Fabrication of Carbon/Silicon Composite as Lithium-ion Anode with Enhanced Cycling Stability

Ag nanoparticle modified porous Si microspheres as high-performance anodes for Li-ion batteries

This study aimed to address the challenges associated with silicon (Si) anode materials in Li-ion batteries, such as their large volume effect and poor electrical conductivity. To overcome these limitations, a novel composite microsphere called pSi/Ag was developed using quartz waste through a combination of high-energy ball-milling, spray drying, and magnesiothermic reduction techniques. The morphology and structure of the pSi/Ag composite were thoroughly characterized using various methods, including X-ray diffraction, field-emission scanning electron microscopy, and transmission electron microscopy. The results revealed that the Ag nanoparticles were uniformly dispersed within the porous micron-sized Si sphere particles, leading to enhanced electrochemical performance compared to pure porous silicon that did not undergo the spray drying process. The use of micron-sized Si prevented the excessive formation of the solid electrolyte interphase film, and the pSi/Ag-5 anode, prepared with 5 wt% AgNO3 as a precursor, demonstrated an impressive initial Coulombic efficiency of 92.8%. Moreover, a high specific capacity of 1251.4 mA h g-1 over 300 cycles at a current density of 4000 mA g-1 was attributed to the improved conductivity provided by the Ag nanoparticles in the Si matrix. The straightforward synthesis method employed in this study to produce pSi/Ag presents a promising approach for the future development of high-performance silicon anodes in Li-ion batteries.

Understanding of the Electrochemical Behavior of Lithium at Bilayer-Patched Epitaxial Graphene/4H-SiC

Novel two-dimensional materials (2DMs) with balanced electrical conductivity and lithium (Li) storage capacity are desirable for next-generation rechargeable batteries as they may serve as high-performance anodes, improving output battery characteristics. Gaining an advanced understanding of the electrochemical behavior of lithium at the electrode surface and the changes in interior structure of 2DM-based electrodes caused by lithiation is a key component in the long-term process of the implementation of new electrodes into to a realistic device. Here, we showcase the advantages of bilayer-patched epitaxial graphene on 4H-SiC (0001) as a possible anode material in lithium-ion batteries. The presence of bilayer graphene patches is beneficial for the overall lithiation process because it results in enhanced quantum capacitance of the electrode and provides extra intercalation paths. By performing cyclic voltammetry and chronoamperometry measurements, we shed light on the redox behavior of lithium at the bilayer-patched epitaxial graphene electrode and find that the early-stage growth of lithium is governed by the instantaneous nucleation mechanism. The results also demonstrate the fast lithium-ion transport (~4.7-5.6 × 10-7 cm2∙s-1) to the bilayer-patched epitaxial graphene electrode. Raman measurements complemented by in-depth statistical analysis and density functional theory calculations enable us to comprehend the lithiation effect on the properties of bilayer-patched epitaxial graphene and ascribe the lithium intercalation-induced Raman G peak splitting to the disparity between graphene layers. The current results are helpful for further advancement of the design of graphene-based electrodes with targeted performance.

Rheological Properties of Aqueous Sodium Alginate Slurries for LTO Battery Electrodes

Rheological properties of electrode slurries have been intensively studied for manifold different combinations of active materials and binders. Standardly, solvent-based systems are under use, but a trend towards water-based electrode manufacturing is becoming more and more important. The different solvent is beneficial in terms of sustainability and process safety but is also accompanied by some disadvantages such as extraction of residual humidity and a higher complexity concerning slurry stability. Li4Ti5O12 (LTO) active material provides good long-term stability and can be processed in aqueous solutions. Combining the LTO active material with sodium alginate (SA) as a promising biobased polymer binder reveals good electrochemical properties but suffers from bad slurry stability. In this work, we present a comprehensive rheological study on material interactions in anode slurries consisting of LTO and SA, based on a complex interaction of differentially sized materials. The use of two different surfactants-namely, an anionic and non-ionic one, to enhance slurry stability, compared with surfactant-free slurry.

Triethoxysilane-derived SiOx-assisted structural reinforcement of Si/carbon nanotube composite for lithium-ion battery

Herein, triethoxysilane-derived SiOx is used as a robust adhesive anchor to bind Si nanoparticles (NPs) and carbon nanotubes (CNTs) to prepare a structurally reinforced Si/CNT microsphere composite. The chemical reaction between the silanol groups of triethoxysilane with the hydroxyl groups on the Si surface and acid-treated CNTs induce strong chemical bonds between the Si NPs and CNTs and among neighboring CNTs, facilitating electron-conduction pathways and structural integrity of the composite, even under severe stress/strain. Thus, the structurally reinforced Si/CNT/SiOx microsphere composite exhibits superior cyclability: ∼88% of its initial capacity of 1112 mA h g-1 is retained after 100 cycles at 0.5 A g-1. Moreover, the Si/CNT/SiOx composite exhibits a negligible change in electrode thickness after 100 cycles. The stable electrochemical behavior and negligible change in the electrode thickness are attributed to the maintenance of the electron-conduction pathways and structural integrity of the Si/CNT/SiOx composite, enabled by the binding of neighboring CNTs with the SiOx anchor.

Low-cost urchin-like silicon-based anode with superior conductivity for lithium storage applications

Poor rate and cycling performance are the most critical drawbacks for Si-based anodes on account of their inferior conductivity and colossal volumetric expansion during lithiation/delithiation. Here we report the fabrication of structurally-integrated urchin-like Si anode, which provides prominent structural stability and distinguished electron and ion transmission pathways for lithium storage. The inexpensive solid Si waste from organosilane industry after acid-washed and further ball-milling serves as the pristine Si-source in this work. Carbon nanotubes (CNTs) are in-situ grown outside Si microparticles, resulting in an urchin-like structure (Si/CNTs). The optimized Si/CNTs presents ascendant invertible capacity and rate performance, achieving up to 920 mAh g^-1 beyond 100 cycles at 100 mA g ^-1, and a capacity of 606.2 mAh g^-1 at 1 A g ^-1 after long cycling for 1000 cycles. The proposed scalable synthesis can be adopted to advance the performance of other electrode materials with inferior conductivity and enormous volume expansions during cycling.

Facile and Scalable Approach To Fabricate Granadilla-like Porous-Structured Silicon-Based Anode for Lithium Ion Batteries

A porous silicon and carbon composite (PSi/C) with granadilla-like structure as an anode material for lithium-ion batteries has been easily fabricated by spray drying and subsequent pyrolysis treatments. For the PSi/C, yolk-shell-structured Si/C nanobeads are equably distributed inside the porous carbon framework. The key point of this work is the combination of the advantages of both the yolk-shell structure and porous structure in one system. The void space inside the yolk-shell Si/C nanobeads and the interconnected three-dimensional porous carbon frameworks can effectively enhance the cyclic stability and conductivity of this composite. As expected, PSi/C with 15.4% silicon content exhibited a specific capacity as high as 1357.43 mAh g^-1 and retained 933.62 mAh g^-1 beyond 100 cycles at 100 mA g^-1. Moreover, it showed a reversible specific capacity as high as 610.38 mAh g^-1 at 1000 mA g^-1, even after 3000 cycles.

Nanostructured Silicon-Carbon 3D Electrode Architectures for High-Performance Lithium-Ion Batteries

Silicon is an attractive anode material for lithium-ion batteries. However, silicon anodes have the issue of volume change, which causes pulverization and subsequently rapid capacity fade. Herein, we report organic binder and conducting diluent-free silicon-carbon 3D electrodes as anodes for lithium-ion batteries, where we replace the conventional copper (Cu) foil current collector with highly conductive carbon fibers (CFs) of 5-10 μm in diameter. We demonstrate here the petroleum pitch (P-pitch) which adequately coat between the CFs and Si-nanoparticles (NPs) between 700 and 1000 °C under argon atmosphere and forms uniform continuous layer of 6-14 nm thick coating along the exterior surfaces of Si-NPs and 3D CFs. The electrodes fabricate at 1000 °C deliver capacities in excess of 2000 mA h g^-1 at C/10 and about 1000 mA h g^-1 at 5 C rate for 250 cycles in half-cell configuration. Synergistic effect of carbon coating and 3D CF electrode architecture at 1000 °C improve the efficiency of the Si-C composite during long cycling. Full cells using Si-carbon composite electrode and Li_1.2Ni_0.15Mn_0.55Co_0.1O_2-based cathode show high open-circuit voltage of >4 V and energy density of >500 W h kg^-1. Replacement of organic binder and copper current collector by high-temperature binder P-pitch and CFs further enhances energy density per unit area of the electrode. It is believed that the study will open a new realm of possibility for the development of Li-ion cell having almost double the energy density of currently available Li-ion batteries that is suitable for electric vehicles.

Basic Medium Heterogeneous Solution Synthesis of α-MnO₂ Nanoflakes as an Anode or Cathode in Half Cell Configuration (vs. Lithium) of Li-Ion Batteries

Nano α-MnO₂ is usually synthesized under hydrothermal conditions in acidic medium, which results in materials easily undergoing thermal reduction and offers single crystals often over 100 nm in size. In this study, α-MnO₂ built up of inter-grown ultra-small nanoflakes with 10 nm thickness was produced in a rapid two-step procedure starting via partial reduction in solution in basic medium subsequently followed by co-proportionation in thermal treatment. This approach offers phase-pure α-MnO₂ doped with potassium (cryptomelane type K_0.25Mn₈O₁₆ structure) demonstrating considerable chemical and thermal stability. The reaction pathways leading to this new morphology and structure have been discussed. The MnO₂ electrodes produced from obtained nanostructures were tested as electrodes of lithium ion batteries delivering initial discharge capacities of 968 mAh g⁻¹ for anode (0 to 2.0 V) and 317 mAh g⁻¹ for cathode (1.5 to 3.5 V) at 20 mA g⁻¹ current density. At constant current of 100 mA g⁻¹, stable cycling of anode achieving 660 mAh g⁻¹ and 145 mAh g⁻¹ for cathode after 200 cycles is recorded. Post diagnostic analysis of cycled electrodes confirmed the electrode materials stability and structural properties.