高性能层状高镍NCM材料的结构调控与性能研究

发布时间：2018-01-12 06:16

本文关键词：高性能层状高镍NCM材料的结构调控与性能研究　出处：《天津理工大学》2017年硕士论文　论文类型：学位论文

【摘要】：LFP型锂离子动力电池目前已在电动汽车上广泛应用,但这种锂离子动力电池的比能量密度较低,不能满足下一代锂离子动力电池的要求(300Wh/KG)。正极材料是限制锂离子动力电池比能量密度的关键。近几年,高镍NCM层状材料以其高能量密度和倍率性能,有望满足下一代锂离子动力电池的要求。但这种材料的循环稳定性和热稳定性较差,有待进一步提高。为了提高高镍NCM材料的循环稳定性和热稳定性,研究者先后将其设计成为核壳结构、多级核壳结构、浓度梯度结构、全浓度梯度结构等特殊结构,希望利用富镍核的高容量和富锰壳的高稳定性,实现核与壳的功能互补。结果也发现特殊结构的NCM材料具有显著提高的循环稳定性和热稳定性。但上述研究均是将特殊结构NCM材料与非核壳NCM材料作比较,没有进行不同特殊结构NCM材料之间的比较,因而无法进一步优化这些特殊结构设计。针对上述问题,本论文以高镍NCM材料(LiNi0.68Co0.13Mn0.19O2)为研究对象,在不改变总成分的条件下,分别将其设计成非核壳结构、核壳结构、多级核壳结构、全浓度梯度结构,并采用共沉淀-高温固相法合成这些特殊结构材料。ICP结果表明,所设计的结构材料其理论含量与实际摩尔含量相近,达到实验设计的要求。根据XRD,SEM以及截面EDS分析可知,成功合成了这些特殊结构材料。振实密度结果表明,核壳结构、多级核壳结构、全浓度梯度结构材料均具有比非核壳材料更高的振实密度。电化学测试表明,全浓度梯度结构材料表现出最为优异的循环性能,核壳结构和多级核壳结构材料也表现出较为优异的循环性能,但多级核壳结构较核壳结构,其优势并不明显,而非核壳结构材料在经过循环后容量明显衰减,低于其余三种结构材料。EIS分析可知,全浓度梯度结构材料在不同循环周数的电荷转移阻抗最小,核壳结构与多级核壳结构也具有较小的电荷转移阻抗,而非核壳结构的电荷转移阻抗最大。热稳定性分析表明,全浓度梯度结构材料具有最好的热稳定性,核壳结构与多级核壳结构也具有较好的结构稳定性,而非核壳结构材料的结构稳定性则较差。综上所述,核壳结构、多级核壳结构、全浓度梯度结构材料均具有比非核壳材料更高的振实密度、电化学性能和热稳定性,尤其是全浓度梯度结构材料最为优异。
[Abstract]:LFP lithium-ion power battery has been widely used in electric vehicles, but its specific energy density is low. The cathode material is the key to limit the specific energy density of Li-ion power battery in recent years. High nickel NCM layered material is expected to meet the requirements of the next generation lithium ion power battery due to its high energy density and rate performance, but the cycle stability and thermal stability of this material are poor. In order to improve the cyclic stability and thermal stability of high-nickel NCM materials, the researchers have designed them as core-shell structure, multi-stage core-shell structure and concentration gradient structure. The high capacity of nickel rich nucleus and the high stability of manganese rich shell are expected to be used in the special structure such as the full concentration gradient structure. It was also found that the special structure of NCM materials had significantly improved cyclic stability and thermal stability. However, all the above studies were to combine the special structure NCM materials with non-core-shell NCM materials. Make a comparison. There is no comparison between NCM materials with different special structures, so it is impossible to further optimize the design of these special structures. In this paper, the high-nickel NCM material LiNi0.68Co0.13Mn0.19O2 was used as the research object, which was designed into non-core-shell structure without changing the total composition. Core-shell structure, multistage core-shell structure, full concentration gradient structure, and coprecipitation-high temperature solid state method to synthesize these special structural materials. ICP results show that. The theoretical content of the designed structural material is close to that of the actual molar content, which meets the requirements of the experimental design. According to the analysis of XRD-SEM and cross-section EDS. These special structural materials have been successfully synthesized. The results of vibrational density show that the core-shell structure, multistage core-shell structure and full-concentration gradient structure have higher vibrational density than that of non-core-shell materials. Electrochemical measurements show that these materials have higher vibrational density than that of non-core-shell materials. The full concentration gradient structure material shows the most excellent cyclic performance, the core-shell structure and the multi-stage core-shell structure material also show the more excellent cyclic performance, but the multi-stage core-shell structure has no obvious advantage over the core-shell structure. However, the capacity of non-core-shell structure material decreases obviously after cycling, which is lower than that of the other three structural materials. EIS analysis shows that the charge transfer impedance of the gradient structure material with full concentration is the smallest at different cycle cycles. The core-shell structure and multistage core-shell structure also have small charge transfer impedance, while the non-core-shell structure has the largest charge transfer impedance. The thermal stability analysis shows that the full concentration gradient structure material has the best thermal stability. Core-shell structure and multistage core-shell structure also have good structural stability, while non-core-shell structure materials have poor structural stability. In conclusion, core-shell structure, multi-stage core-shell structure. The full concentration gradient structure materials have higher vibrational density, electrochemical performance and thermal stability than the non-core-shell materials, especially the full concentration gradient structure materials.
【学位授予单位】：天津理工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TB383.4;TM912

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