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Electrolyte additives have been explored to attain significant breakthroughs in the long-term cycling performance of lithium-ion batteries (LIBs) without sacrificing energy density; this has been a...

In this work, we explore how the chemical reactivity toward an aprotic battery electrolyte changes as a function of lithium salt and silicon surface termination chemistry. The reactions are highly ...

Funding Information: Funding from the European Comission and Tecnio Spring under the Grant agreement TECSPR18-1-0049 Towards High Energy All Solid State Lithium Batteries (SOLBAT) is gratefully acknowledged. IREC acknowledges support of Generalitat de Catalunya. The authors like to acknowledge the support of Aalto University. Publisher Copyright: © 2022, The Author(s). This paper presents the electrochemical performance and characterization of nano Si electrodes coated with titanicone (TiGL) as an anode for Li ion batteries (LIBs). Atomic layer deposition (ALD) of the metal combined with the molecular layer deposition (MLD) of the organic precursor is used to prepare coated electrodes at different temperatures with improved performance compared to the uncoated Si electrode. Coated electrodes prepared at 150 °C deliver the highest capacity and best current response of 1800 mAh g−1 at 0.1 C and 150 mAh g−1 at 20 C. This represented a substantial improvement compared to the Si baseline which delivers a capacity of 1100 mAh g−1 at 0.1 C but fails to deliver capacity at 20 C. Moreover, the optimized coated electrode shows an outstanding capacity of 1200 mAh g−1 at 1 C for 350 cycles with a capacity retention of 93%. The improved discharge capacity, electrode efficiencies, rate capability and electrochemical stability for the Si-based electrode presented in this manuscript are directly correlated to the optimized TiGL coating layer deposited by the ALD/MLD processes, which enhances lithium kinetics and electronic conductivity as demonstrated by equivalent circuit analysis of low frequency impedance data and conductivity measurements. The coating strategy also stabilizes SEI film formation with better Coulombic efficiencies (CE) and improves long cycling stability by reducing capacity lost.

Silicon anodes promise high energy densities of next-generation lithium-ion batteries, but suffer from shorter cycle life. The accelerated capacity fade stems from the repeated fracture and healing of the solid-electrolyte interphase (SEI) on the silicon surface. This interplay of chemical and mechanical effects in SEI on silicon electrodes causes a complex aging behavior. However, so far, no model mechanistically captures the interrelation between mechanical SEI deterioration and accelerated SEI growth. In this article, we present a thermodynamically consistent continuum model of an electrode particle surrounded by an SEI layer. The silicon particle model consistently couples chemical reactions, physical transport, and elastic deformation. The SEI model comprises elastic and plastic deformation, fracture, and growth. Capacity fade measurements on graphite anodesand in-situ mechanical SEI measurements on lithium thin films provide parametrization for our model. For the first time, we model the influence of cycling rate on the long-term mechanical SEI deterioration and regrowth. Our model predicts the experimentally observed transition in time dependence from square-root-of-time growth during battery storage to linear-in-time growth during continued cycling. Thereby our model unravels the mechanistic dependence of battery aging on operating conditions and supports the efforts to prolong the battery life of next-generation lithium-ion batteries., 15 pages, 13 figures

The solid electrolyte interphase (SEI) layer on a silicon anode is investigated by SERS. Gold electrodeposition on a silicon electrode is confirmed by SEM, and Raman enhancement is proved, allowing determination of the partial composition of its SEI. For the first time, organophosphate-derivatives seem to be detected by Raman.

Understanding the failure mechanisms of solid electrolyte interphases (SEI) is important for silicon electrodes because their volume expands substantially during lithiation. This work discusses mat...

A critical review and assessment of 3D columnar Si electrode architectures, as negative electrodes for Li-ion cells, has been undertaken to provide insight on the structure parameters that enable high specific and total Li-storage capacities and high cycling performance. The selected set represents a sufficiently wide variety of columnar architectures, covering most of the possible routes of fabrication, including etching, patterning, photolithography and micromachining. The outcome of this evaluation identifies the structural factors that determine the best performing 3D electrode architecture. Specifically, electrodes with a high mass loading have been shown to correlate very well with high total capacities for Li-storage. Thus, the preferred 3D electrode structures are identified as those with columns of Si with an optimum porosity giving high enough mass loading, but with a balanced column depth and spacing providing effective volume accommodation during cell cycling. The review also provides details of experimental validations of the optimum electrode architecture, which effectively accommodates the volume change, and enables cycling for a larger number of cycles.

Microelectrode arrays form the basis of electrochemical sensing devices because of their unique properties, such as enhanced mass transport and steady-state diffusion currents. However, they demand a predefined and rigid geometry, and require a connecting pad for each element of the array. Here it is reported the formation of microelectrode arrays whose geometry is defined by the shape of a light pattern projected on an unstructured silicon electrode. Spatiotemporally resolved fluxes of charge carriers are used to confine a model electrochemical reaction only to the illuminated areas. Using spatial light modulators, microelectrode geometry is adjusted instantaneously, at will, on a homogeneous semiconductor electrode carrying a single electrical connection. By developing a theoretical model to analyse the current−potential data, it is revealed within which limits spatial light modulation can be used to enhance, on silicon, the mass transport of a diffuse redox system.

In this work we explore how an electrolyte additive (fluorinated ethylene carbonate – FEC) mediates the thickness and composition of the solid electrolyte interphase formed over a silicon anode in situ as a function of state-of-charge and cycle. We show the FEC condenses on the surface at open circuit voltage then is reduced to C-O containing polymeric species around 0.9 V (vs. Li/Li+). The resulting film is about 50 Å thick. Upon lithiation the SEI thickens to 70 Å and becomes more organic-like. With delithiation the SEI thins by 13 Å and becomes more inorganic in nature, consistent with the formation of LiF. This thickening/thinning is reversible with cycling and shows the SEI is a dynamic structure. We compare the SEI chemistry and thickness to 280 Å thick SEI layers produced without FEC and provide a mechanism for SEI formation using FEC additives.

Author(s): Joo, Hannah R; Fan, Jiang Lan; Chen, Supin; Pebbles, Jeanine A; Liang, Hexin; Chung, Jason E; Yorita, Allison M; Tooker, Angela C; Tolosa, Vanessa M; Geaghan-Breiner, Charlotte; Roumis, Demetris K; Liu, Daniel F; Haque, Razi; Frank, Loren M | Abstract: ObjectiveElectrode arrays for chronic implantation in the brain are a critical technology in both neuroscience and medicine. Recently, flexible, thin-film polymer electrode arrays have shown promise in facilitating stable, single-unit recordings spanning months in rats. While array flexibility enhances integration with neural tissue, it also requires removal of the dura mater, the tough membrane surrounding the brain, and temporary bracing to penetrate the brain parenchyma. Durotomy increases brain swelling, vascular damage, and surgical time. Insertion using a bracing shuttle results in additional vascular damage and brain compression, which increase with device diameter; while a higher-diameter shuttle will have a higher critical load and more likely penetrate dura, it will damage more brain parenchyma and vasculature. One way to penetrate the intact dura and limit tissue compression without increasing shuttle diameter is to reduce the force required for insertion by sharpening the shuttle tip.ApproachWe describe a novel design and fabrication process to create silicon insertion shuttles that are sharp in three dimensions and can penetrate rat dura, for faster, easier, and less damaging implantation of polymer arrays. Sharpened profiles are obtained by reflowing patterned photoresist, then transferring its sloped profile to silicon with dry etches.Main resultsWe demonstrate that sharpened shuttles can reliably implant polymer probes through dura to yield high quality single unit and local field potential recordings for at least 95 days. On insertion directly through dura, tissue compression is minimal.SignificanceThis is the first demonstration of a rat dural-penetrating array for chronic recording. This device obviates the need for a durotomy, reducing surgical time and risk of damage to the blood-brain barrier. This is an improvement to state-of-the-art flexible polymer electrode arrays that facilitates their implantation, particularly in multi-site recording experiments. This sharpening process can also be integrated into silicon electrode array fabrication.

The understanding of volume change mechanism of silicon electrode is necessary to design a new negative electrode using silicon-based active materials. Here, the drastic volume expansion of one silicon secondary particle with μm-size was in-situ observed in order to find apparent volume expansion ratio during the first charging by using single particle measurement technique. The apparent volume expansion accompanied with the first lithiation is much larger than theoretical expectation due to the agglutination state and anisotropic property. The importance of direct observation with the single particle measurement has been affirmed for understanding the characteristics of silicon electrodes.

In this study we employed a quantitative immunohistochemical approach to compare the brain tissue response to planar silicon microelectrode arrays that were conformally coated with Parylene-C to uncoated controls at 2, 4, and 12 weeks following implantation into the cortex of adult male Sprague-Dawley rats. We did not find any difference in the relative intensity or the spatial distribution of neuronal or glial markers over the indwelling period, even though Parylene-C-coated substrates supported significantly less cell attachment, indicating that the foreign body response to planar silicon microelectrode arrays has little to do with the composition or decomposition of the silicon electrode. Moreover, our results suggest that changes in microelectrode surface chemistry do not have a strong influence on the cytoarchitectural changes that accompany the brain foreign body response to planar silicon microelectrode arrays. Our quantitative comparison over the indwelling period does not support progressive increases in astrocyte encapsulation and/or progressive neuronal loss in the recording zone as dominant failure mechanisms of the type of chronic recording device. Finally, we found evidence of two potentially new failure mechanisms that were associated with CD68 immunoreactivity including demyelination of adjacent neurons and BBB breakdown surrounding implanted electrodes at long indwelling times.

We demonstrate highly directional etching in silicon 100 nm in diameter with an aspect ratio of 160 with no spiking on the pore walls using magnetic-field-assisted anodization. The relationship between the surface geometry of a silicon electrode and its highly directional etching properties have been investigated. Specifically, we show that the pore shape and pore wall orientation are not determined by the surface pattern but by the etching mechanisms specific to the magnetic-field-assisted anodization. These etching mechanisms enable highly directional and high aspect ratio etching at diameters below 100 nm in scale.

The silicon probe with highly P-doped Si electrodes was realized on 8 inch SOI wafer through standard CMOS process. After additional coatings of nano-composite (CNTs + Au nanoparticles) on silicon electrodes, the functionality of neural recording was verified with a low noise level (< 20 μV) during in vivo recording on rat brain. With built-in silicon nanowires (SiNWs) based piezoresistiors connected in full bridge structure, the capability of monitoring probe mechanical behavior was firstly examined with the probe buckling experiments and further proven through in vivo implantations on rat brain. Besides the large buckling mechanics (during probe insertion), the physiological brain micro-motion (e.g. caused by respiration) was successfully picked up by integrated SiNWs strain sensors. The integrated neural device (including both neural electrode and localized strain sensor) provides the possible research platform to practically understand the correlation between the recorded electrical neural signal and the brain micro-motion.

Nanosized silver particles were uniformly distributed on the surface of silicon particles by electroless deposition (ED) and high-energy mechanical milling (HEMM) methods, respectively. The HEMM-prepared Si/Ag composite with 10 wt.% silver exhibited a high first coulombic efficiency of 83.4% and a large capacity of ca. 800 mA h g − 1 over 30 cycles as a result of conductivity enhancement. It was suggested that electric contact between silicon particles played a significant role in improving the cyclability of silicon electrode.

Two different interfaces prepared via UV-hydrosilylation of undecylenic acid and 1,8-nonadiyne on silicon(111) have been explored to develop a robust electrochemical DNA sensor. Electrodes modified with undecylenic acid were found to stably immobilise DNA but could not resist the growth of insulating oxides, whereas 1,8-nonadiyne modified electrodes satisfy both requirements.

The H-terminated n -Si(111) surface is found to be etched locally under the STM tip in the dilute HF solution by applying a given positive potential to the tip while keeping the silicon electrode potential near its flat-band potential, at which the oxidative etching of silicon is not expected to occur in the absence of light. The induced etching rate is shown to depend on the tunneling current. The mechanism of the etching process is proposed on the basis that the tunneling of electrons occurs directly from the valence band of the silicon electrode into the empty states at the tip, leading to a hole injection in the silicon surface, followed by an electrochemical oxidation on the local surface underneath the tip.

A memory effect occurring on silicon electrodes during lithium insertion/deinsertion was revealed by means of electrochemical characterizations. The reversible capacity fading is triggered when the electrodes are cycled between Li-rich compositions, which are actually achieved in selected conditions (current density, voltage window, electrode thickness). It is correlated with a structural evolution of Li-rich alloys, i.e. the crystallization of Li15Si4 or the probable ordering of other Li-rich phases. It should be avoided in Li-ion practical cells by an appropriate cell design. Keywords: Memory effect, Silicon electrode, Lithium–silicon alloys, Li15Si4, Lithium-ion batteries

cited By 83; International audience; Silicon presents a very high theoretical capacity (3578 mAh/g) and appears as a promising candidate for the next generation of negative electrodes for Li-ion batteries. An important issue for the implementation of silicon is the understanding of the interfacial chemistry taking place during charge/discharge since it partly explains the capacity fading usually observed upon cycling. In this work, the mechanism for the evolution of the interfacial chemistry (reaction of surface oxide, Li-Si alloying process, and passivation layer formation) upon long-term cycling has been investigated by photoelectron spectroscopy (XPS or PES). A nondestructive depth resolved analysis was carried out by using both soft X-rays (100-800 eV) and hard X-rays (2000-7000 eV) from two different synchrotron facilities. The results are compared with those obtained with an in-house spectrometer (1486.6 eV). The important role played by the LiPF6 salt on the stability of the silicon electrode during cycling has been demonstrated in this study. A partially fluorinated species is formed upon cycling at the outermost surface of the silicon nanoparticles as a result of the reaction of the materials toward the electrolyte. We have shown that a similar species is also formed by simple contact between the electrolyte and the pristine electrode. The reactivity between the electrode and the electrolyte is investigated in this work. Finally, we also report in this work the evolution of the composition and covering of the SEI upon cycling as well as proof of the protective role of the SEI when the cell is at rest. © 2013 American Chemical Society.

International audience; The local composition of negative silicon electrodes is studied by ex situ electron energy-loss spectroscopy along the first delithiation in a lithium battery. By measuring dozens of sample areas for over a dozen compositions, the local and overall inhomogeneities in these practical electrodes are evaluated. The statistical treatment of the data highlights the existence of larger inhomogeneities at the beginning of the delithiation as well as at a 100 nm scale. It is also shown that, even if incremental capacity curves are different, the compositional changes during delithiation are identical for nano- and micro-Si. Namely, an initial Li15Si4 phase is replaced by a Li2±0.3Si amorphous phase in a biphasic process, the latter compound being further delithiated to amorphous silicon in single phase process. Results also show that the electrochemical irreversibility associated with the liquid electrolyte reduction/degradation is generated during the lithiation process, not the delithiation process.

Electrodes on planar type microelectromechanical system (MEMS) microprobes mainly record neurons on the top-side of probe shaft (called a top-side electrode). However, it is often necessary to record neurons other than those on the top-side of the probe shaft. This study uses the glass reflowing technique to embed silicon-vias in a glass probe to implement a microprobe capable of recording neurons around the shaft. The proposed technology makes it possible to fabricate, distribute, and integrate four types of electrodes on the shaft: top-side, back-side, double-side, and sidewall electrodes. These electrodes have different recording characteristics. The in vitro and in vivo (using crayfish and rat brain) experiments in this study shows that the top-side and back-side electrodes are respectively more sensitive to neurons on the top-side and back-side of the probe shaft. In contrast, signals recorded by double-side electrode and sidewall electrode are equally sensitive to neurons around the probe shaft. This study enables the implementation and integration of these four types of electrodes, meeting the requirements of various neural applications.

Micro-machined silicon microelectrodes are useful for obtaining high-density, high-spatial resolution sampling of neuronal activity within the brain, and hold promise for revealing the spatiotemporal dynamics of local circuits. However, the fragile nature of silicon electrodes precludes their application in chronic recordings for a long period of time in which electrodes are repeatedly passed through the hardened dura matter. Here, we describe a newly developed holder designed to make a micro-perforation through the dura matter in which a silicon electrode can easily be inserted.

This article highlights recent developments in the assembly of nanosize materials on electrode surfaces. A brief historical background of the field is given, followed by a selection of topics of particular current interest. We focus especially on the assembly of nanosize metallic particles and molecular wires on gold and silicon electrode surfaces. The fabrication, properties, and characteristics of functional nanostructured biointerfaces on electrode surfaces are also described.