Effects of Interfacial Adhesion on Lithium Plating Location in Solid-State Batteries with Carbon Interlayers

Abstract

Carbon interlayers have been implemented in "anode-free" solid-state batteries to improve the uniformity and reversibility of lithium deposition by controlling the location of Li plating. However, there remains a lack of fundamental understanding of the detailed role of how these interlayers function during in situ Li formation. In this study, the relationships between the interfacial adhesion of the carbon interlayer to the solid electrolyte and the location of Li plating are investigated. By varying the lamination pressure used during manufacturing, the ability to systematically tune the resulting interfacial adhesion is demonstrated. Mechanical peel tests are performed, and a 4-fold increase in interfacial toughness is measured as the lamination pressure increases from 100 to 400 MPa. Post-mortem electron microscopy revealed that the location of Li plating with respect to the carbon interlayer transitions from the interface with the solid electrolyte to the current collector above a threshold interfacial toughness, which is consistent when the interlayer material is changed from amorphous to hard carbon. These findings highlight the role of electro-chemo-mechanical relationships in systematically controlling Li deposition in solid-state batteries when interlayers are present.

Keywords: adhesion; anode‐free; carbon interlayer; lithium metal anode; mechanical properties; solid‐state battery.

Figure 1

a) Schematic of the lamination procedure used to adhere the carbon interlayer onto the SE. b,c) Cross‐sectional plasma‐focused ion beam‐scanning electron microscopy images of the interface between the carbon interlayer and the SE using lamination pressures of (b) 100 and (c) 400 MPa. d,e) Schematic of the resulting interfacial morphology of the carbon interlayer after (d) low and (e) high lamination pressures.

Figure 2

a) Schematic of the peel‐test geometry, where Kapton tape was used to delaminate the carbon interlayer from an LPSCl solid electrolyte pellet. Top‐down optical microscopy images of the b) LPSCl pellet and c) Kapton tape after a peel test, when the amorphous carbon interlayer was laminated onto the SE at 300 MPa. d) Measured interfacial toughness values at various lamination pressures for amorphous carbon interlayers. The error bars represent independent measurements from n = 3 samples. The horizontal dashed arrow represents the measured interfacial toughness of the carbon interlayer and stainless‐steel current collector after the initial casting and drying processes.

Figure 3

Cross‐sectional PFIB‐SEM images after Li plating with a capacity of 2.0 mAh cm⁻² at a current density of 0.1 mA cm⁻² for amorphous carbon interlayers that were laminated onto the SE at a) 400 MPa, b) 100 MPa, and c) 5 MPa. The corresponding interfacial toughness values between the carbon and SE are also indicated at each lamination condition.

Figure 4

Schematic of the negative electrode region during charging to low and high capacities. a) Initial plating behavior for an interface with high toughness between the carbon and SE. Various elements in the energy balance are depicted, including the Li (ρ _Li+) and electronic (ρ _e‐) resistivities of the carbon interlayer, interfacial toughness between the CC and carbon (Γ _CC‐carbon), overpotentials at the interfaces between the carbon interlayer and the CC and SE (η _CC‐carbon and η _carbon‐SE), and stresses in the CC, carbon, and Li (σ _CC, σ _carbon, and σ _Li). b) As more capacity is passed, Li continues to deposit at the CC interface with the associated interfacial energies (γ _CC‐Li, γ _carbon‐Li, and γ _carbon‐SE). c) Initial plating behavior for an interface with low toughness between the carbon and SE, including additional elements that must be considered in the energy balance such as interfacial toughness between the carbon and SE (Γ _carbon‐SE) and stress in the SE (σ _SE). d) As more capacity is passed, Li continues to deposit at the SE interface with associated interfacial energy between the Li and SE (γ _Li‐SE).

Figure 5

a) Measured interfacial toughness at various lamination pressures for both amorphous and hard carbon interlayers. The error bars represent independent measurements from n = 3 samples. The solid data points are samples where delamination occurred between the carbon and SE, and the unfilled data points are samples where delamination occurred between the Kapton tape and carbon. b,c) Cross‐sectional PFIB‐SEM images after Li plating to a capacity of 2.0 mAh cm⁻² at a current density of 0.1 mA cm⁻² for hard carbon interlayers at a lamination pressure of (b) 200 and (c) 600 MPa.