Construction of an intimately riveted Li/garnet interface with ultra-low interfacial resistance for solid-state batteries

Abstract

The application of ceramic garnet-type Li₇La₃Zr₂O₁₂ electrolytes is restricted by the challenge of poor contact with metallic lithium, which results in high interfacial resistance, uneven current distribution, and severe lithium dendrite penetration. Herein, a remarkably ultra-low interfacial impedance (∼2.7 Ω cm²) is achieved by employing Si addition into molten Li, because of the realized intimate interface contact resulting from the decreased surface tension of molten Li and, most importantly, the reinforced interfacial connection as a result of the minor reaction between the Li_4.4Si and Li_6.4La₃Zr_1.4Ta_0.6O₁₂ (LLZTO), further improving charge transfer across the Li/LLZTO interface. The generated Li_4.4Si at the interface (I-Li_4.4Si), showing strong combination with garnet, can function as a “rivet” for the stable interface upon cycling. Moreover, the I-Li_4.4Si species with Li⁺ diffusivity favor the reduced local current density and thus the decreased over-potential to some extent. Thus, the resulting symmetric Li–Li_4.4Si|LLZTO|Li–Li_4.4Si cell delivers a stable Li plating–stripping performance for over 1200 h at a current density of 0.1 mA cm⁻² (1000 h)/0.2 mA cm⁻² (200 h) and a temperature of 60 °C with a small over-potential (5.3 mV@0.1 mA cm⁻²; 10.2 mV@0.2 mA cm⁻²). The fabricated full cell with a LiFePO₄ cathode delivers a high reversible capacity of ∼169 mA h g⁻¹ at 0.05C and excellent cycling stability with a capacity decay rate of only 0.038% per cycle.