Encapsulation of MnS Nanocrystals into N,S-Co-doped Carbon as Anode Material for Full Cell Sodium-Ion Capacitors

Sodium-ion capacitors(SICs)have received increasing interest for grid stationary energy storage application due to their affordability,high power,and energy densities.The major challenge for SICs is to overcome the kinetics imbalance between faradaic anode and nonfaradaic cathode.To boost the Na+reaction kinetics,the present work demonstrated a high-rate MnS-based anode by embedding the MnS nanocrystals into the N,S-co-doped carbon matrix(MnS@NSC).Benefiting from the fast pseudocapacitive Na+storage behavior,the resulting composite exhibits extraordinary rate capability(205.6 mAh g−1 at 10 A g−1)and outstanding cycling stability without notable degradation after 2000 cycles.A prototype SIC was demonstrated using MnS@NSC anode and N-doped porous carbon(NC)cathode;the obtained hybrid SIC device can display a high energy density of 139.8 Wh kg−1 and high power density of 11,500 W kg−1,as well as excellent cyclability with 84.5%capacitance retention after 3000 cycles.The superior electrochemical performance is contributed to downsizing of MnS and encapsulation of conductive N,S-co-doped carbon matrix,which not only promote the Na+and electrons transport,but also buffer the volume variations and maintain the structure integrity during Na+insertion/extraction,enabling its comparable fast reaction kinetics and cyclability with NC cathode.     

Electrochemical fabrication of a porous nanostructured nickel hydroxide film electrode with superior pseudocapacitive performance

A porous nickel film is prepared by selectively anodic dissolution of copper from an electrodeposited Ni-Cu alloy film. A porous nanostructured nickel hydroxide film electrode is further fabricated by the cathodic electrodeposition of Ni(OH)₂ film on the obtained porous nickel film. The specific capacitances of the as-prepared porous nanostructured Ni(OH)₂ film electrode at current densities of 2, 5 and 10 A/g are 1634, 1563 and 1512 F/g, respectively. The nanoporous Ni substrate significantly improves the electrochemically cyclic stability of the electrodeposited nickel hydroxide film in 1.0 M KOH solution. The superior pseudocapacitive properties such as large specific capacitance, excellent rate capability and improved electrochemically cyclic stability of the as-prepared nickel hydroxide electrode suggest its potential application in electrochemical capacitors.     

Synthesis and pseudocapacitive studies of composite films of polyaniline and manganese oxide nanoparticles

We report the synthesis and pseudocapacitive studies of a composite film (PANI-ND-MnO₂) of polyaniline (PANI) and manganese oxide (MnO₂) nanoparticles. To enhance the interaction of MnO₂ and PANI, the surfaces of MnO₂ nanoparticles were modified by a silane coupling reagent, triethoxysilylmethyl N-substituted aniline (ND42). The composite film was obtained via controlled electro-co-polymerization of aniline and N-substituted aniline grafted on surfaces of MnO₂ nanoparticles (ND-MnO₂) on a carbon cloth in a electrolyte of 0.5 M H₂SO₄ and 0.6 M (NaPO₃)₆. In comparison to similarly prepared PANI film, the incorporation of MnO₂ nanoparticles substantially increases the effective surface area of the film by reducing the size of rod-like PANI aggregates and avoiding the entanglement of these PANI nanorods. Significantly, we observed significant enhancement of specific capacitance in PANI-ND-MnO₂ film compared to PANI-MnO₂ film prepared in a similar condition, indicating that the presence of the coupling reagent can improve the electrochemical performance of PANI composite film. A symmetric model capacitor has been fabricated by using two PANI-ND-MnO₂ nanocomposite films as electrodes. The PANI-ND-MnO₂ capacitor showed an average specific capacitance of ∼80 F g⁻¹ and a stable coulombic efficiency of ∼98% over 1000 cycles. The results demonstrated that PANI-ND-MnO₂ nanocomposites are promising materials for supercapacitor electrode and the importance of designing and manipulating the interaction between PANI and MnO₂ for fundamentally improving capacitive properties.     

One-step electrochemical deposition of nickel sulfide/graphene and its use for supercapacitors

In this current work, the electrochemical co-deposition of nickel sulfide/electrochemically reduced graphene oxide(ERGO) nanocomposites is presented. During the electrochemical process, the graphene oxide nanosheets loose their hydrophilicity and precipitate onto the electrode. In the meantime, nickel sulfide is also electrochemically deposited on the electrode. The porous structure with ERGO covered by nickel sulfide, which facilitates the charge and ion transport in the electrode, has been observed by a scanning electron microscope. The cycle voltammetry curves as well as the galvanostatic charge/discharge curves of the nickel sulfide/ERGO nanocomposites exhibit distinct pseudocapacitive characteristic. The nanocomposites maintain 66.8% of the initial specific capacitance for the first 500 cycles, and only 4.6% loss of the specific capacitance is experienced for the further 1500 cycles, evidently showing a relatively high cycling stability. The results suggest that the nickel sulfide/ERGO is a promising electrode material for supercapacitors.     

Textural and capacitive characteristics of MnO2 nanocrystals derived from a novel solid-reaction route

Nanostructured manganese dioxide (MnO₂) materials were synthesized via a novel room-temperature solid-reaction route starting with Mn(OAc)₂·4H₂O and (NH₄)₂C₂O₄·H₂O raw materials. In brief, the various MnO₂ materials were obtained by air-calcination (oxidation decomposition) of the MnC₂O₄ precursor at different temperatures followed by acid-treatment in 2 M H₂SO₄ solution. The influence of calcination temperature on the structural characteristics and capacitive properties in 1 M LiOH electrolyte of the MnO₂ materials were investigated by X-ray diffraction (XRD), infrared spectrum (IR), transmission electron microscope (TEM) and Brunauer-Emmett-Teller (BET) surface area analysis, cyclic voltammetry, ac impedance and galvanostatic charge/discharge electrochemical methods. Experimental results showed that calcination temperature has a significant influence on the textural and capacitive characteristics of the products. The MnO₂ material obtained at the calcination temperature of 300 °C followed by acid-treatment belongs to nano-scale column-like (or needle-like) γ,α-type MnO₂ mischcrystals. While, the MnO₂ materials obtained at the calcination temperatures of 400, 500, and 600 °C followed by acid-treatment, respectively, belong to γ-type MnO₂ with the morphology of aggregates of crystallites. The γ,α-MnO₂ derived from calcination temperature of 300 °C exhibited a initial specific capacitance lower than that of the γ-MnO₂ derived from the elevated temperatures, but presented a better high-rate charge/discharge cyclability.     

FeS2@TiO2 nanorods as high-performance anode for sodium ion battery

Sodium-ion battery (SIB) is an ideal device that could replace lithium-ion battery (LIB) in grid-scale energy storage system for power because of the low cost and rich reserve of raw material. The key challenge lies in developing electrode materials enabling reversible Na⁺ insertion/desertion and fast reaction kinetics. Herein, a core-shell structure, FeS₂ nanoparticles encapsulated in biphase TiO₂ shell (FeS₂@TiO₂), is developed towards the improvement of sodium storage. The diphase TiO₂ coating supplies abundant anatase/rutile interface and oxygen vacancies which will enhance the charge transfer, and avoid severe volume variation of FeS₂ caused by the Na⁺ insertion. The FeS₂ core will deliver high theoretical capacity through its conversion reaction mechanism. Consequently, the FeS₂@TiO₂ nanorods display notable performance as anode for SIBs including long-term cycling performance (637.8 mA·h·g⁻¹ at 0.2 A·g⁻¹ after 300 cycles, 374.9 mA·h·g⁻¹ at 5.0 A·g⁻¹ after 600 cycles) and outstanding rate capability (222.2 mA·h·g⁻¹ at 10 A·g⁻¹). Furthermore, the synthesized FeS₂@TiO₂ demonstrates significant pseudocapacitive behavior which accounts for 90.7% of the Na⁺ storage, and efficiently boosts the rate capability. This work provides a new pathway to fabricate anode material with an optimized structure and crystal phase for SIBs.     

Electrochemical lithium storage of sodium titanate nanotubes and nanorods

Layered hydrated sodium titanate nanotubes are synthesized via a hydrothermal reaction in alkaline solution. The as-prepared nanotubes are calcined at different temperatures (300-600 °C) in air. The microstructure of obtained samples is characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). It is observed that the calcined products maintain their parent tubular morphologies below 500 °C. After calcinations at 600 °C, the hollow tubular morphology could completely be converted to the short solid nanorod morphology. In the meanwhile, the monoclinic sodium hexatitanate as a main phase is formed in nanorods, coexisted with sodium trititanate as a residual phase. The electrochemical lithium storage of obtained samples is studied by galvanostatic method and cyclic voltammetry. It is demonstrated that the nanotubes calcined at 500 °C have relatively large reversible capacity, good reversibility and excellent high rate discharge capability. The lithium intercalation process is shown to have pseudocapacitive feature caused by their layered structure and open lithium insertion tunnels, which is in favor of the high rate charge/discharge capability of sodium titanate nanotubes.     

Improvement of the high rate capability of hierarchical structured Li4Ti5O12 induced by the pseudocapacitive effect

Hierarchical structured Li₄Ti₅O₁₂, assembling from randomly oriented nanosheets with a thickness of about 10-16 nm, is fabricated by a facile hydrothermal route and following calcination. It is demonstrated that the as-prepared sample has good cycle stability and excellent high rate performance. In particular, the discharge capacity of 128 mAh g⁻¹ can be obtained at the high current density of 2000 mA g⁻¹, which is about 87% of that at the low current density of 200 mA g⁻¹ upon cycling, indicating that the as-prepared sample can endure great changes of various discharge current densities to retain a good stability. In addition, the pseudocapacitive effect based on the hierarchical structure, also contributes to the high rate capability of Li₄Ti₅O₁₂, which can be confirmed in cyclic voltammograms.     

Porous network of samarium sulfide thin films for supercapacitive application

In the present letter, a novel aqueous chemical method is employed to prepare thin film of Sm₂S₃ material containing porous network of interconnected nanoparticles for supercapacitive application. The orthorhombic phase formation of Sm₂S₃ film is concluded from X–ray diffraction study. The chemical states of samarium and sulfur are determined using X–ray photoelectron spectroscopy study. The pseudocapacitive behavior of Sm₂S₃ showed a maximum specific capacitance of 248 F g⁻¹ in 1.5 M LiClO₄ electrolyte prepared in propylene carbonate electrolyte. The nature of charge and discharge curves confirmed pseudocapacitive behavior of film electrode. The highest power and energy densities of 15.6 kWh kg⁻¹ and 54.6 Wh kg⁻¹, respectively are obtained. An electrochemical stability of 94% is retained after 1500 cycles.     

Enhanced high rate capability of dual-phase Li4Ti5O12–TiO2 induced by pseudocapacitive effect

The dual-phase Li₄Ti₅O₁₂–TiO₂ nanocomposite is successfully synthesized by a hydrothermal route with adding thiourea. The electrochemical performance of the dual-phase nanocomposite as anode for lithium-ion batteries is investigated by the galvanostatic method, cyclic voltammetry and electrochemical impedance spectra. It is demonstrated that the dual-phase Li₄Ti₅O₁₂–TiO₂ nanocomposite presents the improved electrochemical performance over individual single phase Li₄Ti₅O₁₂ and anatase TiO₂ samples. After 300 cycles at 1 C, the dual-phase Li₄Ti₅O₁₂–TiO₂ nanocomposite can still maintain the large discharge capacity of 116 mAh g⁻¹. It indicates that the as-prepared nanocomposite can endure great changes of various discharge current densities to retain a good stability. The large discharge capacity of 132 mAh g⁻¹ is also obtained at the large current density of 1600 mA g⁻¹ upon cycling. In particular, as verified by the cyclic voltammetry, the pseudocapacitive effect is induced due to the presence of abundant phase interfaces in the dual-phase Li₄Ti₅O₁₂–TiO₂ nanocomposite, which is beneficial to the enhanced high rate capability and good cycle stability.