Excellent Stability of a Lithium‐Ion‐Conducting Solid Electrolyte upon Reversible Li⁺/H⁺ Exchange in Aqueous Solutions

Abstract

Batteries with an aqueous catholyte and a Li metal anode have attracted interest owing to their exceptional energy density and high charge/discharge rate. The long‐term operation of such batteries requires that the solid electrolyte separator between the anode and aqueous solutions must be compatible with Li and stable over a wide pH range. Unfortunately, no such compound has yet been reported. In this study, an excellent stability in neutral and strongly basic solutions was observed when using the cubic Li7La3Zr2O12 garnet as a Li‐stable solid electrolyte. The material underwent a Li+/H+ exchange in aqueous solutions. Nevertheless, its structure remained unchanged even under a high exchange rate of 63.6 %. When treated with a 2 M LiOH solution, the Li+/H+ exchange was reversed without any structural change. These observations suggest that cubic Li7La3Zr2O12 is a promising candidate for the separator in aqueous lithium batteries.

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

“…8 indicates that some lithium still occupied the octahedral sites after the ion-exchange process. Since it was reported that ion exchange occurred in the tetragonal sites referred to the instability of the framework of garnet structure [21,32,33], the ion exchange levels in (a) area of Fig. 8 should be the safety ranges for the garnet structure, which also matched with experimental data of our study and other references [2,13,19,32,33].…”

“…The red rhombic symbols stood for the ion exchange data from Refs. [2,13,19,32,33]. The blue ones were from this work.…”

“…As was mentioned that the favorable protonated sites were the octahedral Li2 sites, the reversible ion exchange of LLNZO should preferentially occur in the octahedral sites, as Fig. 7b revealed [21,28,32].…”

“…Since it was reported that ion exchange occurred in the tetragonal sites referred to the instability of the framework of garnet structure [21,32,33], the ion exchange levels in (a) area of Fig. 8 should be the safety ranges for the garnet structure, which also matched with experimental data of our study and other references [2,13,19,32,33]. In conclusion, it is of significant importance to have better understanding of the relationship between the extent of ion exchange and the total lithium content with corresponding structural stability under the deduced schema, which shall shed light on the proper utilization of garnet electrolytes in aqueous solutions.…”

Oxide Electrolytes for Lithium Batteries

“…Thus increasing endeavors have been simulated on mass fabrication of NASICON thin films by techniques like tape‐casting . Recently, Ma et al observed that garnet‐like LLZO in neutral and strongly basic solutions can undergo a reversible Li + /H + exchange under a rate as high as 63.6% without any structural change . Such excellent behavior makes the material a very promising candidate for solid electrolyte separator in aqueous LABs.…”