Active Material Of Negative Electrode Research Articles

Petroleum Coke as the Active Material for Negative Electrodes in Lithium–Sulfur Batteries

The possibility of using carbon materials based on petroleum coke as the cheap and available active material for negative electrodes of lithium–sulfur rechargeable batteries is considered. The comparative studies of characteristics of lithium–sulfur cells with negative electrodes based on metal lithium, graphite, and petroleum coke are carried out. It is found that heat-treated petroleum coke can be successfully used as the active material for negative electrode of lithium–sulfur batteries with acceptable energy characteristics. All other conditions being the same, the lithium–sulfur cells with negative electrodes based on petroleum coke demonstrate the longer cyclability as compared with cells based on metal lithium or graphite. This is explained by the slower destruction of electrolyte components on the negative electrode during cycling of lithium–sulfur cells. It is shown that the use of negative electrodes based on petroleum coke in lithium–sulfur batteries allows their cyclability to be increased and their cost to be reduced.

Improvement of reversible H storage capacity by fine tuning of the composition in the pseudo-binary systems A2-xLaxNi7 (A = Gd, Sm, Y, Mg)

A2B7 compounds (A = rare earth or Mg, B = transition metal) are widely studied as active materials for negative electrode in Ni-MH batteries. By playing on the substitution rate of both A and B elements, it is possible to prepare various compositions. This strategy will help to improve the properties, for example get a higher reversible hydrogen capacity and a well-adapted hydrogen sorption pressure. Indeed, A can be almost all light rare earths (La to Gd), yttrium and alkaline earth metals (Mg or Ca), whereas B can contain various late transition metals (Mn to Ni). To understand the effects of composition on the physicochemical properties of La2Ni7-based compound, various pseudo-binary systems have been investigated: Gd2-xLaxNi7 (x = 0, 0.6, 1, 1.5), Sm2-xLaxNi7 (x = 0, 0.5, 1, 1.5), Y2-xLaxNi7 (x = 0, 0.4, 0.5, 0.6, 0.8, 1, 1.5, 1.75) and A0.5La1.1Mg0.4Ni7 (A = Sm, Gd and Y). To determine their crystallographic properties, X-ray diffraction analysis was performed followed by Rietveld refinement. Thermodynamic properties regarding reversible hydrogen sorption were investigated at room temperature. Quaternary compounds present drastically improved sorption properties in the frame of practical energy storage applications with reversible capacity equivalent to 400 mAh/g for the compound La1.1Sm0.5Mg0.4Ni7.

Continuous Hydrothermal Synthesis of Metal Germanates (M2GeO4; M = Co, Mn, Zn) for High‐Capacity Negative Electrodes in Li‐Ion Batteries

Nanosized metal germanates (M2GeO4; M = Co, Mn, Zn) are synthesized using a continuous hydrothermal flow synthesis process for the first time. The electrochemical properties of all samples as active materials for negative electrodes in Li‐ion half cells are explored. The galvanostatic and potentiodynamic testing is conducted in the potential range of 3.00–0.05 V versus Li/Li+. The results suggest that both alloying and conversion reactions associated with Ge contribute to the stored charge capacity; Zn2GeO4 shows a high specific capacity of 600 mAh g−1 (ten cycles at 0.1 A g−1) due to alloying and conversion reactions for both Ge and Zn. Mn2GeO4 is studied for the first time as a potential negative electrode material in a Li‐ion half cell; an excellent specific charge capacity of 510 mAh g−1 (10 cycles per 0.1 A g−1) is obtained with a significant contribution to charge arising from the conversion reaction of Mn to MnO upon delithiation. In contrast, Co2GeO4 only shows a specific capacity of 240 mAh g−1, after ten cycles at the same current rate, which suggests that cobalt has little or no benefit for enhancing stored charge in germanate.

Petroleum Coke As Active Material of Negative Electrode for Lithium-Sulfur Batteries

We studied the possibility of using graphite and petroleum coke as active materials of negative electrodes for lithium-sulfur batteries. Petroleum coke was previously subjected to thermochemical activation in its own vapor in an air atmosphere for 10 hours at 800 °C.Positive sulfur electrodes were made by casting a slurry on aluminum foil. The composition of the electrode layer was 70% wt. sulfur, 10% wt. carbon (Ketjenblack EC-600JD), and 20% wt. binder (poly(ethylene) oxide, MW 4x106).The separator was 1 layer of microporous polypropylene Celgard®3501. The electrolyte was 1M LiClO4 in sulfolane.Negative electrodes based on graphite and activated petroleum coke were prepared by slurry casting onto copper foil. The composition of the electrode layer was 94% wt. of the active material (petroleum coke or graphite), 1% wt. of the carbon black (Super P), and 5% wt. of the binder (LA-132).Negative electrodes based on carbon materials were pre-lithiated. For this purpose, cells with a lithium electrode and carbon electrode were assembled and subjected to 5 molding cycles. Figure (a) shows the typical charge-discharge voltage profiles of the semi-cells of Li - Carbon electrode. After 5 molding cycles, the cells were transferred to the glove box and lithiated carbon electrodes were removed from them. Lithium sulfur cells were assembled with these lithiated carbon electrodes.It was shown that regardless of the negative electrodes used, there are two plateau on the discharge voltage profiles of lithium-sulfur cells, corresponding to electrochemical reduction (Figure b):(1) sulfur and high ordered lithium polysulfides through a series of intermediate stages to lithium tetrasulfide:S8 + 4Li+ + 4e- → 2Li2S4 (2) Lithium tetrasulfide to lithium disulfide and lithium sulfide:Li2S4 + 4Li+ + 4e- → 2Li2S + Li2S2. It should be noted that the discharge voltage of lithium-sulfur cells with carbon electrodes is decreased by the magnitude of the voltage of lithium-carbon semi-cells (Figure (a) and (b)).At the initial stages, the rate of decrease in the discharge capacity of lithium-sulfur cells weakly depends on the composition of the negative electrode. Cycling efficiency is 91-92%.Based on the obtained results, it can be concluded that activated petroleum coke can be used as the active material of the negative electrode for lithium-sulfur batteries. This work was performed as part of a Government Order to Ufa Institute of Chemistry of the Russian Academy of Sciences by the Ministry of Science and Higher Education of the Russian Federation (Theme No. AAAA-A17-117011910031-7) Russia and was also financially supported by the Russian Science Foundation (project No 17-73-20115). Figure 1

Significant Suppression of Silicon Negative Electrode for Lithium-Ion Battery in Ionic-Liquid Electrolyte

Elemental Silicon (Si) has a high theoretical capacity of 3580 mA h g-1 and has attracted attention as an active material of negative electrode for high energy density lithium-ion batteries. However, it shows poor cycle stability, which is mainly due to a massive volume change in Si during lithiation and delithiation. Here, we report that combination an ionic liquid electrolyte with a charge capacity limit of 1000 mA h g-1 significantly suppresses Si volume expansion, improving the cycle life. On the other hand, the Si layer expands largely in an organic electrolyte even with the charge capacity limit and even in an ionic-liquid electrolyte without the limit. We demonstrated that the homogeneously distributed Si lithiation−delithiation, phase-transition control from the Si to Li-rich Li-Si alloy phases, and formation of a surface film with structural and/or mechanical stability contribute to suppressing Si volume expansion.1 A Si working electrode was fabricated by gas-deposition method, which is without any binder and conductive agent. A 2032-type coin cell was constructed, comprising a Si electrode, a glass fiber filter as the separator, and a Li metal sheet as the counter electrode. An ionic liquid electrolyte used was 1 mol dm-3 (M) lithium bis(fluorosulfonyl)amide (LiFSA) dissolved in N-methyl-N-propylpyrrodinum bis(fluorosulfonyl)amide (Py13-FSA). For comparison, 1 M lithium bis(trifluoromethanesulfonyl)amide (LiFSA) dissolved in propylene carbonate (PC) was employed as a conventional organic electrolyte. Galvanostatic charge-discharge testing was performed with a charge capacity limit of 1000 mA h g-1 unless stated otherwise. The current density was set at 0.36 A g-1 (0.1 C) during the first cycle and 1.44 A g-1 (0.4 C) during subsequent cycles. An electrode cross section was observed by field emission scanning electron microscopy (FE-SEM). The cross section was fabricated using a cross-section polisher or focused ion beam. The electrode was not exposed to the atmosphere until it was introduced into the chamber of the FE-SEM using a transfer vessel. A reversible capacity of the Si electrode decayed at around the100th cycle in the organic electrolyte (1 M LiTFSA/PC). Conversely, in the ionic-liquid electrolyte (1 M LiFSA/Py13-FSA), the Si electrode exhibited a better cycle life with a reversible capacity of 1000 mA h g-1 after the 600th cycle. To determine the difference between the cycle lives of Si electrode in organic and ionic-liquid electrolytes, we investigated the thickness of the lithiated Si active material layers by FE-SEM. The thickness of the nonlithiated Si layer before charge-discharge testing was 1.6 ± 0.3 mm.2 In the organic electrolyte, the Si layer expnads with the cycle number, developing several cracks and becoming porous after the 50th and 100th cycles. The thickness reached ca. 25 mm after the 100th cycle when the capacity faded. The amorphous Li1.0Si (a-Li1.0Si) phase may mainly form with a charge capacity limit of 1000 mA h g-1 because it has a theoretical capacity of 950 mA h g-1. The expansion rate of the Si layer was about 1460%, whereas the calculated rate of increase in thickness from Si to a-Li1.0Si phases is 17%. In the ionic-liquid electrolyte, the Si electrode retained a thickness of 2.7 mm over 300 cycles, with an expansion rate of ca. 69%. Unexpectedly, the Si layer did not expand significantly after repeated cycling. There are no reports on the significant suppression of Si volume expansion after such long-term cycling. However, the expansion rate of 69% is still above the calculated rate of 17% for the a-Li1.0Si phase. After the 600th cycle and just before capacity fading, the layer thickness increased to 13.3 mm with some void and crack formation inside the layer. We discuss differences in the performances of the Si-alone electrode in the organic and ionic-liquid electrolytes based on the Li storage distribution, phase transition, and surface film formation. Reference s : [1] Y. Domi, H. Usui, K. Yamaguchi, S. Yodoya, H. Sakaguchi, ACS Appl. Mater. Interfaces,.2019, in press. [2] K. Yamaguchi, Y. Domi, H. Usui, H. Sakaguchi, ChemElectroChem, 2017, 4, 3257-3263.

Electrochemical Properties of Petroleum Coke As Active Material of Negative Electrode in Lithium Batteries

The possibility of usage of petroleum coke as active materials of negative electrodes in lithium batteries was studied in presented work. Studies show that crude petroleum coke has high specific resistance (1.4·107 Ohm·cm), that is in 7 times greater than the resistance of graphite (0.5-1.0 Ohm·cm), used as the active material of negative electrodes in lithium-ion batteries. Thermal treatment of crude petroleum coke at 800 °C in the atmosphere of air or nitrogen during 5 hours decreases the specific resistance to 1.3 and 1.5 Ohm·cm, correspondingly, and increases their specific surface area from <0.1 m2/g to 5.3 m2/g (nitrogen) and 0.7 m2/g (air). Specific surface area was estimated by sorption of dyes (methyl orange).Crude petroleum coke is not electrochemical active and can not be DC cycled (Figure). Heat treatment of petroleum coke, both in the atmosphere of air and in the atmosphere of nitrogen, leads to the appearance of electrochemical activity and the ability to reversibly intercalate lithium ions. At DC cycling of electrodes based on heat-treated petroleum coke in the range of voltage of 0 - 1.0 V vs Li/Li+ the reversible capacity is 300-350 mA·h/g.The shapes of charge and discharge curves (Figure) of semi-cells with electrodes based on petroleum coke are similar to the charge-discharge curves of semi-cells with electrodes based on structurally disordered carbons. This work was performed as part of the Government Order to Ufa Institute of Chemistry of the Russian Academy of Sciences by the Ministry of Science and Higher Education of the Russian Federation (Theme No. AAAA-A17-117011910031-7). Figure 1

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.

An Optimized PVC-Based Soft Carbon As the Negative Electrode of Sodium-Ion Batteries

The critical role of energy storage is by now self-evident: they are indispensable for an increased share of renewable energy and electric vehicles. Considering the abundance of sodium resources, sodium-ion batteries (NIBs) are poised as an alternative to Li-ion batteries as sustainable electrochemical energy storage (EES) solution.[1−6] However, several technical challenges still remain to be addressed before the commercialization of NIBs, with the anode being one of them. Graphite has been employed as the anode for commercial lithium-ion batteries (LIBs) since 1991.[7] However, for NIB, a high degree of disorder of the carbon structure is needed to allow sodium insertion at positive voltages. Therefore, alternative anode materials are demanded. One family of candidates is nongraphitic carbon, which comes in the forms of “hard carbon” (HC) or “soft carbon” (SC).[8] For both SC and HC the amount of sodium ions that can be inserted at positive voltages between the graphene layers is greatly increased compared to graphite. The specificity of HC is to present an additional capacity traduced by a low voltage plateau (LVP). Since the pioneer work of Stevens and Dahn in the early 2000’s, the sloping voltage below 1V and the low voltage plateau are usually ascribed to defect assisted intercalation and packing of sodium within the voids opened between cross-linked graphitic layers, respectively, [9] although recent results demonstrate that it might be more complicated than that.[10] Due to this extra capacity due to the LVP, the effort of the community has been mainly focused in recent years on hard carbons and on improving their capacities by tuning their micro-porosity. Thus, there is tremendous need to understand deeply the sodium insertion/extraction mechanism into disordered carbons. In the present work an optimized PVC-based SC as active material for NIB negative electrode will be underlined. A comparative study of the performance of PVC-C compared to Sugar-HC with similar particle size and electrode preparation will be presented. Although it does not present the typical low voltage plateau of hard carbons, PVC-SC reaches an initial reversible capacity of 230mAh/g and retains 225mAh/g after 150 cycles at 24.8mA/g. At high current density of 1C (372mA/g), the electrode still can achieve a capacity of 175mAh/g with a Coulombic efficiency near 100%. The microstructure and the morphology of these carbons have been studied by coupling gas adsorption, powder X-ray diffraction (in-situ and ex-situ PXRD) and Small Angle X-ray Scattering (SAXS) measurements, which, by correlating with their electrochemical performance, had led us to identify the and identifying key-microstructural features at origin of the performance of PVC—SC and give new insights into the mechanism of sodium insertion into disordered soft and hard carbons. [11] [1] Kim, S. W.; Seo, D. H.; Ma, X.; Ceder, G.; Kang. Adv. Energy Mater. 2012, 2 (7), 710−721. [2] Kundu, D.; Talaie, E.; Duffort, V.; Nazar, L. F. Angew. Chem., Int. Ed. 2015, 54 (11), 3431−3448. [3] Luo, W.; Shen, F.; Bommier, C.; Zhu, H.; Ji, X.; Hu, L. Acc. Chem. Res. 2016, 49 (2), 231−240. [4] Pan, H.; Hu, Y.-S.; Chen, L. Energy Environ. Sci. 2013, 6 (8), 2338−2360. [5] Slater, M. D.; Kim, D.; Lee, E.; Johnson, C. S. Adv. Funct. Mater. 2013, 23 (8), 947−958. [6] Wenzel, S.; Hara, T.; Janek, J.; Adelhelm, P. Energy Environ. Sci. 2011, 4 (9), 3342−3345. [7] Nagaura, T.; Tozawa, K. Prog. Batteries Sol. Cells 1990, 9, 209. [8] Na-ion batteries for large scale applications: a review on anode materials and solid electrolyte interphase formation; Muñoz-Márquez, M. Á.; Saurel, D.; Gómez-Cámer, J. L.; Casas-Cabanas, M; Castillo-Martínez, E.; Rojo, T.; accepted to Advanced Energy Materials (2017). [9] D. A. Stevens and J. R. Dahn, J. Electrochem.Soc. 148 (2001) A803-A811. [10] C. Bommier, T. Wesley Surta, M.Dolgos and X. Ji, Nano Lett. 15 (2015) 5888–5892. [11] Ultra-microporous soft carbon as high performance active material for the negative electrode of sodium-ion batteries; Orayech, B.; Clarke, C.; Acebedo, B. and Saurel, D.; submitted.

Preparation and characterization of Pb nanoparticles on mesoporous carbon nanostructure for advanced lead-acid battery applications

To enhance the electrochemical energy performance, the lead nanoparticles on mesoporous carbon (Pb on MPC) were prepared and characterized for advanced lead acid battery (Ad-LAB) applications. At present, Ad-LAB garners significant attention in energy storage devices because of its high charge acceptance. However, the major problem has associated with the large crystallization of PbSO4 in negative electrode during unit cell operation. To minimize this issue, Pb nanoparticles have incorporated on MPC in this present investigation. The Pb on MPC has prepared through facile chemical reduction process. The structural analysis of Pb, MPC, and Pb on MPC have confirmed by X-ray diffraction analysis. The specific surface area (SSA) and pore size distribution of MPC and Pb on MPC has obtained through Brunauer-Emmett-Teller measurements. The obtained SSA is 245.38 and 32.42 m2 g−1 for MPC and Pb on MPC, respectively. Additionally, the incorporation of Pb on MPC has confirmed by the microstructural analysis of high resolution transmission electron microscopy. The obtained particle sizes of the Pb nanoparticles are ~5 nm. Based on the structural, microstructural and cyclic voltammetry analysis, we suggest that Pb on MPC can be used as an efficient active material for negative electrode in Ad-LAB systems.

Communication—Iron(II)-Benzene Phosphonate Coordination Polymers as an Efficient Active Material for Negative Electrode of Lithium-Ion Batteries

An Iron based Metal-Organic Framework is proposed as an active material for negative electrode of lithium battery. The material is characterized by scanning electron microscope (SEM), powder X-ray diffraction (XRD), nitrogen uptake (BET) and thermogravimetric Analyses (TGA). Electrochemical properties have been determined by cyclic voltammetry and galvanostatic cycling in coin cells using lithium metal as counter electrodes. The electrochemical evaluation has revealed a significant enhancement in the capacity (550 mAh/g) with a mean voltage of 0.9 V vs Li+/Li compared to the actual graphite (300 mAh/g) or Li4Ti5O12 (170 mAh/g) and a good cyclability showing the interest of such material.

Polyglutamate Binder for Silicon-Graphite Negative Electrode: Effects of Cut-Off Voltage and Electrolyte Additive

Silicon is one of the promising active materials for negative electrodes of Li-ion batteries (LIB) because of its larger reversible capacity (~3600 mAh g-1) through lithiation/delithiation process, compared with that of conventional graphite active material (~370 mAh g-1). However, it is difficult to maintain its superior discharge capacity for long-term cycles because large volume change of Si occurs during cycles, which triggers intensive electrode degradation. To overcome this drawback, binder polymer is thought to be a key factor for improvement of the performance. In particular, polyacrylate binder1,2) and natural polymer binder3) effectively suppress the degradation due to their superior mechanical strength, coatability for active materials, and effects of pre-formed solid electrolyte interphase (SEI)4). Recently, we have focused on polyglutamate (PGlu) as an efficent binder for the Si/graphite composite electrode of LIB. PGlu is known to be contained in Japanese traditional food “Natto,” which is fermented soy beans. In this study, effects of discharge cut-off voltage in the cycles and electrolyte additive on the performance of Si/graphite electrodes with PGlu binder are investigated from the viewpoint of surface chemistry. Figure 1 shows cycle performance of the Si/graphite electrodes with different discharge cut-off voltage. For additive-free cells, capacity retention was highly improved under the cycles with lower discharge cut-off voltage (1.0 V vs. Li/Li+). Furthermore, addition of fluoroethylene carbonate (FEC) to the electrolyte effectively suppressed deterioration of the performance and brought the best capacity retention, leading to discharge capacity of ~800 mAh g-1 even after 100 cycles. To clarify details of the effects, chemical components and thickness of the SEI formed on the electrode surface were examined by hard X-ray photoelectron spectroscopy (HAXPES, hν = 7.94 keV). Figure 2 shows the HAXPES C 1s and Si 1s spectra of Si/graphite electrodes before and after the first cycle with different discharge cut-off voltage. For the electrode with cut-off voltage of 1.0 V, the peak intensity at 284.6 eV is relatively lower than that of the 2.0 V cut-off electrode, which is assigned to sp 2 carbon bonding in graphite of the composite. Similarly, the peaks at 1839.5 eV and 1844 eV in the Si 1s spectra, which are assigned to Si0 and silicon oxide, respectively, are smaller for the case of lower cut-off voltage. These results indicate that thickness of SEI is affected by the discharge cut-off voltage. We presume that moderately-low discharge cut-off voltage of 1.0 V effectively brings thicker and stable SEI on the electrode surface by suppression of oxidative decomposition and dissolution of SEI, which probably occur at higher potential condition in delithiation process. In this presentation, other electrochemical and morphological characterizations of the electrode and superior effects of FEC for the cyclability will be also discussed.

Electrochemical behavior of MgO-templated mesoporous carbons in the propylene carbonate solution of sodium hexafluorophosphate

MgO-templated mesoporous carbons annealed from 900 to 1,500 °C were examined as active materials for negative electrodes in a propylene carbonate electrolyte containing 1 M sodium hexafluorophosphate. The carbons annealed at 1,000 °C exhibited 180 mAh g−1 at a rate of 0.1 A g−1 in a potential range of 2.00–0.01 V versus Na+/Na. The carbons showed good rate capability as well as cyclability. It is considered that mesopores plays a role of easy diffusion pathway for ions, and also significantly relates to both electric double layer capacitance and faradaic reactions involving Na ions. X-ray diffraction patterns, nuclear magnetic resonance spectra and Raman spectra were discussed for characterization of the carbons. Raman spectra indicated a reversible interaction of reduced Na with carbons. However, Na intercalation in the carbon layers was not confirmed for the carbon annealed at 1,000 °C. This is because the Na intercalation sites in the carbon layers are very few due to the disordered structure caused by the relatively low temperature annealing.

Identification of the atomic scale structure of the La0.65Nd0.15Mg0.20Ni3.5 alloy synthesized by spark plasma sintering

Magnesium and neodymium substituted La2Ni7 hydride forming alloys are studied as possible active materials for negative electrodes in Ni–MH battery. La0.65Nd0.15Mg0.20Ni3.5 has been prepared by Spark Plasma Sintering (SPS) and characterized by X-ray diffraction, microprobe, Transmission Electron Microscopy (TEM) and High-Angle annular Dark-Field (HAADF) Scanning Transmission Electron Microscopy (STEM). HAADF-STEM is the optimal technique for the atomic resolution imaging of the crystal structure and defects of this complex material by providing directly interpretable images of the crystal structure with chemical contrast. The rhombohedral [3R] structure has been directly identified from the HAADF images, in agreement with the results obtained from Rietveld analysis of the X-ray diffraction patterns. HAADF image simulations fit the experimental data well. Local hexagonal-type defects and occasional changes in the sequence of building units for these stacking structures have been observed within the grains and are much more readily identifiable by HAADF-STEM imaging.

Elaboration and characterization of magnesium-substituted La 5Ni 19 hydride forming alloys as active materials for negative electrode in Ni-MH battery

The crystallographic structure as well as the thermodynamic and electrochemical properties of the hydrogen absorbing compounds La 5Ni 19 and La 4MgNi 19 have been determined. X-ray diffraction and microprobe analysis have shown the presence of a single hexagonal ( P6 3/ mmc) phase for the Mg-free binary compound whereas only one composition but two different crystallographic structures, hexagonal ( P6 3/ mmc) and rhombohedral ( R-3 m), are observed for La 4MgNi 19. Each phase can be described as the stacking along the c-axis of n[A 2B 4]/ m[AB 5] sub-units with n = 1 and m = 3 and A = La, Mg; B = Ni. Depending on the stacking sequence, either the hexagonal or the rhombohedral phase is obtained. Thermodynamic properties toward hydrogen uptake (capacity and equilibrium pressure) and electrochemical properties (cycling behavior) in alkaline medium have been measured and are compared for these compounds with and without magnesium. It is observed that the Mg-free compound exhibits a much lower reversible hydrogen capacity than the Mg-containing one. However, despite larger capacity, this latter compound remains to be optimized in term of cycle life.

Characterization of silicon- and carbon-based composite anodes for lithium-ion batteries

In recent years development of active materials for negative electrodes has been of great interest. Special attention has been focused on the active materials possessing higher reversible capacity than that of conventional graphite. In the present work the electrochemical performance of some carbon/silicon-based materials has been analyzed. For this purpose various silicon-based composites were prepared using such carbon materials as graphite, hard carbon and graphitized carbon black. An analysis of charging–discharging processes at electrodes based on different carbon materials has shown that graphite modified with silicon is the most promising anode material. It has also been revealed that the irreversible capacity mainly depends on the content of Si. An optimum content of Si has been determined with taking into account that high irreversible capacity is not suitable for practical application in lithium-ion batteries. This content falls within the range of 8–10 wt%. The reversible capacity of graphite modified with 8 wt% carbon-coated Si was as high as 604 mAh g −1. The irreversible capacity loss with this material was as low as 8.1%. The small irreversible capacity of the material allowed developing full lithium-ion rechargeable cells in the 2016 coin cell configuration. Lithium-ion batteries based on graphite modified with silicon show gravimetric and volumetric specific energy densities which are higher by approximately 20% than those for a lithium-ion battery based on natural graphite.

Pechini process-derived tin oxide and tin oxide–graphite composites for lithium-ion batteries

The Pechini process [Ceram. Bull. 68 (1989) 1002] is used to obtain fine tin oxide powders that reduce the specific volume change in Li + insertion and extraction reactions. The suitability of these tin oxides as active materials for negative electrodes in lithium-ion batteries is investigated. From elemental analysis, it is found that the templating polymer network is almost completely obliterated after heating at 500 °C. The best tin oxide does not exhibit extensive crystallization of tin atoms even after 30 cycles of alloying and de-alloying reactions with Li. The structure and the specific capacity of the oxides are dependent on the heat treatment and remnants of the polymeric CH network can impose an unfavorable outcome. A capacity of 600 mAh g −1, which is unchanged for 30 cycles, can be obtained from tin oxide heat treated at 1000 °C. Composites of graphite and SnO 2 are also prepared and exhibit synergistic interactions between graphite and tin oxide which are similar to those reported previously [Electrochem. Solid State Lett. 3 (2000) 167].

ニッケル水素電池の電極材料の硫酸浸出

Leaching treatment of electrode materials has been studied to recover valuable metals in a used nickel-metal hydride rechargeable battery by a hydrometallugical process on the effects of sulfuric acid concentration, temperature, leaching duration and oxidizing agents (air, O2 gas, H2O2 solution). The positive electrode materials were identified to be Ni(OH)2 (active material) and Ni (current collector) by XRD analysis, and the active material of negative electrode to be LaNi5. Leaching behavior was investigated by using positive electrode materials, active material of negative electrode, and reagents such as Ni(OH)2 and Ni. The nickel hydroxide ,Ni(OH)2, reagent was easily leached with diluted sulfuric acid, but leaching of the Ni reagent was difficult. Oxidizing agents were however effective in leaching metal Ni. The nickel hydroxide particles in positive electrode materials and the active material of negative electrode could be leached in 0.5 kmol·m-3 of sulfuric acid solution, dispite no leaching of the current collector in positive electrode materials. The current collector was easily leached by adding oxidizing agents. Both O2 gas and H2O2 solution were found to be effective. A practical process was tested to separate electrode materials from a used battery. The process contained the following treatments; cutting, heat treatment, magnetic separation and screening. NiO which is a product of heating treatment of Ni(OH) 2 could be leached at a higher sulfuric acid concentration or higher temperature.

On the choice of graphite for lithium ion batteries

Graphites as active materials for negative electrode in lithium batteries are particularly attractive because of their large capacity of lithium intercalation and their low average voltage. In some conditions, they are known to suffer from low reversibility of the initial intercalation process. This phenomenon is shown to be unambiguously related to an exfoliation of graphene layers, that can occur even in EC based electrolytes. Occurrence of a clear correlation between the extent of irreversible behaviour and rhombohedral phase content of graphites is discussed. Milling or thermal treatment of pristine graphites are also shown to influence electrochemical properties.

Battery characteristics with various carbonaceous materials

Various carbonaceous particles having a core-shell structure, produced from graphite and pseudo-graphite coated with pitchblended phenol resin and green mesophase-pitch coated with phenol resin and ground graphite powder, were investigated as active materials for negative electrodes. The particles with natural graphite cores, as well as those with pseudo-graphite cores, were stable both in 1 M LiClO 4 PC:EC (50:50) electrolyte and in 1.5 M LiBF 4 PC:EC:BL (25:25:50) electrolyte, and showed excellent electrical capacities. Those produced from green mesophase-pitch cores were of markedly deformed configuration and showed large capacity gains with only small additions of graphite powder to the phenol coating material. Negative electrodes, in which the particles containing natural graphites cores were blended with petroleum coke in various ratios, showed that it may be possible to produce cells with specific discharge voltage curves, by varying the ratio of this blend.

Properties of Cobalt Oxide as an Active Material of Negative Electrode in Alkaline Storage Cell

Properties of Cobalt Oxide as an Active Material of Negative Electrode in Alkaline Storage Cell