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This study shows that storage for a few days in humid air before cell assembling of Si-carboxymethyl cellulose (CMC) composite electrode prepared with a slurry buffered at pH 3 has a major positive impact on its cycle life and coulombic efficiency. Diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy analysis shows that water molecules in humid air partly convert the ester bonds between Si particles and CMC binder into less rigid hydrogen bonds. Complementary to cycling tests, scanning electron microscopy (SEM) observations suggest that the mechanical integrity of the film is better maintained for an optimal ratio of ester bonds to hydrogen bonds between Si particles and the CMC chains. Such a favorable impact of storage in humid air on the cycling behavior of a composite electrode for lithium battery was unexpected when compared to standard practices that show a detrimental aging of active electrode materials when exposed to water. [ABSTRACT FROM AUTHOR]

A simple technique for patterning multilayer graphene shell encapsulated gold nanoparticles (GNPs) on the silicon substrate and their further surface decoration with semiconducting quantum dots (QDs) is reported. This leads to the fabrication of a novel silicon electrode decorated with GNP-QD hybrids or heterostructures. The morphology, structure, and composition of the GNPs and GNP-QD heterostructures were evaluated using microscopic and spectroscopic techniques. The heterostructures decorated silicon electrode was also evaluated for the electronic and electrochemical properties. The results showed that the electrical characteristics of the silicon substrate were significantly improved by decorating with GNPs and quantum dots. Furthermore, GNP-QD heterostructure electrode was observed to show significantly increased electrochemical charge transfer activity. [ABSTRACT FROM AUTHOR]

In this study, nickel plated silicon powders were produced using an electroless deposition process. The nickel content on the surface of silicon powders was changed by using different concentrations of NiCl 2 in the plating bath. The surface morphology of the produced Ni plated composite powders was characterized using scanning electron microscopy (SEM). Energy dispersive spectroscopy (EDS) was used to determine the elemental surface composition of the composites. X-ray diffraction (XRD) analysis was performed to investigate the structure of the nickel plated silicon powders. Electrochemical cycling test of the nickel plated silicon electrodes were performed at a constant current of 100 mA/g in CR2016 test cells. In order to investigate electrochemical reactions of the nickel plated silicon powders with electrolyte, cyclic voltammetry test was performed at a scan rate of 0.1 mV/s. Among the used concentrations, the nickel plated silicon electrode produced using 40 g/L NiCl 2 had a 246 mAh/g discharge capacity after 30 cycles. [ABSTRACT FROM AUTHOR]

As a promising anode material for lithium ion battery, nano-Cu coated porous Si powder was fabricated through two stages: first, preparation of porous nano Si fibers by acid-etching Al-Si alloy powder; second, modified by nano-Cu particles using an electroless plating method. The nano-Cu particles on the surface of nano-Si fibers, not only increase the conductivity of material, but also inhibit the fuse process between nano Si fibers during charge/discharge cycling process, resulting in increased cycling stability of the material. In 1 M LiPF 6 /EC: DMC (1:1) + 1.5 wt% VC solution at current density of 200 mA g −1 , the 150th discharge capacity of nano-Cu coated porous Si electrode was 1651 mAh g −1 with coulombic efficiency of 99%. As anode material for lithium ion battery, nano-Cu coated porous Si nano fiber material is easier to prepare, costs less, and produces higher performance, representing a promising approach for high energy lithium ion battery application. [ABSTRACT FROM AUTHOR]

We perform ab initio calculations on the shear deformation response of the interdiffused Li?Si?Cu phase structure existing between a lithiated Si electrode and a Cu current collector. We show that the formation of well-delineated and weakly bonded Si?Cu and Li?Cu crystalline atomic layers within this phase structure facilitates interface sliding. However, sliding can be terminated by the formation of LiSi3 compounds across these atomic layers, which causes the abrupt capacity fade of the electrode after repeated cycling. [ABSTRACT FROM AUTHOR]

A novel photo-electrochemical and non-enzymatic hydrogen peroxide (HO) sensor was fabricated by electrochemically cathodic plating nickel hydroxide (Ni(OH)) on platinum films coated n-silicon (Pt/n-n-Si electrode). Nickel oxide hydroxide (Ni(OH)-NiOOH) films on the Pt/n-n-Si electrode were formed by cyclic voltammetry in 0.2 M KOH solution. The morphology and composition of Ni(OH)-NiOOH film were characterized via scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS), respectively. A two-electrode cell based on Ni(OH)-NiOOH/Pt/n-n-Si electrode and a platinum counter has been used for determination of HO in the absence of reference electrode by photocurrent measurement at a zero bias. In these conditions a sensitivity of 96.9 μA mM cm and a linear response range from 0.02 up to 0.16 mM with a determination limit (S/N = 3) of 5.4 μM were achieved in KOH solution at pH 13.3. In addition, the electrode also exhibited superior stability, anti-interference and selectivity. [ABSTRACT FROM AUTHOR]

Highlights: [•] An easy method for preparing high performance porous silicon powder was developed by acid etching Al-Si alloy (Al-80%, Si-20%) powder for the first time. [•] In 1M LiPF6, EC:DMC=1:1(V/V) + 15% FEC, at first and 258th cycles, its discharge capacities were 2072mAhg-1Si and 1368 mAhg-1Si, respectively. [•] This new advance method is simple, low cost, and may have good potential for practical application in high energy lithium ion battery area. [Copyright &y& Elsevier]

Abstract: 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. [Copyright &y& Elsevier]

A novel photoelectrochemical hydrogen peroxide (H2O2) sensor was constructed with platinum (Pt) and nickel hydroxyl-oxide (NiOOH) double layers modified n-silicon electrode (NiOOH/Pt/n–n+-Si). About 40nm Pt layer and about 100nm Ni layer were successively coated on the front surface of n–n+-Si (111) wafers by vacuum evaporating. A stable layer of NiOOH was formed through oxidation of the Ni layer on the coated silicon wafer by the electrochemical method. The surface of modified electrode was characterized by scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The NiOOH/Pt/n–n+-Si electrode has been used for determination of H2O2 with a two-electrode cell in the absence of reference electrode by photocurrent measurement at a zero bias. The photoelectrochemical sensor showed a good linear response to H2O2 concentrations in a range from 1.0×10−5 to 6×10−5 M with a determination limit (S/N=3) of 2.2μM. The NiOOH/Pt/n–n+-Si electrode exhibited excellent reproducibility and stability. Particularly, the facile measurement requirements made this novel modified electrode promising for the development of outdoor H2O2 sensors. [ABSTRACT FROM AUTHOR]

Abstract: Few studies relate that the failure mechanism of silicon-based electrodes is the SEI formation. In this work, we used quantitative solid-state high-resolution nuclear magnetic resonance to show that main cause of irreversible capacity is not the decomposition of lithium salt but the degradation of electrolyte solvent with the formation of non lithiated carbon species as polymer or oligomers. [Copyright &y& Elsevier]

A novel hydroquinone (HQ) sensor was developed by depositing a film of copper hexacyanoferrate (CuHCF) on silicon electrode coated by a platinum layer. The stable film of CuHCF was electrochemically deposited onto a phosphorus heavy doped silicon (n+-Si) with 9μm epitaxial layer (n-n+-Si) wafers coated with about 40nm platinum layer (Pt/n-n+-Si). Scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS) and cyclic voltammetry (CV) were used to characterize the morphology, composition and photo-electrochemical behavior of the CuHCF film. A two-electrode cell based on CuHCF/Pt/n-n+-Si electrode was used as sensor for HQ determination by photocurrent measurements at a zero bias. The sensor showed good photocurrent responses by adding different concentrations of HQ with a good stability. The linear range for the detection of HQ was 1.0×10−5 to 2.0×10−4 M, with a detection limit (S/N=3) of 2.2×10−6 M. This provides a facile way of detecting HQ and succeeds in averting from an inconvenient reference electrode. [ABSTRACT FROM AUTHOR]

Abstract: 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 100nm 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. [Copyright &y& Elsevier]

Abstract: 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. [Copyright &y& Elsevier]

Abstract: By depositing a film of cobalt hexacyanoferrate (CoHCF) on silicon electrode coated by a platinum layer, a novel photoelectrochemical sensor for the detection of ascorbic acid (AA) has been developed. The stable film of CoHCF was electrochemically deposited onto a phosphorus heavy doped silicon (n+-Si) with 9μm epitaxial layer (n–n+-Si) wafers coated with about 40nm platinum layer (Pt/n–n+-Si). Scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectra, X-ray diffraction (XRD) and cyclic voltammetry (CV) were used to characterize the CoHCF film on the Pt/n–n+-Si electrode. The CoHCF modified Pt/n–n+-Si electrode has been used for determination of AA with a two-electrode cell in absence of reference electrode by photocurrent measurement at a zero bias. The composite modified electrode demonstrated good photocurrent responses by adding different concentrations of AA with a good stability. The linear range for the detection of AA was 1.0×10−6 to 1.0×10−3 M, with a detection limit (S/N = 3) of 1.0×10−6 M. This provides a facile way of detecting AA and succeeds in averting from inconvenient reference electrode. [Copyright &y& Elsevier]

A prussian blue (PB) film has been deposited on the surface of platinum (Pt) coated n-type epitaxial silicon (Pt/n-n+-Si) wafer. The electro-deposition of PB was achieved by a cyclic scan in a potential range of −0.2 to +0.60V (vs SCE) at 50 mV/s for 5 cycles in a solution containing 2.5 mM FeCl3, 2.5 mM K3Fe(CN)6, 0.1 M KCl and 0.1 M HCl with an illumination from 50 W bromine-tungsten lamp. The emphasis is laid on that this modified silicon electrode can be used as a sensor for the photocurrent determination of hydrogen peroxide at a zero bias by a two-electrode system without reference electrode. The use of the PB modified Pt/n-n+-Si electrode as a hydrogen peroxide sensor was demonstrated with good stability and selectivity. The PB film was characterized by cyclic voltammetry measurements and scanning electronic microscopy (SEM). A new photo-electrochemical sensor based on two-electrode system has been developed for determination of hydrogen peroxide. [ABSTRACT FROM AUTHOR]

In this study, the effect of insertion speed on long-term tissue response and insertion mechanics was investigated. A dummy silicon parylene-coated probe was used in this context and implanted in the rat brain at 10 μm/s (n = 6) or 100 μm/s ( n = 6) to a depth of 9 mm. The insertion mechanics were assessed by the dimpling distance, and the force at the point of penetration, at the end of the insertion phase, and after a 3-min rest period in the brain. After 6 weeks, the tissue response was evaluated by estimating the amount of gliosis, inflammation, and neuronal cell loss with immunohistochemistry. No difference in dimpling, penetration force, or the force after a 3-min rest period in the brain was observed. However, the force at the end of the insertion phase was significantly higher when inserting the probes at 100 μm/s compared to 10 μm/s. Furthermore, an expected tissue response was seen with an increase of glial and microglial reactivity around the probe. This reaction was similar along the entire length of the probe. However, evidence for a neuronal kill zone was observed only in the most superficial part of the implant. In this region, the lesion size was also greatest. Comparison of the tissue response between insertion speeds showed no differences. [ABSTRACT FROM PUBLISHER]

Abstract: 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. [Copyright &y& Elsevier]

Abstract: The nature of Li–Si alloy phases that are generated in electrochemical lithiation is examined as a function of temperature. The electrochemical lithiation is performed at 0.0V (vs. Li/Li+) by short-circuiting an amorphous Si thin-film electrode with a Li metal counter electrode. At 25–85°C, the well-known Li15Si4 phase (theoretical specific capacity=3580mAhg−1) forms. At 100–120°C, however, Li21Si5 (4008mAhg−1) that is known to be the most Li-rich phase in Li–Si system is generated. The crystallization into Li21Si5 is, however, so kinetically slow that it does not appear in the transient cycling experiment. The Li21Si5 phase is converted to amorphous Si upon de-lithiation, but the restoration back to the initial phase is only observed at 100–120°C after a prolonged lithiation at 0.0V. The cycleability of this phase is poor due to a successive Li trapping inside the Si matrix, which is caused by the formation of electrically isolated Si islands. [ABSTRACT FROM AUTHOR]

This work shows the results obtained for the silicon modification with redox molecules derived from ferrocene. The effect of the crystallographic orientation of silicon on the electron-transfer rates was studied. For this study, silicon electrodes (p-type) with two different crystallographic orientations were employed: p-Si (100) and p-Si (111). The redox molecules employed were alkyl ferrocenes with 3, 5 and 10 carbon atoms (propyl, pentyl and decyl ferrocene, respectively). The results showed that the electron-transfer process is not influenced by the crystallographic orientation of silicon and that this process is determinate by electron hopping in a regime of bonded diffusion. [ABSTRACT FROM AUTHOR]

Silicon has become a promising anode material for lithium-ion batteries (LIBs) owing to its high theoretical capacity and low electrochemical potential (vs. Li/Li+). However, its practical application is still hindered by structure degradation and comparable poor capacity retention. Herein, a novel hybrid modification method was proposed to effectively alleviate silicon volume stress. In this structure, polyvinylpyrrolidone (PVP) was served as inner carbon sources to disperse silicon nanoparticles and achieved conjugated N-doped carbon shell coating. Micro-molecule citric acid served as inert layer was to chosen as binder to crosslink silicon particles as well as adjust the component of solid electrolyte interface (SEI) to further stabilize cycling properties. As a result, the obtained electrode has reached to high reversible specific capacity of 1015 mAh/g over 600 cycles at 500 mA/g. This simple combination preparation process would open a new route to exploit silicon electrode. [ABSTRACT FROM AUTHOR]

All-solid-state silicon/LiPON/lithium model batteries are assembled via magnetron sputtering followed by a lithium evaporation process. The cells were characterized via cyclic voltammetry, linear sweep voltammetry and impedance spectroscopy. Cyclic voltammetry confirms a long-term stability and high coulombic efficiency of the solid cells. Also, the assembled batteries were tested at extraordinary high scan rates, showing remarkably high output currents and an exceptional fast-cycling capability. Further rate-dependent investigations via linear sweep voltammetry indicate clearly two different ion-transport mechanisms in the silicon electrode at low and high scan rates. While a diffusion-controlled mechanism is suggested at high scan rates, a homogenous concentration profile is expected at extremely low rates. As a decisive advantage of solid-state cells, electrochemical cycling can be performed at elevated temperatures. This is used to determine the temperature dependence of the diffusion coefficients of lithium in the silicon electrode from room temperature to 165 °C. The effective activation energy of the lithium-ion migration in silicon is obtained to 0.1 eV, which is remarkably lower than that of inside LiPON, i.e. 0.55 eV. Complementary impedance data reveal that the kinetics of transport in the solid-state setup at very high output currents and low temperatures is controlled by lithium-ion migration in the LiPON film. • High rate capability and temperature durability of solid-state battery are shown. • Long-term stability and high coulombic efficiency are demonstrated. • Lithiation of silicon exhibits different kinetic regimes at low and high scan rates. • Temperature dependence of diffusion coefficients of lithium in Si was determined. [ABSTRACT FROM AUTHOR]

Abstract: The electrochemical cycling properties of a Si electrode were drastically improved by the introduction of an ethylene carbonate (EC)-rich electrolyte solution. Cross-sectional morphologies of fully charged Si electrodes were observed with scanning electron microscopy (SEM). The increment of EC in the electrolyte solution showed a tendency to prohibit the deterioration of the Si electrode during Li+ ion insertion. We analyzed the surface films formed on a Si electrode through Fourier transform infrared (FT-IR) spectroscopy. The solvation shell structures of Li+ ions in electrolyte solutions were studied with FT-IR spectroscopy, and the apparent solvation numbers for Li+ ions by EC molecules were calculated. [Copyright &y& Elsevier]

The mechanical behavior of an electrode during implantation into neural tissue can have a profound effect on the neural connections and signaling that takes place within the tissue. The objective of the present work was to investigate the in vivo implant mechanics of flexible, silicon-based ACREO microelectrode arrays recently developed by the VSAMUEL consortium (European Union, grant #IST-1999-10073). We have previously reported on both the electrical [1]-[3] and mechanical [4], [5] properties of the ACREO electrodes. In this paper, the tensile and compression forces were measured during a series of in vivo electrode insertions into the cerebral cortex of rats (7 acute experiments, 2-mm implant depth, 2-mm/s insertion velocity). We compared the ACREO silicon electrodes (40 opening angle, 1-8 shafts) to single-shaft tungsten electrodes (3° and 100 opening angles). The penetration force and dimpling increased with the cross-sectional area (statistical difference between the largest and the smallest electrode) and with the number of shafts (no statistical difference). We consistently observed tensile (drag) forces during the retraction phase, which indicates the brain tissue sticks to the electrode within a short time period. Treating the electrodes prior to insertion with silane (hydrophobic) or piranha (hydrophilic) significantly decreased the penetration force. In conclusion, our findings suggest that reusable electrodes for acute animal experiments must not only be strong enough to survive a maximal force that exceeded the penetration force, but must also be able to withstand high tension forces during retraction. Careful cleaning is not only important to avoid foreign body response, but can also reduce the stress applied to the electrode while penetrating the brain tissue. [ABSTRACT FROM AUTHOR]

The anodic dissolution of silicon in dilute HF electrolyte exhibits some anisotropy in the region of the first electropolishing plateau. This anisotropy can plausibly be assigned to an orientation-dependent surface chemistry. The silicon|dilute fluoride electrolyte interface has been investigated by in situ infrared vibrational spectroscopy in the differential mode, in the potential region where the surface turns from hydrogenated to oxidised. Silicon surfaces of different orientations exhibit closely similar behaviour. However, careful analysis of the ν OH region reveals a significant difference in the concentration of SiOH groups at (1 0 0)- and (1 1 1)-oriented Si surfaces. This observation points to the key role of the SiOH groups in determining the anisotropic behaviour of the electrochemical dissolution of silicon. [Copyright &y& Elsevier]

In-situ infrared spectroscopy is an especially powerful technique when applied to semiconducting electrodes. The use of a multiple-internal-reflection geometry brings an important improvement in sensitivity. Also, it is compatible with a cell geometry featuring low series resistance and allowing for quantitative studies in the presence of a Faradaic reaction and a fast modulation of potential. Additional interests include the possibility of analysing the changes in electronic absorption associated with the space-charge layer and/or electronic surface states, and the possibility of varying the polarisation of the infrared beam, giving extra information on the absorbing species. Here the potentialities of the technique are illustrated through an in-situ study of the modification of the hydrogenated silicon surface by anodic substitution of methyl groups in a Grignard electrolyte. This irreversible reaction is analysed by using a current pulse method. The electrochemical character of the reaction is demonstrated, and unambiguous indications on the reaction mechanism are obtained from the kinetics of modification. The electronic quality of the modified silicon surface is seen to depend on the halogen involved in the Grignard, which can be rationalised in terms of the reaction mechanism. [Copyright &y& Elsevier]

Silicon is a hot candidate for battery anodes as its theoretical storage capacity is almost ten times larger than that of graphite. Volume expansion and kinetic limitations require the nanostructuring in particles, wires or thin films. One feature that still puzzles researchers is the solid electrolyte interface (SEI). Here we use an electrochemical quartz crystal microbalance (QCM) to inspect in-situ SEI formation on Si films. The measured mass uptake is split into a reversible part representing the battery function and an irreversible part attributed to continuous SEI formation. The evaluation of the latter quantifies the dependence of SEI growth on cycling window, rate and anode thickness. More striking is the reversible part. Advanced QCM mass spectrometry enables identification of the ab/desorbed species. Surprisingly, half of the battery storage is not due to lithiation but due to reversible adsorption of Li 2 O to the SEI layer. The dependence on rate and film thickness indicates this Li 2 O is formed by a self-limited, field-driven layer growth. [Display omitted] • Unique approach of Si anode investigations by QCM during cyclic voltammetry. • Evolution of SEI thickness is measured by means of QCM and found in good agreement with TEM micrographs. • Reversible Li 2 O formation during cycling is demonstrated and quantified in dependence on Si thickness and cycling rate. • In realistic operation conditions, half the storage capacity of Si anodes stems from the reversible formation of Li 2 O. • Explanatory model is formulated to explain the dependencies on the Li 2 O formation. [ABSTRACT FROM AUTHOR]

Coin half-cells containing 80 wt% silicon electrodes are assembled and cycled at the ~C/10 rate in the temperature range of 25–55 °C. To the best of our knowledge, this is the first time that the effect of temperature is reported for such high-silicon-containing cells. Two different electrolytes are used in this study, a baseline electrolyte and the baseline electrolyte +10 wt% fluoroethylene carbonate (FEC). Analysis of the capacity vs. cycle count data by curve fitting reveals that the addition of FEC markedly affects the capacity loss mechanism. Without FEC, the kinetic rate law for the capacity loss mechanism can be described as the sum of two logistic growth models. With the addition of FEC, the rate law depends on ln(t). Clearly, the addition of FEC has a profound effect on the mechanism of capacity loss. Interestingly, X-ray photoelectron spectroscopy (XPS) shows that the composition of the solid electrolyte interphase (SEI) layer changes markedly from mostly organic to mostly inorganic in the presence of FEC and how it varies at the different temperatures tested, especially in the absence of FEC. • Without FEC, a double logistic model is followed during silicon (de)lithiation. • With FEC, capacity loss follows ln(t) kinetics at most temperatures, except at 25 °C. • The double logistic model may imply two processes: particle cracking and diffusion. • FEC changes the nature of the SEI layer from mostly organic to mostly inorganic. • Temperature affects the SEI composition and above 45 °C changes are more drastic. [ABSTRACT FROM AUTHOR]

• Effective coverage ratio (ECR) were introduced to mimic the different degrees of pre-existing interface defects. • Battery capacity would have a rapider loss when the ECR reduced below a threshold (about 55%). • Pre-existing defects would "boost" interfacial delamination during subsequent cycles in full discharge condition. Interfacial degradation is one of the root causes of the poor performance of Si-based lithium-ion batteries. Only figure out the role of interfacial degradation in cycling can we optimize electrodes to improve the battery robustness and durability. Here, we performed reactive force field (ReaxFF) atomistic simulations to investigate the "natural" delithiation responses of a-Si-core/a-Al 2 O 3 -coating electrode with different degrees of pre-existing interfacial defects. Effective coverage ratio (ECR) was introduced to mimic different degrees of the pre-existing defects on the a-Li x Si/a-Li x Al 2 O 3 interface. The simulation quantitatively showed that, in any ECR samples, the delithiation could be characterized as two stages: a steady stage with a higher discharge rate and a lower nanoporosity, and an unsteady stage with a lower discharge rate and a larger aggregates of nanopores. The deterioration of ECR caused the steady stage shortened and unsteady stage prolonged. Consequently, further interfacial delamination was easier to form in lower ECR samples in full discharge condition, and the pre-existing defects would "boost" interfacial delamination during subsequent cycles. Besides, the battery capacity would have a rapid loss when the ECR reduced below a threshold (about 55%). This work provides a fundamental understanding of delithiation-induced interfacial degradation mechanism of Si electrodes at atomic-level. [ABSTRACT FROM AUTHOR]

• We first demonstrate the path-independence of Ĵ -integral under chemomechanical loading. • The path-independence of Ĵ -integral for active materials with concentration-dependent material properties is validated. • We developed an incremental constitutive model accounting for the lithiation-induced plastic deformation. • The effect of the crack size and the influx on the Ĵ-integral for a cylindrical Si-electrode with a central-slit crack is examined. The cracking of the active materials in a lithium-ion battery as an adverse consequence of lithiation-induced deformation can significantly cause the capacity loss and likely result in catastrophic failure of the lithium-ion battery. Following the work by Kishimoto et al. [1] , we introduce the Ĵ -integral for the elastoplastic deformation of an active material with a slit-type crack under chemomechanical loading in this work and prove that the Ĵ -integral is path-independent. We also demonstrate that the classical J -integral is path-dependent and is not appropriate for the fracture analysis of the lithiation-induced cracking of the active materials in lithium-ion batteries. Using the incremental constitutive model developed in this work, we numerically analyze the size dependence of the Ĵ -integral under a constant influx for a cylindrical Si-electrode with a central-slit crack. The numerical results reveal that the value of the Ĵ -integral increases with the increase of the crack size and the influx at the same lithiation time, and there exists a maximum value of the Ĵ -integral for a given physical-geometrical configuration. The lithiation-induced softening has a limited effect on the value of the Ĵ -integral. All of these results suggest that the Ĵ -integral can be used to analyze the lithiation-induced propagation of cracks in active materials. [ABSTRACT FROM AUTHOR]

• The volume expansion of thin film amorphous silicon electrodes was investigated during potentiostatic lithiation. • Neutron reflectometry was used for an in-operando study. • A strongly non-linear correlation between volume and state-of-charge is found. Large volume modifications during electrochemical cycling of electrodes in Li-ion batteries often limit successful applications due to stress formation, electrode fracture and delamination from the current collector. In this study, we carried out investigations on the volume changes taking place during potentiostatic lithiation of the high capacity electrode material amorphous silicon. Thin film electrodes were investigated at potentials of 0.45, 0.28, 0.19 und 0.06 V vs Li/Li+ during lithiation using in-operando neutron reflectometry. We found a strongly non-linear correlation between volume and state-of-charge for each potential applied in strong contrast to the results of galvanostatic lithiation. A possible explanation might be that for high current densities occurring at the beginning of each potentiostatic lithiation step free volumes are created in the electrode material leading to disproportionate volume expansion. [ABSTRACT FROM AUTHOR]