A “Lithium-Free” Thin-Film Battery with an Unexpected Cathode Layer

Abstract

A metal/electrolyte/metal (M/E/M) device, with a lithium phosphorus oxynitride electrolyte layer sandwiched between a silver (Ag) thin film and a stainless steel (SS) substrate, was fabricated with a simple structural configuration of . Cyclic voltammetric (CV) and charge/discharge measurements showed that the device was activated as a rechargeable lithium battery upon initial charging up to (vs ). Electrochemical cycling between 4.0 and was demonstrated over 450 cycles at a current density of . By using CV analyses, X-ray photoelectron spectroscopy (XPS), and ac impedance spectroscopy, an electrochemical mechanism of this battery is proposed. During initial charging of the as-prepared device of at , the reduction of Li ion from takes place to form metallic lithium anode with in situ electroplating a lithium layer onto the SS substrate. Meanwhile the cathode current collector of metallic Ag was oxidized to ion at the interface of , and then the ions diffused into the electrolyte and displaced the moveable ions to create an unexpected cathode layer used as a cathode material. In this “lithium-free” thin-film battery, only lithium-ion electrolyte supplies lithium for creating both the Li anode and the Li-containing layer cathode during cycling. Both lithium anode and lithium-containing cathode films were absent prior to the initial charge, which greatly simplified the fabrication, packaging, and storage of all-solid-state, thin-film lithium batteries.