High Active Material Utilization Research Articles

High-Performance Li-S Batteries with an Ultra-lightweight MWCNT-Coated Separator.

A bifunctional separator consisting of a layer of multiwall carbon nanotubes (MWCNTs) on the cathode-side of a Celgard polypropylene sheet has been investigated to overcome the challenges of Li-S cells. The conductive/porous MWCNT-coating functions (i) as an upper current collector to facilitate electron transport and high active-material utilization and (ii) as a filter to intercept/absorb the migrating polysulfides and thereby suppress the polysulfide diffusion. Also, the access to the electrolyte through the porous network of MWCNT along with its fast electronic transport facilitates the reutilization of the trapped active material and superior long-term cyclability. The MWCNT-coating is lightweight (0.17 mg cm(-2)), yet allows the successful use of regular sulfur cathodes (high sulfur content of 70 wt %) with high discharge capacity, excellent rate performance, and long cycle life, demonstrating that the MWCNT-coated separator is a viable solution to practical Li-S batteries.

Effect of calcination methods on electrochemical performance of NiO used as electrode materials for supercapacitor

Ni(OH)2 precursors were prepared via the precipitation transformation method, which was originated from Na2C2O4, NiSO4·6H2O and urea. NiO samples were successfully obtained by calcining Ni(OH)2 precursor with different calcination methods. Some were calcination in a tube furnace under the nitrogen flow and others were calcination in a muffle furnace. The products were well-characterized by thermogravimetric analysis (TGA), X-ray diffraction (XRD) and scanning electron microscopy (SEM). The influence of calcination methods on electrochemical performance of NiO samples were investigated. Moreover, the possible reason was proposed. The charge storage mechanism of NiO positive electrode in aqueous electrolyte was discussed. The electrochemical test showed that the as-prepared NiO prepared in a tube furnace can exhibit a good pseudocapacitance behaviour due to the higher utilization of active material.

Anode performances of mixed LiMn2O4 and carbon black toward lithium-ion battery

The mixed LiMn 2 O 4 and carbon black were served as anodes for lithium-ion batteries and the samples with high active material utilization ratio showed the highest capacity and cycling retention of 407.0 mAh/g after 50 charge/discharge cycles. The galvanostatic cycling and electrochemical impedance measurements were used to study their electrochemical performances. The commercial carbon black showed higher cycling retention, 162.0 mAh/g after 50 charge/discharge cycles. The present results confirmed that the capacity and cycling retention of LiMn 2 O 4 anodes can be improved by the increase of conductivity in lithium-ion batteries, which can increase the utilization ratio of active materials.

Electrochemical preparation of α-Ni(OH)2 ultrafine nanoparticles for high-performance supercapacitors

Well-dispersed nanoparticles of nickel hydroxide were prepared via a simple electrochemical method. Electrodeposition experiments were performed from 0.005 M Ni(NO3)2 bath at a constant current density of 0.1 mA cm−2 on the steel cathode for 1 h. Recording the potential values during the deposition process revealed that the reduction of water has major role in the base electrogeneration at the applied conditions. The obtained deposit was characterized by the X-ray diffraction (XRD), infrared (IR), differential scanning calorimeter–thermogravimetric analysis, carbon–nitrogen–hydrogen (CHN), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) techniques. The CHN, XRD, and IR analyses showed that the obtained deposit has α phase of Ni(OH)2 with intercalated nitrate ions in its structure. Morphological characterization by SEM and TEM revealed that the prepared α-Ni(OH)2 is composed of well-dispersed ultrafine particles with the size of about 5 nm. The supercapacitive performance of the prepared nanoparticles was analyzed by means of cyclic voltammetry and galvanostatic charge–discharge tests. The electrochemical measurements showed an excellent supercapacitive behavior of the prepared α-Ni(OH)2 nanoparticles. It was also observed that the α-Ni(OH)2 ultrafine particles have better electrochemical characteristic and supercapacitive behavior than β-Ni(OH)2 ultrafine nanoparticles, including less positive charging potential, lower E a − E c value, better reversibility, higher E OER − E a, higher utilization of active material, higher proton diffusion coefficient, greater discharge capacity, and better cyclability. These results make the α-Ni(OH)2 nanoparticles as an excellent candidate for the supercapacitor materials.

Activated carbon aerogels with high bimodal porosity for lithium/sulfur batteries

Activated carbon aerogels (ACAs) with high bimodal porosity were obtained for lithium/sulfur batteries by potassium hydroxide (KOH) activation. Then sulfur–activated carbon aerogels (S–ACAs) composites were synthesized by chemical deposition strategy. The S–ACAs composites were characterized by field emission scanning electron microscopy (FESEM), transmission electron microscopy, and N2 adsorption/desorption measurements. It is found that the activated carbon aerogels treated by KOH activation presents a porous structure, and sulfur is embedded into the pores of the ACAs network-like matrix after a chemical deposition process. The Li/S–ACAs (with 69.1 wt% active material) composite cathode exhibits discharge capacities of 1,493 mAh g−1 in the first cycle and 528 mAh g−1 after 100 cycles at a higher rate of C/5 (335 mA g−1). The S–ACAs composite cathode exhibits better electrochemical reversibility, higher active material utilization, and less severe polysulfide shuttle than S–CAs composite cathode because of high bimodal porosity structure of the ACAs matrix.

A sulfur–carbon composite for lithium/sulfur battery based on activated vapor-grown carbon fiber

Abstract A sulfur–carbon composite based on vapor-grown carbon fiber (VGCF) is synthesized for lithium/sulfur batteries by potassium hydroxide (KOH) activation and melt-diffusion strategy. The sulfur-activated VGCF (S–aVGCF) composites were characterized by field emission scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and N 2 adsorption/desorption measurements. It is found that VGCF treated by KOH activation is longitudinally opened and presents a porous structure, and sulfur is embedded into the pores of an aVGCF network-like matrix after a melt-diffusion process. The S–aVGCF composite cathode exhibits better electrochemical reversibility, higher active material utilization and less severe polysulfide shuttle than both a pristine sulfur cathode and a S–raw VGCF composite cathode because of excellent conductivity, and the fibrous and porous structure of the aVGCF matrix.

Self-assembly of stacked layers of Mn3O4 nanosheets using a scalable chemical strategy for enhanced, flexible, electrochemical energy storage

Uniformly stacked nanosheets of Mn3O4 with different sizes and crystallinities have been self-assembled on a titanium substrate by a simple and scalable strategy. When the prepared Mn3O4 nanosheets are applied as electrode materials for supercapacitors, they exhibit enhanced electrochemical performances due to the high utilization of active materials. More significantly, based on these stacked nanostructures, we have discussed the relationships between specific area, crystallinity and the electrochemical performance of this material. The stacked nanostructures exhibit a high specific capacitance of 398 Fg−1 at a scan rate of 0.005 V s−1 over a potential window from −0.1 to 0.9 V with high rate capability and good cycling stability. These results demonstrate the importance of a well-arranged and stacked architecture of Mn3O4 in high-energy-storage applications.

Preparation and Study of Spherical Nickel Hydroxide Coated by Cobalt Oxy-Hydroxide

Nanometer nickel hydroxide particles coated by cobalt oxy-hydroxide are prepared through chemical precipitation method. The properties of coated Ni(OH)2 particles is characterized by using X-ray diffraction, scanning electron microscopy, constant current charge/discharge test and cyclic voltammetry. Studies are focused on the effects of different amounts of cobalt oxy-hydroxide on structure and electrochemical characteristics of nickel hydroxide. The results show that a structure of β-Ni(OH)2 is preserved and 2.5 wt % CoOOH can form a well distributed conductive network on the surface of nickel hydroxide particles, thereby leading to higher utilization of active material; Compared to other electrodes, the electrodes with 2.5 wt % coated CoOOH show higher specific capacity and better cycling durability, and the electrodes also has better reversibility of the Ni(OH)2/NiOOH redox couple, and higher oxygen evolution potential.

Preparation of Co3O4 nanowires grown on nickel foam with superior electrochemical capacitance

Co3O4 nanowires have been successfully synthesized on nickel foam by a hydrothermal method. The morphology of Co3O4 is examined by scanning and transmission electron microscopy and the phase structure of Co3O4 nanowires is confirmed by X-ray diffraction. The electrochemical capacitance behavior of the Co3O4 nanowires electrode is investigated by cyclic voltammetry, galvanostatic charge/discharge test and electrochemical impedance spectroscopy in 6moldm−3 KOH solution. The results show that the Co3O4 nanowires have diameters of around 100nm and the lengths up to 1–2μm. The specific capacitance of Co3O4 nanowires is 1019.58Fg−1 at 3.38Ag−1 and 466.06Fg−1 at 33.80Ag−1. The capacitance loss is less than 5% after 1000 charge/discharge cycles at 3.38Ag−1 and with columbic efficiency higher than 98%. The enhancement of pseudocapacitive properties at a higher charging/discharging rate is due to the porous nanostructure and the high utilization of active material.

Nickel ferrite–graphene heteroarchitectures: Toward high-performance anode materials for lithium-ion batteries

A NiFe2O4–graphene heteroarchitecture with differing graphene content is prepared by a straightforward hydrothermal strategy. The NiFe2O4–graphene (with 20 wt% graphene) nanocomposite as the anode material for lithium-ion batteries shows a high specific reversible capacity up to 960mAhg−1 with good cycling stability and rate capability. The superior electrochemical performance of the NiFe2O4–graphene nanocomposite can be attributed to its unique heteroarchitecture, which enables high utilization of active material, good structural stability and fast charge transport.

Hierarchical porous nanostructures assembled from ultrathin MnO2nanoflakes with enhanced supercapacitive performances

Three kinds of hierarchical porous nanostructures assembled from ultrathin MnO2 nanoflakes with different sizes and crystallinities, have been synthesized by a very simple and scalable strategy. When applied as electrode materials for supercapacitors, all of them exhibited enhanced electrochemical performances due to the high utilization of active materials. More significantly, based on these ultrathin nanostructures, we have discussed the relationships between their specific areas, pore sizes and crystallinities and their electrochemical performances. Among them, the product synthesized in an ice bath with an especially high specific area (269 m2 g−1), uniform pore size distribution (∼5.1 nm) and poor crystallinity, exhibited the highest specific capacitance (328 F g−1) with a high rate and cycling stability. It is thought that the hierarchical ultrathin porous nanostructures can serve as promising electrode materials for supercapacitors.

Towards flexible secondary lithium batteries: polypyrrole-LiFePO4 thin electrodes with polymer electrolytes

A thin flexible polypyrrole-lithium iron phosphate (PPy-LiFePO4) based cathode has been fabricated. A slurry containing carbon black, a binder and the active material prepared by direct polymerization of pyrrole on the surface of LiFePO4 (LFP) was spread on an Al/carbon film substrate by the doctor blade method. Transmission electron micrographs reveal that PPy nanoparticles form a web like structure over the surface of LFP particles. After doping with lithium ions the PPy network becomes conducting. When evaluated as a cathode of 180 μm thickness together with a gel polymer electrolyte and a lithium anode, the charge–discharge performance reveals that the electrochemical properties of LFP are influenced to a considerable extent by the PPy. The cells show high initial discharge capacities of 135 and 110 mA h g−1 for 0.041 (C/10) and 0.21 (C/2) mA cm−2, respectively, and high active material utilization. Furthermore the cells exhibit stable cycle properties even at 0.21 mA cm−2 with a low capacity fade per cycle (∼0.3%).

Electrochemical properties of LiFePO 4/C composite cathode material: Carbon coating by the precursor method and direct addition

Carbon-coated LiFePO 4 (LiFePO 4/C) composite cathode-active materials of submicron size and phase-pure olivine structure were synthesized by a mechanical activation (MA) process. The conductive carbon coating was achieved by addition of (i) carbon powder directly or (ii) sucrose as the carbon precursor, during synthesis. LiFePO 4/C containing 6 wt% carbon prepared by the two methods showed good electrochemical properties as cathodes in lithium batteries at room temperature with high active material utilization of >94% at 0.1 C rate and stable cycle performance. The sucrose precursor method leads to the formation of a thin, porous and more uniform carbon coating around the particles and results in a slightly higher discharge capacity (∼3%) compared to the other sample.

The addition of red lead to flat plate and tubular valve regulated miners cap lamp lead–acid batteries

The study looked at the use of red lead in the manufacturing of valve regulated lead acid (VRLA) miners cap lamp (MCL) batteries that were made with either flat plate or tubular positive electrodes. A problem with using only grey oxide in the manufacture of thick flat plate or tubular electrodes is the poor conversion of the active material to the desired lead dioxide. The addition of red lead to the initial starting material improves the formation efficiency but is considerably more expensive thereby increasing the cost of manufacturing. The study showed that by carefully controlling the formation conditions in terms of the voltage and temperature of a battery, good capacity performance can be achieved for cells made with flat plate electrodes that contain up to 25% red lead. The small amount of red lead in the active cured material reduces the effect of electrode surface sulphate formation and allows the battery to achieve its rated capacity within the first few cycles. Batteries made with flat plate positive electrodes that contained more that 50% red lead showed good initial capacity but had poor structural active material bonding. The study showed that MCL batteries made with tubular positive electrodes that contained less than 75% red lead resulted in a poorly formed electrode with limited capacity utilization. Pickling and soaking times of the tubular electrodes should be kept at a minimum thereby allowing higher active material utilization during subsequent capacity cycling. The study further showed that it is beneficial to use higher formation rates in order to reduce manufacturing time and to improve the active material characteristics.

Physical and electrochemical characterization of PbO 2 electrode prepared at different H 2SO 4/H 2O/PbO ratios

The influence of pastes from various H 2SO 4/H 2O/PbO ratios on the material structure and electrochemical characteristics of PbO 2 electrodes is studied. The structural and electrochemical characteristics of these electrodes are investigated by scanning electron microscopy (SEM), X-ray diffraction, mercury intrusion porosimetry (MIP), ac impedance, and charge–discharge curves. Three pastes (A, B, and C) are studied to assess the influence of H 2SO 4/H 2O/PbO ratios. Paste A, prepared with more water, has a larger specific surface-area and pore-size. The group A plates have a greater porosity, which gives higher active material utilization and higher initial capacity. The plates have poor mechanical strength, however, which results in a high capacity loss for each cycle. In studies on ac impedance, the appearance of a high-frequency inductive loop in the group A plates indicates that these plates have active materials of greater porosity during the electrode processing reactions. The group C plates, prepared with more H 2SO 4, contained more α-PbO 2 crystals which results in a smaller charge-transfer resistance, and a larger exchange current.

Preparation of an improved positive electrode and its application in Ni/MH batteries

Abstract The capacity of Ni/MH batteries depends on the specific capacity of the positive electrode and the utilization of active material because of the positive electrode capacity limitation. The present study is engaged in enhancing the specific capacity of the Ni(OH)2 electrode and the utilization of the active material. Ni(OH)2 or NiOOH in the positive electrode is a semiconductor, which is different from the conductive active material (hydrogen storage alloys) of the negative electrode. In this research a new process has been developed to prepare positive electrodes with excellent electrochemical characteristics. The process consists of the positive electrode being despumated, and then coated with conductive metallic materials on the surface. The new positive electrode exhibits a better collective current effect, higher specific capacity and higher utilization of the active material. The new process comprehensively improves the characteristics of the Ni/MH battery, especially concerning the battery capacity and discharge capacity at high rates.

Lead–acid technology: a look to possible future achievements

The last five years have produced dramatic improvements in understanding lead–acid batteries. Future battery technologies will build on these advances. Battery designs will incorporate more and thinner plates with grids produced from continuous processes using stronger, more corrosion-resistant grid alloys capable of longer life at elevated temperatures. Battery grids will become more sheet-like, producing more uniform discharges and higher utilization of active material. Batteries will be sealed and utilize gel, AGM, or novel separator/acid-retention systems which will apply uniform pressure to the active-material for longer life. Improvements in charging systems will increase life and permit improved active-material utilization via rapid charging, partial state-of-charge operation, and reduction of overcharge. Possible advances are extremely thin film batteries to supply high power for vehicle starting or other applications. Advanced batteries for motive power will be rapidly recharged to provide three shift usage with charging between shifts. Robust lead–acid batteries for remote power locations will be continually operated in partial state-of-charge and charged with low currents. Purposely-built lead–acid batteries will drive hybrid or electric vehicles. Improved batteries for standby power applications will yield uniform cell-to-cell performance and longer life. This paper details the improvements in lead–acid battery technology that will permit these achievements to be realized.

Physical and electrochemical characteristics of aluminium-substituted nickel hydroxide

Substitution of 20 aluminium for nickel in the lattice of nickel hydroxide, prepared by coprecipitation, leads to a hydrotalcite-like compound of formula Ni0.8Al0.2(OH)2(CO3)0.1.0.66H2O. It has been found that the compound has prolonged stability in 6m KOH solution and can be used as the positive electrode material in rechargeable alkaline batteries. The structure, morphology and composition of the compound have been investigated by X-ray diffraction, scanning electron microscopy and infrared spectroscopy. The electrode comprising the aluminium-substituted nickel hydroxide has greater discharge capacity and higher utilization of active material than the β-Ni(OH)2 electrode. Cyclic voltammetry suggest that the aluminium-substituted nickel hydroxide has better reversibility of the Ni(OH)2/NiOOH redox couple and higher oxygen evolution overpotential than β-Ni(OH)2. The mechanism of the electrode reaction has also been discussed and the proton diffusion coefficient in the compound has been determined.

Cyclic voltammetric studies of pasted nickel hydroxide electrode microencapsulated by cobalt

Spherical nickel hydroxide microencapsulated by cobalt has been used as the electrochemically active material in pasted-type nickel electrodes of rechargeable alkaline batteries. Cobalt coating on the surface of nickel hydroxide particles can be converted to CoOOH during charge. Well distributed CoOOH forms the conductive network on the surface of nickel hydroxide particles, thereby leading to higher utilization of active material. Cyclic voltammetric studies suggest that nickel hydroxide microencapsulated by cobalt has better reversibility of the Ni(OH)2/NiOOH redox couple, greater discharge capacity and higher oxygen evolution overpotential than nickel hydroxide with added cobalt metal powder as a conductor. The mechanism of the electrode reaction is still found to be controlled by proton diffusion, and the proton diffusion coefficient is 1. 2×10−9cm2s−1.

ChemInform Abstract: Development of a Pasted Nickel Electrode with High Active Material Utilization.

AbstractIt is demonstrated that high performance and low‐cost pasted nickel electrodes with an active material utilization close to 100% and an energy density of 170 mAh/g can be prepared from a metal fiber substrate pasted with Ni(OH)2 by addition of CoO.