Planar Sodium‐Nickel Chloride Batteries with High Areal Capacity for Sustainable Energy Storage

Abstract

Abstract High‐temperature sodium‐nickel chloride (Na‐NiCl 2 ) batteries are a promising solution for stationary energy storage, but the complex tubular geometry of the solid electrolyte represents a challenge for manufacturing. A planar electrolyte and cell design is more compatible with automated mass production. However, the planar cell design also faces a series of challenges, such as the management of molten phases during cycling. As a result, cycling of planar high‐temperature cells until now focused on moderate areal capacities and current densities. In this work, planar cells capable of integrating cost‐efficient nickel/iron electrodes at a substantially enhanced areal capacity of 150 mAh cm −2 is presented. Due to a low cell resistance during operation at 300 °C, these cells deliver a specific discharge energy of 300 Wh kg −1 at high discharge current densities of 80 mA cm −2 (C/2, 10%–100% state‐of‐charge). This results represent the first demonstration of planar Na‐NiCl 2 cells at a commercially relevant combination of areal capacity, cycling rate, and energy efficiency. It is further identified the secondary molten NaAlCl 4 electrolyte to contribute to the cell capacity during cycling. Mitigating electrochemical decomposition of NaAlCl 4 will play an important role in further enhancing both cycling rates and cycle life of high temperature Na‐NiCl 2 batteries.