The mitigation of pitch-derived carbon with different structures on the volume expansion of silicon in Si/C composite anode

The microstructures of carbon precursors significantly affect the electrochemical performance of Si/C composite anodes.However,the interaction between Si and carbon materials with different structures is still unclear.Pitch-based materials undergoing different thermal treatments are superior sources for synthesizing carbons with different structures.Herein,different types of mesophase pitch(domain,flow-domain and mosaic structure) obtained from controllable thermal condensation are utilized to prepare Si/C composite materials and the corresponding models are established through finite element simulation to explore the correlation between the lithium storage properties of Si/C composites and the structures of carbon materials.The results indicate that the flow-domain texture pitch P2 has a better ability to buffer the volume expansion of silicon particles for its highly ordered arrangement of carbon crystallites inside could disperse the swelling stress uniformly alongside the particle surface.The sample Si@P2 exhibits the highest capacity of 1328 mA h/g after 200 cycles at a current density of 0.1 A/g as well as the best rate performance and stability.While sample Si@P3 in which the mosaic texture pitch P3 composed of random orientation of crystallites undergoes the fastest capacity decay.These findings suggest that highly ordered carbon materials are more suitable for the synthesis of Si/C composite anodes and provide insights for understanding the interaction between carbon and silicon during the charging/discharging process.

Photoluminescent properties of Sb^(3+)-doped and(Sb^(3+),Eu^(3+))co-doped YBO3 phosphors prepared via hydrothermal method and solid-state process

Sb^(3+)-doped YBO3 crystals were prepared through a low-temperature hydrothermal method and a high-temperature solid-state technique,respectively.The effects of preparation methods on the morphologies and luminescent properties of YBO_(3) phosphors were investi-gated.The YBO3 crystals from the hydrothermal system look likeflowers,whereas those from the solid-state process look like some agglomerates of little spheres.The Sb^(3+)-doped YBO3 powders prepared via both methods showed the blue emission with the peak at around 452 nm,which corresponds to the 3P1→1S0 transition of Sb^(3+)ions.However,the emission intensity of the Sb^(3+)-doped YBO3 from the hydrothermal system is about 3.5 times as much as that from the solid-state process.The(Sb^(3+),Eu^(3+))co-doped YBO3 crystals were also prepared through the two methods.The results showed that the emission intensity of Sb^(3+)ions in(Sb^(3+),Eu^(3+))co-doped YBO3 synthesized by the hydrothermal method is stronger than that by the solid-state process.