Portable or stationary batteries have become essential in everyday life. Therefore, the development of new storage technologies with lower cost and greater efficiency is relevant in many technological applications. Nowadays, the most used batteries in portable electronic devices are made with lithium-ion, but lithium is a scarce metal in nature and in less than a century the world demand will not be fully met. One of the most promising alternatives are sodium-ion batteries, as sodium is a more abundant metal than lithium and has some physical and chemical similarities, which makes the working mechanisms of sodium-ion and lithium-ion batteries analogous. One of the main challenges on the development of sodium-ion batteries is considering the anode material, because graphite anodes used in lithium-ion batteries do not have a good performance with sodium ions. The main phenomena that happen at the anode are: intercalation, conversion and alloys formation, which will vary according to the material. Most popular intercalation materials are those based on carbon or titanium oxides, however their main disadvantage is that they have a low initial capacity besides suffering from electrolyte decomposition and formation ofan insoluble layer on the anode surface. This affects its structure and thereforeits cycling performance. Conversion materials (sulfides, oxides and phosphides) or alloying materials (elements of groups 14 and 15 of periodic table) have an initial capacity quite high. However some difficulties are found conserning the high volume variation, which compromises the electrode's morphology and battery life. This change in volume has a relation with the sodium products formed at the anode, making the study of your physical and chemical properties essencial to find the best anode material. Thus, the main objective of this project is to carry out a theoretical study of structural, energetic and electronic properties of different sodium crystals that can be formed in anodes during the electrochemical cycle in order to provide an atomistic understanding of them and assist to select new materials. All calculations will be performed based on the density functional theory implemented by the Vienna Ab initio Simulation Package (VASP) code, which is widely used in the QTNano group.
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