Improving the rate performance of lithium metal anodes: In-situ formation of 3D interface structures by mechanical mixing with sodium metal

Abstract

Lithium metal anodes (LMA) increase the energy density of lithium-ion batteries, but the formation of lithium dendrites above a critical charging current (CCD) is still a severe safety issue that limits their wide industrial application. In this work, we present a simple, scalable method to improve the properties of LMA and increase the CCD by physical mixing with a small amount of Na metal, leading to a formation of self-organized 3D interfacial structures during cycling. The physical premixing of Li and Na metal results in excellent dispersion of the metals without phase separation or clustering. To demonstrate the effectiveness of these LiNa anodes in solid-state cells with oxide-ceramic Li_6.45Al_0.05La₃Zr_1.6Ta_0.4O₁₂ (LLZO) separators, by melt-quenching them directly onto the LLZO surface. The application of a special formation protocol during cycling leads to the in-situ formation of a 3D Na-metal interfacial structure, which improves the cell performance. The symmetric cells prepared in this way were operated without external pressure (0.1 MPa) and showed record CCDs for planar interfaces of over 5.0 mA∙cm⁻², cycling stability of over 1200 cycles, and a total stripping capability of up to 100 µm Li metal, corresponding to a capacity of 21 mAh∙cm⁻². Most remarkably, our approach resulted in a very low impedance of the Li/LLZO interface, which remained constant even at high stripping/plating rates. The new approach provides an industrially scalable method for fabricating next generation LMAs with an inherently reduced tendency to dendrite formation, which can be readily utilized in a variety of next-generation lithium batteries.