The rational design and fabrication of SnO2-based anode materials could offer a powerful way of effectively alleviating their large volume variation and guaranteeing excellent reaction kinetics for electrochemical lithium storage. Herein, we present an ultrarapid, low-cost, and simple microwave-assisted synthesis of ultrathin SnO2 nanosheets at the gram-scale. The two-dimensional (2D) anisotropic growth depends on microwave dielectric irradiation coupled with surfactant structural direction, and is conducted under low-temperature atmospheric conditions. The ultrathin 2D nanostructure holds a great surface tin atom percentage with high activity, where the electrochemical reaction processes could be facilitated that highly dependent on the surface. Compared with 1D SnO2 nanorods, the ultrathin SnO2 nanosheets exhibit remarkably improved electrochemical lithium storage properties with a high reversible capacity of 757.6 mAh g(-1) at a current density of 200 mA g(-1) up to 40 cycles as well as excellent rate capability and cycling stability. Specifically, the ultrathin 2D nanosheet could significantly reduce ion diffusion paths, thus allowing faster phase transitions, while the sufficient external surface interspace and interior porous configuration could successfully accommodate the huge volume changes. Even more importantly, we develop a promising strategy to produce ultrathin SnO2 nanosheets to tackle their intrinsic problems for commercial applications.

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Co x Fe 3Àx O 4 (x ¼ 0-1) spheres are synthesized via a solvothermal reaction using ethylene glycol (EG) as a solvent. They are characterized, and the results show that the prepared spheres are mainly 300-500 nm in diameter and constituted by small grains. For the EG solution containing stoichiometric ingredients (atomic ratio of Co 2+ : Fe 3+ ¼ 1 : 2), the obtained spheres are Co 0.9 Fe 2.1 O 4 at 200 C (sphere A) andCo 0.74 Fe 2.26 O 4 (sphere B) at 300 C, whose crystallites are 23 nm and 30 nm in size, respectively. VSM measurements reveal improved properties with sphere B. Variations of complex permittivity and permeability for different composite (75% mass ratio of spheres) have been studied as a function of frequency. The calculated reflectivity value indicates that the composite containing sphere A displays better microwave absorption capability. The minimum reflection loss reaches À41.089 dB at 12.08 GHz, with a matching thickness of 2 mm. The dielectric loss contributes even more than magnetic loss in the frequency range of 3-14 GHz. The synergistic effect of dual losses makes the submicrosphere a promising absorbent in X and Ku bands. The composite consisting of sphere B is inferior in dielectric properties owing to ferrous ion migration from octahedral to tetrahedral sites and due to the big crystallites lacking defects. After the calcination treatment of the spheres at 700 C, the dielectric loss turns out to be low due to the disappearing Fe 2+ 4 Fe 3+ pairs in adjacent octahedral sites and the loss of defects. Variations of the cobalt ratio in spheres can change the resonance frequency and crystallinity of the spheres and ultimately the minimum reflection loss and corresponding frequency band. The microwave absorption properties of mixed magnetite and cobalt ferrite spheres are influenced by the cationic stoichiometry and crystalline integrity.

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