Thermal Annealing and Graphene Modification of Exfoliated Hydrogen Titanate Nanosheets for Enhanced Lithium-ion Intercalation Properties
来源期刊：JOURNAL OF MATERIALS SCIENCE TECHNOLOG2014年第9期
论文作者：Xinning Luan Ying Wang
文章页码：839 - 846
摘 要：Hydrogen titanate has been considered as a promising lithium intercalation material due to its unique layered structure.In the present work,we fabricate 2D graphene/hydrogen titanate hybrid nanosheets for application as anode materials in lithium-ion batteries.H2Ti3O7nanosheets are synthesized by exfoliation of a layered precursor via interacting bulky tetrabutylammonium（TBAt）cations,followed by ion exchange with Nations and washing with water.The as-prepared hydrogen titanate nanosheets are well-dispersed exhibiting ultra-thin thickness with a lateral size up to a few micrometers.The sample is then annealed at 450,650 and 850 C,to optimize its Lit-intercalation property.Heating at 450 C leads to well-crystallized hydrogen titanate with a trace amount of TiO2.Heating at 650 and 850 C results in mixed sodium titanates,since some sodium ions in the interlayer structure cannot be washed away and become chemically bonded to[TiO6]octahedra at high temperatures.Electrochemical properties of all the four samples are then evaluated by charged/discharged for100 electrochemical cycles at 0.01e2.5 V vs.Lit/Li at a specific current of 170 mA g 1.The unannealed hydrogen titanate delivers the highest initial discharge capacity of 130.5 mA h g 1,higher than124.6 mA h g 1from hydrogen titanate annealed at 450 C,as well as 101.3 and 63.8 mA h g 1from hydrogen titanate annealed at 650 and 850 C,respectively,due to the high surface area from well-dispersed unannealed nanosheets.However,after 100 electrochemical cycles,well-crystallized hydrogen titanate annealed at 450 C retain the highest charge capacity of 115.2 mA h g 1,corresponding to a capacity retention of 92.5%,while unannealed hydrogen titanate exhibits a final capacity of 72.1 mA h g 1and a capacity retention of only 55.2%.To further improve energy density of lithium-ion battery,graphene/hydrogen titanate hybrid nanosheets are fabricated by adding graphene nanosheets into hydrogen titanates.The initial charge capacities of unannealed and annealed hydrogen titanate at 450 C are significantly increased to170.7 and 233.9 mA h g 1,respectively.A charge capacity of 101.0 mA h g 1is retained for unannealed hydrogen titanate with graphene-modification after 100 electrochemical cycles since well-dispersed hydrogen titanate nanosheets can be mixed with 2D graphene more uniformly and thus facilitates diffusion of Litions and retard aggregation of active materials.
Xinning Luan，Ying Wang
Department of Mechanical and Industrial Engineering, Louisiana State University,Baton Rouge, LA 70803, USA
摘 要：Hydrogen titanate has been considered as a promising lithium intercalation material due to its unique layered structure.In the present work,we fabricate 2D graphene/hydrogen titanate hybrid nanosheets for application as anode materials in lithium-ion batteries.H2Ti3O7nanosheets are synthesized by exfoliation of a layered precursor via interacting bulky tetrabutylammonium（TBAt）cations,followed by ion exchange with Nations and washing with water.The as-prepared hydrogen titanate nanosheets are well-dispersed exhibiting ultra-thin thickness with a lateral size up to a few micrometers.The sample is then annealed at 450,650 and 850 C,to optimize its Lit-intercalation property.Heating at 450 C leads to well-crystallized hydrogen titanate with a trace amount of TiO2.Heating at 650 and 850 C results in mixed sodium titanates,since some sodium ions in the interlayer structure cannot be washed away and become chemically bonded to[TiO6]octahedra at high temperatures.Electrochemical properties of all the four samples are then evaluated by charged/discharged for100 electrochemical cycles at 0.01e2.5 V vs.Lit/Li at a specific current of 170 mA g 1.The unannealed hydrogen titanate delivers the highest initial discharge capacity of 130.5 mA h g 1,higher than124.6 mA h g 1from hydrogen titanate annealed at 450 C,as well as 101.3 and 63.8 mA h g 1from hydrogen titanate annealed at 650 and 850 C,respectively,due to the high surface area from well-dispersed unannealed nanosheets.However,after 100 electrochemical cycles,well-crystallized hydrogen titanate annealed at 450 C retain the highest charge capacity of 115.2 mA h g 1,corresponding to a capacity retention of 92.5%,while unannealed hydrogen titanate exhibits a final capacity of 72.1 mA h g 1and a capacity retention of only 55.2%.To further improve energy density of lithium-ion battery,graphene/hydrogen titanate hybrid nanosheets are fabricated by adding graphene nanosheets into hydrogen titanates.The initial charge capacities of unannealed and annealed hydrogen titanate at 450 C are significantly increased to170.7 and 233.9 mA h g 1,respectively.A charge capacity of 101.0 mA h g 1is retained for unannealed hydrogen titanate with graphene-modification after 100 electrochemical cycles since well-dispersed hydrogen titanate nanosheets can be mixed with 2D graphene more uniformly and thus facilitates diffusion of Litions and retard aggregation of active materials.
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