| Co-Investigator(Kenkyū-buntansha) |
NAKAMURA Hiroyoshi Saga University, FACULTY OF SCIENCE & ENGINEERING, Associate Professor, 理工学部, 助教授 (00295023)
NOGUCHI Hideyuki Saga University, FACULTY OF SCIENCE & ENGINEERING, Professor, 理工学部, 教授 (60093978)
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| Research Abstract |
It is found that layered LiNiO_2 forms electroactive solid solution with similar layered Li_2MnO_3 in the all composition range. Though low temperature phase Li_2TiO_3 has same structure with Li_2MnO_3, the structure of solid solution between LiNiO_2 and Li_2TiO_3 changes from layered structure to rock salt structure as the increase in Ti content because of enhanced cation mixing. On the other hand, LiCrO_2 forms layered solid solution with Li_2TiO_3. The solid solution with Ni/Ti=1 shows largest capacity of more than 170 mAh/g. It is finally confirmed that LiCrO_2-Li_2MnO_3 and LiCrO_2-Li_2TiO_3 solid solutions have similar electrochemical and crystallographic properties, however, LiNiO_2-Li_2MnO_3 system is different from LiNiO_2-Li_2TiO_3 system in both character.
LiNiXMn_yCo_<1-x-y>O_2 with lower Mn content of y<0.5 is electroactive material. LiNi_<1/3>Mn_<1/3>Co_<1/3>O_2 with high capacity is a typical compound among LiNi_xMn_yCo_<1-x-y>O_2 and it will be considered as a solid solu
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tion between LiNi_<1/2>Mn_<1/2>O_2 and LiCoO_2. Electrochemical property of LiNi_<1/3>Mn_<1/3>Co_<1/3>O_2 extremely depends on preparation process, and we have found that the battery performance can be predicted from the shape of initial charge curve. The essential reason for lower performance would be due to the presence of impurity, NiO, as a result, electroactive solid solution with Li_2MnO_3, which shows lower performance than pure LiNi_<1/3>Mn_<1/3>Co_<1/3>O_2, is formed.
The research for LiNi_<1/2>Mn_<1/2-x>Ti_xO_2 has been carried out in order to clarify the difference between Mn and Ti in the formation of solid solution. In the course of study, complete Ti substituted compound, LiNi_<1/2>Mn_<1/2-x>Ti_xO_2 with rock salt structure, delivers more than 150 mAh/g at 50 ℃. This fact indicates the possibility of excellent cathode materials with rock salt structure, which has been considered unsuitable because of difficulty in Li diffusion. This finding would lead to the development of rock salt type electrode materials. The new material shows low reproducibility in electrochemical property at room temperature, however, enhanced properties are confirmed by the formation of solid solution with Li_2TiO_3. Less
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