新型钒电池电解液稳定性和电化学性能研究

发布时间：2017-12-27 02:03

本文关键词：新型钒电池电解液稳定性和电化学性能研究　出处：《北京化工大学》2015年硕士论文　论文类型：学位论文

【摘要】：本文旨在提高正极电解液中V5+的热稳定性和电化学性能,将H2SO4与HCl组成的混酸作为正极电解液,通过总酸浓度及盐酸比例的调节,研究其对于V5+热稳定性及参与电极反应历程的影响。此外,还进一步探讨了添加盐酸的负极电解液中V2+的稳定性和电化学性能变化,主要研究内容如下：首先,电解制备2M V5+正极电解液,在30℃至60℃,监测不同混酸体系水浴1Oh后V5+浓度变化,进而考察H2SO4浓度与HCl浓度对于V5+热稳定性的影响。研究表明,HCl的加入可以提高V5+高温稳定性,这可能是由于Cl-可以与五价钒氧离子形成多核的钒氧氯粒子,这种粒子在高温拥有更高的稳定性,可以抑制V205沉淀的生成。并且在40℃至50℃时,这种抑制沉淀生成的效果尤为明显。但是Cl-这种提高V5+稳定性必须建立在一定浓度的H2SO4体系中,即2M V5+必须在2.0M以上的H2SO4中才可以长时间稳定存在。此外,V5+高温热稳定性并非随HCl浓度的提升越高越好,当电解液中氢离子浓度接近10M,V5+高温热稳定性随HCl浓度增加而降低,这可能是由于体系中总酸度过高,自由移动的H20减少,体系中多核的钒氧氯粒子容易重新缔合在一起生成沉淀或者经过碰撞失去Cl原子而又转变成较易形成沉淀的单核钒氧离子而进一步形成沉淀。其次,利用CV、线性极化区扫描、恒电流阶跃、EIS四种电化学测试方法,主要从电机反应历程中电化学步骤和液相传质步骤两个角度,探讨H2SO4含量与HCl含量对于混酸体系中活性物质反应动力学参数的影响。研究表明,由5M、4M及2.5+3、3+2.5、3+3、2+3、2+4、2+6体系观察发现,随着HCl浓度的增加,电极反应中电化学极化电阻Re呈先降低后增大再减小又增大的趋势,这可能是由于HCl的添加,体系中生成了新的单核钒氧氯粒子,这种粒子拥有较好的电活性所致；随着盐酸比例的提高,当H2SO4浓度降低到2.5M以下时,受H2SO4浓度的影响,钒氧离子活性降低,因此Re得以增大,但是随着Cl-的增加,溶液中单核钒氧氯离子相互配合形成大量多核钒氧氯粒子,这种粒子的结构使其拥有更高的电活性,因此Re再降低,但是随着Cl-进一步增加,体系中过剩的Cl-特性吸附在电极表面,降低电极表面活性点,使电极反应电荷转移的难度增大,因此Re出现升高。Rc先减小是由于,随着H2804浓度降低,体系黏度减小,液相传质变得更为容易；而后又升高是由于多核的钒氧氯粒子的半径较大,在双电层中传递到电极表面更为困难所致。最后,利用上述四种电化学研究方法研究了HCl的添加对于V2+参与负极半反应历程的影响,研究发现HCl的加入虽然可以有效的提高了半反应的i0,降低了电化学步骤的阻力大小,但是液相传质步骤阻力明显增大,因其为电极反应的速度控制步骤,因此体系总极化电阻Rp增加,不利于整个体系电极反应的进行。此外,通过电位滴定的方法监测了电解完成10h内负极电解液中V2+浓度的变化,研究表明,HCl的添加不利于V2+保持稳定溶解,因此,H2SO4与HCl组成的混酸不适合作为负极电解液的支持电解质。
[Abstract]:The purpose of this paper is to improve the thermal stability and electrochemical performance of V5+ in positive electrolyte. The mixed acid composed of H2SO4 and HCl is used as the positive electrolyte. The effects of total acid concentration and hydrochloric acid proportion on the thermal stability of V5+ and the participation in electrode reaction process are studied. In addition, further discusses the change of stability and electrochemical performance of cathode electrolyte hydrochloric acid is added in V2+, the main research contents are as follows: firstly, the electrolytic preparation of 2M V5+ cathode electrolyte, at 30 degrees centigrade to 60 degrees centigrade, monitoring the concentration change of V5+ mixed acid system 1Oh water bath after different, and the effects of H2SO4 concentration and HCl concentration on the thermal stability of V5+. The research shows that the addition of HCl can improve the stability of V5+ at high temperature, which may be due to vanadium oxychloride particles Cl- can form polynuclear and pentavalent vanadium oxygen ions, the particles have higher stability at high temperature, V205 can restrain the generation of precipitation. And the effect of this inhibition is particularly obvious at 40 to 50 degrees C. However, the stability of Cl- to improve V5+ must be established in a certain concentration of H2SO4 system, that is, 2M V5+ must be stable in the H2SO4 above 2.0M for a long time. In addition, V5+ thermal stability is not increased with the concentration of HCl is good, when the concentration of hydrogen ions in the electrolyte is close to 10M, V5+ thermal stability decreased with the increase of HCl concentration, which may be due to the total acidity in the system is too high, free mobile H20 reduced vanadium oxychloride particles in multi-core system easy to associate together to form precipitate or after the collision of Cl atoms and lost into the easy formation of mononuclear vanadyl ion precipitation and further the formation of precipitation. Secondly, by using CV and scanning, linear polarization current step and EIS four electrochemical test methods, mainly from two angles of motor in electrochemical reaction process steps and liquid phase mass transfer steps on H2SO4 content and HCl content for the effects of active substances mixed acid system kinetic parameters. Research shows that, by 5M, 4M and 2.5+3, 3+2.5, 3+3, 2+3, 2+4, 2+6 system was observed with the increase of HCl concentration, the electrode reaction in the electrochemical polarization resistance Re decreased first and then increased and then decreased and increased, which may be due to the addition of HCl, the system generates a new single core vanadium oxychloride particles, the particles have better electrical activity induced by hydrochloric acid; with the increase of the proportion of H2SO4, when the concentration is reduced to below 2.5M, affected by the concentration of H2SO4, reduce the activity of vanadium ions, so the Re can be increased, but with the increase of Cl- in the solution of mononuclear vanadyl chloride with each other to form a large number of multi core vanadium oxychloride particles, the particle structure so that it has higher electrical activity, so Re reduce, but with the further increase of Cl- in the system of Cl-, characteristics of the excess adsorption at the electrode surface, reducing the activity of the electrode surface, the electrode reaction power The difficulty of load transfer increased, so Re increased. The reduction of Rc first is due to the decrease of the viscosity of the system and the decrease of liquid mass transfer as the concentration of H2804 decreases, and then the increase is due to the larger radius of the multi core vanadium oxychloride particles, which is more difficult to transfer to the electrode surface in the double layer. Finally, HCl study of the effects of additives on V2+ in the negative half reaction process using the above four kinds of electrochemical methods, the study found that although the addition of HCl can effectively improve the half reaction I0, reduced the electrochemical step size of the resistance, but the steps of liquid phase mass transfer resistance increased significantly, because the speed of electrode reaction the control step, so the total polarization resistance of Rp system increases, is not conducive to the whole system of electrode reaction. In addition, the change of V2+ concentration in the negative electrolyte of 10h was monitored by potentiometric titration. The results showed that the addition of HCl was not good for V2+ to maintain stable dissolution. Therefore, the mixed acid composed of H2SO4 and HCl is not suitable for supporting electrolyte of negative electrolyte.
【学位授予单位】：北京化工大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TM912

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