物理化学学报 >> 2021, Vol. 37 >> Issue (1): 2007058.doi: 10.3866/PKU.WHXB202007058

所属专题: 金属锂负极

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柱状金属锂沉积物:电解液添加剂的影响

杨世杰1,3, 徐向群2, 程新兵2,*(), 王鑫萌2,4, 陈金秀2,5, 肖也1,3, 袁洪1,3,*(), 刘鹤1,3, 陈爱兵4, 朱万诚5, 黄佳琦1,3, 张强2   

  1. 1北京理工大学材料学院,北京 100081School of Materials Science & Engineering, Beijing Institute of Technology, Beijing 100081, China
    2清华大学化学工程系,绿色反应工程与工艺北京市重点实验室,北京 100084Beijing Key Laboratory of Green Chemical Reaction Engineering and Technology, Department of Chemical Engineering, Tsinghua University, Beijing 100084, China
    3北京理工大学前沿交叉科学研究院,北京 100081Advanced Research Institute of Multidisciplinary Science, Beijing Institute of Technology, Beijing 100081, China
    4河北科技大学化学与制药工程学院,石家庄 050018College of Chemical and Pharmaceutical Engineering, Hebei University of Science and Technology, Shijiazhuang 050018, China
    5曲阜师范大学化学与化工学院,山东 曲阜 273165School of Chemistry and Chemical Engineering, Qufu Normal University, Qufu 273165, Shandong Province, China
  • 收稿日期:2020-07-23 录用日期:2020-08-31 发布日期:2020-09-04
  • 通讯作者: 程新兵,袁洪 E-mail:cxb12@mails.tsinghua.edu.cn;yuanhong@bit.edu.cn
  • 基金资助:
    国家重点研发计划(2016YFA0202500);国家重点研发计划(2016YFA0200102);国家自然科学基金(21805161);国家自然科学基金(21808124);国家自然科学基金(U1932220)

Columnar Lithium Metal Deposits: the Role of Non-Aqueous Electrolyte Additive

Shijie Yang1,3, Xiangqun Xu2, Xinbing Cheng2,*(), Xinmeng Wang2,4, Jinxiu Chen2,5, Ye Xiao1,3, Hong Yuan1,3,*(), He Liu1,3, Aibing Chen4, Wancheng Zhu5, Jiaqi Huang1,3, Qiang Zhang2   

  • Received:2020-07-23 Accepted:2020-08-31 Published:2020-09-04
  • Contact: Xinbing Cheng,Hong Yuan E-mail:cxb12@mails.tsinghua.edu.cn;yuanhong@bit.edu.cn
  • About author:Yuan Hong. E-mail: yuanhong@bit.edu.cn
    Cheng Xinbing. E-mail:cxb12@mails.tsinghua.edu.cn
  • Supported by:
    the National Key Research and Development Program of China(2016YFA0202500);the National Key Research and Development Program of China(2016YFA0200102);the National Natural Science Foundation of China(21805161);the National Natural Science Foundation of China(21808124);the National Natural Science Foundation of China(U1932220)

摘要:

二次电池的能量密度已成为推动电动汽车和便携式电子产品技术向前发展的重要指标。使用石墨负极的锂离子电池正接近其理论能量密度的天花板,但仍难以满足高端储能设备的需求。金属锂负极因其极高的理论比容量和极低的电极电位,受到了广泛关注。然而,锂沉积过程中枝晶的生长会导致电池安全性差等问题。电解液对金属锂的沉积有着至关重要的影响。本文设计了一种独特的电解槽体系来进行柱状锂的沉积,研究了不同电解液体系(1 mol·L-1 LiPF6-碳酸乙烯酯/碳酸二乙酯(EC/DEC,体积比为1 : 1)、1 mol·L-1 LiPF6-氟代碳酸乙烯酯(FEC,体积分数5%)-EC/DEC (体积比为1 : 1))对金属锂沉积的影响。对两种电解液中金属锂沉积物长径比的研究表明,电解液的组分可以显著地影响金属锂的沉积形貌,在加入氟代碳酸乙烯酯(FEC)添加剂之后,柱状锂的直径从0.3–0.6 μm增加到0.7–1.3 μm,长径比从12.5下降到5.6。长径比的降低有助于减小金属锂和电解液的反应面积,提高金属锂负极的利用率和循环寿命。通过考察循环后锂片的表面化学性质,发现FEC的分解增加了锂表面固态电解质界面层中氟化锂(LiF)组分的比例,提高了界面层中锂离子的扩散速率,减少了锂的成核位点,从而给予锂核更大的生长空间,降低了沉积出的柱状锂的长径比。

关键词: 金属锂电池, 柱状锂, 电解液, 氟化锂, 长径比

Abstract:

With the booming growth market of electric vehicles and portable electronics, high-energy-density rechargeable lithium ion batteries are being extensively used to advance high-end devices. Lithium-ion batteries with graphite anodes approach the ceiling in energy density, but they cannot satisfy the current demand. Among the next-generation electrodes, lithium metal anodes are strong candidates because of their high theoretical capacity and the most negative electrochemical potential. However, lithium metal batteries have been abandoned because of their poor safety resulting from the growth of lithium dendrites during lithium deposition. Although several strategies have been proposed to suppress the generation of lithium dendrites as well as the side reactions between active lithium and the electrolyte, lithium metal anodes have not been practically applied so far. Various studies have been conducted on the factors influencing lithium deposition, with the aim of understanding the growth behavior of lithium dendrites. The electrolyte plays a crucial role in the performance of the working Li metal anode. In this study, a unique battery system is proposed to realize columnar lithium deposition, which is convenient for obtaining the length and diameter of lithium deposits. The influence of different electrolytes on lithium deposition was investigated by comparing the length-diameter (L/D) ratio of the lithium deposits in two kinds of electrolytes (1.0 mol·L-1 LiPF6-ethylene carbonate/diethyl carbonate (EC/DEC, 1 : 1 by volume) and 1.0 mol·L-1 LiPF6-5% (volume fraction) fluoroethylene carbonate (FEC)-EC/DEC (1 : 1 by volume)). The morphology of the lithium deposits was strongly affected by the electrolyte composition. In the electrolyte with the FEC additive, the diameter of columnar lithium increased from 0.3-0.6 μm to 0.7-1.3 μm, while the L/D ratio decreased from 12.5 to 5.6. The small L/D ratio can reduce the reactive area between the lithium metal anode and the electrolyte, which is beneficial for achieving high lithium utilization and a long lifespan. To probe the origin of this influence, the surface chemistry of the cycled lithium metal anode was investigated by X-ray photoelectron spectroscopy. The FEC additive can increase the proportion of lithium fluoride (LiF) in the solid electrolyte interphase, which is conducive for the rapid diffusion of lithium ions. As a result, fewer nucleation sites are formed, providing more space for the growth of lithium cores with a large diameter. Therefore, the addition of FEC leads to a decrease in the L/D ratio of columnar lithium.

Key words: Lithium metal battery, Columnar lithium, Electrolyte, Lithium fluoride, Length-diameter ratio

MSC2000: 

  • O646