Electrochemical intercalation of lithium into boron-doped CVD diamond electrodes grown on carbon fiber cloths

Boron-doped diamond electrodes grown on a cloth of graphite fibers have demonstrated as an innovative material electrode for lithium intercalation by electrochemical method. It was studied lithium electrochemical intercalation for samples with different levels of boron doping. Diamond films were grown by hot-filament-assisted chemical vapor deposition technique. Boron was obtained from a source of B₂O₃ dissolved in methanol. The electrochemical characterization was carried out by voltammetry cyclic and charge/discharge curves. The electrolyte used was 1 mol l⁻¹ of LiPF₆ in mixture of ethylene carbonate, dimethyl carbonate and diethyl carbonate (1:1:1 wt.). The reference and work electrode were metallic lithium and the cell was assembled a dry-box. The results show that the insertion of lithium Li_x(B_zC_1−z)₆ is reversible and presents specific capacity, which depend on B-concentration. For limits of cut-off potential of 3.0 e 0.01 V vs. lithium we found a reversible specific capacity of 88 mAh g⁻¹ (x∼0.23) for sample with ∼10¹⁸ B cm⁻³ and 43 mAh g⁻¹ (x∼0.11) for sample with 10²¹ B cm⁻³. The voltage vs. capacity presents a hysteresis that increases with decreasing of boron concentration.     

High performance MnO2 nanoflower supercapacitor electrode by electrochemical recycling of spent batteries

MnO₂ nanoflower is prepared by electrochemical conversion of Mn₃O₄ obtained by heat treatment of spent zinc‒carbon batteries cathode powder. The heat treated and converted powders were characterized by TGA, XRD, FTIR, FESEM and TEM techniques. XRD analyses show formation of Mn₃O₄ and MnO₂ phases for the heat treated and converted powders, respectively. FESEM images indicate the formation of porous nanoflower structure of MnO_2, while, condensed aggregated particles are obtained for Mn₃O₄. The energy band gap of MnO₂ is obtained from UV‒Vis spectra to be 2.4 eV. The electrochemical properties are investigated using cyclic voltammetry, galvanostatic charge‒discharge and electrochemical impedance techniques using three-electrode system. The specific capacitance of MnO₂ nanoflower (309 F g⁻¹ at 0.1 A g⁻¹) is around six times higher than those obtained from the heat treated one (54 F g⁻¹ at 0.1 A g⁻¹). Moreover, it has high capacitance retention up to 93% over 1650 cycles. Impedance spectra of MnO₂ nanoflower show very small resistances and high electrochemical active surface area (340 m² g⁻¹). The present work demonstrates a novel electrochemical approach to recycle spent zinc-carbon batteries into high value supercapacitor electrode.     

Enhanced rate capability of nanostructured three-dimensional graphene/Ni3S2 composite for supercapacitor electrode

Three-dimensional graphene/Ni₃S₂ (3DG/Ni₃S₂) composite electrodes were produced by a facile two-step synthesis route involving chemical vapor deposition (CVD) growth of graphene foam and in situ hydrothermal synthesis of Ni₃S₂. The porous structure of the prepared 3DG is ideal for use as a scaffold for fabricating monolithic composite electrodes. The relative content of Ni₃S₂ initially increased and then decreased with increasing hydrothermal reaction time. The basal surface of the electrode was completely covered after 6 h of hydrothermal reaction. The size of the Ni₃S₂ microspheres also increased with increasing hydrothermal reaction time. The composite electrodes exhibited good specific capacitance (11.529 F cm⁻² at 2 mA cm⁻², i.e., 2611.9 F g⁻¹ at 5 mV s⁻¹) and cyclability (retention of 88.97% capacitance after 1000 charge/discharge cycles at 20 mA cm⁻²). These results are attributed to the fact that the uniform distribution of the Ni₃S₂ microspheres increased the specific surface area of the electrode and facilitated electron transfer and ion diffusion. The 3D multiplexed and highly conductive pathways provided by the defect-free graphene foam also ensured rapid charge transfer and conduction to improve the rate capability of the supercapacitors.     

Reduced graphene oxide anchored with δ-MnO2 nanoscrolls as anode materials for enhanced Li-ion storage

We developed a one-pot in situ synthesis procedure to form nanocomposite of reduced graphene oxide (RGO) sheets anchored with 1D δ-MnO₂ nanoscrolls for Li-ion batteries. The as-prepared products were characterized by X-ray diffraction (XRD), Raman spectra, X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscope (FESEM) and transmission electron microscope (TEM). The electrochemical performance of the δ-MnO₂ nanoscrolls/RGO composite was measured by galvanostatic charge/discharge cycling and electrochemical impedance spectroscopy. The results show that the δ-MnO₂ nanoscrolls/RGO composite displays superior Li-ion battery performance with large reversible capacity and high rate capability. The first discharge and charge capacities are 1520 and 810 mAh g⁻¹, respectively. After 50 cycles, the reversible discharge capacity is still maintained at 528 mAh g⁻¹ at the current density of 100 mAh g⁻¹. The excellent electrochemical performance is attributed to the unique nanostructure of the δ-MnO₂ nanoscrolls/RGO composite, the high capacity of MnO₂ and superior electrical conductivity of RGO.     

3D NiCo2S4 nanorod arrays as electrode materials for electrochemical energy storage application

It is essential to develop new electrode materials for electrochemical energy storage to meet the increasing energy demands, reduce environmental pollution and develop low-carbon economy. In this work, binder-free NiCo₂S₄ nanorod arrays (NCS NRAs) on nickel foam electrodes are prepared by an easy and low energy-consuming route. The electrodes exhibit superior electrochemical properties both for alkaline and Li-ion batteries. In 3 M KOH electrolyte, the NCS NRAs achieve a specific capacity of 240.5 mA h g⁻¹ at a current density of 0.2 A g⁻¹, and 105.7 mA h g⁻¹ after 1500 cycles at the current density of 5 A g⁻¹ with capacity retention of 87.3%. As the anode for LIBs, it shows a high initial capacity of 1760.7 mA h g⁻¹ at the current density of 100 mA g⁻¹, corresponding coulombic efficiency of 87.6%, and a rate capacity of 945 mA h g⁻¹ when the current density is improved 10 times. Hence, the NiCo₂S₄ nanorod arrays are promised as electrode materials with competitive performance.     

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

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

High dispersion of γ-MnO2 on well-aligned carbon nanotube arrays and its application in supercapacitors

The well-aligned carbon nanotube arrays (ACNTs) were used as supporting material and the γ-MnO₂/ACNT electrode with high dispersion of γ-MnO₂ has been prepared by electrochemically induced deposition method. The crystal structure and morphology of the γ-MnO₂/ACNT electrode were investigated by X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The capacitive properties of γ-MnO₂/ACNT electrode were characterized by cyclic voltammetry and galvanostatic charge–discharge method. The specific capacitance of the γ-MnO₂/ACNT electrode is as high as 784 F g^− 1 based on γ-MnO₂ and 234 F g^− 1 based on γ-MnO₂/ACNT composites in 0.1 M Na₂SO₄ aqueous solution from 0 to 1 V when the charge–discharge current density is 1 mA cm^− 2. Additionally, the electrode shows excellent power characteristics, high electrochemical reversibility and excellent long-term charge–discharge cycle stability.     

Amaryllis-like NiCo2S4 nanoflowers for high-performance flexible carbon-fiber-based solid-state supercapacitor

Low-cost dynamic materials for Faradaic redox reactions are needed for high-energy storage supercapacitors. A simple and cost-effective hydrothermal process was employed to synthesize amaryllis-like NiCo₂S₄ nanoflowers. The sample was characterized by X-ray powder diffraction, Brunauer–Emmett–Teller method, scanning electron microscopy, and transmission electron microscopy. NiCo₂S₄ nanoflowers were coated onto carbon fiber fabric and used as a binder-free electrode to fabricate a solid-state supercapacitor compact device. The solid-state supercapacitor exhibited excellent electrochemical performance, including high specific capacitance of 360 F g⁻¹ at scan rate of 5 mV s⁻¹ and high energy density of 25 W h kg⁻¹ at power density of 168 W kg⁻¹. In addition, the supercapacitor possessed high flexibility and good stability by retaining 90% capacitance after 5000 cycles. The high conductivity and Faradic-redox activity of NiCo₂S₄ nanoflowers resulted in high specific energy and power. Thus, NiCo₂S₄ nanoflowers are promising pseudocapacitive materials for low-cost and lightweight solid-state supercapacitors.     

Effect of processing parameters on the charge storage properties of MgCo2O4 electrodes

Three morphologies of magnesium cobaltite (MgCo₂O₄), viz. cuboidal microcrystals, nanoflowers, and nanospheres, were synthesized using hydrothermal and molten salt methods and evaluated their electrochemical energy storage properties. Among them cuboidal microcrystal and nanoflowers were obtained by a facile hydrothermal route – the former with ethylene glycol and the latter with hexadecyltrimethylammonium bromide as surfactants. The cuboidal microcrystals showed layered flake microstructure with an appreciable space between the layers (~ 100 nm), which would facilitate ion movement between the flakes. The electrochemical studies of the materials revealed the superiority of MgCo₂O₄ cuboidal microcrystals as a charge storage medium over the nanoflowers and nanospheres, the reasons for this is deeply investigated and reported herewith. The specific charge stored in the MgCo₂O₄ cuboidal microcrystal electrode was ~ 345 C g⁻¹ at a specific current of 1 A g⁻¹ which was superior to nanoflowers (~ 178 C g⁻¹) and nanospheres (~ 139 C g⁻¹) at the similar current density in 3 M LiOH electrolyte. The MgCo₂O₄ cuboidal microcrystals also demonstrated superior charge retention (~ 110%) after 3000 cycles over the other electrodes demonstrating its practical utility as a charge storage material.     

Cathode materials based on carbon nanotubes for high-energy-density lithium–sulfur batteries

The rational integration of conductive nanocarbon scaffolds and insulative sulfur is an efficient method to build composite cathodes for high-energy-density lithium–sulfur batteries. The full demonstration of the high-energy-density electrodes is a key issue towards full utilization of sulfur in a lithium–sulfur cell. Herein, carbon nanotubes (CNTs) that possess robust mechanical properties, excellent electrical conductivities, and hierarchical porous structures were employed to fabricate carbon/sulfur composite cathode. A family of electrodes with areal sulfur loading densities ranging from 0.32 to 4.77 mg cm⁻² were fabricated to reveal the relationship between sulfur loading density and their electrochemical behavior. At a low sulfur loading amount of 0.32 mg cm⁻², a high sulfur utilization of 77% can be achieved for the initial discharge capacity of 1288 mAh g_S⁻¹, while the specific capacity based on the whole electrode was quite low as 84 mAh g_{C/S+binder+Al}⁻¹ at 0.2 C. Moderate increase in the areal sulfur loading to 2.02 mg cm⁻² greatly improved the initial discharge capacity based on the whole electrode (280 mAh g_{C/S+binder+Al}⁻¹) without the sacrifice of sulfur utilization. When sulfur loading amount further increased to 3.77 mg cm⁻², a high initial areal discharge capacity of 3.21 mAh cm⁻² (864 mAh g_S⁻¹) was achieved on the composite cathode.     

Rational design of nickel cobalt sulfide/oxide core-shell nanocolumn arrays for high-performance flexible all-solid-state asymmetric supercapacitors

The development of wearable electronics has created a surge of interest in designing flexible energy storage device with high energy density and long lifespan. In this work, we have successfully fabricated a flexible asymmetric supercapacitor (ASC) based on the NiCo₂S₄@NiCo₂O₄ nanocolumn arrays (NCAs). The nickel cobalt sulfide/oxide core-shell nanostructures were rationally synthesized through a facile stepwise approach. The NiCo₂S₄@NiCo₂O₄ NCAs based electrode delivered a high specific capacitance of 2258.9 F g⁻¹ at a current density of 0.5 A g⁻¹. The as-assembled flexible ASC device exhibited a high energy density of 44.06 Wh kg⁻¹, a high power density of 6.4 kW kg⁻¹, and excellent cycling stability by retaining 92.5% after 6000 cycles. Excitingly, the electrochemical property of the ASC device could be maintained under severe bending, indicating superior flexibility and mechanical stability. The NiCo₂S₄@NiCo₂O₄ core-shell NCAs possess enormous potential for future wearable electronic applications.     

Co9S8–carbon composite as anode materials with improved Na-storage performance

The synthesis and electrochemical performance of a composite of Co₉S₈ nanoparticles and amorphous carbon is studied as an anode material for sodium-ion batteries. The Co₉S₈–carbon composite powder was fabricated through a one-pot spray pyrolysis process using thiourea and polyvinylpyrrolidone as sulfur and carbon sources, respectively. The Co₉S₈ nanoparticles are entirely covered by an amorphous carbon layer. The initial discharge and charge capacities of the Co₉S₈–carbon composite powder were 689 and 475 mA h g⁻¹, respectively, at a current density of 0.5 A g⁻¹. The Co₉S₈–carbon composite powders exhibited a stable cyclability with a reversible capacity of 404 mA h g⁻¹ for the 50th cycle and a superior rate capability compared with bare Co_1−xS powder. The improvement of Na-storage performance could be attributed to the small size and entanglement of the Co₉S₈ nanoparticles within the carbon matrix.     

Enhanced electrochemical properties of LiFePO4–silicon composites as positive electrode materials fabricated using a solid-state method

LiFePO₄–silicon composites were fabricated by using a solid-state method for applying positive electrodes in lithium ion batteries. The LiFePO₄–silicon composites were characterized with X-ray diffraction and field emission scanning electron microscopy. Their electrochemical properties were investigated with cyclic voltammetry, electrochemical impedance spectroscopy, and charge–discharge tests. The added silicon not only suppressed the surface corrosion caused by the decreasing H⁺ concentration in the electrolyte, but it also acted as a barrier between the LiFePO₄ particles and LiPF₆ electrolyte, thereby preventing the dissolution of Fe²⁺ in the electrode and enhancing the electrolyte/active material interactions. This resulted in improved lithium-ion transfer kinetics and excellent positive electrode performance, especially at high current densities and different operating temperatures (0, 25, and 50 °C). At 25 °C, the LiFePO₄ composite containing 2 wt% of silicon delivered the best electrochemical performance with a lithium-ion diffusion coefficient of 1.81×10⁻⁹ cm² s⁻¹, a specific discharge capacity of 143 mA h g⁻¹ for the initial cycle, and a capacity retention of 98% after 100 cycles. In contrast, the corresponding values for the pure LiFePO₄ were 1.19×10⁻¹¹ cm² s⁻¹, 115 mA h g⁻¹, and a capacity retention of 76% after 100 cycles, respectively.     

Sm2O3-doped ZnO beech fern hierarchical structures for nitroaniline chemical sensor

Sm₂O₃-doped ZnO hierarchical composites were prepared via a facile, simple hydrothermal method using Zn(CH₃COO)_2.2H₂O and Sm(NO₃)₃0.6H₂O as precursors. Growth temperature, time, and pH for the reaction were 7 h, 155 °C and 9.5, respectively. Needle-shaped and compound leaf-shaped structures with ovate or triangular-ovate outlines similar to those of Beech Fern (Phegopteris hexagonoptera) for hierarchical composites were formed. Further, the synthesized Sm₂O₃-doped ZnO hierarchical composites were used as efficient electron mediators for the preparation of highly sensitive, fast and reliable nitroaniline electrochemical sensors. A sensitivity of 1.71 μA μM⁻¹ cm⁻² with a very low experimental detection limit of 15.6 μM was reported for Sm₂O₃-doped ZnO hierarchical composites modified Ag electrode. Thus, as synthesized Sm₂O₃-doped ZnO hierarchical composites are potential and efficient electron mediators for the fabrication of sensitive, reliable and reproducible chemical sensors.     

Phase structure and electrochemical performance of layered-spinel integrated LiNi0.5Mn0.5O2-LiMn1.9Al0.1O4 composite cathodes for lithium ion batteries

In recent years, multi-component integrated composite cathodes for lithium ion batteries have attracted considerable attention. In this work, novel layered-spinel integrated cathode materials of (1−x)LiNi_0.5Mn_0.5O₂-xLiMn_1.9Al_0.1O₄ were synthesized by a sol-gel method, and their phase structures, morphologies and electrochemical performance were investigated. The crystal structure of the (1−x)LiNi_0.5Mn_0.5O₂-xLiMn_1.9Al_0.1O₄ is changed from layered to spinel structure with increasing x. All the samples exhibit nanoscale grains with the minimum grain size of ~130 nm when x = 0.5. The composite electrode with x = 0.5 exhibits the optimal discharge capacity, presenting a large initial discharge capacity of 236 mAh g⁻¹ at the current density of 20 mA g⁻¹. Good rate capability is also obtained at the composite electrode with x = 0.5 where the electrode displays the relatively high discharge capacity of 64.9 mAh g⁻¹ at the high rate of 5 C. The improved electrochemical performance is related to the introduction of spinel structure into layered structure and small grain size. The spinel structure can stabilize the layered structure, which leads to the improvement in the electrochemical performance of the composites; and the small grain size in the sample with x = 0.5 provides short lithium ion diffusion way and thus enhances the electrochemical performance.     

One-step hydrothermal synthesis of Sb2S3/reduced graphene oxide nanocomposites for high-performance sodium ion batteries anode materials

Sb₂S₃/reduced graphene oxide (SSR) nanocomposites were successfully synthesized through a facile one-step hydrothermal process, as used as anode materials for sodium ion batteries (SIBs). The characterization and electrochemical performance of the as-prepared samples were characterized by X-ray diffraction, field-emission scanning electron microscopy, transmission electron microscopy, nitrogen adsorption-desorption isotherms, cyclic voltammetry, electrochemical impedance spectroscopy, and galvanostatic charge/discharge tests, respectively. The results show that the introduction of reduced graphene oxide (RGO) can improve the electrochemical performances of SSR nanocomposites. SSR nanocomposites with 10 wt% RGO exhibits the highest reversible capacity of 581.2 mAh g⁻¹ at the current density of 50 mA g⁻¹ after 50 cycles, and excellent rate performance for SIBs. The improved electrochemical performance is attributed to the smaller Sb₂S₃ nanoparticles dispersed on RGO crumpled structure and synergetic effects between Sb₂S₃ and RGO matrix, which can increase specific surface area and improve electrical conductivity, reduce sodium ion diffusion distance, and effectively buffer volume changes during cycling process.     

Synthesis and electrochemical performance of Li4Ti5O12 submicrospheres coated with TiN as anode materials for lithium-ion battery

The TiN coated Li₄Ti₅O₁₂ (LTO) submicrospheres with high electrochemical performance as anode materials for lithium-ion battery were synthesized successfully by solvothermal method and subsequent nitridation process in the presence of ammonia. The XRD results revealed that the crystal structure of LTO did not change after thermal nitridation process. The submicrospheres morphology of LTO and TiN film on the surface of LTO submicrospheres were characterized by FESEM and HRTEM, respectively. XPS result confirmed that a small amount of Ti changed from Ti⁴⁺ to Ti³⁺ after nitridation process, which will increase the electronic conductivity of LTO. Electrochemical results showed that electrochemical performance of TiN coated LTO anode materials compared favorably with that of pure LTO. Also its rate capability and cycling performance were apparently superior to those of pure LTO. The reversible capacity of TiN-LTO is 105.2 mA h g⁻¹ at a current density of 10 C after 100 cycles and maintain 92.9% of its initial discharge capacity, while that of pure LTO is only 83.6 mA h g⁻¹ with a capacity retention of 90.3%. Even at 20 C, the discharge capacity of TiN coated LTO sample is 101.3 mA h g⁻¹, compared with 77.3 mA h g⁻¹ for pristine LTO in the potential range 1.0–2.5 V (vs. Li/Li⁺).     

Ionic conductivity of Mn2+ doped dense tin pyrophosphate electrolytes synthesized by a new co-precipitation method

Mn²⁺-doped Sn_1−xMn_xP₂O₇ (x = 0–0.2) are synthesized by a new co-precipitation method using tin(II)oxalate as tin(IV) precursor, which gives pure tin pyrophosphate at 300 °C, as all the reaction by-products are vaporizable at <150 °C. The dopant Mn²⁺ acts as a sintering aid and leads to dense Sn_1−xMn_xP₂O₇ samples on sintering at 1100 °C. Though conductivity of Sn_1−xMn_xP₂O₇ samples in the ambient atmosphere is 10⁻⁹–10⁻⁶ S cm⁻¹ in 300–550 °C range, it increases significantly in humidified (water vapor pressure, pH₂O = 0.12 atm) atmosphere and reaches >10⁻³ S cm⁻¹ in 100–200 °C range. The maximum conductivity is shown by Sn_0.88Mn_0.12P₂O₇ with 9.79 × 10⁻⁶ S cm⁻¹ at 550 °C in ambient air and 2.29 × 10⁻³ S cm⁻¹ at 190 °C in humidified air. It is observed that the humidification of Sn_1−xMn_xP₂O₇ samples is a slow process and its rate increases at higher temperature. The stability of Sn_1−xMn_xP₂O₇ samples is analyzed.     

A high capacity NiFe2O4/RGO nanocomposites as superior anode materials for sodium-ion batteries

NiFe₂O₄/reduced graphene oxide (NFO/RGO) nanocomposites were prepared by a facile one-step hydrothermal method and used as anode for sodium ion batteries (SIBs). The crystal structures, morphologies and electrochemical properties of as-prepared samples were evaluated by X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and galvanostatic charge/discharge tests. The results show that NFO/RGO-20 (20 wt%) delivers the highest reversible capacity of ~450 mA h g⁻¹ at 50 mA g⁻¹ after 50 cycles with good cycling stability. The excellent sodium storage performance of NFO/RGO should be attributed to the synergistic effect between NFO and RGO to form conductive network structure, which offers the increased specific surface area, the facilitated electron transfer ability and the buffering of volume expansion.     

Improved activity of a graphene–TiO2 hybrid electrode in an electrochemical supercapacitor

We present a simple and fast approach for the synthesis of a graphene–TiO₂ hybrid nanostructure using a microwave-assisted technique. The microstructure, composition, and morphology were characterized by X-ray diffraction, Fourier-transform infrared spectroscopy, Raman microscopy, X-ray photoelectron spectroscopy, and field-emission scanning electron microscopy. The electrochemical properties were evaluated using cyclic voltammetry, electrochemical impedance spectroscopy, and galvanostatic charge–discharge tests. Structural analysis revealed a homogeneous distribution of nanosized TiO₂ particles on graphene nanosheets. The material exhibited a high specific capacitance of 165 F g⁻¹ at a scan rate of 5 mV s⁻¹ in 1 M Na₂SO₄ electrolyte solution. Theenhanced supercapacitance property of these materials could be ascribed to the increased conductivity of TiO₂ and better utilization of graphene. Moreover, the material exhibited long-term cycle stability, retaining ∼90% specific capacitance after 5000 cycles, which suggests that it has potential as an electrode material for high-performance electrochemical supercapacitors.