Poly-dopamine carbon-coated stable silicon/graphene/CNT composite as anode for lithium ion batteries

Synthesizing Si/SiOC composites through different sol-gel reaction routes for lithium-ion battery anode materials

Silicon oxycarbide (SiOC) exhibits good retention and a reasonable specific capacity and is an alternative to silicon used as an anode material for high-performance lithium-ion batteries. However, SiOC generally shows a low Initial Coulombic Efficiency (ICE), wasting the lithium from the cathode. This work explores different sol-gel routes to synthesize SiOC from silanes and compares their performance. We found that the crushed bulk acid-catalyzed SiOC is simple and cost-effective but with excellent performance. Adding dimethyldimethoxysilane (DMDMS) by decreasing the oxygen content further enhances the battery performance. Building upon the excellent performance of SiOC, we further embed nano-silicon into SiOC. The Si/SiOC composites achieved a significantly higher specific capacity of 2185 mAhg-1 and an impressive ICE of 77 % with acceptable battery retention.

Silver-Assisted Chemical Etching for the Fabrication of Porous Silicon N-Doped Nanohollow Carbon Spheres Composite Anodes to Enhance Electrochemical Performance

Silicon (Si) shows great potential as an anode material for lithium-ion batteries. However, it experiences significant expansion in volume as it undergoes the charging and discharging cycles, presenting challenges for practical implementation. Nanostructured Si has emerged as a viable solution to address these challenges. However, it requires a complex preparation process and high costs. In order to explore the above problems, this study devised an innovative approach to create Si/C composite anodes: micron-porous silicon (p-Si) was synthesized at low cost at a lower silver ion concentration, and then porous silicon-coated carbon (p-Si@C) composites were prepared by compositing nanohollow carbon spheres with porous silicon, which had good electrochemical properties. The initial coulombic efficiency of the composite was 76.51%. After undergoing 250 cycles at a current density of 0.2 A·g-1, the composites exhibited a capacity of 1008.84 mAh·g-1. Even when subjected to a current density of 1 A·g-1, the composites sustained a discharge capacity of 485.93 mAh·g-1 even after completing 1000 cycles. The employment of micron-structured p-Si improves cycling stability, which is primarily due to the porous space it provides. This porous structure helps alleviate the mechanical stress caused by volume expansion and prevents Si particles from detaching from the electrodes. The increased surface area facilitates a longer pathway for lithium-ion transport, thereby encouraging a more even distribution of lithium ions and mitigating the localized expansion of Si particles during cycling. Additionally, when Si particles expand, the hollow carbon nanospheres are capable of absorbing the resulting stress, thus preventing the electrode from cracking. The as-prepared p-Si utilizing metal-assisted chemical etching holds promising prospects as an anode material for lithium-ion batteries.

Constructing a Stable Integrated Silicon Electrode with Efficient Lithium Storage Performance through Multidimensional Structural Design

Silicon (Si) stands out as a highly promising anode material for next-generation lithium-ion batteries. However, its low intrinsic conductivity and the severe volume changes during the lithiation/delithiation process adversely affect cycling stability and hinder commercial viability. Rational design of electrode architecture to enhance charge transfer and optimize stress distribution of Si is a transformative way to enhance cycling stability, which still remains a great challenge. In this work, we fabricated a stable integrated Si electrode by combining two-dimensional graphene sheets (G), one-dimensional Si nanowires (SiNW), and carbon nanotubes (CNT) through the cyclization process of polyacrylonitrile (PAN). The integrated electrode features a G/SiNW framework enveloped by a conformal coating consisting of cyclized PAN (cPAN) and CNT. This configuration establishes interconnected electron and lithium-ion transport channels, coupled with a rigid-flexible encapsulated coating, ensuring both high conductivity and resistance against the substantial volume changes in the electrode. The unique multidimensional structural design enhances the rate performance, cyclability, and structural stability of the integrated electrode, yielding a gravimetric capacity (based on the total mass of the electrode) of 650 mAh g-1 after 1000 cycles at 3.0 A g-1. When paired with a commercial LiNi0.5Co0.2Mn0.3O2 cathode, the resulting full cell retains 84.8% of its capacity after 160 cycles at 2.0 C and achieves an impressive energy density of 435 Wh kg-1 at 0.5 C, indicating significant potential for practical applications. This study offers valuable insights into comprehensive electrode structure design at the electrode level for Si-based materials.

Tight Binding and Dual Encapsulation Enabled Stable Thick Silicon/Carbon Anode with Ultrahigh Volumetric Capacity for Lithium Storage

Silicon (Si) is regarded as one of the most promising anode materials for high-performance lithium-ion batteries (LIBs). However, how to mitigate its poor intrinsic conductivity and the lithiation/delithiation-induced large volume change and thus structural degradation of Si electrodes without compromising their energy density is critical for the practical application of Si in LIBs. Herein, an integration strategy is proposed for preparing a compact micron-sized Si@G/CNF@NC composite with a tight binding and dual-encapsulated architecture that can endow it with superior electrical conductivity and deformation resistance, contributing to excellent cycling stability and good rate performance in thick electrode. At an ultrahigh mass loading of 10.8 mg cm-2 , the Si@G/CNF@NC electrode also presents a large initial areal capacity of 16.7 mA h cm-2 (volumetric capacity of 2197.7 mA h cm-3 ). When paired with LiNi0.95 Co0.02 Mn0.03 O2 , the pouch-type full battery displays a highly competitive gravimetric (volumetric) energy density of ≈459.1 Wh kg-1 (≈1235.4 Wh L-1 ).

New Chemical Synthesis Strategy To Construct a Silicon/Carbon Nanotubes/Carbon-Integrated Composite with Outstanding Lithium Storage Capability

The Si/C anode is one of the most promising candidate materials for the next-generation lithium-ion batteries (LIBs). Herein, a silicon/carbon nanotubes/carbon (Si/CNTs/C) composite is in situ synthesized by a one-step reaction of magnesium silicide, calcium carbonate, and ferrocene. Transmission electron microscopy reveals that the growth of CNTs is attributed to the catalysis of iron atoms derived from the decomposition of ferrocene. In comparison to a Si/C composite, the cycle stability of the Si/CNTs/C composite can obviously be improved as an anode for LIBs. The enhanced performance is mainly attributed to the following factors: (i) the perfect combination of Si nanoparticles and in situ grown CNTs achieves high mechanical integrity and good electrical contact; (ii) Si nanoparticles are entangled in the CNT cage, effectively reducing the volume expansion upon cycling; and (iii) in situ grown CNTs can improve the conductivity of composites and provide lithium ion transport channels. Moreover, the full cell constructed by a LiFePO₄ cathode and Si/CNTs/C anode exhibits excellent cycling stability (137 mAh g^-1 after 300 cycles at 0.5 C with a capacity retention rate of 91.2%). This work provides a new way for the synthesis of a Si/C anode for high-performance LIBs.

Solid Silicon Nanosheet Sandwiched by Self-Assembled Honeycomb Silicon Nanosheets Enabling Long Life at High Current Density for a Lithium-Ion Battery Anode

A two-dimensional silicon nanosheet (2D Si NS) is promising as a lithium-ion battery anode. However, insufficient cycling life at high current density hampers its practical applications due to its easy fragileness. Rationally engineering the Si micro/nanostructure is promising to address this issue. Unfortunately, the precise construction of a dedicated micro/nanostructure into 2D Si NS meets serious challenges. Herein, a facile strategy is developed to synthesize a sandwich-like honeycomb Si NS/solid Si NS/honeycomb Si NS (h/s/h-Si NS) anode through self-assembled preparation of a sandwich-like honeycomb SiO₂ NS/solid SiO₂ NS/honeycomb SiO₂ NS template, followed by magnesiothermic reduction. This unique structure effectively enhances the mechanical strength, enlarges the specific surface area, and reserves sufficient space to accommodate the anode volume change. A conductive carbon layer is further coated on the h/s/h-Si NS (h/s/h-Si@C NS) to construct a stable electrode/electrolyte interface. The optimal h/s/h-Si@C NS displays outstanding performance with high initial Coulombic efficiency (86%), high reversible capacity (1624 mAh g^-1 after 100 cycles at 1000 mA g^-1), good rate capability (over 1000 mAh g^-1 at 4000 mA g^-1), and long cycling life even at 4000 mA g^-1 (93% retained capacity after 1000 cycles). This work provides a new strategy for constructing high-performance Si electrodes for lithium-ion battery applications.

Simulation and Verification of the Direct Current Electric Field on Fabricating High Porosity f-MWCNTs Thin Films by Electrophoretic Deposition Technique

Electrophoretic deposition (EPD) is the potential process in high porosity thin films' fabrication or complex surface coating for perovskite photovoltaics. Here, the electrostatic simulation is introduced to optimize the EPD cell design for the cathodic EPD process based on functionalized multiwalled carbon nanotubes (f-MWCNTs). The similarity between the thin film structure and the electric field simulation is evaluated by scanning electron microscopy (SEM) and atomic force microscopy (AFM) results. The thin-film surface at the edge has a higher roughness (Ra) compared to the center position (16.48 > 10.26 nm). The f-MWCNTs at the edge position tend to be twisted and bent due to the torque of the electric field. The Raman results show that f-MWCNTs with low defect density are more easily to be positively charged and deposited on the ITO surface. The distribution of oxygen and aluminum atoms in the thin film reveals that the aluminum atoms tend to have adsorption/electrostatic attraction to the interlayer defect positions of f-MWCNTs without individually depositing onto the cathode. Finally, this study can reduce the cost and time for the scale-up process by optimizing the input parameters for the complete cathodic electrophoretic deposition process through electric field inspection.

Toward the Improvement of Silicon-Based Composite Electrodes via an In-Situ Si@C-Graphene Composite Synthesis for Li-Ion Battery Applications

Using Si as anode materials for Li-ion batteries remain challenging due to its morphological evolution and SEI modification upon cycling. The present work aims at developing a composite consisting of carbon-coated Si nanoparticles (Si@C NPs) intimately embedded in a three-dimensional (3D) graphene hydrogel (GHG) architecture to stabilize Si inside LiB electrodes. Instead of simply mixing both components, the novelty of the synthesis procedure lies in the in situ hydrothermal process, which was shown to successfully yield graphene oxide reduction, 3D graphene assembly production, and homogeneous distribution of Si@C NPs in the GHG matrix. Electrochemical characterizations in half-cells, on electrodes not containing additional conductive additive, revealed the importance of the protective C shell to achieve high specific capacity (up to 2200 mAh.g^-1), along with good stability (200 cycles with an average Ceff > 99%). These performances are far superior to that of electrodes made with non-C-coated Si NPs or prepared by mixing both components. These observations highlight the synergetic effects of C shell on Si NPs, and of the single-step in situ preparation that enables the yield of a Si@C-GHG hybrid composite with physicochemical, structural, and morphological properties promoting sample conductivity and Li-ion diffusion pathways.

Boosting Cyclability and Rate Capability of SiOx via Dopamine Polymerization-Assisted Hybrid Graphene Coating for Advanced Lithium-Ion Batteries

SiO_x suffers from the 200% volume change during cycling and low electronic conductivity, resulting in poor cyclability and rate capability as a lithium-ion battery anode. Herein, we demonstrate a dopamine polymerization-guided carbon coating for SiO_x anodes (SiO_x@PDA@GNH). SiO_x@PDA@GNH delivers charge capacities of 1269 and 1140 mA h·g^-1 at charge rates of 0.05 and 3 C, respectively, and a capacity retention of 79.60% after 150 cycles at 1 C. A full cell with LiNi_0.8Co_0.1Mn_0.1O₂ or cathode demonstrates a capacity retention of >80% after 100 cycles at the rate of 0.33 C with an area capacity over 3.2 mA h·cm^-2. Suppressed crack and overgrowth of the SEI layer are the key contributions for the improved performance. These results enlighten a practical pathway for the designing and modifications of SiO_x anodes for high energy density lithium-ion batteries.

Synergistic effects of CNTs/SiO2 composite fillers on mechanical properties of cement composites

This paper investigated the hybridization use of carbon nanotubes (CNTs) with nano-SiO₂ in cement composites. The (CNTs)/SiO₂ composite fillers were designed and prepared by electrostatic self-assembly technology to reinforce cement composites. The mechanical properties, microstructure and hydration characteristics of cement composites incorporating CNTs/SiO₂ fillers were systematically researched. The morphology and optical microscopy results show that the CNTs inside CNTs/SiO₂ fillers tended to unwind due to the mechanical separation and steric hindrance of nano-SiO₂ particles with certain size, and its agglomeration degree in the suspension greatly alleviated over time. With the appropriate incorporation of CNTs/SiO₂ fillers (containing 0.10 wt% CNTs and 0.50 wt% nano-SiO₂), the flexural strength, compressive strength and flexural toughness of the cement mortar matrix were sharply increased by 33.5%, 36.5% and 56.0% after curing for 28 days compared to the plain sample, respectively. Microscopic observations show that appropriate nano-additives can densify and refine the hydrated microstructure, and the crack-bridging, debonding and pull-out behaviors of CNTs were all observed. Hydration analysis quantitatively reveals that CNTs/SiO₂ fillers significantly accelerated the cement hydration process by virtue of the nano-nucleating action. The reinforcing mechanisms of CNTs/SiO₂ fillers can be attributed to the proposed synergistic effects of CNTs/SiO₂ fillers, which mainly include the better dispersion stability of CNTs, the nucleating effect of nano-additives and the pozzolanic reaction by nano-SiO₂, thus positively leading to increased mechanical properties.

CNTs/SiO₂ composite fillers are prepared by assembling CNTs with nano-SiO₂ paticles. The synergistic reinforcing effects of the prepared CNTs/SiO₂ fillers on cement composites were researched.