CAS OpenIR
基于过渡金属氧化物的微纳多级复合材料的设计制备及储锂性能研究
喻嘉
Subtype博士
Thesis Advisor陈仕谋
2018-07
Degree Grantor中国科学院研究生院
Degree Name博士
Degree Discipline化学工程
Keyword锂离子电池,过渡金属氧化物,微纳多级复合材料,液相合成
Abstract

近年来,业界对二次电池能量密度、功率密度、循环寿命等要求越来越高,传统的锂离子电池体系由此面临很大挑战。作为核心组件之一,电极材料很大程度上决定了锂离子电池的整体性能,而广泛使用的基于嵌入储锂机理的石墨负极由于容量低等特点已经难以满足要求。而基于转化机理的过渡金属氧化物拥有更高的比容量,灵活的组分结构可调节性,丰富的来源,作为一类颇有发展潜力的新型负极材料受到了广泛关注。同时,设计多级空间构造与多重组成分布,已经成为功能材料领域的有效设计策略。因此,本论文以锌-钴基双金属与钴基单金属氧化物为研究主体,围绕着微纳多级复合材料的设计、简便可控的制备工艺、高效的储锂性能等主题展开,成功制备了一系列具备多级结构与复合组分的电极材料,并表现出优秀的电化学性能。同时研究了微纳多级复合材料的制备机理与构筑策略,探索了其高效储锂机制,并通过DFT计算、原位TEM等手段研究其结构与组分优势。具体研究包括以下五个部分工作:(一)提出了基于二维镶嵌&三维梯度结构设计的双金属氧化物双重复合策略:以自然镶嵌显性现象启发的Zn1-xCoxO/ ZnCo2O4二维镶嵌式超薄介孔纳米片为结构单元,组装成三维的锌-钴多级框架。并通过一系列组成和结构上逐渐演化的衍生框架发展出高效的one-pot制备工艺。经DFT验证,受益于双金属互掺杂效应的Zn1-xCoxO与ZnCo2O4的电子/离子传输得到很大增强。更重要地,独特的二维镶嵌复合模式可产生阶梯式缓冲和电化学协同效应,从而实现镶嵌对之间的相互稳定和活化。此外,由内至外的Zn-Co浓度梯度、丰富的氧空位与介孔特性进一步提高了储锂容量和稳定性。该框架在100 mA g?1电流密度下比容量可达~1000 mA hg?1,更在高倍率长循环(1000 mA g?1,800圈)测试中拥有很高的容量保持率。(二)设计了一种仿神经元结构的多尺度协同&二维组装材料,以同时克服微米电极材料的低倍率性能与纳米电极材料的低振实密度缺点。采用了氟诱导的双金属液相反应体系,基于one-pot工艺及后续热处理制备出理想的结构:以Zn1-xCoxO微米星形结构的多个棱柱顶端为基底,多束ZnyCo3-yO4超精细区域纳米线阵列沿着二维方向独立成簇生长。一方面,独特的二维组装模式有利于保留微米星形结构的高振实密度优势;另一方面,多尺度协同效应、高效的传导网络和掺杂作用将会显著提高微米星形结构的高速储锂能力。电化学测试显示,该仿神经元结构同时获得了高达~1.55 mA h cm?2优秀的面积比容量(1.0 mA cm?2,500圈)与倍率性能,并用原位TEM、动力学分析等手段探究了其性能优势原因。(三)受须根结构的启发,采用一个与仿神经元结构工作相似的氟诱导双金属反应体系,设计并合成了在铜网基底上分级生长的ZnxCo3-xO4/Zn1-yCoyO二元多级协同纳米阵列。在Zn1-yCoyO纳米棱柱阵列的顶部,超精细的ZnxCo3-xO4区域纳米线阵列沿着与棱柱一致的方向有序集中生长,构成一个仿须根结构的自支撑二元协同储锂体系,并分别作为其中的支撑单元与功能单元。ZnxCo3-xO4/Zn1-yCoyO多级阵列作为一个无需导电剂与粘结剂的集成电极,在500 mA g?1的电流密度下可以保持超过800 mA h g?1的高容量,在比容量、倍率性能、稳定性等方面远优于单一结构的锌基纳米棱柱阵列或钴基纳米线阵列。(四)通过一个连续转化式制备路径,在3D泡沫镍上生长了由Si/C修饰的Co3O4纳米线阵列,作为一个仿玉米结构的三元多级复合自支撑体系。采用离子液体辅助电沉积的手段,实现了超细Si纳米颗粒在Co3O4纳米线基底上的分散式原位生长(Volmer-Weber岛式生长模式)。分散式Si纳米颗粒(玉米粒)和无定形碳包覆层(玉米皮)分别作为中间增强单元和外部保护单元,发挥协同效应从而有效增强了作为内部基本单元的Co3O4纳米线(玉米芯)的容量和稳定性,在100 mA g?1的电流密度下拥有接近1000 mA h g?1的高容量。(五)设计并制备了以Co基二维纳米片为基本单元,用多层堆叠形式组装而成,并外层包覆碳的千层饼式Co3O4/C微纳多级复合结构。纳米级的多孔片状结构单元以密堆积方式形成微米级整体结构,显著地提高了振实密度并防止了SEI膜的过度生长;同时片层结构可有效缩短电子/离子传输路径并缓冲嵌锂过程的体积膨胀;碳包覆工艺则进一步改良了电极/电解液界面。该结构在比容量、倍率性能、循环稳定性等方面获得了均衡的性能表现,尤其拥有优异的容量保持率与面积比容量。;Recently, the demands on energy density, power density and cycle life are becoming higher for secondary batteries, thus traditional lithium ion batteries (LIBs) have been facing great challenges. As one of core components, the electrode material determines the overall LIB performance to a large extend, however currently wide-used graphite anode becomes difficult to satisfy the demands due to drawbacks including low specific capacity. By contrast, transition metal oxides (TMOs) have attracted plenty of attention as promising next-generation LIB anode materials, owed to advantages such as higher specific capacities, flexible compositional and structural adjustability, rich sources, etc. Meanwhile, imitating the hierarchical architecture and composition arrangement of nature-inspired structures, has emerged as an efficient strategy for designing functional materials. Therefore, based on Zn-Co-based bimetal oxide and Co-based oxide systems, the researches of this dissertation centered on following main themes: design of nature-inspired hierarchical composite materials, facile and controllable preparation process, and efficient Li storage performance. A series of electrode materials with micro-nano hierarchical design and composite components were successfully synthesized, which delivered good electrochemical properties. Besides, the preparation mechanisms and building strategies of micro-nano hierarchical materials were comprehensively studied, accompanied with efficient Li storage processes, and their structural and compositional advantages were further verified by DFT calculations, in situ TEM, etc. The main research content contained five parts as follows:(1) A bimetal oxide dual-composite strategy based on 2D-mosaic & 3D-gradient design is proposed: Zn1-xCoxO/ZnCo2O4 2D-mosaic-hybrid mesoporous ultrathin nanosheets inspired by natural mosaic-dominance phenomena, were served as building blocks to assemble into a 3D Zn-Co hierarchical framework. Moreover, a series of derivative frameworks with highly evolution in composition and structure were controllably synthesized, based on which a facile one-pot synthesis process can be developed. As verified by DFT calculations, the kinetics of electron/ion transport of both Zn1-xCoxO and ZnCo2O4 was greatly enhanced owed to bimetal mutual-doping. More importantly, unique 2D-mosaic-hybrid mode gave rise to ladder-type buffering and electrochemical synergistic effect, thus realizes mutual stabilization and activation between the mosaic pair. Besides, the inside-out Zn?Co concentration gradient, rich oxygen vacancies and mesoporous nature further enhanced Li storage capacity and stability. As a result, a capacity as high as ~1000 mA h g–1 was attained with a current density of 100 mA g?1, more, while excellent capacity retention was observed during high-rate and long-term cycle (1000 mA g–1, 800 cycles). (2) A neuron-inspired electrode material design with multi-scale synergistic and two-dimensional assembled structure was proposed, aiming at tackling the low tap density and poor rate capability problems of nanosized and micronsized materials, respectively. Desired structure was synthesized based on a fluorine-induced bimetal reaction system similar to above fibrous-root-inspired work. Multiple ZnxCo3-xO4 ultrafine regional-nanowire-arrays grow separately in limited two-dimensional directions, from the multiple top platforms of a Zn1-yCoyO micron-star. On one hand, unique two-dimensional assembly mode help to retain the tap density advantage originated from micron-star part. On the other hand, the high rate Li storage capability of micron-star prat could be significantly improved, benefiting from multi-scale synergistic effect, effective transport network and bimetal mutual-doping. As expected, superior areal specific capacities of ~1.55 mA h cm?2 (1.0 mA cm?2, 500cycles) and largely enhanced rate capability were simultaneously obtained. In addition, in situ TEM and kinetic analysis further illustrated the mechanism of performance superiority. (3) Inspired by natural fibrous-root structure, hierarchical ZnxCo3-xO4/Zn1-yCoyO binary synergistic nanoarrays were designed and synthesized on Cu mesh substrates based on a facile one-pot, successive-deposition process, utilizing a fluorine-induced bimetal liquid phase reaction system. From the top platforms of Zn1-yCoyO nanorod arrays, ultrafine ZnxCo3-xO4 regional-nanowire-arrays grew orderly in a direction parallel to the nanorods. The two parts made up a self-supporting binary synergistic Li storage system with fibrous-root-inspired structure, and served as the supporting unit and and functional unit respectively. As an integrated LIB anode without binder or conductive additive, ZnxCo3-xO4/Zn1-yCoyO hierarchical nanoarrays could maintain a high capacity of more than 800 mA h g?1 at a current density of 500 mA g?1, and showed great advantages on specific capacity, rate capability and cycle stability over single zinc-based nanorod arrays or cobalt-based nanowire arrays. (4) Through a sequential transformation route, Si/C-modified-Co3O4 nanowire arrays were constructed on 3D Ni foam, to form a corn-inspired ternary composite hierarchical self-supporting system. An ionic liquid-assisted electrodeposition strategy was employed to realize a discrete in situ fabrication of ultrafine Si nanoparticles onto Co3O4 nanowire substrate, which followed a Volmer-Weber island growth mode. In this synergistic system, corn-kernel-like discrete silicon nanoparticles and corn-husk-like carbon coating layer functioned as the enhancing unit and protecting unit respectively, to improve the capacity and stability of the corn-cob-like Co3O4 nanowire which functioned as the basic unit. And a special capacity nearly 1000 mA h g?1 was obtained at a current density of 100 mA g?1.(5) Aiming at obtaining dense packed and high stable Li storage simultaneously, a “thousand-layer-cake” Co3O4/C nano-mciro hierarchical stack structure was prepared. As the building blocks, the nanosized porous lamellar-structures were densely stacked to assemble into micronsized overall dimension, which obviously improved the tap density and prevents excess formation of SEI film. The lamellar-structure provided shortened electron/ion transport pathway and buffered the volume expansion during lithiation. The carbon coating process further improved the electrode/electrolyte interface. This thousand-layer-cake structure exhibited a capacity of about 740 mA h g?1 with a current density of 100 mA g?1, and maintained stable at neraly 700 mA h g?1 after 500 cycles with a high current density of 500 mA g?1, rending excellent long-term cycle stability and rate performance. 

Language中文
Document Type学位论文
Identifierhttp://ir.ipe.ac.cn/handle/122111/26876
Collection中国科学院过程工程研究所
研究所(批量导入)
Recommended Citation
GB/T 7714
喻嘉. 基于过渡金属氧化物的微纳多级复合材料的设计制备及储锂性能研究[D]. 中国科学院研究生院,2018.
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