Factors Influencing the Lithium Extraction Rate in Layered Oxide Cathodes of Lithium Ion Cells

摘要

The lithium extraction rate and the rate capability of layered LiNi_(0.5-0.5y)Mn_(0.5-0.5y)Co_yO_2 with 0 ≤ y ≤ 1 have been investigated, respectively, by chemically extracting lithium with the oxidizer NO_2BF_4 in acetonitrile medium and electrochemically discharging at various C-rates. Both the chemical lithium extraction rate and the electrochemical rate capability are found to increase with increasing Co content y in LiNi_(0.5-0.5y)Mn_(0.5-0.5y)Co_yO_2. While no clear relationship is seen between electrical conductivity and the rate capability, increasing cation disorder between the lithium and transition metal planes with decreasing Co content is found to decrease the chemical lithium extraction rate and rate capability. The lithium extraction rate also influences the structure (P3 vs O1 vs O3) of the end members Ni_(0.5-0.5y)Mn_(0.5-0.5y)Co_yO_(2-δ) obtained by extracting all the lithium with 100 % excess NO_2BF_4 in an acetonitrile medium.