Hydrothermal-derived carbon as a stabilizing matrix for improved cycling performance of silicon-based anodes for lithium-ion full cells

In situ magnesiothermic reduction synthesis of a Ge@C composite for high-performance lithium-ion batterie anodes

Metallothermic, especially magnesiothermic, solid-state reactions have been widely applied to synthesize various materials. However, further investigations regarding the use of this method for composite syntheses are needed because of the high reactivity of magnesium. Herein, we report an in situ magnesiothermic reduction to synthesize a composite of Ge@C as an anode material for lithium-ion batteries. The obtained electrode delivered a specific capacity of 454.2 mAh·g-1 after 200 cycles at a specific current of 1000 mA·g-1. The stable electrochemical performance and good rate performance of the electrode (432.3 mAh·g-1 at a specific current of 5000 mA·g-1) are attributed to the enhancement in distribution and chemical contact between Ge nanoparticles and the biomass-based carbon matrix. A comparison with other synthesis routes has been conducted to demonstrate the effectiveness of contact formation during in situ synthesis.

Insights into Electrolytic Pre-Lithiation: A Thorough Analysis Using Silicon Thin Film Anodes

Pre-lithiation via electrolysis, herein defined as electrolytic pre-lithiation, using cost-efficient electrolytes based on lithium chloride (LiCl), is successfully demonstrated as a proof-of-concept for enabling lithium-ion battery full-cells with high silicon content negative electrodes. An electrolyte for pre-lithiation based on γ-butyrolactone and LiCl is optimized using boron-containing additives (lithium bis(oxalato)borate, lithium difluoro(oxalate)borate) and CO₂ with respect to the formation of a protective solid electrolyte interphase (SEI) on silicon thin films as model electrodes. Reversible lithiation in Si||Li metal cells is demonstrated with Coulombic efficiencies (C_Eff ) of 95-96% for optimized electrolytes comparable to 1 m LiPF₆ /EC:EMC 3:7. Formation of an effective SEI is shown by cyclic voltammetry and X-ray photoelectron spectroscopy (XPS). electrolytic pre-lithiation experiments show that notable amounts of the gaseous product Cl₂ dissolve in the electrolyte leading to a self-discharge Cl₂ /Cl^- shuttle mechanism between the electrodes lowering pre-lithiation efficiency and causing current collector corrosion. However, no significant degradation of the Si active material and the SEI due to contact with elemental chlorine is found by SEM, impedance, and XPS. In NCM111||Si full-cells, the capacity retention in the 100th cycle can be significantly increased from 54% to 78% by electrolytic pre-lithiation, compared to reference cells without pre-lithiation of Si.

Recent Advances in Carbon-Silica Composites: Preparation, Properties, and Applications

The thermal catalytic conversion of biomass is currently a prevalent method for producing activated carbon with superb textural properties and excellent adsorption performance. However, activated carbon suffers severely from its poor thermal stability, which can easily result in spontaneous burning. In contrast, silica material is famed for its easy accessibility, high specific surface area, and remarkable thermal stability; however, its broader applications are restricted by its strong hydrophilicity. Based on this, the present review summarizes the recent progress made in carbon-silica composite materials, including the various preparation methods using diverse carbon (including biomass resources) and silica precursors, their corresponding structure–function relationship, and their applications in adsorption, insulation, batteries, and sensors. Through their combination, the drawbacks of the individual materials are circumvented while their original advantages are maintained. Finally, several bottlenecks existing in the field of carbon-silica composites, from synthesis to applications, are discussed in this paper, and possible solutions are given accordingly.

Fabrication of Porous Si@C Composites with Core-Shell Structure and Their Electrochemical Performance for Li-ion Batteries

The pores in silicon particles can accommodate the volume expansion of silicon during the charging–discharging process. However, pores in silicon particles are easily occupied by carbon during the preparation of silicon/carbon composites. In this paper, sulfur was adsorbed in the pores of porous silicon particles before polyaniline (PANI) coating by in-situ polymerization, so that the pores were preserved in porous silicon@carbon (p-Si/@C) composites after the sublimation of sulfur during carbonization. The microstructure and the electrochemical performances of the obtained p-Si/@C composites were investigated. The results indicate that p-Si/@C composites prepared with a sulfur-melting process show a better high-rate performance than those without a sulfur-melting process. Remarkably, the former show a better capacity retention when returning to a low current density. The reversible capacities of the former were 1178 mAh·g−1, 1055 mAh·g−1, 944 mAh·g−1, and 751 mAh·g−1 at 0.2 A·g−1, 0.3 A·g−1, 0.5 A·g−1, and 1.0 A·g−1, respectively. Moreover, the reversible capacities could return to 870 mAh·g−1, 996 mAh·g−1, and 1027 mAh·g−1 when current densities returned to 0.5, 0.3, and 0.2 A·g−1, respectively.