Revealing the dynamic evolution of Li filaments within solid electrolytes by operando small-angle neutron scattering

Abstract

Lithium dendrite (filaments) propagation in solid electrolytes (SEs) leading to short circuits is one of the biggest obstacles to the application of all-solid-state lithium metal batteries. Due to the lack of operando techniques that can provide high resolution, the insufficient knowledge of the lithium dendrite growth inside SEs makes it difficult to suppress the dendrite growth. To reveal the mechanism of the Li filament growth in SEs, we achieved real-time monitoring of the nanoscale Li filament growth by operando small-angle neutron scattering (SANS) in representative Li6.5La3Zr1.5Nb0.5O12 SEs. On continuous plating, the Li filament growth is not simply an accumulation of Li, but there is a dynamic evolution due to the competition between the Li filament growth and self-healing. With the aid of simulations and experiments, this dynamic competition was demonstrated to be highly dependent on temperature variation. The enhanced self-healing ability of Li at elevated temperatures plays a positive role in suppressing the Li filament growth. The heat therapy improved the cell's cycle life, which provided insight into suppressing the Li filament growth. Operando SANS with high Li sensitivity provides a platform for investigating Li filaments in SEs.

Direct In Situ Determination of the Surface Area and Structure of Deposited Metallic Lithium within Lithium Metal Batteries Using Ultra Small and Small Angle Neutron Scattering

“…USANS and SANS data for lithium in the cell before and after 2 cycles at 20 mA cm −2 are shown in Figure 2D. Subtraction of inactive components does not substantially change the scattering after cycling (Figure S5B, Supporting Information) as a result of the order of magnitude increase of scattering from lithium, this being a larger increase than previously reported using in situ SANS for lithium metal cells, [ 13b,14 ] possibly as a result of the relatively higher current density. The transmission of neutrons through the cell in the USANS region decreased substantially after cycling (Table S1, Supporting Information) as a result of this increased coherent scattering, while attenuation from absorption and incoherent processes remained constant, as expected.…”

“…S A = S i active Li surface in the beam = S i beam area × number of foils = S V × foil thickness (14)…”

“…[13] Increased SANS intensity from a symmetrical LMB post-cycling confirmed the sensitivity of SANS to changes at a lithium electrode, although morphological details were not derived, [13b] and SANS profile changes from an LMB on cycling revealed the formation of lithium features 1-10 nm, although a quantitative description of the scattering from lithium was not able to be made. [14] Here, we build on these previous concepts to demonstrate that in situ SANS and USANS can provide a quantitative description of the morphology and growth process of metallic lithium deposited within a symmetrical LMB containing liquid electrolyte. We first characterize the signal from individual components to guide the construction of the LMB and our understanding of the scattered intensity, which we subsequently evaluate using simple models to quantitatively describe the in situ SANS and USANS data.…”

“…[ 13 ] Increased SANS intensity from a symmetrical LMB post‐cycling confirmed the sensitivity of SANS to changes at a lithium electrode, although morphological details were not derived, [ 13b ] and SANS profile changes from an LMB on cycling revealed the formation of lithium features 1–10 nm, although a quantitative description of the scattering from lithium was not able to be made. [ 14 ]…”

Recent advances in in situ and operando characterization techniques for Li7La3Zr2O12-based solid-state lithium batteries

“…The growth of Li filaments in LLZO was monitored in real-time on a nanoscale with operando SANS technique. 223 Growth of Li filaments was not seen to occur just by accumulation but relies on competition between the growth rate and self-healing rate. Increasing the temperature can strengthen self-healing ability, which positively suppresses Li filament growth.…”