Mesoporous silicon nanocubes coated by nitrogen-doped carbon shell and wrapped by graphene for high performance lithium-ion battery anodes

Silicon materials have received widespread attention due to their inherent high theoretical specific capacity. However, large volumetric expansion and poor electrical conductivity hinder the large-scale application of silicon materials. To address these issues, we synthesize mesoporous silicon nanocubes coated by nitrogen-doped carbon shell (MSC@C) and wrapped by graphene (MSC@rGO) respectively. The ordered mesoporous silica nanocubes are obtained via a hydrolysis reaction of Tetraethyl Orthosilicate (TEOS) and further reduced by a magnesiothermic reduction to prepare mesoporous silicon nanocubes (MSC). The porous structure of MSC not only speeds up the transfer of ions and electrons, but also buffers the internal stress triggered by the volume expansion of the electrode material. Moreover, in addition to providing additional lithium storage sites and high conductivity, the graphene or nitrogen-doped carbon shell also effectively prevents aggregation and cracking of the mesoporous silicon, greatly promoting the stability of the entire electrode structure. Therefore, the electrochemical properties of composite materials are significantly enhanced by the combination of the mesoporous structure and the nitrogen-doped carbon shell or graphene. MSC@C can deliver the initial discharge specific capacity of 2852.7 mAh·g^?1 and the initial Coulombic efficiency (CE) of 83.74%. After 100 cycles, the MSC@C and MSC@rGO composite materials exhibit reversible specific capacities of 1070.5 mAh·g^?1 and 738.2 mAh·g^?1 at 0.1 A g^?1, respectively.     

Multilayer Si@SiOx@void@C anode materials synthesized via simultaneously carbonization and redox for Li-ion batteries

In the development of high-performance lithium-ion batteries (LIBs), the composition and structure of electrode materials are of critical importance. Silicon has a theoretical specific capacity 10 times that of graphite, nonetheless, its application as an anode material confronts challenge as it undergoes huge volume change and pulverization amidst the alloying and dealloying processes. Herein, a novel method to prepare a multilayer Si-based anode was proposed. Three layers, SiO₂, nickel and triethylene glycol (TEG), were coated successively on Si nanoparticles, which served respectively as the sources of SiO_x, sacrificial templates and carbon. Nickel can not only serve as a hollow template, but also play a catalytic role, which makes carbonization and redox reactions occur synchronously under a mild condition. Amid the carbonization process of TEG at 450 °C, several-nm-thick SiO₂ layer can react with the as-derived carbon to form a silicon suboxides (SiO_x (0 < x < 2)) intermedium layer. After removing the nickel template, a micro-nano scaled Si@SiO_x@void@C with conformal multilayer-structure can be obtained. The BET specific surface area and pore volume of powders were increased dramatically because of the derivation of abundant voids, which can not only buffer the swelling effect of silicon, but also provide richer ionic conductivity. The as-assembled half-cell with Si@SiOx@void@C as the anode material possesses high capacity (～1000 mAh g^?1 at 3 A g^?1), long cycle life (300 cycles with 77% capacity retention) and good rate performance (558 mAh g^?1 at 5 A g^?1).     

NiSe2 encapsulated in N-doped TiN/carbon nanoparticles intertwined with CNTs for enhanced Na-ion storage by pseudocapacitance

Transitional metal selenides are considered as potential anode candidates for sodium-ion batteries (SIBs) because of their relatively high theoretical capacity and environmental benign. However, the large volume change derived from the conversion reaction and the sluggish kinetics due to the inherent low electrochemical conductivity hinder their practical application. Herein, composite materials of NiSe₂ encapsulated in nitrogen-doped TiN/carbon nanoparticles with carbon nanotubes (CNTs) on the surface (NiSe₂@N-TCP/CNTs) are fabricated via pyrolysis and selenization processes. In this composite, TiN inside the carbon matrix can enhance the conductivity and structural stability. CNTs that are in-situ grown on the surface not only further enhance the conductivity of the composites, but also offer sufficient space to buffer the volume expansion and alleviate serious aggregation of NiSe₂ nanoparticles. Benefit from these merits, the NiSe₂@N-TCP/CNTs showed a lower charge transfer resistance and a faster Na⁺ diffusion rate than materials without growing CNTs. When used as the anode of SIBs, the NiSe₂@N-TCP/CNTs electrode delivered a reversible capacity of 344.0 mAh g^?1 after 1000 cycles at 0.2 A g^?1, and still maintained at 272.7 mAh g^?1 even at a high current density of 2 A g^?1. The remarkable electrochemical performance is mainly attributed to the special designed hierarchical structures and pseudocapacitance sodium storage behavior.     

Synthesis of 1D-MoS2/graphene nanotubes aided with sodium chloride for reversible lithium storage

A novel negative material consisting of graphene nanotubes and ultrathin MoS₂ is synthesized by a simple one-step hydrothermal method assisted with Sodium chloride. The MoS₂/Graphene electrodes deliver a specific capacity of 1350 mAh g^?1 under 0.1 A g^?1 and high rate capability (retaining 85.5% capacity from 0.1 A g^?1 to 0.8 A g^?1). A high remarkable capacity of 820 mAh g^?1 can still be recovered at 0.5 A g^?1 after 500 cycles, and the average coulombic efficiency was as high as 99.98% during the additional 500 cycles. The excellent Li-ion storage performance of MoS₂/Graphene nanotubes may be attributed to the ultra-thin MoS₂ flakes and curled graphene nanotubes. This structural feature has a strong adsorption capacity for lithium ions, which can provide a broad space for ion storage. A large number of active sites dispersed in the layered molybdenum disulfide promote the kinetics of the electrochemical reaction, empowering the ultra-thin layered molybdenum disulfide to get a higher theoretical capacity. In addition, the existence of the tubular structure alleviates volume expansion and provides a way for the rapid movement of electrons and diffusion of Li⁺ during repeated cycles.     

Reducing atmosphere improves the conductivity of NaTi2(PO4)3/C material for hybrid aqueous rechargeable lithium-ion battery anode

Hybrid aqueous rechargeable lithium-ion batteries (HARLIBs) have lower cost and better safety performance than conventional lithium-ion batteries (organic electrolytes). The challenge faced by HARLIBs are the narrow selection of anode and cathode materials, and overcoming the problems of capacity decay of anode and cathode materials in aqueous electrolytes. NaTi₂(PO₄)₃, which has a stable three-dimensional open framework structure, shows certain applicability in HARLIBs, but its inherent low electronic conductivity leads to poor utilization of active materials and inferior rate performance. In this article, we propose an experimental method that can improve the conductivity of NaTi₂(PO₄)₃/C, and study the electrochemical performance of NaTi₂(PO₄)₃/C aqueous half-cell and NaTi₂(PO₄)₃/C||LiMn₂O₄ hybrid aqueous full cell. The results show that Ti³⁺/oxygen vacancies can endow NaTi₂(PO₄)₃/C with higher conductivity and improve the specific capacity and rate capability (69 mAh·g^?1, 7C). At 1C, the second discharge specific capacity is 98.46 mAh·g^?1. After 100 cycles, the Rct was 2.92 × 10^?2 Ω. The NaTi₂(PO₄)₃/C//LiMn₂O₄ full cell can provide a discharge specific capacity of up to 101.07 mAh·g^?1. The synthesized NaTi₂(PO₄)₃/C material can be applied to the anode electrode of hybrid aqueous lithium-ion full cell.     

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.     

Electrospinning-derived ZnCo2O4@carbon nanofiber composite for high-performance lithium ion storage

The degradation of the cobalt-zinc oxide structure and its poor conductivity during the charge and discharge limit their further applications for lithium ion storage. Herein, ZnCo₂O₄@carbon nanofiber composite with nano-fibrous structure is obtained by electrospinning, annealing in argon and low-temperature oxidation to effectively overcome the above issue. The active sites of ZnCo₂O₄ are evenly dispersed inside the carbon nanofibers, which can effectively avoid its aggregation and improve electrical conductivity. Additionally, the stable nanofibrous structure can maintain structural stability. The composite exhibits superior lithium ion storage capacity when being served as anode electrode. The ZnCo₂O₄@carbon nanofiber electrode possesses a high capacity of 1071 mA h g⁻¹ at 0.1 A g⁻¹. Besides, the electrode shows an outstanding rate capability of 505 mA h g⁻¹ at 3 A g⁻¹ and maintain 714 mA h g⁻¹ after 250 cycles when current density is adjusted to 0.2 A g⁻¹ again. Additionally, the electrode has an outstanding long-cycle performance, which remains a capacity of 447.165 mA h g⁻¹ at 0.5 A g⁻¹ after 500 cycles and 421.477 mA h g⁻¹ at 1 A g⁻¹ after 518 cycles. This result demonstrates that ZnCo₂O₄@carbon nanofiber composite has potential application prospects in the fields of advanced energy storage.     

Template-free synthesis of novel Co3O4 micro-bundles assembled with flakes for high-performance hybrid supercapacitors

In this paper, a novel Co₃O₄ micro-bundles structure (Co₃O₄ MBs) was obtained at 120 °C after a hydrothermal reaction for 24 h and followed by an annealing treatment at 300 °C in air. The unique Co₃O₄ MBs are constructed by many adjacent flakes with 0.4 μm in thickness, and exhibit a large surface area of 81.2 m² g^?1 and a mean pore diameter of 6.14 nm, which may facilitate a sufficient contact with electrolyte and then shorten the diffusion pathway of ions. A remarkable electrochemical behavior including specific capacity of 282.3 C g^?1 at 1 A g^?1 and 205.9 C g^?1 at 10 A g^?1, and an excellent cycling performance with 74.6% capacity retention after 4000 charge-discharge process at 5 A g^?1 are achieved when the test of Co₃O₄ MBs-modified electrode is performed using three-electrode configuration. Additionally, a hybrid supercapacitor (HSC) was fabricated with the obtained Co₃O₄ MBs as positive electrode and commercial activated carbon (AC) as negative electrode. The HSC exhibits a specific capacity of 144.1 C g^?1 at 1 A g^?1 and 126.4% capacity retention after 5000 cycles at 5 A g^?1. An energy density of 38.5 W h kg^?1 can be obtained at a power density of 962.0 W kg^?1, and 29.5 W h kg^?1 is still retained at 8532.5 W kg^?1. The simple synthetic strategy can be applicable to the synthesis of other transition metal oxides with superior electrochemical performance.     

Nanoparticles constructed mesoporous coral-like Mn2O3 as high performance anode for lithium-ion batteries

As well established, the morphology and architecture of electrode materials greatly contribute to the electrochemical properties. Herein, a novel structure of mesoporous coral-like manganese (III) oxide (Mn₂O₃) is synthesized via a facile solvothermal method coupled with the carbonization under air. When fabricated as anode electrode for lithium-ion batteries (LIBs), the as-prepared Mn₂O₃ exhibits good electrochemical properties, showing a high discharge capacity of 1090.4 mAh g^?1 at 0.1 A g^?1, and excellent rate performance of 410.4 mAh g^?1 at 2 A g^?1. Furthermore, it maintains the reversible discharge capacity of 1045 mAh g^?1 at 0.1 A g^?1 after 380 cycles, and 755 mAh g^?1 at 1 A g^?1 after 450 cycles. The durable cycling stability and outstanding rate performance can be attributed to its unique 3D mesoporous structure, which is favorable for increasing active area and shortening Li⁺ diffusion distance.     

Nanosized Si/cellulose fiber/carbon composites as high capacity anodes for lithium-ion batteries: A galvanostatic and dilatometric study

Recently, we reported a simple method for obtaining nanosized silicon with promising electrochemical properties as an anode material for lithium-ion batteries; the method involves the formation of a composite electrode with cellulose fibers. It is demonstrated that the performance of these electrodes can be enhanced by the addition of conductive carbon black (CCB). This beneficial effect is not only a result of the improvement of electrical conductivity and inter-particle contacts, but also due to a reduction of the expansion and shrinkage undergone by the electrode when Li is inserted into Si or extracted from Li_xSi, as revealed by in situ electrochemical dilatometry measurements. The best results were obtained with a CCB of high surface area and porosity. The Si/cellulose fiber/carbon electrodes obtained delivered charge capacities as high as 1800 mAh g⁻¹ and exhibited good capacity retention on cycling. These electrodes also exhibited lower expansion/shrinkage compared to carbon-free electrodes on discharging and charging the cell, respectively.     

Nanospace‐confined synthesis of coconut‐like SnS/C nanospheres for high‐rate and stable lithium‐ion batteries

Coconut‐like monocrystalline SnS/C nanospheres are developed as anode materials for lithium‐ion batteries by a micro‐evaporation‐plating strategy in confined nanospaces, achieving reversible capacities as high as 936 mAh g^?1 at 0.1 A g^?1 after 50 cycles and 830 mAh g^?1 at 0.5 A g^?1 for another 250 cycles. The remarkably improved electrochemical performances can be mainly attributed to their unique structural features, which can perfectly combine the advantages of the face‐to‐face contact of core/shell nanostructure and enough internal void space of yolk/shell nanostructure, and therefore well‐addressing the pivotal issues related to SnS low conductivity, sluggish reaction kinetics, and serious structure pulverization during the lithiation/delithiation process. The evolutionary process of the nanospheres is clearly elucidated based on experimental results and a multiscale kinetic simulation combining the microscopic reaction‐diffusion equation and the mesoscopic theory of crystal growth. Furthermore, a LiMn₂O₄//SnS/C full cell is assembled, likewise exhibiting excellent electrochemical performance. © 2018 American Institute of Chemical Engineers AIChE J, 64: 1965–1974, 2018     

Tin antimony oxide @graphene as a novel anode material for lithium ion batteries

Bimetal oxides have attracted much attention due to their unique characteristics caused by the synergistic effect of bimetallic elements, such as adjustable operating voltage and improved electronic conductivity. Here, a novel bimetal oxide Sn_0.918Sb_0.109O₂@graphene (TAO@G) was synthesized via hydrothermal method, and applied as anode material for lithium ion batteries. Compared with SnO₂, the addition of Sb to form a bimetallic oxide Sn_0.918Sb_0.109O₂ can shorten the band gap width, which is proved by DFT calculation. The narrower band gap width can speed up the lithium ions transport and improve the electrochemical performances of TAO@G. TAO@G is a structure in which graphene supports nano-sized TAO particles, and it is conducive to the electrons transport and can improve its electrochemical performances. TAO@G achieved a high initial reversible discharge specific capacity of 1176.3 mA h g^?1 at 0.1 A g^?1 and a good capacity of 648.1 mA h g^?1 at 0.5 A g^?1 after 365 cycles. Results confirm that TAO@G is a novel prospective anode material for LIBs.     

Study on electrochemical performance of porous integrated PANI-Fe in supercapacitors

The iron-coordinated polyaniline (PANI-Fe) integrated nanomaterials was prepared by chemical oxidative and in-situ electrochemical polymerization, which was applied to supercapacitor electrodes. The N–Fe coordination bond is formed between FeCl₃ and the N of quinone diimine to enhance the interaction of the polyaniline molecular chain. The PANI-Fe electrode material forms a crosslinked porous fiber framework through two-step oxidation, which greatly improves the energy storage capacity of PANI-Fe. PANI-Fe achieves higher capacitance of 642 F g⁻¹ at 1 A g⁻¹ than PANI of 310 F g⁻¹, and maintains high capacitance retention of 82.4 % when the current density increases from 1 to 10 A g⁻¹. According to first-principles calculations, the Fermi energy (N(E)) of PANI-Fe drop down to 0.265 eV from 0.901 eV of PANI, which proves that its conductivity is improved. The change of the electrostatic potential of PANI-Fe indicates that the formation of the N–Fe coordination bond can improve the carrier transport behavior. PANI-Fe has a smaller HOMO-LUMO energy gap than PANI, indicating that the formation of N–Fe coordination bonds can increase the electrical activity of PANI.     

Oxygen vacancy-rich flower-like nickel cobalt layered double hydroxides for supercapacitors with ultrahigh capacity

One of the main difficulties for high-performance supercapacitors (SCs) is to design rational structures with excellent electrochemical properties. Herein, oxygen vacancy-rich nickel-cobalt layered double hydroxide, which has excellent supercapacitor performance, is prepared through an electrodeposition procedure and in situ oxidation process on nickel foam substrate. The conductivity and electrochemical properties are significantly improved by oxygen vacancies, which can be adjusted via hydrogen peroxide treatment. NiCo-LDH with oxygen vacancy (O_v-NiCo-LDH) attains a superior specific capacity of 1160 C g^?1 at the current density of 1 A g^?1 and shows a good capacity retention rate (61% of its original specific capacity is left at 20 A g^?1). Significantly, when the power density is 1.75 kW kg^?1, the energy density of the assembled symmetric supercapacitor (SSC) device is up to 216.19 Wh·kg^?1. This vacancy engineering strategy is helpful to the design of active materials for energy storage devices in the future.     

Self-doped 2D-V2O5 nanoflakes – A high electrochemical performance cathode in rechargeable zinc ion batteries

Aqueous zinc-ion batteries (AZIBs) are highly promising energy storage systems owing to their high energy and power density, along with their inherent safety in large-scale energy storage. The well-known low-cost potential cathode materials, such as vanadium oxides (e.g., V₂O₅), exhibit lower cycling performance, particularly at higher current densities because of dissolution in the electrolyte and lower electrical conductivity. We synthesized two-dimensional (2D) V₂O₅ nanoflakes, self-doped with V⁴⁺ ions from ammonium vanadates, using an annealing process. These porous V₂O₅ nanoflakes formed by the relatively larger agglomerated V₂O₅ nanoparticles consisting of a significant amount of V⁴⁺ ions, which possess higher electrical conductivity than commercial V₂O₅. V⁴⁺-doped V₂O₅ (d-V₂O₅) were used as the cathode material in AZIBs and delivered a stable specific capacity of 430 mAh g⁻¹ (@ 0.5 A g⁻¹). Furthermore, their electrochemical performance was better than that of the undoped commercial V₂O₅ samples. At a higher current density (10 A g⁻¹), d-V₂O₅ exhibited an excellent highly reversible specific capacity of 190 mAh g⁻¹ and retained 86% of its initial capacity after 1000 cycles. This stable electrochemical performance is attributed to the enhanced electrical conductivity, higher diffusion coefficient of Zn ions, and delayed electrode solubility in the electrolyte owing to the presence of self-doped V⁴⁺ ions in V₂O₅.     

PPy modified 1T-MoS2 hollow spheres with cohesive architecture as high-performance anode material for Li-ion batteries

A cohesive architecture of 1T-MoS₂ covered by PPy composite (1T-MoS₂@PPy) is successfully fabricated by a simple hydrothermal reaction followed by an in-situ polymerization route. The composite material consists of 1T-MoS₂ hollow microsphere and conductive PPy coating layer. The cohesive architecture enables the composite to show rapid shuttle of electrons/lithium ions and good ductility to buffer the volume changes during charging and discharging process when it is used as anode material. As expected, 1T-MoS₂@PPy composite exhibits a favorable discharge capacity up to 970.3 and 407.1 mAh g^?1 at 0.2 and 3 A g^?1, respectively. In addition, the composite also achieves impressive cycling performance of 717.1 mAh g^?1 at 1 A g^-1 after 500 cycles. This study provides a meaningful guidance in rational design of anode materials with cohesive architecture as well as high electrochemical performance.     

Synthesis of mesoporous hollow carbon microcages by combining hard and soft template method for high performance supercapacitors

Carbon materials have been widely used in electrochemistry filed such as supercapacitors because of the good conductivity, abundant sources and low prices. Further improving the electrochemical performance of carbon materials still attracts the interest of researchers. In this work, nitrogen-doped mesoporous hollow carbon microcages (N-MHCC) are successfully prepared by combining hard and soft template method. This hierarchically porous structure (meso- & micro-pore) of N-MHCC provides a large number of active centers, sufficient space and reaction interface, promoting the rapid diffusion of electron and electrolyte ions transport. By comparing the electrochemical performance of nitrogen-doped hollow carbon microcages (N-HCC) and N-MHCC, it can be calculated that N-MHCC shows high specific capacitance of 210.66 F g^?1 at 0.5 A g^?1 while N-HCC only shows 132.6 F g^?1. The cycle retention rate of N-MHCC is as high as 96.92 % at 5 A g^?1 after 4000 cycles. Furthermore, the simple preparation method and attractive performance make N-MHCC a promising candidate for high performance supercapacitors.     

Hydrazine reduction of LaNiO3 for active materials in supercapacitors

To improve the electric conductivity and overall performance of active materials in pseudocapacitors, we have established a novel hydrazine reduction process to transform perovskite oxides into active materials with the desired electrical conductivity and electrochemical behavior. Taking LaNiO₃ (LNO) produced from chemical solution as the starting material, different durations of hydrazine reduction (e.g. from 3, 6 to 12 hours) leads to a significant increase in specific capacitance, from ~70 F·g^?1 at 1 A·g^?1 (LNO) to ~280 F·g^?1 at 1 A·g^?1 (after 12 hours reduction). The desired electrical conductivity of LNO has been retained, as shown by the overall resistance of less than 0.3 Ω in the aqueous electrolyte. The hydrazined LNO demonstrated the desired stability as electrode, where the porous structure provides better accessibility for electrolytes, which is helpful in enhancing the overall electrochemical behaviors.     

MOFs derived (Ni0.75Co0.25)Se2 nanoparticles embedded in N-doped nanocarbon for hybrid supercapacitors

Bimetallic selenides have aroused great interest as the electroactive materials for energy storage because of their high conductivity, robust electrochemical activity, and the synergistic effect. Herein, (Ni_0.75Co_0.25)Se₂ nanoparticles embedded in N-doped nanocarbon ((Ni_0.75Co_0.25)Se₂@NC) hybrids were derived from nickel and cobalt bimetal-organic frameworks (NiCo-MOFs), which were synthesized by ethylene glycol solvothermal method. Due to the synergistic contributions and unique architecture, (Ni_0.75Co_0.25)Se₂@NC hybrids electrode presents a considerable specific capacity of 536.6 C g^?1 at a discharge current density of 1 A g^?1. In addition, an as-assembled (Ni_0.75Co_0.25)Se₂@NC//activated carbon (AC) hybrid supercapacitor (HSC) ((Ni_0.75Co_0.25)Se₂@NC//AC HSC) shows large specific capacitance (73.6 F g^?1 at 0.5 A g^?1), outstanding energy density (26.2 Wh kg^?1 at 400 W kg^?1) with superior cyclic performance (88.7% of capacity retention after 5000 cycles). Furthermore, a (Ni_0.75Co_0.25)Se₂@NC//AC device could drive a mini-fan running for 67 s. Thus, (Ni_0.75Co_0.25)Se₂@NC is an outstanding active material for electrochemical energy storage.     

Growth of yolk-shell CuCo2S4 on NiO nanosheets for high-performance flexible supercapacitors

A poor electrical conductivity and short cycle life limits the wide application of transition metal oxides in energy storage applications. In this study, yolk-shell structured CuCo₂S₄ was grown on NiO nanosheets (NiO@CuCo₂S₄) via a hydrothermal method and vulcanization, which combined the synergistic interactions between Ni, Co, and Cu. The effect of varying the amount of the vulcanizing agent (thiourea) on the electrochemical performance of NiO@CuCo₂S₄ was also investigated. Moreover, the amount of thiourea not only tuned the morphology of the composite, but significantly influenced its electrochemical performance. When the Cu²⁺: Co²⁺: thiourea molar ratio in the precursor solution was 1:2:6, the obtained NiO@CuCo₂S₄ exhibited the best electrochemical performance of the various systems examined, with a specific capacitance of 1658 F g^?1 being achieved at 1 A g^?1. Density functional theory calculations further confirmed the excellent synergistic effect between NiO and CuCo₂S₄. In addition, the asymmetric supercapacitor composed of a NiO@CuCo₂S₄ positive electrode reached an ultrahigh energy density of 73 Wh kg^?1 at a power density of 802 W kg^?1, as well as excellent cycling stability (i.e., 91% capacitance retention after 5000 cycles). These results suggest that NiO@CuCo₂S₄ is a promising candidate for use in energy storage applications.