Li Conductivity of Nanocrystalline Li₄Ti₅O₁₂ Prepared by a Sol-Gel Method and High-Energy Ball Milling

Abstract

Spinel-type structured Li4+xTi5O12 (0 6 x 6 3 ) is actually one of the most promising anode materials for Li ion batteries. In its nanostructured form it is already used in some commercially available Li ion batteries. As was recently shown by our group (Wilkening et al., Phys. Chem. Chem. Phys. 9 (2007) 1239), Li diffusivity in microcrystalline Li4+xTi5O12 with x = 0 is rather slow. In the present contribution the Li conductivity in nanocrystalline samples of the electronic insulator Li4Ti5O12 prepared by different routes is investigated using impedance spectroscopy. The mean crystallite size of the samples is about 20 nm. The ionic conductivity of nanocrystalline Li4Ti5O12 obtained by mechanical treatment is higher by about two orders of magnitude compared to that found for a material which was prepared following a sol-gel method. The latter resembles the behaviour of the microcrystalline sample with an average particle size in the μm range rather than that of a nanocrystalline ball milled one with a mean crystallite size of about than 20 nm. The larger conductivity of the ball milled sample is ascribed to a much higher defect density generated when the particle size is reduced mechanically.

Li Ion Diffusion in Nanocrystalline and Nanoglassy LiAlSi2O6 and LiBO2 - Structure-Dynamics Relations in Two Glass Forming Compounds

“…This effect has also been found for other ion conducting materials (see, e.g., [10,26,64,65,66]) and is attributed to highly defective or amorphous grain boundaries introduced into the sample in mechanical treatment. As the crystallite size is reduced these highly diffusive grain boundaries more and more dominate the over-all properties of the whole sample (see section 1).…”

“…Interestingly, when the glassy sample is ball-milled, this peak is shifted to higher wave numbers (980 cm -1 after 4 h in a ZrO 2 vial set) thus converging to the value found for crystalline spodumene. For vitreous SiO 2 , a direct correlation between the maximum of the SiO stretching vibration peak and the so-called fictive temperature [66], at which the structure is frozen, was shown [52,53]. Here, a larger Si-OSi bond angle is associated with a decrease of the fictive temperature.…”

“…However, the diffusivity of the glass is not reached even though sometimes, as in the present case, amorphization takes place. This might be due to the fact that the structure of the glass refers to a very high fictive temperature, at which the structure is frozen [66]. In mechanical treatment, it is rather improbable that a glass-like structure refering to a high-temperature equilibrium state with its high free volume and local strains is produced.…”

From Micro to Macro: Access to Long‐Range Li+ Diffusion Parameters in Solids via Microscopic 6, 7Li Spin‐Alignment Echo NMR Spectroscopy

“…Let us note that Li 4 + x Ti 5 O 12 turned out to be an attractive anode material for rechargeable Li-ion batteries. [80][81][82][83][84] For comparison, extremely slow Li jumps in the non-intercalated material (x = 0) have been probed by Li SAE NMR spectroscopy [56] as mentioned above (see also Section 4.1). As a matter of course, it is beneficial to record jump rates over a large dynamic range and to follow, for example, changes in the diffusion mechanisms.…”

Improved Electrochemical Performance of Modified Mesocarbon Microbeads for Lithium‐Ion Batteries Studied using Solid‐State Nuclear Magnetic Resonance Spectroscopy

“…Concerning the high electrical conductivity of graphite,t his effect is assumed to be relatively small, thoughitm ay play am ajor role in materials with low electric conductivity, for example,lithium titanate( Li 4 Ti 5 O 12 ). [21] Li NMR spectroscopyc an distinguish between different Li species incorporatedi nt he carbon matrix. 7 Li NMR spectra (Figure 5a,b)a nd 6 Li MMR spectra (Figure 5c,d)a re shown both for MCMBa nd MCMB_Cu.…”