Preparation Of Ti-based Nano-electrode Material By Atomic Layer Deposition And Its Performance In Sodium-ion Battery

Sodium-ion batteries?SIBs?have considered to be one of the energy storage devices most likely to replace the lithium-ion batteries?LIBs?because of the advantages of abundant resources and low cost of sodium.The electrode material has a great influence on the battery performance.Therefore,the research on the electrode material is the key to developing high performance SIBs,which is also the focus and hotspot of current research.The negative electrode materials of the SIBs must have good electrochemical performance,and thus it is also urgent to develop new type of negative electrode materials.In the LIB system,the titanium-based nano-anode materials had small strain,good cycle stability,low price,and environmental protection during charge and discharge.Therefore,the research content of this paper mainly focuses on titanium-based oxides,nitride nanomaterials,as well as materials modified by doping for SIBs,leading to improving the electrochemical performance of the material.1.TiO₂ was prepared by atomic layer deposition?ALD?,and the amorphous Ti O2 and crystalline Ti O2 were deposited on carbon nanotubes?CNTs?by controlling the deposition temperatures.Through SEM testing,it was found that the amorphous Ti O2 exists in a layered form on the surface of CNTs,while the crystalline Ti O2 exists in the form of islands.Electrochemical measurements showed that the amorphous Ti O2 deposited on CNTs had better sodium storage performance than crystalline Ti O2.The charge and discharge capacities of amorphous and crystalline Ti O2 were 84.2 m Ah g-1 and 69.8 m Ah g-1 after 190 cycles at the current density of 20 m A g-1,respectively.This is because the amorphous Ti O2 is layered and continuous,which is conducive to the electron transport.In addition,the amorphous structure is more conductive to the insertion/extraction of sodium ions,thereby improving the electrochemical performance,such as charge and discharge capacity.The higher Na+ diffusion coefficient of amorphous Ti O2 as an electrode material was further proved through the calculation results of the relationship between the peak current and the sweep speed in the CV curves at different scanning speeds.2.Amorphous TiO₂ and nitrogen-doped amorphous Ti O2 were deposited on CNTs by ALD,and XPS test proved that nitrogen was successfully doped into Ti O2 to form nitrogen-doped Ti O2.Electrochemical measurements showed that the diffusion coefficients of Na+ before and after nitrogen doping were 1.20×10-14 cm2 s-1 and 1.99×10-14 cm2 s-1,respectively,indicating that Ti O2 after nitrogen doping has greater electronic conductivity and higher charge transfer rate,which can effectively improve the sodium storage performance of the electrode material,and correspondingly also improve its rate performance.Through the study of charge-discharge reaction mechanism,it is found that the reason for the increase in performance is that after nitrogen doping process,it is beneficial to the formation of oxygen vacancies and trivalent titanium in the material,and the existence of these defects improves the electron transfer rate of the material.3.A flexible carbon nanofiber?CNF?substrate with good conductivity and self-supporting was prepared by electrospinning technology,Ti N particles were deposited on the CNF film by ALD,and N2 was used as a plasma source to participate in the reaction during deposition.The N2 plasma provides not only a nitrogen source but also a functionalization agent of CNF substrate at the same time.Electrochemical performance test results showed that the prepared anode electrode achieved a reversible capacity of 163 u Ah cm-2 at a current density of 50 ?A cm-2 after 300 cycles,which is due to the plasma can enhance the activation of the CNF substrate surface,so that the electrode material is more conducive to infiltration with the electrolyte,thereby increasing the ion transmission rate and conductivity,and thus improving the electrochemical performance.In addition,the electrochemical performance of the electrode before and after deposition as an electrode of a supercapacitor was also investigated.The test results showed that the specific capacity retention rate of the sample before and after the deposition were 88.5% and 95.5% at a current density of 1 m A cm-2 after 10000 cycles.And the specific discharge capacity of after deposition can still reach 82 F cm-2,indicating that the material also has great potential in supercapacitors.