Preparation of manganese monoxide@reduced graphene oxide nanocomposites with superior electrochemical performances for lithium-ion batteries

Manganese monoxide (MnO) nanowire@reduced graphene oxide (rGO) nanocomposites are synthesized using a simple hydrothermal method combined with a calcination process. The structural and morphological characterization of the composites indicates that the MnO nanowires homogeneously anchor on both sides of the cross-linked rGO. The nanocomposites exhibit a high surface area of 126.5?m² g^?1. When employed as an anode material for lithium-ion batteries, the nanocomposites exhibit a reversible capacity of 1195 mAh g^?1 at a current density of 0.1?A?g^?1, with a high charge-discharge efficiency of 99.2% after 150 cycles. The three-dimensional architecture of the present materials exhibits high porosity and electron conductivity, significantly shortening the diffusion path of lithium ions and accelerating their reaction with the electrolyte, which greatly improves the lithium-ion storage properties. These excellent electrochemical performances make the composite a promising electrode material for lithium-ion batteries.     

结构有序的Si/void/C/graphene纳米复合结构的制备及储锂性能

采用简单的超声、冷冻干燥和热还原相结合的自组装方法,设计和构建了纳米硅核/间隙/无定形碳壳层/石墨烯（Si/void/C/graphene） 三维有序纳米复合结构。在该结构中,纳米硅核与碳壳层之间的空隙有效避免了硅的巨大体积膨胀对碳层的破坏,大幅度提高了锂离子电池的循环稳定性;将Si/void/C纳米结构嵌入在石墨烯层与层之间,利用石墨烯卓越的导电性和柔韧性,进一步缓冲了硅材料的体积效应和提高了复合材料的导电性能。该复合材料在4200 mA·h·g^-1（1 C）电流密度下循环1000次后比容量仍高达1603 mA·h·g^-1;在67 A·g^-1（16 C）的高倍率下,比容量仍有310 mA·h·g^-1,显示出了在锂离子电池负极材料领域的巨大应用潜力。     

Sb particles embedded in N-doped carbon spheres wrapped by graphene for superior K+−Storing performances

Antimony (Sb)-based nanocomposites have emerged as an attractive class of anode materials for potassium ion batteries as they exhibit large theoretical capacity and impressive working voltage. However, the tardy potassium ion diffusion characteristic, unstable Sb/electrolyte interphase, and huge volume variation pose a grand challenge that hinder the practical use of Sb-based anodes for potassium ion batteries. Herein, we develop a simple yet robust strategy to fabricate a three-dimensional N-doped carbon (N–C) porous microspheres and reduced graphene oxides (rGO) dual-encapsulated Sb hierarchical structures (denoted Sb@N–C/rGO), which are pursued for resolving the stubborn issues of Sb-based compounds for PIBs. As expected, such judiciously crafted Sb@N–C/rGO anode renders a set of intriguing electrochemical properties, representing a high reversible specific capacity of 586 mAh g^?1 at a current density of 0.2 A g^?1 after 200 cycles and excellent long-cycle stability of 358 mAh g^?1 at 1.0 A g^?1 after 1000 cycles. It is believed that the work can provide deep understanding and new insight to develop the alloying-type electrode materials for rechargeable batteries.     

Sub-20 nm anatase particles uniformly anchored on graphene oxide and reduced graphene oxide nanosheets and their photocatalytic oxidation and Li-ion storage capabilities

Nanosized anatase TiO₂ particles anchored on nanocarbon substrates have great potential for practical applications in high-performance lithium ion batteries and efficient photocatalysts. The synthesis of this material usually utilizes calcination to crystallize amorphous titania, which normally causes the formation of aggregates and some side effects. In this work, we demonstrated that sub-20 nm anatase particles uniformly anchored on graphene oxide and reduced graphene oxide nanosheets in aqueous solution at a temperature of 90 °C and atmospheric pressure, without further calcination. The photocatalytic oxidation activity and electrochemical properties of graphene oxide/anatase TiO₂ (GO/A) and reduced graphene oxide/anatase TiO₂ (RGO/A) were comparatively investigated. We found that GO/A showed higher photocatalytic oxidation activity than RGO/A under UV light irradiation. Graphene oxide accepted electrons and suffered reduction, which finally decreased GO/A’s photocatalytic oxidation activity to an extent similar to RGO/A. We also found that, as anode material for Li-ion battery, the specific capacity of RGO/A was nearly three times that of GO/A at the same current rate. This study will inspire better design of metal oxide/nanocarbon nanocomposites for high performance lithium ion battery and photocatalysis applications.     

Wrapping mesoporous Fe2O3 nanoparticles by reduced graphene oxide: Enhancement of cycling stability and capacity of lithium ion batteries by mesoscopic engineering

The fast capacity fading at high current density turns out to be one of the key challenges limiting the broad applications of transition metal oxide-based electrodes. Herein, Fe₂O₃ nanoparticles with well-defined mesopores wrapped by reduced graphene oxide (RGO) have been synthesized via a facile hydrothermal strategy. The as-prepared nanocomposites were systematically characterized. XPS and Raman analyses confirm the co-existence of Fe₂O₃ and RGO in the nanocomposite system. SEM and TEM reveal that the mesoporous Fe₂O₃ nanoparticles have a size of 20–60?nm and are uniformly dispersed and tightly wrapped by RGO. When used as the anode in lithium ion batteries, the mesoporous-Fe₂O₃/RGO electrode exhibits excellent cycling stability (1098?mA?h?g^?1 after 500 cycles at 1?A?g^?1) and superior rate capability (574?mA?h?g^?1 at 5?A?g^?1). The excellent electrochemical performance can be mainly ascribed to the unique mesoscopic architecture that serves as a cushion to alleviate volume change of Fe₂O₃ during discharge/charge cycles, provides a sustainably large contact area with the electrolyte, and improves electrical conductivity. This unique nanocomposite electrode holds great potential as an anode material for advanced lithium ion batteries.     

Graphene as a conductive additive to enhance the high-rate capabilities of electrospun Li4Ti5O12 for lithium-ion batteries

Spinel Li₄Ti₅O₁₂ (LTO) is a promising candidate anode material for Li-ion batteries due to its well-known zero-strain merits. To improve the electronic properties of spinel LTO, which are intrinsically poor, we processed the material into a nanosized architecture to shorten the distance for Li-ion and electron transport using the versatile electrospinning method. Graphene was chosen as an effective carbon coating to improve the surface conductivity of the nanocomposites. The as-prepared graphene-embedded LTO anode material showed improved discharging/charging and cycling properties, particularly at high rates, such as 22 C, which makes the nanocomposite an attractive anode material for applications in electric vehicles.     

Carbon-coated SnO2/graphene nanosheets as highly reversible anode materials for lithium ion batteries

A simple approach is reported to prepare carbon-coated SnO₂ nanoparticle–graphene nanosheets (Gr–SnO₂–C) as an anode material for lithium ion batteries. The material exhibits excellent electrochemical performance with high capacity and good cycling stability (757 mA h g^?1 after 150 cycles at 200 mA g^?1). The likely contributing factors to the outstanding charge/discharge performance of Gr–SnO₂–C could be related to the synergism between the excellent conductivity and large area of graphene, the nanosized particles of SnO₂, and the effects of the coating layer of carbon, which could alleviate the effects of volume changes, keep the structure stable, and increase the conductivity. This work suggests a strategy to prepare carbon-coated graphene–metal oxide which could be used to improve the electrochemical performance of lithium ion batteries.     

Preparation of graphene supported porous Si@C ternary composites and their electrochemical performance as high capacity anode materials for Li-ion batteries

Graphene supported porous Si@C ternary composites had been synthesized by various routes and their structural, morphological and electrochemical properties were investigated. Porous Si spheres coated with carbon layer and supported by graphene have been designed to form a 3D carbon conductive network. Used as anode materials for lithium ion batteries, graphene supported porous Si@C ternary composites demonstrate excellent electrochemical performance and cycling stability. The first discharge capacity is 2184.7 mA h/g at a high current density of 300 mA/g. After 50 cycles, the reversible capacity is 652.4 mA h/g at a current density of 300 mA/g and the coulomb efficiency reaches at 98.7%. Due to their excellent electrochemical properties, graphene supported porous Si@C ternary composites can be a kind of promising anode materials for lithium ion batteries.     

One-step hydrothermal synthesis of Sb2S3/reduced graphene oxide nanocomposites for high-performance sodium ion batteries anode materials

Sb₂S₃/reduced graphene oxide (SSR) nanocomposites were successfully synthesized through a facile one-step hydrothermal process, as used as anode materials for sodium ion batteries (SIBs). The characterization and electrochemical performance of the as-prepared samples were characterized by X-ray diffraction, field-emission scanning electron microscopy, transmission electron microscopy, nitrogen adsorption-desorption isotherms, cyclic voltammetry, electrochemical impedance spectroscopy, and galvanostatic charge/discharge tests, respectively. The results show that the introduction of reduced graphene oxide (RGO) can improve the electrochemical performances of SSR nanocomposites. SSR nanocomposites with 10 wt% RGO exhibits the highest reversible capacity of 581.2 mAh g⁻¹ at the current density of 50 mA g⁻¹ after 50 cycles, and excellent rate performance for SIBs. The improved electrochemical performance is attributed to the smaller Sb₂S₃ nanoparticles dispersed on RGO crumpled structure and synergetic effects between Sb₂S₃ and RGO matrix, which can increase specific surface area and improve electrical conductivity, reduce sodium ion diffusion distance, and effectively buffer volume changes during cycling process.     

Large-scale and low cost synthesis of graphene as high capacity anode materials for lithium-ion batteries

Graphene has emerged as an intriguing and attractive functional material for a wide range of applications, owing to its unique physical, chemical and mechanical properties. Herein, we report large-scale production of high quality single crystalline graphene sheets based on the ambient pressure chemical vapor deposition (APCVD) method using acetylene (C₂H₂) as the carbon source and coral-like iron with body-centered-cubic structure as the catalyst. The process can be scaled up for large quantity production at a low cost. The optimum APCVD temperature has been identified to be 850 °C, which is much lower than that catalyzed by other metals. Transmission electron microscopy (TEM), atomic force microscopy, Raman spectroscopy and X-ray photoemission spectroscopy characterizations show the single crystalline and high quality nature of the as-prepared graphene produced by the bottom-up APCVD approach. A new horizontal “dissolution–deposition–growth” mechanism is proposed and verified by high resolution TEM. When applied as anode materials in lithium ion batteries, graphene sheets exhibited a high lithium storage capacity and an excellent cyclability. The capability of preparing crystalline graphene on a large scale with low cost opens an avenue for technological applications of graphene in many fields.     

Graphene network enabled high speed electrical actuation of shape memory nanocomposite based on poly(vinyl acetate)

Here strong electroactive shape memory nanocomposites were prepared by incorporating graphene nanoplatelets into poly(vinyl acetate) (PVAc ) through the simple solvent mixing method. TEM and XRD revealed that well exfoliated graphene nanoplatelets formed a continuous network throughout the matrix with a large amount of interconnectedness. Dynamic mechanical analysis showed that the inclusion of graphene significantly improves both glassy and rubbery moduli of the matrix. Furthermore, the prepared nanocomposites demonstrated a marked electrical conductivity up to 24.7 S m^?1 and thereby surprisingly rapid electrical actuation behaviour exhibiting a 100% recovery ratio in 2.5 s. Moreover, PVAc and its nanocomposites displayed scratch self‐healing capability. This work demonstrates that the PVAc /graphene nanocomposites with high modulus and excellent electroactive shape memory performance can be a promising material in many applications such as sensors and fast deployable and actuating devices. © 2016 Society of Chemical Industry     

Copper substituted nickel ferrite nanoparticles anchored onto the graphene sheets as electrode materials for supercapacitors fabrication

Nickel ferrites with high theoretical capacitance value as compared to the other metal oxides have been applied as electrode material for energy storage devices i.e. batteries and supercapacitors. High tendency towards aggregation and less specific surface area make the metal oxides poor candidate for electrochemical applications. Therefore, the improvements in the electrochemical properties of nickel ferrites (NiFe₂O₄) are required. Here, we report the synthesis of graphene nano-sheets decorated with spherical copper substituted nickel ferrite nanoparticles for supercapacitors electrode fabrication. The copper substituted and unsubstituted NiFe₂O₄ nanoparticles were prepared via wet chemical co-precipitation route. Reduced graphene oxide (rGO) was prepared via well-known Hummer's method. After structural characterization of both ferrite (Ni_1-xCu_xFe₂O₄) nanoparticles and rGO, the ferrite particles were decorated onto the graphene sheets to obtain Ni_1-xCu_xFe₂O₄@rGO nanocomposites. The confirmation of preparation of these nanocomposites was confirmed by scanning electron microscopy (SEM). The electrochemical measurements of nanoparticles and their nanocomposites (Ni_0.9Cu_0.1Fe₂O₄@rGO) confirmed that the nanocomposites due to highly conductive nature and relatively high surface area showed better capacitive behavior as compared to bare nanoparticles. This enhanced electrochemical energy storage properties of nanocomposites were attributed to the graphene and also supported by electrical (I-V) measurements. The cyclic stability experiments results showed ~65% capacitance retention after 1000 cycles. However this retention was enhanced from 65% to 75% for the copper substituted nanoparticles (Ni_0.9Cu_0.1Fe₂O₄) and 65–85% for graphene based composites. All this data suggest that these nanoparticles and their composites can be utilized for supercapacitors electrodes fabrication.     

Embedded Si/Graphene Composite Fabricated by Magnesium-Thermal Reduction as Anode Material for Lithium-Ion Batteries

Embedded Si/graphene composite was fabricated by a novel method, which was in situ generated SiO₂ particles on graphene sheets followed by magnesium-thermal reduction. The tetraethyl orthosilicate (TEOS) and flake graphite was used as original materials. On the one hand, the unique structure of as-obtained composite accommodated the large volume change to some extent. Simultaneously, it enhanced electronic conductivity during Li-ion insertion/extraction. The MR-Si/G composite is used as the anode material for lithium ion batteries, which shows high reversible capacity and ascendant cycling stability reach to 950 mAh·g^?1 at a current density of 50 mA·g^?1 after 60 cycles. These may be conducive to the further advancement of Si-based composite anode design.     

The effect of graphene nanosheets as an additive for anode materials in lithium ion batteries

A small amount of graphene nanosheets was added to commercial graphite as an anode active material in lithium ion batteries and its effects were examined through a variety of physical and electrochemical characterization techniques: FE-SEM, XRD, Raman, BET, and EIS. Compared to a commercial graphite electrode, a composite electrode containing 1 or 5 wt% graphene nanosheets showed higher reversible capacity and enhanced cyclability. This was attributed to the large surface area and low charge transfer resistance of the graphene nanosheets.     

Monolithic Fe2O3/graphene hybrid for highly efficient lithium storage and arsenic removal

We fabricated a monolithic Fe₂O₃/graphene hybrid directly by hydrothermal reaction of ferrous oxalate dihydrate and graphene oxide without using a reducing agent. The reduced graphene oxide formed an interconnected network structure that can be used as a support for homogeneous distribution of active Fe₂O₃ nanoparticles. The graphene network and the pore channels in the hybrid facilitate fast electron transfer and ion transport. This hybrid can be directly used as a free-standing anode for lithium ion batteries, which simplifies the fabrication procedure of electrodes, and also exhibited a high capacity of 1062 mA h g⁻¹ at 100 mA g⁻¹, high rate capability and excellent cyclic stability over 100 cycles. Furthermore, as a self-supported adsorbent, it provides a new idea on loading active materials to the suitable substrate, which can be used as a promising material for water purification due to its easy collection and excellent capability in removing As(V) from water. The results demonstrate the promising applications of bulk reduced assembly of graphene with functional metal oxides, which will be helpful for future development of graphene-based multifunctional materials.     

Chemical-free synthesis of graphene–carbon nanotube hybrid materials for reversible lithium storage in lithium-ion batteries

Graphene–carbon nanotube hybrid materials were successfully prepared through the π–π interaction without using any chemical reagent. We found that the ratio between carbon nanotube and graphene had critical influences on the state in aqueous solution and morphology of hybrid materials. Field emission scanning electron microscope and transmission electron microscope analysis confirmed that graphene nanosheets wrap around individual carbon nanotubes and form a homogeneous three-dimensional hybrid nanostructure. When applied as an anode material in lithium ion batteries, graphene–carbon nanotube hybrid materials demonstrated a high reversible lithium storage capacity, a high Coulombic efficiency and an excellent cyclability.     

NiCo2S4/N,S-rGO纳米复合材料的制备和电化学储钠性能

NiCo₂S₄是一种极具发展前景的钠离子电池(SIBs)负极材料。采用简单的一步法(混合和热处理)原位合成了锚定在N、S共掺杂还原氧化石墨烯上的纳米颗粒自组装的NiCo₂S₄亚微米球(NiCo₂S₄/N,S-rGO)。XPS表明了NiCo₂S₄与N,S-rGO之间存在电子转移,证实了NiCo₂S₄与N,S-rGO之间强的协同作用。纳米粒子自组装的NiCo₂S₄亚微米球有效地促进了离子的扩散,N,S-rGO优异的电学和力学性能不仅提高了电极的导电性,而且有效地缓冲了充/放电过程中NiCo₂S₄/N,S-rGO的体积变化。NiCo₂S₄/N,S-rGO作为SIBs的负极材料呈现出高可逆容量,优越的倍率性能和长期稳定性(在电流密度为0.5 A/g时循环130次后仍保持了396.7 mA·h/g的高比容量。即使在电流密度为2 A/g时,经过1000次循环后比容量仍保持在283.3 mA·h/g)。研究结果为高效负极材料的设计和合成提供了新的思路。     

Preparation and sodium storage performance of NiCo2S4/N,S-rGO nanocomposites

NiCo₂S₄ is a promising anode material for sodium ion batteries (SIBs). In this paper, a simple one-step method (mixing and heat treatment) was used to synthesize in-situ synthesized NiCo₂S₄ submicron spheres (NiCo₂S₄/N,S-rGO) anchored on N, S co-doped reduced graphene oxide. XPS characterization demonstrated electron transfer between NiCo₂S₄ and N,S-rGO, which confirmed the strong synergistic effect between NiCo₂S₄ and N,S-rGO. The nanoparticles self-assembled NiCo₂S₄ spheres effectively promoted ion diffusion, and the excellent electrical and mechanical properties of N,S-rGO not only improved the conductivity of the electrode, but also effectively buffeted the large volume changes of NiCo₂S₄/N,S-rGO during the charge/discharge process. Benefiting from the unique nano-architecture and strong synergistic effect, NiCo₂S₄/N,S-rGO applied as anode materials for SIBs presented a high reversible capacity, impressive rate capability and superior long-term stability (396.7 mA·h/g at 0.5 A/g after 130 cycles, 283.3 mA·h/g at 2 A/g after 1000 cycles). Those results open an interesting strategy for rational design and preparation of efficient anode materials for SIBs.     

MXene的制备及其在高比能碱金属电池中的应用

双碳目标下,具有高比能量的碱金属电池受到广泛关注,但电池循环过程中枝晶的生长会带来严重安全隐患。新型二维材料（MXene）具有优异的导电性、充足的层间空间、稳定的层状结构,作为金属负极保护材料具有应用价值。首先介绍了MXene的不同制备方法,之后对MXene在金属负极保护领域的应用现状进行了分析和评价。其中,重点总结了三大类MXene与碱金属复合的方法（滚压法、熔融灌注法、电沉积法）,指出当前方法普遍存在易氧化、操作难度大、难以大规模生产等弊端。最后提出MXene的发展应参考石墨烯材料的发展策略,更多地利用其表面活性官能团和片层结构,构筑独立集流体或保护层以获得更好的循环性能。     

煤沥青基微晶炭的制备及其储锂性能

以工业副产物煤沥青（coal tar pitch, CTP）为原料,采用高温炭化法制备煤沥青基微晶炭,利用XRD、Raman光谱、SEM、TEM和XPS等手段对其微观结构和表面化学性质进行表征,并探究微晶炭用作锂离子电池负极材料的储锂特性。结果表明,煤沥青经不同温度（800~1100℃）炭化处理后可制备出石墨微晶和无定形炭共存的微晶炭。炭化温度是影响煤沥青基微晶炭的微晶片层、纳米孔道和结构缺陷等微观结构特征和表面化学性质的重要因素。当炭化温度为800℃时,煤沥青基微晶炭CTP-800具有较为有序的石墨微晶片层和丰富的纳米孔道、结构缺陷等无定形炭,且两者有机结合,相互镶嵌,构筑成三维网络结构,同时炭基体表面含有适量氧/氮官能团。该微晶炭用作锂离子电池负极材料时具有优异的储锂特性,在50mA/g电流密度下可逆容量可达305mA·h/g,1000mA/g大电流密度下仍可维持在174mA·h/g,经100次循环后可逆容量保持率超过99.0%,显示出良好的倍率性能和优异的循环稳定性,是一种较为理想的锂离子电池负极材料。煤沥青基微晶炭 CTP-800优异的储锂特性与其炭基体中含有石墨微晶片层与纳米孔道、结构缺陷等无定形炭和炭表面富含氧/氮官能团等因素密切相关。