Obtenção e estudo de óxidos de alta entropia para uso em baterias de íons sódio

Abstract

In this work, high-entropy oxides with layered structures were synthesized using a modified Pechini method, aiming to develop new materials for application in energy storage devices. The approach was based on combining multiple metal cations into a single crystalline matrix, exploring the effect of configurational entropy to stabilize complex phases, including metals incorporated into the crystal lattice that have not yet been reported in the literature. Four distinct materials were obtained, named: OHE-ExMn 700 °C (Na1,16[Mn0,304Ni0,11Co0,141 Fe0,115Mg0,112Nb0,104Li0,113]O2), OHE-1:1 900 °C (Na1,17[Mn0,49Fe0,36Mg0,112Nb0,072Li0,078]O2), OHE-2/3 700 °C (Na0,73[Mn0,52Fe0,38Nb0,01Li0,086]O2) e OHE-2/3 900 °C (Na0,72[Mn0,52Fe0,38 Nb0,016Li0,08]O2), and were characterized using structural, morphological, and electrochemical techniques in non-aqueous media. Analyses revealed that the materials exhibited a layered structure and, in some cases, phase segregation of niobium, leading to the formation of sodium niobate, particularly in samples with sodium deficiency. Despite this phase separation, the materials showed significant electrochemical performance. The specific capacities achieved were 83 mAh·g⁻¹, 46 mAh·g⁻¹, 97 mAh·g⁻¹, and 73 mAh·g⁻¹, respectively, for the aforementioned oxides, under a charge/discharge rate of 0.2C. The results indicate that the synthesized high-entropy oxides exhibit promising structural and electrochemical properties, except for the sample OAE-1:1 900 °C, whose maximum capacity was limited to 46 mAh·g⁻¹. The other oxides demonstrated high reversibility, elevated efficiency, and good capacity retention after 100 cycles at a 1C rate. However, all materials showed signs of degradation, probably associated with the formation of stacking faults induced by high mechanical stress during high-rate cycling. These findings suggest that the synthesized materials are strong candidates for application as electrode materials in rechargeable batteries, particularly in ion-insertion devices such as sodium-ion batteries.