| The growing requirement for high-power and high-capacity lithium ion batteries(LIBs) in the emerging technologies (e.g., electric vehicles and hybrid electric vehicles) hasprompted tremendous research efforts towards developing high-performance electrodematerials. Traditional commercial graphite electrodes could not meet the demand ofconsumers because of its low theoretical capacity (372mAh g-1) and poor high-rateperformance. Therefore, developing alternatives with excellent performance is greatlyimportant for the improvement of LIBs.Zn2SnO4has attracted much attention due to its high theoretical capacity and highelectrical conductivity. However, huge volume change during the Li+alloying anddealloying processes for Zn2SnO4will result in their pulverization and exfoliation from thecurrent collector, which leads to fast capacity fading, thus limitating their commercialapplication. To address above problems, in this paper, we refine the grain size of Zn2SnO4as the starting point and introduce graphene or element doping to prepare Zn2SnO4-basednanocomposites for improving their electrochemical performance. The obtained results areshown as follows:(1) Ultrafine Zn2SnO4nanoparticles were synthesized by a simple hydrothermalmethod using potassium sodium tartrate as a structure-directing agent. The average size ofthe as-prepared nanoparticles is about8~10nm. More significantly, based on the effect ofthe reaction time on the morphology evolution of the precursors, a crystal growthmechanism is proposed involving in-situ dissolution-recrystallization accompanied bymorphology and phase change. The influence of tartrate on the preparation of Zn2SnO4 nanoparticles were also studied by adjusting the addition of potassium sodium tartrate.Tartrate ions may be adsorbed on the surface of nanoparticles and prevent nanoparticlesfrom agglomerating and growing during the reaction process, which leads to the formationof fine Zn2SnO4nanoparticles.(2) Zn2SnO4/graphene (Zn2SnO4/G) nanocomposites were prepared under anotherhydrothermal condition using graphene oxides (GO) as a substrate. Zn2SnO4nanoparticlesare well dispersed on graphene sheets. The as-prepared Zn2SnO4/G nanocomposites withlarge specific surface area (144m2g-1) and mesopores (4.5nm) exhibit superior cyclicstability and rate performance. A higher specific capacity of745mAh g-1after100cyclesat200mA g-1with a capacity retention of91.5%and better cyclic stability with a capacityof492mAh g-1after500cycles at500mA g-1were achieved compared to pure Zn2SnO4nanoparticles. The excellent electrochemical performance of Zn2SnO4/G nanocomposites isattributed to the synergistic effects of fine Zn2SnO4nanoparticles and graphene sheets.(3) Co-doped Zn2SnO4–graphene–carbon nanocomposites have been prepared for thefirst time through a convenient one-step hydrothermal method. The as-obtainednanocomposites reveal a uniform distribution of ultrafine Co-doped Zn2SnO4nanoparticleswithin3~5nm in size on graphene nanosheets. It is clearly indicated that Co is successfullydoped into the lattice of Zn2SnO4and may replace Zn2+in the oxidation state of Co2+through XRD、XPS、EDS and elemental mapping analyses.(4) Compared with ZTO–G–C and Co–ZTO–G nanocomposites, Co–ZTO–G–Cnanocomposites deliver a higher reversible capacity of699mAh g-1after50cycles at100mA g-1and a higher rate capacity of461mA h g-1after200cycles at500mA g-1. Theexcellent electrochemical performance of Co–ZTO–G–C nanocomposites is attributed tothe cooperation of graphene nanosheets and the carbon layer, which effectively buffers thevolume changes during charge–discharge process, enhances the electronic conductivity andprevents the detachment of Zn2SnO4nanoparticles from the graphene substrate. Besides,the doping of Co can further increase electron transport and lithium ion diffusion,contributing to the improvement of rate capacity and cyclic stability. |
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