On the Importance of Li Metal Morphology on the Cycling of Lithium Metal Polymer Cells

Abstract

Lithium metal anodes have recently earned greater attention in the context of the development of lithium batteries with high power and energy density for use in both the automotive industry and in portable electronic devices. Lithium metal is indeed an ideal anode for lithium batteries due to its high specific capacity (3860 mAh g−1). However, the growth of dendrites under high charge currents restricts the use of lithium anode in rechargeable batteries until solid electrolytes that can mechanically hamper dendrite growth can be developed. Efforts are currently dedicated to solving these problems by focusing on either improving the shear modulus of the electrolyte, or on the modification of the lithium-electrolyte interface. The electrochemical stability of novel solid electrolytes towards lithium is commonly determined by galvanostatic cycling of Li-Li symmetric cells. However, important characteristics of the lithium foil used in most studies are seldom provided, hence making comparisons between materials trivial. This paper demonstrates the importance of a thorough electrode characterization for the cycling of symmetric cells. In this study, two types of lithium foils are used with polyethylene oxide-based (PEO-based) electrolyte. A detailed characterization of the morphological and physico-chemical properties of the metallic electrodes is first performed by PeakForce Tunneling Atomic force microscopy (PeakForce-TUNA™), and X-ray photoelectron spectroscopy (XPS), followed by an evaluation of the interface with PEO-based electrolyte. It is demonstrated that lithium foil morphology is a key factor in the electrochemical performance of the cell and a novel electrochemical pre-treatment program is presented. This type of pre-treatment, still unreported in the existing literature, results in a longer life for lithium symmetrical cells.