Lithium Ion Diffusion Mechanism in Lithium Lanthanum Titanate Solid‐State Electrolytes from Atomistic Simulations

Abstract

Perovskite‐structured lithium lanthanum titanate (LLT, La2/3–xLi3xTiO3, 0 < x < 0.16) is a promising solid electrolyte with high lithium ion conductivity and a good model system to understand lithium ion diffusion behaviors in solids. Molecular dynamics (MD) and related atomistic computer simulations were used to study the diffusion behavior and diffusion mechanism as a function of composition in LLT solid‐state electrolytes. The effect of defect concentration on the structure and lithium ion diffusion behaviors in LLT was systematically studied using MD simulations and molecular static calculations with the goal to obtain fundamental understanding of the diffusion mechanism of lithium ions in these materials. The simulation results show that there exists an optimal vacancy concentration at around x = 0.067 at which lithium ions have the highest diffusion coefficient and the lowest diffusion energy barrier. The lowest energy barrier from dynamics simulations was found to be around 0.22 eV, which compared favorably with 0.19 eV from static nudged elastic band calculations. It was also found that lithium ions diffuse through bottleneck structures made of oxygen ions, which expand in dimension by 8%–10% when lithium ions pass through. By designing perovskite structures with larger bottleneck sizes can be a means of further improving lithium ion conductivities in these materials.

Structural Origin of the Thermal and Diffusion Behaviors of Lithium Aluminosilicate Crystal Polymorphs and Glasses

“…The MSDs were calculated from NVE trajectories to quantify the lithium diffusion behavior of α–LiAlSi 2 O 6 , β–LiAlSi 2 O 6 , and LiAlSi 2 O 6 glass. All the lithium ions in each simulated structure were used and averaged over large number of origins to obtain statistically meaningful results . Figure shows the logarithm scale of MSDs for lithium ions in LiAlSi 2 O 6 glass which can be classified into three characteristic regions .…”

“…All the lithium ions in each simulated structure were used and averaged over large number of origins to obtain statistically meaningful results. 24 Figure 14 shows the logarithm scale of MSDs for lithium ions in LiAlSi 2 O 6 glass which can be classified into three characteristic regions. 46 The first region is a ballistic region for short times where MSD is proportional to t 2 .…”

Oxide Electrolytes for Lithium Batteries

“…Despite a high‐reported bulk conductivity of 10 −3 S/cm for LLTO, whether this value represents the intrinsic lattice conductivity is still not sure yet since large discrepancy exists among the activation energies obtained from experiments (0.35–0.4 eV) and simulation computations (0.22–0.24 eV). Recently, Moriwake et al proposed that 90° domain boundaries could be an important factor influencing the bulk ionic conductivity of LLTO.…”

“…163 Partial substitution of A-site cations by Nd 3+ can minimize lattice distortion and yield a solid solution of strongly disordered A-sites, which improves the bulk ionic conductivity. 169 Despite a high-reported bulk conductivity of 10 À3 S/cm for LLTO, whether this value represents the intrinsic lattice conductivity is still not sure yet since large discrepancy exists among the activation energies obtained from experiments (0.35-0.4 eV 153,170 ) and simulation computations (0.22-0.24 eV 171,172 ). Recently, Moriwake et al 173 proposed that 90°domain boundaries could be an important factor influencing the bulk ionic conductivity of LLTO.…”

Scratch Testing of Hard Ceramics: Manifestation of Viscoelasticity

“…Carbajal de la Torre et al (2009) developed silica based ceramic coatings for corrosion protection of steels. Chen and Du (2014) studied a lithium lanthanum titanate as a promising solid electrolite-not experimentally but by molecular dynamics and atomistic computer simulations. Salonen and Mäkilä (2018) note applications of porous silicon in areas as diverse as luminescence, drug delivery and battery technology.…”