【作者】 李焕新；

【导师】 旷亚非；

【作者基本信息】 湖南大学 ， 化学工程与技术， 2019， 博士

【摘要】 二次电池不仅是能量转化与储存体系中的重要储能装置,还是移动电子设备的关键动力系统。尤其是当下,新能源电动汽车技术正日渐成熟,而作为其动力核心的电池技术显得尤为重要。锂离子电池已经成功商业化并在动力电池市场占据着重要地位。尽管相比于燃油汽车而言,新能源电动汽车有诸多优势,但其续航里程,使用寿命,充电速率,安全性能等方面的性能仍然难以满足市场的需求。这些方面性能的提升可以从两个方面入手:（1）进一步优化市场上商业化的锂离子电池;（2）探索新型的电化学储能体系。二次电池的能量密度,功率密度,循环寿命及安全性能是制约其发展的几大因素。本论文以碳材料为基础,通过掺杂、改性和复合等方法制备出系列具有不同组成与结构的新型碳基纳米材料,并将其应用于新型二次电池、电化学超级电容器、新型水系铁离子电池等系统,以改善其能量密度、功率密度或循环稳定性能,取得了系列创新性的研究结果。具体如下:（1）设计制备了性能优异的新型锂离子电池负极材料。结合分子束前驱体模板法和后续高温热处理技术,制备出MnO量子点镶嵌的多壁碳纳米管（MnO@CHNTs）复合材料。表征结果表明:该碳纳米管长度可达数微米,直径¹00nm,管壁厚度³0 nm,且大量2-3 nm的MnO量子点均匀镶嵌在碳纳米管管壁中,与普通石墨碳材料形成稳定的异质结构;石墨碳材料的层间距扩大到0.41 nm,远大于石墨的层间距（0.34 nm）。将MnO@CHNTs复合材料应用于锂离子电池负极材料,可以实现28.3 s快速充电,且负极材料在50 A g^-1电流密度下经100次循环后比容量高达392.8 mAh g^-1（高于商业化石墨负极的比容量）。（2）构建了新型钠/钾离子电池并研究了电化学性能。将所制备的MnO@CHNTs复合材料应用于新型钠/钾离子电池中,发现MnO量子点的引入不仅减小了钠/钾离子在石墨层间的迁移能垒,同时还增强了复合材料对钠/钾离子的吸附能力,从而使其作为负极材料表现出优异的容量和倍率性能:在钠离子电池中,2 A g^-1电流密度下,首圈容量为348.8 mAh g^-1,1000次循环后仍保留了223.0 mA h g^-1,远高于纯石墨碳和MnO本身作为钠离子电池负极材料时的容量。作为钾离子电池负极时,在20 A g^-1的电流密度下循环500圈,其容量可稳定保持在220.6 mAh g^-1,且库伦效率接近100%,相当于在39.6秒内可将电池完全充满,可用于构建高能量密度,高功率密度和长循环寿命的新型钾离子电池。（3）设计制备了新型石墨烯-对苯基-石墨烯（GPG）纳米材料,探讨了其作为钾离子电池和铝离子电池电极材料的应用。利用重氮化反应将对苯基通过化学键连接在氧化石墨烯的层间,然后通过高温热处理使其充分还原,最终得到新型的GPG纳米材料。由于对苯基以化学键的形式连接在石墨烯层间,石墨烯的层间距显着扩大至⁰.56 nm,这有利于离子在其层间快速迁移。通过构建钾离子和铝离子电池,分别探究了阳离子（K⁺）和（AlCl₄^-）阴离子在其中的迁移情况,结果表明:层间距扩宽后,阴阳离子在GPG层间可以更快地迁移,其构建的钾离子电池在20 A g^-1的高电流密度下仍能保持242.6 mAh g^-1的容量（在43.7秒内完成充电）;铝离子电池在10 A g^-1的电流密度下保持了78.2 mAh g^-1的容量（28.1秒完全充电）。（4）设计制备了新型石墨烯-联苯基-石墨烯（GBG）及研究了其电容性能。还原的氧化石墨烯由于易多层堆叠,使得真实比表面积下降,因而双电层电容远低于理论值。经联苯基桥连的GBG中,石墨烯被连接成一个整体,而片层之间由于联苯基的引入不会再发生堆叠,当其用作超级电容器电极材料时,带电粒子可以在石墨烯的两个面上吸附形成双电层,因此GBG显示出优异的容量和倍率性能。1 A g^-1的电流密度下,在6 M的KOH水系电解液中,GBG的比容量可达446.8 F g^-1;在有机电解液体系中,两电极条件下其比容量为233.6 F g^-1。同时,GBG可实现快速充电,将其在10 A g^-1的高电流密度充电（56.8 s充满）,0.5 A g^-1的电流密度下放电,其库伦效率达99.9%,且能量密度高达118.2 Wh Kg^-1的,非常接近一般锂离子电池的能量密度,在充放电循环5000次后容量保留率可达98.1%,是一种能量密度,功率密度及循环性能都颇具有应用前景的储能设备。（5）研究了Fe₃C-MC复合材料作为锂硫电池正极载体时活性硫的动力学转化机制及其电化学性能。系统分析研究了锂硫电池正极活性材料硫还原的动力学转化机制,探讨了限制其快速转化的关键因素。基于分析结果,并结合理论计算,设计制备了均匀生长于多孔碳（MC）表面的超薄Fe₃C纳米片（Fe₃C-MC）。其中,多孔碳（MC）有助于高载量活性硫的负载和分散,Fe₃C纳米片不仅可以高效地吸附固定还原过程中产生的可溶性多硫化锂,而且可以实现多硫化锂的快速催化转化过程。结果表明:以Fe₃C-MC作为硫正极的锂硫电池,在0.5C的电流密度下进行1000次循环后,仍可保持920 mA h g^-1的容量;即使在5C的高电流密度下,仍能保持727 mA h g^-1的容量。由此表明,Fe₃C-MC可显著提高了锂硫电池的容量,倍率和循环稳定性能。（6）构建了新型水系铁离子电池体系并研究了其电化学性能。首次实现了可稳定充放电的水系铁离子电池体系。该体系中,Fe³⁺/Fe²⁺和Fe²⁺/Fe分别作为铁离子电池正负极的氧化还原电对,阴离子交换膜作为电池隔膜,金片和铁片分别作为正负极的电极。由于使用了水系电解液,离子可在电解液中快速迁移,使得铁离子电池可实现快速充放电。此外,以石墨电极作为正负极,利用聚甲基丙烯酰氧乙基三甲基氯化铵（METAC）凝胶取代水溶液电解液,可以实现全铁离子电池的充放电循环。该新型铁离子电池无毒无害、对环境友好、且成本低廉,在大规模储能体系中具有很好的应用前景。更多还原

【Abstract】 Secondary batteries are not only the important devices for energy conversion and storage systems,but also the key power for the mobile electronic equipment.Especially for now,as the electric vehicle technology getting mature,the development of battery technology is the top priority.Lithium-ion batteries have been successfully commercialized and occupied the dominant position in the battery market.Although the electric vehicles possess many advantages over fuel vehicles,their safety performance,cruising mileage,and charging rate are still difficult to meet market demands.The improvement of performances in these aspects could be started from two aspects:1.Further optimizing the commercial lithium-ion battery in the commercial market;2.Exploring new secondary battery systems.The energy density,power density,cycle life and safety performan ce of secondary batteries are several factors that constrain their development.Here,series of new carbon-based nanomaterials with different compositions and structures were prepared by doping,modification and compounding methods,which were applied to new secondary batteries,electrochemical supercapacitors,and aqueous Fe-ion battery systems.Series of innovative research results have achieved in such energy storage systems with improved energy density,power density or cycle stability.Details are as follows:（1）Design and prepare a new lithium ion battery anode material to achieve its fast charging performance.MnO inlaid multi-walled carbon nanotubes（MnO@CHNTs）composites were prepared by combining molecular beam precursor template method and subsequent high temperature heat treatment.The characterization results show that the carbon nanotubes can reach several micrometers in length,with diameter about 100 nm and wall thickness about 30 nm,and a large number of 2-3 nm MnO quantum dots are uniformly embedded in the graphite carbon of carbon nanotube walls.The MnO@CHNTs composite forms a stable MnO-graphite heterostructure,increasing the layer spacing of the graphite carbon material to 0.41nm,which is much larger than that of pure graphite（0.34 nm）.Therefore,when MnO@CHNTs composite material served as lithium-ion battery anode,it can be fully charged within 28.3 s,and the specific capacity of anode material is up to 392.8 mAh g^-1 at current density of 50 A g^-1 after 100 cycles（higher than commercial graphite anode）.（2）Construction of a new fast rechargeable sodium/potassium ion battery with prepared MnO@CHNTs composites as anodes.It was found that the MnO quantum dots not only reduced the migration energy barrier of sodium/potassium ions b etween the graphite layers,but also enhanced the adsorption energy towards sodium/potassium ions.Therefore,it delivers excellent capacity and rate performance in the sodium ion battery,demonstrating a capacity of 348.8 mAh g^-1 for the first circle at the current 2 A g^-1,and remains 223.0 mA h g^-1 after 1000 cycles（much higher than the capacity of pure graphite carbon and MnO itself as anodes for sodium ion batteries）.Meanwhile,in potassium ion battery,its capacity can be stably maintained at 220.6 mAh g^-1 after 500 cycles at a current density of 20 A g^-1,meaning a 39.6 seconds charging rate,and the coulomb efficiency is close to 100%,which demonstrates that Fe₃C-MC can significantly improve the capacity,rate and cycle performances of lithium-sulfur batteries.（3）Design and preparation of novel graphene-p-phenyl-graphene（GPG）nanomaterials,and investigation of their applications as potassium and aluminum ion battery electrode materials.The diazotization reaction is carried out to chemically bond the p-phenyl group to the graphene oxide layer,and then completely reducing it by high-temperature heat treatment to obtain a novel GPG nanomaterial.Since the p-phenyl group is chemically bonded between the graphene layers,the interlayer spacing of the graphene is significantly expanded to⁰.56 nm,which facilitates rapid migration of ions between the layers.By constructing potassium ion and aluminum ion batteries,the migration of cation（K⁺）and（AlCl₄^-）anions in GPG was investigated respectively.The results show that the anion and cation can migrate faster between GPG layers after the interlayer spacing is widened.Therefore,the constructed potassium ion battery and aluminum ion battery can be fully charged in43.7 and 28.1 seconds,respectively.（4）Design and preparation of novel graphene-biphenyl-graphene（GBG）and its capacitance properties.The reduced graphene oxides are often stacked in multiple layers,resulting in a decrease in the specific surface area,and thus the electric double layer capacitance is always much lower than the theoretical value.However,the graphene layers are integrated together in the biphenyl bridged GBG,and the interlayers would not be stacked due to the introduction of biphenyl.When the GBG used as a supercapacitor electrode material,ions could be access to the interlayers of graphene,forming electrical double-layer on both two sides of grapheme.Thus,the GBG shows excellent capacity and rate performance.The specific capacity of GBG can reach 446.8 F g^-1 in 6 M KOH aqueous electrolyte at a current density of 1 A g^-1;while in the organic electrolyte system,the specific capacity is 233.6 F g^-1 under two-electrode system.At the same time,GBG achieves fast charging rate when charging it at a high current density of 10 A g^-1（56.8 s full charge）,and discharging at a current density of 0.5 A g^-1,the coulomb efficiency reaches 99.9%and an energy density is up to 118.2 Wh Kg^-1（very close to the energy density of general lithium-ion batteries）.After 5,000 cycles of charge and discharge cycles,the capacity retention rate remains 98.1%,which makes it a promising fast rechargeable energy storage device.（5）Investigation on the kinetic conversion mechanism and electrochemical performance of active sulfur in Fe₃C-MC composites as cathode host for lithium-sulfur batteries.The kinetic conversion mechanism of sulfur reduction in lithium-sulfur battery cathode was systematically analyzed,and the key factors limiting its rapid conversion were discussed.Based on the analysis results,and combined with theoretical calculation,an ultra-thin Fe₃C nanosheets uniformly growing on the surface of porous carbon（Fe₃C-MC）was designed and fabricated for the sulfur host in lithium-sulfur battery.Among them,porous carbon（MC）contributes to the dispersion of high-loading active sulfur species,and Fe₃C nanosheets can not only efficiently adsorb soluble lithium polysulfide produced during the reduction process,but also achieve rapid catalytic conversion process for lithium polysulfide.The results show that the lithium-sulfur battery with Fe₃C-MC as the sulfur positive electrode maintains the capacity of 920 mA h g^-1 after 1000 cycles at a current density of 0.5C,and even at the high current density of 5C,it still remain s a capacity of 727 mA h g^-1.Therefore,Fe₃C-MC accelerates the kinetic conversion process of sulfur reduction,which significantly improves the capacity,rate performances and cycle stability of lithium-sulfur batteries.（6）Construction of novel aqueous Fe-ion battery systems.Here,for the first time,an aqueous rechargeable Fe-ion battery is realized.Fe³⁺/Fe²⁺and Fe²⁺/Fe are used as the redox couples with gold and iron sheets as the electrodes for the cathode and anode electrodes,respectively,and the anion exchange membrane is selected as the battery separator.Since the electrolyte is aqueous,ions can rapidly migrate in the electrolyte,so the Fe-ion battery can achieve rapid charging and discharging rates.In addition,by using graphite as electrodes and a polyethyl methacrylate oxyethyl trimethyl ammonium chloride（METAC）gel as electrolyte instead of the aqueous solution,a rechargeable whole-Fe-ion battery was realized.The new Fe ion battery is non-toxic,environmental friendlyness,and low-cost system,which exhibits promising application prospect in large-scale energy storage systems.更多还原