Oh B. Chae

Direct synthesis of self-assembled ferrite/carbon hybrid nanosheets for high performance lithium-ion battery anodes.

Extensive applications of rechargeable lithium-ion batteries (LIBs) to various portable electronic devices and hybrid electric vehicles result in the increasing demand for the development of electrode materials with improved electrochemical performance including high energy, power density, and excellent cyclability, while maintaining low production cost. Here, we present a direct synthesis of ferrite/carbon hybrid nanosheets for high performance lithium-ion battery anodes. Uniform-sized ferrite nanocrystals and carbon materials were synthesized simultaneously through a single heating procedure using metal-oleate complex as the precursors for both ferrite and carbon. 2-D nanostructures were obtained by using sodium sulfate salt powder as a sacrificial template. The 2-D ferrite/carbon nanocomposites exhibited excellent cycling stability and rate performance derived from 2-D nanostructural characteristics. The synthetic procedure is simple, inexpensive, and scalable for mass production, and the highly ordered 2-D structure of these nanocomposites has great potential for many future applications.

Solventless synthesis of an iron-oxide/graphene nanocomposite and its application as an anode in high-rate Li-ion batteries

An iron-oxide/graphene nanocomposite was directly synthesized from an iron–oleate precursor intercalated between graphene layers via a solventless thermal decomposition method. In the nanocomposite, highly monodisperse γ-Fe2O3 nanoparticles were in close contact with graphene, and they acted as mutual spacers in the nanocomposite to prevent aggregation of the nanoparticles and restacking of the graphene layers. The iron-oxide/graphene nanocomposite shows outstanding electrochemical performance, including high reversible charge/discharge capacity, good cycling stability, and remarkable high-rate-performance (500 mA h g−1 at 5000 mA g−1) when it was employed as a lithium ion battery anode. This nanocomposite can be a potentially valuable candidate anode material for high-rate Li-ion batteries.

A first-cycle coulombic efficiency higher than 100% observed for a Li2MO3 (M = Mo or Ru) electrode.

The lithiation/de-lithiation behavior of a ternary oxide (Li2MO3, where M = Mo or Ru) is examined. In the first lithiation, the metal oxide (MO2) component in Li2MO3 is lithiated by a conversion reaction to generate nano-sized metal (M) particles and two equivalents of Li2O. As a result, one idling Li2O equivalent is generated from Li2MO3. In the de-lithiation period, three equivalents of Li2O react with M to generate MO3. The first-cycle Coulombic efficiency is theoretically 150% since the initial Li2MO3 takes four Li(+) ions and four electrons per formula unit, whereas the M component is oxidized to MO3 by releasing six Li(+) ions and six electrons. In practice, the first-cycle Coulombic efficiency is less than 150% owing to an irreversible charge consumption for electrolyte decomposition. The as-generated MO3 is lithiated/de-lithiated from the second cycle with excellent cycle performance and rate capability.

Electrochemical Characteristics of Cu3Si as Negative Electrode for Lithium Secondary Batteries at Elevated Temperatures

에 이른다. 흑연에 비해서 거의 10배 큰 값을 가지므로 흑연을 대체할 리튬 이차전지의 음극 활물질로 큰 관심을 받고 있다.그러나, 실리콘은 충방전 과정에서 300%가 넘는 부피변화 때문에 전극이 퇴화되어, 10 사이클 이내에 대부분의용량을 잃게 된다. 이와 같이 고용량을 내는 합금계 음극물질이 쉽게 상용화되지 못하는 것은, 이 물질들이 충방전 과정에서 팽창과 수축을 지속적으로 겪으면서 전기적인 접촉을 잃게 되고, 그에 따라 전극 저항이 급격히증가하기 때문이다. 이를 해결하기 위해, 리튬과 반응하지 않으면서 부피변화를 완충해 줄 수 있는 비활성물질을 첨가한 활성/비활성 화합물 또는 복합재를 사용하는 방안이 강구되었다. 이때 비활성 매트릭스상은 활물질보다 전기 전도성이 우수해서 전극 저항의 증가를막아줄 뿐 아니라, 활물질을 내부에 고르게 분산시킴으로써 부피 변화로 인해 생기는 응력(stress)을 완충시키는 역할도 할 수 있다. 그 결과, 단일상 활물질을 사용할때보다 우수한 가역성을 확보할 수 있다고 보고되었다.