| The practical capacity of graphite anode materials is now close to its theoretical value,which can no longer meet the current demands for high energy density of lithium-ion batteries.Therefore,developing anode materials of high-performance becomes an important research direction at present.Among many anode materials,silicon monoxide（Si O）with the advantages of high theoretical specific capacity,environmental,and abundant resources has become hot material for a next generation of lithium-ion batteries.However,Si O exhibits poor cycle and rate characteristics due to its large volume change and low electrical conductivity,which severely slows down its commercialization process.To optimize the electrochemical performance of the Si O anode material,from the point of view of composite of materials,in this article,Si O was modified by introducing carbon materials or titanium dioxide（Ti O2）to improve electrochemical performance.（1）Using polyvinylpyrrolidone and citric acid as carbon sources,carbon-coated Si O composite materials were prepared by high-temperature solid-phase method,corresponding to Si O@C-1 and Si O@C-2,respectively.The influences of carbon sources on the lithium storage characteristics of the material were compared.It is revealed that 1)carbon material can be used as a buffer layer to alleviate the volume change of the material and improve the structural stability of the material;2)the carbon material obtained by carbonization of citric acid has a higher graphitization degree and has a better effect on improving electronic conductivity.Si O@C-2material delivers 242 m Ah g-1 at 1.0 A g-1 is obtained after 150 cycles,while the Si O material can only obtain a reversible specific capacity of 82 m Ah g-1 under the same test conditions.（2）Si O-Ti O2 and Si O@Ti O2 composite materials were synthesized by olid-phase mixing and sol-gel method,respectively,using Ti O2 and tetrabutyl titanate as titanium sources.The lithium storage performance of the material was studied systematically,and the reaction kinetics was analyzed by AC impedance.The research results show that the electrode structure stability and ion diffusion kinetics have been significantly improved after the modification of Ti O2.The Si O@Ti O2composite material possess better lithium storage characteristics,due to the closer contact between Ti O2 and Si O obtained by the sol-gel method,which is more conducive to the improvement of the stability of the electrode/electrolyte interface.The first coulombic efficiency of Si O@Ti O2 is 68%,and the reversible specific capacity of 239 m Ah g-1 is obtained after 150 cycles at 1.0 A g-1,with the capacity retention rate of 33%,while the specific capacity of Si O is only 155 m Ah g-1 and a capacity retention rate of 13%after 150 cycles.（3）Si O@Ti O2/C composite material was obtained through sol-gel combined with high-temperature solid phase method of citric acid by using tetrabutyl titanate as the titanium source and citric acid as the carbon source.The lithium storage performance of the materials was analyzed by a variety of test methods,and the influence of the addition of tetrabutyl titanate on the electrochemical characteristics of the composite material was explored.By comparing the electrochemical performance of between Si O@C and Si O@Ti O2/C,it is found that the Si O@Ti O2/C composite material has a greater improvement in cycle and rate performance,which is due to the promoting of Ti O2 on electrode interface stability and lithium-ion diffusion rate.the reversible specific capacity of Si O@Ti O2/C material is maintained at 710 m Ah g-1 at 1.0 A g-1 after 150 cycles,while Si O@C material reserves only 258m Ah g-1.At 4.0 A g-1,Si O@Ti O2/C can maintain a great charging specific capacity of430 m Ah g-1,which is much higher than Si O@C(77 m Ah g-1)under the same test conditions. |
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