High Capacity, Solid State Lithium Sulfur Battery with Ceramic Electrolytes

Abstract

Solid-state lithium-sulfur (Li-S) batteries with non-flammable, inorganic solid electrolyte can achieve a specific energy of 400 Wh/kg at low cost. The main technical challenges for this type of battery are i) developing a solid electrolyte that is highly conductive (>10 -2 S/cm) with a large electrochemical window, ii) creating a large interface area in the cathode, and iii) ensuring low interface resistance between the electrolyte and electrodes. In addition, the solid electrolyte should be made thin but capable of being manufactured on a large scale. New Li-S-Br-Si-Sn solid electrolytes have been prepared via ball-milling and heat treatment. The elemental composition and ball milling conditions (rpm, etc.) are optimized to get high ionic conductivity (>10 -2 S/cm). Electrochemical stability window and ionic conductivity of the solid electrolytes are determined. All solid-state Li-S cells are fabricated by coating solid electrolyte on the cathode and attaching lithium on the electrolyte surface. Cathode is prepared by coating a slurry made of nanoscale sulfur, electron conductor (e.g., graphene), solid electrolyte, and binder on aluminum foil. A number of solvents and binders are investigated to form a homogeneous slurry with minimal agglomeration of particles like sulfur to generate high electrochemical interface area and desirable 3-D transport network for electrons and lithium ions. The incorporation of binder in the solid electrolyte layer increases the electrochemical resistance of the layer. It is important to use a binder that offers a favorable trade off of lower resistance due to a thinner layer of solid electrolyte being possible and higher resistance due to the binder inhibiting transport of lithium ions. The composition, particle size, degree of compacting, thickness, and structure of cathode materials influence the transport of charge carrying species as well. The effect of binder on the resistance of solid electrolyte bulk and at the solid electrolyte-electrodes interfaces are characterized by AC impedance. Electrochemical performances of the solid-state Li-S cells will be presented. Some suggestions on developing solid electrolyte materials, manufacturing thin electrolyte film, designing the electrochemical interfaces, increasing sulfur loading in the cathode, and maintaining initial morphology of the cathode during the electrochemical processes will be discussed.