Fabrication And Lithium/Sodium Storage Properties Of Carbon-Based Composites

The extensive use of fossil energy has resulted in the increasing shortage of resources and the increasingly serious environmental pollution problem.The research and development of renewable energy has become one of the important issues that cannot be avoided in today’s world.Secondary batteries,especially lithium-ion batteries,have been widely used in portable electronic devices and new energy vehicles due to their excellent performance and environmental protection.In addition,sodium ion battery is considered to be one of the secondary batteries with broad application prospects because of its similar working principle with lithium ion battery and higher reserve of sodium than lithium.The secondary battery is mainly composed of electrode materials（positive electrode,negative electrode）,electrolyte,etc.Electrode material is the core component of the secondary battery,and its performance determines the performance of the battery.The research of electrode materials focuses on high performance and high stability,which are also the main indicators to evaluate the performance of lithium/sodium ion batteries.Although the researchers have developed a variety of lithium/sodium ion battery electrode materials,but the reported study also need to further improve and solve the below problems:（1）improve the conductivity of the electrode materials,（2）increase the specific surface area of the electrode materials,（3）to obtain electrode materials with good uniformity and repeatability,（4）the implementation of the preparation method of quantitative control elements.At present,the synthesis and regulation methods for preparing electrode materials are of low universality and difficult to be popularized and industrialized.Therefore,it is of great significance to explore the carbon-based composites with simple preparation methods,easy to achieve yield preparation,excellent electrical conductivity and adjustable composition elements.In this paper,aerosol spray and freeze-drying assisted preparation methods were used to obtain carbon based electrode materials of lithium/sodium ion battery by soft template method,and the influence of the morphology and structure of the composite electrode materials was discussed through related electrochemical tests and analysis.Specific work includes the following aspects:（1）Using PVP as carbon source,poreforming agent and surfactant,a series of Li₃V₂（PO₄）₃/C composites were prepared by aerosol spray assisted method and segmented heat treatment process.This preparation method has the advantages of high yield,good repeatability,easy industrial mass production and adjustable carbon content.The sample with optimized carbon content has a proper amount of carbon layer and vesicular hollow mesoporous structure.The electrode material is prepared at the voltage range of 3.0-4.8 V and different current densities of 100 m A g^-1,200 m A g^-1 and 400 m A g^-1.The initial discharge capacities are 207.6 m Ah g^-1,204.1 m Ah g^-1and 180.9 m Ah g^-1,respectively.In addition,the sample also has good cycle stability and rate performance.（2）Using egg white as a single solvent,carbon source and soft template,the three-dimensional mesoporous Na₃V₂（PO₄）₃@NC electrode material of SIBs was prepared by freeze-drying method.When the current density reaches 60 m A g^-1,the specific discharge capacity of the material is 117.1 m Ah g^-1,which is very close to the theoretical capacity of 118 m Ah g^-1.Even at 600 and 2400 m A g^-1,after 1000 cycles,the discharge specific capacity of the sample is still as high as 103.2 m Ah g^-1（capacity retention rate 95.8%）and 93.9 m Ah g^-1（capacity retention rate 93.4%）.The sample has good electrochemical properties.（3）By means of freeze-drying method,egg white was used as carbon source and solvent,fluoride ion was introduced into Na₃V₂（PO₄）₃ electrode material to obtain porous and loose Na VPO₄F@NC composite sodium ion battery cathode material with uniform structure and large specific surface area.The first discharge capacity of the composite reaches 126.4 m Ah g^-1 at the current density of 0.2C.When the current density is increased to 20C,the capacity is 94 m Ah g^-1 and the capacity retention rate is 88.3%after 2000 cycles.（4）By freeze-drying method,using gum Arabic as carbon source and urea as nitrogen source,nickel-nitrogen co-doped Ni@NC carbon composite material was prepared.At the current density of 0.2 A g^-1,the first charge specific capacity of the lithium ion battery assembled with carbon material reaches 606.7 m Ah g^-1.After 100cycles,the specific capacity is 400.8 m Ah g^-1,and the capacity retention rate is 66.1%.When the current density is 50 m A g^-1,the initial charging capacity is 190.2 m Ah g^-1.After 400 cycles,the specific charging capacity of the material is 101.8 m Ah g^-1,and the capacity retention rate is 89.4%.The results show that the introduction of N element can significantly increase the doping amount of nickel in carbon materials and optimize the electrochemical properties of carbon cathode.