Institute of Solid State Physics
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SS22 WS22 SS23 WS23 SS24 WS24 Guidelines for Master Students
Small change ¨D great effect: Steep increase of Li ion dynamics in Li4Ti5O12 at the early stages of chemical Li insertion (x = 0.1, x = 0.3) Polycrystalline Li4+xTi5O12 (LTO, 0 < x ¡Ü 3) is one of the most promising negative electrode materials for lithium-ion batteries. It shows a flat Li insertion plateau of about 1.5 V vs. Li/Li+; its theoretic specific capacity is approximately 175 mAh/g. The increased use of LTO, which is commercially available, is due to various properties such as low cost, satisfactory safety and easy preparation. Most importantly, upon Li insertion, the expansion of the material is almost negligible favoring a long cycle life. In samples with x = 0, Li self-diffusion, which can be microscopically probed via Li nuclear magnetic resonance (NMR), is rather low. With increasing Li insertion, however, the diffusivity increases significantly. This is accompanied by a redistribution of Li ions across the 8a and 16c sites in the spinel structure [1]. Recent 7Li NMR studies put emphasis on samples with Li contents of x >1 [2]. As yet, there are, however, no information from NMR available answering the question of how Li self-diffusion changes when x is only slightly increased. The present results show that even at x = 0.1 7Li NMR spin-lattice relaxation, performed in the so-called rotating frame of reference, reveals a drastic enhancement of Li diffusivity [3], which is associated with a considerable reduction of the local hopping barrier pointing to the 8a ¨C 16c ¨C 8a migration pathway discussed in the literature. As a result, the largest increase in Li diffusivity is observed at the early stages of Li insertion [3]. Strong Coulomb repulsions caused by the simultaneous occupation of neighboured 8a and 16c sites might explain the unexpected enhanced Li diffusivity found. |
