基于石榴石型电解质固态电池的界面改性研究

INTERFACE MODIFICATION OF GARNET BASED SOLID STATE BATTERIES

姜益栋

11930261

硕士

材料工程

王军

2021-05-15

2021年6月25号

南方科技大学

深圳

固态锂电池具有高能量密度和高安全性等优势，被认为是一种有望取代现有液态锂离子电池的储能器件。固态电解质作为固态锂电池中最关键的部件，直接影响了固态锂电池的性能。其中，石榴石型Li7La3Zr2O12（LLZO）固态电解质具有高的离子电导率、宽的电压窗口和优异的对锂稳定性等特点，是目前固态电解质材料的研究热点之一。然而，在基于LLZO 固态电解质的固态锂电池中，固态电解质与电极材料之间较差的固-固界面接触所产生的高界面阻抗是阻碍其发展的主要问题之一。当前，针对该界面问题，研究主要针对改善石榴石固态电解质与金属锂界面的亲锂性以及在正极侧采用少量电解液或离子液体等两方面。目前，利用电解液作为石榴石固态电解质界面修饰层的深入研究还鲜有报到，以及原位构建石榴石固态电解质与正极的聚合物界面层的研究也比较少。基于此，本文分别将电解液作为界面修饰层和原位构建正极界面用于石榴石电解质基的固态电池，针对其界面问题进行了相关研究，具体如下：（1）通过将液态电解液滴加在Li6.4La3Zr1.4Ta0.6O12（LLZTO）固体电解质表面，从而有效降低LLZTO 石榴石电解质与锂负极间的界面阻抗，实现锂负极与LLZTO 间的稳定兼容。液态电解液能够有效填充陶瓷电解质的孔隙，并润湿LLZTO 电解质表面，提高其与电极材料的兼容性，并显著降低界面阻抗。因此，改性后的锂对称电池在循环过程中表现出较小的极化电压，并且能够在0.1 mA cm−2 电流密度下稳定循环300 h 以上。（2）采用原位聚合固态电解质层修饰正极侧界面，采用液态金属（LM）修饰LLZTO 与金属锂界面，极大地降低了正负极界面阻抗并改善了基于LLZTO 固态电解质的全固态电池的电化学性能。其中，采用原位聚合方法能够更好浸润整个界面以及正极内部，保证LLZTO 固态电解质与正极活性颗粒的均匀快速锂离子传导，从而使得固态电解质与正极的面电阻值降低至213.9 Ω cm2，与非原位方法相比降低了64.4%。基于以上方法构建的全固态电池具有良好的倍率性能和界面稳定性，在0.1C 倍率下充放电平台间极化电压仅为55 mV，整体面电阻降低至221.8 Ω cm2。循环150 圈后容量保持率为96.7%，平均库伦效率大于99.9%。

Solid-state batteries (SSBs) are considered as one of the most promising alternatives to lithium-ion batteries with liquid electrolyte, due to their improved energy density and enhanced safety. As the most important component of SSBs, solid-state electrolyte (SSE) plays a leading role in the development of battery technology. Among various SSEs, garnet-type Li7La3Zr2O12 (LLZO) electrolyte has become one of the most attractive SSEs due to its high ionic conductivity, broad electrochemical stability window and high chemical stability against lithium.In garnet-based SSBs, the high interface impedance caused by poor solid-solid interfacial contact between solid-state electrolyte and electrode is the main challenge that hinders their development. At present, most investigations regarding interfacial issues of garnet-based SSBs are focused on improving the lithiophilicity of garnet electrolyte with lithium anode and employing a small amount of liquid electrolyte or ionic liquid on cathode side to wet the interface. However, the strategies for improving the lithiophilicity of garnet electrolyte with lithium anode are always complex and expensive. Besides, since the interfacial problem between garnet electrolyte and cathode are more complex compared to that between garnet electrolyte and lithium anode, the conventional way of adding liquid electrolyte would still have problems such as electrolyte decomposition under the catalysis effect of transition metal ions. Therefore, how to solve the interface problem between garnet electrolyte and electrodes (both anode and cathode) is of great significance for the application of garnet-based SSBs. Therefore, in this thesis, interface modified garnet-based SSBs were constructed, and their interface problems were studied: (1) By adding liquid electrolyte on the surface of Li6.4La3Zr1.4Ta0.6O12 (LLZTO) electrolyte, the interface impedance between LLZTO electrolyte and lithium anode is effectively reduced, and the stable compatibility between lithium anode and LLZTO is realized. Liquid electrolyte can effectively fill the pores of ceramic electrolyte and wet the surface of LLZTO electrolyte and thus improving its compatibility with electrode materials and significantly reducing the interfacial resistance. Therefore, the modified Li symmetrical cell exhibits a small polarization voltage during cycling, and can cycle stably for more than 300 h at a current density of 0.1 mA cm-2 without short circuit or obvious increase of polarization voltage.(2) The interface between LLZTO electrolyte and lithium has been modified by liquid metal, and the cathode side interface has been modified by an in-situ polymerized solid polymer electrolyte layer, which greatly reduce the interfacial resistance between electrodes and electrolyte and improve the electrochemical performance of the garnet-based all-solid-state battery. By using an in-situ polymerization method between cathode and SSE, the interfacial issues can be well addressed, and uniform and rapid lithium-ion conduction between LLZTO electrolyte and cathode can be achieved. The interface resistance between solid electrolyte and cathode is reduced to 213.9 Ω cm2, which is 64.4% lower than that of the ex-situ method. All-solid-state battery combining the above two methods delivers good rate capability and interface stability. At 0.1 C, the polarization voltage of charge/discharge platforms is estimated to be only 55 mV, and the overall interface resistance is reduced to 221.8 Ω cm2. After 150 cycles, the cell has capacity retention of 96.7%, and the average Coulombic efficiency is more than 99.9%.

全固态电池 石榴石 电解液 界面改性 原位聚合

all-solid-state batteries garnet liquid electrolyte interface modification in-situ polymerization

中文

独立培养

南方科技大学

姜益栋. 基于石榴石型电解质固态电池的界面改性研究[D]. 深圳. 南方科技大学,2021.