Factors Influencing the Lithium Extraction Rate in Layered Oxide Cathodes of Lithium Ion Cells
- PDF / 108,754 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 52 Downloads / 207 Views
K11.11.1
Factors Influencing the Lithium Extraction Rate in Layered Oxide Cathodes of Lithium Ion Cells A. Manthiram and J. Choi Materials Science and Engineering Program The University of Texas at Austin Austin, Texas 78712 ABSTRACT The lithium extraction rate and the rate capability of layered LiNi0.5-0.5yMn0.5-0.5yCoyO2 with 0 ≤ y ≤ 1 have been investigated, respectively, by chemically extracting lithium with the oxidizer NO2BF4 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 LiNi0.5-0.5yMn0.5-0.5yCoyO2. 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 Ni0.5-0.5yMn0.5-0.5yCoyO2-δ obtained by extracting all the lithium with 100 % excess NO2BF4 in an acetonitrile medium. INTRODUCTION The layered LiNi1-y-z MnyCozO2 (LNMCO) cathodes have become appealing recently due to their higher capacity, lower cost, and enhanced safety compared to the conventional LiCoO2 cathode [1]. The high capacity of the layered LNMCO cathodes originates from the better chemical stability of the Ni2+/3+, Ni3+/4+, and Mn3+/4+ redox couples compared to that of the Co3+/4+ couple as has been demonstrated by our previous studies employing a chemical lithium extraction technique [2]. However, there are a few drawbacks with the LNMCO cathodes that should be overcome in order for them to find wide applications. One of them is the lower rate capability compared to that of LiCoO2, which can limit the power density of the LNMCO cathodes. With an aim to establish a better understanding of the factors that influence the rate capability and develop optimized high performance cathode compositions, we have investigated the layered LiNi0.5-0.5yMn0.5-0.5yCoyO2 oxides by chemically extracting lithium with an oxidizing agent, following the lithium content with lithium extraction time, and analyzing with the Rietveld method the structure of the products formed. A substitution of equal amounts of Co3+ for both Ni2+ and Mn4+ in LiNi0.5-0.5yMn0.5-0.5yCoyO2 maintains the valence states of Ni and Mn unaltered similar to that in the parent LiNi0.5Mn0.5O2 composition. EXPERIMENTAL The LiNi0.5-0.5yMn0.5-0.5yCoyO2 samples with 0 ≤ y ≤ 0.58 were prepared by firing the coprecipitated hydroxides of Co, Ni, and Mn with 7 atom % excess lithium hydroxide in air at 900 oC for 24 h. The coprecipitated hydroxides were obtained by adding an aqueous solution containing required amounts of Co2+, Ni2+, and Mn2+ into LiOH solution. LiCoO2 (y = 1) was prepared by a solid state reaction of required amounts of lithium carbonate and Co3O4 in air at
K11.11.2
900 oC for 24 h. Chemical extraction of lithium was
Data Loading...
