Grain Boundary Engineering in Ta-Doped Garnet-Type Electrolyte for Lithium Dendrite Suppression.

Solid-state lithium batteries (SSLBs) based on Ta-doped Li6.5La3Zr1.5Ta0.5O12 (LLZTO) suffer from lithium dendrite growth, which hinders their practical application. Herein, first principles simulations indicate that the Ta element prefers to segregate along grain boundaries in the form of Ta2O5 precipitates due to a high energy difference induced by Ta doping. Grain boundary engineering is employed to regulate the distribution of the Ta element and enhance the density of LLZTO by introducing the La2O3 additive. The sufficient La2O3 additive reacts with the Ta2O5 precipitates, while the residual La2O3 nanoparticles fill up void defects, promoting the homogeneous distribution of the Ta element and improving the relative density to ∼98%. Critical current density of the symmetric Li battery reaches 2.12 mA·cm-2 at room temperature with the solid-state electrolyte (LLZTO + 5 wt % La2O3), which increases by 41% compared to pure LLZTO. SSLBs with the LiFePO4 cathode achieve a stable cycling performance with a discharge capacity of 138.6 mA·h·g-1 after 400 cycles at 0.2 C. This work provides theoretical insights into the distribution of Ta-doped LLZTO and inhibits lithium dendrite growth through grain boundary engineering.

Oriented Attachment Strategy Toward Enhancing Ionic Conductivity in Garnet-Type Electrolytes for Solid-State Lithium Batteries.

Solid-state lithium batteries (SSLBs) based on garnet-type solid-state electrolytes (SSEs) have attracted much attention due to their high energy density and chemical stability. However, poor room-temperature ionic conductivity and low density of SSEs induced by conventional preparation routes limit their potential future applications. In this work, an oriented attachment strategy is employed to enhance the Li-ion conductivity and density of garnet-type SSE Li6.5La3Zr1.5Ta0.5O12 by introducing La2O3 nanoparticles. The oriented attachment of the ZrO2(Ta2O5) matrix mediates the epitaxial growth of the La-Zr(Ta)-O intermediate phase due to the addition of La2O3 nanoparticles. Continuous Li-ion transport pathways along grain boundaries are produced by the combination of residual La2O3 and gas Li2O. A densification interface is obtained when 10 wt % La2O3 is doped. The maximum value of Li-ion conductivity reaches 8.20 × 10-4 S·cm-1, with a relative density of 97.3%. SSLBs with a LiFePO4 cathode showing a stable cycling performance with a discharge capacity of 123.1 mA·h·g-1 and a Coulombic efficiency of 99.2% after 300 cycles (0.5C) at room temperature. This work is comparable to the state-of-the-art methodology, which provides a feasible approach to creating SSEs with high performances for SSLBs.