Miguel Rodríguez-Gómez

We have carried-out in-operando neutron diffraction analyses of the charge/discharge processes inside the positive active mass (PAM) of industrial lead batteries, where the main problems of charge/discharge efficiency limitations are originated, focusing on the spatial distribution of the different crystallographic phases as a function of the kinetics of the transformations. The experiments were carried out in the VULCAN instrument at the Spallation Neutron Source of the Oak Ridge National Laboratory (Tennessee, USA), where volume gauge experiments were performed comparing fresh and cycled cells. VULCAN is a time-of-flight diffractometer which provides fast volumetric mapping and the possibility to study kinetic behaviours. Both static and dynamic mapping experiments were performed during charge-discharge cycles. More than 8500 diffractograms were obtained and subsequently analysed by using GSAS software. The main object of analysis are the composition maps, but information on lattice parameters, crystallinity, stoichiometry, hydration, grain size, preferred orientation, etc. has also been obtained and studied. All these parameters have been mapped as a function of charge state, time, voxel location, etc. We have observed stratification processes and local inhomogeneities, as well as differences in the behaviour of fresh and cycled cells. These experiments are part of a project to determine how, where and when the formation and charge/discharge electrochemical processes occur in the positive electrode. In this way we will be able to design new strategies to improve the energy efficiency and the partial State of Charge (PSoC) cycle life of batteries for the forthcoming energy storage systems (ESS).