Li 7 La 3 Zr 2 O 12 Protonation as a Means to Generate Porous/Dense/Porous-Structured Electrolytes for All-Solid-State Lithium-Metal Batteries.

Ceramic Li 7 La 3 Zr 2 O 12 (LLZO) represents a promising candidate electrolyte for next-generation all-solid-state lithium-metal batteries. However, lithium-metal batteries are prone to dendrite formation upon fast charging. Porous/dense and porous/dense/porous LLZO structures were proposed as a solution to avoid or at least delay the formation of lithium-metal dendrites by increasing the electrode/electrolyte contact area and thus lowering the local current density at the interface. In this work, we show the feasibility of producing porous/dense/porous LLZO by a new and scalable method. The method consists of LLZO chemical deep protonation in a protic or acidic solvent, followed by thermal deprotonation at high temperatures to create the porous structure by water and lithium oxide elimination. We demonstrate that the produced structure extends the lifetime of Li/LLZO/Li symmetric cells by a factor of 8 compared to a flat LLZO at a current density of 0.1 mA/cm 2 and with a capacity of 1 mAh/cm 2 per half-cycle. We also show clear improvement of the Li/LLZO/LiFePO 4 full cell performance with a thermally deprotonated LLZO.