Overcoming Anode Instability in Solid-State Batteries through Control of the Lithium Metal Microstructure

Enabling the lithium metal anode (LMA) in solid-state batteries (SSBs) is the key to developing high energy density battery technologies. However, maintaining a stable electrode-electrolyte interface presents a critical challenge to high cycling rate and prolonged cycle life. One such issue is the interfacial pore formation in LMA during stripping. To overcome this, either higher stack pressure or binary lithium alloy anodes are used. Herein, it is shown that fine-grained (d = 20 mu m) polycrystalline LMA can avoid pore formation by exploiting the microstructural dependence of the creep rates. In a symmetric cell set-up, i.e., Li vertical bar Li6.25Al0.25La3Zr2O12(LLZO)vertical bar Li, fine-grained LMA achieves > 11.0 mAh cm(-2) compared to approximate to 3.6 mAh cm(-2) for coarse-grained LMA (d = 295 mu m) at 0.1 mA cm(-2) and at moderate stress of 2.0 MPa. Smaller diffusion lengths (approximate to 20 mu m) and higher diffusivity pathway along dislocations (D-d approximate to 10(-7) cm(2) s(-1)), generated during cell fabrication, result in enhanced viscoplastic deformation in fine-grained polycrystalline LMA. The electrochemical performances corroborate well with estimated creep rates. Thus, microstructural control of LMA can significantly reduce the required stack pressure during stripping. These results are particularly relevant for anode-free SSBs wherein both the microstructure and the mechanical state of the lithium are critical parameters.

Automated summary

This study investigates the effect of microstructure on the electrode-electrolyte interface in solid-state batteries, and finds that fine-grained lithium metal anodes can prevent pore formation and improve battery performance. By controlling the microstructure of the lithium metal, the required stack pressure during stripping can be reduced. This is of great significance for anode-free solid-state batteries.