Integrating LiMn2O4(LMO) and different carbon materials to build a mixed cathode system can provide fast transport channels to improve the conduction of both electrons and ions. In this paper, our work studied in situ low-temperature hydrothermal synthesis of LMO nanocomposites based on graphene oxide (GO)/carbon nanotubes (CNTs) hydrogel. Compared with the pure LMO nanoparticles, GO/CNTs/LMO (GCLMO) composites greatly improved electrochemical performance in specific capacity, cycle performance and rate ability. The electrochemical test results showed that the specific capacitance of GCLMO nanocomposites reached 396 F/g at the current density of 0.5 A/g, which was much higher than 221 F/g of pure LMO. Even at the current density of 10 A/g, the specific capacitance was still as high as 309 F/g. Besides, after 2000 cycles, the specific capacitance retention of the composite was 93%. Electrochemical data showed that GCLMO composite is an ideal cathode material for supercapacitors.

Extensive analyses of low-temperature powder x-ray diffraction data for spinel LiMn2O4 (Fd3¯m at room temperature) make it clear that two structural phase transitions occur: first around 285 K from cubic to orthorhombic, second around 65 K from orthorhombic to tetragonal. At temperatures under 285 K, superlattice peaks appear in the diffraction pattern that were successfully indexed by tripling the a and b axes of the spinel unit cell. At 250 K, the unit cell is face-centered orthorhombic, Fddd, F2dd, or Fd2d, with a=24.855(1), b=24.755(2), c=8.2014(3) Å, V=5046.1(4) Å3, Dx=4.284 g/cm3, Z=72. The unit cell at 30 K was confirmed to be body-centered tetragonal I41/amd or I41/a, with a=17.5176(3), c=8.1961(2) Å, V=2515.1(1) Å3, Dx=4.298 g/cm3, Z=36.