A Model of the Structure of the Positive Lead‐Acid Battery Active Mass

Abstract

A general model for the organization of the structure of the positive active mass is proposed based on SEM observations of samples, obtained from PAM and pastes with different phase compositions and crystal morphology. The structure is built up of two levels: a first‐level microstructure, which consists of small crystals with the form of grains, prisms, plates, and needles organized in porous agglomerate, and a second‐level macrostructure. The individual agglomerates (with a screw‐like, spherical, prismatic or rock‐like shape) are linked in a macroporous skeleton, which supports mechanically the active material, conducts the electric current, and serves as memory, where the conditions for the preparation of the paste, the curing, and the formation of the active material are coded. For convenience, two limiting structures are designated: (i) the “agglomerate type,” when the agglomerate structure determines the properties and the cycle life of the plate; and (ii) the crystalline type,” when the microstructure determines the energy performance and the stability of the plate. The “agglomerate‐type” structure is obtained from low sulfatized and dense pastes. During cycling, some irreversible processes occur, whereby the “agglomerate” structure is transformed into the “crystalline‐type” structure, which in turn is dispersed to individual crystallites. This leads to softening and shedding of the active material and finally to cell failure. The proposed general model reveals the relationships between the performance of the positive plate and the technology of its production.