Lithium Half-cells Research Articles

Anodic Oxidation of Carbon and Electrolyte with Different Conducting Salts in High-Voltage Lithium-Ion Batteries Studied By Online Electrochemical Mass Spectrometry

Recently, many research activities have been devoted to the development of near 5 V cathode materials, e.g. the LiMn1.5Ni0.5O4 spinel, in order to raise the energy density of lithium-ion batteries and to allow for longer driving ranges of battery electric vehicles.1 However, the enhanced degradation of carbon and electrolyte by the use of these high-voltage cathodes could not be mitigated so far. It was demonstrated recently by On-line Electrochemical Mass Spectrometry (OEMS),2 that the anodic oxidation of conductive carbon, carbon coatings, and electrolyte at ≈5.0 V can be substantial at high temperature and in the presence of trace water, posing significant challenges for the implementation of 5 V cathode materials.3,4 While these studies were done with LiClO4 as conducting salt in order to study the effect of H2O addition on oxidation without side reactions of salt and water, e.g. HF formation, we want to investigate now to which extent the lithium salt can influence gas generation at high voltage. We employ our newly developed two-compartment cell in which anode and cathode compartments are separated by a Li+-ion conducting solid electrolyte (Ohara glass) laminated with aluminum and polypropylene foil, so that the gas evolution from degradation processes at high voltage can be studied selectively for the positive electrode without cross-diffusion of reaction products and gas generation from the counter-electrode, thereby enabling a more detailed analysis of the decomposition pathways.5 This is a major advance over conventional cells, where the gases come from both electrodes, and thus do not allow a deconvolution of the simultaneously occurring reactions from anode and cathode. Furthermore, OEMS is used to compare three types of lithium salts in terms of their influence on the anodic stability (close to 5 V) of electrolyte and conductive carbon in the battery cell. These are the commercially used salt LiPF6, the sulfur- and nitrogen-containing LiTFSI, and the fluorine-free and oxygen-containing compound LiClO4. The salts are mixed with ethylene carbonate (EC) at a concentration of 1.5 M, so that linear carbonates like EMC or DMC which have a much higher vapor pressure than EC can be avoided, allowing for precise signal quantification in OEMS.3 The comparison of the salts will be done on the basis of the CO/CO2 gas evolution monitored by OEMS at various temperatures between 25 and 60°C. We employ a fully 13C-labeled carbon electrode to deconvolute the CO/CO2 evolution from electrolyte oxidation (12C) from that of the conductive carbon oxidation (13C). We quantify our OEMS results using a calibration gas, and give both, quantitative and mechanistic insights into the effect of the conducting salt on gas evolution in high-voltage lithium-ion batteries. By quantification of both CO/CO2 isotopes we determine the molar oxidation rate and the weight loss of electrolyte and carbon due to anodic oxidation. In summary, this study elucidates to which extent the lithium salt can influence gas generation at high voltage and might allow to deduce design principles for the synthesis of novel electrolyte salts. Figure 1 shows in the upper panel the current-potential profiles of 13C-carbon//lithium half-cells with the three different conducting salts at 1.5 M in EC upon a linear potential sweep from OCV to 5.5 V vs. Li/Li+. The corresponding evolution of both isotopes of CO2 (solid lines) and CO (dotted lines) for the electrolyte oxidation and the 13C-carbon oxidation are shown in the middle panel and the lower panel, respectively. References O. Gröger et al., J. Electrochem. Soc., 162, A2605 (2015).N. Tsiouvaras et al., J. Electrochem. Soc., 160, A471 (2013).M. Metzger et al., J. Electrochem. Soc., 162, A1123 (2015).M. Metzger et al., J. Electrochem. Soc., 162, A1227 (2015).M. Metzger et al., J. Electrochem. Soc., 163, A798 (2016). Acknowledgement The authors gratefully acknowledge BASF SE for financial support of this research through the framework of its Scientific Network on Electrochemistry and Batteries. Figure 1. Carbon and electrolyte oxidation upon linear potential sweep from OCV to 5.5 V vs. Li/Li+ at 0.1 mV/s with a 13C-carbon working-electrode and a metallic lithium counter-electrode for an EC-based electrolyte with 1.5 M LiClO4, LiPF6, or LiTFSI, respectively. (a) Current-potential profile, (b) 12CO/12CO2 from electrolyte oxidation, (c) 13CO/13CO2 from carbon oxidation. Figure 1

Development of a Novel Quartz (SiO2) Based Composite Anode Material for Li-Ion Batteries

Alternative energy sources have received great attention since traditional energy sources, fossil fuels, are non-renewable and causing critical environmental damage. Rechargeable lithium-ion batteries (LIBs) with high power density, long cycle life and environmental friendliness are of huge interest for application as power supply in electric vehicles and renewable energy storage [1]. However, current wide implementation of LIBs is restricted by several factors, such as a low capacity, instability and toxicity of the electrode materials. Silica (SiO2) is an eco-friendly candidate for the next generation anode materials for high energy density LIBs with a high lithium (Li) storage capacity (1961 mAh g-1 for silica) at a lower cost [2]. However, pure silica has a poor electrical conductivity and suffers from rapid capacity fading due to significant volume changes during charge/discharge. These limitations could be overcome by applying carbon and/or polymer coatings [3] and engineering various hollow nanostructures [4] to increase the conductivity and accommodate the volume changes, respectively [5]. Herein, we propose an innovative chemical free approach to prepare a novel composite anode material combining hollow SiO2nanospheres, carbon nanotube and graphene. Hollow SiO2 sphere/carbon nanotube/graphene ternary composite was synthesized using sonication (by Ultrasonic Elma S 30) of SiO2 (30 nm, 25%), multi-walled carbon nanotubes (MWNT, 3 %) and graphene (G, 1%) water suspensions in different ratios. Derived mixtures were dried at 50 ºC overnight in vacuum oven (Memmert), and further annealed in air oven (Carbolite) at 500 ºC for 2 h. Finally, SiO2/MWNT/G composites were obtained. Also, for comparison similar composite with single-walled carbon nanotubes (SiO2/SWNT/G) was prepared. The resulting composites of SiO2/MWNT/G and SiO2/SWNT/G were investigated and characterized by X-ray diffractometry (XRD), Fourier transform infrared spectroscopy (FTIR), thermal gravimetric analysis (TGA), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). XRD analysis confirmed the amorphous nature of the powders and FTIR spectroscopy identified the existence of Si-O, C-C and C=C bonds in these samples. TGA allowed for determination of the carbon content in the prepared composites. SEM revealed morphology of the samples and distribution of the elements in the composites. The TEM results allowed for characterization of the interior structure of the composite materials. CR2032 coin-type cells were used to evaluate the electrochemical performance of SiO2/MWNT/graphene and SiO2/SWNT/graphene composites in a lithium half-cell structure. The cells were tested galvanostatically in a voltage range of 0.01 – and 3.0 V vs. Li+/Li at a current density of 50 mA g-1 (Neware A602-3000W-CT-A). The further results of these studies will be presented at the conference. Acknowledgements This work was supported by the project grant 5097/GF4 “Development of a novel quartz (SiO2) based anode material for Li-ion batteries” from the Ministry of Education and Science of the Republic of Kazakhstan.

Straightforward Solvothermal Synthesis toward Phase Pure Li2CoPO4F

Li2CoPO4F, a promising high potential cathode material, has been synthesized for the first time via a one-pot solvothermal synthesis route. The characterization with respect to its crystal structure and electrochemical performance in a lithium half-cell is reported. Scanning electron microscopy, transmission electron microscopy, and X-ray diffraction studies reveal a strong influence of the solvent on the purity of the obtained crystalline phases and the particle morphology with preferred crystal growth orientations. The electrochemical tests of carbon coated materials demonstrate excellent characteristics in terms of high capacity.

High-Performance Red P-Based P–TiP2–C Nanocomposite Anode for Lithium-Ion and Sodium-Ion Storage

An amorphous red phosphorus-based composite has been synthesized via a facile and simple one-step high-energy mechanical milling process and investigated as an anode material for lithium-ion and sodium-ion batteries. The resultant P–TiP2–C nanocomposite exhibits a high reversible capacity of 1116 mA h g–1, excellent cyclability, and a remarkable initial Coulombic efficiency of 86% in lithium half cells. Furthermore, it delivers an initial desodiation capacity of 755 mA h g–1 with a high initial Coulombic efficiency of 80% and a good capacity retention of 80% after 100 cycles in sodium half cells. The greatly improved electrochemical performance is due to the unique nanoarchitecture composed of well-blended red phosphorus and crystalline TiP2 homogeneously embedded in a conductive carbon network. The presence of the conductive TiP2 inclusions plays a crucial role in offering structural stability as well as high conductivity to the phosphorus-based composite particles during cycling, thereby leading to supe...

A Combined Thermodynamics & Computational Method to Assess Lithium Composition in Anode and Cathode of Lithium Ion Batteries

With aim to address the open question of accurate determination of lithium composition in anode and cathode at a defined state of charge (SOC) of lithium ion batteries (LIB), we developed a method combining electrochemical thermodynamic measurements (ETM) and computational data fitting protocol. It is a common knowledge that in a lithium ion battery the SOC of anode and cathode differ from the SOC of the full-cell. Differences are in large part due to irreversible lithium losses within cell and to electrode mass unbalance. This implies that the lithium composition range in anode and in cathode during full charge and discharge cycle in full-cell is different from the composition range achieved in lithium half-cells of anode and cathode over their respective full SOC ranges. To the authors knowledge there is no unequivocal and practical method to determine the actual lithium composition of electrodes in a LIB, hence their SOC. Yet, accurate lithium composition assessment is fundamental not only for understanding the physics of electrodes but also for optimizing cell performances, particularly energy density and cycle life.

Study on the Lithiation Mechanism in Micro-Grain Structured Amorphous Silicon Anodes in Lithium-Ion Batteries with the Aid of Impedance Spectroscopy

It is well known that silicon presents one of the most important anode materials for the improvement of lithium-ion cells in terms of energy density. Indeed, silicon’s high theoretical specific capacity to lithium (more than 3800 mAh/g at room temperature), environmental friendliness, low potential compared to lithium and material abundance turn silicon to a strong candidate for the replacement of carbon-based anodes [1,2]. However, one of the main drawbacks of silicon’s application to the lithium-ion technology is its poor electrochemical cycling stability over several galvanostatic cycles, mainly due to silicon’s huge volume change (around 300%) during lithiation and delithiation that leads to high internal mechanical stress and therefore to film fracturing and delamination [3]. Many alternatives have been proposed that alleviate this mechanical expansion issue either through the use of nanostructured silicon sometimes combined with carbon-based materials or with special coatings and binders with the current collector [1,4]. Even though many years ago in 1999 amorphous silicon (a-Si) was initially proposed by Bourdereau et al. [5], it is quite recently that it has been found that a-Si can be more resistive to fractures and pulverisation upon lithiation [6] than crystalline silicon (c-Si). It has been demonstrated by McDowell et al., that amorphous silicon compared to the crystalline can resist more efficiently the large volume modifications at least for spheres with 870 nm of diameter and this has been attributed to the different lithiation mechanism [7]. Recently, Farmakis et al. [8] have demonstrated micro-grain structured amorphous silicon anodes delivering specific capacity of more than 2000 mAh/g and 2.0 mAh/cm2for more than 50 cycles. As a goal to comprehend the performance of the silicon and the related lithium kinetics, this contribution attempts to study the lithiation mechanism at micro-grain structures amorphous silicon structures with the aid of impedance spectroscopy. For this purpose, silicon/metal Lithium half cells were prepared with silicon being previously deposited by DC sputtering on rough copper foil and electrochemical characterization including impedance spectroscopy was conducted. After the application of a two semi-circle fitting model, the charge transfer and the Solid Electrolyte Interphase impedances are extracted. It is shown that the charge transfer resistance is highly dependent on the State Of Charge (SOC) and consequently on the charging rate. It is observed that the charge transfer resistance is highly increased (5-6 times) when silicon anode lithiation exceeds 80% of SOC and not. The results can be explained by considering that lithiation of amorphous silicon strongly depends on x at LixSi alloy throughout the silicon bulk material.

Single-Solvent Electrolytes for Lithium-Ion Batteries Studied By Operando Diffusive Reflectance Infrared Fourier Transform Spectroscopy

Stable cycling of Lithium-Ion batteries with graphite anodes is only possible due to the formation of a stable solid-electrolyte interphase (SEI). Thus, there is a big interest in surface characterization techniques such as X-ray photoelectron spectroscopy (XPS) or infrared spectroscopy (IR) in order to characterize the electrode decomposition products on the electrode surface. At the same time, gassing phenomena are characteristic for electrolyte decomposition processes [1, 2], whereby on-line gas analysis can provide insight into the corresponding reaction mechanisms [3, 4]. In the present work, we developed a novel cell design for operando Diffusive Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS). Using this setup, the working electrode is monitored spectroscopically during electrochemical cycling. Compared to the setup described in the literature [5, 6], our operando DRIFTS has two major advantages. First, with our cell we do not only observe the electrode surface and electrolyte, but also gas evolution during electrochemical cycling. Second, for our DRIFTS studies we use half-cell stacks with separator and working electrode materials that are closer to commercial batteries than the setup described in the literature. Operando measurements were performed with lithium half-cells. To facilitate spectral interpretation, single solvent electrolytes such as solutions of LiPF6 in pure ethylene carbonate (EC) or vinylene carbonate (VC) were applied. Inside our setup, the infrared radiation is diffusively scattered at the working electrode surface. We chose materials such as LiFePO4 and Li5Ti4O12 for electrode preparation. They were found to have better infrared reflective properties compared to highly absorbing graphite or carbon electrodes. Due to the fact that the infrared beam penetrates the gas volume in the head space of the cell, formation of gases is detected as well. For instance, we were able to detect gaseous POF3 and CO2 evolution during electrolyte oxidation at high potentials (see Figure 1). We will present EC and VC oxidation and reduction studies using operando DRIFTS. Acknowledgements: We gratefully acknowledge BASF SE for financial support of this research through the framework of its Scientific Network on Electrochemistry and Batteries.

A carbon-free lithium-ion solid dispersion redox couple with low viscosity for redox flow batteries

A new type of non-aqueous redox couple without carbon additives for flow batteries is proposed and the target anolyte chemistry is demonstrated. The so-called “Solid Dispersion Redox Couple” incorporates solid electroactive materials dispersed in organic lithium-ion battery electrolyte as its flowing suspension. In this work, a unique and systematic characterization approach has been used to study the flow battery redox couple in half cell demonstrations relative to a lithium electrode. An electrolyte laden with Li4Ti5O12 (LTO) has been characterized in multiple specially designed lithium half cell configurations. The flow battery redox couple described in this report has relatively low viscosity, especially in comparison to other flow batteries with solid active materials. The lack of carbon additive allows characterization of the electrochemical properties of the electroactive material in flow without the complication of conductive additives and unambiguous observation of the electrorheological coupling in these dispersed particle systems.

High Voltage Li-Ion Battery Using Exfoliated Graphite/Graphene Nanosheets Anode.

The achievement of a new generation of lithium-ion battery, suitable for a continuously growing consumer electronic and sustainable electric vehicle markets, requires the development of new, low-cost, and highly performing materials. Herein, we propose a new and efficient lithium-ion battery obtained by coupling exfoliated graphite/graphene nanosheets (EGNs) anode and high-voltage, spinel-structure cathode. The anode shows a capacity exceeding by 40% that ascribed to commercial graphite in lithium half-cell, at very high C-rate, due to its particular structure and morphology as demonstrated by X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The Li-ion battery reveals excellent efficiency and cycle life, extending up to 150 cycles, as well as an estimated practical energy density of about 260 Wh kg(-1), that is, a value well exceeding the one associated with the present-state Li-ion battery.

On the correlation between electrode expansion and cycling stability of graphite/Si electrodes for Li-ion batteries

A comparative study of the expansion/shrinking properties of graphite/Si electrodes with different formulations is carried out by means of electrochemical in situ dilatometry. The dilatometry reveals the impact of graphite particle size and aspect ratio as well as the binder type on the cycle life of the studied electrode formulations. Two binders, polyvinylidene fluoride (PDVF) and crosslinked carboxymethyl cellulose – polyacrylic acid (CMC/PAA) and two graphites of different particle size and aspect ratios, TIMREX® KS6 and SLP30, are used in composite electrodes and are tested in lithium half cells. The specific charge of electrodes containing Si nanoparticles and PVDF binder declines rapidly in the first cycles. The CMC/PAA based electrodes containing Si exhibit improved cycling stability and better management of dimensional changes occurring during graphite and Si (de)lithiation.

Structural and Morphological Tuning of LiCoPO4 materials Synthesized By Solvo-Thermal Methods for Li-Cell Applications

Olivine-type lithium metal phosphates (LiMPO4) are promising cathode materials for lithium-ion batteries. LiFePO4 (LFP) is commonly used in commercial Li-ion cells but the Fe3+/Fe2+ couple can be usefully substituted with Mn3+/Mn2+, Co3+/Co2+ or Ni3+/Ni2+, in order to obtain higher redox potentials. In this communication we report a systematic analysis of the synthesis condition of LiCoPO4 (LCP) using a solvothermal route at low temperature, being the latter a valuable candidate to overcome the theoretical performances of LFP. In fact LCP shows higher working potential (4.8 V vs 3.6 V) compared to LFP and similar theoretical capacity (167 mAh g-1). Our goal is to show the effect of the synthesis condition of the ability of LCP to reversibly cycle lithium in electrochemical cells. LCP samples have been prepared through a solvo-thermal method in aqueous-non aqueous solvent blends. Different Co2+salts have been used to study the effect of the anion on the crystal growth as well as the effect of solution acidity, temperature and reaction time. Materials properties have been characterized by fast-Fourier transform infrared spectroscopy, X-ray diffraction and scanning electron microscopies. The correlation between structure/morphology and electrochemical performances has been investigated by galvanostatic charge-discharge cycles in lithium half cells with a EC:DMC LiPF6 electrolyte. Going beyond the stoichiometrically-pure LCP phase, we also investigated the effect of iron doping on LCP structural features and the corresponding electrochemical properties. The simultaneous effect of iron doping and post-synthesis high-temperature annealing boosts the electrochemical performances in Li cells. The optimized material has been assempled with an high capacity anode based on a Sn-C composite to demostrate the use of an LCP-based material in a complete Li-ion cell.

Electrochemical Conversion Reaction of NiFe2O4 Electrode As an Anode Material for Li-Ion Battery

Transition metal oxides (TMOs) are recently emerged for the negative electrode of advanced lithium-ion batteries [1,2]. Two transition metal oxides NiM2O4 (where M was Fe or Mn), were synthesized by a simple and easily scalable sol-gel method and evaluated as anode materials for Li-ion batteries. Cyclic voltammetry and Galvano static charge/discharge investigations in lithium half-cells revealed a difference between the first cycle and the following charge-discharge cycles for both samples, which is characteristic for conversion-type electrode systems [3,4]. NiFe2O4 combines high abundant elements and significant lithium storage properties. Battery cycling showed that NiFe2O4 exhibited excellent discharge capacity and rate capability, nonetheless of capacity fading with cycling. From the electrochemical tests performed, the specific capacity of NiFe2O4 electrode at current rates of 10 and 20 Ag-1 were found to be 365 and 150 mAh g-1, respectively. To the best of our knowledge, reports on such outstanding capacities of NiFe2O4 nanoparticles as an anode at these high current rates are quite rare. Investigation by using Ex-situ XRD technique on the discharged and charged electrode were performed, and it was found that the material completely lost its crystallinity after first electrochemical discharge process. This fact restraint the reliability of conventional diffraction technique for the reaction mechanisms study [5]. Thus, different spectroscopic techniques are required to apply for studying the reduced/oxidized electrode vs Li [6]. X-ray absorption near-edge spectroscopy (XANES) and Extended X-ray absorption fine structure (EXAFS) spectroscopy measurements were used to study the environment of iron and nickel ions during cycling in lithium test cells. Ni K-edge and Fe K-edge XANES results give evidence of the successive steps in the reduction/oxidation mechanism of the oxide during the cell dis/charge. In a first step NiFe2O4 reacts with lithium and the reduction of both Ni2+ and Fe3+ to the zero oxidation state and following re-oxidation in a second step were shown by a peak shifting related to energy values. In the subsequent (second) discharging process, nickel oxide was found to undergo complete reduction. In contrast, more or less amount of iron oxide remained in the oxidized state at the end of the discharge (end of third cycle). This incomplete reduction of iron oxide in the applied voltage range could be the main reason behind reversible capacity fading over the cycling often reported for this conversion electrode system.

A Long-Life Lithium Ion Battery with Enhanced Electrode/Electrolyte Interface by Using an Ionic Liquid Solution.

In this paper, we report an advanced long-life lithium ion battery, employing a Pyr14 TFSI-LiTFSI non-flammable ionic liquid (IL) electrolyte, a nanostructured tin carbon (Sn-C) nanocomposite anode, and a layered LiNi1/3 Co1/3 Mn1/3 O2 (NMC) cathode. The IL-based electrolyte is characterized in terms of conductivity and viscosity at various temperatures, revealing a Vogel-Tammann-Fulcher (VTF) trend. Lithium half-cells employing the Sn-C anode and NMC cathode in the Pyr14 TFSI-LiTFSI electrolyte are investigated by galvanostatic cycling at various temperatures, demonstrating the full compatibility of the electrolyte with the selected electrode materials. The NMC and Sn-C electrodes are combined into a cathode-limited full cell, which is subjected to prolonged cycling at 40 °C, revealing a very stable capacity of about 140 mAh g(-1) and retention above 99 % over 400 cycles. The electrode/electrolyte interface is further characterized through a combination of electrochemical impedance spectroscopy (EIS) and scanning electron microscopy (SEM) investigations upon cell cycling. The remarkable performances reported here definitively indicate that IL-based lithium ion cells are suitable batteries for application in electric vehicles.

Hierarchical Carbon with High Nitrogen Doping Level: A Versatile Anode and Cathode Host Material for Long-Life Lithium-Ion and Lithium-Sulfur Batteries.

Nitrogen-rich carbon with both a turbostratic microstructure and meso/macroporosity was prepared by hard templating through pyrolysis of a tricyanomethanide-based ionic liquid in the voids of a silica monolith template. This multifunctional carbon not only is a promising anode candidate for long-life lithium-ion batteries but also shows favorable properties as anode and cathode host material owing to a high nitrogen content (>8% after carbonization at 900 °C). To demonstrate the latter, the hierarchical carbon was melt-infiltrated with sulfur as well as coated by atomic layer deposition (ALD) of anatase TiO2, both of which led to high-quality nanocomposites. TiO2 ALD increased the specific capacity of the carbon while maintaining high Coulombic efficiency and cycle life: the composite exhibited stable performance in lithium half-cells, with excellent recovery of low rate capacities after thousands of cycles at 5C. Lithium-sulfur batteries using the sulfur/carbon composite also showed good cyclability, with reversible capacities of ∼700 mA·h·g(-1) at C/5 and without obvious decay over several hundred cycles. The present results demonstrate that nitrogen-rich carbon with an interconnected multimodal pore structure is very versatile and can be used as both active and inactive electrode material in high-performance lithium-based batteries.

Effects of Propylene Carbonate Content in CsPF6-Containing Electrolytes on the Enhanced Performances of Graphite Electrode for Lithium-Ion Batteries

The effects of propylene carbonate (PC) content in CsPF6-containing electrolytes on the performances of graphite electrode in lithium half cells and in graphite∥LiNi0.80Co0.15Al0.05O2 (NCA) full cells are investigated. It is found that the performance of graphite electrode is significantly affected by PC content in the CsPF6-containing electrolytes. An optimal PC content of 20% by weight in the solvent mixtures is identified. The enhanced electrochemical performance of graphite electrode can be attributed to the synergistic effects of the PC solvent and the Cs(+) additive. The synergistic effects of Cs(+) additive and appropriate amount of PC enable the formation of a robust, ultrathin, and compact solid electrolyte interphase (SEI) layer on the surface of graphite electrode, which is only permeable for desolvated Li(+) ions and allows fast Li(+) ion transport through it. Therefore, this SEI layer effectively suppresses the PC cointercalation and largely alleviates the Li dendrite formation on graphite electrode during lithiation even at relatively high current densities. The presence of low-melting-point PC solvent improves the sustainable operation of graphite∥NCA full cells under a wide temperature range. The fundamental findings also shed light on the importance of manipulating/maintaining the electrode/electrolyte interphasial stability in various energy-storage devices.

Compatibility of microwave plasma chemical vapor deposition manufactured Si/C electrodes with new LiTDI-based electrolytes

A synthesis of new types of Si/C composite anodes for lithium-ion batteries is reported. Thin layers of graphitic carbon decorated in 3D with Si nanoparticles were produced from liquid organic precursors—1-phenyl-2-trimethylsilylacetylene and triethoxy(octyl)silane, using a one-step microwave plasma chemical vapor deposition (MPCVD) method. Thin-film Si/C electrodes were electrochemically tested in lithium half cells and produced a good reversible capacity of up to 900mAh g−1 (after 100cycles) and ~370mAh g−1, depending on the precursor type. The electrode easily endured 100cycles at 1C rate with only a 10% loss in capacity.

In-Situ Examination of Microstructural Changes within a Lithium-Ion Battery Electrode Using Synchrotron X-ray Microtomography

In this work, we use synchrotron X-ray microtomographic imaging to examine in-situ changes in a silicon / lithium half-cell before and after lithiation. We visualize volume expansion within the silicon electrode matrix and active particle fracturing as a result of the lithiation process. A change in volume fraction of silicon with respect to electrode state-of-charge was also characterized.

ChemInform Abstract: Synthesis of NixCo(1‐x)F2 (x = 0, 0.25, 0.50, 0.75, 1.0) and Application in Lithium Ion Batteries.

AbstractSolid solutions of NixCo(1‐x)F2 (x = 0, 0.25, 0.5, 0.75, 1.0) are precipitated by addition of aq.

Direct Synthesis of Carbon-Doped TiO2-Bronze Nanowires as Anode Materials for High Performance Lithium-Ion Batteries.

Carbon-doped TiO2-bronze nanowires were synthesized via a facile doping mechanism and were exploited as active material for Li-ion batteries. We demonstrate that both the wire geometry and the presence of carbon doping contribute to the high electrochemical performance of these materials. Direct carbon doping for example reduces the Li-ion diffusion length and improves the electrical conductivity of the wires, as demonstrated by cycling experiments, which evidenced remarkably higher capacities and superior rate capability over the undoped nanowires. The as-prepared carbon-doped nanowires, evaluated in lithium half-cells, exhibited lithium storage capacity of ∼306 mA h g(-1) (91% of the theoretical capacity) at the current rate of 0.1C as well as excellent discharge capacity of ∼160 mAh g(-1) even at the current rate of 10 C after 1000 charge/discharge cycles.

Nickel Hexacyanoferrate Nanoparticles as a Low Cost Cathode Material for Lithium-Ion Batteries

Potassium nickel hexacyanoferrate KNi[Fe(CN)6] (NiHCF) was synthesized by a simple co-precipitation method and investigated as a cathode material for lithium-ion batteries. The X-ray diffraction and transmission electron microscopy studies revealed the formation of pure phase of agglomerated NiHCF nanoparticles of about 20–50nm in size. The material exhibited stable cycling performance as a cathode in a lithium half-cell within a wide range of current densities, and a working potential around 3.3V vs. Li+/Li. The lithium ion diffusion coefficient in this system was determined to be in a range of 10−9 to 10−8 cm2 s−1, which is within the values for the cathode materials for lithium-ion batteries with high rate capability. Considering promising electrochemical performance and attractive lithium-ion diffusion properties of this material along with its economical benefits and simplified preparation, NiHCF could be considered as a very promising cathode for large scale lithium-ion batteries.