EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

Layered O3-LiCoO2 (analogue to NaFeO2 structure, crystallizing in the R-3m space group with ahex = 2.816 Å; chex = 14.05 Å) is one of the most widely used positive electrode materials in lithium ion batteries due to its high volumetric energy density which can be further improved by charging at high voltages. However, working at high potential (above 4.3 V vs. Li+/Li) causes a deterioration in cycling performance induced by structural instabilities, electrolyte oxidation and Co dissolution. Extensive studies have been devoted to increasing energy density by increasing the cutoff voltage. The substitution of cobalt with various metals is one of the classic methods, the choice of aluminum as dopant for example is based on several criteria: low cost and non-toxicity, a similar radius for Al3+ compared to Co3+ (0.535 Å vs. 0.545 Å) facilitates the replacement of the latter and maintains the structure leading to the complete solid solution LiCo1-yAlyO2. We will focus here on LiCo0.96Al0.04O2, synthesized by the solid route and characterized by 7Li, 27Al and 59Co Nuclear Magnetic Resonance (NMR) and synchrotron X-Ray Diffraction (XRD). In addition to the characterization of the mean structure by XRD, the NMR allows us to study the local environments of the different nuclei. In order to better understand the role of Al-doping on the mechanisms involved during cycling, several phases LixCo0.96Al0.04O2 were prepared by electrochemical deintercalation and studied by 7Li, 59Co, and 27Al NMR and by XRD. First, we will discuss the homogeneity of the doping, then the changes in the average, local and electronic structures of the material during cycling.