Analysis of the bending negative electrode technology of lithium metal battery

【introduction】

Lithium metal batteries, including lithium-sulfur batteries and lithium-oxygen batteries, have higher theoretical energy densities 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 flexible energy storage systems with high energy density, and we hope that lithium metal batteries meet such requirements. However, under the conditions of bending, the local plastic deformation due to bending and the pulverization of the lithium filaments further increase the growth of the dendrites. How to design and prepare a bendable metal lithium anode has become a major challenge.

[Results show]

Recently, Professor Luo Jiayan of Tianjin University published a research paper entitled “Bending-Tolerant Anodes for Lithium-meal Batteries” in Adv. Mater, which proposed to combine lithium into a flexible scaffold material (such as reduced graphite oxide). A lithium metal negative electrode which is resistant to bending is prepared in an ene film. In composite materials, the bending stress is largely dissipated by the scaffold material. The scaffolding material increases the effective surface area of ​​the uniform lithium plating, reduces the volume change of the lithium electrode during the cycle, and thus the cycle performance under bending conditions is significantly improved. A bendable high cycle stability lithium-sulfur battery and lithium-oxygen battery are realized using a bend-resistant r-GO/Li metal electrode. Not only that, but the paper also shows a flexible integrated solar cell-battery system and a high-voltage series bendable battery pack that can stabilize the output. It is envisioned that this bend-resistant anode will be further connected to the electrolyte and the positive electrode to develop a new flexible energy system.

[Graphic introduction]

Figure 1 Bending increases the dendrite growth of lithium metal anodes

(a) The schematic shows that the bending of the lithium metal foil causes 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 bent lithium during electroplating.

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

(c) SEM images of lithium metal surfaces subjected to different processes. The different processes are after the initial stage, after the cycle, after the cycle and then after the bending, after the bending, after the bending and after the cycle, and after the cycle under the bending conditions. A symmetrical lithium metal coin cell battery using 1 M LiTFSI-TEGDME as an electrolyte was measured. The image shows that bending can exacerbate the growth of dendrites.

Figure 2 Bending lithium metal negative electrode using r-GO as support material

(a) The effective surface area of ​​the stent increases to make the plated lithium more uniform.

(b) The bending stress in the composite material can be greatly dispersed by the flexible stent material. Even if tiny creases/cracks are produced, they are not easily diffused because the underlying scaffold material protects the remaining lithium.

The (c,d) electrodes are pure lithium and r-GO/Li composites respectively, and the electrolyte is a 1M LiTFSI-DME/DOL symmetrical lithium metal button battery with no plating and stripping voltage diagram under bending and bending conditions.

(e, f) Electrode is a pure lithium and r-GO/Li composite material, and the electrolyte is a 1M LiTFSI-TEGDME symmetrical lithium metal coin cell battery plating/peeling voltage diagram without bending and bending.

(g) SEM image of the lithium surface after different processes using the r-GO/Li composite as the electrode. The different processes are after the initial stage, after the cycle, after the cycle and then after the bending, after the bending, after the bending and after the cycle, and after the cycle under the bending conditions. A symmetrical lithium metal coin cell battery using 1 M LiTFSI-TEGDME electrolyte was tested. The image shows that the surface of the r-GO/Li electrode is more uniform and there are no obvious protrusions under different test conditions.

Figure 3 bendable lithium-sulfur battery

(a) Illustration of a bendable lithium-sulfur battery.

(b, c, d) Photographs of the S-CNT cathode, SEM images, and X-ray energy spectrum element images.

(e) Photograph and cycle performance of CR2032 lithium-sulfur battery with pure lithium and r-GO/Li.

(f) The photo and cycle performance of the soft lithium-sulfur battery (7 cm × 5 cm) of pure lithium and r-GO/Li were bent at 180 °.

(g, h) SEM images show that the pure lithium anode after cycling under bending conditions has severe dendritic growth and is heavily contaminated by polysulfides. In contrast, the r-GO/Li electrode surface is more uniform after cycling, and there are fewer SEI films and Li2Sn.

(i) The infrared absorption spectrum of the anode after the cycle under bending conditions indicates that the degree of contamination of the r-GO/Li anode is smaller than that of pure lithium.

Figure 4 Flexible integrated solar cell - battery system and series laminated battery

(a, b) A photograph of a power supply line connecting a lithium-sulfur battery and a lithium-oxygen battery to a light-emitting diode.

(c) Charge-discharge curves for bendable integrated solar cells-lithium-sulfur battery systems at different current densities. The illustration is a photo of the integrated device.

(d) Charge and discharge curves for tandem lithium-sulfur battery packs, the inset is the symbols and photographs of the series battery pack.

【to sum up】

The article introduces that the lithium metal electrode prepared by using r-GO as a scaffold material has bending resistance and can be used in a flexible lithium metal battery. In the r-GO/Li anode, the growth of lithium dendrites is remarkably suppressed even under bending conditions. In addition, the r-GO layer can also reduce lithium loss by promoting homogenization of the electroplated lithium and confining lithium to the scaffold material. Embedding a flexible r-GO layer in lithium metal under bending conditions can help eliminate bending stress, slow down the diffusion of defects, and cracks during bending. The composite negative electrode can significantly improve the cycle life in the electrochemical plating/peeling process, and can also greatly improve the bending resistance. The use of such an anode enables the construction of high-performance lithium-sulfur batteries and lithium-oxygen batteries, and can be easily compatible with flexible solar cells, thereby achieving a flexible integrated solar cell-battery system.