| From the perspective of environmental protection and energy security,it is an inevitable trend for electric vehicles to replace traditional fuel vehicles in the future.Among them,the kinetics of Li+intercalatiion reaction of of commercial graphite anode is poor,and the Li+insertion potential is very close to the deposition potential of lithium metal.In the process of high current charging and discharging,it is easy to cause the irreversible deposition of lithium metal on the surface of the graphite anode,which induces potential safety hazards and causes a sharp attenuation of electrochemical performance.Therefore,it is urgent to develop new anode materials with suitable lithium insertion potential and excellent kinetic performance.Among many anode electrode materials,titanium niobium oxide has relatively high lithium insertion potential,which can effectively avoid the deposition of lithium metal and the decomposition of electrolyte,and improve the safety performance of batteries.At the same time,the lithium storage capacity of titanium niobium oxide is close to 400 mAh g-1,which is higher than the theoretical specific capacity of graphite electrode.Therefore,titanium niobium oxide is regarded as a new anode material which is expected to replace graphite.However,the low electron/ion conductivity of titanium niobium oxide leads to cause large electrode polarization during high current charging,which results in low reversible specific capacity and poor rate performance of lithium ion batteries.Based on this,this paper takes titanium niobium oxide material as the research object,and carbon material composite,ion doping and structure regulation were adopted to solve the problem of low electronic/ionic conductivity in order to improve the electrochemical properties of titanium niobium oxide material.The specific research contents are as follows:(1)MXene,a two-dimensional material with excellent electrical conductivity,is an ideal substrate.Therefore,TiNb2O7@MXene(TNO@MXene)composite material was successfully prepared by sol-gel method combined with high temperature solid phase method.Under the action of MXene,the electron/ion conductivity of TNO composites are improved.The reversible specific capacity of TNO@MXene electrode was 313 mAh g-1 at 0.5 C and can still maintain 153 mAh g-1 after 1000 cycles at 10 C.(2)As a simple and effective modification method,ion doping can also improve the conductivity of materials.Therefore,P-doped Ti2Nb10O29-P(TNO-P)composites were successfully prepared by atmosphere sintering.The introduction of P element can induce a large number of oxygen defects,which significantly increases the conductivity and Li+diffusion rate,and thus improves the electrochemical activity of electrode materials.The reversible specific capacity of the TNO-P electrode was 192 mAh g-1 after 200 cycles at 1 C,and 100 mAh g-1 after 1000 cycles at 10 C.(3)Oxygen defects are easy to form when titanium niobium oxide are sintered in reducing atmosphere,and oxygen defects can improve the conductivity of the materials.Therefore,Od-Ti2Nb10O29@NC-GO(Od-TNO@NC-G)composite with oxygen defects two-carbon layer were successfully prepared.Among them,the double-carbon layer structure facilitates the migration of Li+diffusion,while the oxygen defect improves the conductivity of the material.The composite has excellent electrochemical properties under the synergistic action of double-carbon layer structure and oxygen defects.The reversible specific capacity of Od-TNO@NC-G electrode was 235 mAh g-1 after 200 cycles at 1 C.At the same time,Od-TNO@NC-G electrode can complete 20,000 cycles at 10 C. |
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