First-principles Calculation Of Two-dimensional Titanium Boride-based Ion-battery Anode Materials

With the excessive consumption of traditional fossil energy(coal,oil and natural gas,etc.),the global energy structure is rapidly shifting to clean and renewable energy.People are strongly aware of the importance of developing and using clean,environmentally friendly and renewable energy.Therefore,in the field of energy storage,some novel environmentally friendly,higher energy density rechargeable secondary batteries have received more and more favors.In particular,the rapid growth of the portable electronic equipment and new energy automobile industries has greatly stimulated people to find rechargeable secondary batteries with higher capacity,longer cycle life and safer.However,the function of the battery depends to a large extent on the performance of the electrode material,and the lack of high-performance electrode materials greatly limits the development of secondary batteries.Compared to the traditional experimental research method,the first-character principle calculation method can help people better design new high-performance electrode materials from atoms and electronic scale.Currently,commercial lithium-ion batteries limit the further development of lithium batteries due to their low capacity.Therefore,on the one hand,there is an urgent need to make breakthroughs in enhancing the electrode materials of lithium batteries.On the other hand,to develop new ion batteries.And considering that Na and Li have similar physical and chemical properties and similar storage mechanisms,mature technologies in lithium-ion batteries can be directly migrated to sodium-ion batteries.In addition,as the second lightest metal element after lithium,metallic sodium is richer resources,lower price,and the safety of sodium-ion batteries is better than that of lithium-ion batteries.Thus,sodium ion batteries have become one of the best candidates for energy storage devices.Further,to find a battery system with more abundant element reserves and higher energy density,new metal ion batteries(K,Mg,Ca,Al)have also attracted more and more attention,and are very There is hope to meet the requirements of future electronic equipment and many large-scale energy storage scenarios.As one of the key components of rechargeable metal ion batteries,negative electrode materials play a vital role in the performance of metal ion batteries.At present,the lack of high-performance anode materials have become the main obstacle to these metal ion batteries.Two-dimensional(2D)materials with large surface area can achieve rapid ion diffusion and provide more ion storage sites when the entire surface is exposed,are very suitable to act as electrode materials for rechargeable secondary battery.Among various 2D materials,the new two-dimensional transition metal boride compound,namely"MBene"has become a hot topic.MBene have many excellent properties like good conductivity,strong structural stability,high specific capacity,and has attracted wide attention.These advantages ensure the excellent performance of MBene as the electrode material of ion batteries,especially the anode electrode material.As an emerging two-dimensional material,although a lot of work has been done to study its basic properties and potential applications.The performance of the MBenes energy system has not been fully explored on the experimental and theoretical levels.To design a better electrode material for ion batteries,several key factors need to be considered,including high electron/ion conductivity,high stability,small molecular weight and enough ion occupied site,which can be theoretically attributed to more ion adsorption capacity and faster ion migration rate.Considering that the existing MBene structure still has a metal-rich form similar to MXene,the metal-rich composition will greatly reduce the absorption capacity of metal atoms,making it have a lower theoretical specific capacity,and greatly hinder biology compatibility and chemical stability.In this paper,taking the lightest transition metal(titanium)as a representative,the performance of B-rich MBenes as an anode material of LIBs and SIBs was explored.Combining the crystal structure prediction technology with the first-principles method,we conducted an extensive structure search on the stable Ti-B monolayer,and we found four stable Ti-B monolayers,namely TiB₃,TiB₄,TiB₅ and TiB₆,and studied its physical and chemical properties and battery performance.The results showed that:When TiB₃ as Li-ion battery and Na-ion battery anode material with a higher theoretical capacity,a lower migration barrier and a lower working voltage,which makes it an excellent anode material for ion battery.More importantly,a novel surface electrostatic potential analysis method found that the unique boron chains on the boron-rich TiB₃ surface provide a negative potential to enhance the adsorption capacity of the TiB₃,and can be used to quickly screen the best adsorption sites on the surface of the TiB₃.The migration properties of metal ions on the surface of TiB₆ monolayers as cathode materials for Na and Ca ion batteries were systematically studied.The results show that compared with the migration of single metal ions,multiple metal ions have a lower migration barrier on the surface of the structure,which is due to the synergistic effect between multiple metal ions,which promotes the faster migration of multiple ions on the surface of the TiB₆.Therefore,TiB₆ as the cathode material of Na ion battery and Ca ion battery not only has higher theoretical capacity and working voltage,but also has lower migration barrier and better kinetic migration properties.About TiB₄ and TiB₅,after a variety of metal ion tests,it is found that TiB₄ and TiB₅ are very suitable for use as cathode materials of Na ion battery,with more stable adsorption,higher capacity and better electronic properties.The results show that these four structures are not only dynamically stable and thermodynamically stable,but still have good metallic properties after adsorbing a large number of metal atoms,ensuring good electrical conductivity during battery cycling.By calculating the migration barriers of single ions and multiple ions on the surface of the structure,it is found that these structures have lower migration barriers and open circuit voltages,which can greatly increase the overall charging and discharging rate and ensure the safety of the entire charging and discharging process.The extremely high theoretical battery capacity also means that these four structures are very suitable for use in lithium-ion and sodium-ion batteries.These results can help us provide a useful strategy for the design of new two-dimensional transition metal materials.