Study on Li₃BO₃ Interface Modification of Garnet Solid Electrolyte

Authors

Gui-Wei Chen, College of Energy, Xiamen University, Xiamen 361005, Fujian, China;
Zheng-Liang Gong, College of Energy, Xiamen University, Xiamen 361005, Fujian, China;Follow

Corresponding Author

Zheng-Liang Gong(zlgong@xmu.edu.cn)

Abstract

Garnet solid-state electrolytes have become the research hotspot due to their high ionic conductivity, wide electrochemical stability window and good air stability. However, there are still a series of problems to be solved. The poor contact between the lithium (Li) metal and garnet pellet make it difficult to build stable ion diffusion channels, resulting in large interfacial resistance. The continuous growth of lithium dendrites can penetrate the electrolyte pellet and cause a short circuit in the solid-state battery. Herein, a novel strategy is proposed to improve the wettability of LLZTO electrolyte with Li metal, via interfacial modification of LLZTO electrolyte with tri-lithium borate (Li₃BO₃). Li₃BO₃ is chemically stable with Li metal and effective to improve the wettability between Li and LLZTO pellet. A stable and even Li₃BO₃ interfacial layer was constructed on the LLZTO electrolyte surface by liquid-phase deposition combing with high temperature sintering. The low melting point (700℃) of Li₃BO₃ facilitated the formation of a dense and uniform coating layer. SEM images show that the Li₃BO₃ layer was about 2.5 μm thick and completely covered the pellet surface. Intimate contact between Li metal and LLZTO electrolyte could be realized after the Li₃BO₃ interfacial modification, which was confirmed by SEM analysis and wettability experiment. Benefiting from the significantly improved interfacial contact, the interfacial impedance was dramatically reduced from 1780 Ω·cm² of Li/LLZTO interface to 58 Ω·cm² of Li/LBO-LLZTO interface. The Li|LBO-LLZTO|Li symmetric cell could produce a low overpotential and work stably at the current density of 0.1 mA·cm^-2 for more than 700 h. By contrast, the Li|LLZTO|Li symmetric cell displayed high overpotential and was short circuited after 20 min of lithium plating/stripping at the current density of 0.05 mA·cm^-2. Our results show that Li₃BO₃ interfacial modification is an effective approach to improve the wettability and interfacial stability between Li metal and garnet electrolyte, which is a key to the successful use of solid-state battery.

Graphical Abstract

Keywords

Garnet electrolyte, Li3BO3 layer, interfacial modification, Li anode, interfacial wettability

DOI Link

https://doi.org/10.13208/j.electrochem.200516

Publication Date

2021-02-28

Online Available Date

2020-06-28

Revised Date

2020-06-22

Received Date

2020-05-15

Recommended Citation

Gui-Wei Chen, Zheng-Liang Gong. Study on Li₃BO₃ Interface Modification of Garnet Solid Electrolyte[J]. Journal of Electrochemistry, 2021 , 27(1): 76-82.
DOI: Garnet solid-state electrolytes have become the research hotspot due to their high ionic conductivity, wide electrochemical stability window and good air stability. However, there are still a series of problems to be solved. The poor contact between the lithium (Li) metal and garnet pellet make it difficult to build stable ion diffusion channels, resulting in large interfacial resistance. The continuous growth of lithium dendrites can penetrate the electrolyte pellet and cause a short circuit in the solid-state battery. Herein, a novel strategy is proposed to improve the wettability of LLZTO electrolyte with Li metal, via interfacial modification of LLZTO electrolyte with tri-lithium borate (Li₃BO₃). Li₃BO₃ is chemically stable with Li metal and effective to improve the wettability between Li and LLZTO pellet. A stable and even Li₃BO₃ interfacial layer was constructed on the LLZTO electrolyte surface by liquid-phase deposition combing with high temperature sintering. The low melting point (700℃) of Li₃BO₃ facilitated the formation of a dense and uniform coating layer. SEM images show that the Li₃BO₃ layer was about 2.5 μm thick and completely covered the pellet surface. Intimate contact between Li metal and LLZTO electrolyte could be realized after the Li₃BO₃ interfacial modification, which was confirmed by SEM analysis and wettability experiment. Benefiting from the significantly improved interfacial contact, the interfacial impedance was dramatically reduced from 1780 Ω·cm² of Li/LLZTO interface to 58 Ω·cm² of Li/LBO-LLZTO interface. The Li|LBO-LLZTO|Li symmetric cell could produce a low overpotential and work stably at the current density of 0.1 mA·cm^-2 for more than 700 h. By contrast, the Li|LLZTO|Li symmetric cell displayed high overpotential and was short circuited after 20 min of lithium plating/stripping at the current density of 0.05 mA·cm^-2. Our results show that Li₃BO₃ interfacial modification is an effective approach to improve the wettability and interfacial stability between Li metal and garnet electrolyte, which is a key to the successful use of solid-state battery.

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