An Intermediate-Temperature High-Performance Na-Zncl2 Battery

The Na-beta-alumina battery (NBB) is one of the most promising energy storage technologies for integrating renewable energy resources into the grid. In the family of NBBs, Na-NiCl2, battery has been extensively studied during the past decade because it has a lower operating temperature, better safety, and good battery performance. One of the major issues with the Na-NiCl2, battery is material cost, which is primarily from Ni metal in the battery cathode. As an alternative, Zn is much cheaper than Ni, and replacing Ni with Zn in the cathode can significantly reduce the cost. In this work, we investigate the performance and reaction mechanism for a Na-ZnCl2 battery at 190 degrees C. Two-step reversible reactions are identified. During the first step of charging, NaCl reacts with Zn to produce a ribbon-type Na-2 ZnCl4 layer. This layer is formed at the NaCl-Zn interface rather than covering the surface of the Zn particles, which leads to an excellent cell rate capability. During the second step, the produced Na-2 ZnCl4 is gradually consumed to form ZnCl2 on the surface of Zn particles. The formed ZnCl2 covers most of the surface area of the Zn particles and shows a limited rate capability compared to that of the first step. We conclude that this limited performance of the second step is due to the passivation of Zn particles by ZnCl2, which blocks the electron pathway of the NaCl-Zn cathodes.