Synthesis And Electrochemical Properties Of TiO₂ Composites Anode For Sodium-ion Batteries

Energy storage is one of the most difficult problems facing sustainable development in the new century.Rechargeable ion batteries have achieved a huge success over the past two decades.Lithium ion batteries have been commercialized on a large scale due to its clean,efficient and stable energy storage and transformation,bringing great convenience to human production and life.Because of limited lithium resources,Sodium,a member of the same group as lithium,has attracted researchers'attention.Sodium has similar chemical and electrochemical properties with lithium and is widely distributed in the earth's crust,giving sodium ion batteries huge commercial potential.However,the anode materials used in lithium ion batteries generally cannot be directly used in sodium ion batteries due to differences in chemical and electrochemical properties.Based on titanium dioxide,two kinds of anode materials for sodium ion batteries were designed and synthesized,and their electrochemical properties in sodium ion button batteries were studied.The details are as follows:?1?CoSe₂ is a potential anode material for sodium-ion batteries in terms of their high sodium storage capacity and tunable properties.However,structural degradation and unstable interphase during the reversible sodiation and de-sodiation lead to fast capacity decay.In this work,we develop a nanocomposite architecture based on CoSe₂ nanoparticles embedded in N-doped carbon matrix with conformal TiO₂ coating?CoSe₂@NC@TiO₂?by using a metal-organic framework-assisted strategy.The small CoSe₂ nanoparticles and N-doped carbon matrix facilitate charge transport and suppress the structural degradation,while the redox-active TiO₂ shell further strengthens the structural and interfacial stability without decreasing the capacity.The as-prepared CoSe₂@NC@TiO₂ nanocomposite particles deliver a reversible sodium storage capacity of 520 mAh g^-1 at 0.1 A g^-1 with a capacity retention of 78%after 200 cycles,in contrast to the rapid capacity fading after 50cycles of the pristine CoSe₂@NC particles without TiO₂ shell.?2?Sodium-ion batteries offers an alternative to lithium-ion batteries as the promise of a scalable,low-cost and abundant resources renewable energy storage.However,the poor ionic conductivity and low practical capacity of anode materials present an unavoidable challenge.In this work,we demonstrate a novel composite architecture based on primary TiO₂ nanoparticles assembled into three-dimensional porous submicrometer spheres filled with red phosphorus in internal mesoporous by means of physical vapor deposition?denoted as P-TiO₂?.At the heterogeneous interface between TiO₂ and red phosphorus,a functional group,phosphate,was formed,which give two advantages:?1?providing reversible sodium storage sites;?2?increasing diffusion rate of Na⁺ions.Benefiting from above advantages,the P-TiO₂electrodes deliver a reversible volumetric capacity of 400 mAh cm^-3 at a current density of 0.05 A g^-1,which is about two times as much as the commercial hard carbon and two times of the pristine TiO₂.Even at a current density of 0.2 A g^-1,a high reversible volumetric capacity 300 mAh cm^-3 can keep for 400 cycles.When tested in a full cell,the P-TiO₂//Na₃V₂?PO₄?₃ battery is equivalent to⁹2%of the practical capacity of Na₃V₂?PO₄?₃.