Preparation And Electrochemical Performance Of Anode Materials For Sodium Ion Batteries Based On Synergistic Regulation Of Piezoelectric Effect And Alloying Reaction

Lithium ion batteries,cannot meet the demand for chemical batteries in future medium-and large-scale energy storage systems due to resource problems.Sodium ion batteries are expected to replace lithium ion batteries due to their similar working mechanism and abundant sodium resources,making them the most widely used energy storage system for the next generation battery.Since ionic radius of sodium ion is larger than that of lithium ion,the graphite anode,a conventional one for commercial lithium ion batteries,cannot effectively insert sodium ion.Sodium ion batteries need to develop other anode materials.Compared with other materials,alloy-based anode materials have higher theoretical capacities,safe working voltages and low cost,so which are easier to meet the demand for high energy density,high power density and light weight of new energy vehicles and portable wearable devices.However,the alloy-based anode materials have some disadvantages:large volume expansion,poor conductivity,and slow reaction kinetics.In this paper,barium titanate?BTO?is introduced to overcome the drawbacks of alloy-based anode material.The mechanical force generated by volume expansion acts on BTO,and produces piezoelectric effects.Whether the piezoelectric electric field can promote the diffusion of sodium ions is discussed prominently.The specific research results are as follows:?1?Red phosphorus?red-P?,BTO and graphene?G?were combined together by a simple ball milling method as anode for sodium ion batteries.The red-P contents in red-P/BTO/G and red-P/G materials were 22%and 32%,respectively.The first reversible charge capacities of red-P/BTO/G,red-P/G and red-P at 200 mA·g^-1 were 1557,472,and 450 mA h·g^-1,respectively.After 100 cycles,the discharge capacities were 823,197,and 80 mA h·g^-1,respectively,which proved that BTO and graphene could improve the sodium storage capacities and cycling stability of the composite.According to the electrochemical performances,the optimal ball milling conditions were as follows:the material ratio was 1:1:1;ball milling time was 5 h;ball milling sequence was two steps ball milling.Red-P/BTO/G material was polarized under different conditions,and the sodium ion diffusion coefficients were calculated using cyclic voltammety?CV?tests under different scan rates,which confirmed that the introduction of BTO and the positive polarization could improve sodium ion diffusion speed.The speed of 10 kV positively polarized red-P/BTO/G material was 450 times higher than that of red-P/G material.Scanning electrochemical microscopy?SECM?test was used to characterize micro-area electrochemical reaction intensity of the material under various polarization conditions.It was found that the average feedback current of 10 kV positively polarized red-P/BTO/G was 15times higher than that of red-P/G material.Finally,the mechanism of the piezoelectric effect of BTO to promote the diffusion of sodium ions was explained in detail.?2?SnO₂ nanowires were prepared by chemical vapor deposition method?CVD?,BTO coated by hydrothermal method,and carbon coated by in-situ polymerization of aniline.SnO₂@BTO@C material was prepared as anode of sodium ion battery.At 200 mA·g^-1,the discharge capacities of SnO₂@BTO@C,SnO₂@C,SnO₂@BTO and SnO₂ materials after 100cycles is 765,142,13,and 87 mA h·g^-1,respectively.It proved that BTO and carbon coating could effectively improve electrochemical performance of composite.The peak positions of BTO?110?characteristic peak at different voltage points during charge and discharge processes were tested by XRD tests.It was found that during the discharge process,the peak redshifted,while blueshifted during charge process.The periodic shifts of BTO followed the volume expansion of SnO₂ periodically.BTO was subjected to volume expansion of SnO₂,produced piezoelectric effects.The mechanism of BTO promoting sodium ion diffusion was presented in the one-dimensional composite scale.