Silicon-based Electrodes Research Articles

Improving the Performance of Silicon-Based Negative Electrodes in All-Solid-State Batteries by In Situ Coating with Lithium Polyacrylate Polymers.

In all-solid-state batteries (ASSBs), silicon-based negative electrodes have the advantages of high theoretical specific capacity, low lithiation potential, and lower susceptibility to lithium dendrites. However, their significant volume variation presents persistent interfacial challenges. A promising solution lies in finding a material that combines ionic-electronic conductivity, stable physicochemical properties, and adhesive characteristics. Poly(acrylic acid) (PAA) is widely used in liquid-state batteries due to its superior properties compared to polyvinylidene fluoride (PVDF). In this study, silicon particles were coated with varying concentrations of PAA and LiPAA using an in situ liquid-phase coating method to form electrode sheets. The experimental and analytical results revealed significant trends in the impact of different additive concentrations on the electrochemical performance, with 1.0 wt % LiPAA showing notable improvements in Coulombic efficiency, rate capability, and long-term cycling stability. The assembled all-solid-state batteries exhibited a high initial discharge capacity of 3200 mAh/g, with a capacity retention of 81.9% after 300 cycles at 0.3 C, and a stable discharge capacity of 1300 mAh/g at a 2 C rate. A rapid and efficient in situ liquid-phase coating method for LiPAA was developed and confirmed through FTIR, XRD, and TEM characterization. SEM and XPS analyses demonstrated that LiPAA encapsulation effectively alleviates interfacial issues. This study demonstrated for the first time that an appropriate amount of LiPAA coating on silicon particles can mitigate the interfacial challenges caused by the volume expansion of silicon-based negative electrodes. These findings improve electrochemical performance and promote the application of silicon-based negative electrodes in all-solid-state batteries.

Preparation of high strength and rigidity carbon layer on SiO material surface by dynamic CVD method using gas carbon source C2H2

The main issue in the application of silicon-based negative electrode materials is the inevitable volume expansion, leading to negative electrode material fracture, which severely impacts the performance of batteries. This study employed Chemical Vapor Deposition (CVD) (C2H2@SiO), solid-phase coating method (Pitch@SiO), and liquid-phase coating method (RGFQ@SiO) to coat the surface of SiO materials with a dense amorphous carbon structure. Material property analysis revealed that C2H2@SiO has a relatively small specific surface area (1.8 m2 g−1) and surface carbon increment (2.4 %). It exhibited high reversible specific capacity (1563.4 mAh g−1), high initial Coulombic efficiency (81.45 %), and low volume expansion rate (9.3 %). Mechanical performance testing indicated that the surface carbon layer Young's modulus of C2H2@SiO was the highest (35 GPa), suggesting that using the CVD method to obtain a dense carbon layer can enhance the structural strength of the material. Based on the electrochemical-mechanical coupling theory simulation analysis of the stress during the charge-discharge process of electrode materials, the evolution of concentration and stress field during lithium insertion process was obtained, showing that the coating can further improve the electrochemical and mechanical performance of the negative electrode materials effectively. Additionally, the negative electrode sheets fabricated using sample C2H2@SiO were assembled into 18650 cylindrical batteries, exhibiting excellent cycling performance in 1000 cycles at 25 °C with a capacity retention rate of 85.7 %, along with good rate capability and high/low-temperature performance. The conclusions of this study provide certain guidance for the design and optimization of negative electrode materials for battery electrodes.

A 3D flexible conductive network skeleton by SWCNT-COOH and PVA-PAA enabling high performance for Si anode

Silicon anode undergoes dramatic volume expansion during charge and discharge, causing structural and interfacial instability that severely degrades battery cycling performance. Herein, we propose a three-dimensional (3D) flexible self-standing SiMP/SWCNT-COOH@PVA/PAA anode, in which carboxylation-modified single-walled carbon nanotubes (SWCNT-COOH) construct a highly conductive and flexible skeleton to provide rapid electron transport channels for micron silicon (SiMP), while polyacrylic acid-polyvinyl alcohol (PVA-PAA) cross-linking layer forms a high-strength polymer interface to strengthen the conductive skeleton and helps to maintain the structural integrity of SiMP. The resulting electrode exhibits ultra-high electrical conductance (12406 S m−1) and exceptional mechanical characteristic (tensile strength of 46.95 MPa). More importantly, it demonstrates extremely stable electrochemical properties, with an impressive maximum capacity of approximately 2868.5 mAh g−1 at 0.2C, while retaining an exceptional 96.49 % of capacity even after 100 cycles. A consistent capacity of 1000 mAh g−1 at 1C throughout 1000 cycles is also realized. Furthermore, a flexible full battery based on SiMP/SWCNT-COOH@PVA/PAA anode achieves a discharge capacity of 49.5 mAh g−1 following 100 cycles, and illuminates a LED strip normally under various bending conditions. These results are expected to open a new way towards enhanced performance silicon-based electrodes within flexible LIBs.

The Effect of a Dual-Layer Coating for High-Capacity Silicon/Graphite Negative Electrodes on the Electrochemical Performance of Lithium-Ion Batteries

Silicon-based electrodes offer a high theoretical capacity and a low cost, making them a promising option for next-generation lithium-ion batteries. However, their practical use is limited due to significant volume changes during charge/discharge cycles, which negatively impact electrochemical performance. This study proposes a practical method to increase silicon content in lithium-ion batteries with minimal changes to the manufacturing process by using dual-layer electrodes (DLEs). These DLEs are fabricated with two slurries containing silicon and graphite as active materials. Notably, the electrode with the silicon as the outermost layer on top of the graphite layer (Si-on-top) demonstrated a superior initial capacity of 935 mAh/g and retained 70% of its capacity (537 mAh/g) after 100 cycles at 0.5 C. In contrast, a single-layered electrode (SLE) with a silicon–graphite mixture retained only 50.3% of its capacity (370 mAh/g) under the same conditions. These findings suggest that DLEs, particularly with the silicon layer located on top, effectively increase silicon content in the negative electrode while remaining compatible with existing manufacturing processes. This approach offers a realistic strategy for enhancing the performance of lithium-ion batteries without significant process modifications.

Poly(ethylene) Oxide Electrolytes for All-Solid-State Lithium Batteries Using Microsized Silicon/Carbon Anodes with Enhanced Rate Capability and Cyclability.

Silicon (Si) has been widely studied as one of the promising anodes for lithium-ion batteries (LIBs) because of its ultrahigh theoretical specific capacity and low working voltage. However, the poor interfacial stability of silicon against conventional liquid electrolytes has largely impeded its practical use. Therefore, the combination of silicon-based anodes and solid electrolytes has attracted a great deal of attention in recent years. Here, we demonstrate three types of microsized porous silicon/carbon (Si/C) electrodes (i.e., pristine, prelithiated by liquid electrolyte, and preinfiltrated by polymer electrolyte) that are paired with poly(ethylene) oxide (PEO)-based electrolytes for all-solid-state lithium batteries (ASSLBs). We found that when compared with ionic conductivity, the mechanical stability of the PEO electrolyte dominates the electrochemical performance of ASSLBs using Si/C electrodes at elevated temperature. Additionally, both prelithiated and preinfiltrated Si/C electrodes show higher specific capacity in comparison to the pristine electrode, which is attributed to continuous lithium-ion conducting pathways within the electrode and thus improved utilization of active material. Moreover, owing to good interfacial lithium-ion transport in the electrode, a solid-state half-cell with preinfiltrated Si/C electrode and PEO-lithium bis (trifluoromethanesulfonyl)imide electrolyte delivers a specific capacity of ∼1,000 mAh g-1 after 100 cycles under 800 mA g-1 at 60 °C with average Coulombic efficiency >98.9%. This work provides a strategy for rationally designing the microstructure of silicon-based electrodes with solid electrolytes for high-performance all-solid-state lithium batteries.

Experimental and theoretical investigation of silicon-based carbon composite electrode for high performance Li-ion capacitors

Lithium-ion capacitors (LICs) have garnered significant attention in recent years due to their ability to overcome the shortcomings of lithium-ion batteries (LIBs) and supercapacitors (SCs). Silicon (Si) stands out as a superior anode material for LICs due to its compelling attributes, including a high theoretical specific capacity (4200 mAh/g) and a low de-lithiation potential. Nevertheless, the inherent challenges of Si, such as low electrical conductivity and significant volume expansion (300 %), contribute to low electrochemical performance. To address this issue, a conductive carbon layer is introduced on Si using a simple and scalable approach. The resulting architecture, known as carbon-encapsulated Si (Si/C), not only improves electrical properties by enhancing Li+ diffusion but also mitigates volume expansion, leading to enhanced capacity and cyclic stability. Theoretical findings based on density functional theory (DFT) support these enhancements, confirming improved interactive properties at an atomic scale, including low binding energy and accelerated charge transfer kinetics (higher valence charge transfer) between the Si/C electrode and Li ions. As a result, the ‘binder-free’ and flexible Si/C electrode exhibits a notable initial discharge capacity (3450 mAh/g at 0.05 C) with improved rate capability (3010 mAh/g at 0.1 C). When employed as an anode in LICs, the Si/C electrode exhibits outstanding performance, boasting a large energy density (222.29 Wh/kg), high power density (25 kW/kg), and superior cyclic stability (81.3 % over 10,000 cycles). These findings highlight the potential of the Si/C electrode as a formidable candidate for advanced energy storage applications.

A GOX/RGO-CS-Fc/AuNPs nanosensing membrane in a light-addressable potentiometric biosensor for glucose specific detection

Glucose (Glu) is an important source of energy and metabolic intermediate for animal and plant cells. In this study, a high-performance biosensor for specific detection of Glu was constructed by combining a light-addressable potentiometric biosensor (LAPS) and a specific sensitive unit. The specific sensitive unit was adopted a silicon-based capacitive structure, and the glucose oxidase/reduced graphene oxide -chitosan-ferrooxidase/gold nanoparticles (GOX/RGO-CS-Fc/AuNPs) was modified onto the silicon-based working electrode to construct an nanosensing membrane. The interaction between the specific sensitive unit and Glu resulted in the formation of a bilayer potential, and the field effect generated by the bilayer potential caused a change in the capacitance of the silicon structure, which resulted in a change in the photocurrent-voltage characteristics of the LAPS. Through the potential shift in the photocurrent-voltage characteristics, the LAPS was capable of detection the concentration of Glu. Under optimal conditions, the potential shift was linearly correlated with the Glu concentration from 0.01 mg/mL to 4.00 mg/mL with R2 of 0.9821, and the limited detection was 0.001 mg/mL. In addition, the LAPS showed good recovery (97.92 %–105.72 %), admirable specificity and stability in detection Glu in human serum samples.

Optimization of Si-containing and SiO based Anodes with Single-Walled Carbon Nanotubes for High Energy Density Applications

Lithium-ion batteries require a high energy density when being used in applications such as electric vehicles or portable electronics. This can be achieved on a large scale by improving packaging and implementation, or on a material scale by selecting more energy dense electrode active material. Silicon can be used as a replacement for graphite in negative electrodes if the detrimental volume expansions can be contained. These volume expansions cause continuous mechanical degradation capacity loss leading to short lifetimes that do not meet industry standards. These high-capacity high volume expansion materials such as silicon and SiO must be used in conjunction with more stable electrode materials like graphite to reduce the mechanical degradation caused by volume change. Single-walled carbon nanotubes are shown to be a simple yet effective drop in addition to improve electrical connectivity and increase capacity retention in these silicon-based composite negative electrodes. This added particle interconnectivity from the high tensile strength carbon nanotubes allows for the use of simple binders such as CMC/SBR to create composite electrodes with competitive performance without the use of expensive polymers or complex nanostructures.

Approach for Mitigating Interfacial Degradation in Silicon-Based Electrodes to Enhance Cycling Stability of Lithium-Ion Batteries and Capacitors

The growing demand for high energy density in lithium-ion batteries has led to extensive investigations on silicon negative electrodes. In this study, we propose a novel approach to address the interfacial degradation of electrodes caused by volume expansion during lithium insertion/extraction. The approach involves a sandwich structure consisting of a carbon nanofiber (CNF) undercoating electrode and a CNF-coated separator. The CNF is treated with acid to form carboxyl and hydroxyl groups on its surface, which improves the dispersion of the coating slurry and enhances adhesion to the electrode. Through electrochemical testing, the improved silicon electrode shows a high retention rate of 82% compared to the initial capacity after 100 cycles, and high electrochemical performance when applied to both lithium-ion batteries and lithium-ion capacitors. These results are attributed to the improved adhesion between the electrode and current collector, as well as the formation of a stable solid electrolyte interphase layer on the electrode surface. These findings suggest that the conductive coating process, applied to the separator and current collector, effectively mitigates interfacial issues that are associated with silicon-based electrodes. This approach has the potential to overcome the degradation characteristics of silicon electrodes and significantly contribute to improving the cycling stability of lithium-ion batteries and capacitors.

Laser-Induced Printing of Next Generation Silicon-Graphite Anodes for the Development of Advanced Lithium-Ion Batteries

The expansion of renewable causing a rising demand for affordable and improved energy storage systems. Lithium-ion batteries (LIB) are one of the most promising technologies for this achievement, with further improvements to be made in terms of new materials and an advanced electrode architecture. As a new generation electrode material to be included in LIB, silicon is in the focus of the today’s investigations. Silicon offers one order of magnitude higher theoretical specific capacity (3579 mAh/g) compared to the state-of-the-art material graphite (372 mAh/g). However, during lithiation of silicon a volume expansion of up to 300 % takes place. Due to the huge volume expansion tremendous mechanical degradation of the anode occurs, resulting in a drop in capacity and a shorten lifetime.Laser induced forward transfer (LIFT) is applied in this study as printing technology to develop enhanced silicon-graphite electrode compositions and electrode architectures. LIFT was performed using a pulsed nanosecond UV-laser with a maximum power of 10 W and repetitions rate of up to 30 kHz. For the LIFT process of anodes, polyacrylic acid (PAA) is used as binder, in contrast to the polyvinylidene fluoride (PVDF) binder commonly used for LIFT assisted printing of electrodes. PAA is a more appropriate binder for silicon-containing anodes than PVDF. In addition, also a customized architecture using subtractive and additive laser process techniques is introduced for an increase in lifetime of batteries containing silicon-based electrodes. For this purpose, graphite electrodes were structured with an ultrashort pulse laser with pattern widths of 100 µm. Subsequently, silicon rich slurry was printed into the patterns to increase the areal capacity. The as-prepared electrodes have spatially separated graphite and silicon regions. The respective electrodes were electrochemically cycled in half-cells and charged at different C-rates up to 5C to investigate their lithiation capability. After the rate capability analysis, the cells were cycled at C/2 to investigate the long-term degradation. The cells with the printed electrodes were cycled for more than 450 cycles with a capacity fade of 5 %. At their end-of-life, the cells were analyzed post-mortem. Finally, full-cells were assembled with cathodes containing NMC 622 as the active cathode material. Subsequently to the cell priming a lifetime analysis was performed at a C-rate of C/2 and cycle stability as well as lithium loss during cycling were evaluated.

Sustainable SiO2 Nanostructures from Different Diatom Species As Anode Material for Future Generation Lithium-Ion Batteries

Energy harvesting and storage devices occupy a more prominent place in the 21st century than at any time in the past. Intensive efforts have been devoted to next-generation energy storage devices such as rechargeable lithium-ion batteries (LIBs) to develop high energy density and long cycle life electrode materials from sustainable sources. In the present anode, graphite is severely restricted by capacity and unavoidable solid electrolyte interface (SEI) formation. Besides, it has been listed as a critical material by the European Commission. Recently, silicon-based electrodes have been pinpointed as promising anode candidates due to their high theoretical capacity (~4200 mAhg-1 for Li4.4Si), low operating voltage (0.4V/Li/Li+), abundant resources, and environmental friendliness. Interestingly, nanostructures of Silica (SiO2) can be extracted from the frustules (exoskeletons) of a type of microalgae called diatoms. In this current work, SiO2 frustules were grown from two different diatom species, constituting a sustainable source for producing nanostructured Si-based materials. Scanning electron microscopy (SEM) images confirmed the highly nanoporous structure of diatom silica, which was retained even after ball-milling. The electrochemical performance of SiO2 was investigated as an anode material for LIBs. Herein, we have tested both species A & B milled and un-milled samples (denoted as SPAUM, SPAM, SPBUM, and SPBM). The diatom SiO2 un-milled species A (SPAUM) exhibited a high specific capacity of ~ 810 mAhg-1 with remarkable capacity retention and coulombic efficiency even after 100 cycles at 0.1 Ag-1 and delivered a high specific capacity of ~ 400 mAhg-1 even at high current density 3 Ag-1. For comparison and understanding, commercially available diatomaceous earth milled, and un-milled silica (denoted as EDAM & EDAUM) has been subjected to the same cycling protocol. Results clearly showed species A & B milled and un-milled displaying better electrochemical performance than diatomaceous earth milled and un-milled silica. Such improved electrochemical properties like cycle life, and rate capability of SPAUM are mainly ascribed to their highly porous nature which significantly facilitates fast Li ion diffusion, its unique morphology, which favors a faster kinetics and its complete lithiation/de-lithiation after the initial activation cycle. In view of the superior electrochemical properties, such sustainably sourced SiO2 materials can be considered a potential anode material for future LIBs. Figure 1

(Invited) Coordinatively Cross-Linked Binders for Silicon-Based Electrodes for Lithium Ion Batteries

We have proposed a simple and versatile preparation of Cu(II)- or Zn(II)-poly(carboxylates) reticulated binders by the addition of Cu(II) or Zn(II) precursors into a pre-optimized carboxymethyl cellulose / citric acid binder solution. These binders lead systematically to a significantly improved electrochemical performance when used for the formulation of silicon-based negative electrodes [1,2]. Mechanical characterizations reveal that the coordinated binders offer a better electrode coating cohesion and adhesion to the current collector, as well as higher hardness and elastic modulus, which are even preserved in presence of a carbonate solvent (i.e. in battery operation conditions). Ultimately, as shown from operando dilatometry experiments, the electrode expansion during lithiation is reduced, mitigating electrode mechanical failure [2]. In complement, we used scanning transmission electron microscopy coupled with energy dispersive X-ray spectroscopy to probe the nanoscale morphology of such electrodes. This technique reveals the homogeneous coordination of carboxylated binder with Zn cations and its layering on the silicon surface. The SEI formed after the first cycle is denser with Zn-coordinated binder and preferentially observed on binder-depleted zones [3]. In summary, the superiority of coordinated binders can be attributed to their capacity to better stabilize the electrode and the SEI layer due to improved mechanical properties. This resulted in a lower SEI impedance, a higher first cycle coulombic efficiency, and a 40% improvement of capacity retention after 60 cycles for highly loaded electrodes of over 6 mAh.cm-2. Noteworthy, this formulation principle allows for better reproducibility and manufacturing quality of the electrodes [4].[1] D. Mazouzi, R. Grissa, M. Paris, Z. Karkar, L. Huet, D. Guyomard, L. Roué, T. Devic, B. Lestriez, Electrochimica Acta, 304 (2019) 495-504[2] L. Huet, D. Mazouzi, P. Moreau, N. Dupré, M. Paris, S. Mittelette, D. Laurencin, T. Devic, L. Roué, B. Lestriez, ACS Applied Materials & Interfaces, 15 (2023) 15509-15524[3] L. Huet, P. Moreau, N. Dupré, T. Devic, L. Roué, B. Lestriez, Small Methods, 2022, 2200827[4] L. Huet, H. Houisse, N. Herkendaal, T. Devic, L. Roué, B. Lestriez, Energy Technology, 2023, 2201483 Figure 1

Modeling and Analysis of Coupled Thermal and Mechanical Capacity Degradation in Silicon-Based Lithium-Ion Batteries

Large-format cells are gaining popularity for battery electric vehicles (BEVs) to maximize volumetric and gravimetric energy densities but are associated with challenges in ensuring adequate thermal management. Spatial current density and temperature variations negatively affect overall cell utilization and lifetime.In addition, the mechanical stresses generated within the silicon-based battery electrodes also cause aging and resultant capacity loss. The coupled effects of the thermal and mechanical factors could thus particularly exacerbate cell capacity degradation. Rigorous mechano-thermo-electrochemical models for battery degradation can be a powerful complementary tool to understand these phenomena better. Simulating performance scenarios can significantly improve cell design and experimentation while reducing time and cost commitments. Model-based design approaches thus have the potential to yield substantial economic benefits.This work shall serve as an extension to the previously developed thermal degradation model for non-uniform aging in lithium-ion batteries by coupling with mechanical models predicting the effects of volume change within the batteries over cycling. The observed capacity fade trend for a given battery is ultimately the result of an interplay between multiple degradation mechanisms, which depend on a range of design and operating parameters. The errors between the model predictions and experimental data can provide information on the suitability of a given model and the relative prevalence of a given degradation mechanism, with functional and practical benefits, as there exists significant variation in the parameters, mechanisms, and predictive capability of models in the literature. In addition, a rigorous model of volume changes increases the accuracy of predictions of dynamic stress-strain profiles, which in turn helps improve predictions of associated mechanical degradation phenomena. As a first step towards including mechanical effects, the current model builds on the previously reported studies for modeling volume change in porous electrodes due to intercalation (deintercalation) during lithiation (delithiation). This volume change leads to dimensional and porosity changes in the porous electrodes. Furthermore, these mechanical models will help predict generated stresses and strain profiles within the battery and will be related to models of resultant degradation, especially in the case of silicon/graphite electrodes characterized by substantial volume changes.

High Carbon Doping of Amorphous Silicon Nanoparticles in a One-Step Gas-Phase Process for Increased Cycling Stability

Silicon as an anode material for Lithium-Ion-Batteries (LIB) is a promising candidate to increase overall specific energy of batteries in comparison to state-of-the-art graphite anodes. Yet the cycling stability of silicon-based electrodes is still an issue, mainly due to problems related to the swelling of silicon during lithiation to up to 300 % of its original volume. While a breakage of silicon particles can be prevented by choosing a nano-material this has the detrimental effect of increasing the surface exposed to the electrolyte, i.e. reducing coulombic efficiency. Other solutions like coatings of silicon particles and complex electrode structures are shown to increase cycling stability, but are typically connected to higher manufacturing cost.By doping silicon nanoparticles already during production in a gas-phase one-step process, this study investigates the influence of high carbon concentrations up to 20 wt.%. This causes the silicon to stay amorphous, even at elevated temperatures. Furthermore it is shown, that the disturbance of the lattice by carbon atoms helps mitigating stress during lithiation, and can form a less reactive surface. By varying precursor concentrations during material synthesis, a range of materials were produced and analyzed physicochemically and electrochemically. For carbon values up to 15 wt.% our results show a strong increase in cycling stability of up to 80 % capacity retention after 500 cycles, and first cycle coulombic efficiencies of 80 – 90 %. Yet the increased stability is going along with a decrease in specific capacities to 1000 – 1500 mAh/g. These values were obtained for a 75 wt.% silicon, 15 % PAA, 10% C65 electrode and 1 mg/cm2, tested against lithium at 0.5 C. By linking further electrochemical results to particle properties the effects of the carbon doping are further unravelled. This material engineering offers another promising pathway to increase overall performance of silicon containing LIBs and is industrially viable, due to its inclusion in a scalable one-step material synthesis process. Figure 1

MXene Clay (Ti2C)-Containing In Situ Polymerized Hollow Core-Shell Binder for Silicon-Based Anodes in Lithium-Ion Batteries.

Silicon, an attractive anode material, suffers fast capacity fading due to the electrical isolation from massive volumetric expansion upon cycling. However, it holds a high theoretical capacity and low operation voltage in its practical application. In this study, a new water-based binder, MXene clay/hollow core-shell acrylate composite, was synthesized through an in situ emulsion polymerization technique to alleviate the fast capacity fading of the silicon anode efficiently. The efficient introduction of conductive MXene clay and the hollow core-shell structure, favorable to electron and ion transport in silicon-based electrodes, gives a novel conceptual design of the binder material. Such a strategy could alleviate electrical isolation after cycling and promises better electrochemical performance of the high-capacity anodes. The effect of the MXene introduction and hollow core-shell on the binder performance is thoroughly investigated using various characterization tools by comparison with no MXene-containing, core-shell acrylate, and commercial styrene-butadiene latex binders. Consequently, the silicon-based electrode containing the MXene clay/hollow core-shell acrylate binder exhibits a high capacity retention of 1351 mAh g-1 at 0.5C after 100 cycles and good rate capability of over 1100 mAh g-1 at 5C.

Silicon Negative Electrodes—What Can Be Achieved for Commercial Cell Energy Densities

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%.

Spidroin-Inspired Hierarchical Structure Binder Achieves Highly Integrated Silicon-Based Electrodes.

As a promising component for next-generation high energy lithium-ion batteries, silicon-based electrode has attracted increasing attention by virtue of ultrahigh theoretical specific capacities. Nevertheless, fast capacity fade posed by tremendous silicon-based electrode volume changes during cycling remains a huge challenge before large-scale applications. Herein we develop an aqueous-oil binary solution based blend (AOB) binder characterized by a spidroin-like hierarchical structure for tolerating huge volume change of silicon-based electrodes. In AOB binder, the hydrophobic tetrazole groups-containing polymer (donate as PPB) and water-soluble amorphous poly(acrylic acid) mimicks the β-sheet and α-helix structure of spidroin, respectively. Benefitted by such biomimetic design, AOB binder enables both high tensile strength and elasticity, and strong electrode adhesion, therefore apparently stabilizing silicon-based electrode structure and rendering prolonged electrode cycle life. Such a strategy endows a 3.3 Ah soft package cells assembled with Si/C composite anode and NCM811 cathode with a discharge specific capacity of 2.92 Ah after 700 cycles. This work marks a milestone in developing state-of-the-art silicon-based electrodes towards high energy density lithium battery applications. This article is protected by copyright. All rights reserved.

A comparative study on silicon-based negatrode materials in metallic cavity electrode and button half cell — Uncovering unseen microscopic and dynamic features

The electrochemical characterization of lithium storage materials using the button cell is commonplace, but it is also tedious and time-consuming. Also, the results are often affected by the use of the binders and separator membranes, and by the electrode forming and cell assembly methods. To study the changes in materials before and after dis-/charging, one has to break up the button cell and disturb the packing structure of electrode. In this work, the metallic cavity electrode made of copper (Cu-MCE) was used to study silicon-based negative electrode (negatrode) materials during electrochemical de-/lithiation. The initial apparent reaction area (i.e. the contacting area between the Cu substrate and the active materials, 0.785 mm2) of the Cu-MCE was much smaller than that of the half-button cell (153.86 mm2), reducing significantly the overall current and hence polarization in the Cu-MCE. Powders of commercial silicon and phosphorus-doped silicon (P-doped Si) were tested in the Cu-MCE and a conventional button cell. Cyclic voltammograms (CVs) recorded using the Cu-MCE showed full activation in the first cycle, unlike the button cell whose CVs expanded continuously beyond 5 cycles. Current peaks on the CVs of the Cu-MCE agreed with the expected redox reactions but were more pronounced. The subtle differences between P-doped Si and pure Si could also be revealed by the Cu-MCE with the current peaks becoming more obvious, apparently due to modification in material structures and improved ion transport dynamics. The peak currents on the CVs of the Cu-MCE were plotted against the square root of scan rate (v1/2), showing non-linearity for the two oxidation peaks at 0.35 and 0.54 V, indicating both diffusion and surface of the delithiation processes. Linear plots were obtained for the two reduction peaks at 0.165 and 0.245 V with comparable slopes (−0.024 and 0.029 mA mV−1/2 s1/2), confirming diffusion control with insignificant polarization. However, similar analyses of the button cell revealed diffusion control in both oxidation and reduction, indicating slower dynamics with large polarization to delithiation. More importantly, the Cu-MCE can be inspected directly after dis-/charging without any disturbance, and provides unseen variation in the packing structure, particle morphology, and elemental information of the active materials. It is hoped that the higher accuracy, better details, and greater efficiency offered by the Cu-MCE for studying the intrinsic electrode reaction characteristics of Si-based electrode materials can be extended to other powdery materials for charge storage.

Influence of different anode active materials and blends on the performance and fast-charging capability of lithium-ion battery cells

To further extent the driving range of battery electric vehicles, an increase of the energy density of lithium-ion battery cells is necessary. One way to increase the energy density is the use of high-capacity electrodes. The challenges for this kind of electrodes are transport limitations, like the long lithium-ion diffusion path to the layers near the substrate of the electrode, leading to performance degradation during cycling. To get a better understanding on how the material selection influences the battery cell performance, various active materials (graphite, silicon, and hard carbon) are investigated, both, pure and in blends and the relation between material, structure and performance is studied. On material level pure silicon active material has a very high electric resistance compared to carbon-based materials. Nevertheless, on electrode level, the high gravimetric energy density, and the round-shaped particle morphology of silicon result into a lower tortuosity and layer thickness, hence, ionic resistance of the electrode. With respect to cell performance, the ionic resistance seems to have a greater impact compared to the charge-transfer and electric resistance. Therefore, silicon-based electrodes show the best performance.

Co-electrodeposition hybrid reduced graphene oxide and nickel-cobalt selenide nanosheets on silicon nanowires for high-performance supercapacitor

Due to inherent compatibility with IC technology, 3D silicon is prone to build a skeleton for the energy storage electrodes. Herein, a unique 3D hierarchical core-shell electrode was first developed with silicon nanowire arrays (SiNWs), metal selenide (TMSe) and reduced graphene oxide (RGO) nanosheets, where SiNWs decorated with Ni particles (Si/Ni) served as the conductive core and co-electrodeposited hybrid nickel-cobalt selenide (NCSe) and RGO nanosheets (NCSe-RG) functioned as the high capacitive outer shell. Owing to the synergy effect between NCSe and RGO, high-speed electron transport channels of Si/Ni, and abundant electroactive sites of porous NCSe layer, the synthesized Si/Ni/NCSe-RG electrode delivered a large capacitance of 2268 F g−1 (1973 mF cm−2) at 1 A g−1 which was higher than most reported silicon-based electrodes, and an excellent rapid-charging capability (1540 F g−1 at 30 A g−1). Furthermore, a solid asymmetric supercapacitor (SC) was prepared by using Si/Ni/NCSe-RG as the positive electrode, demonstrating an excellent energy density of 53.23 Wh kg−1 at the power density of 800 W kg−1. Our results suggest that high-performance SC electrodes can be engineered with TMSe and 3D silicon with a simple and time-saving method.