Improving the electrochemical performance of a natural molybdenite/N-doped graphene composite anode for lithium-ion batteries via short-time microwave irradiation

In the present work, low-cost natural molybdenite was used to make a MoS₂/N-doped graphene composite through coulombic attraction with the aid of (3-aminopropyl)-triethoxysilane and the electrochemical performance was greatly improved by solvent-free microwave irradiation for tens of seconds. The characterization results indicated that most (3-aminopropyl)-triethoxysilane can decompose and release N atoms to further improve the N-doping degree in NG during the microwave irradiation. In addition, the surface groups of N-doped graphene were removed and the particle size of MoS₂ was greatly decreased after the microwave irradiation. As a result, the composite electrode prepared with microwave irradiation exhibited a better rate performance (1077.3 mA h g⁻¹ at 0.1C and 638 mA h g⁻¹ at 2C) than the sample prepared without microwave irradiation (1013.6 mA h g⁻¹ at 0.1C and 459.1 mA h g⁻¹ at 2C). Therefore, the present results suggest that solvent-free microwave irradiation is an effective way to improve the electrochemical properties of MoS₂/N-doped graphene composite electrodes. This work also demonstrates that natural molybdenite is a promising low-cost anode material for lithium-ion batteries.

In this work, low-cost natural molybdenite was used to make a MoS₂/N-doped graphene composite with the aid of (3-aminopropyl)-triethoxysilane and the electrochemical performance was greatly improved by solvent-free microwave irradiation.     

Preparation of cobalt sulfide@reduced graphene oxide nanocomposites with outstanding electrochemical behavior for lithium-ion batteries

Cobalt sulfide@reduced graphene oxide composites were prepared through a simple solvothermal method. The cobalt sulfide@reduced graphene oxide composites are composed of cobalt sulfide nanoparticles uniformly attached on both sides of reduced graphene oxide. Some favorable electrochemical performances in specific capacity, cycling performance, and rate capability are achieved using the porous nanocomposites as an anode for lithium-ion batteries. In a half-cell, it exhibits a high specific capacity of 1253.9 mA h g⁻¹ at 500 mA g⁻¹ after 100 cycles. A full cell consists of the cobalt sulfide@reduced graphene oxide nanocomposite anode and a commercial LiCoO₂ cathode, and is able to hold a high capacity of 574.7 mA h g⁻¹ at 200 mA g⁻¹ after 200 cycles. The reduced graphene oxide plays a key role in enhancing the electrical conductivity of the electrode materials; and it effectively prevents the cobalt sulfide nanoparticles from dropping off the electrode and buffers the volume variation during the discharge–charge process. The cobalt sulfide@reduced graphene oxide nanocomposites present great potential to be a promising anode material for lithium-ion batteries.

Cobalt sulfide@reduced graphene oxide nanocomposites obtained through a dipping and hydrothermal process, exhibit ascendant lithium-ion storage properties.     

Construction of 1T@2H MoS2 heterostructures in situ from natural molybdenite with enhanced electrochemical performance for lithium-ion batteries

Natural molybdenite, an inexpensive and naturally abundant material, can be directly used as an anode material for lithium-ion batteries. However, how to release the intrinsic capacity of natural molybdenite to achieve high rate performance and high capacity is still a challenge. Herein, we introduce an innovative, effective, and one-step approach to preparing a type of heterostructure material containing 1T@2H MoS₂ crafted from insertion and expansion of natural molybdenite. The metallic 1T phase formed in situ can significantly improve the electronic conductivity of MoS₂. At the same time, 1T@2H MoS₂ heterostructures can provide an internal electric field (E-field) to accelerate the migration rate of electrons and ions, promote the charge transfer behaviour, and ensure the reaction reversibility and lithium storage kinetics. Such worm-like 1T@2H MoS₂ heterostructures also have a large specific surface area and a large number of defects, which will help shorten the lithium-ion transmission distance and provide more ion transmission channels. As a result, it exhibits a discharge capacity of 788 mA h g⁻¹ remarkably at 100 mA g⁻¹ after 485 cycles and stable cycling performance. It also shows excellent magnification performance of 727 mA h g⁻¹ at 1 A g⁻¹, compared to molybdenite concentrate. Briefly, this work''s heterostructure architectures open up a new avenue for applying natural molybdenite in lithium-ion batteries, which has the potential to achieve large-scale commercial applications.

Natural molybdenite, an inexpensive and naturally abundant material, can be directly used as an anode material for lithium-ion batteries.     

Design and synthesis of graphene/SnO2/polyacrylamide nanocomposites as anode material for lithium-ion batteries

Tin dioxide (SnO₂) is a promising anode material for lithium-ion batteries owing to its large theoretical capacity (1494 mA h g⁻¹). However, its practical application is hindered by these problems: the low conductivity, which restricts rate performance of the electrode, and the drastic volume change (400%). In this study, we designed a novel polyacrylamide/SnO₂ nanocrystals/graphene gel (PAAm@SnO₂NC@GG) structure, in which SnO₂ nanocrystals anchored in three-dimensional graphene gel network and the polyacrylamide layers could effectively prevent the agglomeration of SnO₂ nanocrystals, presenting excellent cyclability and rate performance. A capacity retention of over 90% after 300 cycles of 376 mA h g⁻¹ was achieved at a current density of 5 A g⁻¹. In addition, a stable capacity of about 989 mA h g⁻¹ at lower current density of 0.2 A g⁻¹ was achieved.

Tin dioxide (SnO₂) is a promising anode material for lithium-ion batteries owing to its large theoretical capacity (1494 mA h g⁻¹).     

Sb2O3 nanoparticles anchored on N-doped graphene nanoribbons as improved anode for sodium-ion batteries

Sodium-ion batteries (SIBs) are emerging as a promising alternative to conventional lithium-ion technology, due to the abundance of sodium resources. Still, major drawbacks for the commercial application of SIBs lie in the slow kinetic processes and poor cycling performance of the devices. In this work, a hybrid nanocomposite of Sb₂O₃ nanoparticles anchored on N-doped graphene nanoribbons (GNR) is implemented as anode material in SIBs. The obtained Sb₂O₃/N-GNR anode delivers a reversible specific capacity of 642 mA h g⁻¹ after 100 cycles at 0.1 A g⁻¹ and exhibits a good rate capability. Even after 500 cycles at 5 A g⁻¹, the specific capacity is maintained at about 405 mA h g⁻¹. Such good Na storage performance is mainly ascribed to the beneficial effect of N doping for charge transfer and to the improved microstructure that facilitates the Na⁺ diffusion through the overall electrode.

A hybrid nanocomposite of Sb₂O₃ nanoparticles anchored on N-doped graphene nanoribbons is used as anode in SIBs. These hybrid electrodes demonstrate a high charge transfer and improved microstructure, facilitating the Na⁺ diffusion in the electrode.     

An investigation of Li2TiO3–coke composite anode material for Li-ion batteries

Anode material Li₂TiO₃–coke was prepared and tested for lithium-ion batteries. The as-prepared material exhibits excellent cycling stability and outstanding rate performance. Charge/discharge capacities of 266 mA h g⁻¹ at 0.100 A g⁻¹ and 200 mA h g⁻¹ at 1.000 A g⁻¹ are reached for Li₂TiO₃–coke. A cycling life-time test shows that Li₂TiO₃–coke gives a specific capacity of 264 mA h g⁻¹ at 0.300 A g⁻¹ and a capacity retention of 92% after 1000 cycles of charge/discharge.

Anode material Li₂TiO₃–coke was prepared and tested for lithium-ion batteries. The as-prepared material exhibits excellent cycling stability and outstanding rate performance.     

Hierarchical porous ZnMnO3 yolk–shell microspheres with superior lithium storage properties enabled by a unique one-step conversion mechanism

ZnMnO₃ has attracted enormous attention as a novel anode material for rechargeable lithium-ion batteries due to its high theoretical capacity. However, it suffers from capacity fading because of the large volumetric change during cycling. Here, porous ZnMnO₃ yolk–shell microspheres are developed through a facile and scalable synthesis approach. This ZnMnO₃ can effectively accommodate the large volume change upon cycling, leading to an excellent cycling stability. When applying this ZnMnO₃ as the anode in lithium-ion batteries, it shows a remarkable reversible capacity (400 mA h g⁻¹ at a current density of 400 mA g⁻¹ and 200 mA h g⁻¹ at 6400 mA g⁻¹) and excellent cycling performance (540 mA h g⁻¹ after 300 cycles at 400 mA g⁻¹) due to its unique structure. Furthermore, a novel conversion reaction mechanism of the ZnMnO₃ is revealed: ZnMnO₃ is first converted into intermediate phases of ZnO and MnO, after which MnO is further reduced to metallic Mn while ZnO remains stable, avoiding the serious pulverization of the electrode brought about by lithiation of ZnO.

ZnMnO₃ has attracted enormous attention as a novel anode material for rechargeable lithium-ion batteries due to its high theoretical capacity.     

Effect of porous structural properties on lithium-ion and sodium-ion storage: illustrated by the example of a micro-mesoporous graphene1−x(MoS2)x anode

In this work, we synthesized micro-mesoporous graphene_1−x(MoS₂)_x with different compositional ratios via co-reduction of graphite oxide and exfoliated MoS₂ platelets. We systematically studied the performance of the micro-mesoporous graphene_1−x(MoS₂)_x as anodes in lithium-ion batteries and sodium-ion batteries. The results show that the specific surface areas of the composites decrease with introducing MoS₂. The irreversible capacitance, which is related to the formation of solid electrolyte interphases, also decreases. Besides specific surface area, we found that micropores can benefit the lithiation and sodiation. We demonstrated that a specific charge capacity of 1319.02 mA h g⁻¹ can be achieved at the 50th cycle for the graphene_½(MoS₂)_½ anode in lithium-ion batteries. Possible relationships between such a high specific capacity and the micro-mesoporous structure of the graphene_1−x(MoS₂)_x anode are discussed. This work may shed light on a general strategy for the structural design of electrode materials in lithium-ion batteries and sodium-ion batteries.

In this work, we systematically studied the effect of porous structural properties on performance of the micro-mesoporous graphene_1−x (MoS₂)_x as anodes in lithium-ion and sodium-ion batteries.     

Ultrafast-charging and long cycle-life anode materials of TiO2-bronze/nitrogen-doped graphene nanocomposites for high-performance lithium-ion batteries

Emerging technologies demand a new generation of lithium-ion batteries that are high in power density, fast-charging, safe to use, and have long cycle lives. This work reports charging rates and specific capacities of TiO₂(B)/N-doped graphene (TNG) composites. The TNG composites were prepared by the hydrothermal method in various reaction times (3, 6, 9, 12, and 24 h), while the N-doped graphene was synthesized using the modified Hummer''s method followed by a heat-treatment process. The different morphologies of TiO₂ dispersed on the N-doped graphene sheet were confirmed as anatase-nanoparticles (3, 6 h), TiO₂(B)-nanotubes (9 h), and TiO₂(B)-nanorods (12, 24 h) by XRD, TEM, and EELS. In electrochemical studies, the best battery performance was obtained with the nanorods TiO₂(B)/N-doped graphene (TNG-24h) electrode, with a relatively high specific capacity of 500 mA h g⁻¹ at 1C (539.5 mA g⁻¹). In long-term cycling, excellent stability was observed. The capacity retention of 150 mA h g⁻¹ was observed after 7000 cycles, at an ultrahigh current of 50C (27.0 A g⁻¹). The synthesized composites have the potential for fast-charging and have high stability, showing potential as an anode material in advanced power batteries for next-generation applications.

The TiO₂-bronze/nitrogen-doped graphene nanocomposites have the potential for fast-charging and have high stability, showing potential as an anode material in advanced power batteries for next-generation applications.     

Reduced graphene oxide promoted assembly of graphene@polyimide film as a flexible cathode for high-performance lithium-ion battery

Organic carbonyl polymers have been gradually used as the cathode in lithium-ion batteries (LIB). However, there are some limits in most organic polymers, such as low reversible capacity, poor rate performance, cycle instability, etc., due to low electrochemical conductivity. To mitigate the limits, we propose a strategy based on polyimide (PI)/graphene electroactive materials coated with reduced graphene oxide to prepare a flexible film (G@PI/RGO) by solvothermal and vacuum filtration processes. As a flexible cathode for LIB, it provides a reversible capacity of 198 mA h g⁻¹ at 30 mA g⁻¹ and excellent rate performance of 100 mA h g⁻¹ at high current densities of 6000 mA g⁻¹, and even a super long cycle performance (2500 cycles, 70% capacity retention). The excellent performance results in a special layer structure in which the electroactive PI was anchored and coated by the graphene. The present synthetic method can be further applied to construct other high-performance organic electrodes in energy storage.

G@PI/RGO is prepared by a combination of solvothermal reaction and carbonization. With good mechanical flexibility and high conductivity, it shows excellent performance when directly used as the cathode for LIB.     

MoS2/carbon composites prepared by ball-milling and pyrolysis for the high-rate and stable anode of lithium ion capacitors

Lithium ion capacitors (LICs), bridging the advantages of batteries and electrochemical capacitors, are regarded as one of the most promising energy storage devices. Nevertheless, it is always limited by the anodes that accompany with low capacity and poor rate performance. Here, we develop a versatile and scalable method including ball-milling and pyrolysis to synthesize exfoliated MoS₂ supported by N-doped carbon matrix derived from chitosan, which is encapsulated by pitch-derived carbon shells (MoS₂/CP). Because the carbon matrix with high nitrogen content can improve the electron conductivity, the robust carbon shells can suppress the volume expansion during cycles, and the sufficient exfoliation of lamellar MoS₂ can reduce the ions transfer paths, the MoS₂/CP electrode delivers high specific capacity (530 mA h g⁻¹ at 100 mA g⁻¹), remarkable rate capability (230 mA h g⁻¹ at 10 A g⁻¹) and superior cycle performance (73% retention after 250 cycles). Thereby, the LICs, composed of MoS₂/CP as the anode and commercial activated carbon (21 KS) as the cathode, exhibit high power density of 35.81 kW kg⁻¹ at 19.86 W h kg⁻¹ and high energy density of 87.74 W h kg⁻¹ at 0.253 kW kg⁻¹.

MoS₂/carbon composites prepared by ball-milling and pyrolysis for the high-rate anode of lithium ion capacitors.     

Electrochemical performance of CoSe2 with mixed phases decorated with N-doped rGO in potassium-ion batteries

Potassium-ion batteries (PIBs) have received much attention as next-generation energy storage systems because of their abundance, low cost, and slightly lower standard redox potential than lithium-ion batteries (LIBs). Nevertheless, they still face great challenges in the design of the best electrode materials for applications. Herein, we have successfully synthesized nano-sized CoSe₂ encapsulated by N-doped reduced graphene oxide (denoted as CoSe₂@N-rGO) by a direct one-step hydrothermal method, including both orthorhombic and cubic CoSe₂ phases. The CoSe₂@N-rGO anodes exhibit a high reversible capacity of 599.3 mA h g⁻¹ at 0.05 A g⁻¹ in the initial cycle, and in particular, they also exhibit a cycling stability of 421 mA h g⁻¹ after 100 cycles at 0.2 A g⁻¹. Density functional theory (DFT) calculations show that CoSe₂ with N-doped carbon can greatly accelerate electron transfer and enhance the rate performance. In addition, the intrinsic causes of the higher electrochemical performance of orthorhombic CoSe₂ than that of cubic CoSe₂ are also discussed.

Potassium-ion batteries (PIBs) have received much attention as next-generation energy storage systems because of their abundance, low cost, and slightly lower standard redox potential than lithium-ion batteries (LIBs).     

Three-dimensional macroporous graphene monoliths with entrapped MoS2 nanoflakes from single-step synthesis for high-performance sodium-ion batteries

Layered metal sulfides (MoS₂, WS₂, SnS₂, and SnS) offer high potential as advanced anode materials in sodium ion batteries upon integration with highly-conductive graphene materials. However, in addition to being costly and time-consuming, existing strategies for synthesizing sulfides/graphene composites often involve complicated procedures. It is therefore essential to develop a simple yet scalable pathway to construct sulfide/graphene composites for practical applications. Here, we highlight a one-step, template-free, high-throughput “self-bubbling” method for producing MoS₂/graphene composites, which is suitable for large-scale production of sulfide/graphene composites. The final product featured MoS₂ nanoflakes distributed in three-dimensional macroporous monolithic graphene. Moreover, this unique MoS₂/graphene composite achieved remarkable electrochemical performance when being applied to Na-ion battery anodes; namely, excellent cycling stability (474 mA h g⁻¹ at 0.1 A g⁻¹ after 100 cycles) and high rate capability (406 mA h g⁻¹ at 0.25 A g⁻¹ and 359 mA h g⁻¹ at 0.5 A g⁻¹). This self-bubbling approach should be applicable to delivering other graphene-based composites for emerging applications such as energy storage, catalysis, and sensing.

A single-step, template-free, high-throughput synthesis method is developed to produce graphene/MoS₂ composites for improved performances in sodium-ion batteries.

Sodium-ion batteries (NIBs) have been proposed as promising alternatives to lithium-ion batteries (LIBs) in the megawatt- and kilowatt-scale energy storage scenarios (i.e.; electric vehicles, stationary grids) for their high cost-effectiveness, sustainability, and environmental benignity.¹ Since the operation chemistry of NIBs is very similar to that of LIBs, knowledge gained from developing LIB technology can be mostly applied to NIBs with the exception of electrode materials.^2,3 In particular, the larger ionic radius of Na⁺ (0.102 nm) than that of Li⁺ (0.076 nm) makes graphite, the most commonly used anode in LIBs, unable to accommodate sodium ions in a satisfactory regime.⁴ Inspired by the findings on LIBs, scientists have tested carbonaceous materials,^5,6 alloy materials (Sn, Sb),^7,8 and metal oxides (Fe₂O₃, CuO, TiO₂)^9–11 as anode materials for NIBs. Unfortunately, due to the large volume change and/or the sluggish kinetics during charge/discharge cycles, these materials delivered either low reversible capacity or poor cyclability.¹² Consequently, layered metal sulfides (MoS₂, WS₂, SnS₂ and SnS) have also been explored as anode materials in NIBs due to their unique structural characteristics.¹³ For example, molybdenum sulfide (MoS₂), stemming from its large interlayer spacing (0.62 nm, compared to 0.34 nm for graphite) and high capacity for hosting foreign species, has been recently highlighted as a possible candidate for anode material in NIBs.^14–19 According to the intercalation and conversion reaction between one MoS₂ molecule and four Na⁺, the theoretical capacity of MoS₂ is as high as 670 mA h g⁻¹.²⁰However, there are two major issues when using MoS₂ as anodes in large-scale applications: poor electronic conductivity and drastic volume expansion upon conversion reaction from MoS₂ to Mo and Na₂S.^18,20–27 One effective approach to address the problems and thus improve the electrochemical performance of MoS₂ in NIBs is by supporting MoS₂ with conductive scaffolds to create porous composites, so as to simultaneously improve its conductivity as well as buffer the volumetric variation.¹² In this regard, carbon materials, especially graphene, have been repeatedly confirmed to be an efficient conductive additive in electrode materials in resolving the above issues.^28,29 Some examples of such effective treatment on electrode materials include sulfur/graphene cathode in lithium–sulfur batteries,³⁰ lithium metal phosphates/carbon cathode materials in LIBs,^31–34 and various metal oxides/graphene anode materials in LIBs.³⁵To improve the electrical conductivity and enhance the structural integrity of MoS₂ anode, MoS₂/graphene composites have been synthesized via several methods and applied in NIBs.^{17,18,21,23,26,36–41} For instance, David et al. prepared MoS₂/graphene composite paper through vacuum filtration of homogeneous dispersions consisting of exfoliated MoS₂ and graphene oxide sheets, followed by thermal reduction at elevated temperatures.¹⁸ Wang et al. and Xie et al. also synthesized MoS₂/graphene composites via hydrothermal reactions plus thermal annealing, respectively.^23,26 In spite of the significant synthetic achievements made, the existing strategies for synthesizing MoS₂/graphene composites present a few shortcomings as these methods often involve complicated procedures (graphene oxide preparation, MoS₂ preparation, compositing or mixing step, thermal treatments, etc.) in addition to be costly and time-consuming.²⁸ Another issue with existing MoS₂/graphene compositing methods is that some of them do not ensure the intimate contact between MoS₂/graphene interfaces, an unfavorable condition for electrochemical applications (charge-transfer process).²⁶ Finally, most of the present MoS₂/graphene compositing methods are faced with the issue of low yield, ranging from several tens to hundreds milligrams of powders under laboratory conditions.Herein, we report a single-step, template-free, high-throughput “self-bubbling” method for synthesizing MoS₂/graphene composite. Our method is cost-effective, simple and scalable. The synthesis utilizes the thermal decomposition of solid precursor to generate MoS₂; meanwhile, the released gas from the decomposition reaction blows premixed, melted glucose into crowded bubbles, which then evolve into graphene structures during annealing. The final product is microscopically featured as highly crystalline MoS₂ nanoflakes distributed in three-dimensional (3D) macroporous monolithic graphene. With the additional assistance of intimate interfacial contacts between MoS₂ and graphene, our composite demonstrates considerably improved electrochemical performance when compared with those of conventional MoS₂/graphene composite upon application in NIBs. It is expected that such a unique MoS₂/graphene composite should hold potential in promoting the development of practical MoS₂ anode in NIBs, while the straightforward self-bubbling method could offer the opportunity in producing MoS₂/graphene composites in industrial scale as well as synthesizing other advanced graphene-based composites.     

Preparation of novel two-stage structure MnO micrometer particles as lithium-ion battery anode materials

MnO micrometer particles with a two-stage structure (composed of mass nanoparticles) were produced via a one-step hydrothermal method using histidine and potassium permanganate (KMnO₄) as reagents, with subsequent calcination in a nitrogen (N₂) atmosphere. When the MnO micrometer particles were utilized in lithium-ion batteries (LIBs) as anode materials, the electrode showed a high reversible specific capacity of 747 mA h g⁻¹ at 100 mA g⁻¹ after 100 cycles, meanwhile, the electrode presented excellent rate capability at various current densities from 100 to 2000 mA g⁻¹ (∼203 mA h g⁻¹ at 2000 mA g⁻¹). This study developed a new approach to prepare two-stage structure micrometer MnO particles and the sample can be a promising anode material for lithium-ion batteries.

MnO micrometer particles with a two-stage structure (composed of mass nanoparticles) were produced via a one-step hydrothermal method using histidine and potassium permanganate (KMnO₄) as reagents, with subsequent calcination in a nitrogen (N₂) atmosphere.     

Carbon-coated SnO2 riveted on a reduced graphene oxide composite (C@SnO2/RGO) as an anode material for lithium-ion batteries

The research on graphene-based anode materials for high-performance lithium-ion batteries (LIBs) has been prevalent in recent years. In the present work, carbon-coated SnO₂ riveted on a reduced graphene oxide sheet composite (C@SnO₂/RGO) was fabricated using GO solution, SnCl₄, and glucose via a hydrothermal method after heat treatment. When the composite was exploited as an anode material for LIBs, the electrodes were found to exhibit a stable reversible discharge capacity of 843 mA h g⁻¹ at 100 mA g⁻¹ after 100 cycles with 99.5% coulombic efficiency (CE), and a specific capacity of 485 mA h g⁻¹ at 1000 mA g⁻¹ after 200 cycles; these values were higher than those for a sample without glucose (SnO₂/RGO) and a pure SnO₂ sample. The favourable electrochemical performances of the C@SnO₂/RGO electrodes may be attributed to the special double-carbon structure of the composite, which can effectively suppress the volume expansion of SnO₂ nanoparticles and facilitate the transfer rates of Li⁺ and electrons during the charge/discharge process.

The combined action of GO and glucose makes the SnO₂ dispersed uniformly. The synergistic effect of the unique double-carbon structure can effectively improve the electrical conductivity of the SnO₂ and strengthen lithium storage capability.     

Hydrothermal-template synthesis and electrochemical properties of Co3O4/nitrogen-doped hemisphere-porous graphene composites with 3D heterogeneous structure

Despite the high capacity of Co₃O₄ employed in lithium-ion battery anodes, the reduced conductivity and grievous volume change of Co₃O₄ during long cycling of insertion/extraction of lithium-ions remain a challenge. Herein, an optimized nanocomposite, Co₃O₄/nitrogen-doped hemisphere-porous graphene composite (Co₃O₄/N-HPGC), is synthesized by a facile hydrothermal-template approach with polystyrene (PS) microspheres as a template. The characterization results demonstrate that Co₃O₄ nanoparticles are densely anchored onto graphene layers, nitrogen elements are successfully introduced by carbamide and the nanocomposites maintain the hemispherical porous structure. As an anode material for lithium-ion batteries, the composite material not only maintains a relatively high lithium storage capacity (the first discharge specific capacity can reach 2696 mA h g⁻¹), but also shows significantly improved rate performance (1188 mA h g⁻¹ at 0.1 A g⁻¹, 344 mA h g⁻¹ at 5 A g⁻¹) and enhanced cycling stability (683 mA h g⁻¹ after 500 cycles at 1 A g⁻¹). The enhanced electrochemical properties of Co₃O₄/N-HPGC nanocomposites can be ascribed to the synergistic effects of Co₃O₄ nanoparticles, novel hierarchical structure with hemisphere-pores and nitrogen-containing functional groups of the nanomaterials. Therefore, the developed strategy can be extended as a universal and scalable approach for integrating various metal oxides into graphene-based materials for energy storage and conversion applications.

The Co₃O₄/N-HPGC nanocomposites synthesized by a hydrothermal-template approach with polystyrene microspheres as the template possess excellent electrochemical performance.     

Polyimide-derived carbon nanofiber membranes as free-standing anodes for lithium-ion batteries

Free-standing and flexible carbon nanofiber membranes (CNMs) with a three-dimensional network structure were fabricated based on PMDA/ODA polyimide by combining electrospinning, imidization, and carbonization strategies. The influence of carbonization temperature on the physical-chemical characteristics of CNMs was investigated in detail. The electrochemical performances of CNMs as free-standing electrodes without any binder or conducting materials for lithium-ion batteries were also discussed. Furthermore, the surface state and internal carbon structure had an important effect on the nitrogen state, electrical conductivity, and wettability of CNMs, and then further affected the electrochemical performances. The CNMs/Li metal half-cells exhibited a satisfying charge–discharge cycle performance and excellent rate performance. They showed that the reversible specific capacity of CNMs carbonized at 700 °C could reach as high as 430 mA h g⁻¹ at 50 mA g⁻¹, and the value of the specific capacity remained at 206 mA h g⁻¹ after 500 cycles at a high current density of 1 A g⁻¹. Overall, the newly developed carbon nanofiber membranes will be a promising candidate for flexible electrodes used in high-power lithium-ion batteries, supercapacitors and sodium-ion batteries.

Free-standing and flexible carbon nanofiber membranes (CNMs) with a three-dimensional network structure were fabricated based on PMDA/ODA polyimide by combining electrospinning, imidization, and carbonization strategies.     

Enhanced storage behavior of quasi-solid-state aluminum–selenium battery

The current aluminum batteries with selenium positive electrodes have been suffering from dramatic capacity loss owing to the dissolution of Se₂Cl₂ products on the Se positive electrodes in the ionic liquid electrolyte. For addressing this critical issue and achieving better electrochemical performances of rechargeable aluminum–selenium batteries, here a gel-polymer electrolyte which has a stable and strongly integrated electrode/electrolyte interface was adopted. Quite intriguingly, such a gel-polymer electrolyte enables the solid-state aluminum–selenium battery to present a lower self-discharge and obvious discharging platforms. Meanwhile, the discharge capacity of the aluminum–selenium battery with a gel-polymer electrolyte is initially 386 mA h g⁻¹ (267 mA h g⁻¹ in ionic liquid electrolyte), which attenuates to 79 mA h g⁻¹ (32 mA h g⁻¹ in ionic liquid electrolyte) after 100 cycles at a current density of 200 mA g⁻¹. The results suggest that the employment of a gel-polymer electrolyte can provide an effective route to improve the performance of aluminum–selenium batteries in the first few cycles.

A quasi-solid-state aluminum–selenium battery has been established using gel-polymer electrolyte between the Se positive electrode and Al negative electrode which increasing the utilization of the active materials.     

FeNb2O6/reduced graphene oxide composites with intercalation pseudo-capacitance enabling ultrahigh energy density for lithium-ion capacitors

Lithium-ion capacitors (LICs), which combine the characteristics of lithium-ion batteries and supercapacitors, have been well studied recently. Extensive efforts are devoted to developing fast Li⁺ insertion/deintercalation anode materials to overcome the discrepancy in kinetics between battery-type anodes and capacitive cathodes. Herein, we design a FeNb₂O₆/reduced graphene oxide (FNO/rGO) hybrid material as a fast-charge anode that provides a solution to the aforementioned issue. The synergetic combination of FeNb₂O₆, whose unique structure promotes fast electron transport, and highly conductive graphene shortens the Li⁺ diffusion pathways and enhances structural stability, leading to excellent electrochemical performance of the FNO/rGO anode, including a high capacity (770 mA h g⁻¹ at 0.05 A g⁻¹) and long cycle stability (95.3% capacitance retention after 500 cycles). Furthermore, the FNO/rGO//ACs LIC achieves an ultrahigh energy density of 135.6 W h kg⁻¹ (at 2000 W kg⁻¹) with a wide working potential window from 0.01 to 4 V and remarkable cycling performance (88.5% capacity retention after 5000 cycles at 2 A g⁻¹).

FeNb₂O₆/reduced graphene oxide (FNO/rGO) hybrid material as a fast charge anode for LICs that provides a solution to overcome the discrepancy in kinetics between battery-type anodes and capacitive cathodes.     

Preparation of SiO2 nanowire arrays as anode material with enhanced lithium storage performance

SiO₂ nanowire arrays have been prepared by a template-assisted sol gel method and used as a negative electrode material for lithium ion batteries. Amorphous SiO₂ was confirmed by X-ray diffraction and Fourier transform infrared spectroscopy. The results of scanning electron microscopy and transmission electron microscopy confirmed that the SiO₂ nanowire had a diameter of about 100 nm and a length of about 30 μm. Cyclic voltammetry and constant current charge and discharge tests showed the prepared SiO₂ nanowire arrays were electrochemically active at a potential range of 0.05–3.0 V. At a current density of 200 mA g⁻¹, the first discharge specific capacity was as high as 2252.6 mA h g⁻¹ with a coulombic efficiency of 60.7%. Even after about 400 cycles, it still maintained 97.5% of the initial specific capacity. Moreover, a high specific capacity of 315 mA h g⁻¹ was exhibited when the current density was increased to 2500 mA g⁻¹. SiO₂ nanowire array electrodes with high reversible capacity and good cycle performance provide potential anode materials for future lithium-ion batteries.

SiO₂ nanowire arrays were synthesized using an AAO template-assisted sol–gel method. As a lithium negative electrode material, the sample exhibited excellent electrochemical properties.