钼基金属氧化物锂电池负极材料的制备及电化学性能研究

发布时间：2018-03-05 12:14

本文选题：锂电池　切入点：二氧化钼　出处：《上海交通大学》2014年博士论文　论文类型：学位论文

【摘要】：二氧化钼（MoO2）具有导电性好、稳定性高和理论容量高等优点，是目前锂离子电池负极材料研究的热点材料之一。但是，二氧化钼的实际充放电比容量很低。这是由于在充放电过程中，二氧化钼初步锂化形成的低导电性的Li0.98MoO2阻止了二氧化钼的进一步锂化。同时，由于充放电过程中二氧化钼有很大的体积膨胀，使得二氧化钼的循环性能也很差。更重要的是，不同于一般的金属氧化物，二氧化钼的充放电比容量在前30个循环会有一个增加的过程。这个不寻常的现象在目前文献中还没有得到很好的解释，，一般被简单的认为是电极材料活化的过程。因此，本文主要的工作包括以下几方面： (1)通过引入多级孔结构来提高二氧化钼充放电过程中锂离子和电子的传输速率和二氧化钼材料结构的稳定性，从而提高二氧化钼的充放电容量和改善其循环性能。本文中以介孔碳CMK-3为模板剂和还原剂，用一步碳热还原法合成了二氧化钼纳米管。在深入研究了不同三氧化钼和CMK-3的质量比，煅烧的温度和时间对于二氧化钼结构和形貌影响的基础上，研究了这些因素对二氧化钼电化学性能的影响。研究表明：当三氧化钼和CMK-3的质量比为10:1、煅烧温度为820°C、反应时间为90分钟时合成出的二氧化钼纳米管具有最好的循环性能和倍率性能。在电流密度为100mA g-1下充放电70圈之后，二氧化钼的放电比容量仍有720mAh g-1。 (2)在含有多级孔结构二氧化钼纳米管的基础上，通过引入具有高导电性的碳化钼（Mo2C）进一步提高二氧化钼的充放电比容量和改善其循环性能。仍然采用一步碳热还原法，通过控制前驱物三氧化钼和CMK-3的比例成功合成了具有多级孔结构的MoO2/Mo2C纳米管。研究了不同二氧化钼和碳化钼的质量比对二氧化钼和碳化钼复合材料的循环性能和倍率性能的影响。研究表明，在碳化钼含量为30%时，二氧化钼和碳化钼复合材料具有最高的充放电比容量和最好的循环性能和倍率性能。在电流密度为200mAg-1下充放电100圈之后，二氧化钼和碳化钼复合材料的放电比容量仍有790mAh g-1。 (3)通过原位碳包覆的方法来提高二氧化钼的导电性，从而提高二氧化钼的充放电比容量和循环性能。采用新颖的模板辅助法来达到原位碳包覆的目的。本文中以甲醛和间苯二酚为软模板剂，在水热条件下与四水合七钼酸铵（AHM）作用首先得到三氧化钼（MoO3）/酚醛树脂的球型复合物。再将此三氧化钼酚醛树脂复合物在氮气保护下的管式炉中煅烧后获得刺状球型二氧化钼/碳复合物。研究了不同酚醛树脂与AHM质量比和煅烧温度对于二氧化钼/碳复合物的形貌和电化学性能的影响。研究表明，在加入的间苯二酚质量为3.20g、AHM质量为3.09g、甲醛溶液为7mL、煅烧温度为600°C时所合成的二氧化钼/碳复合物具有最好的循环性能和倍率性能。在电流密度为1.0A/g下循环400圈后，二氧化钼/碳复合物的充放电比容量仍有520mAh g-1。 (4)二氧化钼材料在进行前30圈充放电时，充放电比容量会逐渐上升。这个不同于一般金属氧化物材料的现象，一般被解释成二氧化钼电极材料逐渐活化的过程。本文中利用原位XRD技术，观察了在充放电过程中电极材料的物相变化。通过研究所得的XRD谱图和二氧化钼结构的特点，发现二氧化钼前30圈充放电比容量上升是由于二氧化钼锂化机制的转化所引起的。二氧化钼通过脱嵌机制首先形成Li0.98MoO2，这个过程高度可逆。在充放电循环过程中，少量的Li0.98MoO2通过转化机制转化为Mo和Li2O。经过30圈循环后，二氧化钼通过转化机制与Mo和Li2O进行高度可逆的充放电过程。
[Abstract]:Two molybdenum oxide (MoO2) has good conductivity, high stability and high theoretical capacity, is one of the hot material of anode materials for lithium ion batteries at present. However, the actual charge and discharge two molybdenum oxide low specific capacity. This is because in the process of charge and discharge, low conductive molybdenum oxide is formed at the beginning of two step Li0.98MoO2 lithium prevents further lithiation of two molybdenum oxide. At the same time, because the two molybdenum oxide charge discharge process a large volume expansion cycle performance of the two molybdenum oxide is also very poor. More importantly, different from the general metal oxide, molybdenum oxide two charge discharge capacity than before 30 cycles there will be an increase in the process. This is an unusual phenomenon in the literature has not been well explained, generally known simply as the process of electrode material activation. Therefore, the main work of this paper includes the following aspects:
(1) to improve the stability of the transmission rate of lithium ions and electrons of two molybdenum oxide charge discharge process and two molybdenum oxide material structure by introducing hierarchical pore structure, so as to enhance the two molybdenum oxide charge discharge capacity and improve the performance of the cycle. The template agent and reducing agent with mesoporous carbon CMK-3 in this paper, two molybdenum oxide nanotubes were synthesized by one-step carbothermal reduction method. The quality of in-depth study of different MoO3 and CMK-3 ratio, calcination temperature and time effect for two molybdenum oxide structure and morphology, studied the effects of these factors on the electrochemical performance of two molybdenum oxide. The results show that: when the MoO3 and CMK-3 the mass ratio of 10:1, calcining temperature is 820 C, the reaction time is two to 90 minutes when the molybdenum oxide nanotubes synthesized with the cycle performance and rate performance is the best. When the current density is 100mA g-1 after 70 charge discharge cycles, two oxygen The discharge specific capacity of Mo is still 720mAh g-1.
(2) based on hierarchical pore structure containing two molybdenum oxide nanotubes, we introduce a molybdenum carbide high conductivity (Mo2C) to further improve the charge discharge specific capacity of two molybdenum oxide and improve the performance of the cycle. Still by one-step carbothermal reduction method by controlling the precursor of three oxygen molybdenum and CMK-3 the proportion of successful synthesis of hierarchical pore structure of MoO2/Mo2C nanotubes was studied. The cycle performance and rate performance of mass ratio of two different molybdenum oxide and molybdenum carbide two molybdenum oxide and molybdenum carbide composites. The results show that the molybdenum carbide content of 30%, two molybdenum oxide and molybdenum carbide composite with the cycle performance and the charge discharge rate performance of the highest specific capacity and the best. When the current density is 200mAg-1 after 100 charge discharge cycles, discharge two molybdenum oxide and molybdenum carbide composite material specific capacity is still 790mAh g-1.
(3) to improve the conductivity of two molybdenum oxide by means of in-situ carbon coating, thereby improving two molybdenum oxide charge discharge specific capacity and cycle performance. To achieve the purpose of in-situ carbon coating using template assisted method. The novel formaldehyde and resorcinol as soft template in this paper, and seven in four hydrated ammonium molybdate under hydrothermal conditions (AHM) function is firstly obtained MoO3 (MoO3) / ball type composite phenolic resin. Then after calcination furnace the MoO3 phenolic resin composites under the protection of nitrogen in the spiny ball type two molybdenum oxide / carbon composites. Effects of different phenolic resin and AHM mass ratio the effect of the calcination temperature and the morphology and electrochemical performance of carbon composite molybdenum oxide / two. The results show that in the presence of resorcinol mass 3.20g, AHM quality 3.09g, Formaldehyde Solution 7mL, two oxygen molybdenum synthesis calcination temperature is 600 ~ C / The carbon composite has the best cycle performance and rate performance. When the current density is 1.0A/g, the charge and discharge capacity of two moo / C composite is 520mAh g-1. after 400 cycles.
(4) two molybdenum oxide material in the first 30 charge / discharge cycles, the charge discharge capacity will gradually increase. This is different from the metal oxide material phenomenon, is generally interpreted as the process of two molybdenum oxide electrode materials gradually activated by in situ XRD technology. In this paper, the observation of electrode materials in charge and discharge in the process of phase change. Through the study of the XRD spectrum and the structure of two molybdenum oxide, molybdenum oxide was found in two before the 30 ring discharge capacity is increased due to the transformation of two molybdenum oxide lithium mechanism caused by two. Molybdenum oxide intercalation mechanism first form Li0.98MoO2, this process is highly reversible. The charge discharge cycle process, a small amount of Li0.98MoO2 by the transformation mechanism into Mo and Li2O. after 30 cycles, the charge and discharge process of two molybdenum oxide were highly reversible by the transformation mechanism with Mo and Li2O.

【学位授予单位】：上海交通大学
【学位级别】：博士
【学位授予年份】：2014
【分类号】：TQ136.12;TM912

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