Evolution of the Interphase between Argyrodite-Based Solid Electrolytes and the Lithium Metal Anode─The Kinetics of Solid Electrolyte Interphase Growth

Abstract

Argyrodite-based solid electrolytes (SEs) are promising candidates for application in solid-state batteries (SSBs) due to their high ionic conductivity and mechanical malleability. However, they are reduced by lithium and form interphases when they are in contact with a lithium metal anode, which are needed to construct cells with high energy density. If the interphase is electronically insulating, a so-called solid electrolyte interphase (SEI) is formed that can protect the solid electrolyte from further degradation and grows only slowly. Careful evaluation of individual lithium metal anode|SE interface reactions and their growth kinetics is necessary to advance the concept of lithium metal batteries.Here, the interphase growth in symmetric Li|Li 6 PS 5 Cl|Li cells is studied quantitatively by impedance spectroscopy using a three-electrode cell setup. Unidirectional plating experiments show that the three-electrode cell is well suited to study the SEI evolution. Passivated and freshly prepared lithium foils are investigated, and the impedance evolution is studied to explore the influence of the lithium metal anode surface on SEI growth. The study reveals that an inherent passivation layer, present on most commercial lithium foils, influences the rate of SEI formation and causes high internal cell resistance. The lithium reservoir-free anode ("anode-free concept") is recommended to overcome the issues caused by chemically poorly defined lithium foil surfaces.

Interfacial dynamics of carbon interlayers in anode-free solid-state batteries

“…The high-frequency feature is attributed to the bulk SE impedance, which does not change significantly over the course of the experiment. 64,65 At lower frequencies, the Nyquist plot before cycling approaches a vertical line indicating blocking electrode behavior in the unlithiated carbon, which is essentially acting as a current collector with high electronic conductivity and negligible Li activity (Fig. 5b).…”

SEI growth on Lithium metal anodes in solid-state batteries quantified with coulometric titration time analysis

“…We like to add that—according to classical solid state reaction kinetics with diffusion control—SEI formation should not come to an end at a certain time. However, it appears that finite SEI growth can be observed in some cases 55 . The reasons are yet not clear, and further work in the fine tuning of the SEI is required.…”

Conductive carbon embedded beneath cathode active material for longevity of solid-state batteries

“…Argyrodite (Li 6 PS 5 X, X = Cl, Br) SEs possess both high ionic conductivity and relatively good interfacial compatibility against a lithium-metal anode compared with other sulfide SEs such as Li 10 GeP 2 S 12 and Li 3 PS 4 electrolytes. 15,16 However, in the composite cathode, both the cathode active material (CAM)/argyrodite SE and carbon/argyrodite SE interfaces are not thermodynamically stable. 10,17,18 Recent studies have demonstrated that inorganic coating layers such as LiNbO 3 (LNO), 19 Li 2 O–ZrO 2 (LZO), 20 and Li 1.175 Nb 0.645 Ti 0.4 O 3 (LNTO) 21 can suppress the degradation at the CAM/argyrodite SE interface.…”