Study On The Preparation And Electrochemical Performance Of Anode Materials For Lithium/sodium Ion Batteries

Due to the advantages of high energy density,long cycle life and good safety performance,lithium ion batteries are widely used in electronic products and electric vehicles.However,commercial lithium-ion batteries have the disadvantages of fixed shape,poor scalability and difficulty in miniaturization,so they cannot meet the growing energy storage needs of new electronic devices that are flexible and miniaturized.In addition,the inadequate lithium content and uneven distribution in the earth's crust make the cost of lithium-ion batteries increase sharply,which will greatly limit the application of lithium-ion batteries in large-scale energy storage fields such as grid energy storage.Therefore,there is an urgent need to develop lithium ion batteries for flexible and miniaturized electronic devices with good electrochemical performance,and to look for inexpensive rechargeable batteries that can replace lithium ion batteries for large-scale energy storage.Compared with traditional electrode materials,the self-supporting thin-film electrode material is directly and firmly grown on the current collector,which is not easy to separate from the current collector when bent,so it can improve the shortcomings of the traditional coating method that is difficult to prepare a flexible lithium ion battery.In addition,the thin-film lithium-ion batteries prepared from the self-supporting electrode material not only have high energy density and reliable safety,but also can be designed into any shape according to requirements.Thanks to the above advantages,thin-film lithium-ion batteries are more suitable for energy storage requirements that require flexibility and miniaturization.On the other hand,compared with lithium,sodium has more abundant reserves in the earth's crust.Low cost and similar physical and chemical properties make it more suitable for energy storage devices such as grid energy storage that have higher requirements for energy density and cost control.In recent years,research on sodium ion batteries has developed rapidly.Among them,carbon-based materials are the most widely studied anode materials for sodium ion batteries due to their low cost,stable structure and controllable morphology.The introduction of heteroatoms in carbon materials can effectively control the electronic structure and physical and chemical properties of carbon materials,which is an effective strategy to improve the energy storage performance of carbon materials.In order to meet the needs of flexible and miniaturized lithium ion batteries,this thesis prepared a self-supporting amorphous SnO₂/TiO₂ nanocomposite films using pulse laser deposition system.The prepared nanocomposite films showed excellent electrochemical performance as anode material for conventional and quasi-solid film lithium ion batteries.In order to develop anode electrode material for sodium ion batteries with excellent electrochemical performance,safety and environmental protection,we prepared the amorphous nanoporous carbon material co-doped with Fe and N by calcining the Fe-ZIF-8 precursor at high temperature,and explored its electrochemical performance as anode material.The specific work content mainly includes the following two parts:1.Preparation of self-supporting amorphous SnO₂/TiO₂ nanocomposite films electrode material and study on its electrochemical properties.At room temperature,SnO₂/TiO₂ nanocomposite films were prepared by alternately depositing 60 nm SnO₂ and10 nm TiO₂ using pulsed laser deposition system.The prepared nanocomposite film as anode material for lithium ion batteries exhibits excellent electrochemical performance.It not only has a specific capacity of 175?A h cm^-2 after 200 cycles with a current density of 13.8?A cm^-2,but also exhibits excellent rate performance(specific capacity of 111?A h cm^-2 when the current density is 276?A cm^-2).In addition,the prepared SnO₂/TiO₂ nanocomposite films also showed excellent electrochemical performance in quasi-solid films lithium-ion batteries(the specific capacity was 136?A h cm^-22 when the current density is 13.8?A cm^-2).The excellent electrochemical performance is attributed to the special structure of the SnO₂/TiO₂ nanocomposite films.The amorphous structure can buffer the stress changes.The alternately deposited TiO₂ layer can limit the volume expansion of the SnO₂ layer.More importantly,the tightly packed thin film structure can avoid the aggregation of SnO₂ layers.The multiple synergistic effects of these characteristics make the amorphous SnO₂/TiO₂ nanocomposite films as a lithium ion anode material with excellent electrochemical performance.2.Preparation of Fe,N co-doped amorphous porous carbon materials and their electrochemical properties.By calcining the Fe-ZIF-8 precursor at high temperature,an amorphous carbon material?Fe-N/C?co-doped with Fe and N was prepared,and the prepared Fe-N/C retained the morphology and porous structure of ZIF-8 precursor.By changing the calcination time,amorphous carbon materials Fe-N/C-1 and Fe-N/C-3 with different calcination times were prepared.For comparison,the N/C-3 without doped Fe was prepared.Fe-N/C-1,Fe-N/C-3,and N/C-3 were applied to lithium-ion batteries and sodium-ion batteries.The test results show that the carbon material doped with Fe and has a short calcination time has the best electrochemical performance.In the test of lithium ion batteries,Fe-N/C-1 has a specific capacity of 915.7 mA h g^-1 after 500 cycles at a current density of 500 m A g^-1.In the test of sodium ion battery,the specific capacity of Fe-N/C-1after 500 cycles at a current density of 500 mA g^-1 was 249.7 mA h g^-1.The excellent electrochemical performance is attributed to the introduction of heteroatoms Fe and N to provide a large number of active sites;the amorphous structure buffers the stress changes;the carbon material derived from ZIF-8 retains the porous structure and large specific surface area,which conducive to improving electrochemical performance.The multiple synergistic effects of these characteristics make the amorphous porous carbon materials co-doped with Fe and N exhibit excellent electrochemical performance when used as anode materials for lithium ion batteries and sodium ion batteries.