| The crises of energy and environment promote the rapid development of energy storage devices especially lithium-ion batteries(LIBs).As a novel intercalated anode material,titanium niobate(Ti2Nb10O29)has received much attention for its higher safety and coulomb efficiency than commercial graphite,and higher specific capacity(396 mA h g-1)than Li4Ti5O12.However,the inherent low electronic conductivity and slow Li+ diffusivity limit its commercial application.To adress the above issues,a flexible conductive carbon foam substrate was introduced into the Ti2Nb10O29(TNO)electrode system to design a new-type self-supported Ti2Nb10O29 anode electrode with high conductivity and ion diffusivity in this paper.In addition,to solve the problems of poor compressive strength of carbon foam and low load of active material,a high-strength carbon foam with spiral carbon fibers anchoring on original carbon foam was synthesized by in-situ growth method.The challenge that the direct carbonization of polymer could not change the porosity of the foam was also overcome.Moreover,the combination of conductive foam coating,Mo doping and oxygen vacancy achieved a comprehensive improvement in energy storage performance of Ti2Nb10O29,including energy density,rate capacity and cycle life.The main research work and results are as follows:(1)A kind of self-supported anode electrode of Ti2Nb10O29 with flexible carbon foam as substrate was designed.The introduction of porous carbon foam can not only avoid the addition of insulating binder,but also build a conductive network,which can greatly improve the conductivity of Ti2Nb10O29 anode electrode(from～10-9 S cm-1 to～10-3 S cm-1).In addition,the uniform large pores can act as reservoirs to store electrolyte,which can improve the contact area between active substances and electrolytes,reduce the transport distance of ions,and finally realize the high-speed transfer and diffusion of ions and electrons.Benefit from the above advantages,the TNO@MCF electrode exhibited remarkable high-rate capacities(317 mA h g-1 at 1 C,and 205 mA h g-1 at 40 C)and excellent cycling stability with a high capacity retention of 81.4%(1000 cycles)at 10 C.After 100 compression-rebound cycles,the TNO@MCF electrode showed a reversible capacity of 315 mA h g-1 at 1 C and a capacity retention of 72.3%for 1000 cycles at 10 C,showing outstanding cycle stability.(2)A micro-nano hierarchy of spiral carbon fiber anchoring on carbon foam(SCF@MCF)was designed to solve the problems of poor compressive strength and particle aggregation.By changing the concentration of catalyst,the pore structure and morphology of carbon foam can be accurately controlled,which means the challenge that the direct carbonization of polymer cannot change the porosity of foam has been overcome.The intertwining spiral carbon fibers anchored on the surface of the skeleton showed special strength and extraordinary resilience,which can not only create an extra layer of stiffness,but also reduce the radial stress and shear stress at the interface between carbon fiber and carbon foam.Benefit from the above advantages,the maximum compressive strength of SCF@MCF is 6.3 times of the original MCF,and the maximum tensile strength is 4.5 times of the original MCF.In addition,the thickness loss after 50 cycles was only 6%,much lower than MCF(28.6%),showing remarkable mechanical strength.(3)A self-supported electrode(TNO@SCF/MCF)with Ti2Nb10O29 as active material and spiral carbon fibers reinforced carbon foam as substrate was designed.The introduction of spiral carbon fi bers can overcome the defect of poor compressive strength and reduce the risk of electrode cracking during the battery pressing process.In addition,the nanoscale diameter(～100 nm)of the spiral carbon fibers improved the dispersion of the nanoparticles,which solved the aggregation and shedding problems of Ti2Nb10O29 on the large carbon foam skeleton.The half cell of TNO@SCF/MCF delivered high capacity of 330 mA h g-1 at 1 C,and 259 mA h g-1 at 20 C,showing excellent rate performance.After 2000 cycles at 10 C,the reversible capacity maintained about 81.2%,showing excellent cyclic stability.Moreover,the full cell of TNO@SCF/MCF delivered a reversible specific capacity of 181 mA h g-1 after 2000 cycles at 10 C.The capacity retention of 74.2%indicated the rapid redox kinetics and high reactivity.(4)The modification strategy combining conductive foam coating,crystal structure modification and nanostructure regulation was proposed to synthesize a flexible selfsupported anode electrode(Mo-MST)with Mo-doped Ti2Nb10O29-X anchoring on the spiral carbon fibers reinforced carbon foam.Mo doping and oxygen vacancy widened the lattice spacing,limited the accumulation of cells,refined the grain size,reduced the Li+diffusion energy barrier,reduced the band gap,and significantly enhanced the intrinsic electron conductivity and ion diffusivity of Ti2Nb10O29.The modification strategy achieved a comprehensive improvement in energy storage performance of Ti2Nb10O29.At the current density of 1 C,the reversible capacity of Mo-TSM half-cell was 342 mA h g-1.When the current density increased to 40 C,it still retained 271 mA h g-1 with the capacity retention of 79.3%.After 2000 cycles at 10 C,Mo-TSM delivered a capacity retention rate of 92.1%.In addition,the Mo-TSM all-solid-state battery retained 85.5%of its initial capacity after 2000 cycles at 10 C,demonstrating the high rate performance and cycle stability of Mo-TSM.(5)Based on the high porosity and excellent mechanical properties of SCF@MCF,the application in the field of oil absorption,especially photo-thermal oil absorption was studied.The micro-nano structure constructed by the porous carbon skeletons and entwined nanofibers can improve the surface roughness of the MCF,avoid the contact between hydrophilic sodium salt and water droplets on the skeleton,and create more air interfaces,which endowed the SCF@MCF superhydrophobic properties.Benefit from its high porosity and low packing density,SCF@MCF possessed a high absorption capacity of 60～128 g g-1 for organic solvents.In addition,the multi-dimensional grown spiral carbon fibers can absorb more incident light and internal reflected light,resulting in a further increase in the absorption to more than 90%.The pure carbon component can also reduce the interfacial resistance to achieve efficient absorption and conversion of light energy.Under sunlight,the SCF@MCF can be quickly heated up to 70℃ and achieve ultra-high absorption of crude oil,up to 62 g g-1.After extruded for 10 times,the recovery efficiency remained above 85%,showing excellent absorption stability. |
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