Lithium ion secondary batteries have been widely used in the field of portable electronic equipment due to their high energy density, but they still cannot meet the high energy density requirements of large-capacity energy storage devices such as electric vehicles and power grids. Lithium metal has a high specific capacity (3860 mAh g‒1) and a low electrochemical potential (‒3.04 V relative to a standard hydrogen electrode), and is an ideal high energy density negative electrode material. The solid-state battery with metal lithium as the negative electrode is considered to be the future development direction of high energy density and high safety rechargeable energy storage devices.
However, the research and development of lithium metal batteries is extremely challenging. Although it has taken many years, high-energy-density rechargeable batteries with lithium metal as the negative electrode have not been commercialized. The most important reason is the uncontrollable lithium dendrites (a kind of The dendrites, whose needle-like protrusions are called whiskers) grow, when lithium dendrites grow to a certain degree, they can penetrate the solid electrolyte, making the battery short-circuit failure; in addition, if the lithium dendrites are entangled or broken, it will form " "Dead lithium" causes a serious decline in battery capacity, so the growth of lithium dendrites is the biggest obstacle to the application of metal lithium batteries.
Many studies are devoted to exploring how to suppress the generation of lithium dendrites, but previous studies have mainly stayed at the macro scale. The microscopic mechanism, mechanical properties, mechanism of piercing solid electrolytes and the scientific basis for inhibiting the growth of lithium dendrites are not clear.
Today, Professor Huang Jianyu, Professor Shen Tongde and Associate Professor Tang Yongfu of Yanshan University, together with Professor Zhu Ting of the Georgia Institute of Technology and Professor Zhang Sulin of the University of Pennsylvania, published in Nature Nanotechnology entitled "Lithium whiskers growth and stress generation in an in situ atomic force microscope-environmental The research paper "transmission electron microscope setup" recorded the microscopic mechanism of lithium dendrite growth in real time and intuitively, accurately measured its mechanical properties and force-electricity coupling characteristics, and proposed a feasible solution to inhibit the growth of lithium dendrites in solid-state batteries. . Dr. Zhang Liqiang and Dr. Yang Tingting are co-first authors of the paper.
Figure 1: AFM-ETEM nanoelectrochemical test platform. It can realize in-situ observation and precise quantitative measurement of lithium dendrite growth mechanism and its mechanical properties and force-electricity coupling in nano-solid batteries.
The researchers combined atomic force microscopy (AFM) and environmental transmission electron microscopy (ETEM) to achieve in-situ nanometer-scale lithium dendrite growth and its mechanical properties and force-electricity coupling accurate determination. It was found that the stress that can be generated during the growth of lithium dendrites is as high as 130 MPa. The yield strength of lithium dendrites is found to be as high as 244 MPa through in-situ compression experiments, which is much higher than the yield strength of macroscopic lithium metal (~ 1 MPa).
The innovation of this paper lies in:
Invented an in-situ electrochemical testing platform based on atomic force microscope-environmental transmission electron microscope (AFM-ETEM). On the one hand, AFM is used as an electrode for growing lithium dendrites, and on the other hand, it has a binding force on the growth process of lithium dendrites, and it can also monitor the growth stress in real time. The platform can be widely used to study the mechanics and force-electricity coupling of dendrite growth in sodium, potassium, magnesium, calcium and other battery systems.
An effective new in-situ characterization technique for studying lithium dendrites was established, the mechanical properties of micro-nano-scale lithium dendrites under electrochemical driving and non-electrochemical driving were determined, and a structure based on solid electrolyte was proposed. The matching relationship between defects, mechanical properties and mechanical properties of lithium dendrites achieves a feasible scheme for inhibiting the growth of lithium dendrites.
Clever use of ETEM technology, through the introduction of CO2 in ETEM, in-situ growth of nano-scale Li2CO3 solid electrolyte (SEI) protective layer on the surface of Li metal. It is this ultra-thin Li2CO3 SEI protective layer that significantly improves the stability of ultra-active lithium metal in transmission electron microscopy and protects it from electron beam damage, thereby realizing the growth process of sub-micron lithium dendrites at room temperature. In-situ imaging, mechanical properties, and force-electricity coupling measurements.
This study subverts the researchers' traditional understanding of the mechanical properties of lithium dendrites and provides a new quantitative benchmark for inhibiting the growth of lithium dendrites in all-solid-state batteries. It provides a scientific basis for designing metal lithium solid-state batteries with high capacity and long life. The research results will help solid-state batteries in electric vehicles, large-scale energy storage and portable electronic devices and other fields of research and development. This work is strongly supported by the National Fund Committee and the Ministry of Science and Technology.
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