【作者】 刘璇；

【导师】 方海涛；

【作者基本信息】 哈尔滨工业大学 ， 材料与化工（专业学位）， 2024， 硕士

【摘要】 锂金属阳极在充放电过程中存在体积变化大、界面副反应多、锂枝晶生长快等问题,导致电池库伦效率（CE）降低且循环稳定性变差。碳纳米纤维-碳纳米管三维（3D）集流体具有质量轻、导电性好、比表面积大等优点,但其亲锂性较差。本文利用氟化镁和银对碳纳米纤维-碳纳米管三维集流体的亲锂性进行改善,并研究三维集流体的锂沉积/溶解性能。首先,在酸氧化后的碳纳米纤维（AVGCF）和单壁碳纳米管（ACSWCNT）表面修饰MgF₂,制备出MgF₂@ACSWCNT、MgF₂@AVGCF-ACSWCNT、MgF₂@AVGCF-MgF₂@ACSWCNT三种集流体。通过SEM、EDS等表征发现酸氧化VGCF时间从2 h（AVGCF-2）增加至10 h（AVGCF-10）后,并未影响MgF₂在碳纳米纤维表面的沉积均匀性,并且当MgF₂含量为20 wt%时,在AVGCF上以及周围分布较为均匀。对比三种集流体的充放电循环性能,结果表明MgF₂@AVGCF-ACSWCNT比MgF₂@ACSWCNT和MgF₂@AVGCF-MgF₂@ACSWCNT表现出较高的循环稳定性。与AVGCF-2-ACSWCNT相比,适量氟化镁（15 wt%、20 wt%、30 wt%）修饰AVGCF-2后,库伦效率和循环稳定性有所提升,但含量过低（10 wt%）或过高（40 wt%）时循环性能反而下降。20%MgF₂@AVGCF-2-ACSWCNT的形核过电位从AVGCF-2-ACSWCNT的30.1 m V降低至4.6 m V,库伦效率波动极小（CE标准差～0.25%）且稳定循环超825次。20%MgF₂@AVGCF-10-ACSWCNT上更多的含氧官能团有利于内部锂的均匀沉积/溶解,平均库伦效率达98.84%,并稳定循环超1100次。为进一步提高碳纳米纤维-碳纳米管三维集流体的内部空间利用率,采用磁控溅射在20%MgF₂@AVGCF-2-ACSWCNT的一侧沉积银,研究沉积的银对集流体锂沉积/溶解的影响。20%MgF₂@AVGCF-2-ACSWCNT/Ag底部梯度分布的银诱导锂从集流体底部自下而上沉积,并且在1 m A cm^-2与1 m Ah cm^-2条件下表现出高平均库伦效率（～98.85%）和长循环寿命（超750次）。更多还原

【Abstract】 During the charging/discharging process of lithium metal anode,there are problems such as large volume change,many interfacial side reactions and rapid growth of lithium dendrites,which lead to the decrease of Coulombic efficiency（CE）and poor cycle stability of lithium-metal batteries.A three-dimensional（3D）current collector of carbon nanofiber-carbon nanotube has the advantages of light weight,good conductivity and large specific surface area,but its lithium philicity is poor.In this study,magnesium fluoride and Ag were induced to improve the lithiophilicity of carbon nanofiber-carbon nanotube three-3D collector.The lithium deposition/stripping performance of the 3D current collector also were studied.Firstly,MgF₂ was decorated on acid-oxidized carbon nanofibers（AVGCF）and single-wall carbon nanotubes（ACSWCNT）.Then three kinds of 3D current collectors were prepared.They are MgF₂@ACSWCNT,MgF₂@AVGCF-ACSWCNT,and MgF₂@AVGCF-MgF₂@ACSWCNT.SEM and EDS characterization show that the deposition of MgF₂ on AVGCF is not apparently affected by the increase of the acid oxidation time from 2 h（AVGCF-2）to 10 h（AVGCF-10）.MgF₂ particles are more evenly distributed on and around AVGCF at a content of 20 wt%.Comparing the cycling performance of the three 3D current collectors,the results show that MgF₂@AVGCF-ACSWCNT exhibited best cycle stability.Compared to AVGCF-2-ACSWCNT,the CE and cycle stability of MgF₂@AVGCF-2-ACSWCNT are improved by the decoration of AVGCF-2 with an appropriate amount of MgF₂ at 15 wt%,20 wt%and 30 wt%.But the cycle performance decreases when the content is as low as10 wt%or as high as 40 wt%.When the MgF₂ content is 20 wt%,the nucleation overpotential of MgF₂@AVGCF-2-ACSWCNT decreases from 30.1 m V of AVGCF-2-ACSWCNT to 4.6 m V,and the CE fluctuates little within a CE standard deviation of0.25%,and the charge-discharge process is stable for more than 825 cycles.The more oxygen-containing functional groups on AVGCF of 20%MgF₂@AVGCF-10-ACSWCNT favour the uniform deposition/stripping of lithium inside with an average CE of 98.84%and stable cycles for more than 1100 cycles.To further improve the utilization rate of internal space in the 3D current collectors,silver was deposited at the one side of 20%MgF₂@AVGCF-2-ACSWCNT via magnetron sputtering.The effect of deposited silver on lithium deposition/stripping was investigated.For 20%MgF₂@AVGCF-2-ACSWCNT/Ag current collector,gradiently distributed silver directs lithium deposition from the bottom to the top.This leads to a high average CE of 98.85%and a long life of～750 cycles at 1 mA cm^-2 and 1 mAh cm^-2.更多还原