Original Article

Citation: NPG Asia Materials (2016) 8, e272; doi:10.1038/am.2016.61
Published online 20 May 2016

Graphene quantum dots: structural integrity and oxygen functional groups for high sulfur/sulfide utilization in lithium sulfur batteries
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Jungjin Park1,2,13, Joonhee Moon3,13, Chunjoong Kim4,13, Jin Hyoun Kang3, Eunhak Lim3, Jaesung Park5, Kyung Jae Lee1,2, Seung-Ho Yu1,2, Jung-Hye Seo6,7, Jouhahn Lee6, Jiyoung Heo8, Nobuo Tanaka9, Sung-Pyo Cho10, Jeffrey Pyun11, Jordi Cabana12, Byung Hee Hong3 and Yung-Eun Sung1,2

  1. 1School of Chemical and Biological Engineering, Seoul National University, Seoul, Republic of Korea
  2. 2Center for Nanoparticle Research, Institute for Basic Science, Seoul, Republic of Korea
  3. 3Department of Chemistry, College of Natural Science, Seoul National University, Seoul, Republic of Korea
  4. 4School of Materials Science and Engineering, Chungnam National University, Daejeon, Republic of Korea
  5. 5Korea Research Institute of Standards and Science, Daejeon, Republic of Korea
  6. 6Korea Basic Science Institute, Daejeon, Republic of Korea
  7. 7Yonsei Center for Research Facilities, Seoul, Republic of Korea
  8. 8Department of Biomedical Technology, Sangmyung University, Chungnam, Republic of Korea
  9. 9EcoTopia Science Institute, Nagoya University, Nagoya, Japan
  10. 10National Center for Inter-University Research Facilities, Seoul National University 1 Gwank-ro Gwanak-gu, Seoul, Republic of Korea
  11. 11Department of Chemistry and Biochemistry, University of Arizona, Tucson, AZ, USA
  12. 12Department of Chemistry, University of Illinois at Chicago, Chicago, IL, USA

Correspondence: Professor BH Hong, Department of Chemistry, College of Natural Science, Seoul National University, Seoul 151-747, Republic of Korea. E-mail: byunghee@snu.ac.kr; Professor Y-E Sung, School of Chemical and Biological Engineering, Seoul National University, Republic of Korea and Center for Nanoparticle Research, Institute for Basic Science, Seoul 151-742, Republic of Korea. E-mail: ysung@snu.ac.kr

13These authors contributed equally to this work.

Received 14 December 2015; Revised 29 February 2016; Accepted 6 March 2016

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Abstract

Lithium–sulfur (Li–S) batteries are expected to overcome the limit of current energy storage devices by delivering high specific energy with low material cost. However, the potential of Li–S batteries has not yet been realized because of several technical barriers. Poor electrochemical performance is mainly attributed to the low electrical conductivity of the fully charged and discharged species, the irreversible loss of polysulfide anions and the decrease in the number of electrochemically active reaction sites during battery operation. Here, we report that the introduction of graphene quantum dots (GQDs) into the sulfur cathode dramatically enhanced sulfur/sulfide utilization, yielding high performance. In addition, the GQDs induced structural integrity of the sulfur–carbon electrode composite by oxygen-rich functional groups. This hierarchical architecture enabled fast charge transfer while minimizing the loss of lithium polysulfides, which is attributed to the physicochemical properties of GQDs. The mechanisms through which excellent cycling and rate performance are achieved were thoroughly studied by analyzing capacity versus voltage profiles. Furthermore, experimental observations and theoretical calculations further clarified the role played by GQDs by proving that C–S bonding occurs. Thus, the introduction of GQDs into Li–S batteries will provide an important breakthrough allowing their use as high-performance and low-cost batteries for next-generation energy storage systems.

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