Synergistic multi-doping effects on the Li7La3Zr2O12 solid electrolyte for fast lithium ion conduction.

Dong Ok Shin,Kwang Man Kim,Young-Gi Lee,Kisuk Kang,Byungju Lee,Kyungbae Oh,Kyu-Young Park

doi:10.1038/srep18053

Abstract

Here, we investigate the doping effects on the lithium ion transport behavior in garnet Li7La3Zr2O12 (LLZO) from the combined experimental and theoretical approach. The concentration of Li ion vacancy generated by the inclusion of aliovalent dopants such as Al3+ plays a key role in stabilizing the cubic LLZO. However, it is found that the site preference of Al in 24d position hinders the three dimensionally connected Li ion movement when heavily doped according to the structural refinement and the DFT calculations. In this report, we demonstrate that the multi-doping using additional Ta dopants into the Al-doped LLZO shifts the most energetically favorable sites of Al in the crystal structure from 24d to 96 h Li site, thereby providing more open space for Li ion transport. As a result of these synergistic effects, the multi-doped LLZO shows about three times higher ionic conductivity of 6.14 × 10−4 S cm−1 than that of the singly-doped LLZO with a much less efforts in stabilizing cubic phases in the synthetic condition.

Highlights

MethodsPreparation of the single Al-doped and multi-doped L7La3Zr2O12. Li2CO3 (99.9%), La2O3 (99.9%), ZrO2 (99.9%), Al2O3 nanopowder (< 50 nm particle size), Ta2O5 (99.9%) were purchased from Sigma-Aldrich and used as received
We have demonstrated that the fast stabilization of cubic phase is feasible for the multi-doped LLZO compared to single Al-doped LLZO, through Li vacancies generated by the inclusion of aliovalent dopants
The additional Ta doping moves a majority of Al from the 24 d to 96 h Li sites, providing more open space for Li ion transport as well as the increased amount of Li vacancy

Summary

Methods

Preparation of the single Al-doped and multi-doped L7La3Zr2O12. Li2CO3 (99.9%), La2O3 (99.9%), ZrO2 (99.9%), Al2O3 nanopowder (< 50 nm particle size), Ta2O5 (99.9%) were purchased from Sigma-Aldrich and used as received. Garnet-structured cubic LLZO solid electrolytes with the desired amounts of doping elements (only Al, only Ta, or both Al and Ta) was prepared through a solid-state reaction. The collected powder was calcined at 1000 ̊C for 2–4 h to obtain the cubic LLZO powder. The calcined LLZO powder was reground and pressed into a pellet at 50 MPa. the pellet was sintered at 1200 ̊C from 1 to 24 h to ensure the formation of well-dense body. The pellet was covered with the mother LLZO power to minimize the Li loss at high temperature. During the synthesis of cubic LLZO powder and the sintering of pellet, Al2O3 crucible with boron nitride (BN) coating was used to prevent the unintentional Al doping

Results

Discussion

Conclusion