Nanostructured Layered Oxide Cathodes for Lithium Ion Batteries
Krista L. Hawthorne,a Ryan Franck,a Siu on Tung,c James Mainero,b Yi Ding,b Levi T. Thompsona
aDepartment of Chemical Engineering, University of Michigan, Ann Arbor, MI 48109
bUnited States Army Tank Automotive Research, Development, and Engineering Center, Warren, MI 48092
aDepartment of Macromolecular Engineering, University of Michigan, Ann Arbor, MI 48109
Lithium ion batteries typically operate by reversibly intercalating lithium ions in layered oxide cathodes, such as LiCoO2; consequently the capacity is directly correlated to the amount of lithium ions that can be inserted and extracted.1 This repeated insertion of lithium ions causes strain on the crystal structure, leading to fracture and capacity fade.2-4 Additionally, diffusion of the lithium ions through the crystal is relatively slow, limiting the rate capabilities of the battery. Several efforts reported in the literature have focused on engineering the structure of the cathode materials. We propose a nanostructuring of layered oxides by the chemical insertion of pillars between the layers.5,6 These pillars act as scaffolds, providing structural support and increasing the interlayer spacing, which in turn increases the battery capacity and lifetime.
Our efforts focused on vanadium pentoxide xerogels (V2O5)7 and manganese oxide (MnO2). Typical manganese oxide cathodes are in a spinel structure; however, the birnessite phase of manganese oxide is a layered structure, with potassium ions between the layers.8 Both materials were pillared with Al13 Keggin ions. The pillared vanadium oxide xerogels exhibit an increase in the (001) interlayer spacing from 11 to 13 Ĺ, as observed by XRD and an increase in thermal stability over the unpillared xerogel. During cycling, pillared V2O5 shows an increase in capacity at high rates as well as an increase in capacity retention, when returning to cycling at low rates after the high rate experiments (Figure 1). We will report thermal stability of coin cells with pillared V2O5 cathodes, through the use of an Accelerating Rate Calorimeter, and mechanical and electrochemical properties of pillared birnessite materials. Pillared manganese oxide structures may exhibit similar increases in capacity. Additionally, other pillars such as SiO2 and TiO2 can be used in birnessite.
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