| High power lithium ion battery has an important application prospect in electric vehicles,heavy duty hybrid commercial vehicles and directional energy equipment.Research on anode materials with high rate performance,safety and cyclic stability has been paid much attention.Titanium niobium oxide has a high theoretical specific capacity.During the process of lithium ion insertion and extration,the lattice parameters and cell volume change little,and the reversibility is high.Its lithium intercalation potential is about 1.6 V which makes it difficult to produce SEI and lithium dendrites in the cycling process.Compared with Li4Ti5O12,it has a higher specific capacity and is a new anode material with a promising application prospect.However,as a transition metal oxide,titanium niobium oxide has a low electronic conductivity and ionic conductivity,which greatly limits its electrochemical performance.In this paper,nano porous microsphere structure,holey redox graphene oxide composite,oxygen vacancy introduction,nano silver coating and other methods were used to modify the titanium niobium oxide,which significantly increased the ionic conductivity and electronic conductivity of the material,obtained the high electrochemical performance of the negative electrode material of titanium niobium oxide,and discussed the reasons for improving the electrochemical performance,the conclusions were as follows:(1)The TNOx/HRGO composite was obtained by solvothermal followed by annealing and freeze-drying methods.Its structure is TNO microspheres with abundant oxygen vacancies wrapped by gossamer-like HRGO.TNOx/HRGO composite exhibited excellent reversible capacity of 316 mAh/g,278 mAh/g,242 mAh/g,225 mAh/g,and 173 mAh/g at 1 C,5 C,10 C,20 C,and 40 C,respectively.After 300 cycles at 10C,it still has a high capacity of 238 mAh/g with a high retention of 98%,revealing excellent cycling stability.(2)XPS,ESR,EIS and TEM were used to study the valence state,unpaired electronic state,impedance,crystal structure and morphology of TNOx/HRGO composite.The reasons for its performance enhancement are as follows:a.TNO microspheres consist of nanoparticles,thus having shorter electron/ions transfer paths and more transfer channels through which Li+-ion can move rapidly from electrolyte to electrode.b.The introduction of oxygen vacancies into TNO can increase electron density,resulting in higher internal electronic conductivity.c.An excellent conductor,HRGO can decrease the electronic resistance of a whole electrode.Through the introduction of HRGO,the restriction of poor electrical conductivity of TNO anode material can largely be broken through.Meanwhile,when Li+-ion transfers in the perpendicular direction of RGO or HRGO,HRGO can offer more Li+-ion transfer paths than RGO because of the existence of holes,resulting in a higher ion conductivity.d.Due to its high specific surface area,HRGO can efficiently buffer volume expansion,which is beneficial for the enhancement of cyclic capability.(3)The TNO/Ag composite was prepared by two-step solvothermal method.It can be found that silver nanoparticles were uniformly distributed on the surface of TNO nanospheres.As an excellent conductor,the conductivity of TNO can be improved by 5 orders of magnitude to 1.9×10-4 S cm-1 after composited with silver nanoparticles,which effectively overcomes the disadvantage that the poor conductivity of TNO which limit the rate performance.In the rate performance test,the sample with the addition amount of silver of 6.8 wt.%(0.06-TNO/Ag)showed excellent rate performance.At the rates of 0.1 C,2 C,5 C,10 C,and 20 C,the capacity are 302 mAh/g,282 mAh/g,271 mAh/g,252 mAh/g and 238 mAh/g,respectively.The capacity of TNO/Ag composite material shows a trend of increasing first and then decreasing with the addition of silver nitrate,and reach the optimum at the addition of 0.06 g silver nitrate. |
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