[2017-06-27]Towards a new era of all-solid lithium batteries

Most of the cells consist of a solid, electrochemically active electrode layer at both ends separated by a polymer membrane that incorporates a liquid or gel electrolyte. Recently, however, researchers have discovered the possibility of making all-solid-state lithium batteries. Liquid electrolytes (and potentially flammable hazards) may be replaced by solid electrolytes, which increase the energy density and safety of batteries.

 

 

 

     Today, a research team at MIT has for the first time tested the mechanical properties of a sulfur-based solid electrolytic material used to determine its mechanical performance in a battery.

The MIT research team used specialized instruments to test in which they used a pyramidal tip probe to cut the surface of a piece of sulfur-based material. Around the tapered groove in the middle of the picture, the crack indicated by the arrow is formed in the material, showing the mechanical properties of the material.

 

 

 

    MIT graduate students Frank McGrogan and Tushar Suamy, materials science and engineering professor Krystyn Van Vliet, the Michael (1949) and Sonja Koerner, professor of materials science and engineering porcelain, Jiang Yeming, and four research groups including undergraduates The publication was published in this week's Advanced Materials Magazine. The four undergraduate participants came from the National Science Foundation's undergraduate research experience project team, which was incorporated by the MIT Materials Science and Engineering Research Center and Processing Center.

 

 

 

    Lithium-ion batteries have proven to be a lightweight energy storage method and are used in many types of high-tech equipment today, from smartphones to electric vehicles. However, replacing the traditional liquid electrolytes in these batteries with solid electrolytes has several significant advantages. This all-solid-state lithium-ion battery has a more powerful power reserve capability under the premise of the same battery pack. It also substantially eliminates the risk of short-circuiting of fingertip-sized defect substances called dendrites along the electrolyte layer leading to short circuits.

 

 

 

    “Batteries made up of solid components are an attractive option both in terms of performance and safety, but we also face some challenges,” Van Vliet said. In the current market, lithium-ion batteries are freed from the one end electrode to the other end during the charging process, and are oppositely released during the discharge process. Such batteries are highly efficient, but "the chemical properties of their liquid electrolytes are not particularly stable and can be safer, smaller, and lighter."

 

 

 

    However, a major problem faced by such an all-solid-state battery in use is that when the electrode is subjected to multiple discharges, mechanical stresses of unknown origin are generated inside the battery. Such a cycle can cause the battery to swell or shrink as lithium ions enter and exit its lens structure. In a hard electrode, a change in size causes an increase in pressure. If the electrolyte is too weak, continuous changes in size can cause electrolyte breakdown and can significantly affect the performance of the battery, and may even form orbits that promote the formation of dendrites, as may occur in liquid electrolytes. However, if the electrolyte is quite resistant to cracking, the pressure will be resolved to some extent and rapid cracking will not occur. However, to date, the high sensitivity of sulfur-based materials to laboratory air has placed no small challenge on measuring mechanical properties including its fracture toughness. To circumvent this problem, members of the research team conducted mechanical performance tests in a mineral oil environment to prevent the reaction of sulfur-based substances with air or air. Through this technology, the team was able to accurately measure the mechanical properties of the sulphur-based lithium-ion polymer, which made it a strong competitor for the electrolyte component of all-solid-state lithium-ion batteries.

 

 

 

    "There are many candidates for solid electrolytes," McGrogan said. Other groups have studied the mechanical properties of oxides and lithium-ion polymers, but there are not many studies on sulfur-based materials, even sulfur-based and lithium-ion. The combination of simple and fast, the prospects are very bright.

 

 

 

    Previous researchers used acoustic measurement techniques to detect the mechanical properties of materials based on sound waves, but this method could not measure the fracture toughness of the material. In this new study, however, the researchers used a pointed probe to puncture the surface of the material to detect the material's reaction, resulting in a more complete set of parameters for the material, including hardness, fracture toughness, Young's modulus (a unit of measure for measuring the ability of a material to stretch under applied stress).

 

 

 

    "Researchers have measured the tensile strength of sulfur-based solid electrolytes, but have not measured their fracture toughness," Van Vliet said. Fracture toughness is a visually important factor in determining whether the material will be broken or broken in the battery.

 

 

 

    The researchers found that the properties of the substance are similar to elastic rubber or salt water toffee to a certain extent: when pressure is applied, the material is easily deformed; but under great pressure, the material will look like The piece is broken like a fragile glass.

 

 

 

    With these detailed parametric properties, “you can measure how much pressure the material can withstand before breaking,” Van Vliet said, knowing the relevant information and then designing a new battery system.

 

 

 

    It turns out that the material is more fragile than the ideal solid electrolyte material, but McGrogan said that with the acquisition of this parameter and its tailored battery system, it still has potential use value, "you need to pass Its understanding is tailored."

 

 

 

    "The cycle life of the most advanced lithium-ion batteries is currently influenced by the chemical/electrochemical stability of the electrolyte and the way the electrolyte reacts with the electrodes," said Jeff Sakamoto, a professor of mechanical engineering at the University of Michigan, who did not participate. In the study. “However, in solid-state batteries, the degree of mechanical degradation plays a decisive role in the durability and performance of the battery. Therefore, understanding the mechanical properties of solid-state battery electrolytes is particularly important.”

 

 

 

    Sakamoto also said: "Lithium metal anodes have shown a significant increase in capacity compared to the most advanced graphite anodes available. In other words, in terms of energy density, compared to conventional lithium-ion battery technology, this electrode allows The energy density of the battery has increased by nearly 100%."

 

 

 

    The research team also includes MIT researchers Sean Bishop, Erica Eggleton, Lukas Porz and Chen Xinwei. The project is supported by the US Department of Energy's Office of Basic Energy Science, which is away from the equilibrium interface mechanical chemistry department.

 

 

 

News source: Materials provided by the MIT Press Office, formerly author David L. Chandler.

 

Note: In order to adapt to the length of the news, the original text has been modified as appropriate.

 

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