A facile process is developed to prepare SnO2-based composites through using metal–organic frameworks (MOFs) as precursors. The nitrogen-doped graphene wrapped okra-like SnO2 composites (SnO2@N-RGO) are successfully synthesized for the first time by using Sn-based metal–organic frameworks (Sn-MOF) as precursors. When utilized as an anode material for lithium-ion batteries, the SnO2@N-RGO composites possess a remarkably superior reversible capacity of 1041 mA h g–1 at a constant current of 200 mA g–1 after 180 charge–discharge processes and excellent rate capability. The excellent performance can be primarily ascribed to the unique structure of 1D okra-like SnO2 in SnO2@N-RGO which are actually composed of a great number of SnO2 primary crystallites and numerous well-defined internal voids, can effectively alleviate the huge volume change of SnO2, and facilitate the transport and storage of lithium ions. Besides, the structural stability acquires further improvement when the okra-like SnO2 are wrapped by N-doped graphene. Similarly, this synthetic strategy can be employed to synthesize other high-capacity metal-oxide-based composites starting from various metal–organic frameworks, exhibiting promising application in novel electrode material field of lithium-ion batteries.Keywords: anodes; lithium-ion battery; metal−organic frameworks; nitrogen-doped graphene; okra-like SnO2;

Lithium sulfur (Li–S) batteries show great prospect as a next generation high energy density rechargeable battery systems. However, the practical utilization of Li–S batteries is still obstructed by the shuttle effects which inducing the fast capacity fading and the loss of active sulfur. Herein, a special graphene @ nitrogen and phosphorous dual-doped porous carbon (N–P–PC/G) is presented to modify a commercial separator for an advanced Li–S battery. The N–P–PC/G nanosheet employs graphene layer as an excellent conductive framework covered with uniform layers of N, P dual-doped porous carbon on both sides which possessing massive interconnected meso-/micropores. It is demonstrated that the N–P–PC/G-modified separator can suppress the shuttle effects by coupling interactions including physical absorption, chemical adsorption and interfacial interaction. With the aid of the N–P–PC/G-modified separator, the pure sulfur cathode with high-sulfur loading of 3 mg cm−2 offers a high initial discharge capacity of 1207 mA h g−1 at 0.5 C (1 C = 1675 mA h g−1), and a maintained capacity of 635 mA h g−1 (fading rate of only 0.095% per cycle), after 500 cycles. This work suggests that combining hybrid nanocarbon with multi-heteroatom doping to modify the commercial separator is an effective approach to obtain high electrochemical performance Li–S batteries.

MnO is a promising anode material for lithium-ion batteries because of its high capacity and abundant source, yet some critical issues such as the low conductivity and huge volume changes during cycling are still challenging its real application. Here, a facile strategy is proposed to realize the uniform decoration of MnO nanoparticles (20–40 nm) on graphene encapsulated with N-doped carbon layer (MnO@rGO/NC). In this structure, graphene acts as a robust and conductive platform for the anchoring of MnO nanoparticles and the outer N-doped carbon can further guarantee the structural integrity and conductivity of the composite. When evaluated as anode materials in lithium-ion batteries, the prepared MnO@rGO/NC composite with an optimized amount of MnO (58%) exhibits stable cycling performance and superior high rate capability, which delivers a reversible capacity as high as 989.8 mA h g−1 at 0.2 A g−1 after 130 cycles. The design and synthetic strategy presented in this work can be extended to other anode materials with large capacity, which endure large volume expansion and low conductivity during the charge–discharge processes.

•LF composites is prepared by a facile and low-cost synthetic method.•Li3FeF6 is in-situ formed on the surface of FeF3·0.33H2O particles.•The Li3FeF6 is also an insertion-style cathode material.•Cycle performance is improved by the introduction of Li3FeF6.Iron fluoride based on the multi-electron reaction is a typical representative among the new-style cathode materials for Lithium-ion batteries, which is attracting extensive attentions. To relieve the cathode dissolution and interfacial side reactions and improve the electrochemical performance of FeF3·0.33H2O, we design an ultra-thin Li3FeF6 protective layer, which is in-situ formed on the surface of FeF3·3H2O particles by a facile process. The prepared Li3FeF6/FeF3·0.33H2O (LF50) composite displays a superior rate performance (152 mAh g−1 at 1000 mA g−1), which is remarkable to many other carbon-free iron fluorides. And it is noticeable that a reversible capacity of 174 mAh g−1 can be retained after 100 cycles, indicating an outstanding cycling stability contrast to the bare FeF3·0.33H2O. The enhanced electrochemical performance is attributed to the protection of Li3FeF6 layer which reduces the cathode dissolution and interfacial side reactions. Moreover, the agglomeration of first particles in the calcination process is effectively suppressed resulting from the introduction of the Li3FeF6 protective layer, which promotes electrolyte penetration and charge transfer in the composites. It is expected that the strategy can provide a new approach for the modification of other metal fluoride.

•A new strategy to produce both hydrogen and Si materials was developed.•Al alloy with the addition of Si promotes generation of hydrogen.•R-Si shows encouraging electrochemical performance as anode material in LIBs.Silicon has been considered as one of the most promising anode materials for the next generation of lithium-ion batteries (LIBs) because of its ultrahigh theoretical capacity. However, not only its poor cycle stability and low coulombic efficiency, but also the high-cost, complex preparation methods present significant challenges for its commercialization. Hydrogen, an environmentally friendly and sustainable resource, can be used as fuel or reductant. In this study, we propose an effective strategy for the generation of hydrogen subsequent with the recovery of Si products (R-Si). The addition of Si in the initial Al alloy was demonstrated to be critical for the high-yield production of hydrogen via hydrolysis process. Si product was obtained subsequently by acid washing procedure. When the recovered Si was evaluated as anode material in LIBs, a high initial charge capacity of 3073 mAh/g at a rate of 150 mA/g was obtained. And it also showed excellent initial coulombic efficiency of 86% without any other modification. Furthermore, the R-Si could deliver a reversible capacity of 1735 mAh/g at 1.5 A/g after 100 cycles and have a reversible capacity of 521 mAh/g at 6 A/g. This work will provide referential significance for the research of hydrogen production with Al alloy and facile synthesis of Si anodes.

•A Partial Magnesiothermic Reduction Method is used to obtain mesoporous Si.•The internal pores could accommodate the volume changes of Si.•The carbon coating layer could effectively stabilize the interface during cycling.Owing to its high theoretical capacity, Si based anode materials have been regarded as the most promising alternative anode materials for lithium-ion batteries. Unfortunately, the commercial application of Si based anode materials has been greatly hindered, due to the large volume change of Si materials during their lithiation/delithiation process, which results in severe pulverization, loss of electrical contact and rapid capacity fading. To address these issues, we reported a partial magnesiothermic reduction method by adjusting the proportion of added Mg powder to convert SiO2 into Si/SiO2 and subsequently to coat such a composite with a carbon layer. After removing unreacted SiO2 using HF, carbon-coated mesoporous Si (p-Si@C) can be obtained. The internal pores could accommodate the volume changes of Si and the carbon coating layer could effectively stabilize the interface during cycling. With this design, the as-prepared p-Si@C shows superior electrochemical performance compared with bare Si. When the p-Si@C electrode evaluated at a rate of 0.5 A g−1, a reversible capacity of 1146 mAh g−1 could still be maintained after 100 cycles.

Interconnected highly graphitic carbon nanosheets (HGCNS) have been successfully synthesized via a combined hydrothermal and graphitization process that uses biomass waste (wheat stalk) as the precursor. The as-obtained HGCNS show favorable features for electrochemical energy storage such as high degree of graphitization (up to 90.2%), ultrathin nanosheet frameworks (2–10 atomic layers), graphite-like interlayer spacing (0.3362 nm), and a mesoporous structure. Due to these unique features of HGCNS, they not only can supply multiple sites for the storage and insertion of Li ions, but also can facilitate rapid mass transport of electrons and Li ions. As a result, the HGCNS when used as an anode material for lithium ion batteries show high reversible capacity (502 mA h g−1 at 0.1 C), excellent rate capability (461.4, 429.3, 305.2, and 161.4 mA h g−1 at 1, 2, 5, and 10 C, respectively), and superior cycling performance (215 mA h g−1 at 5 C after 2000 cycles and 139.6 mA h g−1 at 10 C after 3000 cycles). What's more, the relatively flat voltage profiles with a negligible charge/discharge voltage hysteresis of HGCNS would be particularly meaningful for its widespread commercialized application in real lithium ion batteries.

•Halloysite clay is converted into ultrafine Si nanoparticles.•The as-prepared HSi is composed of many interconnected Si nanoparticles.•The interconnected network enhances the electrochemical performance of electrodes.Recently, nanostructured Si has been intensively studied as a promising anode candidate for lithium ion batteries due to its ultrahigh capacity. However, the downsizing of Si to nanoscale dimension is often impeded by complicated and expensive methods. In this work, natural halloysite clay was utilized for the production of Si nanoparticles through selective acid etching and modified magnesiothermic reduction processes. The physical and chemical changes of these samples during the various processes have been analyzed. The as-prepared HSi from halloysite clay is composed of many interconnected Si nanoparticles with an average diameter of 20–50 nm. Owing to the small size and porous nature, the HSi nanoparticles exhibit a satisfactory performance as an anode for lithium ion batteries. Without further modification, a stable capacity over 2200 mAh g−1 at a rate of 0.2 C after 100 cycles and a reversible capacity above 800 mAh g−1 at a rate of 1 C after 1000 cycles can be obtained. As a result, this synthetic route is cost-effective and can be scaled up for mass production of Si nanoparticles, which may facilitate valuable utilization of halloysite clay and further commercial application of Si-based anode materials.

•A facile hydrothermal method is proposed to prepare cross-linked NSG/CNTs@SnO2.•The graphene/CNTs anchored with untrasmall SnO2 nanoparticles can be obtained.•The N, S are successfully incorporated into the carbon matrix.•The NSG/CNTs@SnO2 presents enhanced cycling stability and good high-rate capacity.SnO2-based nanostructures have attracted considerable interest as a promising high-capacity anode materials for lithium ion batteries. We present herein a facile one step hydrothermal approach for in situ growth of SnO2 nanoparticles in heteroatoms doped cross-linked carbon framework (NSG/CNTs@SnO2). Thiourea is employed as a single source of nitrogen and sulfur in the cross-linked carbon framework (NSG/CNTs). Characterization shows that the SnO2 nanoparticles with an average size of 6–10 nm are uniformly anchored on NSG/CNTs matrix. When evaluated for the electrochemical properties in lithium ion batteries, the obtained NSG/CNTs@SnO2 composite with ultrasmall SnO2 particle size (6–10 nm) delivers a high reversible capacity of 999 mAh g−1 at 200 mA g−1 after 120 cycles and excellent rate performance. Such outstanding electrochemical performance of the peculiar cross-linked NSG/CNTs@SnO2 composite can be primarily attributed to the synergistic effect of the ultrasmall anchored SnO2 nanoparticles and the dual-doped NSG/CNTs matrix. The uniformly distributed SnO2 nanoparticles can deliver large capacity and the robust dual-doped NSG/CNTs matrix can guarantee the good structural integrity and high electrical conductivity during cycling. Besides, the porous structure can provide free space for the volume expansion of SnO2 and accommodate the strain formed during repeated lithiation/delithiation processes.

•The separator is modified by N-doped porous carbon nanowire.•High N-doped level promotes the chemical adsorption of polysulfides.•The pure sulfur cathode exhibits excellent electrochemical performance.•The strategy of preparation is easy and efficient.Lithium–sulfur (Li–S) batteries are an attractive candidate for the next generation energy storage systems. However, the practical use of Li–S batteries is hindered by poor cycle life and low Coulombic efficiency, which are induced by shuttle effect. Modifying the properties of a separator is an effective way to inhibit the shuttle effect. However, only physical interactions of common carbon materials are not enough to confine lithium polysulfides. In this paper, a porous carbon nanowire (N-PCNW) is designed to modify the separator. The N-PCNW with high N-doped level (7.12 wt%) not only possesses excellent electron conductivity, but also traps the soluble polysulfides effectively with both physical and chemical interactions. With the N-PCNW modified separator, the pure sulfur cathode exhibits enhanced electrochemical performance, showing a high initial discharge capacity of 1430 mA h g− 1 at 0.2 C (1 C = 1675 mA h g− 1) and good long-term cycling stability at 0.5 C with 0.08% capacity fading per cycle. This design is easy and efficient, providing a great promise for the pratical use of Li–S batteries.

In this work, a material consisting of MnOx nanoparticles sandwiched between nitrogen-doped carbon plates (C/MnOx/C) has been successfully synthesized via a step-by-step strategy. It is demonstrated that the MnOx nanoparticles are well sandwiched between the double nitrogen-doped platelike carbon sheets. As an anode material for lithium-ion batteries, the double nitrogen-doped platelike carbon sheets encapsulating MnOx can not only address the issues related to the aggregation and volumetric changes of manganese oxides during the Li+ insertion/extraction, but also effectively shorten the transport path of Li+ ions and enhance the conductivity. As a result, the prepared C/MnOx/C composite exhibits stable cycling performance and superior high rate capability. The reversible capacity of C/MnOx/C after 100 cycles is as high as 770.9 mA h g−1, which is comparable with the initial capacity at 0.2 A g−1, and even at a high rate at 1 A g−1, it can deliver a high reversible of 443.9 mA h g−1, demonstrating the rational architecture design of the encapsulation of MnOx with nitrogen-doped platelike carbon layers.

MnO@C composites with three-dimensional cross-linked structure were designed and fabricated through hydrothermal treatment. Cation exchange resin was used as the precursor to create a three-dimensional cross-linked porous carbon structure, which was evenly decorated by nanosized MnO particles. When compared with pristine MnO, those MnO@C composites showed much better stability during charge-discharge cycling, retaining a specific capacity of 615 mAh g−1 (62.5 wt% MnO) after 100 cycles at a current density of 0.2 A g−1. This could be ascribed to the special three-dimensional cross-linked porous carbon that not only accelerated the transport of Li+ ions but also buffered the volume change and prevented agglomeration of MnO particles during the repeated lithiation and delithiation process.

•NiCo2O4 nanowire arrays are grown on nickel foam.•A simple hydrothermal method followed by an annealing process is adopted.•NiCo2O4 are uniformly distributed and anchored on the surface of nickel foam.•The freestanding electrode exhibits excellent electrochemical performance.With the ever-increasing power and energy needs in application of advanced consumer electronics and related technologies, developing electrode materials with both high energy and power densities holds the key for satisfying the urgent demand of energy storage worldwide. Herein, we report the successful preparation of NiCo2O4 nanowire arrays that are grown on nickel foam via a simple hydrothermal method followed by an annealing process. The electron microscopy images of the obtained NiCo2O4 nanowires reveal that the NiCo2O4 nanowires are uniformly distributed and anchored on the surface of nickel foam. Benefited from the unique structure of NiCo2O4 nanowires on a nickel foam substrate, the as prepared materials exhibit a high reversible capacity of 1048.8 mAh g−1 at 100 mA g−1 and show excellent rate performance for lithium storage.

•A novel PCNRs was synthesized from an ion-exchange resin.•A hybrid structure by incorporating the merits of PCNRs and graphene sheets.•The GS@PCNRs/S sulfur cathode exhibits excellent rate capability and cycle stability.•The GS@PCNRs/S composite presents electrochemical stability up to 500 cycles at 1 C.A low-cost carbon/sulfur material has been prepared using interconnected porous carbon nanorods (PCNRs) as the framework, and self-assembled graphene sheets (GS) as the coating layer. This GS@PCNRs/S sulfur cathode exhibits excellent rate capability and cycle stability. It delivers a maximum discharge capacity of 549.9 mAh g−1 at 1 C and keeps superior cyclability over 500 cycles with an average capacity fading rate of only 0.083% per cycle. The improved electrochemical performance is primarily attributed to the wrapped, internally porous architecture of GS@PCNRs/S, which not only can offer an excellent transport of lithium ions and electrons within the electrodes, but also can inhibit polysulfide diffusion by the external chemical and physical barrier of graphene sheets.

High yield porous carbon is prepared via the chemical oxidative polymerization of pyrrole and subsequent the decomposition of polypyrrole nanowires with KOH activation. The obtained carbon materials take on a seaweed-like porous morphology. The effects of the KOH mass and activation temperature on the morphology, structure and electrochemical performance of the porous carbon materials are studied in detail. When evaluated for the electrochemical properties in lithium ion batteries as anode materials, one of the unique porous products exhibits an ultra-high reversible capacity of about 1010.2 mA h g−1 at the first cycle and excellent capacity retention in the following cycles.

•A novel approach for solving the capacity loss in mesoporous carbon/sulfur material.•A hybrid structure by incorporating the merits of CMK-3 matrix and graphene skin.•Graphene-coated mesoporous carbon/sulfur composite was synthesized.•The RGO@CMK-3/S composite cathode exhibits improved electrochemical properties.A graphene coating mesoporous carbon/sulfur (RGO@CMK-3/S) composite, which is characteristic of a hybrid structure by incorporating the merits of CMK-3 matrix and graphene (RGO) skin, is synthesized by a facile and scalable route. The CMK-3/S composite is synthesized via a simple melt-diffusion strategy, and then a thin RGO skin is absorbed on the CMK-3/S composite surface in aqueous solution. When evaluating the electrochemical properties of as-prepared RGO wrapped nanostructures as cathode materials in lithium–sulfur batteries, it exhibits much improved cyclical stability and high rate performance. The RGO@CMK-3/S composite with 53.14 wt.% sulfur presents a reversible discharge capacity of about 734 mA h g−1 after 100 cycles at 0.5 C. The improved performance is attributed to the unique structure of RGO@CMK-3/S composite. CMK-3 with extensively mesopores can offer buffering space for the volume change of sulfur and efficient diffusion channel for lithium ions during the charge/discharge process. Meanwhile, the conductive RGO coating skin physically and chemically prevents the dissolution of polysulfides from the cathode, both of which contribute to the reduced capacity fade and improved electrochemical properties..

Silicon is a promising candidate for the anode material in lithium ion batteries due to its ultrahigh theoretical capacity of 4200 mAh g−1, which is approximately ten times larger compared to current commercial graphite anodes. However, the pulverization and capacity fading caused by the dramatic volume changes during cycling are still challenging its widespread application. To address these problems, a novel Si@C heterostructure with tunable preformed voids between Si core and carbon shell is synthesized via a flexible and tunable route. When evaluated for their electrochemical properties, these hollow Si@C spheres show enhanced electrochemical properties.Graphical abstractHighlights► Unique Si@C composites with preformed voids were synthesized. ► A facile template coating-etching to generate voids between core and shell. ► The preformed voids act as electrolyte reservoirs. ► This material manifests enhanced electrochemical performance.

•The electrochemical performance of coke powder for Li-ion batteries was studied.•The effects of boron content and graphitization temperature were investigated.•Proper content of boron can improve the electrochemical properties of coke powder.•Higher graphitization temperature helps to improve the electrochemical properties.•A mechanism on how and why doping increases the capacity was proposed.Coal-based coke powder is a by-product when coke is smashed for metallurgy and chemical industry. There is a vast output of coke powder every year around world, most of which is combusted as cheap fuel or abandoned directly. In this work, the electrochemical performance of graphitized boron-doped coal-based coke powder as anode for lithium ion batteries was investigated. The effects of boron content and graphitization temperature on the anode performance of boron-doped coal-based coke powder were also investigated in this paper. Results showed that a reversible capacity of 360.3 mA h/g of boron-doped coal-based coke powder can be obtained, while that of unboron-doped was 292.9 mA h/g. X-ray diffraction (XRD) analysis for the boron-doped coal-based coke powder showed that the distance between carbon layers was lowered by a proper amount of doped boron and higher graphitization temperature. X-ray photoelectron spectrometer (XPS) analysis was carried out to explain the effect of boron doping on the electrochemical performances of coal-based coke anodes.

A nano sulfur-based composite cathode material featured by uniform core@shell-structured sulfur@polypyrrole nanoparticles sandwiched in three-dimensional graphene sheets conductive network (S@PPy/GS) is fabricated via a facile solution-based method. The S@PPy nanoparticles are synthesized by in situ chemical oxidative polymerization of pyrrole on the surface of sulfur particles, and then graphene sheets are covered outside the S@PPy nanoparticles, forming a three-dimensional conductive network. When evaluating the electrochemical performance of S@PPy/GS in a lithium–sulfur battery, it delivers large discharge capacity, excellent cycle stability, and good rate capability. The initial discharge capacity is up to 1040 mAh/g at 0.1 C, the capacity can remain 537.8 mAh/g at 0.2 C after 200 cycles, even at a higher rate of 1 C, the specific capacity still reaches 566.5 mAh/g. The good electrochemical performance is attributed to the unique structure of S@PPy/GS, which can not only provide an excellent transport of lithium and electron ions within the electrodes, but also retard the shuttle effect of soluble lithium polysulfides effectively, thus plays a positive role in building better lithium-sulfur batteries.Description Portion: A nano sulfur-based composite cathode material featured by uniform core@shell-structured sulfur@polypyrrole nanoparticles sandwiched in three-dimensional graphene sheets conductive network is fabricated via a facile solution-based method for the first time.Download high-res image (187KB)Download full-size image

Activated carbons for electrochemical capacitor electrodes are prepared from soyabean using chemical activation with KOH. The pore size is easily controllable by changing the mass ratio between KOH and carbonized product. The as-prepared materials possess a large specific surface area, unique structure, well- developed hierarchical porosity and plentiful heteroatoms (mainly O and N). Thus resulted in its high specific capacitance, good rate capacity and cycling stability. Moreover, attributing to worldwide availability, renewable nature and low-cost, activated carbon prepared from soyabean has a good potential in energy conversion and storage devices.Download high-res image (223KB)Download full-size imageActivated carbons possessing unique structure, well-developed hierarchical porosity and plentiful heteroatoms (mainly O and N) are prepared from soyabean using chemical activation with KOH and applied as electrode material for electrochemical capacitors.

Lithium-sulfur (LiS) batteries have been considering as a very promising energy storage system since their high theoretical specific capacity and energy density. Nevertheless, the practical commercialization of LiS batteries is hindered by their poor cycle stability and fast capacity fading. Herein, a carbonized bacterial cellulose/titania (CBC/TiO2) modified separator is designed to restrain the shuttle effect of LiS cells with its strong physical and chemical adsorption of polysulfides. Cells with CBC/TiO2 modified separator show an initial discharge capacity of 1314 mAh g− 1 at 0.2C, and the capacity retention is 1048.5 mAh g− 1 after 50 cycles. A discharge capacity of 475 mAh g− 1 is obtained after 250 cycles at 2C. And during the rate test, LiS cells can deliver a discharge capacity of 537.1 mAh g− 1 at 2C. The outstanding electrochemical performance of LiS cells with CBC/TiO2 modified separator shows a new approach for the application of LiS batteries.

High yield porous carbon is prepared via the chemical oxidative polymerization of pyrrole and subsequent the decomposition of polypyrrole nanowires with KOH activation. The obtained carbon materials take on a seaweed-like porous morphology. The effects of the KOH mass and activation temperature on the morphology, structure and electrochemical performance of the porous carbon materials are studied in detail. When evaluated for the electrochemical properties in lithium ion batteries as anode materials, one of the unique porous products exhibits an ultra-high reversible capacity of about 1010.2 mA h g−1 at the first cycle and excellent capacity retention in the following cycles.