聚合物微凝胶模板法制备纳米碳结构电极材料及电化学性能研究

发布时间：2018-07-22 21:18

【摘要】：基于嵌锂的电化学反应,其电极过程动力学取决于Li+离子和电子的迁移速率。人们通常以纳米碳包覆纳米材料同时实现Li+离子和电子的快速迁移,但是每个纳米颗粒上均匀包覆纳米碳层是一项非常困难的事情。现行锂离子电池的电极制作一般采用在金属(铝、铜)箔上先涂膜再烘干的工艺流程,球形电极材料有利于涂膜流畅和均匀。因此,如何将纳米颗粒均匀镶嵌在多孔的碳基体中,形成具有三维离子-电子混合导电的球形电极材料,是一项非常有意义的工作。聚合物微凝胶是一类交联聚合物微球,具有三维网孔,其分子链上的极性官能团可以与金属离子相互作用,使其陷入聚合物微凝胶内。如果过渡金属离子发生水解,就会于三维网孔中原位沉淀,生成有机-无机杂化材料。以其为前驱体,高温惰性气氛处理,可以合成纳米碳结构(纳米颗粒均匀镶嵌在碳基体中)电极材料。LiMn2O4作为商业动力锂离子电池正极材料之一,具有倍率性能好、环境友好、储量丰富等优点。但是,由于姜-泰勒效应,Mn2+离子的溶解等原因造成容量衰减严重,特别是在高温下。目前应对LiMn2O4容量衰减的策略主要是表面包覆和形貌控制。如果能让LiMn2O4均匀镶嵌在多孔碳基体中,不仅可以减少材料与电解液的直接接触面积,以减少Mn2+离子的溶解,而且可以缓冲其在充放电过程中的体积变化,大大改善LiMn2O4的电化学性能。相对于目前商业的锂离子电池正极材料,基于多电子反应的V2O5具有比容量高的特点,其理论容量达到了441 mAh g-1(3电子每摩尔V2O5)。但是,其较低的离子和电子导电率,限制了它的快速充放电能力;而且,它在电解液中的溶解性,导致材料循环性能较差。通过碳包覆可以改善材料的倍率性能和循环性能。为此,我们进行了以下研究工作。1.P(AM-co-AA)模板合成,碳化条件选择,以及碳微球的电化学性能研究优化交联P(AM-co-AA)聚合物微凝胶的合成工艺,通过KCl和SiO2填充,高温碳化后除去KCl和SiO2,制备多孔碳微球。以KCl为填充物的碳微球的孔径分布在2 nm以下和3.7 nm,2 nm以下孔的孔容为0.22 cm3 g-1,比表面积为420 m2 g-1;3.7 nm孔的孔容为0.13 cm3 g-1,比表面积为136 m2 g-1。以SiO2为填充物的碳微球的粒径在10-20μm之间,比表面积达到了617 m2 g-1,孔径呈3.8 nm和7.8 nm的分级多孔结构。3.8 nm孔的孔容为0.05 cm3 g-1,比表面积为62.1 m2g-1;7.8 nm孔的孔容为0.289 cm3 g-1,比表面积为118 m2 g-1。以6 mol L-1的KOH为电解液,在0.5 A g-1的电流密度下,以KCl和SiO2为填充物的比容分别达到了159 F g-1和110 F g-1。相比微孔的KCl填充,以纳米SiO2填充制备的分级多孔活性炭的表面积利用率更高。2.P(AM-co-AA)模板合成LiMn2O4@C复合材料及电化学性能研究通过静电吸附将Mn2+离子负载于P(AM-co-AA)模板内部,改变体系的pH值,Mn2+离子原位水解,填充在聚合物微凝胶内部的三维网孔中,形成杂化Mn(OH)2@P(AM-co-AA)前驱体;然后,前驱体经过高温处理,合成纳米碳包覆LiMn2O4复合材料(LMO@C)。LMO@C具有球形外貌,粒径范围为1~2μm,由LiMn2O4纳米微球(20nm)均匀镶嵌于多孔碳基体中构成。N2吸附测试结果显示,LMO@C的BET比表面积为24.9 m2 g-1,BJH孔径分布为3.67和6.46 nm。以LMO@C材料为正极材料,锂金属为负极材料组装半电池进行恒流充放电测试。结果表明,在0.1,1,5,10和20C(1C=148 mA g-1)倍率下,LMO@C可以分别输出142,137,126,107和91 mAh g-1的比容量。LMO@C在室温下1C循环1000次后,容量保持率为80%;60 oC、1C循环200次后,容量保持率为86%,表现出优异的电化学性能。3.PMMA模板合成V2O5@C复合材料及电化学性能研究使用一种廉价的PMMA微凝胶模板合成多孔V2O5@C微球,产物的粒径范围10-30μm,由平均粒径200nm的一次颗粒聚集而成。一次颗粒由30 nm粒径的V2O5纳米颗粒均匀镶嵌在碳基体构成。多孔V2O5/C微球的BET比表面积为23.5 m2 g-1,BJH孔径为3.8 nm。以所制备的多孔V2O5/C微球为正极材料,锂金属为负极材料的半电池,在0.1、0.5、2、5和10C下首次放电容量分别为291、263、239、192和166 mAh g-1.在0.5、5和10C下循环300次之后,容量保持率分别为90%、77%和63%。研究结果表明,多孔V2O5@C微球具有优异的倍率性能和循环性能。总之,聚合物微凝胶不仅可以直接用来合成分级多孔碳微球,也可以以其为模板合成多孔LiMn2O4@C和多孔V2O5@C复合材料,制备的多孔碳和纳米碳结构电极材料均表现出优异的电化学性能。
[Abstract]:Based on the electrochemical reaction of lithium intercalation, the kinetics of the electrode process depends on the migration rate of Li+ ions and electrons. People usually encapsulate nanomaterials with nanomaterials to realize the rapid migration of Li+ ions and electrons. However, the uniform coating of carbon nanoscale on each nanoparticle is a very difficult task. The electrode of the current lithium ion battery The process is generally used to film the metal (aluminum, copper) foil first and then dry. The spherical electrode material is beneficial to the smooth and uniform coating of the coating. Therefore, it is a very meaningful work to make the nanoparticles inlaid evenly in the porous carbon matrix to form a spherical electrode material with three-dimensional ionic electron mixed conduction. Microgel is a class of crosslinked polymer microspheres with three-dimensional mesh. The polar functional groups on the molecular chain can interact with metal ions and fall into the polymer microgels. If the transition metal ions are hydrolyzed, they will be in situ precipitated in a three-dimensional mesh hole to produce organic inorganic hybrid materials. The carbon nanostructure (nanoparticles embedded in carbon matrix) can be synthesized by atmosphere treatment, and.LiMn2O4 is one of the positive electrode materials of the commercial power lithium ion battery. It has the advantages of good performance, friendly environment and abundant reserves. However, because of the ginger Taylor effect and the dissolution of Mn2+ ions, the capacity attenuation is serious. At present, the main strategies to deal with the LiMn2O4 capacity attenuation are surface coating and morphology control. If LiMn2O4 can be evenly embedded in the porous carbon matrix, the direct contact area between the material and the electrolyte can be reduced to reduce the dissolution of the Mn2+ ions, and the volume change in the charge discharge process can be slowed down greatly. The electrochemical performance of LiMn2O4 is improved. Compared with the current commercial lithium ion battery positive material, the V2O5 based on the multi electron reaction is characterized by high specific capacity, and its theoretical capacity reaches 441 mAh g-1 (3 electron mole V2O5). However, its low ionic and electronic conductivity limits its rapid charge discharge capacity; moreover, it is in electrolysis. The solubility in the liquid leads to poor cycling performance. Carbon coating can improve the ratio and cycle performance of the material. Therefore, we have done the following research work.1.P (AM-co-AA) template synthesis, the selection of carbonization conditions, and the electrochemical properties of carbon microspheres. After KCl and SiO2 filling, the porous carbon microspheres were prepared by removing KCl and SiO2 after high temperature carbonization. The pore size of the carbon microspheres with KCl as filling material was below 2 nm and 3.7 nm, and the Kong Rong of the holes below 2 nm was 0.22 cm3 g-1, and the specific surface area was 420 M2 g-1; 3.7 of the pores of the pores were 0.13, and the carbon microspheres with the surface area of 136 The particle size is between 10-20 and 10-20 m, the specific surface area is 617 M2 g-1, the pore size of 3.8 nm and 7.8 nm is 0.05 cm3 g-1, and the specific surface area is 62.1 m2g-1; the 7.8 nm hole Kong Rong is 0.289 cm3, and the specific surface area is 118. The specific volume of O2 for the filler reached 159 F g-1 and 110 F g-1. compared with microporous KCl filling. The surface area utilization ratio of the graded porous activated carbon prepared by nano SiO2 was higher.2.P (AM-co-AA) template synthesis of LiMn2O4@C composite and electrochemical properties. The pH value of the variable system, Mn2+ ion in situ hydrolysis, filled in the three-dimensional mesh hole inside the polymer microgel, forming a hybrid Mn (OH) 2@P (AM-co-AA) precursor. Then, the precursor is treated by high temperature, and the synthesis of carbon nanocoated LiMn2O4 composite (LMO@C).LMO@C has a spherical appearance, the particle size range is 1~2 u m, and the LiMn2O4 nano microspheres are homogeneous. The results of.N2 adsorption test in porous carbon matrix show that the specific surface area of LMO@C is 24.9 M2 g-1, BJH pore size distribution is 3.67 and 6.46 nm. with LMO@C material as positive material, and lithium metal is used as negative material to assemble semi battery for constant current charge discharge test. The results show that the ratio of 0.1,1,5,10 and 20C (1C=148 mA) can be obtained. The specific capacity.LMO@C of 142137126107 and 91 mAh g-1 respectively at room temperature 1000 times 1C cycle, the capacity retention rate is 80%, 60 oC, 1C cycle 200 times, the capacity retention rate is 86%, exhibiting excellent electrochemical performance.3.PMMA template synthesis V2O5@C composite material and electrochemical performance research using a cheap PMMA microgel template synthesis The particle size of the porous V2O5@C microspheres is 10-30 mu m, which is composed of an average particle size of 200nm particles. The primary particles are composed of 30 nm particles of V2O5 nanoparticles in the carbon matrix. The BET specific surface area of the porous V2O5/C microspheres is 23.5 M2 g-1 and the BJH aperture is 3.8 nm. with the prepared porous V2O5/C microspheres as the positive material, lithium gold. The initial discharge capacity under 0.1,0.5,2,5 and 10C is 291263239192 and 166 mAh g-1. under 0.5,5 and 10C cycles for 300 times respectively. The capacity retention rate is 90%, 77% and 63%., respectively. The results show that the porous V2O5@C microspheres have excellent multiplier performance and cyclic performance. In conclusion, polymer microgels are not only available. In order to synthesize porous carbon microspheres directly, porous LiMn2O4@C and porous V2O5@C composites can be synthesized by the template. The prepared porous carbon and carbon nanostructure electrode materials have excellent electrochemical performance.
【学位授予单位】：湘潭大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TB383.1;O646.54

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