Research On Preparation And Modification Of Anode Materials For Sodium/Lithium-ion Batteries

Large-scale energy storage systems(ESS) have been developed to convert and utilize the electrical energy efficiently from the renewable and clean energy sources, such as wind, solar and tidal energy. It is no doubt that rechargeable batteries are the key components in ESS. Lithium-ion batteries(LIBs), which are widely applied in portable electronic devices and electric vehicles(EVs), are holding a significant market share. However, the rapid consumption of lithium resources will eventually push the cost to be expensive. Thus the demanding for higher energy density and volume density bring formidable challenge on future LIBs. Subsequently, sodium-ion batteries(SIBs), taking similar electrochemical mechanism and properties with LIBs, have been extensively studied. The possible reasons are attributed to their reliability, environment-friendly, abundant sodium-based materials and low cost. On the other hand, organic material as the alternative to inorganic active materials have recently attracted much more attention, owing to its minimal environmental footprint, abundant resources, flexibility and availability from natural resources. In this dissertation, our aim is to promote the electrochemical performance of few anode materials for SIBs and LIBs.Na2Ti3O7 with monoclinic layered structure has been reported as the anode of SIBs, due to its outstanding advantages like high theoretical capacity(178 mAh g-1) and low operating voltage(0.3 V vs. Na/Na+). In spite of that, the intrinsic low diffusion of Na+ ion for its large radius(0.102 nm) and low electronic conductivity still severely limit its large-scale application. These issues have been addressed via the following methods in this dissertation: 1) The spherical Na2Ti3O7 was synthesized by spray drying of the sol-gel prepared precursor suspension, and the calcinated Na2Ti3O7 spherical powders consist of well crystallized Na2Ti3O7 primary particles with three-dimensional porous structure. The discharge capacity of 66 mAh g-1 was recorded even at current rate of 4 C. 2) Na2Ti3O7@ multi-walled carbon nanotubes(MWCNTs) composite was synthesized by spray-drying of sol-gel precursor, where the core consists of Na2Ti3O7 coated MWCNTs and the shell is made of well crystallized Na2Ti3O7 microspheres. Na2Ti3O7@MWCNTs exhibited much better rate capability of 81 mAh g-1 even at current rate of 4 C and prolongated cycling lifetime at 0.1 C. 3) Na2Ti3O7/carbon(Na2Ti3O7/C) composite nanofibers have successfully been synthesized via a simple electrospinning method. The nanofiber has the diameter of ~120 nm and the particle size of ~40 nm, exhibiting the best rate performance of 101 mAh g-1 at 4 C and excellent capacity retention of 82%(99 mAh g-1) at 1 C after 100 cycles.In carpter 5, another titanium-based anode material for LIBs, spinel Li4Ti5O12 has been applied as the anode of SIBs, owing to its safety and stable crystal structure. However, its electronic conductivity is intrinsically low. To overcome this drawback, we synthesized Li4Ti5O12/TiO2/C(LTO/TO/C) nanofiber composites by the electrospinning method. As the anode of LIBs, LTO/TO/C nanofiber composites achieved excellent rate performance(131 mAh g-1 under 24 C) and good capacity retention(89%, after 500 cycles at 6 C). Moreover, LTO/TO/C delivered excellent electrochemical performance when applied in SIBs. Such outstanding rate performance and cycling lifetime should benefit from the particular structure, because the nanosized Li4Ti5O12 particles coated with highly electric conducting carbon can facilitate electron transport, and the synergistic effect of interfacial interaction between Li4Ti5O12 and TiO2 is responsible for excellent electrochemical performance.In carpter 6, we proposed organic terephthalate acid(C8H6O4, H2BDC) as anode material of LIBs the first time. Its theoretically low intercalation potential(0.8 V vs. Li+/Li) and specific capacity of(324 mAh g-1) are similar to lithium terephthalate(Li2C8H4O4, Li2BDC). However, the H2 BDC actually displayed better electrochemical performance than that of Li2 BDC. It can achieve reversible capacity of 301 mAh g-1 at 0.1 C and good capacity retention(76%, 228 mAh g-1 at 0.1 C). Furthermore, H2 BDC was composited with multi-walled carbon nanotubes(MWCNTs) to improve its electrochemical performance.In carpter 7, we prepared two kinds of metal arrays with a periodic structure which were regulated via block copolymer film of poly(ethylene oxide) segment and polymethacrylate segment with azobenzene mesogen(PEO-b-PMA(Az)): 1) An ordered porous Ag layer was created on the template surface through vapor deposition process due to preferential interaction of Ag toward to the PMA(Az) phase; 2) Ordered arrays of Au/polymer composite nanorods with the orientation in the vertical direction was obtained by immersing the template in HAuCl4 solution, then exposed to the ultraviolet light irradiation. These ordered metal/composite nanostructures could be used as templates for further preparing and modifying the anode materials in LIBs and SIBs.