【作者】 唐宏；

【导师】 郭荣辉；

【作者基本信息】 四川大学 ， 纤维技术与工程， 2021， 硕士

【摘要】 锂离子电池具有使用寿命长、能量密度高、质量轻、安全性好和污染低等优点,是一种非常重要的可充电电池,已广泛用于各种便携式电子设备、新能源电动汽车和电网系统。然而,随着对电能储存设备需求的增加导致人们对高能量密度锂离子电池需求也快速增长,促使人们开始对高能量密度和优异循环性能的新型电极材料的开发。在电极材料中,钴锌氧化物因其高的理论容量而具有作为高性能电极材料的潜力。本文围绕制备高容量钴锌及氧化物体系的电极材料进行研究,利用静电纺丝和氩气高温退火制备Co@Zn@碳纳米纤维复合材料;利用静电纺丝、氩气高温退火和低温氧化方法制备Zn Co₂O₄@碳纳米纤维复合材料和Ti3C2@Zn Co₂O₄@碳纳米纤维复合材料;利用水热反应和氩气高温退火制备Ti3C2@Co O/Zn O复合材料,并系统研究它们应用于锂离子电池负极材料时的锂离子存储性能。本文具体研究内容和结果如下:（1）通过静电纺丝制备金属离子Co²⁺@Zn²⁺@聚丙烯腈（PAN）纳米纤维,然后在氩气（Ar）中煅烧后制备得到Co@Zn@碳纳米纤维复合材料,结果表明,金属离子Zn²⁺和Co²⁺被还原成单质并均匀的分散在纤维内部,此外Co还以纳米簇形式镶嵌在碳纳米纤维内部。Co@Zn@碳纳米纤维复合材料具有独特稳定的纳米纤维结构,同时PAN碳化后产生的大量杂原子N掺杂在碳纳米纤维内部,它能够显著提升Co@Zn电子导电性,此外,均匀分散的Co@Zn活性位点能够在反复的锂离子嵌入/脱嵌过程中不发生聚集。结果表明,在电流密度为0.1A g-1时,Co@Zn@碳纳米纤维电极具有高达890.513 m A h g-1的可逆容量;在1 A g-1和2 A g-1时,容量分别有497.509 m A h g-1和376.75 m A h g-1,表明电极具有优异的倍率性能;此外,Co@Zn@碳纳米纤维电极在大电流密度下表现出优异的长循环稳定性,能在0.5 A g-1进行150次循环后仍具有527.412 m A h g-1的容量,且能在1 A g-1进行320次循环后仍保持458.435 m A h g-1的容量。（2）将Co@Zn@碳纳米纤维复合材料在空气氛围中进行低温氧化处理得到Zn Co₂O₄@碳纳米纤维复合材料。结果表明,Zn Co₂O₄以纳米簇形式稳定镶嵌在碳纳米纤维内部,有利于在反复充放电过程中保持结构稳定而不发生活性位点的聚集;同时,PAN碳化后产生的大量杂原子N有利于提升导电性以及锂离子亲和能力。此外,Zn Co₂O₄@碳纳米纤维复合材料具有大的比表面积,它可为锂离子在材料内插入/抽出提供更多的活性位点。结果表明,Zn Co₂O₄@碳纳米纤维电极在电流密度为0.1 A g-1时具有高达1053.881 m A h g-1容量;另外,该电极具有优异的倍率性能,在3 A g-1电流密度下仍保持505.145 m A h g-1容量并在电流密度回到0.1 A g-1时仍保持946.998 m A h g-1;同时,该电极具有好的循环稳定性,在0.5 A g-1的电流下循环135次后容量为635.175 m A h g-1,在1 A g-1循环300次后保持424.615 mA h g-1的容量。（3）在静电纺丝液中加入二维材料Ti3C2 MXene,通过静电纺丝制备纳米纤维,然后在Ar气中高温退火碳化,最后在空气中低温氧化得到异质结构的Ti3C2@Zn Co₂O₄@碳纳米纤维复合材料。结果表明,Ti3C2 MXene促进Zn Co₂O₄纳米颗粒在碳纳米纤维表面和内部均匀生长纳米颗粒。异质结构的纤维具有丰富的多孔性和Zn Co₂O₄纳米颗粒均匀分散在碳纳米纤维内部,有利于提供大量的活性位点用于锂离子在材料内发生嵌入/脱嵌反应。碳纳米纤维内部的Ti3C2能进一步提升Zn Co₂O₄电子电导率和锂离子迁移率。Zn Co₂O₄纳米颗粒均匀分散在纤维内部和表面有助于抑制其在循环过程中活性位点发生聚集而造成容量衰减。相对于Ti3C2@Co@Zn@碳纳米纤维电极,Ti3C2@Zn Co₂O₄@碳纳米纤维电极展示出更高的可逆容量（在0.1 A g-1时具有970.794 m A h g-1的可逆容量）、优异的倍率性能（在2 A g-1时传递出488.073 m A h g-1的容量）和循环稳定性（在0.5 A g-1循环60次后保持539.699 m A h g-1的容量和在1.0 A g-1循环120次后保持460.486 m A h g-1的容量）,表明利用Ti3C2 MXene独特的锂离子亲和性优点来改进钴锌金属氧化物电化学性能具有巨大的潜力。（4）通过将CoO/ZnO纳米点均匀的锚定在Ti3C2 MXene的表面上得到分层异质结构的Ti3C2@Co O/Zn O复合材料,从而有效解决Co O和Zn O的结构不稳定性和低电导率导致其容量快速衰减。Ti3C2具有出色的电化学性能,有效提高了Co O/Zn O的电导率并促进锂离子迁移,而均匀地锚定在Ti3C2表面上的Co O/Zn O纳米点有效地抑制了循环过程中Co O/Zn O纳米点的聚集。Ti3C2@Co O/Zn O电极用作锂离子电池的负极时,它表现出出色的倍率性能（在3 A g-1时容量保持498 m A h g-1,并当电流再次控制在0.1 A g-1时保持794.3 m A h g-1循环110圈）,具有极高的可逆容量（在0.2 A g-1电流密度下进行120圈循环后,仍能保持1069 m A h g-1的容量）和出色的循环性能（0.5 A g-1保持1052mA h g-1容量循环200圈,1 A g-1保持627 mA h g-1容量循环300圈）。本文制备得到Co@Zn@碳纳米纤维复合材料、Zn Co₂O₄@碳纳米纤维复合材料、Ti3C2@Zn Co₂O₄@碳纳米纤维复合材料和Ti3C2@Co O/Zn O复合材料,它们用作锂离子电池负极材料时表现出优异的电化学性能,在锂离子储存领域有着广泛的应用前景。更多还原

【Abstract】 Lithium-ion batteries are a very important type of rechargeable batteries due to their high energy density,long service life,light weight,good safety and low pollution,so it has been widely used in various portable electronic devices,new energy electric vehicles and power-grid systems.Nevertheless,the rapidly increasing demand for lithium-ion batteries with high energy density has prompted the pursuit of finding electrode materials with high energy density and excellent recyclability.Among the electrode materials,cobalt-zinc oxide has the potential to become excellent electrode materials.The thesis focuses on the preparation of high-performance cobalt-zinc-based electrode materials.The Co@Zn@carbon nanofiber composites was prepared by electrospinning and annealing.The Zn Co₂O₄@carbon nanofiber composites and Ti₃C₂@Zn Co₂O₄@carbon nanofiber composites were prepared by electrospinning,annealing and oxidation.Ti₃C₂@Co O/Zn O composites were obtained by hydrothermal reaction and annealing.Their lithium ion storage performance was systematically studied when being used as anode electrode for lithium-ion batteries.The research content and results are as follows.（1）The metal ion Co²⁺@Zn²⁺@PAN nanofibers were prepared by electrospinning,and then calcined in Ar to prepare Co@Zn@carbon nanofiber composites.The metal ions Zn²⁺and Co²⁺were directly reduced to metal state.The Co was also embedded in the carbon nanofibers as nanoclusters.The Co@Zn@carbon nanofiber composites have stable nanofiber structure and the N-doped carbon nanofibers can significantly improve the electronic conductivity of Co@Zn.In addition,the uniformly dispersed active sites of Co@Zn can avoid its aggregate during being repeated intercalation/deintercalation of lithium ions.As a result,the Co@Zn@carbon nanofiber composites has excellent electrochemical performance when being used as an annode electrode of lithium-ion batteries.A reversible capacity of 890.513 m A h g^-1 was delivered at 0.1 A g^-1.Additionally,the electrode has excellent rate performance,which can deliver a capacity of 497.509 m A h g^-1 and 376.75 m A h g^-1at 1 A g^-1 and 2 A g^-1,respectively.In addition,the electrode also exhibits an excellent long-cycle stability,maintains a capacity of 527.412 m A h g^-1 at 1 A g^-1 after 150cycles,and retains a capacity of 458.435 m A h g^-1 at 1 A g^-1 for 320 cycles.（2）The ZnCo₂O₄@carbon nanofiber composites were obtained by oxidizing Co@Zn@carbon nanofiber composites in the air at low temperature.The Zn Co₂O₄nanoclusters are embedded in the carbon nanofibers to form a stable structure,which is conducive to the stable insertion and extraction of lithium ions in the electrode during repeated charging and discharging.The large amount of heteroatoms N in the carbon nanofibers is beneficial to improve the conductivity of the composites and enhance the lithium ion affinity of the material.Besides,Zn Co₂O₄@carbon nanofiber composites can provide a large specific surface area to provide more active sites for electrochemical reactions.Benefiting from this advantage,Zn Co₂O₄@carbon nanofiber composites exhibit excellent rate performance and cycle stability when being used as anode electrode.The Zn Co₂O₄@carbon nanofiber electrode can deliver a capacity of 1053.881 m A h g^-1 when the current density is 0.1 A g^-1.In addition,the electrode has excellent rate performance,which maintains 505.145 m A h g^-1 at 3 A g^-1 and delivers 946.998 m A h g^-1 when the current density returns to 0.1 A g^-1 again.Moreover,the electrode has excellent recyclable performance,which delivers 635.175m A h g^-1 at 0.5 A g^-1 over 135 cycles and maintains 424.615 m A h g^-1 at 1 A g^-1 over300 cycles.（3）The Ti₃C₂@Zn Co₂O₄@carbon nanofiber composites with a heterogeneous structure were prepared by adding Ti₃C₂ MXene to the electrospinning solution through electrospinning,annealing in Ar gas and being oxidized in the air.The Ti₃C₂MXene promotes the growth of Zn Co₂O₄ nanoparticles in carbon nanofibers.The Ti₃C₂@Zn Co₂O₄ carbon fiber with heterostructure has rich porosity and the Zn Co₂O₄nanoparticles are uniformly dispersed inside the carbon nanofibers,which is benefitial to provide more reactive sites for the insertion and extraction of lithium ions.Additionally,the heteroatom N and the Ti₃C₂ in the carbon nanofibers can effectively enhance the electronic conductivity and improve the mobility of lithium ions of Zn Co₂O₄.The uniform dispersion of Zn Co₂O₄ nanoparticles in carbon nanofiber helps to inhibit the aggregation of active sites during the cycle.As a result,the Ti₃C₂@Zn Co₂O₄@carbon nanofiber electrode exhibits a higher reversible capacity(deliver a capacity of 970.794 m A h g^-1 at 0.1 A g^-1),an excellent cycle stability(maintain a capacity of 539.699 m A h g^-1 at 0.5 A g^-1 after 60 cycles and 460.48 m A h g^-1 at 1.0 A g^-1 after 120 cycles),and an outstanding rate performance(488.073 m A h g^-1 is delivered at 2 A g^-1)when being used as an annode electrode,which shows that Ti₃C₂ MXene has a great potential for improving the electrochemical performance of cobalt-zinc metal oxides due to its unique lithium ion affinity.（4）The Ti₃C₂@Co O/Zn O composites with a layered heterogeneous structure were obtained by uniformly anchoring the Co O/Zn O nanodots on the surface of Ti₃C₂MXene,thereby effectively solving the structural instability and low conductivity of Co O and Zn O cause their capacity to fade rapidly.The Ti₃C₂ has an excellent electrochemical performance which effectively enhances the electrical conductivity of Co O/Zn O and facilitate lithium ion mobility.Additionally,the Co O/Zn O nanodots which are uniformly anchored on the Ti₃C₂ surface can effectively inhibit the aggregation of Co O/Zn O nanodots in the process of during cycling.As a result,the Ti₃C₂@Co O/Zn O electrode exhibits a high reversible capacity(1069 m A h g^-1 for over 120 cycles at 0.2 A g^-1),excellent cycleability(1052 m A h g^-1 for over 200 cycles at 0.5 A g^-1,and 627 m A h g^-1 for over 300 cycles at 1 A g^-1)and exceptional rate capacity(498 m A h g^-1 at 3 A g^-1,and 794.3 m A h g^-1 after 110 cycles when the current is controlled at 0.1 A g^-1 again).In this study,Co@Zn@carbon nanofiber composites,Zn Co₂O₄@carbon nanofiber composites,Ti₃C₂@Zn Co₂O₄@carbon nanofiber composites and Ti₃C₂@Co O/Zn O composites were prepared,which have excellent electrochemical properties such as high capacity,excellent rate performance and good cycle stability when being used as an anode electrode of lithium ion battery.They have a wide range of application prospects in the field of lithium ion storage,which also provides an important reference for the preparation of high-performance lithium ion battery anode materials.更多还原