Preparation And Electrochemical Investigation Of Li₄Ti₅O₁₂ Nanosheets/Graphene Composite Anode Materials

Spinel Li₄Ti₅O₁₂ is considered as a prospective lithium-ion batteries anode materials to ameliorate the safety and fast charging performance because it is featured with higher voltage plateau（1.55V vs Li/Li⁺）,superior cycling stability and stable voltage plateau.However,there still exist some drawbacks that greatly affect its rate and long cycle performance,for example,its intrinsic poor electronic conductivity and low lithium diffusion coeffcient.Up to date,researchers have made great efforts to overcome these drawbacks including decreasing the particle size,doping with heterogeneous atoms,forming composites with carbon materials.Among these strategies,composite material formed of carbon material and nanosized Li₄Ti₅O₁₂ is an efficient way to improve the rate capability.While its electrochemical performance is also closely related to its electrochemical performance the structure of the composite material.Based on these,we use Li₄Ti₅O₁₂2 nanosheets and graphene to build a self-supporting film structure and 3D internal connected porous microsphere structure for improving the rate capability of Li₄Ti₅O₁₂.Firstly,we prepared precursor nanosheets of Li₄Ti₅O₁₂ by solvothermal method.And the self-supporting film structure was prepared through electrostatic attraction,vacuum filtration and high temperature annealing treatment.The Li₄Ti₅O₁₂ nanosheets distribute uniformly between graphene sheets,which can suppress irreversible aggregation and restacking of graphene sheets.Meanwhile,graphene sheets could not only act self-supporting carrier,but also provide a conductive matrix.Electrochemical tests showed that the reversible capacity of the sample was 130 mAh·g^-1 at 20C.However,the self-supporting film structure is stacked tightly while the electrolyte could hardly fully infiltrate.So it is necessary to further optimize the structure.Secondly,in view of the above problems,we adopt spray drying techniques to synthesis 3D internal connected porous microsphere structure composites.Compared with other Li₄Ti₅O₁₂ particles/graphene composites,this porous porous microsphere structure can ensure electrolyte fully infiltrate electrode materials.While,grapheme with Li₄Ti₅O₁₂ nanosheets formed a three-dimensional spatial lattice structure,which ensures the excellent conductivity of the composite material.The Li₄Ti₅O₁₂ nanosheets wrapped by graphene,so that the microsphere structure is not easy to break.The Li₄Ti₅O₁₂ nanosheets/graphene electrode exhibited a high capability 118.6 mAh·g^-1 at 50C and good capacity retention of 88.1%at 20C after 1000 cycles.The test results showed that the content of graphene had a great influence on the microscopic morphology of the material.Electrochemical test showed that the composite material has a high reversible capacity 132 mAh·g^-1 at 50C when the mass radio of graphene oxide is 10%.The type of carbon source also has a great influence on the morphology and electrochemical performance of the material.Compared with glucose and carbon nanotubes,the Li₄Ti₅O₁₂ nanosheets/graphene electrode has the highest capacity retention.