锂—氧电池碳基正极材料的设计、制备及其性能研究

发布时间：2018-05-06 08:49

本文选题：锂-氧电池 + 正极材料　；参考：《南京航空航天大学》2016年博士论文

【摘要】：可充电锂-氧电池被认为是取代常规锂电池的最有希望的储能介质候选者,其超高的理论能量密度(3485 Wh kg-1),是目前商用锂离子电池(387 Wh kg-1)的8-10倍。目前,由于碳材料或碳基材料具有大的比表面积和孔容,同时具有一定的氧还原(ORR)催化活性及放电产物过氧化锂(Li2O2)的存储空间,所以常被用来作为锂-氧电池的正极材料。然而,碳材料对ORR和析氧催化(OER)的催化性能较差,基于碳材料的正极面临了诸多严峻的挑战,限制了锂-氧电池性能的提升。因此,基于碳材料的优点,我们设想通过设计具有合理的电极结构,并结合高效的双功能催化剂,从而大幅提升锂-氧电池的电化学性能。本论文尝试将廉价、高催化活性的尖晶石型氧化物(Co3O4,NiCo2O4)与多种不同结构的碳材料相结合,并通过对电极结构进行合理设计、调控,构筑了四种碳基正极,研究了电极材料结构、形貌与电催化性能,及作为锂-氧电池正极的电化学性能之间的关系。论文的主要内容介绍如下:1、通过溶剂蒸发诱导自组装法,经800℃氮气结合300℃空气两步热处理,制备得到Co3O4纳米颗粒均匀负载在氮掺杂有序介孔碳上的复合材料(Hollow Co3O4/NOMC),其比表面积大(~650 m2 g-1),介孔有序性好,碳载体石墨化程度高,空心结构的Co3O4纳米颗粒结晶度良好。电化学测试表明,得益于材料自身特性和结构设计上的优势,Hollow Co3O4/NOMC的起始电位和半波电位分别为-0.15 V和-0.23 V,极限扩散电流密度达到4.99 mA cm-2,显示出良好的ORR催化活性,组装成电池后测得其放电比容量为3472 mAh g-1。此外,通过旋涂法将其与碳纸集流体复合作为无粘结型一体式正极,电极的电子传输能力得到大幅提高,使其可承受大电流(1000 mA g-1)充放电;更多开放的孔洞,使其放电比容量提升至4190 mAh g-1;粘结剂的摒弃减少了副反应的发生,提高了循环稳定性,在200 mAg-1的电流密度下,1000 mAh g-1定容量充放电达72次。2、为提升催化剂的催化活性和利用率,加强碳载体的石墨化程度,通过静电纺丝技术,制备了负载有过渡金属氧化物(Fe2O3,Co3O4,NiCo2O4)的氮掺杂碳纳米纤维(NCF)膜。其中,20 nm左右的氧化物颗粒均匀负载在直径约为250 nm的碳纳米纤维表面,氮元素主要以吡啶型氮的形式掺杂,掺杂量较大(7%)。电化学性能的测试表明,三种复合材料中,NiCo2O4@NCF具有最优的ORR与OER催化性能,得益于NiCo2O4更高的电催化活性。作为锂-氧电池正极材料,基于优良的电催化性能,NiCo2O4@NCF正极极化度最小,放电比容量最大(5304 mAh g-1)。通过对比传统的压片式导电炭黑正极和纯的碳纤维薄膜正极,自支撑无粘结剂型NiCo2O4@NCF正极均表现出更优异的性能,不仅放电容量更大,倍率性能好,循环寿命也显著提升,可稳定循环92次(电流密度:200 mAg-1,定容量1000 mAh g-1)。其优异的性能主要来源于NiCo2O4@NCF的高催化活性,提供了电子高速传输网络的碳纤维薄膜,且无粘结剂引起的副反应,同时丰富的分级孔道利于电解液的浸润、氧气的扩散、及Li2O2的大量储存。3、为近一步提升碳载体的导电性,同时更大限度的发挥NiCo2O4的高效ORR和OER催化活性,通过溶剂热合成法,将NiCo2O4纳米颗粒均匀负载在氮掺杂石墨烯表面(NCO@N-rGO),冷冻干燥后形成三维多孔结构。结构表征显示约为7nm的NiCo2O4均匀锚定在石墨烯表面,负载量达72.4%。与机械混合的NiCo2O4/石墨烯相比,原位合成的NCO@N-rGO复合材料作为锂-氧电池正极材料,表现出更优异的电化学性能。三维多孔的石墨烯不仅可以作为导电网络,而且提供了大量开放的孔道,便于储存大量Li2O2,同时高负载的NiCo2O4纳米颗粒提供了丰富的催化活性位点。因此,NCO@N-rGO放电比容量高达6716 mAh g-1,能在200 mA g-1的电流密度下,定容量1000 mAh g-1,可稳定循环112次。4、在获得高导电性碳载体、高催化活性的催化剂的基础上,为解决碳材料引起的诸多副反应,利用溶剂热法,在碳布(CT)上原位生长针状NiCo2O4纳米线阵列(NCONWAs)。随着溶剂热反应时间的增加,NiCo2O4纳米线的直径和长度显著增加,16h溶剂热反应得到的NCONWAs/CT复合材料中,每一根垂直阵列生长的NiCo2O4纳米线均由颗粒尺寸(7~10 nm)的NiCo2O4颗粒组成,形成的介孔纳米线比表面积达90 m2 g-1,孔径更高达11 nm。NCONWAs/CT复合材料相比于常规需要粘结剂和导电剂的正极材料,4221 mAh g-1的放电比容量高于常规电极的3409 mAh g-1。同时,NiCo2O4纳米线阵列紧密包裹住碳纤维,有效地防止副反应产物Li2CO3的形成,加上其分级的多孔结构和高的催化活性,NCONWAs/CT复合材料可稳定循环200次(电流密度:200 mA g-1),远超过常规电极材料,并可在大电流密度(1000 mA g-1)下,实现稳定充放电。最后,利用碳布基底的柔韧性,以NCONWAs/CT复合材料为正极,构造了柔性的锂-氧电池,可在弯曲过程中实现充放电,并具有优异的倍率性能和循环稳定性。
[Abstract]:Rechargeable lithium - oxygen battery is considered as the most promising candidate for energy storage medium to replace conventional lithium batteries. Its ultra high theoretical energy density (3485 Wh kg-1) is 8-10 times the current commercial lithium ion battery (387 Wh kg-1). At present, the carbon material or carbon based material has a large specific surface area and Kong Rong, and has a certain oxygen reduction (ORR ) the catalytic activity and the storage space of the lithium peroxide (Li2O2) of the discharge products are often used as positive materials for lithium oxygen batteries. However, the catalytic performance of carbon materials for ORR and oxygen evolution Catalysis (OER) is poor. The cathode based on carbon materials faces many severe challenges and limits the performance of lithium oxygen batteries. Therefore, carbon materials are based on carbon materials. In this paper, we try to combine the cheap, high catalytic active spinel oxide (Co3O4, NiCo2O4) with a variety of different structure carbon materials and through the electrode structure. Four kinds of carbon based positive poles were designed and regulated reasonably. The structure, morphology and electrocatalytic properties of the electrode materials were studied, and the relationship between the electrochemical properties of the positive electrode of the lithium oxygen battery. The main contents of the paper were as follows: 1, the self assembly method was induced by solvent evaporation, and the Co was treated by two steps by two steps of nitrogen combined with 300 centigrade air. 3O4 nanoparticles are uniformly loaded on nitrogen doped ordered mesoporous carbon (Hollow Co3O4/NOMC), with a large specific surface area (~650 M2 g-1), good mesoporous order, high degree of graphitization of carbon carriers and good crystallinity of Co3O4 nanoparticles in hollow structures. The electrochemical test chart is shown to benefit from the advantages of the material itself and the structural design advantages, Hol. The starting potential and the half wave potential of low Co3O4/NOMC are -0.15 V and -0.23 V respectively. The limit diffusion current density reaches 4.99 mA cm-2, showing a good ORR catalytic activity. After assembling the battery, the discharge specific capacity is 3472 mAh g-1.. The electrode is combined with the carbon paper collector as an unbonded integral positive pole by spin coating. The electronic transmission capacity is greatly improved, making it able to withstand large current (1000 mA g-1) charging and discharging; more open holes to increase the discharge ratio to 4190 mAh g-1; the abandonment of the binder reduces the occurrence of side reactions and improves the cycle stability. Under the current density of 200 mAg-1, 1000 mAh g-1 capacity is charged and discharged to 72 times.2, The catalytic activity and utilization of the catalyst were enhanced and the degree of graphitization of the carbon carrier was strengthened. By electrospinning, a nitrogen doped carbon nanofiber (NCF) membrane loaded with transition metal oxides (Fe2O3, Co3O4, NiCo2O4) was prepared. Among them, the oxide particles around 20 nm were uniformly loaded on the surface of carbon nanofibers with a diameter of about 250 nm. The elements are doped mainly in the form of pyridine type nitrogen, and the amount of doping is larger (7%). The electrochemical performance test shows that NiCo2O4@NCF has the best catalytic performance of ORR and OER in the three composites, and is benefited from the higher electrocatalytic activity of NiCo2O4. As a cathode material for lithium oxygen battery, the NiCo2O4@NCF positive polarity is the least, based on the excellent electrocatalytic properties. The maximum discharge specific capacity (5304 mAh g-1). By comparing the traditional compression conductive carbon black positive electrode and pure carbon fiber film positive pole, the self supporting NiCo2O4@NCF positive pole without adhesive type shows better performance, not only the discharge capacity is greater, the multiple performance is better, the cycle life is also significantly improved, and the stable cycle is 92 times (the current density: 200 mAg-1). It has a fixed capacity of 1000 mAh g-1). Its excellent performance mainly comes from the high catalytic activity of NiCo2O4@NCF, which provides the carbon fiber film of the electronic high-speed transmission network, and the side effects caused by the non binder. At the same time, the rich hierarchical channel is beneficial to the infiltration of the electrolyte, the diffusion of oxygen, and the large storage of.3 in the Li2O2, for the promotion of the carbon carrier in a close step. Electrical conductivity, at the same time, give full play to the high efficient ORR and OER catalytic activity of NiCo2O4. Through the solvent thermal synthesis, the NiCo2O4 nanoparticles are uniformly loaded on the surface of the nitrogen doped graphene (NCO@N-rGO) and freeze-drying to form a three-dimensional porous structure. The structural characterization shows that the NiCo2O4 uniform of about 7Nm is anchored on the surface of graphene with a load of 72.4%.. Compared with the mechanically mixed NiCo2O4/ graphene, the in-situ synthesized NCO@N-rGO composite exhibits excellent electrochemical performance as a cathode material for the lithium oxygen battery. The three-dimensional porous graphene can not only be used as a conductive network, but also provide a large number of open channels to facilitate the storage of a large number of Li2O2 and high load NiCo2O4 nanoscale. The particles provide a rich catalytic activity site. Therefore, the specific capacity of NCO@N-rGO discharge is up to 6716 mAh g-1, and can be fixed at a capacity of 1000 mAh g-1 at the current density of 200 mA g-1, and can circulate 112 times.4. On the basis of high conductivity carbon carrier and high catalytic activity catalyst, many side reactions caused by carbon materials are solved and solvent is used to use solvent. The needle like NiCo2O4 nanowire array (NCONWAs) was grown on the carbon cloth (CT) by thermal method. The diameter and length of the NiCo2O4 nanowires increased significantly with the increase of the solvent thermal reaction time. In the NCONWAs/CT composites obtained by the 16h solvothermal reaction, each vertical array of NiCo2O4 nanowires grew by the particle size (7~10 nm) NiCo2O4 particles. The mesoporous nanowires have a specific surface area of 90 M2 g-1, and the pore size is up to 11 nm.NCONWAs/CT, compared to the normal material requiring binder and conductive agent, the discharge specific capacity of 4221 mAh g-1 is higher than the 3409 mAh g-1. of the conventional electrode, and the NiCo2O4 nanowire array tightly encapsulated carbon fiber, effectively preventing the side reaction. The formation of the product Li2CO3, with its graded porous structure and high catalytic activity, can be stabilized by NCONWAs/CT composites for 200 times (current density: 200 mA g-1), far exceeding the conventional electrode materials, and can achieve stable charge and discharge at a high current density (1000 mA g-1). Finally, the flexibility of the carbon substrate is used as a NCONWAs/CT composite. For the positive electrode, a flexible lithium oxygen battery is constructed, which can realize charging and discharging in bending process, and has excellent rate performance and cycle stability.

【学位授予单位】：南京航空航天大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TM911.41;TB332

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