Preparation And Sodium Storage Properties Of Titanium-based Anode Composites

In recent years,with the aggravation of fossil energy pollution and national support policies,the new energy industry has achieved unprecedented rapid development.However,with the widespread use of lithium-ion batteries,lithium resources have gradually been unable to meet the application of large-scale energy storage devices in society.Therefore,finding suitable new energy batteries to replace lithium-ion batteries has become a research hotspot in the future energy field.Sodium and lithium are in the same group of the periodic table of elements,so the element properties are similar,and sodium resources are more abundant and evenly distributed than lithium resources,and have obvious cost advantages.Because the radius of sodium ion is larger than that of lithium ion,the traditional anode material graphite for lithium ion batteries cannot be applied to sodium ion batteries.Finding suitable anode materials is a step to speed up the commercialization of sodium ion batteries.At present,the most studied anode materials for sodium-ion batteries are mainly divided into carbon-based materials,alloy-based materials and titanium-based materials.Among them,TiO₂ anode materials are due to their low cost,stable cycle performance and extremely low charge-discharge process.Advantages such as volume expansion rate can be used as one of the most promising anode materials for Na-ion batteries.However,the low theoretical specific capacity(335 m Ah·g^-1)and poor electrical conductivity of TiO₂ limit its further development in anode materials.In this thesis,the electrochemical properties of TiO₂ are improved by nanometerization and atomic doping.The effects of different calcination temperatures on the structure,morphology and electrochemical properties of the materials were investigated.Firstly,dual-phase titanium dioxide heterojunctions（TiO₂（A/B））（anatase phase/bronze phase）were prepared by hydrothermal method and ion exchange method.XRD and Raman studies showed that the synthesized materials were composed of anatase phase and bronze phase.With the increase of temperature,the proportion of anatase phase also increases gradually.SEM and TEM studies show that the synthesized materials are all nano-needle structures with a particle size of 50-150 nm.The material exhibits the best electrochemical performance at 300°C,exhibiting a discharge specific capacity of 108 m Ah·g^-1 after 500cycles at a current density of 200 m A·g^-1,even after 2000 cycles at a high current density of2000 m A·g^-1,it still has a specific discharge capacity of 92.5 m Ah·g^-1.On the basis of the previous chapter,the surface of TiO₂（A/B）-300°C material was coated with P by gas phosphating method to prepare TiO₂（A/B）-300°C-P material.XRD,SEM and TEM studies showed that gas phosphorus The chemical method has no obvious effect on the structure of the material.XPS and EDS studies show that the TiO₂（A/B）-300°C-P material obviously contains the existence of P.The test results show that the electrochemical performance of TiO₂（A/B）-300°C-P material is further improved compared with that of TiO₂（A/B）-300°C material.After 200 cycles at a rate of 200 m A·g^-1,the discharge specific capacity of 144.2 m Ah·g^-1 was maintained,and after 1000 cycles at a high rate of 2000 m A·g-1,there was still a discharge specific capacity of 108.9 m Ah·g^-1,and the advantage of capacity growth is more obvious at low rate,indicating that the doping of P atoms can modulate the electronic structure of the material and enhance the surface activity,which significantly improves the sodium storage performance of the material.TiO₂ and hydrogen titanate（T0）were prepared by simple and safe alkaline boiling treatment and acid washing.XRD and Raman studies showed that anatase TiO₂ and hydrogen titanate coexisted at 300°C.SEM study showed that T0 Materials are all polymerized from chestnut-like pom-poms/microspheres.The material exhibits the best electrochemical performance at 300°C,and exhibits a specific discharge capacity of 157.8 m Ah·g^-1 after 200cycles at a current density of 100 m A·g^-1.After 1000 cycles at a high current density of 2000m A·g^-1,the discharge specific capacity of 104.1 m Ah·g^-1 remains.