钠金属电池的铜集流体表面改性探究

RESEARCH ON SURFACE MODIFICATION OF COPPER CURRENT COLLECTOR FOR SODIUM METAL BATTERY

郑依依

11849431

硕士

化学

权泽卫

2020-05-30

2020-07-15

哈尔滨工业大学

深圳

时代变革，随着科学技术的进步，各类新能源储能系统逐渐投入使用。随着电动汽车和大规模储能系统等领域的快速发展，加快开发新一代具有高能量密度的电池已经成为了当今社会的共识。在众多的电池负极材料中，钠金属负极由于具有较低的氧化还原电势和较高的理论容量而被认为是理想的下一代的负极材料。然而，钠金属负极存在着反应活性较高、容易与电解液反应等问题，此外，钠金属负极在电池的循环过程中会产生钠枝晶，钠枝晶的产生会导致电池容量降低，体积膨胀等问题，还可能引发电池爆炸，产生安全隐患。钠枝晶的产生也是目前钠金属负极最突出的问题，极大地阻碍了钠金属电池的发展。研究表明，构建稳定均匀的人工固态电解质界面膜是一种能有效改善钠枝晶问题的方法，基于这一思路，本文研究了具有双层复合保护层的铜集流体对钠金属负极性能的改善效果。本文使用简单的旋涂法，在纯铜集流体表面制备分别涂上了两层不同的保护层，其中，底层为Al2O3层，顶层为聚偏氟乙烯（PVDF）层（简称为Cu@APDL）。双层保护层中，底层的Al2O3层具有较高的机械模量，可以有效抑制钠枝晶的生长，顶层柔性的PVDF层可以缓解循环过程中负极表面的体积变化，两层保护层共同作用，协同保护钠金属负极，改善钠枝晶生长问题。在探索过程中，本文先对混合浆料的原料比例及旋涂转速进行了筛选，经测试，Al2O3:PVDF=4:1为最佳比例，4000 rpm为最佳转速。然而，采用一步旋涂法改性后的铜集流体存在表面不均匀的问题，针对这一问题，本文对旋涂方法进行了优化，经研究，相较于刮刀涂敷法及一步旋涂法而言，两步旋涂法为最佳的涂膜方式，采用此方法进行改性的铜集流体表面均匀，且循环性能优异。本文对两步旋涂法改性而得的双层复合集流体（Cu@APDL）的各项电化学性能进行了探究，在1 mAh cm-2的容量及1 mA cm-2的电流密度下，Cu@APDL集流体能稳定循环长达1600小时，其循环寿命远超过纯铜集流体的循环寿命。此外，在大电流密度下（5 mA cm-2），Cu@APDL集流体能稳定循环近400小时。在库伦效率的测试中，Cu@APDL集流体在1mA cm-2的电流密度下循环600圈后，其库伦效率仍能保持在99.88%。本文还通过对循环后的Cu@APDL集流体的表面成分进行了测试，探究了双层复合保护层对集流体的保护机理。在50圈的循环后，Cu@APDL集流体表面的固态电解质界面膜主要由Na2CO3、NaF、Na2O及ROCO2Na构成，多种的无机物成分极大地提高了固态电解质界面膜的致密性及刚性模量，能有效阻碍负极与电解液进行接触，从而提高电池性能。Cu@APDL集流体的改性过程操作简便，且Cu@APDL集流体展出了优异的电化学性能，这凸显了采用旋涂法构建双层保护层这一改性策略的优点，为提高钠金属电池性能提供了新的方法。

With the change of the times, various types of new energy storage systems are gradually put into use. With the rapid development of electric vehicles and large-scale energy storage systems, research and development of a new generation of batteries with high energy density has become an urgent task. Among many battery anode materials, sodium metal anodes are considered as the ideal next-generation anode materials due to their lower redox potential and higher capacity. However, sodium metal has high reactivity and is easy to react with the electrolyte. In addition, sodium metal anode will generate sodium dendrites during the cycle of the battery. The generation of sodium dendrites will cause the battery capacity to decrease and the volume to expand, which may cause the battery to explode and cause safety hazards. The generation of sodium dendrites is also the most prominent problem of sodium metal anodes at present, which greatly hinders the practical application of sodium metal batteries. Studies have shown that constructing a stable and uniform artificial solid electrolyte interphase is an effective method to improve the generation of sodium dendrites. Based on the idea, this paper studies the effect of copper current collectors with double-layer protective layers on the performance of sodium metal anodes.This article uses a simple and easy-to-operate spin coating method to prepare two different protective layers on the surface of a commercial copper current collector. The bottom layer is an Al2O3 layer and the top layer is a PVDF polymer layer (referred to as Cu@APDL). For the double-layer composite protective layer, the underlying Al2O3 layer has a high hardness, which can effectively inhibit the growth of sodium dendrites. The flexible PVDF layer on the top layer can alleviate the volume change of the anode. The two protective layers work together to protect sodium metal anode. In this paper, the ratio of raw materials and the speed of spin coating were screened. After testing, Al2O3: PVDF = 4: 1 is the best ratio, and 4000 rpm is the best speed. However, the copper current collector modified by the one-step spin coating method has the problem of uneven surface. In this paper, the spin coating method is optimized. Compared with the blade coating method and the one-step spin coating method, the two-step spin coating method is the best coating method. The copper current collector modified by this method has a uniform surface and excellent cycle performance.In this paper, the electrochemical performance of a copper current collector (Cu@APDL) with a double-layer composite protective layer modified by a two-step spin coating method is investigated. Under the capacity of 1 mAh cm-2 and the current density of 1 mA cm-2, Cu@APDL can stably cycle up to 1600 hours, and its cycle life is far longer than that of copper current collector. In addition, under high current density (5 mA cm-2), Cu@APDL can be stably cycled for nearly 400 hours. In the test of Coulomb efficiency, after the Cu@APDL was circulated over 600 times at a current density of 1 mA cm-2, its Coulomb efficiency was still maintained at 99.88%. In this paper, by testing the Cu@APDL current collector after cycling, the protective mechanism of the double-layer protective layer on the current collector was explored. After 50 cycles, the solid electrolyte interphase of Cu@APDL is mainly composed of Na2CO3, NaF, Na2O, and ROCO2Na. A variety of inorganic components greatly improve the density and rigid modulus of the solid electrolyte interphase, which can effectively protect the sodium anode and improve battery performance.The modification process of the Cu@APDL current collector is easy to operate, and the Cu@APDL current collector exhibits excellent electrochemical performance, which highlights the advantages of the modification strategy of using the spin coating method to build a double protective layer and provides a new method to protective sodium metal anode.

钠金属负极 双层复合保护层 固体电解质界面膜 铜集流体 钠枝晶

sodium metal anode solid electrolyte interphase Cu current collector double-layer composite protective layer sodium dendrite

中文

联合培养

南方科技大学

郑依依. 钠金属电池的铜集流体表面改性探究[D]. 深圳. 哈尔滨工业大学,2020.