Study On Synthesis And Electrochemical Performance Of Titanium-based Materials As Anode Material For Sodium Ion Batteries

Titanium-based materials have attracted interesting attention because of their advantages such as suitable discharge voltage platform,good stability and security,negligible volume expansion,lower prices and environmental friendliness and so on.Na₂Ti₃O₇ and TiO₂ have promising application prospects in fields such as photoelectric conversion,water splitting and sensor.However,the defects of Titanium-based materials,such as wide band gap and low conductivity,seriously restrict theirs development as new anode materials for sodium ion batteries.In most recent,black phosphorus has been attracting increasing attention in various fields which include secondary batteries,field-effect transistors,photocatalysis and photodetectors.However,it is easy to be oxidized in the air,which limits its practical application.In this paper,Na₂Ti₃O₇ and TiO2materials were taken as the main research objects,and their electrochemical properties were studied by combining them with black phosphorus.The specific research content of this paper is as follows:?1?Self-doping of Ti³⁺into Na₂Ti₃O₇/C powder material was synthesized by one-step sol-gel method and calcined in H2/Ar?5%?The self-doping of Ti³⁺into the Na₂Ti₃O₇/C?H-NTO?electrode material was prepared by sol-gel method,through a very simple post heat-treatment process,that is,annealing the Na₂Ti₃O₇ precursor at an argon atmosphere containing 5%H₂.Benefiting from this self-doped Ti³⁺with larger ionic radius and better electronic conductivity,the obtained Na₂Ti₃O₇demonstrates improved ion diffusion properties,and further improves the electrochemical properties.In addition,since Ti³⁺has one more electron than Ti⁴⁺,the electronic conductivity of Na₂Ti₃O₇ is also enhanced.In other words,self-doping Ti³⁺not only increases the ionic conductivity,but also improves the electronic conductivity.At the same time,combined with a carbon coating,this self-doped Na₂Ti₃O₇ electrode material exhibits superior electrochemical performance to that of non-doped electrode?N-NTO?.The average reversible capacities are 187 and 160.9 mA h g^-1 for H-NTO and N-NTO at 0.1C,respectively.Moreover,the discharge capacities(51.9 mA h g^-1)of H-NTO are still better than that of N-NTO(39.8 mA h g^-1)at 10C.Therefore,current work results indicate that proper doping might be a promising method to increase the electrochemical properties for SIBs,in particular the rate performance.At the same time,this fabrication strategy provides the possibility for large scale energy storage device practical?2?Carbon coated Na2Ti3O7?NTO/C?powder materials were synthesized by one-step sol-gel,then NTO/C-BP powder materials were firstly synthesized by high-energy ball milling NTO/C and BP nanoparticle.Although the preparation method of sol-gel is simple and easy scaled,the electrochemical performance of nano-structure materials are better than powder materials.Therefore,how to improve the reversible capacity of electrode materials should be considered.The NTO/C-BP were assembled by the high energy mechanical milling technique the mixtures of NTO/C and BP nanoparticle under argon?Ar?atmosphere.BP can form strong P-O-Ti bonds with bare NTO,and meanwhile form stable P-C bonds with the carbon coating layer on the surface of NTO.The as-prepared NTO/C-BP anode material can deliver very high specific capacity,(?225 mA h g^-1 after55 cycles at 20 mA g^-1)as well as long cycling performance(?143.3 mA h g^-1 after 400 cycles at 200 mA g^-1)and high coulombic efficiency?¹00%?.The present results show one of the competitive property of NTO/C-BP as a hopeful anode material for SIBs because of their advantages such as the commercialization and mass production.?3?The TiO2?P25?and sulfur was commercial raw material,progress was carried out with sulfur-doped black phosphorus-TiO₂ hybrids?TiO2-BP-S?working as a high specific capacity,antioxidant anode material for SIBs produced via a one-step high energy ball milling.Although this method of preparing NTO/C-BP composite material is simple,easy to mass produce,high specific capacity and stable in the air,its electrochemical performance as anode material is not satisfactory compared with that of hard carbon.In fact,the structure of Na₂Ti₃O₇ was slightly damaged after high-energy ball milling.Therefore,TiO₂ with more stable structure combined with sulfur is adopted in this chapter to fabricate TiO₂-BP-S anode material for SIBs.During the procedure,BP nanoparticles can form the stable P-S bonds with sulfur and strong P-Ti bonds with TiO₂;this double modification of BP enhances air stability and suppresses volume expansion.In addition,the sulfur and TiO₂ raw materials are commercially available.The as-obtained TiO₂-BP-S anode material can display superior specific capacity;after 100 cycles at a current density of 50 mA g^-1,a high reversible capacity of 490 mA h g^-1 was achieved.During the long cycling property measurement,and the discharge capacity can reach 290 mA h g^-1 at 500 mA g^-1 after 600 cycles.The excellent performance demonstrates that the TiO₂-BP-S hybrids are competitive electrode materials for SIBs.At the same time,the possibility of using black phosphorus in practice is further improved.