层状Ni-Co-Mn基正极材料在电化学储能中的研究与应用

发布时间：2018-01-12 02:36

本文关键词：层状Ni-Co-Mn基正极材料在电化学储能中的研究与应用　出处：《武汉大学》2014年博士论文　论文类型：学位论文

【摘要】：在科技技术日新月异的今天,锂离子二次电池的应用已经逐渐从小型电子产品朝大规模动力型产品方向发展,但目前商业应用的锂离子电池还不能完全满足大规模动力型产品的需求,因此,我们需要开发高能量、高功率、安全性好的锂离子电池。在锂离子二次电池中,正极材料对其整体电化学性能起着至关重要的作用,所以开发新型正极材料和改善已有正极材料的综合性能是当前的主要任务。相对于钴酸锂材料,Li-Ni-Co-Mn-O层状材料作为锂离子电池正极材料具有较高的比容量、优异的循环性能、适宜的电压平台、较低的工艺成本、稳定的热安全性等特点,因此,其成为近年来研究的热点。本论文从应用研究的角度,对计量比Ni-Co-Mn基层状材料及富锂固溶体Ni-Co-Mn基层状材料在锂离子电池中的应用进行了探讨研究,重点针对这类材料在倍率性、安全性等方面的不足,希望通过各种改性手段的应用使其更好发挥它的实用价值,真正应用到锂离子二次电池中。此外,我们对Na-Ni-Co-Mn基层状材料的合成及在钠离子二次电池中的应用进行了初步探究。综上,本论文的研究工作主要分为以下几个部分： (1) LiNixCoyMn1-x-yO2材料的性能研究采用流变相法合成了三种计量比Ni-Co-Mn基层状材料LiNi1/3Co1/3Mn1/3O2、 LiNi0.6Co0.2Mn0.2O2和LiNi0.4Co0.2Mn0.4O2,将商业化的Sb203粉末分别与三种计量比层状材料直接机械混合得到混合材料。其中以LiNi1/3Co1/3Mn1/3O2为重点,探讨分析了Sb203粉末修饰活性材料前后的电化学性能和热安全性能。采用粉末衍射光谱仪(XRD)、扫描电子显微镜(SEM)及透射电子显微镜(TEM)来检测和观察样品的结构和表面形貌。根据充放电数据显示,混合材料Sb2O3/LiNixCoyMn1-x-yO2的循环性能、倍率性能和热安全性能均比原材料LiNixCoyMn1-x-yO2有明显改进。通过对比混合前后LiNi1/3Co1/3Mn1/3O2材料的充放电曲线可以发现,循环过程中混合材料的电极极化明显减小。进一步的阻抗实验表明,相对于LiNi1/3Co1/3Mn1/3O2材料电极,混合材料Sb2O3/LiNi1/3Co1/3Mn1/3O2电极具有更小的SEI膜阻抗值Rf和电荷转移阻抗值Rct。我们猜测混合后材料的性能改进主要是由于Sb203的存在抑制了电解液与正极材料间的消极反应,减少有害物质的生成,稳定了正极片表层的SEI膜。另外,根据Sb203不同加入方式的比较,我们认为使用Sb203包覆的隔膜将对电池性能起到相似的积极作用。 (2)Li1.182Ni0.182Co0.091Mn0.545O2的研究在700-900℃C的不同煅烧温度条件下,使用流变相法合成了富锂固溶体材料Li1.182Ni0.182Co0.091Mn0.545O2。XRD、SEM实验结果表明：所得到富锂固溶体材料具有层状六面体结构,阳离子混排度较小,颗粒为亚微米级。随着煅烧温度的升高,所得材料的颗粒粒径逐渐增大,团聚现象明显减小。同时充放电曲线显示,随着煅烧温度的逐渐升高,所得材料首周的放电比容量逐渐减小,但材料的容量保持率依次增大。在此基础上,我们尝试使用阶梯升温法从600-750-8500C逐步升温煅烧得到Li1.182Ni0.182Co0.091Mn0.545O2材料。实验表明,这种改进既可以有效的抑制材料颗粒生长过大,又可以减小材料颗粒的团聚,增强样品的均一性,并且得到的材料具有相对较好的电化学性能。 (3)粘接剂对Li1.182Ni0.182Co0.091Mn0.545O2电极的影响以流变相法阶梯升温得到的固溶体材料Li[Li0.182Ni0.182Co0.091Mn0.545]O2为活性物质,分别使用粘接剂羧甲基纤维素盐(CMC)、聚偏氟乙烯(PVDF)、海藻酸钠(SA)制得正极电极片,并且与聚四氟乙烯(PTFE)作为粘接剂制得的电极片进行电化学性能对比。根据充放电性能、循环性能、倍率性能、电压衰退情况及库伦效率等数据来看,我们认为相对于其他几种粘接剂来说,使用海藻酸钠(SA)作为粘接剂的固溶体电极片具有相对较优的综合电化学性能。此外,通过测试比较使用不同粘接剂的电极片的膨胀性能及循环后电极的表面形貌,我们发现以聚偏氟乙烯(PVDF)为粘接剂制得的富锂固溶体电极由于吸收了较多的电解液,极片内部发生膨胀,电极表面出现裂纹,从而造成活性材料与导电剂或者电极片与集流体之间接触不好,影响了电极片的整体导电性,材料的循环性能逐渐恶化。 (4)Li1.2Ni0.16Co0.08Mn0.56O2的改性研究采用流变相法合成了富锂固溶体材料Li1.2Ni0.16Co0.08Mn0.56O2,使用不同浓度的过硫酸铵溶液对其进行浸泡处理,从而改进了Li1.2Ni0.16Co0.08Mn0.56O2材料的首周库伦效率及倍率性能。通过XRD、拉曼光谱及ICP-AES表征了富锂固溶体材料处理前后的结构变化及元素含量变化。根据实验结果发现,处理后的活性材料保持着基底材料的层状结构框架,但随着过硫酸铵处理浓度的增加,材料中锂离子的含量有所减少,说明有部分锂离子从材料的结构空间中脱出。根据XPS数据和首周充放电曲线,可以说明过硫酸铵处理后的富锂固溶体材料中过渡金属阳离子没有发生明显的价态变化,脱出的锂离子主要来自于材料中的Li2MnO3相。使用过硫酸铵处理后的富锂固溶体材料虽然初始放电比容量略低,但在随后的循环过程中放电比容量会逐渐增大,并保持良好的循环性能。通过综合比较,我们认为过硫酸铵使用量为活性材料质量的30%-40%时,所得材料的电化学性能总体最优。其中采取30%的过硫酸铵处理量,得到的最终产物不仅具备优异的循环稳定性,而且在4C时放电比容量仍接近200mAh g-1。 (5)的研究通过流变相法在700-900℃的不同煅烧温度条件下,一步煅烧得到层状材料NaxNi1/3Co1/3Mn1/3O2,使用XRD和SEM检测了所得材料的结构和形貌。SEM实验和充放电结果表明,随着煅烧温度的逐渐升高,三种材料的颗粒粒径逐渐增大,形貌由块状转变为片状,首周放电比容量逐渐增大,循环性能总体较好。其中,900℃煅烧得到的Na-Ni-Co-Mn基材料具有较优的电化学性能。根据其XRD分析和首周充放电曲线,认为900℃煅烧得到的Na-Ni-Co-Mn基层状材料中钠元素的含量x小于1,此材料为缺钠材料。
[Abstract]:In the science and technology change rapidly today, the application of lithium ion secondary battery two has been gradually from small electronic products toward large-scale power product development, but the current lithium ion battery business applications can not fully meet the needs of large-scale power products, therefore, we need to develop a high energy and high power lithium ion battery safety two. In the lithium ion secondary battery, cathode material plays a vital role in the overall electrochemical properties of cathode materials, comprehensive performance so the development of new cathode materials and improve the existing is the main task at present. Compared with the lithium cobalt oxide material, Li-Ni-Co-Mn-O layered materials as cathode materials for lithium ion batteries with high specific capacity. Excellent cycling performance, voltage platform for the process of low cost, stable characteristics, thermal safety etc. Therefore, it has become a research hotspot in recent years.
This paper from the application point of view, the application of layered materials iometric Ni-Co-Mn based layered Li rich material and Ni-Co-Mn based solid solution in lithium ion batteries was studied, focusing on this kind of material in the rate, lack of security and other aspects of the application, hope through a variety of modified methods to make it better its practical value to the real application of lithium ion secondary battery two. In addition, we based on Na-Ni-Co-Mn layered material synthesis and in two sodium ion battery applications were discussed. In conclusion, the research work of this thesis is mainly divided into the following sections:
(1) properties of LiNixCoyMn1-x-yO2 materials
The three kinds of measurement than LiNi1/3Co1/3Mn1/3O2 Ni-Co-Mn based layered materials synthesized by rheological phase method, LiNi0.6Co0.2Mn0.2O2 and LiNi0.4Co0.2Mn0.4O2, Sb203 powder commercial respectively with three kinds of measurement than the direct mixing of layered materials mixed materials. The LiNi1/3Co1/3Mn1 /3O2 as the key to investigate the electrochemical properties and thermal safety performance of Sb203 powder before and after modification of the activated material analysis the powder diffraction spectrometer. (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) structure and surface morphology to detect and observe the samples. According to the charge and discharge data show that the cycle performance of the hybrid Sb2O3/LiNixCoyMn1-x-yO2 materials, heat rate performance and safety performance are better than the original LiNixCoyMn1-x-yO2 material. Through the charging and discharging LiNi1/3Co1/3Mn1/3O2 curve of the contrast of materials before and after mixing can be found in the process of mixing cycle The electrode polarization material significantly reduced. Further experiments show that the impedance of electrode materials, compared with LiNi1/3Co1/3Mn1/3O2, the resistance of SEI hybrid material Sb2O3/LiNi1/3Co1/3Mn1/3O2 electrode has a smaller value of Rct. after mixing we guess improvement of material performance is mainly due to the presence of Sb203 inhibited the negative reaction of electrolyte and cathode materials between Rf and charge transfer resistance, reduce the generation of harmful the material, stable SEI film cathode surface. In addition, according to the Sb203 of different adding methods of comparison, we believe that the use of diaphragm coated Sb203 the positive effect to similar to the battery performance.
(2) research on Li1.182Ni0.182Co0.091Mn0.545O2
Different calcination temperature conditions at 700-900 DEG C, using rheological phase synthesis of lithium rich solid solution materials Li1.182Ni0.182Co0.091Mn0.545O2.XRD, SEM experimental results show that the lithium rich solid solution material having a layered hexahedral structure, cation mixing of small particles is sub micron. With the increase of calcination temperature, the materials of the the particle size increases, agglomeration significantly reduced. At the same time the charge discharge curves showed that gradually increased with the calcination temperature, the first week of the discharge specific capacity of the material decreases, but the capacity retention rate of the materials increases. On this basis, we try to use the ladder temperature method from 600-750-8500C gradually heating and calcining to obtain Li1.182Ni0.182Co0.091Mn0.545O2 material. Experiments show that this improvement can not only inhibit the growth of material particles is too large, and can reduce material particles, enhance the sample The homogenization of the products and the obtained materials have relatively good electrochemical performance.
(3) the effect of the adhesive on the Li1.182Ni0.182Co0.091Mn0.545O2 electrode
The rheological phase method of step temperature obtained solid solution material Li[Li0.182Ni0.182Co0.091Mn0.545]O2 as active material, respectively using adhesive carboxymethyl cellulose salt (CMC), polyvinylidene fluoride (PVDF), sodium alginate (SA) to prepare a positive electrode sheet, and polytetrafluoroethylene (PTFE) as electrode adhesive prepared for electrochemical performance comparison according to the charge and discharge performance, cycle performance, rate capability, voltage and efficiency decline of Kulun data, we believe that compared to other kinds of binders, using sodium alginate (SA) as the adhesive solid solution electrode with electrochemical properties are relatively better. In addition, through the test electrode using the comparison of different adhesives after the cycle expansion performance and electrode surface morphology, we found that using polyvinylidene fluoride (PVDF) as the adhesive prepared by lithium rich solid solution electrode by absorption The more electrolytes, the internal expansion of the electrode plates, the cracks on the electrode surface, resulting in a bad contact between the active material and conductive agent or electrode and collector, which affects the overall conductivity of the electrode, and the cycling performance of the material gradually deteriorates.
(4) research on the modification of Li1.2Ni0.16Co0.08Mn0.56O2
The lithium rich solid solution material Li1.2Ni0.16Co0.08Mn0.56O2 was synthesized by rheological phase method, using different concentrations of ammonium persulfate were soaked in the first week of Kulun so as to improve the efficiency and rate performance of Li1.2Ni0.16Co0.08Mn0.56O2 materials. By XRD, Raman spectroscopy and ICP-AES characterization of the lithium rich solid solution changes and structural change of element content before and after the body material processing. According to the experimental results, the active material after treatment maintained a layered structure of substrate material framework but with the increase of ammonium persulfate, the concentration of lithium ion content in the material decreased, indicating that some lithium ion to emerge from the spatial structure of the material. According to the XPS data and the first charge discharge curve. Can be explained with ammonium sulfate after lithium rich solid solution materials in transition metal cation valence changes did not occur, lithium ion becomes the main. From the material in the Li2MnO3 phase. Used with ammonium sulfate after lithium rich solid solution materials although the initial discharge capacity is slightly lower, but the discharge during the subsequent cycle capacity will gradually increase, and maintain a good cycle performance. By comparison, we think that the amount of ammonium persulfate used as active materials the quality of 30%-40%, the electrochemical properties of the material. The overall optimal income taken with ammonium sulfate 30%, finally the product not only has excellent cycle stability and discharge capacity in 4C than 200mAh is still close to g-1.
(5) research
The rheological phase method at 700-900 DEG C under different calcination temperature, calcination step layered materials NaxNi1/3Co1/3Mn1/3O2, XRD and SEM were detected using the materials of the structure and morphology of.SEM and charge discharge experiment results show that when increasing the calcination temperature, three kinds of material particle size increases, the morphology of the massive transformation for the first week of flake, the discharge capacity increases gradually, the cycle performance is generally good. Among them, Na-Ni-Co-Mn based materials 900 C calcined has better electrochemical performance. According to the XRD analysis and the first week of the charge discharge curves, X sodium content of Na-Ni-Co-Mn based layered materials of 900 DEG C calcined in this less than 1. Material for sodium deficient material.

【学位授予单位】：武汉大学
【学位级别】：博士
【学位授予年份】：2014
【分类号】：O646;TM912

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