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Study of Codoping Effects of Ta⁵⁺ and Ga³⁺ on Garnet Li₇La₃Zr₂O₁₂.

ABSTRACT: Garnet Li₇La₃Zr₂O₁₂ (LLZO) is a promising solid electrolyte for all-solid-state Li-ion batteries because of its outstanding performance. However, LLZO exists in two polymorphic phases, tetragonal (∼10^-3 mS cm^-1) and cubic (1-10^-1 mS cm^-1), where the cubic phase exhibits higher Li-ion conductivity but is thermodynamically unstable at ambient room temperature. To stabilize the cubic phase with high ionic conductivity, we fabricated mono- and codoped garnet with Ta⁵⁺ and Ga³⁺ (Li_7-3x-z=6.4Ga _x La₃Zr_2-z Ta _z O₁₂) and investigated the doping effects. The doping effects on the crystal structure and ionic conductivity were systematically investigated using X-ray diffraction, Raman scattering, scanning electron microscopy, alternative current (AC) impedance, and direct current (DC) polarization methods. The characterization results revealed that Ta-doping favors higher occupation of Li-ions on the mobile octahedral (LiO₆) site and improves ionic conductivity of the grain boundary. However, it showed poor total ionic conductivity (2.044 × 10^-4 S cm^-1 at 1100 °C for 12 h) due to the low sinterability [relative density (RD): ∼80.3%]. On the other hand, Ga-doping provides better sinterability (RD: ∼93.1%) and bulk conductivity. Considering the beneficial effects of Ga- and Ta-doping, codoped Li_6.4Ga_0.133La₃Zr_1.8Ta_0.2O₁₂ garnet with enhanced ionic conductivity (6.141 × 10^-4 S cm^-1) and improved high-density microstructure (RD: ∼95.7%) was obtained.

SUBMITTER: Enkhbayar E

PROVIDER: S-EPMC9773338 | biostudies-literature | 2022 Dec

REPOSITORIES: biostudies-literature

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Study of Codoping Effects of Ta5+ and Ga3+ on Garnet Li7La3Zr2O12.

Enkhbayar Enkhjargal E Kim JunHo J

ACS omega 20221206 50

Garnet Li7La3Zr2O12 (LLZO) is a promising solid electrolyte for all-solid-state Li-ion batteries because of its outstanding performance. However, LLZO exists in two polymorphic phases, tetragonal (∼10-3 mS cm-1) and cubic (1-10-1 mS cm-1), where the cubic phase exhibits higher Li-ion conductivity but is thermodynamically unstable at ambient room temperature. To stabilize the cubic phase with high ionic conduc ...[more]

PMID: 36570224

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Project description:Ionic transport in solid electrolytes can often be approximated as ions performing a sequence of hops between distinct lattice sites. If these hops are uncorrelated, quantitative relationships can be derived that connect microscopic hopping rates to macroscopic transport coefficients; i.e. tracer diffusion coefficients and ionic conductivities. In real materials, hops are uncorrelated only in the dilute limit. At non-dilute concentrations, the relationships between hopping frequency, diffusion coefficient and ionic conductivity deviate from the random walk case, with this deviation quantified by single-particle and collective correlation factors, f and fI, respectively. These factors vary between materials, and depend on the concentration of mobile particles, the nature of the interactions, and the host lattice geometry. Here, we study these correlation effects for the garnet lattice using lattice-gas Monte Carlo simulations. We find that, for non-interacting particles (volume exclusion only), single-particle correlation effects are more significant than for any previously studied three-dimensional lattice. This is attributed to the presence of two-coordinate lattice sites, which causes correlation effects intermediate between typical three-dimensional and one-dimensional lattices. Including nearest-neighbour repulsion and on-site energies produces more complex single-particle correlations and introduces collective correlations. We predict particularly strong correlation effects at xLi=3 (from site energies) and xLi=6 (from nearest-neighbour repulsion), where xLi=9 corresponds to a fully occupied lithium sublattice. Both effects are consequences of ordering of the mobile particles. Using these simulation data, we consider tuning the mobile-ion stoichiometry to maximize the ionic conductivity, and show that the 'optimal' composition is highly sensitive to the precise nature and strength of the microscopic interactions. Finally, we discuss the practical implications of these results in the context of lithium garnets and other solid electrolytes.

Dataset Information

Study of Codoping Effects of Ta⁵⁺ and Ga³⁺ on Garnet Li₇La₃Zr₂O₁₂.

Publications

Study of Codoping Effects of Ta<sup>5+</sup> and Ga<sup>3+</sup> on Garnet Li<sub>7</sub>La<sub>3</sub>Zr<sub>2</sub>O<sub>12</sub>.

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