Reversible ion exchange and structural stability of garnet-type Nb-doped Li7La3Zr2O12 in water for applications in lithium batteries

Abstract H + /Li + ion exchange and structural stability of the high ionic conductivity Nb-doped Zr-garnet Li 6.75 La 3 Nb 0.25 Zr 1.75 O 12 (LLNZO) are investigated in this study. Relationships between ion exchange and Li-population per unit cell, which are necessary to establish the practical framework of garnet electrolytes, are deduced for garnet oxides within ion-exchange process. H + /Li + ion exchange of cubic LLNZO powder is performed continuously in distilled water and products with various exchange levels are obtained via this simple method. FTIR spectra show the evolution of H–O bonding through the ion-exchange process. A maximum of 74.8% exchange of Li + by H + was found, consistent with a preferential replacement of octahedrally coordinated Li. The cubic garnet phase is maintained throughout all levels of proton exchange observed. The formation of garnet-type solid solution of Li 6.75−x H x La 3 Nb 0.25 Zr 1.75 O 12 is indicated by well-resolved lattice fringes as well as the linear evolution of crystal lattice parameters with the ion exchange level. The reverse ion exchange of H + by Li + is successfully achieved in Li + containing aqueous solutions, demonstrating its high structural stability and good compatibility for promising applications in lithium batteries.