Research Of High Performance Titanium-based Nanostructure Materials For Energy Storage

In recent years,titanium-based nanostructured materials have been widely studied as anode materials due to their stable structure and better safety.However,traditional titanium-based nanomaterials like TiO₂ and Li₂TiO₃ still have key scientific issues to be further solved,such as relatively low mass specific capacity,low volume specific capacity,poor conductivity and rate performance.Increasing the tap density of the electrode materials is one of the most important means for increasing the volume energy density of the battery,and it is also one of the decisive factors for the large-scale commercial application of the material.In general,anode materials with high tap density feature the large size and small specific surface area,which is not conducive to the rapid migration of ions and electrons and sufficient infiltration of the electrolyte.Thereby,it is difficult to achieve high power density while maintaining high energy density and long cycling life.In this thesis,aiming at the key constraints of the traditional titanium-based nanomaterials in terms of small capacity,low tap density and poor rate performance,it is proposed to develop high tap density titanium-based bimetallic compounds as precursors.By rationally controlling the recrystallization process and introducing the grain boundary and pore structure into the secondary particles,NiTiO₃ and CoTiO₃anode materials with high capacity,high rate,and high tap density were successfully developed,which solved the above key problems and achieved the balance between high rate,long durability and high tap density.The results may provide an important reference for the development of a new generation of long-life,high-power,high-energy-density electrode materials for lithium-ion batteries and sodium-ion batteries.The main research contents are as follows:?1?Through optimizing the self-assembly process,a hexagonal nickel-titanium bimetallic organic framework Ni-Ti-EG was successfully prepared,and its growth mechanism was further explored by means of ex-situ transmission electron microscopy,which realized the visual aid quality monitoring during the preparation process.After studying the thermal decomposition process of Ni-Ti-EG,it was found that a mesoporous NiTiO₃ micro-prism with rich grain boundary and high tap density(2.5 g cm^-3)can be obtained at 600?.The obtained Ni TiO₃ features interconnected grain-boundary-rich and mesoporous structure,endowing highly conductive path for charge transportation and shortcut for ion diffusion.This anode materials delivered superior rate and capacity retention for both sodium and lithium ion storage,respectively.For example,a high capacity of 562 mAhg^-1reached at 0.5 C.It is also noteworthy that even after cycling for 1000 cycles at 5 A g^-1,the capacity retention ratio is maintained 60.4%for lithium ion storage.?2?A novel cobalt-titanium bimetallic organic framework Co-Ti-EG was successfully prepared as a precursor by the above synthesis method,and the dual-metal-organic crystal derived carbon-free mesoporous CoTiO₃ micro-prism with a tap density of 1.8 g cm^-3was developed as the negative electrodes of lithium-ion batteries and sodium-ion batteries,which showed good rate and cyclic performance.After comparison,CoTiO₃ has a larger pore size and lower band gap than that of NiTiO₃,delivering a superior Na⁺storage than Ni TiO₃,other similar reported titania,titanate and their carbon composites.Its achieved capacity retention ratios for 200 cycles are 72.2%,81.6%,86.5%and 94.5%at 0.5 C,1 C,5 C,10 C,respectively.Even after 1,000 cycles,the capacity retention ratio could also be up to 90.3%at 10 C.