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Three-Dimensional Porous Si and SiO2 with In Situ Decorated Carbon Nanotubes As Anode Materials for Li-ion Batteries Junming Su, Jiayue Zhao, Liangyu Li, Congcong Zhang, Chunguang Chen, Tao Huang, and Aishui Yu* Department of Chemistry, Shanghai Key Laboratory of Molecular Catalysis and Innovative Materials, Institute of New Energy, Collaborative Innovation Center of Chemistry for Energy Materials, Fudan University, Shanghai 200438, China S Supporting Information *
ABSTRACT: A high-capacity Si anode is always accompanied by very large volume expansion and structural collapse during the lithium-ion insertion/extraction process. To stabilize the structure of the Si anode, magnesium vapor thermal reduction has been used to synthesize porous Si and SiO2 (pSS) particles, followed by in situ growth of carbon nanotubes (CNTs) in pSS pores through a chemical vapor deposition (CVD) process. Field-emission scanning electron microscopy and high-resolution transmission electron microscopy have shown that the final product (pSS/CNTs) possesses adequate void space intertwined by uniformly distributed CNTs and inactive silica in particle form. pSS/CNTs with such an elaborate structural design deliver improved electrochemical performance, with better coulombic efficiency (70% at the first cycle), cycling capability (1200 mAh g−1 at 0.5 A g−1 after 200 cycles), and rate capability (1984, 1654, 1385, 1072, and 800 mAh g−1 at current densities of 0.1, 0.2, 0.5, 1, and 2 A g−1, respectively), compared to pSS and porous Si/CNTs. These merits of pSS/CNTs are attributed to the capability of void space to absorb the volume changes and that of the silica to confine the excessive lithiation expansion of the Si anode. In addition, CNTs have interwound the particles, leading to significant enhancement of electronic conductivity before and after Si-anode pulverization. This simple and scalable strategy makes it easy to expand the application to manufacturing other alloy anode materials. KEYWORDS: chemical vapor deposition, carbon nanotubes, lithium-ion battery, magnesium vapor thermal reduction, silicon anode
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INTRODUCTION Rechargeable Li-ion batteries have been widely used in computer, communication, and consumer electronics (3C) products and have the potential to eliminate lead-acid cell use in electrical vehicles owing to their higher energy density, lower pollution levels in manufacturing processes, and longer cycle life.1−3 High-capacity cathode and anode materials are required for large-scale application of lithium-ion batteries. Currently, however, commercialized Li-ion batteries with graphite as an anode material (theoretical capacity 372 mAh g−1) are still far from practical use in electric vehicles (EVs) because of their limited capacity and unsatisfactory cycling performance.4 Beyond graphite, many other materials with higher theoretical capacities, such as silicon5−8 and Cu6Sn5,9 have been proposed. Among these, silicon is more attractive because of its highest theoretical specific capacity (∼4200 mAh g−1), low redox potential (
