Heteroepitaxy-Induced Rutile VO2 with Abundantly Exposed (002) Facets for High Lithium Electroactivity Sangbaek Park,†,⊥ Chan Woo Lee,†,⊥ Jae-Chan Kim,‡ Hee Jo Song,† Hyun-Woo Shim,‡ Sangwook Lee,§ and Dong-Wan Kim*,‡ †
Department of Materials Science and Engineering, Seoul National University, Seoul 151-744, Korea School of Civil, Environmental and Architectural Engineering, Korea University, Seoul, 136-713, Korea § School of Materials Science and Engineering, Kyungpook National University, 80 Daehakro, Bukgu, Daegu 41566, Korea ‡
S Supporting Information *
ABSTRACT: Research on VO2 cathodes for lithium ion batteries has been mainly focused on the VO2 (B) phase. However, rutile VO2 (M/R) has rarely been studied because of the intrinsically low lithium activity resulting from the highly anisotropic nature of lithium accommodation. Here, we demonstrate that heteroepitaxial engineering can be an effective strategy for activating the anisotropic electrode and developing kinetically superior electrodes. Appropriate lattice mismatch between the active material (VO2) and conductive support (Sb:SnO2) yields a coherent interface, where tensile strain aids preferential growth along the rutile c-axis as well as expansion in the ab plane and thereby the exposure of reactive (002) facets. The VO2−Sb:SnO2 electrode exhibits high reversible capacity (350 mA h g−1 at 100 mA g−1) and ultrafast rate capability (196 mA h g−1 at 2000 mA g−1) with structural stability, which represents record-high performance compared with previous VO2 reports, including those on other polymorphs such as VO2 (A) and VO2 (B).
L
principally in the ab plane and to a negligible extent along the caxis.20 Lithium electroactivity of an anisotropic electrode is strongly dependent on crystallite size at room temperature. Nanosized rutile showed much higher reversible capacity of 150 mA h g−1, corresponding to 0.45 Li ion per TiO2, compared to that of the bulk rutile (10 mA h g−1).20 Also, mesoporous rutile β-MnO2 could deliver a reversible capacity of 200 mA h g−1, whereas bulk crystalline β-MnO2 has no ability to intercalate lithium.21 This behavior is because the decrease in the crystallite size reduces the energetic barrier of the lithium accommodation that results in anisotropic lattice expansion. Furthermore, facet engineering has been considered as a critical strategy to enhance the performance of active materials exhibiting anisotropic lithium diffusion. For example, anatase TiO2 and Li[Li1/3−2x/3NixMn2/3−x/3]O2 electrodes with a large portion of reactive facets have shown much higher reversible capacity at the same rate compared to unturned crystals.22−24 Also, (010) facet-exposed LiFePO4 exhibited excellent rate performance because of the lower energy barrier for lithium ion
ithium ion batteries (LIBs) have been favorable power sources in portable electronics and for electric vehicle applications because of their high energy density, long cycle life, and environmental benignity.1−4 Vanadium oxides such as VO2 (B), V2O5, V3O7, V4O9, and V6O13 have long been investigated as cathode materials for LIBs because of their high capacity, low cost, and abundant sources.5−11 VO2 (B) has shown a prominent performance because of its structural stability resulting from edge-sharing VO6 octahedra bilayers, fast lithium ion diffusion rate, and high capacity (theoretically 320 mA h g−1 for Li1.0VO2).7,12−14 However, rutile VO2 (M/R) phases are regarded unsuitable for a LIB cathode, and there are only several reports that demonstrate lower capacity (
