High Performance Cathode Materials for Lithium Ion Batteries

Department of Energy Engineering(Battery Science and Technology)With increasing interest in environmental and energy issues, the application fields of lithium ion batteries have been used for electric vehicle as well as portable devices. However, lithium ion batteries with present technology can’t fulfill the requirement of full-range electric vehicles due to insufficient energy density and power density. The promising candidates of cathode materials for those drawbacks are Li-rich (Li2MnO3-LiMO2, M=Ni, Mn and Co) and spinel (LiM2O4, M=Al, Li, Mg, etc.) cathode materials. However, those materials still has problem which should be overcome for application of electric vehicles. For examples, the Li-rich materials have very high gravimetric energy density but suffer from low initial coulombic efficiency, voltage decay upon cycling, large side reaction at elevated temperature and poor rate capability. The spinel cathode materials have high rate capability and thermal stability but suffer from Mn dissolution at elevated temperature. Also it delivers low capacity at high C rate if secondary particle size is large (>10㎛). To overcome this barrier, newly developed material modification methods for Li-rich and spinel cathode materials are proposed in this dissertation. 1) The chemical activation is frequently used to improve the first cycle efficiency for Li-rich material. However, it causes the formation of lithium impurities. Also the surface coating is carried out to reduce side reaction on the surface, but this method can solve the coulombic efficiency at 1st cycle and rate capability. To overcome these barriers, we here report an efficient and effective surface modification method. The chemical activation (acid treatment) and LiCoPO4 coating were carried out simultaneously. During synthesis process, the lithium ions were extracted from the lattice leading to the improved columbic efficiency and these ions were used for the formation of LiCoPO4. The Ni and Co doped spinel phase was formed at the surface of host material, which gives rise to the facile pathway of lithium ions. The LiCoPO4 and highly doped spinel on the surface acted as the double protection layers that effectively prevented side reactions on the surface at 60oC. 2) The surface coating is widely used to protect surface of spinel cathode material from acidic present electrolyte. However, metal compound coatings cause surface resistance because usually coating material is electrically and electrochemically inactive. Also even though the coating material is electrode material, it still has resistance issues due to structural mismatch (grain boundary). To overcome this barrier, we here report an imaginative material design; a novel hetero-structure LiMn2O4 with epitaxially grown layered (R3 ?m) surface phase. No defect was observed at the interface between the host spinel and layered surface phase, which provides an efficient path for the ionic and electronic mobility, leading to the improved rate capability. In addition, the layered surface phase protects the host spinel from being directly exposed to the highly active electrolyte at 60 oC. 3) Many researchers have investigated nanosized spinel cathode materials to increase their rate capability because the lithium diffusion pathway is reduced and the surface where the electrochemical reaction can occur increase. However, the nanosized materials can’t fulfill the requirement of electrode density for the application of electric vehicles. Also the carbon coating is not able to be conducted on the spinel cathode materials due to the formation of oxygen deficiency. To overcome these problems, we report composites with super-p and nanosized spinel material via spray drying process. The acid-treated super-p was used for better distribution of super-p in secondary particle. The developed material showed outstanding rate capabilities at -10 oC as well as 24 oC.ope

Charge density functional plus UU calculation of lacunar spinel GaM4_4Se8_8 (M = Nb, Mo, Ta, and W)

Charge density functional plus $U$ calculations are carried out to examine the validity of molecular $J_\text{eff}$=1/2 and 3/2 state in lacunar spinel GaM$_4$X$_8$ (M = Nb, Mo, Ta, and W). With LDA (spin-unpolarized local density approximation)$+U$, which has recently been suggested as the more desirable choice than LSDA (local spin density approximation)$+U$, we examine the band structure in comparison with the previous prediction based on the spin-polarized version of functional and with the prototypical $J_\text{eff}$=1/2 material Sr$_2$IrO$_4$. It is found that the previously suggested $J_\text{eff}$=1/2 and 3/2 band characters remain valid still in LDA$+U$ calculations while the use of charge-only density causes some minor differences. Our result provides the further support for the novel molecular $J_\text{eff}$ state in this series of materials, which can hopefully motivate the future exploration toward its verification and the further search for new functionalities

Topological Structure of Dense Hadronic Matter

We present a summary of work done on dense hadronic matter, based on the Skyrme model, which provides a unified approach to high density, valid in the large $N_c$ limit. In our picture, dense hadronic matter is described by the {\em classical} soliton configuration with minimum energy for the given baryon number density. By incorporating the meson fluctuations on such ground state we obtain an effective Lagrangian for meson dynamics in a dense medium. Our starting point has been the Skyrme model defined in terms of pions, thereafter we have extended and improved the model by incorporating other degrees of freedom such as dilaton, kaons and vector mesons.Comment: 13 pages, 8 figures, Talk given at the KIAS-APCTP Symposium in Astro-Hadron Physics "Compact Stars: Quest for New States of Dense Matter", November 10-14, 2003, Seoul, Korea, published by World Scientific. Based on talk by B.-Y. Par

A New p53 Target Gene, RKIP, Is Essential for DNA Damage-Induced Cellular Senescence and Suppression of ERK Activation

Abstractp53, a strong tumor suppressor protein, is known to be involved in cellular senescence, particularly premature cellular senescence. Oncogenic stresses, such as Ras activation, can initiate p53-mediated senescence, whereas activation of the Ras-mitogen-activated protein kinase (MAPK) pathway can promote cell proliferation. These conflicting facts imply that there is a regulatory mechanism for balancing p53 and Ras-MAPK signaling. To address this, we evaluated the effects of p53 on the extracellular signal-regulated kinase (ERK) activation and found that p53 could suppress ERK activation through de novo synthesis. Through several molecular biologic analyses, we found that RKIP, an inhibitor of Raf kinase, is responsible for p53-mediated ERK suppression and senescence. Overexpression of RKIP can induce cellular senescence in several types of cell lines, including p53-deficient cells, whereas the elimination of RKIP by siRNA or forced expression of ERK blocks p53-mediated cellular senescence. These results suggested that RKIP is an essential protein for cellular senescence. Moreover, modification of the p53 serine 46 residue was critical for RKIP induction and ERK suppression as well as cellular senescence. These results indicated that RKIP is a novel p53 target gene that is responsible for p53-mediated cellular senescence and tumor suppressor protein expression

The Effectiveness of Moxibustion: An Overview During 10 Years

Moxibustion has been used to treat various types of disease. However, there is still insufficient evidence regarding its effectiveness. This study was performed to summarize and evaluate the effectiveness of moxibustion. A search was performed for all randomized controlled trials in PubMed between January 1998 and July 2008 with no language restriction. The results yielded 47 trials in which six moxibustion types were applied to 36 diseases ranging from breech presentation to digestive disorders. Moxibustion was compared to three types of control group: general care, Oriental medical therapies or waiting list. Moxibustion was superior to the control in 14 out of 54 control groups in 46 studies. There were no significant differences among groups in 7 studies, and the outcome direction was not determined in 33 studies. Seven studies were included in a meta-analysis. Moxibustion was more effective than medication in two ulcerative colitis studies (relative risk (95% CI), 2.20 (1.37, 3.52), P = .001, I2 = 0%). Overall, our results did not support the effectiveness of moxibustion in specific diseases due to the limited number and low quality of the studies and inadequate use of controls. In order to provide appropriate evidence regarding the effectiveness of moxibustion, more rigorous clinical trials using appropriate controls are warranted

Ultraviolet photodepletion spectroscopy of dibenzo-18-crown-6-ether complexes with alkali metal cations

Ultraviolet photodepletion spectra of dibenzo-18-crown-6-ether complexes with alkali metal cations (M+-DB18C6, M = Cs, Rb, K, Na, and Li) were obtained in the gas phase using electrospray ionization quadrupole ion-trap reflectron time-of-flight mass spectrometry. The spectra exhibited a few distinct absorption bands in the wavenumber region of 35450−37800 cm^(−1). The lowest-energy band was tentatively assigned to be the origin of the S_0-S_1 transition, and the second band to a vibronic transition arising from the “benzene breathing” mode in conjunction with symmetric or asymmetric stretching vibration of the bonds between the metal cation and the oxygen atoms in DB18C6. The red shifts of the origin bands were observed in the spectra as the size of the metal cation in M^+-DB18C6 increased from Li^+ to Cs^+. We suggested that these red shifts arose mainly from the decrease in the binding energies of larger-sized metal cations to DB18C6 at the electronic ground state. These size effects of the metal cations on the geometric and electronic structures, and the binding properties of the complexes at the S_0 and S_1 states were further elucidated by theoretical calculations using density functional and time-dependent density functional theories

A Surgically Treated Case of Chronic Necrotizing Aspergillosis with Pleural Invasion

Aspergillus is a ubiquitous fungus and can cause many levels of disease severity. Chronic necrotizing aspergillosis is a rare disease and few cases have been reported in Korea. We experienced a case of pleural aspergillosis that was treated successfully with medical and surgical interventions. The 52-year-old man who was diagnosed with chronic necrotizing pulmonary aspergillosis underwent surgical treatment including a lobectomy, decortication, and myoplasty. The patient was also medically treated with amphotericin B followed by voriconazole. Pleural irrigation with amphotericin B was also performed. A multi-dimensional approach should be considered for treating chronic necrotizing pulmonary aspergillosis