Investigation Of Conductive Polymers And Titanium-Based Nano-Structure Materials For Electrochemical Energy Storage

The energy storage systems play increasingly important roles in life,while supercapacitors and lithium-ion batteries are two of the most cutting-edge and important ones.Over the past few years,conducting polymer-based electrode materials have been widely used for fabricating flexible supercapacitors because of their high redox active capacitance,high electrical conductivity,the most important inherent flexibility;and because the electrical properties,chemical properties and mechanical properties of materials will have a lot of ascension when the size of them reach to nanoscale,as a result,efforts mainly focused on the development of nano-electrode material to improve the performance of the battery,recently.So this paper focused on these aspects and fabricated a kind of flexible electrode and a kind of nanostructure electrode.And the main results are as follows:（1）BC nanofibers have a very fine diameter（40-50 nm）,excellent mechanical properties,and hydrophilic functional groups such as-OH and-COOH.And PEDOT is one of the most popular conductive polymers for the preparation of flexible supercapacitors due to its high working voltage（about 1.2 V）and excellent stability.Therefore we can take advantage of its intrinsic hydrophilic to adsorb the oxidant on its surface.And because the solubility of EDOT in water is very small,so we can take control of the polymerization rate of EDOT easily and then manipulate the slow polymerization of PEDOT only on the BC nanofibers’surface evenly.In this way,we got a kind of ultra-thin（about 12μm）flexible BC-PEDOT electrode with three-dimensional porous structure.The areal capacitance of resulted flexible electrode reached 442.2 mF cm^-2 at a current density of 1 mA cm^-2.And the symmetric supercapacitors fabricated with BC-PEDOT10 paper electrodes,whose electrochemical performance still remained stable under various flexible conditions,presented a specific volumetric capacitance of 106.3 F cm^-3 at a current density of 0.83 A cm^-3.（2）Potassium titanates with an open tunnel structure and large sufficiently lattice spacing are beneficial to the insertion/extraction and diffusion of Li⁺/Na⁺.In addition,the nanometrization of electrode materials is very effective for the rapid insertion/extraction of Li⁺/Na⁺,shortening the diffusion path and the rapid transfer of electrons to the collector.Therefore,we prepared K2Ti4O9 nano-belt arrays,KTi8O16.5 micron-bar arrays and KTi8O16.5 nano-belt arrays,and studied the performances of them when they served as the cathodes of lithium ion battery and sodium ion battery.By analyzing their crystal structure,morphology and electrochemical properties,their capacities of lithium ion storage and sodium ion storage was investigated.We found that the capacities of lithium ion storage and sodium ion storage of potassium titanate with nano-structure was much better than that of potassium titanate with micron-structure.Compared with K2Ti4O9 nano-belt arrays,we found that KTi8O16.5 nano-belt arrays with a bigger lattice spacing have a stronger lithium ion storage capacity and sodium ion storage capacity.So we investigated the performances of the KTi8O16.5 nano-belt arrays served as the cathodes of lithium ion battery and sodium ion battery in detail.At the current density of 200 mA g^-1,the capacity of lithium ion battery is as high as 601.7 mAh g^-1,and the capacity of sodium ion battery can reach 246.4 mAh g^-1.Moreover,at a high current density of 5 A g^-1,the capacity of sodium ion battery still has61.95 mAh g^-1 after 10,000 cycles,which means the capacity retention rate can reach 94.3%.These results showed that the KTi8O16.5 nano-belt arrays have a good capacities of lithium ion storage and sodium ion storage and it is very safe and stable,so it will be a promising candidate as the cathode of lithium ion batteries and sodium ion batteries.