title: Facile Synthesis of Ge/N-Doped Carbon Spheres with Varying Nitrogen Content for Lithium Ion Battery Anodes.
abstract: The simple fabrication of composites of germanium nanoparticles dispersed on nitrogen-doped carbon nanospheres (Ge/NC) of varying nitrogen content and their performance in lithium ion battery anodes are reported. A heavily nitrogen-doped carbon gel was formed by condensing m-phenylenediamine with formaldehyde (PF-gel); a less heavily N-doped gel was formed by condensing resorcinol and m-phenylenediamine with formaldehyde (RPF-gel); and an undoped gel was formed by condensing resorcinol with formaldehyde (RF-gel). Pyrolises of the gels with GeCl4at 750 °C produced nanocrystalline Ge composites with 7.5 atom % N-doped carbon, termed Ge/NC (PF), with 3.9% N-doped carbon, termed Ge/NC (RPF) and undoped carbon, termed Ge/C (RF). The heavily N-doped Ge/NC (PF) anode retained a reversible capacity of 684 mAhg-1at a specific current of 0.2 Ag-1after 200 cycles, versus 337 mAhg-1retained by anode made with Ge/NC (RPF) and 278 mAhg-1retained by anode made with undoped Ge/C (RF). At a specific current 2.0 Ag-1, the capacity of the Ge/NC (PF) anode was 472 mAhg-1, versus the 210 mAhg-1of the Ge/NC (RPF) anode and 83 mAhg-1of the Ge/C (RF) anode. The enhanced performance of the Ge/NC (PF) anode is attributed to the better electrical conductivity of Ge/NC (PF) and to the higher density of Li+binding defects in its N-doped carbon.
authors.affiliation: Department of Chemical Engineering and Department of Chemistry, Center for Electrochemistry, University of Texas at Austin , 1 University Station C0400, Austin, Texas 78712-0231, United States.
authors.forename: Duck Hyun
authors.initials: DH
authors.lastname: Youn
authors.affiliation: Department of Chemical Engineering and Department of Chemistry, Center for Electrochemistry, University of Texas at Austin , 1 University Station C0400, Austin, Texas 78712-0231, United States.
authors.forename: Nicholas A
authors.initials: NA
authors.lastname: Patterson
authors.affiliation: Department of Chemical Engineering, Pohang University of Science and Technology (POSTECH) , Pohang 790-784, South Korea.
authors.forename: Hunmin
authors.initials: H
authors.lastname: Park
authors.affiliation: Department of Chemical Engineering and Department of Chemistry, Center for Electrochemistry, University of Texas at Austin , 1 University Station C0400, Austin, Texas 78712-0231, United States.
authors.forename: Adam
authors.initials: A
authors.lastname: Heller
authors.affiliation: Department of Chemical Engineering and Department of Chemistry, Center for Electrochemistry, University of Texas at Austin , 1 University Station C0400, Austin, Texas 78712-0231, United States.
authors.forename: C Buddie
authors.initials: CB
authors.lastname: Mullins
keywords: anode; germanium; lithium ion battery; nitrogen-doped carbon