Geun-Bae Kim

Electrochemical Properties and Thermal Stability of Li a Ni1 − x CO x O 2 Cathode Materials

Conductive and electrochemical properties as well as thermal stability of Li{sub a}Ni{sub 1{minus}x}Co{sub x}O{sub 2} where x = 0--0.3 and a = 1.0--0.4 have been studied using impedance spectroscopy, galvanostatic intermittent titration technique, cyclic voltammetry, electrochemical cycling, and differential scanning calorimetry (DSC). The electronic conductivity of partially charged material (a {le} 0.8) increases substantially when the cobalt content is increased to x = 0.3 from 0.2. The mobility, chemical diffusion coefficient, and Li{sup +} ion diffusion coefficient in the partially charged material are in the neighborhood of 10{sup {minus}6}cm{sup {minus}2}/V x, 10{sup {minus}8}cm{sup 2}/s, and 5 x 10{sup {minus}10}cm{sup 2}/s, respectively, and are rather insensitive to the values of a and x. Results of electrochemical and DSC studies show that LiNi{sub 0.7}Co{sub 0.3}O{sub 2} is the best cathode material for a Li cell of all materials studied here in view of the best cycle stability, the smallest irreversible capacity, and the greatest thermal stability with minimal reduction of specific capacity from that of LiNiO{sub 2}.

Effect of Preparation Methods of LiNi1 − x Co x O 2 Cathode Materials on Their Chemical Structure and Electrode Performance

We have studied effects of different starting materials on preparation of LiNi 1-x Co x O 2 cathode material for a Li-ion cell where x = 0.1, 0.2, and 0.3, and the electrochemical properties of resulting compounds from two different preparation methods. A preparation method (method B) which uses spherical powder of Ni 1-x Co x (OH) 2 as one of the starting material produced a much superior cathode material than the other method (method A) which uses Ni(OH) 2 and Co(OH) 2 . Method A produced compounds with relatively high degrees of cation mixing which reduces electrochemical utilization (discharge capacity), increases irreversible capacity, and reduces stability on cycling of the cathode material. Method B, in contrast, produced cathode material with a much reduced degree of cation-mixing, thus improving the electrochemical properties. The spherical particle of material prepared by method B has the additional advantage of improved packing density of the electrode with improved volumetric energy density. The ratio of c/a was increased and the electrochemical stability on cycling of the material was improved as the content of Co (value of x) is increased.

Enhancement of Thermal Stability of LiCoO2 by LiMn2 O 4 Coating

A significant improvement in thermal stability of the charged with a particle size of has been achieved by coating its particle surface with . An onset temperature for thermal decomposition of the prepared by heating at was , whereas that of the bare is . In addition, the coating also improved the capacity retention on cycling at charge cut‐off significantly. These results appear to indicate that the coating is effective in retarding the decomposition reaction of with the electrolytes as well as sustaining its structural stability on cycling. ©1999 The Electrochemical Society

Nanosize Si anode embedded in super-elastic nitinol (Ni–Ti) shape memory alloy matrix for Li rechargeable batteries

A nanosize Si embedded in super-elastic Nitinol alloy matrix composite was synthesized in large-scale using arc melting followed by a rapid quenching method. Both X-ray diffraction and high resolution transmission electron microscope with energy dispersive spectroscopy analyses confirmed that approximately 50 nm Si crystallites were surrounded by the Ni–Ti matrix. Ex situsynchrotron XRD was performed to elucidate the phase transition of active materials during lithiation and delithiation. The local structural changes of the Ni–Ti inactive matrix during cycling were investigated by ex situX-ray absorption spectroscopy analyses. This anode material showed an excellent electrochemical stability since the elastic behavior of the inactive Nitinol matrix absorbed the stress generated due to the volume expansion during lithiation of the nanosized Si embedded.

Electrochemical Properties of GeS2‐Based Glass‐Polymer Composite Electrolytes for Lithium‐Ion Batteries

Electrochemical properties of glass‐polymer composite (GPC) electrolytes, consisting of 0.4 glass and polymer, have been investigated using impedance spectroscopy and four‐probe dc measurements. Results indicate that the GPC electrolyte with 13 vol % polymer exhibits conductivity of at room temperature, and at 80°C. Further, the GPC electrolyte is more stable against than against Li. The interfacial resistance of a GPC/ interface remains constant at 80°C for 250 h. The cycling behavior of a cell consisting of carbon as the negative electrode and as the positive electrode showed that the capacity decreased from an initial value of 110 to 100 mAh/g after 50 cycles.

Analysis of process margin in EUV mask repair with nano-machining

Reduced design rules demand higher sensitivity of inspection, and thus small defects which did not affect printability before require repair now. The trend is expected to be similar in extreme ultraviolet lithography (EUVL) which is a promising candidate for sub 32 nm node devices due to high printing resolution. The appropriate repair tool for the small defects is a nanomachining system. An area which remains to be studied is the nano-machining system performance regarding repair of the defects without causing multilayer damage. Currently, nanomachining Z-depth controllability is 3 nm while the Ru-capping layer is 2.5 nm thick in a Buffer-less Ru-capped EUV mask. For this report, new repair processes are studied in conjunction with the machining behavior of the different EUVL mask layers. Repair applications to achieve the Edge Placement(EP) and Z-depth controllability for an optimal printability process window are discussed. Repair feasibility was determined using a EUV micro exposure tool (MET) and Actinic Imaging Tool (AIT) to evaluate repairs the 30 nm and 40 nm nodes. Finally, we will report the process margin of the repair through Slitho-EUVTM simulation by controlling side wall angle, Z-depth, and EP (Edge Placement) on the base of 3-dimensional experimental result.

Requirements of nano-machining repair system for 45-nm node

Nano-machining repair tool plays an important role in the current 65 nm node photomask repair. It removes defects mechanically with nanometer sized diamond tip with high accuracy and low damage using high accuracy AFM data. The repair performance of nano-machining repair system largely depends on the diamond tip whose aspect ratio decides the minimum reparable feature size. As the device shrinks to 45 nm or 32 nm node, higher aspect ratio tip with weak structure is required. It is contradiction to the fact that more accurate edge placement and better repair slope is required in smaller node repair, because deflection or tip wear effect could happen in high aspect ratio tip. In this article, deflection and wear effect were investigated in single layer repair recipe using SEM and AIMSTM. Multilayer recipe which complements weak structure was estimated carefully, and some limits were discussed. Finally some requirements of nano-machining repair system for 45 nm node were presented.

Development of glass-polymer composite electrolytes for Li-ion cells

A new type of solid-state electrolyte, the glass-polymer composite (GPC) electrolyte, has been developed. The electrochemical behavior of the GPC, consisting of 100-x vol% 0.54 Li/sub 2/S/spl middot/0.21 B/sub 2/S/sub 3//spl middot/0.25 LiI glass and x vol% P(EO)/sub 8//spl middot/LiN(CF/sub 3/SO/sub 2/)/sub 2/ polymer with x=7, 13, and 25, has been investigated. Results show that the addition of polymer to the glass powder increases not only the mechanical flexibility but also the ionic conductivity. The combination of impedance spectroscopy and four-probe DC measurements indicates that the GPC with x=13 vol% polymer exhibits the highest lithium ion conductivity, varying from 3/spl times/10/sup -4/ /spl Omega//sup -1/ cm/sup -1/ at room temperature to 1.4/spl times/10/sup -3/ /spl Omega//sup -1/ cm/sup -1/ at 80/spl deg/C. The evolution of impedance spectra of the cells show that kinetic stability of the GPC electrolytes against Li/sub x/C/sub 6/ and LiMn/sub 2/O/sub 4/ electrodes is reasonably good, although there is an initial increase in interfacial resistance during cycling.