New perspective to understand the effect of electrochemical prelithiation behaviors on silicon monoxide (original) (raw)
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Approval of the thesis: REDUCTION OF SILICON DIOXIDE BY ELECTROCHEMICAL
2010
, 67 pages Electrochemical reductions of porous SiO2 pellets and bulk SiO2 plate were investigated in molten CaCl2 and/or CaCl2-NaCl salt mixture. The study focused on effects of temperature, particle size of the starting material, electrolyte composition and cathode design on the reduction rate. The behavior of the cathode contacting materials was also examined. Moreover, cyclic voltammetry study was conducted to investigate the mechanism of the electrochemical reaction. Mainly, XRD analysis and SEM examinations were used for characterizations. The rates of electrochemical reduction were interpreted from the variations of current and accumulative electrical charge that passed through the cell as a function of time under different conditions. The results showed that reduction rate of SiO2 increased slightly with increasing temperature or decreasing the particle size of SiO2 powder. Higher reduction rate was obtained when porous pellet was replaced by bulk SiO2 plate. Use of Kanthal wire mesh around the SiO2 cathode increased but addition of NaCl to the electrolyte decreased the reduction rate. v X-ray diffraction results confirmed the reduction of SiO2 to Si in both CaCl2 salt and CaCl2-NaCl salt mixture. However, silicon produced at the cathode was contaminated by the nickel and stainless steel plates which were used as the cathode contacting materials. Microstructures and compositions of the reduced pellets were used to infer that electrochemical reduction of SiO2 in molten salts may become a method to produce solar grade silicon (SOG-Si). In addition, overall reduction potential of SiO2 pellet against the graphite anode and the potential of the cathode reaction at 750°C in molten CaCl2-NaCl salt mixture were determined as 2.3 V (at 1.19 A current) and 0.47 V, respectively by cyclic voltammetry.
Electrochemistry Communications, 1999
The effects of anodic polarization of p-Si electrodes in alkaline medium have been investigated by the probe beam deflection (PBD) or 'mirage' technique and the optical cantilever or bending beam method (BBM). The PBD technique permits a monitoring of dissolution and passivation processes and provides an estimate of the oxide etchback times during open circuit corrosion. The BBM technique has been used to estimate the stress of the thin oxide layer, which appears to be in the order of 180 MPa for very thin oxide films (nm range). The result is discussed in comparison with literature properties of thermally generated oxides.
A New View of Silicon Electrochemistry
physica status solidi (a), 2000
The salient features of the current burst model for the Si-electrolyte interface is presented in a short overview. In the current burst model, charge transfer at the Si-electrolyte interface is localized in space and time and intrinsically stochastic; all phenomena encountered in Si electrochemistry then are manifestations of the nucleation probabilities for current bursts, which depend on the system parameter in an unambiguous way. One of the unique features of the model is the existence of an internal time constant (equal to the average duration of a current pulse) which ultimately is the reason for the observed oscillations of the current in time and in space-the latter case describing pores. For pores, the intrinsic time constant is expressed as an intrinsic length scale which is determined by the interaction of current bursts within the same cycle, i.e. by the size of synchronized domains. The pore morphology is the result of the interaction of the intrinsic length scale with external length scales, e.g. the space charge region depth; smooth macropores are obtained when the relevant length scales are similar. The existence of an intrinsic time constant and length scale will be demonstrated by resonance phenomena which were observed for the first time in pore growth.
Journal of Power Sources, 2012
Silicon which has a theoretical capacity around 3500 mAh g −1 and low insertion/deinsertion potentials is one of the most promising candidates to replace graphite as a negative electrode in lithium-ion batteries. Electrochemical performances of Si electrodes are highly dependent on the quality of the SEI. Therefore, the effect of an electrolyte additive, the vinylene carbonate (VC) on electrochemical performances was investigated on sputtered silicon thin films which constitute a simple system (avoiding the use of binders or any conducting additive material). The addition of only 2% of VC significantly improves the capacity retention as well as the coulombic efficiency leading to a capacity retention of 84% after 500 cycles and a coulombic efficiency around 99.5%. To explain the behaviour differences, thorough electrochemical analyses (capacity, coulombic efficiency, polarization at half charge.. .) combined with scanning electron and atomic force microscopies were carried out. Some correlations have been established between the electrochemical performances and the morphology evolution of the electrode. Thus, VC limits the formation of cracks induced by repeated expansion/contraction cycles and the liquid electrolyte/electrode interactions. In addition, the mechanical pressure locally applied to the thin film allows to maintain a dense morphology and hence has a beneficial effect, too. These two key parameters limit the deterioration of the electrode over cycles.
This work focuses on the mechanisms of interfacial processes at the surface of amorphous silicon thin-film electrodes in organic carbonate electrolytes to unveil the origins of the inherent non-passivating behavior of silicon anodes in Li-ion batteries. Attenuated total reflection Fouriertransform infrared spectroscopy (ATR-FTIR), X-ray absorption spectroscopy (XAS), and infrared near-field scanning optical microscopy (IR aNSOM) were used to investigate the formation, evolution and chemical composition of the surface layer formed on Si upon cycling. We found that the chemical composition and thickness of the solid/electrolyte interphase layer (SEI) continuously change during the charging/discharging cycles. This SEI layer "breathing" effect is directly related
Surfaces and Interfaces, 2020
The role of substrate orientation on the electrochemical lithiation of single crystalline Si has been investigated using Si single crystal having two orientations. It has been demonstrated that the lithiation process in Si (100) occurs via amorphization while that in Si (111) occurs through the intermediacy of various Li-Si alloying phases ranging from Li x Si to Li 15 Si 4. Three phase lithiation process has been observed in Si (111). Post electrochemical cycling analysis by ex-situ XRD, XPS and AFM studies reveals that the lithiation in two differently oriented Si facets {i.e. Si (100) and Si (111)} indeed occurs differently. The model developed on the basis of insights gained from the AFM studies also supports the hypothesis built on the basis of initial CV measurements.
Properties of silicon-electrolyte junctions and their application to silicon characterization
Applied Physics A Solids and Surfaces, 1991
A number of interesting and still not fully understood phenomena occur if silicon is used as an electrode in an electrochemical cell. Effects include porous silicon layer (PSL) formation with features on a nan0meter scale, surface roughening on a micrometer scale, quantum efficiencies for light generated currents much larger than 1, preferential etching of defects, electropolishing, and voltage or current oscillations. It is shown that despite the complexities of chemical reactions involved, a basic understanding of the electrode behavior is possible from a semiconductor physics point of view and that it can be advantageous to use the siliconelectrolyte junction for analytical purposes. Topics such as defect characterization, measurements of minority carrier diffusion length, or surface recombination velocities can be addressed in unique ways by taking advantage of particular properties of the silicon-hydrofluoric acid system. Based on the general description of the Si-electrolyte junction given in this paper, strengths and limitations of some electrochemical methods are discussed in some detail and illustrated by examples. a) b) to Silicon Characterization 9
The Journal of Physical Chemistry C
A pluri-disciplinary approach and a combination of techniques are used here to finely describe the surface of silicon nanoparticles used as active material in negative composite electrodes for lithium batteries. Although the surface of silicon particles is playing a major role in the electrochemical performance, it has rarely been characterized in depth. With respect to infrared analysis, we propose an analytical protocol, derived from the studies devoted to high specific area silica samples. Three different nanometric silicon powders are studied: a commercial one and two home synthesized silicon powders with specially designed surfaces. With respect to previous works and common belief, we demonstrate, on the electrochemical performance, a favorable effect of a particular thin layer silicon oxide with a well-defined SiO2 composition at the extreme surface of the silicon particles.
Influence of silicon nanoparticle coating on the electrolyte decomposition in Li-ion batteries
2016
In chapter 5, the mechanical properties of several applied coatings are tested during (dis)charging using in situ transmission electron microscopy. Table of contents Chapter 1: Introduction 1.1 Why do we need batteries? 1.2 History of the battery 1.3 Li-ion technology 1.3.1 Development of Li-ion technology 1.3.2 Positive electrode materials 1.3.3 The electrolyte 1.3.4 Negative electrode materials 1.4 How can silicon replace graphite as a negative electrode material? 1.4.1 The negative electrode market 1.4.2 Challenges in the use of silicon as a negative electrode material 1.4.3 Approaches to increase the cyclability of Si-based electrodes 1.5 The contribution of this thesis Chapter 2: Experimental setups 2.1 Battery setup 2.1.1 Types of batteries 2.