Lithium nmc cathode2/14/2024 ![]() It was commonly observed that Li plating causes fracture of the CC, leading to “dead Li” formation, low Coulombic efficiencies, and even short-circuiting in the case of LLZO. Recent studies have investigated the Li nucleation behavior at the interface of sputtered CCs and LiPON or LLZO electrolytes, which allows for visualization of the plating process 19, 20, 21, 22. However, unlike most LiPON systems, under certain conditions LLZO is susceptible to Li filament propagation and subsequent short-circuiting 16, 17, 18. One of the most promising solid-state electrolytes is Li 7La 3Zr 2O 12 (LLZO), which has high ionic conductivity and excellent stability against Li metal. Indeed, the pioneering development of thin-film LiPON technology demonstrated the feasibility of Li-metal solid-state secondary batteries however, current approaches are pursuing bulk-scale manufacturing approaches to achieve cost parity with large format technologies such as Li-ion. Lithium phosphorus oxynitride (LiPON) is one of the few stable solid-electrolyte materials that demonstrate the ability to resist Li filament propagation, thereby enabling the fabrication of “Li-free” batteries 15. In liquid-based batteries, this concept has been demonstrated, but it’s feasibility is limited by the high reactivity of Li with traditional liquid electrolytes, leading to low cycling efficiency 9, 10, 12, 13, 14. The Li-metal anode is then formed electrochemically on the first charge cycle by electroplating Li contained within the cathode. ![]() For these reasons, in both liquid- and solid-state Li-metal batteries, there is a growing interest in “Li-free” (or anode-free) manufacturing 9, 10, 11, 12, in which the battery is fabricated in the discharged state, with a bare current collector (CC) replacing the conventional anode. In addition to manufacturing, integration of the Li-metal anode with a solid-electrolyte with relevant thickness, low interfacial resistance, high chemical purity, and using scalable processes still remains a major challenge. However, given the difficulty and cost of handling, free-standing Li foils may not be viable 8. Although advanced cathode chemistries would undoubtedly further improve the theoretical energy densities, it is believed that state-of-the-art cathodes (e.g., NMC, NCA, LFP) are currently the most viable chemistries to achieve energy densities >1000 Wh L −1, cycle life > 1000 cycles with ≤80% capacity fade, and current cost 200 μm) Li foils, although Li foils down to ~20 μm have been made. Along with the replacement of the flammable liquid electrolyte, solid electrolytes may enable the replacement of graphite anodes with metallic Li, which allows for a dramatic (40–50%) increase in energy density 1, 2, 3, 4, 5. Owing to the combination of high energy density and safety, solid-state batteries are a promising candidate to enable the widespread adoption of electric vehicles. These findings demonstrate the viability of “Li-free” configurations using LLZO which may guide the design and manufacturing of high energy density solid-state batteries. A full cell consisting of in situ formed Li, LLZO, and NCA is demonstrated, which exhibits stable cycling over 50 cycles with high Coulombic efficiencies. We demonstrate that Li-metal anodes >20 μm can be electroplated onto a current collector in situ without LLZO degradation and we propose a model to relate electrochemical and nucleation behavior. Here we show the potential for “Li-free” battery manufacturing using the Li 7La 3Zr 2O 12 (LLZO) electrolyte. However, integrating metallic Li with solid-electrolytes using scalable processes is not only challenging, but also adds extraneous volume since SOA cathodes are fully lithiated. The coupling of solid-state electrolytes with a Li-metal anode and state-of-the-art (SOA) cathode materials is a promising path to develop inherently safe batteries with high energy density (>1000 Wh L −1).
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