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Historically, lithium cobalt oxide and graphite have been the positive and negative electrode active materials of choice for commercial lithium-ion cells. It has only been over the past ~15 years in which alternate positive electrode materials have been used. As new positive and negative active materials, such as NMC811 and silicon-based electrodes, are being developed, it is crucial to evaluate the potential of these materials at a stack or cell level to fully understand the possible increases in energy density which can be achieved. Comparisons were made between electrode stack volumetric energy densities for designs containing either LCO or NMC811 positive electrode and silicon-graphite negative electrodes, where the weight percentages of silicon were evaluated between zero and ninety percent. Positive electrode areal loadings were evaluated between 2.00 and 5.00 mAh cm−2. NMC811 at 200 mAh g−1 has the ability to increase stack energy density between 11% and 20% over LCO depending on percentage silicon and areal loading. At a stack level, the percentage of silicon added results in large increases in energy density but delivers a diminishing return, with the greatest increase observed as the percentage of silicon is increased from zero percent to approximately 25–30%. [ABSTRACT FROM AUTHOR]

• Characteristics like electrode thickness and electrolyte volume affect performance. • Large electrolyte to electrode volume (20:1) significantly improves capacity. • Relationship between electrolyte and electrode volume needs to be understood. Silicon electrodes are being investigated as potential high-capacity replacements for graphite electrodes in lithium-ion batteries. Various factors affecting silicon electrodes need to be understood to maintain increased capacity and high performance at subzero temperatures. This work investigates electrode thickness and volume of electrolyte used that can affect performance of a copper modified silicon electrode at −20 °C. When electrolyte volume is large compared to electrode volume (20:1 ratio), the performance of these cells at low temperature is noticeably improved, retaining approximately 400 mAh/g capacity at −20 °C after 50 cycles. [ABSTRACT FROM AUTHOR]

Silicon electrodes are widely used in semiconductor etching machines. The periodic consumption of silicon electrodes has become an important consumable in wafer manufacturing. Due to the limited number of silicon electrode manufacturers and the increasing demand for silicon electrodes in global market, the newly processed silicon electrodes need to be immediately delivered to wafer manufacturers to ensure uninterrupted production. Driven by this, this paper introduces a new integrated scheduling problem called the silicon electrode production and transportation integrated scheduling problem (SEPTISP), whose criterion is to minimize the makespan. This problem is modeled as a combination of the production scheduling subproblem (PSS) and the transportation scheduling subproblem (TSS). These two subproblems are coupled with each other. Considering the SEPTISP's NP-hard and coupling properties, a novel collaborative Q-learning hyper-heuristic evolutionary algorithm integrated with reinforcement learning scheme (CQHEA_RLS) is proposed to handle them. In the CQHEA_RLS, the production agent and the transportation agent are focused on executing exploitation in the reduced but promising regions via their specific search actions, while the joint agent is centered on performing exploration in the whole solution space through its joint search actions and determining the suitable search regions for the other two agents. Meanwhile, the joint agent also integrates the historical performance information of its own and the other two agents' search actions to dynamically choose its subsequent search actions. Moreover, each agent is devised as an effective Q-learning hyper-heuristic evolutionary algorithm. This new collaborative framework ensures that the CQHEA_RLS can continuously search downwards to obtain truly high-quality solutions in a relatively short runtime. The experimental results demonstrate that the designed algorithm can achieve better performance than the existing state-of-the-art algorithms. [ABSTRACT FROM AUTHOR]

The plastic flow in a silicon electrode during lithiation can alter the stress state in the silicon electrode and retard the fracture of the silicon electrode. In this work, we develop a rate-dependent model to investigate the plastic flow and phase transformation, which concurrently occur during the lithiation of a cylindrical silicon electrode. Using a power law for the plastic-flow potential and neglecting elastic deformation, we obtain analytical solutions of the stresses in the silicon electrode, which are dependent on the temporal evolution of the interface between lithiated phase and un-lithiated phase. A simplified diffusion model, which captures the temporal evolution of the interface, is proposed in the framework of the Cahn-Hilliard phase-field theory. The numerical results are in good accord with the results from the phase-field model with finite deformation. Under galvanostatic operation, the stresses are dependent on the lithiation rate, and the stresses on the surface of the silicon electrode are independent of initial radius and lithiation time. Under potentiostatic operation, the stresses in a silicon electrode of a smaller radius is larger than that in a silicon electrode of a larger radius. The magnitudes of the stresses on the surface decrease with the increase of both initial radius and the lithiation time. [ABSTRACT FROM AUTHOR]

Cycling number, crystal orientation, temperature and electric field strength play key roles in affecting the capacity and cycling ability of Li-ion battery. However, the detailed dynamic and continuous process of capacity decline mechanism from above factors need to be further understood at nanoscale. Herein, we report deformation behavior and microstructure evolution of Si anode under electric field using molecular dynamics simulations. The results show larger cycling number and electric field strength cause larger volume expansion of Si electrode, leading to the capacity loss and the reducing cycling ability as well as the decreasing structural stability. The phase transformation from diamond cubic structure to body-centred tetragonal structure and the amorphous formation depend on lithiated and delithiated depths. The crystal orientation [100] Si anode produces the volume expansion owing to a large number of nanoscale void. The various temperatures strongly affect the number and radius of nanovoid. The associated transition in the nanovoid nucleation due to the involuntary diffusion process is driven by larger cycling number or electric field strength, resulting in the irreversible capacity loss of Li-ion battery. An established analytical model suggests that diffusion-induced stress not only relies on the position of Si anode but depends upon the cycling time. [ABSTRACT FROM AUTHOR]

The microstructural degradation of a composite silicon electrode at different stages in its cycle life was investigated in 3D using X-ray nano-computed tomography. A reconstructed volume of 36 μm × 27 μm × 26 μm from the composite electrode was imaged in its pristine state and after 1, 10 and 100 cycles. Particle fracturing and phase transformation was observed within the electrode with increased cycling. In addition, a distinct, lower X-ray attenuating phase was clearly resolved, which can be associated with surface film formation resulting from electrolyte breakdown and with silicon particle phase transformation. Changes in quantified microstructural properties such as phase volume fraction and particle specific surface area were tracked. Electrode performance loss is associated with loss of active silicon. These imaging results further highlight the capability of high resolution X-ray tomography to investigate the role of electrode microstructure in battery degradation and failure. [ABSTRACT FROM AUTHOR]

The application of silicon (Si) substrate as photoelectrode in light-addressable electrochemistry (LAE) is severely limited due to its ease of surface oxidation. The resulted silicon oxide (SiO x) layer is electronically insulating and blocks charge transfer between the electrode and electrolyte. Keeping the Si from being oxidized is a key challenge for its practical use as a semiconductor electrode. In this work, we find that by developing a thin layer of polydopamine film on the surface of Si substrate, followed by carbonization at 550 °C, the natural oxidation of Si substrate can be successfully forestalled. When applied as an electrode, it is further found that the carbonized polydopamine (cPDA) layer can also prevent anodic oxidation of Si. The cPDA layer-modified Si substrate exhibits good photoelectrochemical performance and great stability, with no obvious signal decrease under ambient environment over 32 h. Our work here provides a new modification strategy for anti-oxidation of Si substrate and it is promising in the application of light-addressable electrochemical sensing and imaging. [Display omitted] • A thin layer of c-PDA was successfully coated on Si surface to protect it from both natural and anodic oxidation. • The cPDA layer-protected Si presents good charge transfer ability and stability. • The cPDA layer-protected Si shows great potential in application of light-addressable electrochemical sensing and imaging. [ABSTRACT FROM AUTHOR]

Silicon is a promising candidate to substitute or complement graphite as anode material in Li-ion batteries due, mainly, to its high energy density. However, the lithiation/delithiation processes of silicon particles are inherently related to drastic volume changes which, within a battery's physically constrained case, can induce significant deformation of the fundamental components of the battery that can eventually cause it to fail. In this work, we use non-destructive time-lapse X-ray imaging techniques to study the coupled electrochemo-mechanical phenomena in Li-ion batteries. We present X-ray computed tomography data acquired at different times during the first lithiation of custom-built silicon-lithium battery cells. Microstructural volume changes have been quantified using full 3D strain field measurements from digital volume correlation analysis. Furthermore, the extent of lithiation of silicon particles has been quantified in 3D from the grey-scale of the tomography images. Correlation of the volume expansion and grey-scale changes over the silicon-based electrode volume indicates that the process of lithiation is kinetically affected by the reaction at the Si/Li x Si interface. [ABSTRACT FROM AUTHOR]

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]

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]

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]

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]

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]

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]

• 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]