batteries have led to search for electrode materials whose capacities and performance are better than those available today. Carbon nanotubes (CNTs), because of their unique 1D tubular structure, high electrical and thermal conductivities and extremely large surface area, have been considered as ideal additive materials to improve the electrochemical characteristics of both the anode and cathode of Li-ion batteries with much enhanced energy conversion and storage capacities. Recent development of electrode materials for LIBs has been driven mainly by hybrid nanostructures consisting of Li storage compounds and CNTs. In this paper, recent advances are reviewed of the use of CNTs and the methodologies developed to synthesize CNT-based composites for electrode materials. The physical, transport and electrochemical behaviors of the electrodes made from composites containing CNTs are discussed. The electrochemical performance of LIBs affected by the presence of CNTs in terms of energy and power densities, rate capacity, cyclic life and safety are highlighted in comparison with those without or containing other types of carbonaceous materials. The challenges that remain in using CNTs and CNT-based composites, as well as the prospects for exploiting them in the future are discussed.     

LiCoO2/LiNi0.8Co0.15Al0.05O2混合正极的颗粒级配与电化学性能

通过机械球磨制备不同质量比的LCO/NCA混合正极材料,采用X射线衍射仪(XRD)和扫描电子显微镜(SEM)表征其相结构和微观形貌,研究了这种材料的电化学性能。结果表明,两种正极材料球磨混合后其晶体结构均未改变,但是初始的NCA球形二次颗粒被打散,形成的纳米粒子弥散填充在LCO微米颗粒的孔隙之间,提高了正极材料的涂膜密度和二者之间的接触紧密性。当LCO:NCA=6:4时混合正极材料具有最佳的颗粒级配效果,其首次充放电效率最高,为92.4%;在10 C (1 C=140 mA·g^-1)倍率下的比容量(136 mA·h·g^-1)是0.2 C时的78.0%,出现了明显的协同增强效果;在1 C倍率下循环100次其容量保持率为89.8%,表现出优异的电化学性能。     

Bioinspired Redox‐Active Catechol‐Bearing Polymers as Ultrarobust Organic Cathodes for Lithium Storage

Redox‐active catechols are bioinspired precursors for ortho ‐quinones that are characterized by higher discharge potentials than para ‐quinones, the latter being extensively used as organic cathode materials for lithium ion batteries (LIBs). Here, this study demonstrates that the rational molecular design of copolymers bearing catechol‐ and Li⁺ ion‐conducting anionic pendants endow redox‐active polymers (RAPs) with ultrarobust electrochemical energy storage features when combined to carbon nanotubes as a flexible, binder‐, and metal current collector‐free buckypaper electrode. The importance of the structure and functionality of the RAPs on the battery performances in LIBs is discussed. The structure‐optimized RAPs can store high‐capacities of 360 mA h g^?1 at 5C and 320 mA h g^?1 at 30C in LIBs. The high ion and electron mobilities within the buckypaper also enable to register 96 mA h g^?1 (24% capacity retention) at an extreme C‐rate of 600C (6 s for total discharge). Moreover, excellent cyclability is noted with a capacity retention of 98% over 3400 cycles at 30C. The high capacity, superior active‐material utilization, ultralong cyclability, and excellent rate performances of RAPs‐based electrode clearly rival most of the state‐of‐the‐art Li⁺ ion organic cathodes, and opens up new horizons for large‐scalable fabrication of electrode materials for ultrarobust Li storage.     

Metal Halides for High-Capacity Energy Storage

High-capacity electrochemical energy storage systems are more urgently needed than ever before with the rapid development of electric vehicles and the smart grid. The most efficient way to increase capacity is to develop electrode materials with low molecular weights. The low-cost metal halides are theoretically ideal cathode materials due to their advantages of high capacity and redox potential. However, their cubic structure and large energy barrier for deionization impede their rechargeability. Here, the reversibility of potassium halides, lithium halides, sodium halides, and zinc halides is achieved through decreasing their dimensionality by the strong π–cation interactions between metal cations and reduced graphene oxide (rGO). Especially, the energy densities of KI-, KBr-, and KCl-based materials are 722.2, 635.0, and 739.4 Wh kg⁻¹, respectively, which are higher than those of other cathode materials for potassium-ion batteries. In addition, the full-cell with 2D KI/rGO as cathode and graphite as anode demonstrates a lifespan of over 150 cycles with a considerable capacity retention of 57.5%. The metal halides-based electrode materials possess promising application prospects and are worthy of more in-depth researches.     

Joint Charge Storage for High‐Rate Aqueous Zinc–Manganese Dioxide Batteries

Aqueous rechargeable zinc–manganese dioxide batteries show great promise for large‐scale energy storage due to their use of environmentally friendly, abundant, and rechargeable Zn metal anodes and MnO₂ cathodes. In the literature various intercalation and conversion reaction mechanisms in MnO₂ have been reported, but it is not clear how these mechanisms can be simultaneously manipulated to improve the charge storage and transport properties. A systematical study to understand the charge storage mechanisms in a layered δ‐MnO₂ cathode is reported. An electrolyte‐dependent reaction mechanism in δ‐MnO₂ is identified. Nondiffusion controlled Zn²⁺ intercalation in bulky δ‐MnO₂ and control of H⁺ conversion reaction pathways over a wide C‐rate charge–discharge range facilitate high rate performance of the δ‐MnO₂ cathode without sacrificing the energy density in optimal electrolytes. The Zn‐δ‐MnO₂ system delivers a discharge capacity of 136.9 mAh g^?1 at 20 C and capacity retention of 93% over 4000 cycles with this joint charge storage mechanism. This study opens a new gateway for the design of high‐rate electrode materials by manipulating the effective redox reactions in electrode materials for rechargeable batteries.     

Hollow Carbon Nanobelts Codoped with Nitrogen and Sulfur via a Self‐Templated Method for a High‐Performance Sodium‐Ion Capacitor

Sodium‐ion capacitors (SICs) have attracted enormous attention due to their high energy density and high power density. In this work, N and S codoped hollow carbon nanobelts (N/S‐HCNs) are synthesized by a self‐templated method. The as‐synthesized carbon nanobelts exhibit excellent performance in pseudocapacitance and electric double layer anions adsorption. After pairing the N/S‐HCNs cathode with a tin foil anode in a carbonate electrolyte, the obtained SIC achieves a high specific capacity of 400 mAh g^?1 at 1 A g^?1 (based on the mass of cathode material) and energy density of 250.35 Wh kg^?1 at 676 W kg^?1 (based on the total mass of cathode and anode materials). Besides, the presented SIC also demonstrates high cycling stability with almost 100% capacity retention after 10 000 cycles, which is among the best results of the reported SICs, suggesting the potential for high‐performance energy storage applications.     

Ultrathin 2D Metal–Organic Framework Nanosheets In situ Interpenetrated by Functional CNTs for Hybrid Energy Storage Device

The controllable construction of two-dimensional(2D)metal–organic framework(MOF)nanosheets with favorable electrochemical performances is greatly challenging for energy storage.Here,we design an in situ induced growth strategy to construct the ultrathin carboxylated carbon nanotubes(C-CNTs)interpenetrated nickel MOF(Ni-MOF/C-CNTs)nanosheets.The deliberate thickness and specific surface area of novel 2D hybrid nanosheets can be effectively tuned via finely controlling C-CNTs involvement.Due to the unique microstructure,the integrated 2D hybrid nanosheets are endowed with plentiful electroactive sites to promote the electrochemical performances greatly.The prepared Ni-MOF/C-CNTs nanosheets exhibit superior specific capacity of 680 C g^−1 at 1 A g^−1 and good capacity retention.The assembled hybrid device demonstrated the maximum energy density of 44.4 Wh kg^−1 at a power density of 440 W kg^−1.Our novel strategy to construct ultrathin 2D MOF with unique properties can be extended to synthesize various MOF-based functional materials for diverse applications.     

ZIF‐8@ZIF‐67‐Derived Nitrogen‐Doped Porous Carbon Confined CoP Polyhedron Targeting Superior Potassium‐Ion Storage

Potassium ion batteries (KIB) have become a compelling energy‐storage system owing to their cost effectiveness and the high abundance of potassium in comparison with lithium. However, its practical applications have been thwarted by a series of challenges, including marked volume expansion and sluggish reaction kinetics caused by the large radius of potassium ions. In line with this, the exploration of reliable anode materials affording high electrical conductivity, sufficient active sites, and structural robustness is the key. The synthesis of ZIF‐8@ZIF‐67 derived nitrogen‐doped porous carbon confined CoP polyhedron architectures (NC@CoP/NC) to function as innovative KIB anode materials is reported. Such composites enable an outstanding rate performance to harvest a capacity of ≈200 mAh g^?1 at 2000 mA g^?1. Additionally, a high cycling stability can be gained by maintaining a high capacity retention of 93% after 100 cycles at 100 mA g^?1. Furthermore, the potassium ion storage mechanism of the NC@CoP/NC anode is systematically probed through theoretical simulations and experimental characterization. This contribution may offer an innovative and feasible route of emerging anode design toward high performance KIBs.     

Self-Transformation Strategy Toward Vanadium Dioxide Cathode For Advanced Aqueous Zinc Batteries

In the lithium-dominated era, rechargeable Zn batteries are emerging as a competitive alternative. However, the sluggish kinetics of ion diffusion and structural destruction of cathode materials have thus far hampered the realization of future large-scale energy storage. Herein, an in situ self-transformation approach is reported to electrochemically boost the activity of a high-temperature, argon-treated VO₂ (AVO) microsphere for effective Zn ion storage. The presynthesized AVO with hierarchical structure and high crystallinity allows efficient electrochemical oxidation and water insertion to induce self-phase transformation into V₂O₅·nH₂O within the first charging process, which leads to rich active sites and fast electrochemical kinetics. Using AVO cathode, an outstanding discharge capacity of 446 mAh g⁻¹ at 0.1 A g⁻¹, high rate capability of 323 mAh g⁻¹ at 10 A g⁻¹ and excellent cycling stability for 4000 cycles at 20 A g⁻¹ with high capacity retention are demonstrated. Importantly, such zinc-ion batteries with phase self-transition can also perform well at high-loading, sub-zero temperature, or pouch cell conditions for practical application. This work not only paves a new route to design in situ self-transformation in energy storage devices, but also broadens the horizons of aqueous zinc-supplied cathodes     

High-Entropy Doping Boosts Ion/Electronic Transport of Na4Fe3(PO4)2(P2O7)/C Cathode for Superior Performance Sodium-Ion Batteries

Fe-based mixed phosphate cathodes for Na-ion batteries usually possess weak rate capacity and cycle stability challenges resulting from sluggish diffusion kinetics and poor conductivity under the relatively low preparation temperature. Here, the excellent sodium storage capability of this system is obtained by introducing the high-entropy doping to enhance the electronic and ionic conductivity. As designed high-entropy doping Na₄Fe_2.85(Ni,Co,Mn,Cu,Mg)_0.03(PO₄)₂P₂O₇ (NFPP-HE) cathode can release 122 mAh g⁻¹ at 0.1 C, even 85 mAh g⁻¹ at ultrahigh rate of 50 C, and keep a high retention of 82.3% after 1500 cycles at 10 C. Besides, the cathode also exhibits outstanding fast charge capacity in terms of the cyclability and capacity with 105 mAh g⁻¹ at 5 C/1 C, corresponding 94.3% retention after 500 cycles. The combination of in situ X-ray diffraction, density functional theory, conductive-atomic force microscopy, and galvanostatic intermittent titration technique tests reveal that the reversible structure evolution with optimized Na⁺ migration path and energy barrier boost the Na⁺ kinetics and improve the interfacial electronic transfer, thus improving performance.     

聚丙烯酰胺改性LiFePO4/C正极材料的研究

以聚丙烯酰胺(PAM)作为分散剂, 采用液相控制结晶-碳热还原法制备LiFePO₄/C正极材料, 考察了PAM对LiFePO₄/C正极材料性能的影响, 采用热化学分析、X射线衍射、扫描电镜、碳含量分析和充放电测试等分析测试手段对材料进行表征。结果表明, 将PAM溶于酸液中且添加量为1.5wt%时制备的LiFePO₄平均粒径约为100 nm, 颗粒分散较为均匀; 该材料在0.1C、1C、2C、5C和10C倍率下首次放电比容量分别为153.8、142.5、138.4、128.7和124.3 mAh/g, 1C倍率下循环100次后容量保持率仍在99%以上; 交流阻抗分析表明: 1.5wt%PAM改性后的材料的各种阻抗值均降低, 锂离子的导电速率提高了28倍。PAM改性后的LiFePO₄/C正极材料的离子及电子导电性提高了, 具有优良的倍率性能与循环性能, 有利于大规模推广应用。     

A Composite Structure of Cu3Ge/Ge/C Anode Promise Better Rate Property for Lithium Battery

Much effort has been made to search for high energy and high power density electrode materials for lithium ion batteries. Here, a composite structure among Ge, C and Cu3Ge in Cu3Ge/Ge/C materials with a high rate performance of lithium batteries has been reported. Such Cu3Ge/Ge/C composite is synthesized through the in‐situ formation of Ge, C and Cu3Ge by one‐pot reaction. Density function theory (DFT) calculations and electrochemical impedance spectroscopy (EIS) suggest a higher electron mobility of the hibrid Cu3Ge/Ge/C composites through the in‐situ preparation. As a result, remarkable charge rate over 300 C (fast delithiated capability) and outstanding cycling stability (≈0.02% capacity decay per cycle for 500 cycles at 0.5 C) are achieved for the Cu3Ge/Ge/C composites anode. These Cu3Ge/Ge/C composites demonstrate another perspective to explore the energy storage materials and should provide a new pathway for the design of advanced electrode materials.     

Defect-Healing Induced Monoclinic Iron-Based Prussian Blue Analogs as High-Performance Cathode Materials for Sodium-Ion Batteries

Prussian blue analogs (PBAs) have attracted wide interest as a class of ideal cathodes for rechargeable sodium-ion batteries due to their low cost, high theoretical capacity, and facile synthesis. Herein, a series of highly crystalline Fe-based PBAs (FeHCF) cubes, where HCF stands for the hexacyanoferrate, is synthesized via a one-step pyrophosphate-assisted co-precipitation method. By applying this proposed facile crystallization-controlled method to slow down the crystallization process and suppress the defect content of the crystal framework of the PBAs, the as-prepared materials demonstrate high crystallization and a sodium-rich induced rhombohedral phase. As a result, the as prepared FeHCF can deliver a high specific capacity of up to 152.0 mA h g⁻¹ (achieving ≈90% of its theoretical value) and an excellent rate capability with a high-capacity retention ratio of 88% at 10 C, which makes it one of the most competitive candidates among the cathodes reported regarding both capacity and rate performance. A highly reversible three-phase-transition sodium-ion storage mechanism has been revealed via multiple in situ techniques. Furthermore, the full cells fabricated with as-prepared cathode and commercial hard carbon anode exhibit excellent compatibility which shows great prospects for application in the large-scale energy storage systems.     

A Molecularly Engineered Cathode Lithium Compensation Agent for High Energy Density Batteries

Prelithiating cathode is considered as one of the most promising lithium compensation strategies for practical high energy density batteries. Whereas most of reported cathode lithium compensation agents are deficient owing to their poor air-stability, residual insulating solid, or formidable Li-extracting barrier. Here, this work proposes molecularly engineered 4-Fluoro-1,2-dihydroxybenzene Li salt (LiDF) with high specific capacity (382.7 mAh g⁻¹) and appropriate delithiation potential (3.6–4.2 V) as an air-stable cathode Li compensation agent. More importantly, the charged residue 4-Fluoro-1,2-benzoquinone (BQF) can synergistically work as an electrode/electrolyte interface forming additive to build uniform and robust LiF-riched cathode/anode electrolyte interfaces (CEI/SEI). Consequently, less Li loss and retrained electrolyte decomposition are achieved. With 2 wt% 4-Fluoro-1,2-dihydroxybenzene Li salt initially blended within the cathode, 1.3 Ah pouch cells with NCM (Ni92) cathode and SiO/C (550 mAh g⁻¹) anode can keep 91% capacity retention after 350 cycles at 1 C rate. Moreover, the anode free of NCM622+LiDF||Cu cell achieves 78% capacity retention after 100 cycles with the addition of 15 wt% LiDF. This work provides a feasible sight for the rational designing Li compensation agent at molecular level to realize high energy density batteries.     

Nanostructured covalent organic frameworks with elevated crystallization for (electro)photocatalysis and energy storage devices

Nanostructured covalent organic frameworks (COFs) have attracted great attentions over the past few decades due to their unique physical and chemical properties. Crystallization is sought in many application fields since it allows enhancing or even promoting properties of catalysis, energy storage and photoelectric properties. However, the crystallization process of nanostructured COFs remains to be challenging. Synthetic approaches to establish nucleation and elongation growth of COFs for controlling crystallization have drawn substantial amount of attentions. Nanostructured COFs have exhibited significant advantages when applied in (electro)photocatalysis and energy storage devices as well. In this review, recent progress in precisely design strategy of fabricating various nanostructured COFs and their applications as (electro)photocatalyzer and energy storage devices are summarized. After a brief introduction of the design principles, composition and interior architecture, the morphology of nanostructured COFs including porous and mesoporous stacked-layer structure, nanosheet structure, nanorod structure, ordered stripe arrays and various nanocomposites are thoroughly described. Reactions dedicated to crystallization process for two-dimensional (2D) COFs are discussed further. Then, the applications of nanostructured COFs as (electro)photocatalysis and energy storage devices are demonstrated. Finally, the potential advantages and challenges for the synthetic technology of nanostructured COFs materials are particularly discussed. Personal insights into the challenges and opportunities on pursuing topologies as hollow structures, dense spheres, yolk–shell structures were raised to broaden the applications.

     

Activating C‐Coordinated Iron of Iron Hexacyanoferrate for Zn Hybrid‐Ion Batteries with 10 000‐Cycle Lifespan and Superior Rate Capability

Prussian blue analogue (PBA)‐type metal hexacyanoferrates are considered as significant cathodes for zinc batteries (ZBs). However, these PBA‐type cathodes, such as cyanogroup iron hexacyanoferrate (FeHCF), suffer from ephemeral lifespan (≤1000 cycles), and inferior rate capability (1 A g^?1). This is because the redox active sites of multivalent iron (Fe(III/II)) can only be very limited activated and thus utilized. This is attributed to the spatial resistance caused by the compact cooperation interaction between Fe and the surrounded cyanogroup, and the inferior conductivity. Here, it is found that high‐voltage scanning can effectively activate the C‐coordinated Fe in FeHCF cathode in ZBs. Thanks to this activation, the Zn–FeHCF hybrid‐ion battery achieves a record‐breaking cycling performance of 5000 (82% capacity retention) and 10 000 cycles (73% capacity retention), respectively, together with a superior rate capability of maintaining 53.2% capacity at superhigh current density of 8 A g^?1 (≈97 C). The reversible distortion and recovery of the crystalline structure caused by the (de)insertion of zinc and lithium ions is revealed. It is believed that this work represents a substantial advance on PBA electrode materials and may essentially promote application of PBA materials.     

Sodium-Ion Substituted Water Molecule in Layered Vanadyl Phosphate Enhancing Electrochemical Kinetics and Stability of Zinc Ion Storage

Vanadyl phosphate (VOPO₄·2H₂O) has been regarded as one of the most promising cathode materials for aqueous Zn-ion batteries due to its distinct layered structure. However, VOPO₄·2H₂O has not yet demonstrated the exceptional Zn ion storage performance owing to the structural deterioration during repeated charging/discharging process and poor intrinsic conductivity. In this work, 2D sodium vanadyl phosphate (NaVOPO₄·0.83H₂O, denoted as NaVOP) is designed as a cathode material for Zn-ion batteries, in which sodium ions are preinserted into the interlayer, replacing part of water. Benefiting from the in situ surface oxidization, improved electronic conductivity, and increased hydrophobicity, the NaVOP electrode exhibits a high discharge capacity of 187 mAh g⁻¹ at 0.1 A g⁻¹ after activation, excellent rate capability and enhanced cycling performance with 85% capacity retention after 1500 cycles at 1 A g⁻¹. The energy storage mechanism of the NaVOP nanoflakes based on the rapid Zn²⁺ and H⁺ intercalation pseudocapacitance are investigated via multiple ex situ characterizations.