Syntheses And Characterization Of Titanium Based Anode Materials For Sodium-lon Batteries

Owing to the high energy density and high energy-conversion efficiency,lithium-ion batteries(LIBs)have been widely applied in portable electronic devices,hybrid electric vehicles(HEVs)and electric vehicles(EVs).Recently,the application of renewable and clean energy is developing rapidly,which leads to various innovations of the energy storage technologies.Compared with the LIBs,the energy density of sodium-ion batteries(SIBs)is relatively lower.However,SIBs have advantages in the cost and the abundance of the sodium resources.These advantages made them promising candidates of large-scale energy storage devices,if the long cycle performance can be further improved.Among the anode materials of SIBs,titanium-based materials is working following the mechanism of intercalation reactions.These anode materials usually have advantages of the stable structure,low volume change and the diversified species.Nevertheless,they suffer from low intrinsic electronic conductivity.Also,their cycling and rate performances are still to be enhanced.In this thesis,the synthesis and characterization of two kinds of titanium-based SIBs anodes,i.e.Na2Ti3O7 and P2-Na0.66[Li0.22Ti0.78]O2,are mainly investigated.In Chapter 1,the development history,working mechanism and key components of SIBs are introduced.Moreover,a detailed summary of all sorts of electrode materials for SIBs is also presented.We focus on the materials with intercalation reaction mechanism.Based on the review,research background and strategies are also provided.Chapter 2 lists the description of reagents,characterization methods and equipment used in this thesis.In Chapter 3,a facile wet chemical route has been adopted to synthesize the composite of in-situ carbon network and Na2Ti3O7 for SIBs anode.Compared with traditional hydrothermal or solid state reaction methods,this moderate synthesis route can make use of the functional groups in tetrabutyl titanate(TBT)to form in-situ carbon network during thermal treatment under an inert atmosphere without additional carbon source.The existence of carbon network leads to the improvement of the cycling performance and rate capability of Na2Ti3O7.Chapter 4 uses the same synthesis strategy as in Chapter 3 to prepare the composite of in-situ carbon network and P2 type Na0.66[Li0.22Ti0.78]O2 as titanium-based SIBs anode.The gas leaking problem of tube furnace under high temperature conditions has been solved by optimizing the gas rate and the calcination temperature,so as to obtain the in-situ carbon network.Besides,several contributions to initial discharge capacity are also analyzed.Furthermore,in order to improve the electronic conductivity of this material,the carbon coated Na0.66[Li0.22Ti0.78]O2 and N0.66[Li0.22Ti0.78]O2/carbon-nanotube hybrid samples are prepared.The modified samples show enhanced rate capability with about 10 mAh g-1 increase in capacity at various current densities,without a loss in initial coulombic efficiency.In Chapter 5,a thermal polymerization method is firstly adopted to prepare Li2MoO4 as one high capacity anode material for LIBs.Furthermore,a facile carbon coating method is used to improve the cycling and rate performance.Chapter 6 gives a brief summary of the highlights and drawbacks in this thesis.The prospects for the future research are also pointed out.