Synthesis And Electrochemical Performance Of Vanadium Based Nanomaterials As Cathodes For Lithium Ion Batteries

Due to its small volume,lightweight,high energy density and high cycle stability,lithium ion batteries?LIBs?is considered to be the key to promote the rise of portable electronic equipment industry and the electric vehicle industry.However,the cathode material already become a bottleneck,which restrict the development and application of lithium ion batteries because of its low discharge specific capacity and poor cycle stability.For the researches of LIBs fields,vanadium oxide and its derivatives with layered structure have always attracted their lot of attention due to theirs larger energy density,lower prices and a variety of valence state.In this paper,we will summary and analysis the research progress and development status of battery cathode materials in details,taking vanadium oxide cathode material of lithium ion battery as the research objects,preparing vanadium based oxide cathode materials of lithium ion battery through different method,such as controlling the morphology,ion doping,grapheme composite or coating,et al.By these method,we expect to achieve the purpose of improving the electrochemical properties of vanadium based oxide cathode materials.The article can be divided into the following sections:synthesis of VO₂?B?nanobelts by hydrothermal method,then enhance its electrochemical performance by ion doping and grapheme composite;synthesis hierarchical V₂O₅ nanobelts with the nanobelt bands as the precursor followed with heat treatment for the first time;synthesis the NH₄V₄O₁₀ nanotextile with good electrochemical performance under the conditions of hydrothermal conditions;synthesis core-shell structure V₂O₅microspheres by using solvent thermal method,and enhance its electrochemical properties by self-doping V⁴⁺and graphene coating.Layered structure VO₂?B?with preferred orientation was prepared by hydrothermal method with acrylic acid as reducing agent.The electrochemical properties of VO₂?B?nanobelts cathode materials was enhanced to a certain extent by doping cation(Al³⁺),the initial specific capacity of 172 mAh g^-1.After 50 cycles remains in 98 mAh g^-1,which still cannot meet the requirements of high performance LIBs.Graphene composites can greatly reduce the impedance between the electrolyte and the electrode interface,and improve the efficiency of the charge transfer of electrode materials.Grapheme-VO₂?B?compound material was prepared by using simultaneous reduction method in hydrothermal condition.Compared with VO₂?B?and Al-VO₂?B?cathode materials,the electrochemical properties of the composite were greatly improved.The initial discharge specific capacity of grapheme-VO₂?B?compound is 307.1 mAh g^-1,and after 50 cycles,the discharge capacity still maintain at 240.7 mAh g^-1,which was 78.4%of the initial discharge specific capacity.Lithium storage performance are increased by 117.8%and 78.6%more than VO₂?B?and Al-VO₂?B?cathode materials,respectively;and the discharge capacity retention after 50cycles was also higher than that of VO₂?B?and Al-VO₂?B?by 41.1%and 57%,respectively.Obviously,grapheme composite has a great advantage in improving the electrochemical performance of the cathode material.Hierarchical V₂O₅ nanobelts and V₂O₅ block were prepared by hydrothermal method followed with heat treatment.It takes precursor as self-template to prepare hierarchical V₂O₅ nanobelts.The hierarchical V₂O₅ nanobelts inherit the overall morphology characteristics of the nanobelt precursor,and the secondary structure is composed of V₂O₅nanosheets and microcracks.By using XRD,SEM,TEM,XPS,BET and other technical means,the morphology characteristics,valence state and formation mechanism of hierarchical V₂O₅ nanobelts were analyzed.Compared with bulk V₂O₅ cathode materials,the hierarchical structure of V₂O₅ demonstrate obvious advantages.The initial specific capacity is 288 mAh g^-1 in the voltage of 2.0-4.0 V,showing good lithium storage performance.After 50 cycles,the specific capacity can still be maintained at 246 mAh g^-1,the capacity retention rate reaches 85.4%of the initial capacity,showing excellent cycle stability.NH₄V₄O₁₀ nanotextile was successfully prepared by hydrothermal method by controlling the crystal structure and morphology of the product.The nanotextile is weaved by ultrathin?³ nm?and long?100?m?NH₄V₄O₁₀ nanobelts with crisscross weave,and a large number of interconnected pores speared between these nanobelts in the textile.Compared with the NH₄V₄O₁₀ nanobelts,the 3D structure nanotextile has a better performance in the electrochemical reaction and the cycle stability.The initial discharge specific capacity is 328.9 mAh g^-1,which is much higher than that of NH₄V₄O₁₀ nanobelts(209.7 mAh g^-1),showing a more excellent performance of the lithium storage capacity.Even at current density of 1000 mA g^-1,the discharge capacity of NH₄V₄O₁₀ nanotextile still maintain 86.8%of initial capacity after 550 cycle,which is much higher than that of NH₄V₄O₁₀ nanobelts,showing excellent cycle stability.V⁴⁺-V₂O₅@rGO cathode material was successful prepared by the following steps:firstly,V₂O₅ core-shell microspheres were prepared by solvent thermal method,then low valence vanadium(V⁴⁺)was introduced through external reducing agent while the microspheres are coated by rGO.Compared with the V₂O₅ core-shell microspheres,V⁴⁺-V₂O₅@rGO microspheres electrode materials show a better electrochemical performance in more stringent discharge conditions?window voltage is 1.5-4 V?,the initial discharge capacity is 321.5 mAh g^-1,after 40 cycles capacity retention in 253.3 mAh g^-1,much higher than that of V₂O₅ core-shell microsphere.Therefore,graphene coating and self-doping is an alternative method to further improve the electrochemical performance of electrode materials,and also has practical application value in improving the electrochemical performance of other electrode materials.