Papers by Keyword: Li Diffusion

Abstract: The currently used cathode material for secondary batteries such as LiCoO2 exhibited limit to further improve the functionality of the batteries, since the screen printing method cannot reduce the thickness of the battery further with the solid state reacted powder which has the size of several micrometer. In this study, we have synthesized Li(NiCoMn)O2 thin film to replace LiCoO2 thick film by employing Li-diffusion reaction on the surface of the textured Ni-Co-Mn alloy. The cube-textured Ni-Mn alloy was prepared by cold-isostatic pressing of mixed Ni-Mn powder, sintering, repeated rolling process, and annealing heat treatment for texture development. After thin layer of metallic Li was deposited on the surface of Ni-Co-Mn template using thermal evaporation method in the glove box or pulsed laser deposition, the Li/Ni-Co-Mn composite tape were heat treated at 800~900°C for 1~2hrs in oxidizing atmosphere to induce Li diffusion into the Ni-Co-Mn template and Li(NiCoMn)O2 phase formation. The Li(NiCoMn)O2 phase evolution was confirmed by XRD and microstructural characteristics such as grain size and surface morphology were analyzed by scanning electron microscopy and atomic force microscopy. Also the charge and discharge test was conducted to confirm the electrical characteristics of Li(NiCoMn)O2/Ni-Co-Mn thin film for the cathode application.

Abstract: The currently commercialized cathode material for Li ion batteries such as LiCoO2 exhibited limit to further improve the performance of the batteries, since the employed screen printing method for cathode fabrication is difficult to reduce the thickness and control the microstructure of the oxide layer. In this studies, we have synthesized Li(Ni1-xCox)O2 thin film by utilizing Li-diffusion reaction on the surface of Ni-Co alloy substrates. For the preparation of Ni-Co alloy rod, Ni and 20at.%Co powder were mixed for 24hrs by ball milling, and then pressed into rod-shape by cold-isostatic pressing. The Ni-Co rods were sintered at 1100°C for 6hrs in the reducing atmosphere of Ar 96% and H2 4%. The sintered Ni-20at%Co rod was cold-rolled into tape at 5% reduction ratio with the final thickness of 100㎛, and the recrystallization heat treatment for the development of the cube texture of the rolled Ni alloy tape was carried out at 1000°C in Ar 96% and H2 4%. After thin layer of metallic Li was deposited on the surface of Ni-Co template using thermal evaporation method in the glove box, the Li/Ni-Co composite tape were heat-treated at 700~850°C for 1~2hrs in oxidizing atmosphere to induce Li-diffusion into Ni-Co substrate and Li(Ni0.8Co0.2)O2 phase formation. The phase evolution of Li(Ni0.8Co0.2)O2 was confirmed by X-ray diffraction and the grain size and morphology of the surface were analyzed by scanning electron microscopy and atomic force microscopy. Also the charge and discharge test were conducted to confirm the electrical characteristics of Li(Ni1-xCox)O2/Ni-Co thin film for the cathode application.

Abstract: In this paper structural, electrical, electrochemical and thermal (DSC) characterization of series of manganese spinel samples with manganese substituted to different degree (x = 0 – 0.5) with nickel are presented. The conductivity and thermoelectric power measurements were performed in wide temperature range also versus oxygen partial pressure and for deintercalated samples. Electrochemical studies of these cathode materials were conducted in Li / Li+ / LiyNixMn2−xO4 type cells. Substitution of manganese with nickel causes disappearance of the phase transition characteristic of LiMn2O4 spinel. Studies of electrical properties reveal that Ni ions do not participate in charge transport at low temperatures. In the charge curves of Li / Li+/ LiyNixMn2−xO4 cells there are two visible plateaux, separated with distinct potential jump (~0.5V), which position on Li content perfectly matches the Mn3+ content in the doped cathode material. The lower plateau is related to the Mn3+ → Mn4+ oxidation, while the next of higher voltage, of the dopant Ni2+ → Ni4+ oxidation. The schematic diagrams of relative Mn – Ni electronic levels alignment are proposed.