Garnet Nb-Doped Li7La3Zr2O12 Ceramic Electrolyte and Its Composite Electrolyte for Solid-State Lithium Batteries

Abstract

Garnet Li7La3Zr2O12 (LLZO) is a promising candidate of solid-state electrolytes for advanced solid-state lithium batteries (SSLBs). In this work, the Nb-doped LLZO (Li6.5La3Zr1.5Nb0.5O12, Nb-LLZO) ceramic electrolyte is synthesized, and its mechanical properties are explored. An extremely small bending force can break Nb-LLZO ceramic sheets. Moreover, the improved composite membrane composed of as-prepared Nb-LLZO particles, lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) matrix is prepared through a modified tape-casting method. Nb-LLZO/PVDF-HFP/LiTFSI composite electrolyte membranes show excellent uniformity and high flexibility. The assembled Li|Nb-LLZO/PVDF-HFP/LiTFSI|LiFePO4 cell exhibits good battery performance. Notably, the cell delivers a high reversible discharge capacity (over 145 mAh g-1) in the first 20 cycles and the Coulombic efficiencies of the major cycling process approach 100% during 35 cycles. This work demonstrates that the Nb-LLZO/PVDF-HFP/LiTFSI composite electrolyte membranes are competent to be applied in SSLBs.