An air-stable and waterproof lithium metal anode

Lithium metal anode is promising to upgrade the energy density of lithium ion batteries for its high specific capacity (3800 mAh g-1) and low voltage (-3.04 V vs. Li/Li+). But the safety issues caused by the dendrite growth and the instability in air caused by its high chemical activity limit its large-scale use as an electrode material. Lithium metal is highly sensitive to moisture and oxidative components in the air, leading to the generation of insulating products like lithium hydroxides on its surface and the resultant deterioration of the electrochemical performance. Moreover, when lithium contacts with water, combustion and explosion might happen due to the production of hydrogen and heat. The sensitivity of lithium metal raises demanding requirement for the transport, storage and process of the lithium metal anode. It is hence highly desired to develop an air-stable and waterproof lithium metal anode for its real use in the future.

In the electronics field, the packaging technology protects electronic components from the physical damage and the corrosion in humid air and water by a coating, which provides a design thought for the protection of lithium metal. Recently, a research team led by Prof. Quan-Hong Yang in Tianjin University and Prof. Wei Lv in Tsinghua University developed a wax-PEO coating on lithium metal surface by a simple dip coating method to realize an air-stable and waterproof lithium metal anode. Wax as a commonly-used inert sealing material is easily coated on the surface of lithium metal. The obtained wax-based composite coating prevents the adverse reactions of lithium metal in the air and water. In batteries, the coating retards the etching of electrolyte to the surface of lithium metal anodes while the homogeneously distributed PEO guarantees the uniform lithium ion conduction at the interface and inhibits the growth of lithium dendrites.

Under the protection of wax-PEO coating, lithium surface keeps unchanged in the air with high relative humidity of 70% for 24h, and the high capacity retention of 85% is achieved. Even contacting lithium with water immediately, there is no combustion or capacity decay occurred. The coated lithium metal anode keeps stable for as long as 500 h in symmetric cells and the lithium sulfur batteries assembled with the coated lithium metal anode show a low capacity decay rate of 0.075% per cycle for 300 cycles. This work demonstrates an efficient package technology for the air-stable and waterproof lithium metal anodes, which is easily scalable and applicable to other sensitive electrode materials.