储能科学与技术 ›› 2020, Vol. 9 ›› Issue (2): 368-374.doi: 10.19799/j.cnki.2095-4239.2020.0062

• 庆祝陈立泉院士八十寿辰专刊 • 上一篇    下一篇

锂合金薄膜层保护金属锂负极的机理

王成林, 屈思吉, 李晶泽()   

  1. 电子科技大学材料与能源学院,四川 成都 611731
  • 收稿日期:2020-02-03 修回日期:2020-02-13 出版日期:2020-03-05 发布日期:2020-03-15
  • 通讯作者: 李晶泽 E-mail:lijingze@uestc.edu.cn
  • 作者简介:王成林(1992—),男,硕士研究生,研究方向为薄膜锂电电池,E-mail:442566228@qq.com;
  • 基金资助:
    国家自然科学基金项目(21673033)

Protective mechanism of the Li alloy film-buffered Li metal anode

Chenglin WANG, Shiji QU, Jingze LI()   

  1. School of Materials and Energy, University of Electronic Science and Technology of China, Chengdu 611731, Sichuan, China
  • Received:2020-02-03 Revised:2020-02-13 Online:2020-03-05 Published:2020-03-15
  • Contact: Jingze LI E-mail:lijingze@uestc.edu.cn

摘要:

金属锂是下一代高能锂电池的首选负极材料,在其表面包覆锂合金薄膜层可以大幅度延长其循环寿命,但当前对其保护机理缺乏深入的认识。通过在金属锂箔衬底上磁控溅射制备74 nm厚的Al薄膜,采用扫描电子显微镜观察在锂沉积、锂溶解不同循环周数的锂负极的表面及截面,发现Li-Al合金混合导体保护层展现出异于纯电子导体或纯离子导体保护层的特性。锂离子在合金层的表面被还原,随即快速扩散进入锂合金层中,避免了金属锂在合金层表面的沉积,有效抑制了锂枝晶和副反应的产生。实现了将锂原子的还原和成核生长限域在负极的不同空间位置上,这种新颖的保护模式有效提高了金属锂负极的循环性能。但是,在充放电的中后期,合金层由于周期性的体积变化,出现了大量裂纹,致使电解液可以直接接触金属锂衬底,从而导致合金层的保护作用逐渐失效,电池性能快速恶化。开发具有高机械强度、高离子电导率、膜结构完整、化学反应活性低的薄膜保护层是金属锂负极商业化的必由之路。

关键词: 金属锂电池, 锂负极, 锂合金, 薄膜, 溅射, 保护层

Abstract:

Lithium (Li) is the ideal anode material for next-generation high-energy-density Li batteries. The performance of a Li anode can be improved by coating it with a Li alloy film, the mechanism for which has not been well interpreted. Herein, a Li-Al alloy layer as a mixed conductor, which is formed by sputtering a 74 nm-thick Al film onto a Li sheet, demonstrates a different protection mechanism with respect to those of electron-conducting and ion-conducting protection layers. Scanning electron microscopy images show that Li ions are reduced on the alloy surface and spontaneously diffuse into the alloy layer because the Li+ concentration in the alloy layer is poor. Furthermore, the Li+ diffusion coefficient of the Li-Al alloy is superior to that of the bulk Li. Both factors ensure that Li is not plated on the surface of the alloy layer. A part of the diffused Li atoms is stored in the alloy layer, which considerably increases the layer thickness, and the remaining diffused Li is condensed at the interface between the alloy layer and the Li metal sheet. However, the alloy protection layer cracks after 200 cycles owing to the severe volume variation. Then, a liquid electrolyte can come in contact with Li through the cracks, and the alloy layer is gradually invalidated. This novel protection mechanism, i.e., the isolation of the reduction of Li+ from the nucleation/growth of Li in space, is very promising for improving the cycling performance of the Li metal anode. An ideal alloy-protection layer with high ion conductivity and excellent mechanical stability should guarantee the commercialization of Li anodes in the near future.

Key words: lithium metal battery, lithium anode, li alloy, thin film, sputtering, protective layer

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