NANO LETTERS
Silicon Nanotube Battery Anodes Mi-Hee Park,† Min Gyu Kim,‡ Jaebum Joo,§ Kitae Kim,| Jeyoung Kim,| Soonho Ahn,| Yi Cui,*,⊥ and Jaephil Cho*,†
2009 Vol. 9, No. 11 3844-3847
School of Energy Engineering, Ulsan National Institute of Science & Technology, Ulsan, Korea 689-798, Beamline Research DiVision, Pohang Accelerator Laboratory, Pohang, Korea 790-784, Department of Applied Chemistry, Hanyang UniVersity, Ansan, Korea 426-791, Battery R&D, LG Chem, Ltd. 104-1, Moonji-dong, Yuseong-gu, Daejeon, Korea 305-380, and Department of Materials Science and Engineering, Stanford UniVersity, Stanford, California 94305 Received June 26, 2009; Revised Manuscript Received August 23, 2009
ABSTRACT We present Si nanotubes prepared by reductive decomposition of a silicon precursor in an alumina template and etching. These nanotubes show impressive results, which shows very high reversible charge capacity of 3247 mA h/g with Coulombic efficiency of 89%, and also demonstrate superior capacity retention even at 5C rate ()15 A/g). Furthermore, the capacity in a Li-ion full cell consisting of a cathode of LiCoO2 and anode of Si nanotubes demonstrates a 10 times higher capacity than commercially available graphite even after 200 cycles.
The specific energy storage capacity and the charge/discharge rate of lithium ion batteries are critical for their use in electric vehicles (EVs) and to store energy produced by intermittent sources such as solar cells and wind.1 Despite significant gains in rate capability and safety through the use of new materials,2,3 increasing specific energy capacity remains a challenge. Replacing graphitic carbon with Si as the anode material can result in an increase in anode capacity by a factor of 10 and can considerably increase the energy capacity of the total battery. However, a rapid loss of the reversible capacity upon cycling, which is associated with the large volume expansion of Si, is a challenge.4 Recent studies on Si nanowires5,6 and nanoporous Si7 show great promise in overcoming this issue. When reacting with Li, Si is known to incorporate 4.4 Li atoms per Si atom. In Li-ion batteries, this results in the extremely high specific capacity of 4200 mA h/g, which is 10 times higher than the capacity of graphitic carbon (372 mA h/g).8,9 However, the 300% volume change upon lithium insertion commonly causes pulverization and thus a loss of electrical contact between Si and the current collector. Previous studies on improving the capacity of Si-based materials have been focused on nanoparticle composites and carbon prepared by ball-milling and thermal reduction.10-17 Despite these efforts, these electrodes still suffer from rapid * Corresponding authors,
[email protected] and
[email protected]. † School of Energy Engineering, Ulsan National Institute of Science & Technology. ‡ Beamline Research Division, Pohang Accelerator Laboratory. § Department of Applied Chemistry, Hanyang University. | Battery R&D, LG Chem, Ltd. ⊥ Department of Materials Science and Engineering, Stanford University. 10.1021/nl902058c CCC: $40.75 Published on Web 09/11/2009
2009 American Chemical Society
capacity fading. Recently, Si nanowires5,6 and 3D porous Si particles18 have been demonstrated to exhibit good cycling performance as anode materials since both types of structures provide empty space to accommodate Si volume changes and allow for facile strain relaxation without mechanical fracture upon lithium insertion. However, these materials exhibited increased polarization at higher current rates and some degree of capacity fading over many cycles, which could possibly be due to the limited surface area accessible to the electrolyte and the continuous growth of solid electrolyte interphase (SEI) at the interface between the silicon and electrolyte. For instance, hollow nestlike silicon nanospheres showed the first discharge capacity (lithium dealloy) of 3052 mA h/g at a rate of 2000 mA/g, but its Coulombic efficiency and capacity retention ratio after 50 cycles were 73% and
