Interlayer Regulation Of The Two-Dimensional Titania Nanosheets For Electrochemical Energy Storage

Lithium ion batteries(LIBs)have been widely used in portable devices and electric vehicles due to their high energy density and long cycle performance.However,the rapid consumption of lithium resources and increasing production costs limit the large-scale application of lithium ion batteries,the development of low-cost energy storage technology is urgent.Due to the low cost and similar chemical properties of sodium and potassium to lithium,new types of sodium and potassium ion batteries have attracted extensive attention in recent years.However,due to the much greater size of Na-and K-ions,the fast redox intercalation of large-radius Na or K ions into a solid lattice in nonaqueous electrolytes has remained an elusive goal.Therefore,conventional materials are difficult to be used as electrode materials,and it is still a challenge to develop high-performance and low-cost energy storage devices with rapid charge and long cycle capability.In order to solve this problem,two-dimensional titania sheets is taken as the research object,the two-dimensional channel between neighboring sheets was completely open to guest intercalation,allowing fast intercalation that was practically irrespective of the carrier ion sizes.The main contents are summarized as follows(1)Interlayer regulation of titania nanosheetsLayered titanate was synthesized via a typical high-temperature solid-state reaction and the titania nanosheets were obtained by liquid exfoliation.After that,metal ions were self-assembly into the nanosheets to achieve interlayer regulation.The characterization showed that the interlayer structure of the nanosheet changed significantly compared with that of the precursor material,the disordered stacked structure weakened the interlayer interaction and improved the ability of ion storage(2)Study on electrochemical properties of titania nanosheetsDue to weakened layer-to-layer interactions and a robustly pillared gallery space,the two-dimensional channel between neighboring sheets was completely open to fast intercalation ions with various sizes,include regular Li-or large radius Na-and K-ions.Most remarkably,the rate capability and cycling stability observed for both Na-and K-ion storage are extraordinary and superior to most existing titanium-based electrode materials.By comparing with the precursors materials,it is proved that the interlayer regulation strategy plays an important role in improving electrochemical properties.In addition,we report a K-ion full cell based on Prussian blue nanoparticles cathode and interlayer-regulated layered titania sheets as anode,exhibited excellent rate and cycle performance.(3)Energy storage mechanism of titania nanosheetsThe structural changes of the titania nanosheets electrode after ion insertion and extraction were traced via a series of ex situ measurements,the material manifested zero strain-like behavior with no significant change in both host structure and interlayer space.Additionally,a detailed electrochemical kinetic analysis indicates that the charge storage in the present structure follows an intercalation pseudocapacitance mechanism.Meantime,the important effect of interlayer structure on ion intercalation was confirmed by theoretical calculation.