Silicon-based nanosheets synthesized by a topochemical reaction for use as anodes for lithium ion batteries

Abstract

Silicon is the most promising anode material for the next generation highperformance lithium ion batteries. However, its commercial application is hindered by its poor performance due to the huge volume change during cycling. Although two-dimensional silicon-based materials show significantly improved performance, flexible synthesis of such materials is still a challenge. In this work, silicon-based nanosheets with a multilayer structure are synthesized for the first time by a topochemical reaction. The morphology and oxidation state of these nanosheets can be controlled by appropriate choice of reaction media and oxidants. Benefiting from the hierarchical structure and ultrathin size, when the silicon-based nanosheets are employed as anodes they exhibit a charge (delithiation) capacity of 800 mAh/g after 50 cycles with a maximum coulombic efficiency of 99.4% and good rate performance (647 mAh/g at 1 A/g). This work demonstrates a novel method for preparing nanosheets not only for lithium ion batteries but also having various potential applications in other fields, such as catalysts, electronics and photonics.

Highly Stable Lithium−Sulfur Batteries Promised by Siloxene: An Effective Cathode Material to Regulate the Adsorption and Conversion of Polysulfides

“…Fourier transform infrared (FTIR) and Raman spectra were conducted to further reveal the chemical composition of resultant siloxene nanosheets. Figure 2b displays the FTIR spectrum with characteristic bands at 452, 869, 1050, and 2137 cm −1 , attributing to the stretching vibrations of Si–Si, Si–H, Si–O–Si, and OSi 2 Si‐H modes, respectively 39,41. The FTIR spectrum bands at 3400 cm −1 originate from vibrations of –OH, revealing the oxidation and hydroxylation during the exfoliation process of silicene from CaSi 2 .…”

“…Corresponding energy dispersive X‐ray spectroscopy (EDS) analysis is depicted in Figure S1, Supporting Information, which reveals the presence of Si and O atoms throughout the siloxene nanosheets. The introduction of O atoms into planar Si begins in the process of the Si layer being stripped from CaSi 2 , owing to that newly formed layered Si nanosheets (silicene) are highly reactive and thus can be rapidly oxidized 39. SEM images (Figure S2, Supporting Information) display the graphene‐like structure of siloxene nanosheets with crumpled morphology, which is in contrast to the bulk CaSi 2 with clearly compact stepped stacking structure (Figure S3, Supporting Information), revealing the effective exfoliation of siloxene nanosheets from CaSi 2 .…”

“…Figure a exhibits the core‐level spectrum of Si 2p states of the siloxene nanosheets. In order to confirm the oxidation states of siloxene nanosheets, the Si 2p spectrum can be fitted into five peaks with binding energy between 99.3 and 103.5 eV, attributed to Si 0 , Si 1+ , Si 2+ , Si 3+ , and Si 4+ 39,40. The results of XPS fitting also indicate that the chemical states of Si in the resultant siloxene distinguish from the one in bulk SiO 2 (Si 4+ ).…”

“…The introduction of O atoms into planar Si begins in the process of the Si layer being stripped from CaSi 2 , owing to that newly formed layered Si nanosheets (silicene) are highly reactive and thus can be rapidly oxidized. [39] SEM images ( Figure S2, Supporting Information) display the graphene-like structure of siloxene nanosheets with crumpled morphology, which is in contrast to the bulk CaSi 2 with clearly compact stepped stacking structure ( Figure S3, Supporting Information), revealing the effective exfoliation of siloxene nanosheets from CaSi 2 . In the high-resolution TEM (HRTEM) image ( Figure 1c), it is clear that the atomic arrangement of such siloxene nanosheets have amorphous characteristics, which is consistent with the selected area electron diffraction (SAED) pattern (inset in Figure 1c).…”

“…)34,35 from CaSi 2 , which is a hexagonal layered structure consisting of alternating Ca layers and corrugated Si (111) planes 36. In the fields of solar‐electric energy conversion37 and lithium storage,38,39 siloxene has been demonstrated as an efficient metal‐free semiconductor for photocatalytic water‐splitting, and an excellent anode material for Li‐ion batteries. Nevertheless, as a unique 2D material, the exploration of siloxene's potential application in electrochemical energy storage is still very much in its infancy.…”