cr2032 button battery.Analysis of bend-resistant negative electrode technology for lithium metal batteries

　　Recently, Professor Luo Jiayan of Tianjin University proposed to prepare a bend-resistant lithium metal anode by combining lithium into a bendable scaffold material. Not only that, the article also demonstrates a flexible integrated solar cell-battery system and a high-voltage series-connected flexible battery pack that can provide stable output. It is envisioned that new bendable energy systems can be developed by further connecting this bend-resistant anode to electrolytes and positive electrodes.

　　Lithium metal batteries, including lithium-sulfur batteries and lithium-oxygen batteries, have higher theoretical energy density than lithium-ion batteries. However, as an ideal anode material, the direct use of lithium metal faces many challenges, especially the formation and growth of lithium dendrites. In addition, the field of conformal electronic devices requires bendable energy storage systems with high energy density, and we hope that lithium metal batteries can meet such requirements. However, under bending conditions, the growth of dendrites will be further aggravated due to local plastic deformation and crushing of lithium filaments caused by bending. How to design and prepare a bendable metallic lithium anode has become a big challenge.

　　【Achievements Display】

　　Recently, the research group of Professor Luo Jiayan of Tianjin University published a research paper titled "Bending-Tolerant Anodes for Lithium-Metal Batteries" in Adv.Mater, proposing to prepare it by combining lithium into bendable scaffold materials (such as reduced graphene oxide films). A bend-resistant lithium metal anode was developed. In composite materials, bending stresses can be dispersed to a large extent through the scaffold material. The scaffold material increases the effective surface area for uniform lithium plating and reduces the volume change of the lithium electrode during cycling, resulting in significantly improved cycling performance under bending conditions. Using bend-resistant r-GO/Li metal electrodes, bendable high cycle stability lithium-sulfur batteries and lithium-oxygen batteries are realized. Not only that, the article also demonstrates a flexible integrated solar cell-battery system and a high-voltage series-connected flexible battery pack that can provide stable output. It is envisioned that new bendable energy systems can be developed by further connecting this bend-resistant anode to electrolytes and positive electrodes.

　　Figure 1 Bending aggravates dendrite growth of lithium metal anode

　　(a) Schematic showing that bending of lithium metal foil leads to the formation of creases/cracks. The electric field around these creases/cracks is stronger than the flat areas, resulting in severe irregular dendrite growth on the curved lithium during plating.

　　(b) Formation of dendrites during lithium metal plating. Bending loose lithium layers can shatter the lithium filaments, resulting in partial loss of lithium. At the same time, bending creates new creases/cracks and accelerates new dendrite growth.

　　(c) SEM images of lithium metal surfaces after different processes. The different processes are initial stage, post-cycling, post-cycling-rebending, post-bending, post-bending-recirculating, and post-cycling under bending conditions. What was tested was a symmetrical lithium metal coin cell using 1MLiTFSI-TEGDME as the electrolyte. The image shows that bending increases dendrite growth.

　　Figure 2 Bend-resistant lithium metal anode using r-GO as supporting material

　　(a) The increased effective surface area of the scaffold makes the lithium plating more uniform.

　　(b) The bending stress in the composite material can be greatly dispersed by the bendable scaffold material. Even if tiny creases/cracks occur, they are less likely to spread because the underlying scaffold material protects the remaining lithium.

　　(c, d) Electroplating/stripping voltage diagrams of symmetrical lithium metal button cells with pure lithium and r-GO/Li composite electrodes and 1MLiTFSI-DME/DOL electrolyte under non-bending and bending conditions.

　　(e, f) Plating/stripping voltage diagrams of symmetrical lithium metal button cells under no-bending and bending conditions with pure lithium and r-GO/Li composite electrodes and 1MLiTFSI-TEGDME electrolyte.

　　(g) SEM images of the lithium surface after using r-GO/Li composite materials as electrodes after different processes. The different processes are initial stage, post-cycling, post-cycling-rebending, post-bending, post-bending-recirculating, and post-cycling under bending conditions. What was tested was a symmetrical lithium metal coin cell using 1MLiTFSI-TEGDME electrolyte. The images show that the r-GO/Li electrode surface is more uniform and has no obvious protrusions under different test conditions.

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