Electrochemical double layer capacitor and lithium-ion capacitor based on carbon black

In this paper we report the physical investigation and the electrochemical performance of the carbon black SC3 from Cabot Corporation. The SC3 carbon black was investigated in terms of BET surface area, pore size distribution, resistivity and morphology. Composite electrodes containing SC3 as active material were prepared and used for the realization of electrochemical double layer capacitor (EDLC) and lithium-ion capacitor (LIC). In EDLC, at 5 mA cm⁻² charge-discharge currents, the carbon black displays a specific capacity of 40 mAh g⁻¹ and a specific capacitance of 115 F g⁻¹. It also displays a very good cycling stability for over 50,000 cycles and excellent performance retention at currents up to 50 mA cm⁻². The performance retention at high currents outstandingly differentiates this carbon black from a few commercially available EDLC-grade activated carbons. Because of the high specific capacity of SC3, the carbon black electrodes were also used in combination with LiFePO₄ electrodes in LIC. The results of this study indicate that SC3 carbon black is an interesting carbonaceous candidate for the realization of LIC.     

Preparation of mesoporous carbons from amphiphilic carbonaceous material for high-performance electric double-layer capacitors

Amphiphilic carbonaceous material (ACM), with nanoscale dispersion in alkaline aqueous solutions, is synthesized from green needle coke. As a special precursor with small particle size, plenty of functional groups and widened d₀₀₂ simultaneously, ACM guarantees subsequent ACM-based activated carbons (AACs) with high specific surface area over 3000 m² g⁻¹ as well as well-developed mesoporous structure after KOH activation. Such pore properties enable AACs’ high performances as electrode materials for electric double-layer capacitors (EDLCs). In particular, surface area up to 3347 m² g⁻¹ together with notable mesopore proportion (26.9%) gives sample AAC814 outstanding EDLC behaviors during a series of electrochemical tests including galvanostatic charge/discharge, CV and electrochemical impedance spectroscopy. The electrode gets satisfactory gravimetric and volumetric specific capacitance at the current density of 50 mA g⁻¹, up to 348 F g⁻¹ and 162 F cm⁻³, respectively. Furthermore, for the mesoporosity, there is only a slight capacitance reduction for AAC814 as the current density reaches 1000 mA g⁻¹, indicating its good rate performance. It is all the ACM's unique characteristics that make AACs a sort of competitive EDLC electrode materials, both in terms of specific capacitance and rate capability.     

Nickel hydroxide/activated carbon composite electrodes for electrochemical capacitors

In this paper, a nickel hydroxide/activated carbon (AC) composite electrode for use in an electrochemical capacitor was prepared by a simple chemical precipitation method. The structure and morphology of nickel hydroxide/AC were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results showed that nano-sized nickel hydroxide was loading on the surface of activated carbon. Electrochemical performance of the composite electrodes with different loading amount was studied by cyclic voltammetry and galvanostatic charge/discharge measurements. It was demonstrated that the introduction of a small amount of nickel hydroxide to activated carbon could promote the specific capacitance of a composite electrode. The composite electrodes have good electrochemical performance and high charge–discharge properties. Moreover, when the loading amount of nickel hydroxide was 6 wt.%, the composite electrode showed a high specific capacitance of 314.5 F g⁻¹, which is 23.3% higher than pure activated carbon (255.1 F g⁻¹). Also, the composite electrochemical capacitor exhibits a stable cyclic life in the potential range of 0–1.0 V.     

Electrochemical properties of magnesium-based hydrogen storage alloys improved by transition metal boride and silicide additives

Transition metal borides and silicides prepared by mechanical alloying (MA) and chemical reduction methods (CR) were introduced to improve the corrosion resistance of magnesium-based hydrogen storage alloys. The additive of FeB prepared by MA can remarkably enhance the discharge capacity and cycling stability which has initial discharge capacity of 355.9 mA h g⁻¹ and keeps 224 mA h g⁻¹ after 100 cycles, and the exchange density I₀ of MgNi–NiB(CR) electrodes is 344.80 mA g⁻¹ but MgNi is only 67.6 mA g⁻¹ which leads to the better rate capability of the composite alloys. The results of SEM characterization, cyclic charge–discharge tests, potentiodynamic polarization, linear polarization and AC impedance experiment show that the corrosion inhibition property of MgNi in alkaline is improved by transition metal boride and silicide additives.     

Converting rice husk activated carbon into active material for capacitor using three-dimensional porous current collector

We have successfully applied rice husk activated carbon (RHAC) as an active material for the electric double layer capacitor using a three-dimensional (3D) porous current collector. The capacity and cycle stability were evaluated in a 1.0 mol dm⁻³ tetraethylammonium tetrafluoroborate/propylene carbonate solution in the range of 0-2.5 V. The specific capacity of the RHAC was about 14 mAh g⁻¹ at the 50 mA g⁻¹ discharge rate, corresponding to 19 F g⁻¹ under the present conditions. The RHAC cell using the 3D porous current collector possessed a lower internal resistance and better high-rate discharge properties than the RHAC cell using a conventional aluminum (Al) foil collector. After 5000 cycles of charging and discharging, the RHAC cell with the 3D current collector maintained 95% of its initial capacity, while the capacity of the one with the Al foil collector dropped to only 30%.     

Vertically aligned carbon nanotube electrodes for lithium-ion batteries

As portable electronics become more advanced and alternative energy demands become more prevalent, the development of advanced energy storage technologies is becoming ever more critical in today's society. In order to develop higher power and energy density batteries, innovative electrode materials that provide increased storage capacity, greater rate capabilities, and good cyclability must be developed. Nanostructured materials are gaining increased attention because of their potential to mitigate current electrode limitations. Here we report on the use of vertically aligned multi-walled carbon nanotubes (VA-MWNTs) as the active electrode material in lithium-ion batteries. At low specific currents, these VA-MWNTs have shown high reversible specific capacities (up to 782 mAh g⁻¹ at 57 mA g⁻¹). This value is twice that of the theoretical maximum for graphite and ten times more than their non-aligned equivalent. Interestingly, at very high discharge rates, the VA-MWNT electrodes retain a moderate specific capacity due to their aligned nature (166 mAh g⁻¹ at 26 A g⁻¹). These results suggest that VA-MWNTs are good candidates for lithium-ion battery electrodes which require high rate capability and capacity.     

Preparation and electrochemical properties of La0.4Sr0.6FeO3 as negative electrode of Ni/MH batteries

Perovskite-type oxide La_0.4Sr_0.6FeO₃ powder was prepared by a stearic acid combustion method, and its phase structure, kinetic characteristics, and electrochemical properties were systematically investigated as the negative electrode for Ni/MH batteries. X-ray diffraction (XRD) shows that the as-prepared powder consists of a single phase with rhombohedral structure. After 20 cycles, perovskite-type structure still remains in the electrode sample. The electrochemical test shows that the reaction at the La_0.4Sr_0.6FeO₃ electrode is reversible. With an increase in temperature from 298 K to 333 K, its initial discharge capacities increase from 153.4 mA h g⁻¹ to 502.6 mA h g⁻¹ at 31.25 mA g⁻¹, and from 56.0 mA h g⁻¹ to 279.6 mA h g⁻¹ at 125 mA g⁻¹, respectively. At a discharge current density of 125 mA g⁻¹, its capacities keep steady at about 80.0 mA h g⁻¹, 195 mA h g⁻¹ and 370 mA h g⁻¹ at 298 K, 313 K and 333 K, respectively. Both the exchange current density and the proton diffusion coefficient of the La_0.4Sr_0.6FeO₃ oxide electrode also increase with temperature in a manner similar to the discharge capacity.     

Microstructural controls of titanate nanosheet composites using carbon fibers and high-rate electrode properties for lithium ion secondary batteries

Composite electrodes of reassembled titanate and two kinds of carbon fibers were prepared and their high-rate electrode properties were examined. Multi-walled carbon nanotubes (MWNT) and vapor-grown carbon fibers (VGCF) were used for preparing the composites. The electronic conductivity of the MWNT composites increased with increasing contents of MWNT and exhibited a typical insulator-conductor transition. The MWNT composite with a MWNT content of 50 wt.% showed a capacity of 150 ± 5 mAh (g titanate)⁻¹ at a discharge rate of 0.67 C, and did not show a good high-rate capability due to the large content of hydrated water. The effect of the porous structure of the electrodes was revealed in the high-rate electrode properties of the microstructurally controlled composites with both MWNT and VGCF. The composites with 50 wt.% VGCF and 10 wt.% MWNT showed a reversible capacity of approximately 160 mAh (g titanate)⁻¹ at a discharge rate of 0.63 C and almost no capacity fading at relatively large discharge rate up to 19 C. A composite electrode with excellent high-rate capability was obtained by the microstructural control with carbon fibers.     

Evaluation of carbon cryogels used as cathodes for non-flowing zinc–bromine storage cells

Monolithic megaloporous carbon cryogels were examined for their potential applications as cathodic electrodes in secondary zinc–bromine cells. This work investigates the possibility of using their particular macroporous texture as microscopic bromine tanks in a zinc/bromine battery. The electrochemical behaviour of a cell based upon such a Br₂ electrode was studied and discussed in terms of energy yields, energy storage capability and cycle life. Good storages (over 20 Wh kg⁻¹) could be obtained during the first 2 h of cell charging for currents between 10 and 20 mA g⁻¹. The energy yield remains almost constant during a fairly large number of cycles, basically for weak charges (e.g. 25 C g⁻¹). Our findings show that the good cyclability of the cathodic electrode is a consequence of the liquid state of the active bromine phase.     

A study on the electrochemical characteristics of LiFePO4 cathode for lithium polymer batteries by hydrothermal method

Phospho-olivine LiFePO₄ cathode materials were prepared by hydrothermal reaction at 150 °C. Carbon black was added to enhance the electrical conductivity of LiFePO₄. LiFePO₄-C powders (0, 3, 5 and 10 wt.%) were characterized by X-ray diffraction (XRD) and transmission electron microscope (TEM). LiFePO₄-C/solid polymer electrolyte (SPE)/Li cells were characterized electrochemically by charge/discharge experiments at a constant current density of 0.1 mA cm⁻² in a range between 2.5 and 4.3 V vs. Li/Li⁺, cyclic voltammetry (CV) and ac impedance spectroscopy. The results showed that initial discharge capacity of LiFePO₄ was 104 mAh g⁻¹. The discharge capacity of LiFePO₄-C/SPE/Li cell with 5 wt.% carbon black was 128 mAh g⁻¹ at the first cycle and 127 mAh g⁻¹ after 30 cycles, respectively. It was demonstrated that cycling performance of LiFePO₄-C/SPE/Li cells was better than that of LiFePO₄/SPE/Li cells.     

Improvement of capacitance value as the electrode of an electrochemical capacitor by mixing starch with guanidine phosphate

Starch or starch mixed with phosphoric acid, guanidine carbonate, or guanidine phosphate is heat-treated for use as an electrode in an electrochemical capacitor. In the case of starch, the capacitance value is low (31.2 F g⁻¹ at 50 mA g⁻¹). However, the capacitance value significantly increases with the addition of guanidine phosphate, which can act as a flame-retardant (124.1F g⁻¹ at 50 mA g⁻¹). The method used in this study, which involves mixing with a flame-retardant by immersion, should be a promising candidate for improving of the capacitance value of starch-derived carbon.     

Investigation on electronically conductive additives to improve positive active material utilization in lead-acid batteries

In order to adapt lead-acid batteries for use in hybrid electric vehicles, its specific energy must be improved. Specific energy is greatly dependant on active material utilization. In this study, we improve active material utilization in positive electrodes by the addition of electronically conductive additives. Titanium silicide particles (<44 μm diameter), titanium dioxide fibers (<10 μm, diameter), and titanium wire (76 μm, diameter) were incorporated into the positive electrode and each of their effects on discharge capacity and utilization of active material were examined. The percent mass of each additive was varied from 2–5%. Results indicate that titanium wire at 2.3 wt.% had the optimal effect of increasing the utilization by 12.3% (57 to 64% utilization) relative to control with no additive at a slow discharge rate (10 mA cm⁻²) without detrimental effect at fast discharge rate (50 mA cm⁻²). This additive also features reduction in weight and formation enhancement.     

Application of Si-C-O glass-like compounds as negative electrode materials for lithium hybrid capacitors

The Si-C-O glass-like compound (a-SiCO) was applied to a negative electrode of a lithium hybrid capacitor (LHC) with activated carbon positive electrodes. The performance as a negative electrode (by a three-electrode system) and LHC (by a two-electrode system) was evaluated in LiClO₄ (EC-DEC) and LiBF₄ (PC) electrolytes. With a-SiCO reversible insertion/extraction of lithium ions at high current densities (0.5-2.0 A g⁻¹) was possible. By prior short-circuiting of the negative electrode with lithium metal in the electrolytes for appropriate periods, the charge/discharge performance of the assembled LHC compared favorably with an electric double layer capacitor (EDLC) made of the activated carbon used for LHC. The cycle performance of the LHC was better but the capacitance was smaller in the LiBF₄ (PC) electrolyte than in LiClO₄ (EC-DEC) electrolyte. Smaller capacitance is mainly due to lower electric conductivity and higher viscosity of LiBF₄ (PC) electrolyte than LiClO₄ (EC-DEC) electrolyte. The energy density of the assembled LHC reached a maximum of about three times that of EDLC, with the power density comparable to that of the EDLC.     

Investigation of discharge reaction mechanism of lithium|liquid electrolyte|sulfur battery

The influence of current density on the discharge reaction of Li–S batteries is investigated by discharge tests (first discharge curve), differential scanning calorimetry (DSC), X-ray diffraction (XRD) (discharge products), and scanning electron microscopy (the surface morphology of sulfur electrodes). The first discharge capacity and the plateau potential both decrease with increasing current density. When the current density is increased from 100 to 1600 mA g⁻¹ S, the discharge capacity decreases from 1178 to 217 mAh g⁻¹ S.     

Crystalline CoB: Solid state reaction synthesis and electrochemical properties

Using a facile and effective method based on the solid phase reaction between Co(OH)₂ and KBH₄, we successfully synthesize orthorhombic CoB. It is shown that this CoB obtained is of high purity and thermal stability. A possible formation process for orthorhombic CoB is discussed in detail. In addition, crystalline CoB shows excellent electrochemical reversibility and considerable high charge-discharge capacities when it is used as the anode material for nickel-based secondary batteries. The reversible discharge capacities of the CoB electrode are found to be about 380 mAh g⁻¹ at a discharge current of 25 mA g⁻¹ and 360 mAh g⁻¹ at 100 mA g⁻¹. Moreover, electrochemical reaction mechanism of CoB is investigated in detail.     

All-solid-state lithium secondary batteries with high capacity using black phosphorus negative electrode

Black phosphorus was prepared from red phosphorus by using mixer mill and planetary ball-mill apparatuses. The composites with black phosphorus and acetylene black (AB) were also prepared by using the mixer mill apparatus. The mechanical milling of black phosphorus and AB brought about a decrease in size of secondary particles of the composites. The all-solid-state lithium cells with the composite and the Li₂S-P₂S₅ glass-ceramic electrolyte exhibited the first discharge capacity of 1962 mAh g⁻¹ and the coulombic efficiency of 89% at the current density of 0.064 mA cm⁻² (24 mA g⁻¹). The all-solid-state cells worked at 3.8 mA cm⁻² (1.47 A g⁻¹) at 25 °C and showed the excellent cycle performance with a high capacity of over 500 mAh g⁻¹ for 150 cycles. Black phosphorus is one of the most attractive negative electrodes with both high capacity and high-rate performance in all-solid-state lithium rechargeable batteries with sulfide electrolytes.     

Anode properties of thick-film electrodes prepared by gas deposition of Ni-coated Si particles

Thick-film electrodes of Si particles coated with Ni, Ni-Sn, and Ni-P were fabricated by electroless deposition followed by gas deposition to form the anode of a Li-ion battery. The electrode of Ni-coated Si showed remarkably improved cycling performance with a discharge capacity of 580 mA h g⁻¹ at the 1000th cycle, which is possibly caused by its higher elastic modulus than that of the uncoated Si electrode. The electrode of Si coated with Ni-P, which consisted of Ni₃P, with the lower coating amount exhibited a higher initial capacity and excellent cycling performance with a capacity of 790 mA h g⁻¹ at the 1000th cycle, whereas poor performance was obtained for the electrode of Si coated with Ni-Sn. The excellent performance in the case of Ni-P coating is attributed to the smaller amount of coating, the high elastic modulus, and the lower reactivity of Ni₃P with Li ions in comparison with Ni₃Sn in Ni-Sn.     

Comparative study on the structure and electrochemical hydriding properties of MgTi, Mg0.5Ni0.5Ti and MgTi0.5Ni0.5 alloys prepared by high energy ball milling

MgTi, Mg_0.5Ni_0.5Ti and MgTi_0.5Ni_0.5 alloys doped with 10 wt.% Pd were prepared by high energy ball milling and evaluated as hydrogen storage electrodes for Ni-MH batteries. X-ray diffraction analyses indicated that the Mg_0.5Ni_0.5Ti and MgTi_0.5Ni_0.5 alloys could be monophased or composed of a nanoscale mixture of MgTi + NiTi and MgTi + MgNi phases, respectively. Their hydrogen storage characteristics were investigated electrochemically in KOH electrolyte. No activation step was observed during the cycling of the Mg-Ti-Ni electrodes in contrast to that observed with the MgTi electrode. The highest hydrogen discharge capacity was obtained with the MgTi_0.5Ni_0.5 electrode (536 mAh g⁻¹) compared to 401 and 475 mAh g⁻¹ for the Mg_0.5Ni_0.5Ti and MgTi electrodes, respectively. The ternary Mg-Ti-Ni alloys showed a better cycle life with an average capacity decay rate per cycle lower than 1.5% compared to ∼7% for the binary MgTi electrode. The Mg-Ni-Ti electrodes also displayed a much higher discharge rate capability than the binary MgTi electrode, especially with the Mg_0.5Ni_0.5Ti electrode. The origin of this was established on the basis of the anodic polarization curves, where a substantial decrease of the concentration overpotential (reflecting a higher hydrogen diffusivity) was observed for the Mg_0.5Ni_0.5Ti electrode.     

Electrochemical characterizations of multi-layer and composite silicon-germanium anodes for Li-ion batteries using magnetron sputtering

To improve the electrochemical performance of Si film, we investigate the addition of two film forms of Ge. Si/Ge multi-layered and Si-Ge composite electrodes that are fabricated by magnetron sputtering onto Cu current collector substrates are investigated. X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), and extended X-ray absorption fine structure (EXAFS) are employed to analyze the structures of the Si-Ge electrodes. When used as an anode electrode for a lithium ion battery, the first discharge capacity of a Si/Ge 150 multi-layer cell with a ratio of Si 15 nm/Ge 3 nm is 2099 mAh g⁻¹ between 1.1 and 0.01 V. A stable reversible capacity of 1559 mAh g⁻¹ is maintained after 100 cycles with a capacity retention rate of 74.25%. Additionally, the Si_0.84Ge_0.16 composite has an initial discharge capacity of 1915 mAh g⁻¹ and a capacity retention of 74.25%. In full cell tests of Si-Ge electrodes, the Si_0.84Ge_0.16/LiCoO₂ cell delivers a specific capacity of approximatly 160 mAh g⁻¹ and a capacity retention of 52.4% after 100 cycles. The results reveal that these two systems of sputtered Si-Ge electrodes can be used as anodes in lithium ion batteries with higher energy densities.     

Pseudocapacitive properties of electrochemically prepared nickel oxides on 3-dimensional carbon nanotube film substrates

Nickel oxides on carbon nanotube electrodes (NiO_x/CNT electrodes) are prepared by depositing Ni(OH)₂ electrochemically onto carbon nanotube (CNT) film substrates with subsequent heating to 300 °C. Compared with the as deposited Ni(OH)₂ on CNT film substrates (Ni(OH)₂/CNT electrodes), the 300 °C heat treated electrode shows much high rate capability, which makes it suitable as an electrode in supercapacitor applications. X-ray photoelectron spectroscopy shows that the pseudocapacitance of the NiO_x/CNT electrodes in a 1 M KOH solution originates from redox reactions of NiO_x/NiO_xOH and Ni(OH)₂/NiOOH. The 8.9 wt.% NiO_x in the NiO_x/CNT electrode shows a NiO_x-normalized specific capacitance of 1701 F g⁻¹ with excellent high rate capability due to the 3-dimensional nanoporous network structure with an extremely thin NiO_x layer on the CNT film substrate. On the other hand, the 36.6 wt.% NiO_x/CNT electrode has a maximum geometric and volumetric capacitance of 127 mF cm⁻² and 254 F cc⁻¹, respectively, with a specific capacitance of 671 F g⁻¹, which is much lower than that of the 8.9% NiO_x electrode. This decrease in specific capacitance of the high wt.% NiO_x/CNT electrodes can be attributed to the dead volume of the oxides, high equivalent series resistance for a heavier deposit, and the ineffective ionic transportation caused by the destruction of the 3-dimensional network structure. Deconvolution analysis of the cyclic voltammograms reveals that the rate capability of the NiO_x/CNT electrodes is adversely affected by the redox reaction of Ni(OH)₂, while the adverse effects from the reaction of NiO_x is insignificant.