Negative Electrode Active Materials Research Articles

Hybrid nickel-metal hydride/hydrogen battery

High capacity, high efficiency and resource-rich energy storage systems are required to store large scale excess electrical energy from renewable energy. We proposed “Hybrid Nickel-Metal Hydride/Hydrogen (Ni-MH/H2) Battery” using high capacity AB5-type hydrogen storage alloy and high-pressure H2 gas as negative electrode active materials. It was experimentally confirmed that hydrogen gas can be utilized as an active material of negative electrode by the presence of the AB5-type hydrogen storage alloy. The experimental average cell voltage suggested that H2 gas passed through the alloy in the form of atoms. The calculated gravimetric energy density of this hybrid battery increased up to 1.5 times of the conventional Ni-MH battery with low content of rare-earth element which is 32 wt% of the Ni-MH battery.

Synthesis of rose-like ZnAl-LDH and its application in zinc–nickel secondary battery

Rose-like zinc–aluminum hydrotalcite (ZnAl-LDH) was synthesized in an organic/water mixed solvent system by a simple hydrothermal method and applied to zinc–nickel secondary battery, and its electrochemical performance as a negative electrode active material was also studied. Rose-like ZnAl-LDH has the characteristic diffraction peaks of ZnAl-LDH. SEM and TEM results show that the rose-like ZnAl-LDH was assembled by LDH nanosheets with the center as the axis and inclined at certain angles to form a rose-like structure. Through cyclic voltammetry, EIS and galvanostatic charge and discharge tests, rose-like ZnAl-LDH is superior to the coprecipitation synthesized flake-like ZnAl-LDH in cycle stability and discharge capacity. The initial discharge specific capacity of rose-like ZnAl-LDH is 363.4 mAh g−1, after 1250 cycles, the specific discharge capacity was 366.848 mAh g−1, the average discharge specific capacity was 392.455 mAh g−1 during the entire charge/discharge process. The results show that the rose-like ZnAl-LDH is a promising material with good cycle stability and high specific discharge capacity for energy storage devices.

Mechanochemical synthesis of Si/Cu3Si-based composite as negative electrode materials for lithium ion battery

Mechanochemical synthesis of Si/Cu3Si-based composite as negative electrode materials for lithium ion battery is investigated. Results indicate that CuO is decomposed and alloyed with Si forming amorphous Cu-Si solid solution due to high energy impacting during high energy mechanical milling (HEMM). Upon carbonization at 800 °C, heating energy induces Cu3Si to crystallize in nanocrystalline/amorphous Si-rich matrix enhancing composite rigidity and conductivity. In addition, residual carbon formed on outside surface of composite powder as a buff space further alleviates volume change upon lithiation/delithiation. Thus, coin cell made of C-coated Si/Cu3Si-based composite as negative electrode (active materials loading, 2.3 mg cm−2) conducted at 100 mA g−1 performs the initial charge capacity of 1812 mAh g−1 (4.08 mAh cm−2) columbic efficiency of 83.7% and retained charge capacity of 1470 mAh g−1 (3.31 mAh cm−2) at the end of the 100th cycle, opening a promised window as negative electrode materials for lithium ion batteries.

Sustainable hierarchical porous biomass carbons enriched with pyridinic and pyrrolic nitrogen for asymmetric supercapacitor

Asymmetric supercapacitors usually possess higher energy density than symmetric supercapacitors. It's still a big challenge to synthesize low-cost and high-performance negative electrode active materials for the practical production of asymmetric supercapacitors. In this research, ginkgo leaf derived nitrogen-doped carbon was prepared and investigated as an electrode active material for the utilization in supercapacitors. Due to the hierarchical porous architecture, high N content, and ultrahigh ratio (86.5%) of pyridinic plus pyrrolic N species, the ginkgo leaf derived nitrogen-doped carbon material delivered a better specific capacitance (345Fg−1 at 0.2Ag−1) compared to pristine ginkgo leaf derived carbon and KOH-activated carbon without N-doping. Moreover, an asymmetric supercapacitor with this nitrogen-doped carbon as the negative electrode material also displayed an excellent energy density (42.2Whkg−1 at 700Wkg−1) and satisfactory electrochemical cycling reliability. In addition, these performances are also superior to those of some similar carbon materials, manifesting a good potential of this nitrogen-doped carbon to fabricate high-performance asymmetric supercapacitors.

Synthesis of Conjugated Carbonyl Containing Polymer Negative Electrodes for Sodium Ion Batteries

A polymer attached to the sodium terephthalate moiety as a side group is synthesized for the first time, and evaluate as a negative electrode active material. Both monomer and polymer are electrochemically characterized by cyclic voltammetry and battery performance. Compared to monomer, the polymer-based sodium terephthalates exhibit a lower oxidation peak. The electrochemical performance of polymer salt reveals the discharge potential (0.4 V vs. Na/Na+) along with discharge capacities up to 222 mAh g−1 and a better cycling stability (130 cycles, 77%). The disodium terephthalate polymer is most suitable among the conjugated carbonyl organic compounds for use in the sodium ion battery.

Optimized hard carbon derived from starch for rechargeable seawater batteries

The recently introduced seawater battery concept is an eco-friendly energy storage system that offers appealing electrochemical performance. Its radically innovative design, compared to conventional lithium-ion batteries, makes use of seawater as an almost infinite sodium reservoir for the positive electrode and, thereby, avoids the use of expensive, scarce, and toxic elements like nickel and cobalt. So far, the problems identified mostly originate from the available negative electrode active materials. In this study, a starch-derived hard carbon was used to optimize the system. Due to its improved disordered structure compared with commercial hard carbon, the starch hard carbon exhibits an increased reversible capacity, current-rate capability, and cycling ability. The material, in fact, depicts a high maximum power density of 700 W kg−1 (based on hard carbon weight) upon discharge at 900 mA g−1, while still being active at 2700 mA g−1. These results represent an important step toward practical application of the sodium-based seawater battery technology.

Cell Performance Comparison between C14- and C15-Predomiated AB2 Metal Hydride Alloys

The performance of cylindrical cells made from negative electrode active materials of two selected AB2 metal hydride chemistries with different dominating Laves phases (C14 vs. C15) were compared. Cells made from Alloy C15 showed a higher high-rate performance and peak power with a corresponding sacrifice in capacity, low-temperature performance, charge retention, and cycle life when compared with the C14 counterpart (Alloy C14). Annealing of the Alloy C15 eliminated the ZrNi secondary phase and further improved the high-rate and peak power performance. This treatment on Alloy C15 showed the best low-temperature performance, but also contributed to a less-desirable high-temperature voltage stand and an inferior cycle stability. While the main failure mode for Alloy C14 in the sealed cell is the formation of a thick oxide layer that prevents gas recombination during overcharge and consequent venting of the cell, the failure mode for Alloy C15 is dominated by continuous pulverization related to the volumetric changes during hydride formation and hysteresis in the pressure-composition-temperature isotherm. The leached-out Mn from Alloy C15 formed a high density of oxide deposits in the separator, leading to a deterioration in charge retention performance. Large amounts of Zr were found in the positive electrode of the cycled cell containing Alloy C15, but did not appear to harm cell performance. Suggestions for further composition and process optimization for Alloy C15 are also provided.

Novel core–shell structure of a lead-activated carbon (Pb@AC) for advanced lead–acid battery systems

To enhance the power and energy densities of advanced lead–acid batteries (Ad-LAB), a novel core–shell structure of lead-activated carbon (Pb@AC) was prepared and used as a negative electrode active material. The AC could be formed as a shell around a core of Pb nanoparticles. The active core–shell structures were synthesized using a simple chemical process to overcome the limitations in the negative Pb electrode, specifically the large crystallization of lead sulfate (PbSO4) that leads to a short cycle life. The key role of the carbon material in the negative electrode is to enhance the electrochemical performances and decrease the formation of PbSO4. The X-ray diffraction study reveals that the formation of lead oxide was prevented by the AC during the synthetic process. The novel core–shell structure of Pb@AC was confirmed through transmission electron microscopy. In order to obtain high-performance Ad-LAB, a high surface area of the AC is necessary to provide a super capacitive effect in the negative electrode. The unit cell performance of the as-prepared active materials exhibits significant increased discharge capacity at 1C rate. The unit cell with the Pb@AC negative electrode has a capacity per unit volume of 0.0165 Ah/cc. Hence, the low cost of AC and the simple synthetic core–shell structure of Pb@AC make this material a promising negative electrode active material for Ad-LAB applications.

Construction of Lithium-Ion Battery Tin Anode Utilizing Cu/CNT Composite Plating Method

IntroductionLithium-ion batteries are compact and lightweight secondary batteries with high capacity. They have already been put into practical use in electric and hybrid vehicles, but the development of lithium-ion batteries with higher capacity has advanced even further. Although graphite (theoretical capacity, 372 mAh g-1) is typically employed as the negative electrode active material, the development of a new, higher capacity negative electrode material using tin (theoretical capacity, 991 mAh g-1) as the active material has been investigated.1) However, the volume of tin changes significantly during charge-discharge cycles, and as a result, the tin slips down from the current collector, lowering the lifetime of the lithium-ion battery. Anchoring at the interface between the tin layer and the underlying copper layer to improve the adhesion to the fibrous material is considered to be an effective method of resolving this problem.2) In this study, an anode structure in which carbon nanotubes (CNTs) anchor the tin layer and the copper current collector was fabricated, and its charge-discharge characteristics were evaluated. ExperimentalAn EDTA copper plating bath was used as the basic plating bath. To prepare the plating bath for Cu/CNT composites, CNTs, sodium dodecyl sulfate (SDS), and hydroxypropyl cellulose (HPC) were added to the basic bath. The latter two were used as dispersing agents for the CNTs. The CNTs employed (Baytubes C70P, Bayer Material Science Co., Ltd.) were multi-walled (MWCNTs), with a diameter of 13–16 nm and a length of 10–20 μm. The pH was adjusted to 12 with KOH.3) The tin plating bath used was a pyrophosphoric acid tin plating bath. To prepare it, polyethylene glycol (PEG) and formaldehyde (HCHO) were added to a pyrophosphoric acid tin plating bath. PEG was used as a smoothing agent and HCHO was used as a reducing agent. Electroplating was performed under current regulation conditions, using a pure copper anode and a cathode. Reverse electrolysis was carried out to exposing CNTs in Cu/CNT composite plating films. The microstructure of the samples was observed using field-emission scanning electron microscopy (FE-SEM), and the phase structure of the deposited material was analyzed using X-ray diffraction (XRD). Finally, electrochemical studies on the prepared plating films were carried out with coin cells that were assembled in an Ar-filled glove box. Each coin cell consisted of a lithium foil as the counter electrode and the prepared plating films as the working electrode. The electrolyte was 1 M LiPF6 in ethylene carbonate (EC) and diethyl carbonate (DEC) (1:1 vol%). Cycling tests were performed in the range of 0.02–1.5 V (vs. Li/Li+). Results and DiscussionCu/CNT composite plating films containing many CNTs were fabricated by electrodeposition. CNTs in the produced Cu/CNT composite plating film was incorporated with little agglomeration. The morphology of the electrodeposited tin on the composite films was found to depend on the current density. When the current density was low, tin was deposited primarily on the copper underlayer (see Fig. 1a). In contrast, when the current density was high, tin was deposited not only on the copper underlayer, but also on the CNTs (see Fig. 1b). The results of charge-discharge testing and electrochemical measurements on the new anode material will be presented at the meeting. References 1) Dongjoon Ann, Xingcheng Xiao, Yawen Li, Anil. K, Sachdev, Hey Woong Park, Aiping Yu, Zhongwei Chen ; Journal of Power Sources 212, p.66-72 (2012) 2) S.Arai R. Fukuoka, J. Appl. Electrochem.,46 331 (2016). 3) K. Kirihata, T. Mano, S. Arai, M. Ueshima, K. Hirota ; The Surface Finishing Society of Japan 131nd lecture tournament s, p.7 (2015) Figure 1

Improvement of Charge-Discharge Cycling Performances of Zinc Electrode By Using Porous-TiO2-Coated Zinc As a Negative Electrode Active Material

Zinc electrodes are of great interest as a candidate for metal negative electrode that has high theoretical energy density, low cost and high safety owing to the use of aqueous electrolytes. However, rechargeable zinc electrodes still suffer from poor cycle life due to dendrite growth and shape change. These degradation phenomena of the zinc electrode are known to be promoted by the high solubility of the zinc species in the electrolyte. In an strong alkaline electrolyte usually employed in aqueous alkaline batteries, a discharge reaction of zinc takes place to produce Zn(OH)4 2-. Such soluble discharge products of zinc can migrate through the electrolyte, resulting in a redistribution of zinc. Therefore, inhibiting the migration of the discharge products of zinc are thought to be effective in minimizing dendrite growth and shape change. In this study, based on the concept of inhibition of the migration of the zinc discharge products into electrolyte, we report the synthesis, characterization and charge-discharge characteristics of porous-TiO2-coated Zn.We have newly synthesized zinc particles uniformly coated with porous TiO2 layers (porous-TiO2-coated Zn), as follows. Fine zinc powder (ca. 0.1-0.6 μm in diameter) was dispersed in the solution of titanium tetrabutoxide diluted with 1-butanol. While stirring and heating this solution, aqueous ammonia was added to form TiO2-precursor nanoparticles by the hydrolysis of titanium tetrabutoxide. Subsequently, in order to attach TiO2-precursor nanoparticles to the surface of zinc particles, urea as a linker molecule was added into this solution. After stirring and heating this solution, the samples obtained by filtration and washing with distilled water were dried and calcined in air. Core particles and uniform coating layers with the thickness of approximately 40 nm were observed in TEM images of the cross-section of the porous-TiO2-coated Zn particles. From a result of EDX analysis, it can be concluded that the coating layers mainly consist of titanium and oxygen. To further elucidate the characteristics of TiO2 coating layers, the pore-size distributions of uncoated-Zn and porous-TiO2-coated Zn were evaluated from nitrogen desorption isotherm. The porous-TiO2-coated Zn contains mainly pores with diameters smaller than 10 nm, in contrast to the uncoated-Zn which has no nano-sized pores. The peak pore diameter of porous-TiO2-coated Zn was 3.5 nm. This indicates that the porous-TiO2-coated Zn is composed of dense zinc particles and nanoporous TiO2coating layers.Comparison of the cycle life between uncoated-Zn and porous-TiO2-coated Zn was carried out. The zinc electrode was assembled in pouch cells with a large and a small sintered Ni(OH)2/NiOOH electrodes, which were respectively used as the counter and reference electrodes. 4 M KOH aqueous solution saturated with dissolved ZnO was used as electrolyte. Test cells were subjected to charge-discharge cycling test at 298 K. During the charge-discharge cycling test, the test cells were charged at 0.5 C rate for 1.5 h (615 mAh/g-Zn, zinc utilization of 75 %) and discharged at 0.5 C rate either for 1.5 h or until the zinc electrode potential reached at the cut-off potential of -0.9 V vs. Hg/HgO. From the charge-discharge cycling tests, reproducible results were obtained that the average values of the cycle life for 3 test cells employed each uncoated-Zn and porous-TiO2-coated Zn were 20 cycles and 117 cycles, respectively. It was found that the negative electrode using the porous-TiO2-coated Zn as an active material has achieved more than 5 times longer cycle life than that using uncoated-Zn in spite of a small TiO2 content.We propose the mechanism of improving the cycle life by using porous-TiO2-coated Zn that porous TiO2 coating layers act as a protection layer for the zinc oxides films formed through the discharge reactions and the pores of the TiO2 layers (< 10 nm) are sufficiently small to keep the zinc oxides. It should be noted that the effect of the TiO2 coating on the cycle performance cannot directly be attributed to the physical inhibition of the Zn(OH)4 2- migration because the average pore size of 3.5 nm is too large to block the migration of Zn(OH)4 2-.AcknowledgementThis work was supported by the Research and Development Initiative for Scientific Innovation of New Generation Batteries (RISING) project from NEDO in Japan.

고상법을 사용한 Li4Ti5O12의 합성공정 중 카본블랙 추가를 통한 입자뭉침 억제

<TEX>$Li_4Ti_5O_{12}$</TEX>는 우수한 사이클 특성과 구조적 안정성을 지니고 있으며 급속충전 및 고출력 특성을 지닌 리튬이온 이차전지용 음극 활물질이다. 고상법을 통한 <TEX>$Li_4Ti_5O_{12}$</TEX>의 합성 중에 발생하는 입자간의 뭉침을 억제하기 위하여, 원료인 <TEX>$TiO_2$</TEX>와 <TEX>$Li_2CO_3$</TEX>에 카본블랙을 소량 첨가하여 합성을 진행하였다. 원재료 대비하여 카본블랙을 각각 0, 0.5, 1.0, 및 3.0 질량%로 추가하여 고상법으로 <TEX>$Li_4Ti_5O_{12}$</TEX>를 합성하였으며, 얻어진 각 분말의 탭밀도와 분급속도를 비교하였다. 카본블랙의 함량이 증가함에 따라 입자의 뭉침이 감소하여 탭밀도가 감소하였으며, 카본블랙을 1.0 질량% 사용한 경우에 가장 빠르게 분급이 진행되었다. 또한, 카본블랙의 사용량에 무관하게 전기화학적 속도특성에서는 차이가 발생하지 않았기 때문에 1.0 질량%의 카본블랙의 추가를 통하여 성능의 손실없이 분말의 제조속도를 높일 수 있다. <TEX>$Li_4Ti_5O_{12}$</TEX> is prepared through a solid-state reaction between anatase <TEX>$TiO_2$</TEX> and <TEX>$Li_2CO_3$</TEX> for the negative electrode active materials in quick-charging lithium-ion batteries. The small amount of carbon black (0, 0.5, 1.0, and 3.0 wt%) is added for the reduction of powder agglomeration during heat-treatment. As the amount of the added carbon black increases, the tap density of <TEX>$Li_4Ti_5O_{12}$</TEX> powder gradually decreases. Furthermore, the <TEX>$Li_4Ti_5O_{12}$</TEX> powder prepared with 1.0 wt% of carbon black shows the highest sieved fraction at the powder classification by 325 mesh standard sieve. The <TEX>$Li_4Ti_5O_{12}$</TEX> powders with various contents of carbon black are almost same at the rate capability for the negative electrode materials in lithium-ion batteries.

Rechargeable Batteries Using Molecular Ions As a Charge Carrier

Is it possible to exceed the lithium redox potential in electrochemical systems? One may think the answer to be “No” because among all the elements the redox potential of the elemental lithium is the lowest, which leads to the high voltage characteristics of the widely used lithium ion batteries. However, the answer should turn “Yes” in principle when we use a molecule-based ion which is not reduced even at the lithium potential. Here we examined a model battery system using a few molecular ion charge carriers such as PF6 – and Me4N+with organic active materials. Although the potential of the negative-electrode is not yet lower than that of lithium at present, this study reveals that molecular ions can work as a “rocking chair” type charge carrier in a battery [1]. There are so far a few studies [2-5] describing the use of a molecular ion as the charge carrier; however, its stoichiometery has rarely been analyzed. To construct a “rocking chair” type molecular ion battery using, for instance, an anion charge carrier, we used a PF6 –-based electrolyte solution with two redox polymers (poly(N-vinylcarbazole): PVK, poly(1,1'-pentyl-4,4'-bipyridinium dihexafluorophosphate): PBPy) (Fig. 1a) as active materials. As for the molecular ion battery which uses a cation charge carrier, we chose a Me4N+-based electrolyte with some low molecular weight quinone type organic active materials. As shown in Fig.1b, the prepared sealed full cell using a PF6 –-based electrolyte system exhibited the potential difference of about 1.8 V with about 100 mAh/g(PVK). The cell exhibited a fairly good cycle stability; the cell maintained about 65% of the initial capacity after 100 cycles. The cell using the Me4N+-based electrolyte system also showed a repeatable charge/discharge behavior. The concept of these molecular ion batteries was proved by energy dispersive X-ray (EDX) measurement: we evaluated the change in stoichiometry of PF6 – in the electrode of the former cell ex situ by EDX and found that the charge carrier in this system is PF6 – and the prepared system is certainly a PF6 –-based “rocking chair type” battery. When succeeded in further developing the molecular ion battery, the benefits we would gain are: Breaking through the Li potential limitation, High ion conductivity in the electrolyte solution, Free from the dendrite risk, Minor metal free, and so on. To enjoy these benefits, the development in the active materials of both the positive- and negative-electrodes is indispensable. Searching for a negative electrode active material with a low redox potential is especially significant, which, we believe, will pave the way for the progress of this new battery system.

Development of Practical Sodium-Ion Batteries Using Amide Ionic Liquids: High Energy Efficiency, Excellent Cycleability and Wide Temperature Range Operation

Over five years, we have been conducting R&D of sodium secondary batteries using amide ionic liquids as electrolytes. The new batteries intrinsically have high safety due to the nonflammability and nonvolatility of ionic liquids. Moreover, they can be operated in a wide temperature range of 273-363 K. We found that several types of FSA-based (FSA: bis(fluorosulfonyl)amide) ionic liquids exhibit superior properties for the application to sodium secondary batteries. In the present paper, we first investigated the fundamental electrolyte properties for the binary Na[FSA]-[C3C1pyrr][FSA] (C3C1pyrr: N-methyl-N-propylpyrrolidinium) ionic liquid system. Then, NaCrO2 and hard carbon (HC) were selected as positive electrode and negative electrode active materials, respectively, and their fundamental charge–discharge characteristics were examined with coin-type half-cells. A 1.5 mAh coin-type full cell composed of HC/NaCrO2 exhibited excellent cycle properties, maintaining 90% of its initial capacity after 1000 cycles at 333 and 363 K. On the basis of these results, the 1.5 mAh full cell was fabricated and its performance was tested. It showed a high charge–discharge energy efficiency of 97.5% at 363 K and C/5 rate. Finally, we constructed a large-sized prismatic HC/NaCrO2full cell with a capacity of 27 Ah by a mass production process. We confirmed that its performance is comparable with that of the 1.5 mAh coin-type cell. Acknowledgements This study was partly supported by Advanced Low Carbon Technology Research and Development Program (ALCA) of Japan Science and Technology Agency (JST) and the Japanese Ministry of Education Culture, Sports, Science and Technology (MEXT) program “Elements Strategy Initiative to Form Core Research Center” (since 2012).

Ti–V–Cr–Ni alloys as high capacity negative electrode active materials for use in nickel–metal hydride batteries

TiV2.1−xCrxNi0.3 (x = 0.1–0.6 and 1.0), TiyV1.7Cr0.4Ni0.3 (y = 0.9–1.1) and TiV1.7Cr0.4Niz (z = 0.3–0.5) alloys were prepared by arc-melting, and their negative electrode properties such as the maximum discharge capacity (Cdis), charge–discharge cycle performance and high-rate dischargeability (HRD) were evaluated. All the alloys consisted of two phases. The V and Cr constituents were mainly distributed in the primary phase, whereas the Ti and Ni constituents were mainly distributed in the secondary phase. The Cmax was dependent on the lattice volume of the primary phase, mole fraction of the primary phase and the plateau potential in charging. The average decrement of discharge capacity (ΔCdis) from Cmax to the discharge capacity at 30th cycle was used as an indicator of charge–discharge cycle performance. The ΔCdis was decreased or cycle performance was improved with the Cr content in the primary phase. The discharge potential at DOD = 50% (ΔE50) was linearly changed with specific discharge current (idis), and the ΔE50/Δidis and charge transfer resistance (Rct) as indicators of HRD were decreased with an increase in the Ni content in the secondary phase.

Performance validation of sodium-ion batteries using an ionic liquid electrolyte

Charge–discharge properties of sodium-ion batteries using the Na[FSA]–[C3C1pyrr][FSA] (FSA: bis(fluorosulfonyl)amide, C3C1pyrr: N–methyl–N–propylpyrrolidinium) ionic liquid were investigated over a temperature range of 273–363 K. NaCrO2 and hard carbon (HC) were used as positive electrode and negative electrode active materials, respectively, and their fundamental charge–discharge characteristics were examined with coin-type half-cells. A 1.5 mAh coin-type full cell composed of HC/NaCrO2 showed excellent cycle properties, maintaining 90 % of its initial capacity after 1000 cycles at 333 and 363 K. The 1.5 mAh full cell also exhibited a high charge–discharge energy efficiency of 97.5 % at 363 K and C/5 rate. A large-sized prismatic HC/NaCrO2 full cell with a capacity of 27 Ah was fabricated by a mass production process, and its performance was confirmed to be comparable with that of the 1.5 mAh coin-type cell.

Investigation of Influence of Ebonex on the Formation of Lead-Acid Accumulator Positive Electrode

This article is focused on lead-acid batteries used in hybrid electric vehicles and battery-powered vehicles. These cells work in specific conditions, particularly under partial charge referred to as PSOC and DoD. This fact is responsible for the premature loss of capacity cell lead-acid batteries and their short lifetime. The task of this work is to examine the effect of conductive ceramics as possible additives to the negative electrode active materials of lead-acid battery cells operating in a DoD, in order to prolong their life. This article compares the properties of experimental cells with varying amounts of Ebonex added in the positive active mass. For this experiment were selected electrodes in admixture with 0 wt.%, 0,15 wt.%, 0,46 wt.% and 0,78 wt.% of Ebonex.

A highly electronic conductive cobalt nickel sulphide dendrite/quasi-spherical nanocomposite for a supercapacitor electrode with ultrahigh areal specific capacitance

In this study, a spinel binary transition metal sulphide Co1.5Ni1.5S4 dendrite/quasi-spherical nanocomposite with high electronic conductivity and a suitable porous structure was synthesized via a facile hydrothermal process. The morphology and structure of the Co1.5Ni1.5S4 nanocomposite were easily manipulated by tuning the hydrothermal reaction time. To the best of our knowledge, due to its good electronic conductivity and suitable structure for the electrochemical redox reaction, the Co1.5Ni1.5S4 electrode exhibited the highest areal specific capacitance of 41.0 F cm−2. The electrochemical impedance spectroscopy (EIS) results demonstrate that Co1.5Ni1.5S4 possesses a higher electronic conductivity and faster charge transfer than single-component sulphides (CoS and NiS) or cobalt-nickel hydroxides and oxides. These characteristics contribute to the high specific capacitance of the Co1.5Ni1.5S4 electrode even at high material loading, corresponding to an ultrahigh areal specific capacitance. An asymmetric supercapacitor, which was assembled with Co1.5Ni1.5S4 as the positive electrode active material and HNO3-treated activated carbon as the negative electrode active material, exhibited a superior energy density of 32.4 Wh kg−1 at a power density of 103.4 W kg−1 and 25.0 Wh kg−1 at a high power density of 5.5 kW kg−1.

Hydrogen Evolution Behavior of Dissolving Magnesium Investigated By EIS and Gas Chromatography

An air battery is expected as a power source for the automobile and disaster battery because it has a high energy density and charge voltage. Since the magnesium is the less noble material, it is expected as a negative electrode active material of air battery. It is well known that the cathodic reaction of hydrogen evolution was occurred at magnesium surface during anodic polarization measurement of magnesium (1). Petty et. al (1) suggested that the fraction of dissolving magnesium enters the solution as univalent magnesium (Mg+), where it is oxidized by water. Samaniego et. al (2) reproduced the experiment performed by Petty et. al (1) and supplemented with modern in situ Raman spectroscopy. They concluded that the existence of univalent magnesium was not established by Petty et. al (1). Frankel et. al (3) suggested that the ability of magnesium to support the cathodic reaction is enhanced during the anodic dissolution as the result of an increase on the exchange current density for the hydrogen reaction. Although the mechanisms of hydrogen evolution on the magnesium surface have been suggested, reactions of the hydrogen evolution have not been clarified in detail yet. In this study, the relation between the anodic dissolution of magnesium and the hydrogen evolution occurred during anodic polarization of magnesium is investigated by the simultaneous measurements of electrochemical measurement and gas chromatography. The hydrogen evolution of the dissolving magnesium was examined by the 3D impedance measurement in 0.5 M NaCl. The amount of the hydrogen gas during anodic polarization of magnesium was detected by the gas chromatography.

Analysis of aging of commercial composite metal oxide – Li4Ti5O12 battery cells

Commercial battery cells with Li4Ti5O12 negative electrode and composite metal oxide positive electrode have been analyzed with respect to aging mechanisms. Electrochemical impedance spectroscopy (EIS), differential capacity analysis (dQ/dV), differential voltage analysis (dV/dQ) and scanning electron microscopy (SEM) with energy dispersive X-ray analysis (EDX) were used to identify different ageing mechanisms such as lithium inventory loss, loss of active electrode material and surface film growth. The active material of the positive electrode was also examined by X-ray diffraction (XRD). Aging mechanisms were studied for both calendar-aged and cycle-aged cells. Data from half cells prepared from post mortem harvested electrode material, using lithium foil as negative electrode and pouch material as encapsulation, were used as reference to full cell data. Electrochemical analysis of full and half cells combined with material analysis showed to be a powerful method to identify aging mechanisms in this type of commercial cells. The calendar-aged cell showed insignificant aging while the cycle-aged cell showed noticeable loss of positive electrode active material and loss of cyclable lithium, but only minor loss of negative electrode active material. The results imply that Li4Ti5O12 negative electrode material is a good alternative to other materials if high energy density is not the primary goal.

Nanostructured TiO2-Coated Activated Carbon Composite as an Electrode Material for Asymmetric Hybrid Capacitors

A nanostructured TiO2-coated activated carbon (TAC) composite was synthesized by a modified sol-gel reaction and employed it as a negative electrode active material for an asymmetric hybrid capacitor. The structural characterization showed that the TiO2 nano-layer was deposited on the surface of the activated carbon and the TAC composite has a highly mesoporous structure. The evaluation of electrochemical characteristics of the TAC electrode was carried out by galvanostatic charge/discharge cycling tests and electrochemical impedance spectroscopy. The obtained specific capacitance of the TAC composite was 42.87 F/g, which showed by 27.1% higher than that of the activated carbon (AC). The TAC composite also exhibited an excellent cycle performance and kept 95% of initial capacitance over 500 cycles.