Design of Porous Solid Electrolytes for Rechargeable Metal Batteries

Abstract

Recently there has been interest in porous lithium metal electrodes, which have demonstrated improvements in cycle life and charge-rate capability compared to planar lithium metal for rechargeable batteries. Here, the porous electrode consists of a rigid porous solid electrolyte with void space in the discharged state. During charge, metal plates onto the surface of the solid electrolyte, filling the pores. The rigid electrolyte's shape remains fixed. Here, we present an electrochemical model for a cell with a porous anolyte based on porous-electrode theory, and apply the model to optimize the design of the porous anolyte for energy density and mitigation of dendrites. For example, because the electronic conductivity of lithium metal is over 7 orders of magnitude higher than the ionic conductivity of present state-of-the-art solid electrolytes, electronically conductive agents are not necessary. Furthermore, if the charge-transfer resistance of the porous electrode is too low, the reaction rate can be very high next to the separator, which can have deleterious consequences for cycle life and safety. We evaluate design options for avoiding the build up of stress next to the separator.