Design,Preparation And Lithium Storage Properties Of TiO₂/Au/SnO₂ Array Composite Electrodes

In the new generation of green electrochemical energy storage systems,lithium-ion batteries have been widely used in portable electronic products,such as mobile phones and computers due to their high energy density,excellent cycle performance,and environmental protection.At the same time,it also shows broad application prospects in electric vehicles and hybrid vehicles.Anode material is an important part of lithium-ion battery,which is one of the main factors to determine its capacity.Although graphite is the most successful commercial anode material,after years of development,it has basically approached the theoretical capacity and can not meet the needs of people.Therefore,it is urgent to develop a new generation of high specific capacity anode materials to replace the traditional carbon materials.In recent years,SnO₂ has the advantages of relatively high theoretical specific capacity,low lithium intercalation potential,and green pollution-free.It has received more and more attention and is regarded as a promising new generation of power battery anode material.However,SnO₂ produces a large volume expansion(about 300%)during the lithium insertion/delithiation process,which causes a large internal stress to cause the electrode material to break and fall off.The continuous generation of SEI film consumes a large amount of Li⁺,which reduces the reversible capacity during the SnO₂ cycle,and also makes the capacity of SnO₂ decay rapidly in the next cycle;In addition,the conductivity of SnO₂ is low,which limits the utilization and rate performance of SnO₂ based materials.These two problems are also the main reasons why SnO₂-based materials have not been commercialized.In response to the above problems,this paper designed a TiO₂/Au/SnO₂ composite array electrode,using the"zero strain"material TiO₂ nanotube array as the framework,and restricting SnO₂ in the gap of the nanotube array to suppress its volume expansion.The Au layer can effectively increase the conductivity of the composite electrode and at the same time increase the bonding force of the TiO₂ and SnO₂ interface.This paper focuses on the design of the TiO₂/Au/SnO₂ composite electrode,the mechanism of Au nanolayer in the composite electrode and its influence on the composite electrode,and the influence of SnO₂ content on the composite electrode.The main contents are as follows:as follows:(1)TiO₂/Au/SnO₂ composite array electrode is designed.Explored and successfully prepared a series of TiO₂ nanotube arrays with adjustable tube diameter and tube spacing;compared the electrochemical performance of TiO₂ nanotube arrays with small tube diameters,narrow gaps and large tube diameters and wide spacing when loaded with SnO₂,among which the large tube diameters When the wide-pitch TiO₂ nanotube array is loaded with SnO₂,the lithium storage performance is the best.At a current density of 0.1A·g^-1,the first-turn discharge specific capacity is 632.5 m Ah·g^-1,and the second-turn specific capacity is 316.4 m Ah·g^-1,the discharge specific capacity after 100 cycles is 302 m Ah·g^-1.Established a large-diameter and wide-spacing TiO₂ nanotube array as the SnO₂ supporting framework,and successfully designed and prepared a TiO₂/Au/SnO₂ composite array electrode.Under the condition of a current density of 0.1A·g^-1,the specific discharge capacity of the first cycle is 722.8 m Ah·g^-1,the first cycle Coulomb efficiency is 66.2%,and the specific discharge capacity of the second cycle is 567.4 m Ah·g^-1.The specific discharge capacity after 100 cycles is 365.77 m Ah·g^-1.(2)The mechanism of Au nano-layer in the TiO₂/Au/SnO₂ array composite electrode and its influence on the composite electrode are discussed.When Au was magnetron sputtered on the TiO₂ nanotube array,the average size of the nano Au particles near the root of the TiO₂nanotube was the smallest,and the average size near the top was the largest.As the sputtering time increases,the average size of the nano-Au particles in the"same"spatial position increases.After electrochemical cycling,a large number of nano-Au particles are present on the outer surface of the TiO₂ nanotube array,and the size of nano-Au particles increases;these all indicate that there is a strong interaction between Au and TiO₂ nanotubes,and electrochemical cycling does not cause the nanometer Au particles fall off.With the increase of Au content,the specific capacity attenuation of the first-turn discharge of the TiO₂/Au/SnO₂ array composite electrode gradually decreases,and the specific capacity and cycle stability of the electrode are improved.The addition of nano-Au particles enhances the conductivity of TiO₂ and SnO₂,increases the charge transfer rate of the TiO₂/Au/SnO₂ array composite electrode and the diffusion rate of lithium ions,reduces the loss of the irreversible capacity of the first loop of SnO₂,and makes TiO₂/Au/SnO₂ nanocomposite electrode capacitance increase.(3)The influence of SnO₂ content on the lithium storage performance of TiO₂/Au/SnO₂composite electrode was analyzed.With the increase of SnO₂ loading,the distance between the tube and the tube in the TiO₂/Au/SnO₂ array composite electrode is decreasing.When the SnO₂sputtering time is 45 or 60 minutes,the SnO₂ film gradually covers the TiO₂ nanotube array.A small part of the nozzle is even closed.At a current density of 0.1A·g^-1,the specific discharge capacity of the TiO₂/Au/SnO₂ electrode showed an overall downward trend.When the sputtering time of SnO₂ is longer than 30 min,SnO₂ gradually accumulates near the orifice of the nanotube array,blocking the orifice,which is not conducive to the diffusion and transmission of lithium ions,and aggregates into large nano-particles near the orifice.During the charging and discharging process,the insertion and extraction of lithium-ions will cause huge volume expansion,causing a large amount of fragmentation,leading to capacity attenuation.After 50 cycles of TAS-45 and TAS-60 electrode materials,the discharge specific capacity decreased to 354.4 and 322.1 m Ah·g^-1,respectively,which were lower than TAS-15electrode materials(357 m Ah·g^-1)and TAS-30(411 m Ah·g^-1).The dynamic analysis of the TAS-30 electrode proved that the structure has significant pseudocapacitance behavior,and the capacitance behavior has a great effect on the specific capacity and rate performance of TAS-30.At a CV sweep rate of 10 m V·s^-1,71.4%of the capacity generated by the TAS-30 electrode comes from the lithium storage mechanism controlled by the pseudocapacitance.