Blocking Lithium Dendrite Growth in Solid-State Batteries with an Ultrathin Amorphous Li-La-Zr-O Solid Electrolyte

Abstract

Lithium metal dendrites have become a roadblock in the realization of next-generation solid-state batteries with lithium metal as high-capacity anode. The presence of surface and bulk inhomogeneities with non-negligible electronic conductivity in crystalline electrolytes such as the lithium garnet Li7La3Zr2O12 (LLZO) facilitates the growth of lithium filaments, posing a critical safety risk. Here we explore the amorphous phase of LLZO (aLLZO) as a lithium dendrite shield owing to its grain-boundary-free microstructure, stability against metallic lithium, and high electronic insulation. We demonstrate that by tuning the lithium stoichiometry in sputtered aLLZO films, the ionic conductivity can be increased up to 10-7 S cm-1 while retaining an ultralow electronic conductivity of 10-14 S cm-1. In Li/aLLZO/Li symmetric cells, plating-stripping results in no degradation of the films and current densities up to 3.2 mA cm-2 can be applied with no signs of lithium penetration. The defect-free and conformal nature of the films enables microbatteries with an electrolyte thickness as low as 70 nm, which withstand charge-discharge at 0.2 mA cm-2 for over 500 cycles. Finally, we demonstrate that the application of aLLZO as a coating on crystalline LLZO lowers the interface resistance and significantly impedes the formation of lithium dendrites, increasing the critical current density of a symmetric cell up to 1.3 mA cm-2 at room temperature and without external pressure. The effectiveness of the amorphous Li-La-Zr-O as lithium dendrite blocking layer can accelerate the development of more powerful and safer solid-state batteries.

A Deeper Understanding of Metal Nucleation and Growth in Rechargeable Metal Batteries Through Theory and Experiment

“…[16,104] However, there are other factors such as internal pressure exerted by a solid-state electrolyte, that should be considered in Li and Na growth investigations. [105][106] Solid-state electrolytes appear to propagate dendrites differently to liquid electrolytes, particularly through grain boundaries. [107][108] It is important to understand how solidstate electrolytes should be considered in comparison to liquid electrolytes, which many of the previous models and theories are based on.…”

In situ and operando characterisation of Li metal – Solid electrolyte interfaces

“…[77] The large stresses from the plating process lead to further growth of the crack network well ahead of the plating, with the final portion of the network only around 20% full of lithium. [80] The observation of total mechanical breakdown of widely used electrolytes has driven experimental work including the development of sintering additives [83], single-crystal electrolytes [84], and blocking layers [85] all enabling an increase in the critical current density of solid-state cells. Looking forward, there's an opportunity to conduct system-atic characterisation experiments around the best-performing modified solid electrolytes, to accelerate their improvement.…”

Chemomechanics: friend or foe of the "AND problem" of solid-state batteries?

“…The confinement of plated Li at this interface is an indication of the dendrite suppression by LiPON solid electrolyte. Along a similar theme, amorphous LLZO has shown promise over crystalline LLZO for stable cycling [130]. However, high electronic conductivity of other solid electrolytes in comparison to LiPON is also being considered as a key reason for dendrite growth [89].…”