The low-temperature (400 u C) coating of few-layer graphene on porous Li 4 Ti 5 O 12 via C 28 H 16 Br 2 pyrolysis for lithium-ion batteries { Zelang Jian, ab Liang Zhao, b Rui Wang, b Yong-Sheng Hu,* b Hong Li, b Wen Chen* a and Liquan Chen b Received 8th December 2011, Accepted 9th December 2011 DOI: 10.1039/c2ra01263d Porous Li 4 Ti 5 O 12 coated with few-layer graphene was prepared via the low-temperature pyrolysis of C 28 H 16 Br 2 at 400 uC. The coating layer was very thin and uniform. The coated sample shows superior Li storage performance compared with the as- prepared sample. Capacities of 131 and 104 mA h g 21 can be reached at current rates of 5 and 10 C, respectively. Moreover, cyclic performance is significantly improved after coating. The capacity decreases from 144.6 to 124.4 mA h g 21 after 2400 cycles at a current rate of 2 C in a half cell versus Li/Li + , with high capacity retention of 86%. Lithium-ion batteries (LIBs) have been considered one of the most promising power sources for various types of electric vehicles and large-scale energy storage because of their high energy density, high power density, and environmental friendly features. 1–3 Thus, the search for electrode materials with high power density, long cycle life, and good safety features has become a key issue in the past several years. Spinel Li 4 Ti 5 O 12 has attracted increasing attention as an anode material for LIBs because of the minimal change in its lattice parameter and relatively high voltage during Li + insertion/extraction; these attributes lead to potentially good cyclability and high safety. 4–12 However, pure Li 4 Ti 5 O 12 has limited applications in electric vehicles and large-scale storage because of its low electronic conductivity and moderate Li + diffusion coefficient. 13–15 Strategies such as decreasing particle size and carbon coating have been proposed to solve the problems of pure Li 4 Ti 5 O 12 . Carbon coating can enhance the surface electrical conductivity of electrode materials, and decreasing particle size can reduce the Li + diffusion length; both are effective ways of improving rate performance. 16–19 Typically, carbon coating of electrode materials is conducted at over 700 uC. 8,11,20–23 At such a high temperature, some electrode materials, including lithium transition metal oxides, may be reduced or may become unstable during the carbon coating process. 24 Thus, few reports on the carbon coating of lithium transition metal oxides have been published. Furthermore, high temperature pyrolysis means more energy consumption, which is contrary to our aim of energy saving. Our group has recently reported porous Li 4 Ti 5 O 12 coated with N-doped carbon derived from ionic liquid at 600 uC, which significantly improved the high rate and cyclic performance of the sample. 25 However, this working temperature is still too high for the coating of some lithium transition metal oxides. The low- temperature coating of a highly conductive surface layer has been an essential technology for optimizing poorly conductive and less thermally stable anode and cathode materials for LIBs. Graphene, a two-dimensional one-atom thick sheet of carbon, has attracted considerable attention in the field of nanoscience because of its high surface area of over 2600 m 2 g 21 , excellent thermal and mechanical properties, and superior electrical conductivity. 26–30 Recently, many graphene based composites have been widely in- vestigated as electrode materials for LIBs and supercapacitors. 31–33 However, most of them are mechanical mixtures of graphene and the active materials or are prepared in a complicated way. 10,109-Dibromo-9,99-bianthryl (C 28 H 16 Br 2 ) has a highly symme- trical structure and high carbon content (up to 65.66%). Its molecular structure is shown in Fig. 1. Recently, Cai et al. 34 reported the use of C 28 H 16 Br 2 as a precursor for the preparation of graphene on the (111) surface of Au and Ag at 400 uC, in which Au and Ag were used as substrates. These may also act as catalysts. As shown in Fig. 1, the precursor undergoes dehalogenation to form single covalent C–C bonds between each monomer to create polymer chains at around 200 uC. Then, the polymer chains are subject to cyclodehydrogenation to form graphene nanoribbons at around 400 uC. Here, we extended this approach to coating the electrode materials with few-layer graphene at a rather low temperature of 400 uC. The rough surfaces of the electrode materials (e.g., Li 4 Ti 5 O 12 ) were successfully coated with few-layer graphene using C 28 H 16 Br 2 as a precursor. The porous Li 4 Ti 5 O 12 microspheres were prepared by spray drying. 35 The primary particle size was about 50 nm, and these nanoparticles aggregated to form porous microspheres (the morphologies of the as-prepared Li 4 Ti 5 O 12 are shown in Fig. S1{). Then, the porous Li 4 Ti 5 O 12 powder was mixed with appropriate proportions of the C 28 H 16 Br 2 solution. After the evaporation of the organic solvent, the mixture of C 28 H 16 Br 2 and Li 4 Ti 5 O 12 was heat- treated at 400 uC to obtain the resultant composite. The experimental a State Key Laboratory of Advanced Technology for Materials Synthesis and Processing, School of Materials Science and Engineering, Wuhan University of Technology, Wuhan, 430070, China. E-mail: chenw@whut.edu.cn; Fax: +86 27 87864580 b Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing, 100190, China. E-mail: yshu@aphy.iphy.ac.cn; Fax: +86 10 82649808 { Electronic supplementary information (ESI) available: SEM images for the as-prepared Li 4 Ti 5 O 12 sample; XRD patterns for the as prepared Li 4 Ti 5 O 12 and Li 4 Ti 5 O 12 /graphene samples; TG curve and rate performance for the Li 4 Ti 5 O 12 /graphene sample with a carbon content of 3.51 wt%; HRTEM image for the Li 2 MnO 3 /graphene. See DOI: 10.1039/c2ra01263d RSC Advances Dynamic Article Links Cite this: RSC Advances, 2012, 2, 1751–1754 www.rsc.org/advances COMMUNICATION This journal is ß The Royal Society of Chemistry 2012 RSC Adv., 2012, 2, 1751–1754 | 1751 Downloaded on 22 February 2012 Published on 10 January 2012 on http://pubs.rsc.org | doi:10.1039/C2RA01263D View Online / Journal Homepage / Table of Contents for this issue