Chapter 6 - Secondary zinc-air batteries – mechanically rechargeable

Abstract

The mechanical recharge of zinc-air batteries is described in this chapter. These systems can be divided into mechanically rechargeable systems with cassettes and hydraulically rechargeable systems with either pumped electrolyte or pumped zinc slurry. A zinc slurry usually consists of zinc particles in a binder-stabilized alkaline electrolyte. A special feature of the hydraulic systems is that the power (size of the active electrode area) and the capacity of the battery (size of the electrolyte tank) can be scaled independently of each other. Hydraulically rechargeable zinc-air technologies can either be operated below or above the zincate solubility limit. These two operation modes show significant differences with respect to the maximum achievable specific capacity and specific energy of the battery system. Further characteristics of zinc slurry electrodes are described with focus on the energy density and the electrolyte conductivity. The chapter also contains a description of discharge characteristics which includes power densities and depth-of-discharge with passivation effects, as well as methods to determine the state of charge. In addition, an overview on the development history of mechanically rechargeable zinc-air batteries is given. This includes among others the work at Compagnie Générale d'Electricité (CGE) and Pinnacle Research Institute with slurry-based systems. The work with pumped electrolyte systems with a static bed of zinc articles at Lawrence Livermore National Laboratory and Metallic Power/Zincnyx/MGX Renewables are also described. Additionally the work with mechanically rechargeable cassettes at Electric Fuel Limited is reported. The chapter concludes with an assessment of the operational capability of mechanically and hydraulically rechargeable zinc-air batteries and a comparison with other metal-air batteries.