Strategy and technology for universal welding of 903242 battery pack alloys on different battery substrates

Lithium metal batteries have broad application prospects in the field of energy storage in the future due to their lowest reduction potential and ultra-high theoretical specific capacity. However, problems such as lithium dendrite growth and the flammability of liquid organic electrolytes seriously threaten the safe use of lithium metal batteries. Therefore, the most effective strategy is to use non-flammable and mechanically strong solid electrolytes (SSEs) to inhibit the growth of lithium dendrites. Among so many SSEs, cubic garnet phase SSEs have obvious advantages because of their good chemical stability, high ionic conductivity and wide electrochemical potential window. A major challenge in the application of garnet-based solid-state lithium metal batteries is that the surface contact between garnet solid electrolytes and electrode materials is very poor. Direct contact between lithium metal and garnet ceramic sheets generally results in poor contact and large surface impedance. By adding polymer interfaces or applying pressure, the interface will be improved, but the impedance is still very high. [Brief Introduction] Recently, Associate Professor Hu Liangbing from the University of Maryland published a paper titled "Universal Soldering of Lithium and Sodium Alloy on Various Substrates for Batteries" in the famous journal Advanced Energy Materials. The first author is Dr. Wang Chengwei and the co-first author is doctoral student Xie Hua. The article reports a universal welding technology that can quickly coat molten metallic lithium or metallic sodium on different substrates for solid-state batteries and other applications. By adding alloy components, the surface energy and viscosity of molten lithium are increased. Lithium-rich molten alloys show good wettability on substrates such as ceramics, metals and polymers. When this welding coating technology is applied to solid-state batteries, the molten lithium-tin alloy is successfully coated on the freshly polished garnet ceramic sheet within 10 seconds, like a fast welding process. The SEM image confirms the close contact between the alloy and the garnet surface, and its interface impedance is only 7Ωcm2. Lithium insertion-extraction cycle tests confirm the stability of the interface contact between the lithium-rich alloy anode and the garnet SSEs. The same wettability phenomenon is also observed when sodium-based molten alloys and sodium-tin alloys are applied to alumina substrates. [Picture guide] Figure 1: Schematic diagram of welding lithium and lithium alloys on substrates.

a) Pure molten lithium has very low wettability on solid substrates; b) Lithium alloys can be easily welded to substrates with better contact. Figure 2: Wettability of lithium-tin alloys on ceramic substrates.

a) Wettability of lithium-tin alloys with different tin ratios on alumina substrates; b) Lithium-tin alloys are effectively welded to garnet SSE ceramic sheets; c)/d) SEM cross-sectional images of lithium-tin alloys at different resolutions. Figure 3: Electrochemical testing of solid-state symmetric batteries.

a) EIS impedance graph; b) EIS impedance graph before and during cycling; c) Voltage distribution of lithium-tin/garnet/lithium-tin symmetric batteries during insertion-extraction cycles. Figure 4: Morphology and surface characterization of lithium-tin/garnet/lithium-tin symmetric batteries during lithium insertion-extraction processes.

a) Schematic diagram of symmetrical battery; b) SEM cross-section of garnet before lithium-tin alloy coating; c) SEM cross-section of garnet after lithium-tin alloy coating; d) EDS image in image c; e) SEM cross-section of garnet before lithium-tin alloy coating; f) SEM cross-section of garnet after lithium-tin alloy coating; g) EDS image in image f. Figure 5: Alloys welded on different substrates.

a) XRD pattern of binary alloy with good wettability; molten lithium welded on b) titanium foil and c) polyimide film; d) molten sodium on alumina substrate; molten lithium-tin alloy coated on e) titanium foil and f) polyimide film; g) molten sodium-tin alloy welded on alumina substrate. [Summary] By adding alloy components to molten lithium and sodium, the surface energy and negative electrode viscosity are regulated, so the alloy can be directly welded on different substrates. Lithium-tin alloy can be welded on the surface of garnet SSEs within 10s and have good close contact. This alloy can effectively reduce the surface impedance of garnet phase SSE to 7Ωcm2. Electrochemical tests confirmed the stability of the surface and alloy electrodes in long-term and high-capacity tests. In order to explore the versatility of this alloy-based welding technology, other lithium binary alloys have also been studied, and similar wettability has been shown on metal, ceramic and polymer substrates. In addition, this welding technology can be migrated to the molten sodium alloy system, and sodium-tin alloy has also been successfully coated on an alumina substrate.

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