Abstract：A new type globular MnO2 flowers anchored graphene composites was synthesized via redox reactions among potassium permanganate/ethanol/graphene. The crystalline structure, chemical component, and microstructure of the composites were determined by XRD, TG, SEM/TEM and BET analysis. The electrochemical test demonstrates the globular MnO2 material possesses excellent specific capacitance while poor rate capability and cycling stability. By means of anchoring these globular MnO2 flowers onto graphene, the specific capacitance of graphene is significantly improved. Meanwhile, rate capability and cycling stability of the globular MnO2 material can be promoted remarkably. In 0.5mol/L K2SO4 electrolyte, the specific capacitance of the composites reaches as high as 295F·g-1 at 2mV·s-1, and maintains at 102F·g-1 even at a high scan rate of 1000mV·s-1.An outstanding capacitance retention of 96.3% is achieved for the composites after 1000 cycles at 100mV·s-1. It demonstrates the globular MnO2 flowers anchored graphene composites is a very potential electrode material for supercapacitors.
 WANG J G, KANG F, WEI B. Engineering of MnO2-based nanocomposites for high-performance supercapacitors[J]. Progress in Materials Science, 2015, 74:51-124.
 CHEN X, YAN S, WANG N, et al. Facile synthesis and characterization of ultrathin δ-MnO2 nanoflakes[J]. RSC Advances, 2017, 7(88):55734-55740.
 POSR J E. Crystal structure determinations of synthetic sodium, magnesium, and potassium birnessite using TEM and the Rietveld method[J]. American Mineralogist, 1990, 75(5/6):477-489.
 DEVARAJ S, MUNICHANDRAIAH N. Effect of crystallographic structure of MnO2 on its electrochemical capacitance properties[J]. Journal of Physical Chemistry C, 2008, 112(11):4406-4417.
 BROUSSE T, TOUPIN M, DUGAS R, et al. Crystalline MnO2 as possible alternatives to amorphous compounds in electrochemical supercapacitors[J]. Journal of the Electrochemical Society, 2006, 153(12):A2171-A2180.
 TURNER S, BUSECK P R. Todorokites:a new family of naturally occurring manganese oxides[J]. Science, 1981, 212(4498):1024-1027.
 RAGUPATHY P, PARK D H, CAMPET G, et al. Remarkable capacity retention of nanostructured manganese oxide upon cycling as an electrode material for supercapacitor[J]. Journal of Physical Chemistry C, 2009, 113(15):6303-6309.
 XU M W,KONG L B,ZHOU W J,et al.Hydrothermal synthesis and pseudocapacitance properties of α-MnO2 hollow spheres and hollow urchins[J].Journal of Physical Chemistry C,2007,111(51):19141-19147.
 SUBRAMANIAN V, ZHU H, WEI B. Nanostructured MnO2:hydrothermal synthesis and electrochemical properties as a supercapacitor electrode material[J]. Journal of Power Sources, 2006, 159(1):361-364.
 YU P, ZHANG X, CHEN Y, et al. Preparation and pseudo-capacitance of birnessite-type MnO2, nanostructures via microwave-assisted emulsion method[J]. Materials Chemistry & Physics, 2009, 118(2/3):303-307.
 CAO J, LI X, WANG Y, et al. Materials and fabrication of electrode scaffolds for deposition of MnO2 and their true performance in supercapacitors[J]. Journal of Power Sources 2015, 293:657-674.
 REN Y, XU Q, ZHANG J, et al. Functionalization of biomass carbonaceous aerogels:selective preparation of MnO2@CA composites for supercapacitors[J]. ACS Applied Materials & Interfaces, 2014, 6(12):9689.
 HE Y, CHEN W, LI X, et al. Freestanding three-dimensional graphene/MnO2 composite networks as ultralight and flexible supercapacitor electrodes[J]. ACS Nano, 2013, 7(1):174.
 LI L, HU Z A, AN N, et al. Facile synthesis of MnO2/CNTs composite for supercapacitor electrodes with long cycle stability[J]. Journal of Physical Chemistry C, 2014, 118(40):22865-22872.
 SONG Y, FENG D Y, LIU T Y, et al. Controlled partial-exfoliation of graphite foil and integration with MnO2 nanosheets for electrochemical capacitors[J]. Nanoscale, 2015, 7(8):3581.
 MA S B, AHN K Y, LEE E S, et al. Synthesis and characterization of manganese dioxide spontaneously coated on carbon nanotubes[J]. Carbon, 2007, 45(2):375-382.
 SINGH V, JOUNG D, LEI Z, et al. Graphene based materials:past, present and future[J]. Progress in Materials Science, 2011, 56(8):1178-1271.
 MENDOZA-SÁNCHEZ B, COELHO J, POKLE A, et al. A 2D graphene-manganese oxide nanosheet hybrid synthesized by a single step liquid-phase co-exfoliation method for supercapacitor applications[J]. Electrochimica Acta, 2015, 174:696-705.
 MALARD L M, PIMENTA M A, DRESSELHAUS G, et al. Raman spectroscopy in graphene[J]. Physics Reports, 2009, 473(5/6):51-87.
 JORIO A. Raman spectroscopy in graphene-based systems:prototypes for nanoscience and nanometrology[J]. Isrn Nanotechnology, 2012, 2012(2):1-16.
 FERRARI A C, MEYER J C, SCARDACI V, et al. The Raman fingerprint of graphene[J]. Physical Review Letters, 2006, 97(18):41-47.
 KANG L, ZHANG M, LIU Z H, et al. IR spectra of manganese oxides with either layered or tunnel structures.[J]. Spectrochimica Acta Part A Molecular & Biomolecular Spectroscopy, 2007, 67(3/4):864.
 QI F. Synthesis of Cs-birnessite and transformation reaction to (2×4) tunnel structure by heat-treatment[J]. Journal of Materials Science Letters, 2003, 22(14):999-1001.
 TERAYAMA K, IKEDA M. Study on thermal decomposition of MnO2 and Mn2O3 by thermal analysis[J]. Materials Transactions Jim, 2007, 24(11):754-758.
 BELLO A, BARZEGAR F, MOMODU D, et al. Symmetric supercapacitors based on porous 3D interconnected carbon framework[J]. Electrochimica Acta, 2015, 151:386-392.