A novel synthesis of Si/mesoporous carbon (MC) composite is investigated in this work, as well as its lithium storage ability as an anode material. Nanosized Si particles are deposited in the pores of carbon matrix via magnesiothermic reduction, the content of Si is around 43 wt.% in the composite. The electrochemical performance of the composite electrode is effectively improved due to the buffering effect of carbon matrix and its Si-embedded structure. It exhibits an initial reversible capacity of 1220.9 mA h g⁻¹, and an modified cycleability having the capacity of 594 mA h g⁻¹ in the 50th cycle. Additionally, the good rate capability of the electrode can be ascribed to the rich porous channels and the good conductive network of mesoporous carbon.

Silicon–carbon composites consisting of Si particles embedded in a dense and non-porous carbon matrix are prepared by the pyrolysis of intimate mixtures of poly(vinyl chloride) (PVC) and Si powder at 900 °C under a flow of N₂. In contrast to bare micrometer-sized (1–10 μm) and nanometer-sized (10–100 nm) Si powders, which show poor cycling behavior with almost no capacity remaining after 15 cycles, the texture of the composite is seen to greatly enhance the reversibility of the alloying reaction of Si with Li. For instance, a capacity of ca. 1000 mA h g^–1 is achieved for 20 cycles (0–2.0 V vs. Li⁺/Li) for a silicon–carbon composite containing nanometer-sized Si particles. We also demonstrate that a mild manual grinding treatment degrades the cycling performance of the composites to levels as low as the parent Si, even though free Si is not released. The electrochemical measurements in conjunction with Raman spectroscopy data indicate that a huge stress is exerted on the Si domains by the in situ formed carbon. This carbon-induced stress is found to disappear during the milling of the composites, indicating that the carbon-induced pressure, along with the accompanying improvement in electrical connectivity, are the key parameters for the improved cycling behavior of Si versus Li.

Diatomite, a natural clay mineral, is mainly composed of silica and contains a large number of fine microscopic pores. In the present work, a series of porous Si/C composites are successfully synthesized by employing diatomite as a raw material, followed by low temperature magnesiothermic reduction, impregnation and carbonization of phenolic resin. The obtained Si/C composites are consisted of porous Si coated with a 15 nm thick amorphous layer of carbon. Porous Si/C composites with different ratios of Si and C are investigated as anode materials for Li-ion batteries. The porous Si/C composite containing 33% carbon exhibits the highest reversible capacity of about 1628 mAh g⁻¹ at the first cycle with excellent capacity retention in the following cycles. Moreover, the porous Si/C composites display the excellent rate performance at high current densities such as 1 and 2 A g⁻¹. The optimum electrochemical performance could also be tuned by varying the proportions of porous Si and carbon precursors during the preparation process. The results indicate that the natural pore structures of Si and C are conducive to the electrochemical performance and clay mineral diatomite could be considered as a promising raw material for Si/C composites for lithium-ion batteries.

Silicon/carbon composite was prepared by an in situ carbon-thermal reduction method that used pyrolyzed carbon to reduce silicon monoxide. The composite was confirmed by X-ray diffraction and high-resolution transmission electron microscope. It was demonstrated that nano-scale (ca. 20 nm) crystal silicon particles were obtained and simultaneously distributed in amorphous carbon matrix. Compared with the silicon/carbon composite having commercial nano-silicon particles (50–100 nm), the as-prepared composite displayed a good capacity retention. The superior electrochemical properties were attributed not only to small volume changes of silicon particles, but also to better buffering effect of matrix and better electrical contact between the matrix and silicon particles.

Abstract

Nanostructured Si–C composite materials were prepared by dispersing nanocrystalline Si in carbon aerogel and subsequent carbonization. Through this process, nanosize Si was homogeneously distributed in a carbon matrix. The Si–C composites exhibit a reversible lithium storage capacity of 1450 mA h/g when used as anodes in lithium-ion cells. The nanostructured Si–C composite electrodes demonstrated good cyclability. The Si–C composites could provide a novel anode material for lithium-ion batteries.

Abstract

Nano-porous silicon composite incorporated with graphite and pyrolyzed carbon was synthesized and investigated as a promising anode material for lithium-ion batteries. The nano-porous Si/graphite composite was prepared via two-step ball-milling followed by etching process. Then carbon was incorporated by using different approaches. The nano-porous Si/graphite/C composite exhibits a reversible capacity of about 700 mAh/g with no capacity loss up to the 120th cycle at a constant current density of 0.2 mA/cm². The superior electrochemical characteristics are attributed to the nanosized pores in Si particles, which suppress the volume effect, and buffering action as well as excellent electronic and ionic conductivity of carbon materials.

In this study the effect of the carbon coating on the electrochemical properties of LiFePO₄ as a cathode for Li-ion batteries were investigated. The carbon-coated LiFePO₄ particles were synthesized by the mechanochemical process and one-step heat treatment. Microscopic observations using SEM and TEM revealed that the carbon coating reduced the particle size of the LiFePO₄. The carbon-coated LiFePO₄ showed much better performances in terms of the discharge capacity and cycle stability than bare LiFePO₄. It was confirmed that the carbon coating decreased the migration distance of Li-ion and enhanced the charge transfer from CV and ac impedance measurements. The improved electrochemical properties of the carbon-coated LiFePO₄ were, therefore, attributed to the reduced particle size and enhanced electrical contacts by carbon.