Ultrathin MoS 2 @C layered structure as an anode of lithium ion battery
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Ultrathin MoS2@C layered structure as an anode of lithium ion battery Jae-Min Jeong1, Seunghwan Seok1, Bong Gill Choi 2 and Do Hyun Kim1 1 Department of Chemical & Biomolecular engineering, KAIST, 291 Daehak-ro, Yuseong-gu, Daejeon 305-701, Republic of Korea. 2 Department of Chemical Engineering, Kangwon National University, Samcheok 245-711, Republic of Korea. ABSTRACT We report a simple and scalable process to synthesize the core–shell nanostructure of MoS2@N-doped carbon nanosheets (MoS2@C), in which polydopamine is coated on the MoS2 surface and then carbonized. Transmission electron microscopy reveals that the assynthesized MoS2@C possesses a nanoscopic and ultrathin layer of MoS2 sheets with a thin and conformal coating of carbon layers (૫5 nm). The MoS2@C demonstrates a superior electrochemical performance as an anode material for lithium ion batteries compared to exfoliated MoS2 sample. This unique core–shell structure is capable of excellent delivery of Li+ ion in charging–discharging process: a specific capacity as high as 1239 mA h gí1, a high rate of charging-discharging capability even at a high current rate of 10 A gí1 while retaining 597 mA h gí1, and a good cycle stability over 70 cycles at a high current rate of 2 A gí1. INTRODUCTION The development of novel electrodes with high capacity, good cyclability and low cost for lithium batteries is of pivotal importance in applications to portable electronics, electric vehicles and stationary power backups [1, 2]. The combination of high capacity, low cost, ease of fabrication and low discharged voltage makes the layered metal sulfide (LMS) family (e.g. MoS2, WS2 and SnS2) an attractive candidate for an anode in lithium ion batteries [3, 4]. Moreover, these materials, with thin layers close to a monolayer, demonstrated much better electrochemical performance compared to the pristine bulk materials [5]. However, most LMSbased electrodes suffer from limited cyclability and poor rate capability caused by the intrinsically poor electrical conductivity of the LMS as well as the generation of polysulfide Li2Sx (2 < x < 8) during the Li charging process [6]. There have been attempts to resolve these issues by the construction of carbon/LMS composites or the expansion of the interlayer distance of metal sulfides using polymers [7]. Nevertheless, the electrochemical performance of LMS is not satisfactory yet. Most of the synthesized or mixed LMS with carbon support (e.g. graphene, carbon nanotubes and mesoporous carbons) has undesirable electronic pathways because of their partial carbon coating and non-exfoliating state of LMS. Although the incorporation of polymers such as polyethylene oxide is an effective way to exfoliate LMS sheets, additional carbon is required to increase the electrical conductivity of LMS [6]. Consequently, a fully carbon wrapped and exfoliated LMS with a core–shell structure has been investigated to improve electrical conductivity and prevent the dissolution of polysulfide. Here, we report a simple and efficient method for the preparation
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