Heterostructure conductive interface and melt-penetration-bonding process to enable all-solid-state Li-FeF3 garnet batteries with high cathode loading

High energy all-solid-state lithium metal batteries (AS-LMBs) are challenging due to anode dendrite growth, high interfacial resistance and low cathode loading. Here, a dual conversion reaction strategy is proposed to construct compact multiple herterostructure interface with mixed ion/electron conductive (MIEC) domains. The obtained LiF/Cu-Mo MIEC layer can inhibit Li dendrite growth and reduce interfacial resistance by regulating the diffusion and migration of charged species at the heterogeneous interfaces. Additionally, a hot melt-penetration-bonding process of ionic wires is developed to address the issues of high contact impedance at cathode/garnet interface and insufficient conduction in bulk cathode, allowing full cells to function normally without adding any ionic liquid/electrolyte wetting agent. It enables the construction of high-loading cathode with continuous Li-ion transport channels and intimate contact with garnet electrolyte. Thus, the Li symmetric cells exhibit stable cycling for more than 10000 h without short-circuiting at 0.2 mA/cm2, with low overpotential of only ~ 10 mV and ultrahigh cumulative capacity close to 2.5 Ah/cm2. The all-solid-state conversion reaction batteries, with a high mass loading of FeF3 cathode up to 6 mg/cm2, achieve the high specific capacity of 300 mAh/g after 300 cycles at 0.3 C. The reversible capacity still exceeds 250 mAh/g even under an ultrahigh current density of 712 mA/g. This study demonstrates a dual fluorination effect on both anode and cathode sides to develop high-capacity AS-LMBs based on conversion cathode systems.