In Situ Visualization of Lithium Penetration through Solid Electrolyte and Dead Lithium Dynamics in Solid-State Lithium Metal Batteries

Abstract

The two biggest promises of solid-state lithium (Li) metal batteries (SSLMBs) are the suppression of Li dendrites by solid-state electrolyte (SSE) and the realization of a high-energy-density Li anode. However, LMBs have not met their expectations due to Li dendrite growth causing short-circuiting. In fact, Li dendrites grow even more easily in SSE than in liquid electrolyte, but the reason for this remains unclear. Here we report in situ transmission electron microscopy observations of Li dendrite penetration through SSE and “dead” Li formation dynamics in SSLMBs. We show direct evidence that large electrochemomechanical stress generates cracks in the SSE and drives Li through the SSE directly. We revealed that fresh Li nucleation sites emerged in every discharge cycle, creating new “dead” Li in the following charging cycle and becoming the dominant Coulombic efficiency decay mechanism in SSLMBs. These results indicate that engineering flaw size and reducing electronic conductivity in SSEs are essential to improve the performance of SSLMBs.

Nano-scale mechanism of crack nucleation/propagation and lithium penetration in solid electrolyte

“…It has been used to study the lithium dendrite growth process. [38][39][40] For example, lithium penetration through an Li 6.4 La 3 Zr 1.4 Ta 0.6 O 12 (LLZTO) SSE was revealed, 38 and a direct measurement of the growth force was conducted. 39,40 However, the quantitative details on the electrochemomechanics during the penetration process is still missing.…”

Towards understanding the nucleation and growth mechanism of Li dendrites on zinc oxide-coated nickel electrodes

“…These results are similar to those shown in a recent report by Sun et al , where the authors revealed that during Li deposition on the Li 6.4 La 3 Zr 1.4 Ta 0.6 O 12 (LLZTO) solid-state electrolyte, some dark particles broke off from the LLZTO bulk and were carried away by Li dendrite. 53…”

“…To depict more surface details of these dendrites, (LLZTO) solid-state electrolyte, some dark particles broke off from the LLZTO bulk and were carried away by Li dendrite. 53 To further understand the accumulation of zinc at the bottom of the Li nuclei, elemental mapping images were collected at high magnication on the top surface of the sample (Fig. 2d).…”

Vertically Heterostructured Solid Electrolytes for Lithium Metal Batteries

“…[28] Once commenced, the deposited Li accumulates and propagates along the flaws of the SSE as well as the grain boundaries, causing SSE fracture or a cell short circuit. [29] The process of Li accumulation in preexisting voids of the SSEs is identified into three stages: metal plating initiation, metal growth, and metal compression.…”