Hydrazine hydrate-induced hydrothermal synthesis of MnFe2O4 nanoparticles dispersed on graphene as high-performance anode material for lithium ion batteries

Herein, a MnFe₂O₄/graphene (MnFe₂O₄/G) nanocomposite has been synthesized via a facile N₂H₄·H₂O-induced hydrothermal method. During the synthesis, N₂H₄·H₂O is employed to not only reduce graphene oxide to graphene, but also prevent the oxidation of Mn²⁺ in alkaline aqueous solution, thus ensuring the formation of MnFe₂O₄/G. Moreover, MnFe₂O₄ nanoparticles (5–20 nm) are uniformly anchored on graphene. MnFe₂O₄/G electrode delivers a large reversible capacity of 768 mA h g⁻¹ at 1 A g⁻¹ after 200 cycles and high rate capability of 517 mA h g⁻¹ at 5 A g⁻¹. MnFe₂O₄/G holds great promise as anode material in practical applications due to the outstanding electrochemical performance combined with the facile synthesis strategy.     

Ag enhanced electrochemical performance for Na2Li2Ti6O14 anode in rechargeable lithium-ion batteries

Due to the characteristics of an electronic insulator, Na₂Li₂Ti₆O₁₄ always suffers from low electronic conductivity as anode material for lithium storage. Via Ag coating, Na₂Li₂Ti₆O₁₄@Ag is fabricated, which has higher electronic conductivity than bare Na₂Li₂Ti₆O₁₄. Enhancing the Ag coating content from 0.0 to 10.0 wt%, the surface of Na₂Li₂Ti₆O₁₄ is gradually deposited by Ag nanoparticles. At 6.0 wt%, a continuous Ag conductive layer is formed on Na₂Li₂Ti₆O₁₄. While, particle growth and aggregation take place when the Ag coating content reaches 10.0 wt%. As a result, Na₂Li₂Ti₆O₁₄@6.0 wt% Ag displays better cycle and rate properties than other samples. It can deliver a lithium storage capacity of 131.4 mAh g⁻¹ at 100 mA g⁻¹, 124.9 mAh g⁻¹ at 150 mA g⁻¹, 119.1 mAh g⁻¹ at 200 mA g⁻¹, 115.8 mAh g⁻¹ at 250 mA g⁻¹, 111.9 mAh g⁻¹ at 300 mA g⁻¹ and 109.4 mAh g⁻¹ at 350 mA g⁻¹, respectively.     

Synthesis and electrochemical performance of reduced graphene oxide/maghemite composite anode for lithium ion batteries

Reduced graphene oxide (rGO) tethered with maghemite (γ-Fe₂O₃) was synthesized using a novel modified sol–gel process, where sodium dodecylbenzenesulfonate was introduced into the suspension to prevent the undesirable formation of an iron oxide 3D network. Thus, nearly monodispersed and homogeneously distributed γ-Fe₂O₃ magnetic nanoparticles could be obtained on surface of graphene sheets. The utilized thermal treatment process did not require a reducing agent for reduction of graphene oxide. The morphology and structure of the composites were investigated using various characterization techniques. As-prepared rGO/Fe₂O₃ composites were utilized as anodes for half lithium ion cells. The 40 wt.%-rGO/Fe₂O₃ composite exhibited high reversible capacity of 690 mA h g⁻¹ at current density of 500 mA g⁻¹ and good stability for over 100 cycles, in contrast with that of the pure-Fe₂O₃ nanoparticles which demonstrated rapid degradation to 224 mA h g⁻¹ after 50 cycles. Furthermore, the composite showed good rate capability of 280 mA h g⁻¹ at 10C (∼10,000 mA g⁻¹). These characteristics could be mainly attributed to both the use of an effective binder, poly(acrylic acid) (PAA), and the specific hybrid structures that prevent agglomeration of nanoparticles and provide buffering spaces needed for volume changes of nanoparticles during insertion/extraction of Li ions.     

A green strategy for the synthesis of graphene supported Mn3O4 nanocomposites from graphitized coal and their supercapacitor application

A by-product free strategy based on modified Hummers method was proposed to synthesize graphene/Mn₃O₄ composites without any additional manganese source. Coal-derived graphite (CDG) was used as carbon source instead of conventional natural graphite flakes and MnSO₄ produced from the modified Hummers was in situ transformed into Mn₃O₄ by precipitation in air. After reduction with hydrazine, the reduced coal-derived graphene oxide/Mn₃O₄ (RCDGO/Mn₃O₄) was obtained and employed as the electrode material for the supercapacitors. In addition, K₂SO₄ produced from the modified Hummers was used as electrolyte, as a result, residual-free was achieved during the whole process, and the atom utilization was calculated as high as about 97%. A maximum specific capacitance of 260 F g⁻¹ was achieved for RCDGO/Mn₃O₄ composite with 86% Mn₃O₄ in saturated K₂SO₄ electrolyte solution based on the synergetic effects between coal-derived graphene and attached Mn₃O₄ nanoparticles. Its specific energy density reached 8.7 Wh kg⁻¹ at a current density of 50 mA g⁻¹ when used as a symmetrical supercapacitor. The good capacitance retention (92–94%) was also observed after 1000 continuous cycles of galvanostatic charge–discharge.     

Simple fabrication of a Fe2O3/carbon composite for use in a high-performance lithium ion battery

A simple approach was developed for the fabrication of a Fe₂O₃/carbon composite by impregnating activated carbon with a ferric nitrate solution and calcinating it. The composite contains graphitic layers and 10 wt.% Fe₂O₃ particles of 20–50 nm in diameter. The composite has a high specific surface area of ∼828 m² g⁻¹ and when used as the anode in a lithium ion battery (LIB), it showed a reversible capacity of 623 mAh g⁻¹ for the first 100 cycles at 50 mA g⁻¹. A discharge capacity higher than 450 mAh g⁻¹ at 1000 mA g⁻¹ was recorded in rate performance testing. This highly improved reversible capacity and rate performance is attributed to the combination of (i) the formation of graphitic layers in the composite, which possibly improves the matrix electrical conductivity, (ii) the interconnected porous channels whose diameters ranges from the macro- to meso- pore, which increases lithium-ion mobility, and (iii) the Fe₂O₃ nanoparticles that facilitate the transport of electrons and shorten the distance for Li⁺ diffusion. This study provides a cost-effective, highly efficient means to fabricate materials which combine conducting carbon with nanoparticles of metal or metal oxide for the development of a high-performance LIB.     

Porous Fe2O3 nanorods anchored on nitrogen-doped graphenes and ultrathin Al2O3 coating by atomic layer deposition for long-lived lithium ion battery anode

Porous iron oxide (Fe₂O₃) nanorods anchored on nitrogen-doped graphene sheets (NGr) were synthesized by a one-step hydrothermal route. After a simple microwave treatment, the iron oxide and graphene composite (NGr-I-M) exhibits excellent electrochemical performances as an anode for lithium ion battery (LIB). A high reversible capacity of 1016 mAh g⁻¹ can be reached at 0.1 A g⁻¹. When NGr-I-M electrode was further coated by 2 ALD cycles of ultrathin Al₂O₃ film, the first cycle Coulombic efficiency (CE), rate performance and cycling stability of the coated electrode can be greatly improved. A stable capacity of 508 mAh g⁻¹ can be achieved at 2 A g⁻¹ for 200 cycles, and an impressive capacity of 249 mAh g⁻¹ at 20 A g⁻¹ can be maintained without capacity fading for 2000 cycles. The excellent electrochemical performance can be attributed to the synergy of porous iron oxide structures, nitrogen-doped graphene framework, and ultrathin Al₂O₃ film coating. These results highlight the importance of a rational design of electrode materials improving ionic and electron transports, and potential of using ALD ultrathin coatings to mitigate capacity fading for ultrafast and long-life battery electrodes.     

Reduced graphene oxide with superior cycling stability and rate capability for sodium storage

Sodium ion battery is a promising electrical energy storage system for sustainable energy storage applications due to the abundance of sodium resources and their low cost. In this communication, the electrochemical properties of sodium ion storage in reduced graphene oxide (RGO) were studied in an electrolyte consisting of 1 M NaClO₄ in propylene carbonate (PC). The experimental results show that the RGO anode allowed significant sodium ion insertion, leading to higher capacity at high current density compared to the previously reported results for carbon materials. This is due to the fact that RGO possesses higher electrical conductivity and is a more active host, with large interlayer distances and a disordered structure, enabling it to store a higher amount of Na ions. RGO anode exhibits high capacity combined with long-term cycling stability at high current densities, leading to reversible capacity as high as 174.3 mAh g⁻¹ at 0.2 C (40 mA g⁻¹), and even 93.3 mAh g⁻¹ at 1 C (200 mA g⁻¹) after 250 cycles. Furthermore, RGO could yield a high capacity of 141 mAh g⁻¹ at 0.2 C (40 mA g⁻¹) over 1000 cycles.     

Electrospinning combined with hydrothermal synthesis and lithium storage properties of ZnFe2O4-graphene composite nanofibers

ZnFe₂O₄-graphene composite nanofibers were prepared through electrospinning technique, then with graphene oxide by the facile solvothermal method to get the final products for the first time. The obtained ZnFe₂O₄ nanofibers composed of numerous same size nanoparticles wrapped by graphene sheets to form a unique nanostructure. When the ZnFe₂O₄-graphene electrode was evaluated as anode for lithium-ion batteries, good rate capability and long-term cycling stability could be achieved. The ZnFe₂O₄-graphene electrode exhibited a first discharge capacity of 2166 mAh g⁻¹ cycling at 0.05 C, remained an average reversible capacity of 1000 mAh g⁻¹ after 50 cycles, and kept the high rate capacities of 899, 822, 760 and 711 mAh g⁻¹ at the current rates of 0.5, 1, 2 and 5 C, respectively. The excellent electrochemical performance could be ascribed to the following reasons: the large electrochemical active surface area provided by the composite nanofibers; the graphene sheets decreased the internal resistance of the lithium-ion batteries, which resulted from the electrical conductivity of the graphene sheets; the graphene sheets as conductive network could effectively restrain the agglomeration of ZnFe₂O₄ nanopaiticals.     

Simple self-assembly of SnS2 entrapped graphene aerogel and its enhanced lithium storage performance

In this work, SnS₂ nanoplates entrapped graphene aerogel has been successfully prepared by simple self-assembly of reduced graphene oxide obtained through mild chemical reduction. Structural and morphological investigations demonstrated that SnS₂ nanoplates are highly dispersed in the three dimensional (3D) porous graphene matrix. When served as anode material for lithium-ion batteries, the electrochemical properties of SnS₂/graphene aerogel (SnS₂/GA) were evaluated by galvanostatic discharge–charge tests, cyclic voltammetry and impedance spectroscopy measurement. Compared with pristine SnS₂, the SnS₂/GA nanocomposite achieved a much higher initial reversible capacity (1186 mAh g⁻¹), superior cyclic stability (1004 mAh g⁻¹ after 60 cycles, corresponding to 84.7% of the initial reversible capacity), as well as better rate capability (650 mAh g⁻¹ at a current density of 1000 mA g⁻¹). This significantly improved lithium storage performance can be attributed to the good integration of SnS₂ nanoplates with 3D porous graphene network, which can not only provide much more active sites and easy access for Li ions intercalation, but also prevent the aggregation of SnS₂ nanoplates and facilitate fast transportation of Li ions and surface electrons during the electrochemical process.     

Dopamine derived nitrogen-doped carbon sheets as anode materials for high-performance sodium ion batteries

Designed as an anode material for sodium ion batteries, nitrogen-doped carbon sheets (NCSs) were successfully synthesized using graphene and dopamine as template and carbon precursor, respectively. The NCSs demonstrate high reversible capacity and excellent rate performance, delivering a high reversible capacity of 382 mAh g⁻¹ at 50 mA g⁻¹ after 55 cycles. Even up to 10 A g⁻¹, a rate capacity of 75 mAh g⁻¹ can be obtained. Furthermore, NCSs also have remarkable cycling stability with specific capacity of 165 mAh g⁻¹ after 600 cycles (under 200 mA g⁻¹). The excellent performance of NCSs can be ascribed to the nitrogen-doped two-dimension sheet structure.     

NiCo2O4 nanosheets and nanocones as additive-free anodes for high-performance Li-ion batteries

Development of novel electrode materials with high energy and power densities for lithium-ion batteries (LIBs) is the key to meet the demands of electric vehicles. Transition metal oxides that can react with large amounts of Li⁺ for electrochemical energy storage are considered promising anode materials for LIBs. In this work, NiCo₂O₄ nanosheets and nanocones on Ni foam have been synthesized via general hydrothermal growth and low-temperature annealing treatment. They exhibit high rate capacities and good cyclic performance as LIB anodes owing to their architecture design, which reduces ion and electron transport distance, expands the electrode–electrolyte contact, increases the structural stability, and buffers volume change during cycles. Notably, NiCo₂O₄ nanosheets deliver an initial capacity of 2239 mAh g⁻¹ and a rate capacity of 964 mAh g⁻¹ at current densities of 100 and 5000 mA g⁻¹, respectively. The corresponding values of nanocones are 1912 and 714 mAh g⁻¹. Hence, the as-synthesized NiCo₂O₄ nanosheets and nanocones, which are carbon-free and binder-free with higher energy densities and stronger connections between active materials and current collectors for better stability, are promising for use in advanced anodes for high-performance LIBs.     

LiSixMn2−xO4 (x≤0.10) cathode materials with improved electrochemical properties prepared via a simple solid-state method for high-performance lithium-ion batteries

LiSi_xMn_2−xO₄ (x≤0.10) cathode materials were prepared via a simple solid-state process with tetraethylorthosilicate (TEOS) as the silicon source. The effects of Si-doping on the structure, morphology and electrochemical performance were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), galvanostatic charge-discharge tests and electrochemical impedance spectroscopy (EIS), respectively. All the Si-doped LiMn₂O₄ samples showed the intrinsic spinel structure. With the increasing of Si-doping concentration, the crystal lattice constant of LiSi_xMn_2−xO₄ samples increased and the particle size distribution becomes more uniform to some extent. Among these samples, the optimal Si-doped LiMn₂O₄ exhibited an initial discharge capacity of 134.6 mAh g⁻¹ at 0.5 C, which was higher than that of the undoped spinel. After 100 cycles, the discharge capacity could still reach up to 114.5 mAh g⁻¹ with capacity retention of 85.1%. Especially, at the high rate of 5.0 C, a high discharge capacity of 87.5 mAh g⁻¹ was obtained while the undoped spinel only exhibited 33.7 mAh g⁻¹. Such high performance indicated that doping the manganese sites with appropriate amount of silicon ions could effectively improve the specific capacity and cycling stability.     

Evaluation of reduced graphene oxide-supported NiSb2O6 nanocomposites for reversible lithium storage

NiSb₂O₆ and reduced graphene oxide (NiSb₂O₆/rGO) nanocomposites are successfully fabricated by a solid-state method combined with a subsequent solvothermal treatment and further used as anode material of lithium-ion battery. The NiSb₂O₆/rGO nanocomposites exhibit a higher reversible capacity (of ca. 1240.5 mA h g⁻¹ at a current density of 50 mA g⁻¹), along with a good rate capability (395.2 mA h g⁻¹ at a current density of 1200 mA g⁻¹) and excellent capacity retention (684.5 mA h g⁻¹ after 150 cycles). These good performances could be attributed to the incorporated reduced grapheme oxide, which significantly improves the electronic conductivity of the NiSb₂O₆.     

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.     

Nb2O5 nanospheres/surface-modified graphene composites as superior anode materials in lithium ion batteries

Uniform Nb₂O₅ nanospheres/surface-modified graphene (SMG) composites for anode materials in lithium ion batteries were synthesized by hydrothermal method. The microstructure and morphology of composites were investigated by X-ray diffraction, scanning electron microscopy and transmission electron microscope techniques. The experimental results showed that Nb₂O₅ nanospheres were tightly and uniformly grown on the surface of SMG nanosheets. Nb₂O₅ nanospheres/SMG composites exhibited an impressive reversible capacity of 404.6 mA h g⁻¹ at the current density of 40 mA g⁻¹ after 100 cycles, and an excellent rate capacity of 345.5 mA h g⁻¹ at the current density of 400 mA g⁻¹.     

Facile synthesis of porous hollow Co3O4 microfibers derived-from metal-organic frameworks as an advanced anode for lithium ion batteries

Co₃O₄, as a promising anode material for the next generation lithium ion batteries to replace graphite, displays high theoretical capacity (890 mAh g⁻¹) and excellent electrochemical properties. However, the drawbacks of its poor cycle performance caused by large volume changes during charge-discharge process and low initial coulombic efficiency due to large irreversible reaction impede its practical application. Herein, we have developed a porous hollow Co₃O₄ microfiber with 500 nm diameter and 60 nm wall thickness synthesized via a facile chemical precipitation method with subsequent thermal decomposition. As an advanced anode for lithium ion batteries, the porous hollow Co₃O₄ microfibers deliver an obviously enhanced electrochemical property in terms of lithium storage capacity (1177.4 mA h g⁻¹ at 100 mA g⁻¹), initial coulombic efficiency (82.9%) and cycle performance (76.6% capacity retention at 200th cycle). This enhancement could be attributed to the well-designed microstructure of porous hollow Co₃O₄ microfibers, which could increase the contact surface area between electrolyte and active materials and accommodate the volume variations via additional void space during cycling.     

Iodine doped graphene as anode material for lithium ion battery

I-doped graphene is synthesized by a facile heat treatment method and used as anode material for lithium ion battery. The doped graphene exhibits high reversible capacity (1690 mAh g⁻¹ at 100 mA g⁻¹), good cyclability (retaining 92.6% reversible capacity after 200 cycles) and excellent rate performance compared with undoped graphene. The superior electrochemical performance of the I-doped graphene is explained by the change of graphene lattice, defects and positive charge density introduced by the doping of I atoms.     

A nest-like hierarchical porous V2O5 as a high-performance cathode material for Li-ion batteries

In this article, V₂O₅ with a novel nest-like hierarchical porous structure has been synthesized by a facile solvothermal method and investigated as cathode material for lithium-ion batteries. The nest-like V₂O₅ with a diameter of about 1.5 µm, was composed of interconnected nanosheets with a highly porous structure. Without other modification, the as-prepared V₂O₅ electrode exhibited superior capacity. An initial discharge capacity of 330 mAh g⁻¹ (at a current density of 100 mA g⁻¹) could be delivered and a stable discharge capacity of 240 mAh g⁻¹ after 50 cycles is maintained. The excellent performance was attributed to the hierarchical porous structure that could buffer against the local volume change and shorten the lithium-ions diffusion distance.     

Nitrogen-doped carbon nanofibers derived from polyacrylonitrile for use as anode material in sodium-ion batteries

Nitrogen-doped carbon nanofibers (N-CNFs) derived from polyacrylonitrile were successfully synthesized by a combination of electrospinning and thermal treatment processes. The as-prepared N-CNFs were used as anode material for sodium-ion batteries due to their unique fabric and weakly-ordered turbostratic structure as well as large spacing between graphene layers. Results show that N-CNFs carbonized at 800 °C delivered a high reversible capacity of 293 mAh g⁻¹ at a current density of 50 mA g⁻¹ in the first cycle. Even though the first-cycle Coulombic efficiency was 64%, it increased to nearly 100% only after a few initial cycles. Additionally, these N-CNFs showed excellent cycling and high-rate performance, and maintained a capacity of up to 150 mAh g⁻¹ even at an extremely high current density of 1000 mA g⁻¹ for over 200 cycles. It is, therefore, demonstrated that N-CNFs prepared under appropriate conditions are promising anode material candidate for sodium-ion batteries.     

The effect of AlF3 modification on the physicochemical and electrochemical properties of Li-rich layered oxide

Lithium (Li)-rich layered oxides are considered promising cathode materials for Li-ion batteries because of their favorable properties. Here, we report our recent finding in the novel oxide, aluminum fluoride (AlF₃)-modified Li_1.2Mn_0.54Ni_0.13Co_0.13O₂ (LMNCAF), which was synthesized via a facile, cost-effective and readily scalable solid-state reaction. LMNCAF possess an F and Al co-doped core structure with a LiF nano-coating on its surface which leads to considerably enhancement in the electrochemical performance of the oxide. The initial discharge capacity (at 0.05 C) increased from 212 mA h g⁻¹ for Li_1.2Mn_0.54Ni_0.13Co_0.13O₂ to 291 mA h g⁻¹ for LMNCAF. A much higher discharge capacity of 211 mA h g⁻¹ was obtained for LMNCAF after 99 charge/discharge cycles at 0.2 C compared with that of Li_1.2Mn_0.54Ni_0.13Co_0.13O₂ (160 mA h g⁻¹). Our preliminary results suggest that AlF₃ modification is an effective strategy to tailor the physicochemical and electrochemical properties of Li-rich layered oxides.