Min Seob Song

Germanium sulfide(II and IV) nanoparticles for enhanced performance of lithium ion batteries

Germanium sulfide (GeS and GeS2) nanoparticles were synthesized by novel gas-phase laser photolysis and subsequent thermal annealing. They showed excellent cycling performance for lithium ion batteries, with a maximum capacity of 1010 mA h g(-1) after 100 cycles. Metastable tetragonal phase Ge nanoparticles were suggested as active materials for a reversible lithium insertion-extraction process.

Germanium–tin alloy nanocrystals for high-performance lithium ion batteries

Germanium-tin (Ge(1-x)Sn(x)) alloy nanocrystals were synthesized using a gas-phase laser photolysis reaction of tetramethyl germanium and tetramethyl tin. A composition tuning was achieved using the partial pressure of precursors in a closed reactor. For x < 0.1, cubic phase alloy nanocrystals were exclusively produced without separation of the tetragonal phase Sn metal. In the range of x = 0.1-0.4, unique Ge(1-x)Sn(x)-Sn alloy-metal hetero-junction nanocrystals were synthesized, where the Sn metal domain becomes dominant with x. Thin graphitic carbon layers usually sheathed the nanocrystals. We investigated the composition-dependent electrochemical properties of these nanocrystals as anode materials of lithium ion batteries. Incorporation of Sn (x = 0.05) significantly increased the capacities (1010 mA h g(-1) after 50 cycles) and rate capabilities, which promises excellent electrode materials for the development of high-performance lithium batteries.

Investigation of design parameter effects on high current performance of lithium-ion cells with LiFePO4/graphite electrodes

Electrode design is an essential task for successful development of lithium-ion batteries. Provided that the same materials are given, proper dimensioning of the electrodes and balanced composition of the materials in them can maximize the cell performance, such as the discharge capacity. However, many electrode design parameters have conflicting effects on the performance, and thus careful optimization of these parameters is required. This study experimentally investigated the effects of several electrode design parameters on the performance of lithium ion cells with a LiFePO4 cathode and a natural graphite anode, focusing on their high current operations. The conflicting effects of the conductor ratio (the weight fraction of electronic particle additives), electrode thickness, and electrode density (porosity) on the cell capacity were studied. In addition, a detailed one-dimensional electrochemical model was also used to simulate the observed performance characteristics and to identify their underlying mechanisms limiting the performance. Based on the experimental and numerical results, the optimal ranges for the electrode design parameters were discussed to achieve better performance of the LiFePO4/graphite batteries.

High-Yield Gas-Phase Laser Photolysis Synthesis of Germanium Nanocrystals for High-Performance Lithium Ion Batteries

We developed a new high-yield synthesis method of free-standing germanium nanocrystals (Ge NCs) by means of the gas-phase photolysis of tetramethyl germanium in a closed reactor using an Nd-YAG pulsed laser. Size control (5-100 nm) can be simply achieved using a quenching gas. The Ge1-xSix NCs were synthesized by the photolysis of a tetramethyl silicon gas mixture and their composition was controlled by the partial pressure of precursors. The as-grown NCs are sheathed with thin (1-2 nm) carbon layers, and well dispersed to form a stable colloidal solution. Both Ge NC and Ge-RGO hybrids exhibit excellent cycling performance and high capacity of the lithium ion battery (800 and 1100 mAh/g after 50 cycles, respectively) as promising anode materials for the development of high-performance lithium batteries. This novel synthesis method of Ge NCs is expected to contribute to expand their applications in high-performance energy con- version systems.

Characterization on the electrochemical and structural properties of polyanion cathode material Li2MnSiO4/C depending on the synthesis process

Abstract ―Li 2 MnSiO 4 /C was synthesized by solid state reaction and solution synthesis with sucrose for carbon source. The X-ray diffraction patterns of solid state reaction indicates small amount of impurities. By FE-SEM and HR-TEM, solution synthesis comprised several tens of nanometer comparing to 500~600 nm of Li 2 MnSiO 4 /C prepared by solid state reaction. The Li 2 MnSiO 4 /C prepared by solution synthesis show better electrochemical performance than solid state reaction. The first charge-discharge capacity are 236, 189 mAh/g respectively by solution synthesis. But its cycle performance was poor as yet and its capacity retention was 62% after 10 cycles. Key words : Lithium manganese silicate, Lithium-ion battery, cathode, solid state reaction, solution synthesis 1. 서 론 모바일 통신 및 장비의 발달에 따라 전원 공급원인 리튬이차전지의 수요가 증가하고 있고 플러그인 하이브리드 자동차(Plug-in hybrid electric vehicles; PHEV), 전기자동차(Electric vehicles; EV)와 대용량 전기저장 장치(Electric energy storage)의 발달은 대용량 리튬이차전지의 개발을 필요로 한다 . 하지만 현재 사용되고 있는 양극 활물질은 LiCoO