纳米结构钒酸钠电极活性材料的制备及电化学性能研究

发布时间：2018-07-07 22:52

本文选题：锂离子电池 + 钒酸钠　；参考：《长沙理工大学》2015年硕士论文

【摘要】：近年来,钒氧化物和钒酸盐嵌锂材料由于其较高的比容量、低廉的成本以及简便的合成方法成为了研究热点。在我国,存在着钒资源丰富,但综合利用程度不高的问题,因此有必要开发高比容量的钒系化合物,用作新型锂离子二次电池的电极材料,这对于优化我国钒资源的有效利用和促进经济的快速发展都具有重要的意义。但是目前,钒系化合物嵌锂材料仍然存在着一些问题,主要是倍率性能差,循环性能不够稳定,这就限制了钒系化合物嵌锂材料的商业化应用。本论文着眼于结构相对稳定的钒酸盐材料,通过采用两种新型的制备方法,分别获得了具有较高性能的钒酸钠材料,并分别探讨了在有机系锂离子电池体系和水溶液锂离子电池体系中的电化学性能和脱嵌锂机制。尝试了用高能超声分散法对合成的材料进行超薄化处理,并研究处理后的材料的电化学性能。本论文的主要工作和结果如下:设计了一种新型的水热-固相烧结两步法,合成了分散均匀的NaV_3O_8纳米片材料。通过研究发现,NaV_3O_8纳米片材料在有机系锂离子电池中具有良好的可逆脱嵌锂能力。300 mA/g电流密度下首次放电容量为81.6 mAh/g(基于NaV_3O_8的质量),100次循环后容量依然有80 mAh/g,显示出了良好的循环稳定性能和容量保持率。当用作水系锂离子电池负极时,300 mA/g电流密度下首次放电容量为60.4 mAh/g(基于NaV_3O_8的质量),120次循环后容量依然有60.6 mAh/g,循环稳定性和容量保持率都很高。本文还探索了以NH_4VO_3和NaOH?H_2O为原料一步烧结法合成钒酸钠的可能性,并通过超声分散的方法对合成的材料进行分散处理,对比分析超声前后材料的电化学性能差异。超声前该材料组装的水溶液锂离子电池在300mA/g电流密度下首次放电容量为72.7 mAh/g(基于NaV_3O_8的质量)。200次循环后,容量为66 mAh/g,容量保持率高达91%,体现出了优良的循环稳定性。600mA/g电流密度下初始放电容量为70.9 mAh/g,200次循环后容量为53 mAh/g,容量保持率为75%,循环稳定性较好,但是与300mA/g下的循环稳定性相比有了一定下降,这也说明了所合成的材料的倍率性能有待提高。该NaV_3O_8纳米材料在有机锂电池体系中,30mA/g电流密度下的初始放电容量虽高达240 mAh/g,但是40次循环后,容量保持率仅为45%,说明该方法合成的NaV_3O_8纳米片在有机锂电池体系中低倍率下的循环稳定性能较差;300mA/g电流密度下的初始放电容量达到了150mAh/g,100次循环后容量保持率为55%;600mA/g电流密度下的初始放电容量可以达到138.5mAh/g,100次循环后容量保持率为62%;1500mA/g电流密度下的初始放电容量可达到111.3mAh/g,100次循环后的容量保持率为79%。很明显该NaV_3O_8纳米材料在大倍率下的循环稳定性更好。尝试通过高能超声法对材料进行超薄化处理,改善材料的电化学性能,并对比处理前后材料性能的改善情况。超声处理后在有机体系中30mA/g电流密度下的初始放电容量为138 mAh/g,对比超声前容量有了较大下降。前30次循环后放电容量为116mAh/g,容量保持率为84%,相比于超声前54%的容量保持率,有了大幅度提升,循环稳定性较好。但是大倍率下,材料的循环稳定性和放电容量都有了明显的下降,说明超声处理对材料的电化学性能的改进有很大的局限性,没能从根本上解决材料循环稳定性差的问题。通过对比超声前后材料的形貌改变,从材料结构的改变方面入手,探明超声处理后材料容量和循环稳定性能改变的原因。
[Abstract]:In recent years, vanadium oxide and vanadate lithium intercalation materials have become the focus of research because of their high specific capacity, low cost and simple synthesis methods. In our country, there is a problem of rich vanadium resources but low comprehensive utilization degree. Therefore, it is necessary to develop vanadium compounds with high specific capacity as a new lithium ion two battery. Electrode materials are of great significance to optimize the effective utilization of vanadium resources in China and promote the rapid economic development. However, at present, there are still some problems in the vanadium series lithium intercalation materials, which are mainly due to poor multiplying performance and low cycling performance. This restricts the commercial application of vanadium based lithium intercalation materials. With a view to the relatively stable structure of vanadate materials, the high performance sodium vanadate was obtained by two new preparation methods. The electrochemical performance and the mechanism of lithium intercalation in the organic lithium ion battery system and the lithium ion battery system in aqueous solution were discussed respectively. The ultrathin treatment of synthetic materials and the electrochemical properties of the processed materials are studied. The main work and results of this paper are as follows: a new type of hydrothermal solid phase sintering two step method was designed, and the dispersed homogeneous NaV_3O_8 nanoscale material was synthesized. Through the study, the NaV_3O_8 nanomaterials were found in the organic lithium ion battery. The first discharge capacity of.300 mA/g current density with a good reversible.300 mA/g current density is 81.6 mAh/g (based on the mass of NaV_3O_8), and the capacity is still 80 mAh/g after the cycle. It shows good cyclic stability and capacity retention. The first discharge capacity of the 300 mA/g current density is 6 when it is used as the negative pole of the lithium ion battery in the water system. 0.4 mAh/g (based on the mass of NaV_3O_8), the capacity is still 60.6 mAh/g after 120 cycles, and the cycle stability and capacity retention are very high. This paper also explored the possibility of synthesizing sodium vanadate with NH_4VO_3 and NaOH? H_2O as raw materials for one step sintering process, and the ultrasonic dispersion method was used to disperse the synthetic materials and to compare and analyze the ultrasound. The electrochemical performance of the front and rear materials is different. The first discharge capacity of the lithium ion battery assembled by this material at 300mA/g current density is 72.7 mAh/g (based on the mass of NaV_3O_8) and.200 secondary cycle, the capacity is 66 mAh/g and the capacity retention rate is up to 91%, which shows the initial discharge of the excellent cyclic stability.600mA/g current density. The capacitance is 70.9 mAh/g, the capacity of the 200 cycle is 53 mAh/g, the capacity retention rate is 75%, the cycle stability is better, but it has a certain decline compared with the cyclic stability under the 300mA/g, which also shows that the ratio of the synthesized material needs to be improved. The NaV_3O_8 nano material is under the 30mA/g current density in the organic lithium battery system. The initial discharge capacity is up to 240 mAh/g, but the capacity retention rate is only 45% after 40 cycles, which indicates that the cyclic stability performance of the NaV_3O_8 nanometers synthesized by this method is poor at low ratio in the organic lithium battery system; the initial discharge capacity under the 300mA/g current density reaches 150mAh/g, and the capacity retention rate is 55% after the 100 cycle, 600mA/g electricity. The initial discharge capacity under the flow density can reach 138.5mAh/g, the capacity retention rate after 100 cycles is 62%, the initial discharge capacity under the 1500mA/g current density can reach 111.3mAh/g. The capacity retention rate of the 100 cycles is 79%., it is obvious that the cyclic stability of the NaV_3O_8 nanomaterial at large ratio is better. The material was treated with ultra thin treatment to improve the electrochemical performance of the material and to improve the performance of the material before and after treatment. The initial discharge capacity of the 30mA/g current density in the organic system was 138 mAh/g after ultrasonic treatment. The capacity of the first 30 cycles was 116mAh/g and the capacity retention rate was 84%. Compared with the capacity retention rate of 54% before ultrasonic, the cycle stability is better, but the cyclic stability and discharge capacity of the material have been obviously reduced under the large ratio. It shows that the improvement of the electrochemical performance of the material is very limited, and it can not solve the problem of poor material circulation stability. By comparing the changes of the morphology of the material before and after the ultrasonic and the change of the material structure, the reasons for the change of the material capacity and the cyclic stability after ultrasonic treatment are explored.
【学位授予单位】：长沙理工大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TQ131.12;O646

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