Tianjin University and Tsinghua University develop wax-PEO coating to make waterproof/air-stable lithium metal anodes

According to foreign media reports, a research and development team led by Professor Quanhong Yang of Tianjin University and Professor Wei Lv of Tsinghua University prepared a wax-PEO (plasma electrolytic oxidation) coating on the surface of lithium metal through a simple dip coating method, thereby making an air-stable and waterproof lithium metal anode. Wax, as a commonly used inert sealing material, can be easily coated on the surface of lithium metal.

(Image source: Science China)

Lithium metal anodes have the characteristics of high specific capacity, low potential and light weight, which can effectively improve the energy density of batteries. That is, switching to lithium metal anodes will significantly increase the range of electric vehicles and reduce the cost of batteries used for grid energy storage . However, due to the high chemical activity of lithium, it is easy to cause dendrite growth and air instability, which leads to safety problems, thus limiting its large-scale application as an electrode material.

Lithium metal is very sensitive to moisture and oxidizing components in the air, which will cause insulating substances such as lithium hydroxide to form on its surface, which will lead to the deterioration of its electrochemical performance. In addition, when lithium comes into contact with water, it will produce hydrogen and heat, which may cause fire or explosion. This sensitivity of lithium metal places higher requirements on the transportation, storage and processing of lithium metal anodes. Therefore, there is an urgent need to develop an air-stable and waterproof lithium metal anode so that lithium metal anodes can be truly applied in the future.

In the field of electronic equipment, packaging technology can be used to protect electronic components from physical damage and corrosion from humid air and water, which also provides design ideas for how to protect lithium metal.

The wax-based composite coating developed by the researchers can prevent lithium metal from reacting adversely in air and water. In batteries, such coatings slow down the corrosion of the electrolyte on the surface of the lithium metal anode; while the evenly distributed PEO ensures that lithium ions can conduct electricity evenly at the interface, inhibiting the growth of lithium dendrites.

Under the protection of the wax-PEO coating, the surface of lithium metal did not change in air with a relative humidity of 70% within 24 hours, and the high specific capacity retention rate was 85%. Even if it was in direct contact with water, there was no fire or capacity decay. After the lithium metal anode was coated with the coating, it remained stable in a symmetrical battery for up to 500 hours, and the lithium-sulfur battery made of the lithium metal anode coated with the coating had a capacity decay rate as low as 0.075% after each cycle in 300 charge and discharge cycles.

This study demonstrates an efficient packaging technology for air-stable and water-resistant lithium metal anodes, which is easily scalable and applicable to other sensitive electrode materials.