Current-Dependent Lithium Metal Growth Modes in 'Anode-Free' Solid-State Batteries at the CuLLZO Interface

摘要

Controlling the lithium growth morphology in lithium reservoir-free cells(RFCs), so-called “anode-free” solid-state batteries, is of key interest to ensurestable battery operation. Despite several benefits of RFCs like improvedenergy density and easier fabrication, issues during the charging of the cellhinder the transition from lithium metal batteries with a lithium reservoirlayer to RFCs. In RFCs, the lithium metal anode is plated during the firstcharging step at the interface between a metal current collector and thesolid electrolyte, which is prone to highly heterogeneous growth instead ofthe desired homogeneous film-like growth. Herein, the lithium morphologyduring the first charging step in RFCs is explored as a function of currentdensity and current collector thickness. Using operando scanning electronmicroscopy, an increase in the lithium particle density is observed withincreasing current density at the Cu|Li_(6.25_Al_(0.25)La_3Zr_2O_(12) interface. Thisobservation is then applied to improve the area coverage of lithium by pulsedplating. It is also shown that thin current collectors (d = 100 nm) are unsuitedfor RFCs, as lithium whiskers penetrate them, resulting in highly heterogeneousinterfaces. This suggests the use of thicker metal layers (several μm) tomitigate whisker penetration and facilitate homogeneous lithium plating.