Study Of Titanium-based One-dimensional Nanostructured Arrays For Electrochemical Energy Storage

With the increasing of the demand of energy in our society,energy storage devices have been playing a critical role in our daily life.As an efficient and environmentally friendly electrochemical energy storage technology,lithium-ion batteries（LIBs）are widely used in portable electronic devices,electric transportation and renewable energy storage,owing to their high working potential,large energy density,and long cycle life.Currently,graphite is the widely used anode material in LIBs.However,this material suffers from serious safety issue caused by the growth of lithium dendrites.Besides,the electrochemical performance of graphite is hardly to be improved,which is unable to meet the demands of high energy and power densities.In recent years,the large-scale use of LIBs has caused the increasing consumption of lithium resources,thus leading to higher lithium prices.Sodium-ion batteries（SIBs）have been regarded as the promising candidates for the upcoming markets of large-scale energy storage systems,owing to the similar physics-chemistry characteristics and more abundant resources of sodium compared to lithium.Nevertheless,the anode materials that feature favorable lithium storage performance exhibit inappreciably reversible sodium storage ability.In a word,to explore efficient anode materials is of overreaching importance to both LIBs and SIBs.Titanium-based materials have been studied extensively as anode materials for LIBs and SIBs due to their high activity,excellent structure stability,good safety,abundant resources,and environmental benignity.However,these materials face the issues of intrinsically low electronic conductivity and initial Coulombic efficiency.To overcome these problems,one-dimensional titanium-based arrays are synthesized and their electrochemical performance is enhanced by fabricating heterogeneous nanostructured arrays or doping.The main research content is as follows:First of all,three-dimensional（3D）TiO₂ nanowire@NiMoO₄ ultrathin nanosheet core-shell arrays are prepared by a two-step hydrothermal strategy.In such a 3D core-shell nanowire array architecture,the TiO₂ nanowire arrays and the ultrathin NiMoO₄nanosheets exhibit strong synergistic effects by adjusting the NiMoO₄ content.The TiO₂nanowire arrays can maintain mechanical integrity of the electrode and the ultrathin NiMoO₄ nanosheets contribute to high capacity and favorable electronic conductivity.Secondly,the electronic conductivity of TiO₂-B nanowire arrays is significantly enhanced by decorating with layered VS₂ nanoparticles.Meanwhile,the VS₂ nanoparticles demonstrate high reversible lithium storage,thus leading to extra capacity contribution.As a result,the VS₂ decorated TiO₂-B nanowire arrays electrode shows a reversible capacity of 365.4 mAh g^-1 after 500 cycles at the current density of 1 C(335 mA g^-1).Impressively,this electrode delivers a high rate capacity of 171.2 mAh g^-1 at 10 C rate.Thirdly,phosphorus-doped TiO₂-B nanowire arrays are synthesized through a facile hydrothermal method and subsequent heating treatment under phosphorous atmosphere.The phosphorus-doped TiO₂-B nanowire arrays exhibit large capacity caused by high interfacial lithium storage.DFT calculations verify the phosphorus-doped TiO₂-B nanowire arrays feature high surface lithium affinity.More importantly,the phosphorus doping can dramatically promote the lithium reaction kinetics of TiO₂-B nanowire arrays by significantly intensifying the electronic conductivity and pseudocapacitive lithium storage behavior.In addition,a full cell assembled with P-TNAs anode and LiCoO₂cathode affords a high specific energy of over 180 Wh kg^-1（based on the mass of both electrodes）.Finally,K₂Ti₄O₉ nanoribbon arrays are grown onto Ti foils through a hydrothermal process.Owing to their unique morphology and large interlayer spacing（0.91 nm）,the K₂Ti₄O₉ nanoribbons show favorable lithium storage performance.When working as anode materials for SIBs,the modification of graphene quantum dots（GQDs）can significantly improve the initial Coulombic efficiency and rate performance of K₂Ti₄O₉nanoribbon arrays.The GQDs modified K₂Ti₄O₉ nanoribbon arrays deliver a reversible capacity of 62.8 mAh g^-1 at the high rate of 5.0 A g^-1.Impressively,a capacity of 82.3mAh g^-1（95.9%of the initial value）can be retained over 5000 continuous cycles at 2.0 A g^-1.