SEI-component formation on sub 5 nm sized silicon nanoparticles in Li-ion batteries: The role of electrode preparation, FEC addition and binders

Silicon is a promising negative electrode for secondary lithium-based batteries, but the electrochemical reversibility of particularly nanostructured silicon electrodes drastically depends on their interfacial characteristics, commonly known as the solid electrolyte interface (SEI). The beneficial origin of certain electrolyte additives or different binders is still discussed controversially owing to the challenging peculiarities of interfacial post-mortem investigations of electrodes. In this work, we address the common difficulties of SEI investigations of porous silicon/carbon nanostructures and study the addition of a fluoroethylene carbonate (FEC) as a stabilizing additive as well as the use of two different binders, carboxymethyl cellulose/styrene-butadiene rubber (CMC/SBR) and polyacrylic acid (PAA), for the SEI formation. The electrode is composed of silicon nanocrystallites below 5 nm diameter allowing a detailed investigation of interfacial characteristics of silicon owing to the high surface area. We first performed galvanostatic long-term cycling (400 times) and carried out comprehensive ex situ characterization of the cycled nanocrystalline silicon electrodes with XRD, EDXS, TEM and XPS. We modified the preparation of the electrode for post-mortem characterization to distinguish between electrolyte components and the actual SEI. The impact of the FEC additive and two different binders on the interfacial layer is studied and the occurrence of diverse compounds, in particular LiF, Li2O and phosphates, is discussed. These results help to understand general issues in SEI formation and to pave the way for the development of advanced electrolytes allowing for a long-term performance of nanostructured Si-based electrodes

Lifetime vs. rate capability: Understanding the role of FEC and VC in high-energy Li-ion batteries with nano-silicon anodes

Fluoroethylene carbonate (FEC) and vinylene carbonate (VC) are the most frequently used electrolyte components to enhance the lifetime of anode materials in Li-ion batteries, but for silicon it is still ambiguous when FEC or VC is more beneficial. Herein, a nanostructured silicon/carbon anode derived from low-cost HSiCl3 is tailored by the rational choice of the electrolyte component, to obtain an anode material outperforming current complex silicon structures. We demonstrate highly reversible areal capacities of up to 5 mA h/cm2 at 4.4 mg/cm2 mass loading, a specific capacity of 1280 mA h/gElectrode, a capacity retention of 81% after 500 deep-discharge cycles versus lithium metal and successful full-cell tests with high-voltage cathodes meeting the requirements for real application. Electrochemical impedance spectroscopy and post-mortem investigation provide new insights in tailoring the interfacial properties of silicon-based anodes for high performance anode materials based on an alloying mechanism with large volume changes. The role of fluorine in the FEC-derived interfacial layer is discussed in comparison with the VC-derived layer and possible degradation mechanisms are proposed. We believe that this study gives a valuable understanding and provides new strategies on the facile use of additives for highly reversible silicon anodes in Li-ion batteries.Fil: Jaumann, Tony. Ifw Dresden; AlemaniaFil: Balach, Juan Manuel. Ifw Dresden; AlemaniaFil: Langklotz, Ulrike. Technische Universität Dresden; AlemaniaFil: Sauchuk, Viktar. Fraunhofer Institute for Ceramic Materials and Systems; AlemaniaFil: Fritsch, Marco. Fraunhofer Institute for Ceramic Materials and Systems; AlemaniaFil: Michaelis, Alexander. Technische Universität Dresden; AlemaniaFil: Teltevskij, Valerij. Leibniz Institute for Solid State and Materials Research; AlemaniaFil: Mikhailova, Daria. Leibniz Institute for Solid State and Materials Research; AlemaniaFil: Oswald, Steffen. Leibniz Institute for Solid State and Materials Research; AlemaniaFil: Klose, Markus. Leibniz Institute for Solid State and Materials Research; Alemania. Technische Universität Dresden; AlemaniaFil: Stephani, Guenter. Branch Lab Dresden. Fraunhofer Institute for Manufacturing Technology and Advanced Materials; ArgentinaFil: Hauser, Ralf. Branch Lab Dresden. Fraunhofer Institute for Manufacturing Technology and Advanced Materials; ArgentinaFil: Eckert, Jürgen. Technische Universität Dresden; Alemania. Leibniz Institute for Solid State and Materials Research; AlemaniaFil: Giebeler, Lars. Leibniz Institute for Solid State and Materials Research; Alemania. Technische Universität Dresden; Alemani

Lifetime vs. rate capability: Understanding the role of FEC and VC in high-energy Li-ion batteries with nano-silicon anodes

Fluoroethylene carbonate (FEC) and vinylene carbonate (VC) are the most frequently used electrolyte components to enhance the lifetime of anode materials in Li-ion batteries, but for silicon it is still ambiguous when FEC or VC is more beneficial. Herein, a nanostructured silicon/carbon anode derived from low-cost HSiCl3 is tailored by the rational choice of the electrolyte component, to obtain an anode material outperforming current complex silicon structures. We demonstrate highly reversible areal capacities of up to 5 mA h/cm2 at 4.4 mg/cm2 mass loading, a specific capacity of 1280 mA h/gElectrode, a capacity retention of 81% after 500 deep-discharge cycles versus lithium metal and successful full-cell tests with high-voltage cathodes meeting the requirements for real application. Electrochemical impedance spectroscopy and post-mortem investigation provide new insights in tailoring the interfacial properties of silicon-based anodes for high performance anode materials based on an alloying mechanism with large volume changes. The role of fluorine in the FEC-derived interfacial layer is discussed in comparison with the VC-derived layer and possible degradation mechanisms are proposed. We believe that this study gives a valuable understanding and provides new strategies on the facile use of additives for highly reversible silicon anodes in Li-ion batteries

Micro‐electrochemical investigation of the passive behavior of thin anodic titanium oxide films on TiAlV6‐4

The present work describes the passive film behavior of thin anodic oxide films on polycrystalline TiAlV6‐4. Firstly, the influence of the microstructure was addressed. Therefore, the crystallographic grain orientations of the substrate were determined by EBSD and selected grains were investigated with an electrochemical micro‐capillary cell. The barrier‐like oxide films were produced by local anodization in an acetate buffered electrolyte (pH 5.9) and investigated by electrochemical impedance spectroscopy and optical reflectometry. Second, the chemical composition of the native oxide film was determined by XPS, and the results related with the micro‐electrochemical experiments. The work shows a strong effect of the basal orientation on the electrochemical behavior. During anodic oxidation, strong electron transfer reactions occur at this orientation, while the enhanced conductivity of the oxide film is also proved by electrochemical impedance spectroscopy. Moreover, a non‐highfield conformal oxide growth and crystallization was observed on the basal plane. These effects, especially the electron conductivity, is related to the incorporation of alloying elements in the passive film

Microelectrochemical investigation of anodic oxide formation on the aluminum alloy AA2024

The present paper deals with the influence of the most relevant intermetallic phases (S- and Θ-phases) of the aluminum alloy AA2024 under anodizing conditions in citric acid. The study is a combinatorial approach of localized microelectrochemistry and complementary material diagnostic using SEM/EDX-analysis. The EDX-analysis is carried out quantitatively. It is shown that different individual electrochemical processes, e.g. anodic oxide formation and corrosion effects, superimpose and dominate the anodizing process at different time scales. The complexing effect of citric acid on copper can be excluded at the chosen acidic pH value. Though, the formation of obviously dense barriers such as oxide films leads to a oxidation behavior in citric acid similar to the anodizing in neutral electrolytes

Ionically conductive polymer/ceramic separator for lithium-sulfur batteries

Lithium-sulfur batteries are highly promising as energy storage device for various applications due to their high theoretical energy densities, though their full potential is not yet reached. The cell component with the highest potential for overcoming the well-known degradation effects of the polysulfide shuttle during cycling is the separator. This study reports on a polymer/ceramic separator, which efficiently enhances the cell performance. Therefore, we prepared a series of polyvinylidenfluoride-hexafluoropropylene (PVdF-HFP) membranes with different amounts of a NASICON type ceramic of high intrinsic lithium ion conductivity. Electrochemical testing proves the good ionic conductivity of the composite separator as well as the reduced polysulfide shuttle within the cell

The combination of minimally invasive electrochemical investigations and FTIR-spectroscopy to analyze atmospheric corrosion product layers on zinc

The present work describes the combination of electrochemical investigations by using a gel-type electrolyte with Fourier-transformed infrared spectroscopy to investigate partially extremely thin corrosion product films on titanium-zinc. The gel pad method enables the determination of corrosion relevant parameters such as the potential and the linear polarization resistance without altering the corrosion product layers, which are extremely prone to re-dissolution when freshly formed. Complementary infrared spectroscopy enables the determination of main compounds of even very thin surface layers of few tenth of nanometers with a certain lateral resolution. It was found that zinc forms mostly zinc carboxy-hydroxides such as hydrozincite, under various exposure conditions. The protective properties of these hydrozincite layers depend on the structure of the corrosion product film rather than on its thickness. In mid-term exposure tests, shallow corrosion pits were found even in the absence of corrosive agents such as chloride

3D-cathode design with foam-like aluminum current collector for high energy density lithium-ion batteries

Increasing the area specific capacity and reducing the inactive/active material ratio of cathodes and anodes is considered to be a promising approach to improve the energy density of lithium-ion batteries. In principle, this can be achieved by increasing the thickness and the active material mass loading of the electrodes. However, the fabrication of thick electrodes with good electrochemical performance is challenging regarding the drying process, mechanical stability, electronic conductivity, etc. The application of Al-foams as current collector provides a 3D electronic conductive network, which can host high loadings of active material combined with high mechanical stability. Herein, we demonstrate a slurry infiltration process capable to fabricate cathodes with high active material loading. A variety ofLiNi1/3Mn1/3Co1/3O2 (NMC111) based cathodes with thicknesses up to 260 mm and area specific capacities high as 7 mAh cm 2 are investigated comprehensively. The electrodes exhibit good cycle life and rate capability performance due to the unique 3D current collector concept. Even at the 2.0C discharge rate, an area specific capacity of 2.3 mAh cm 2 is obtained, which is high in comparison to conventional Al-foil concepts. The design freedom of the presented approach is illustrated by the fabrication of cathodes optimized for high rate capability

Electrochemical single-particle measurements of electrode materials for Li-ion batteries: Possibilities, insights and implications for future development

The development of high performance active storage materials is considered one of the most promising approaches to increase the energy and power density of secondary batteries. The assessment of novel or refined active materials is typically done using composite electrodes, consisting of an active material, binder, conductive additive mixture coated on a metallic current collector foil. The electrochemical properties of such composite electrodes are known to be affected by their design, microstructure and composition, hence not representing the intrinsic properties of the active material employed. To overcome these constraints, researchers developed single-particle measurements (SPMs) that allow stripping away any matrix effects and determining the intrinsic properties of the active material used. Herein, the research progress of SPMs for investigations of active materials for secondary batteries is reviewed. The different experimental approaches to realize SPMs are presented and advantages and disadvantages are discussed. Results obtained with SPMs and composite electrodes are compared, regarding typical battery performance metrics and the analysis of insertion kinetics. The insights gained from the SPMs are discussed with respect to the most expedient development trends of future secondary batteries

The influence of different pre-treatments of current collectors and variation of the binders on the performance of Li4Ti5O12 anodes for lithium ion batteries

In order to optimize the electron transfer between the Li4Ti5O12-based active mass and the current collector, the surface of aluminum foil was modified either by alkaline etching or by a carbon coating. The as-modified aluminum foils were coated with an active mass of Li4Ti5O12 mixed with polyvinylidene fluoride, sodium carboxymethyl cellulose, or polyacrylic acid as binders. Untreated aluminum and copper foils served as reference current collectors. The corrosion reactions of aluminum foil with the applied binder solutions were studied and the electrode structure has been analyzed, depending on the binder. Finally, the electrochemical performance of the prepared electrodes was investigated. Based on these measurements, conclusions concerning the electrical contact between the different current collectors and the active masses were drawn. The energy density of the Li4Ti5O12 electrodes cast on carbon-coated aluminum foils was significantly increased, compared to the corresponding electrodes with a copper current collector