Changes in the Lattice Constants of Thin-Film LiCoO2 Cathodes at the 4.2 V Charged State

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Kim, Yong Jeong; Lee, Eung-Kyu; Kim, Hyemin; Cho, Jaephil; Cho, Young Whan; Park, Byungwoo; Oh, Seung Mo; Yoon, Jong Kyu
Issue Date
Electrochemical Society
J. Electrochem. Soc., 151, A1063 (2004)
The lattice constants of thin-film Li12xCoO2 cathodes at the 4.2 V charged states were influenced by various deposition conditions.
Li12xCoO2 thin films @yielding a strong ~003! texture# on a Pt or Au current collector, which were unheated during sputtering
deposition and ex situ annealed, showed negligible lattice expansion at 4.2 V during the first charge. This is in contrast to the
Li12xCoO2 powders exhibiting ;3% c axis expansion at x > 0.5 ~from ;14.05 to ;14.45 Å!. The total energy of the constrained
Li0.5CoO2 lattice ~0% c axis expansion! obtained by a pseudopotential total-energy calculation was slightly higher than that of the
relaxed one by ;1.0 eV per 12 Li0.5CoO2 ~or ;80 meV/Li0.5CoO2), indicating no difficulty of limited lattice expansion during the
first cycle. However, splitting of the ~009! diffraction peak was observed at 4.2 V as cycling proceeded: one has a lattice constant
c of 14.01 6 0.05 Å as LiCoO2 before charging, and the other has a lattice parameter of 14.40 6 0.05 Å, which is similar to the
Li0.5CoO2 powders. In contrast, the lattice constants c of the Li12xCoO2 thin films deposited at different conditions @yielding a
weak ~003! texture# expanded when first charged to 4.2 V, which is similar to that observed in the powder geometry.
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College of Engineering/Engineering Practice School (공과대학/대학원)Dept. of Chemical and Biological Engineering (화학생물공학부)Journal Papers (저널논문_화학생물공학부)
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