Very fast bulk Li ion diffusivity in crystalline Li_1.5Al_0.5Ti_1.5(PO₄)₃as seen using NMR relaxometry

Abstract

The realization of large powerful all-solid-state batteries is still hampered by the availability of environmentally friendly and low-cost Li ion conductors that can easily be produced on a large scale and with high reproducibility. Advanced solid electrolytes benefit from fast ion-selective transport and non-flammability, but they may have low electrochemical stability with respect to Li metal. Sol-gel-synthesized lithium titanium aluminum phosphate Li(1.5)Al(0.5)Ti(1.5)(PO4)3 (LATP), which was prepared via a new synthesis route taking advantage of an annealing step at relatively low temperatures, has the potential to become one of the major players in this field although it may suffer from reduction upon direct contact with metallic lithium. Its ion dynamics is, however, as yet poorly understood. In the present study, (7)Li nuclear magnetic resonance (NMR) spectroscopy was used to monitor the key Li jump processes on the atomic scale. NMR relaxation clearly reveals heterogeneous dynamics comprising distinct ultra-fast and slower diffusion processes. The high Li ion self-diffusion coefficients deduced originate from a rapid Li exchange with activation energies as low as 0.16 eV which means that sol-gel synthesized LATP is superior to other solid electrolytes. Our NMR results fully support recent theoretical investigations on the underlying diffusion mechanism, indicating that to rapidly jump from site to site, the ions use interstitial sites connected by low-energy barriers in LATP.

Ion dynamics in solid electrolytes for lithium batteries

“…8(a) represent so-called joint or global fits that simultaneously reproduce the peak in the laboratory and in the rotating frame. For the two pairs of relaxation processes activation energies were found to be rather small (0.174 eV and 0.160 eV) [125]. Such low values are in agreement with a diffusion pathway that involves interstitial positions as has been the outcome of recent calculations performed by Lang et al using density functional theory [135].…”

“…Li NMR relaxometry corroborates the high Li diffusivity indicated by line shape measurements; the rates R 1 diff and R 1 ρ diff when plotted vs the inverse temperature reveal several distinct peaks that point to multiple Li jump processes in Li 1.5 Al 0.5 Ti 1.5 PO 4 [125]. The first R 1 ρ diff (1/T ) peak shows up at ca.…”

“…8(d) the NMR rate peaks of LATP are compared with those of garnet-type c-Li 6.6 La 3 Zr 1.6 Ta 0.4 O 12 [125] and one of the best ion conducting sulfides: Li 6 PS 5 Br, which, in terms of conductivity, is comparable to Li 10 GeP 2 S 12 , see above [35,62]. Since the locking frequencies used are comparable, the lower the temperature at which the …”

“…Its electrochemical stability against Li metal and other high-voltage cathode materials needs to be ensured by protective coatings. Via NMR we have investigated bulk ion dynamics in LATP with the composition Li 1.5 Al 0.5 Ti 1.5 PO 4 [125]. In contrast to a recent NMR study [132], the sample investigated by us was prepared by a novel sol-gel method that allowed precisely controlling the composition and morphology of the product (1/T 1,1ρ…”

The Evolution of Microstructures and the Properties of Bulk Metallic Glass with Consubstantial Composition Laser Welding

“…BMGs have been found in many different alloy groups, such as Pd-, Mg-, Ln-, Ti-, Fe-, Co-, Ni-, Ca-, Zr-, and Cu-based systems [3], and new alloys have been fabricated and reported with a variety of different properties. Nowadays, a substantial amount of research has been carried out and is being carried out on BMGs investigating their structural and thermal stabilities, mechanical properties, fracturing behavior, preparation and glass-forming abilities, and so on [11,12]; meanwhile, impurity diffusions in the amorphous alloys have been studied primarily [13][14][15]. However, in BMGs, the welding performance research, which is an important field that should be carried out and has close relations to mechanical properties and structural and thermal stabilities, have rarely been reported.…”