ORIGINAL PAPER Electrochemical performance of modified artificial graphite as anode material for lithium ion batteries Chunmei Wang & Hailei Zhao & Jing Wang & Jie Wang & Pengpeng Lv Received: 29 March 2012 / Revised: 28 April 2012 / Accepted: 1 May 2012 / Published online: 15 May 2012 # Springer-Verlag 2012 Abstract Artificial graphite anode material was modified by coating an amorphous carbon layer on the particle sur- face via a sol-gel and pyrolysis route. The electrochemical measurements demonstrate that appropriate carbon coating can increase the specific capacity and the initial coulombic efficiency of the graphite material, while excessive carbon coating leads to the decrease in specific capacity. Thick coating layer is obviously unfavorable for the lithium ion diffusion due to the increased diffusion distance, but the decreased specific surface area caused by carbon coating is beneficial to the decrease of initial irreversible capacity loss. The sample coated with 5 wt.% glucose exhibits a stable specific capacity of 340 mAhg -1 . Carbon coating can re- markably enhance the rate capability of the graphite anode material, which is mainly attributed to the increased diffu- sion coefficient of lithium ion. Keywords Li ion batteries . Electrodes . Anodes . Electrochemical characterizations Introduction Artificial graphite (noted as AGP) has been widely used as an anode material for lithium ion batteries due to its desirable charge potential profile, excellent cyclability, and good safety feature since the invention of lithium ion re- chargeable batteries in the early 1990s. However, its low theoretical capacity (372 mAhg -1 ) cannot satisfy the in- creasing requirements of the electronic devices and electric vehicles to the batteries. Besides, the drawbacks related to graphite, such as cointercalation phenomenon of solvent molecules and anisotropic structure feature, limit its electro- chemical performance. The former can result in exfoliation of graphite and thereby cause the consequent destruction of the graphite structure. This prevents the use of small mole- cule solvent with high ionic conductivity. The latter restricts the random diffusion of lithium ions into the graphite struc- ture. Both of them limit the rate capability of graphite anode. Moreover, large initial irreversible capacity loss is another serious problem for graphite anode, which is mainly caused by the complex and imperfect surface structure, such as sp 3 - hybridized carbon, carbon chains, and edge carbon [1]. Many works have been carried out to improve the electro- chemical performance of graphite anode, such as employing smaller particles [2], preparing graphite/nanopowder com- posite [3–5], and oxidizing or purifying the graphite [6–9]. Recently, a lot of research findings have confirmed that cycling performance and rate capability can be improved by surface coating with amorphous carbon [10–13]. Compared with graphite, amorphous carbon has an iso- tropic feature, which enables lithium ions to transport inside randomly and thereby exhibits a good rate capability. Be- sides, amorphous carbon shows minor volume change dur- ing charge/discharge process [14, 15] and thus has a good cyclic performance. Therefore, surface modification by coating amorphous carbon is as an effective approach to improve the electrochemical performance of graphite. Re- cently, many works have been reported, which focused mainly on the effect of carbon precursor [16, 17], coating C. Wang : H. Zhao (*) : J. Wang : J. Wang : P. Lv School of Materials Science and Engineering, University of Science and Technology Beijing, Beijing 100083, China e-mail: hlzhao@ustb.edu.cn H. Zhao Beijing Key Lab of New Energy Materials and Technology, Beijing 100083, China Ionics (2013) 19:221–226 DOI 10.1007/s11581-012-0733-9