Abstract
The energy density of Li-metal batteries is governed by the composition of the materials, which affects their crystallographic and electronic structure, and hence their redox potential. Replacing sulfur with oxygen produces high-potential electrodes such as V2O5and even V6O13, whose electrochemical performance with respect to Li+ has been clarified. Although these oxides can be used in Li-metal batteries with liquid electrolyte, for safety reasons linked to dendrites, such oxides have enabled the development of Li-metal polymer technology, the industrialization of which has been mentioned. Li-ion technology, the advent of which was also mentioned, is also designed to overcome dendrite problems. Its realization requires the replacement of the Li electrode by carbon and, consequently, the use of a positive electrode compound, serving not only as a reservoir of Li, but also presenting a high redox potential to compensate for the penalty associated with the replacement of Li by carbon. LiCo(Ni)O2 phases, long studied for their magnetic properties, were identified as excellent electrode materials by J.B. Goodenough. Due to its instability at high potentials, the LiNiO2 phase was neglected in favor of LiCoO2, which was the basis of the first rechargeable batteries. Over the years, this phase has been the subject of rich substitution chemistry, leading to today's LiNi1-x-yCoxAlyO2 (NCA) and LiNi1-x-yMnxAlyO2 (NMC) materials. The science behind this substitution chemistry, based on considerations of size, oxidation state, electronegativity and crystal field, has been extensively detailed and explained.
