A core-shell structured Si nanoparticles@TiO2-x/C mesoporous microfiber composite has been synthesized by an electrospinning method. The core-shell composite exhibits high reversible capacity, excellent rate capability, and improved cycle performance as an anode material for Li-ion batteries. Furthermore, it shows remarkable suppression of exothermic behavior, which can prevent possible thermal runaway and safety problems of the cells. The improved electrochemical and thermal properties are ascribed to the mechanically, electrically, and thermally robust shell structure of the TiO2-x/C nanocomposite encapsulating the Si nanoparticles, which is suggested as a promising material architecture for a safe and reliable Si-based Li-ion battery of high energy density.

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We have first grown single crystals of multiferroic double-perovskite Lu 2 CoMnO 6 and studied the directional dependence of their magnetic and dielectric properties. The ferromagnetic order emerges below T C ≈48 K along the crystallographic c axis. Dielectric anomaly arises along the b axis with no electric polarization at T C , contrary to the polycrystalline work suggesting ferroelectricity along the c axis. It is proposed that the incommensurate centric spin modulation leads to the antiferroelectric order with the large dielectric anomaly. Through the strongly coupled ferromagnetic and dielectric states, the highly non-linear variation of both dielectric constant and magnetization was achieved in application of magnetic fields. This concurrent tunability provides a new route to manipulation of multiple order parameters in multiferroics. a) phylove@yonsei.ac.kr Realization of strong magnetoelectric coupling in multiferroics where ferroelectricity and magnetism coexist, opens new opportunities for novel device applications such as magnetoelectric data storage and sensors utilizing cross-coupling effects between electric and magnetic order parameters. [1][2][3][4] The current research on multiferroics is mainly focused on magnetism-driven ferroelectrics in which the ferroelectricity originates from the lattice relaxation via exchange strictions in the ordered magnetic state. Both symmetric and antisymmetric parts of the magnetic exchange coupling can contribute to the ferroelectric distortions. Symmetric exchange interaction is active for multiferroics such as Ca 3 CoMnO 6 and GdFeO 3 5,6 while multiferroicity in spiral magnets of TbMnO 3 and CuBr 2 7,8 results primarily from antisymmetric exchange interaction. In principle, the substantial coupling between structural distortions and magnetic order can lead to a large variation of the dielectric properties under the application of magnetic fields. However, only few of single phase multiferroics possess the net magnetization, which is advantageous for achieving the mutual control of multiple order parameters. 9,10 In spite of enormous efforts made on multiferroics research, it is still anticipated to design and discover new systems accompanying enhanced cross-coupled functionalities for practical applications. Various systems have been suggested as a candidate belonging to a new class of multiferroics, however, many of them studied so far have been synthesized only in the polycrystalline form, preventing characterization of their intrinsic properties. [11][12][13][14] Lu 2 CoMnO 6 (LCMO) crystallizes in a monoclinic P2 1 /n double-perovskite structure with a unit cell of a=0.516 nm, b=0.554 nm, and c=0.742 nm. Co 2+ and Mn 4+ ions are alternatingly located in corner-shared octahedral environments as shown in Figs. 1(a) and (b). It has drawn an interest due to its newly-found multiferroicity in the previous polycrystalline work. 15 The polycrystalline specimen exhibits a broad temperature dependence of dielectric anomaly below ~50 K. It has been predicted that ...

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