Puravankara Sreeraj

Li ion diffusion in the anode material Li12Si7: ultrafast quasi-1D diffusion and two distinct fast 3D jump processes separately revealed by 7Li NMR relaxometry.

The intermetallic compounds Li(x)Si(y) have attracted considerable interest because of their potential use as anode materials in Li ion batteries. In addition, the crystalline phases in the Li-Si phase diagram turn out to be outstanding model systems for the measurement of fast Li ion diffusion in solids with complex structures. In the present work, the Li self-diffusivity in crystalline Li(12)Si(7) was thoroughly probed by (7)Li NMR spin-lattice relaxation (SLR) measurements. Variable-temperature and -frequency NMR measurements performed in both the laboratory and rotating frames of reference revealed three distinct diffusion processes in Li(12)Si(7). The diffusion process characterized by the highest Li diffusivity seems to be confined to one dimension. It is one of the fastest motions of Li ions in a solid at low temperatures reported to date. The Li jump rates of this hopping process followed Arrhenius behavior; the jump rate was ~10(5) s(-1) at 150 K and reached 10(9) s(-1) at 425 K, indicating an activation energy as low as 0.18 eV.

NMR relaxometry as a versatile tool to study Li ion dynamics in potential battery materials.

NMR spin relaxometry is known to be a powerful tool for the investigation of Li(+) dynamics in (non-paramagnetic) crystalline and amorphous solids. As long as significant structural changes are absent in a relatively wide temperature range, with NMR spin-lattice (as well as spin-spin) relaxation measurements information on Li self-diffusion parameters such as jump rates and activation energies are accessible. Diffusion-induced NMR relaxation rates are governed by a motional correlation function describing the ion dynamics present. Besides the mean correlation rate of the dynamic process, the motional correlation function (i) reflects deviations from random motion (so-called correlation effects) and (ii) gives insights into the dimensionality of the hopping process. In favorable cases, i.e., when temperature- and frequency-dependent NMR relaxation rates are available over a large dynamic range, NMR spin relaxometry is able to provide a comprehensive picture of the relevant Li dynamic processes. In the present contribution, we exemplarily present two recent variable-temperature (7)Li NMR spin-lattice relaxation studies focussing on Li(+) dynamics in crystalline ion conductors which are of relevance for battery applications, viz. Li(7) La(3)Zr(2)O(12) and Li(12)Si(7).

Lithium-Transition Metal-Tetrelides – Structure and Lithium Mobility

Abstract Lithium-transition metal (T)-tetrelides (tetr.= C, Si, Ge, Sn, Pb) are an interesting class of materials with greatly differing crystal structures. The transition metal and tetrel atoms build up covalently bonded networks which leave cavities or channels for the lithium atoms. Depending on the bonding of the lithium atoms to the polyanionic network one observes mobility of the lithium atoms. The crystal chemistry, chemical bonding, 7Li solid state NMR, and the electrochemical behavior of the tetrelides are reviewed herein.

The Stannide LiRh3Sn5 – Synthesis, Structure, and Chemical Bonding

The lithium rhodium stannide LiRh3Sn5 was synthesized from the elements in a sealed tantalum tube and investigated via X-ray powder and single crystal diffraction: Pbcm, a = 538.9(1), b = 976.6(3), c = 1278.5(3) pm, wR2 = 0.0383, 1454 F2 values, and 44 variables. Refinement of the occupancy parameters revealed a lithium content of 92(6)%. LiRh3Sn5 crystallizes with a new structure type. The structure is built up from a complex three-dimensional [Rh3Sn5] network, in which the lithium atoms fill channels in the b direction. The [Rh3Sn5] network is governed by Rh-Rh (274 - 295 pm), Rh-Sn (262 - 287 pm), and Sn-Sn (289 - 376 pm) interactions. The lithium atoms have CN 13 (4 Rh+9 Sn). Electronic band structure calculations and the COHP bond analysis reveal strong Rh−Sn bonds and also significant Rh−Rh bonding within the Rh3Sn5 network, which is additionally stabilized by weak but frequent Sn−Sn interactions.