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

The wide application of high-energy all-solid-state lithium metal batteries (AS-LMBs) is still challenging due to their dendrite growth at anode, high interfacial resistance and low cathode loading. Herein, a dual conversion reaction strategy is proposed to construct a compact multiple heterostructure 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 the 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 the cathode/garnet interface and insufficient conduction in the bulk cathode, allowing full cells to function normally without adding any ionic liquid/electrolyte wetting agent. It enables the construction of a high-loading cathode with continuous Li-ion transport channels and intimate contact with the garnet electrolyte. Thus, the Li symmetric cells exhibit stable cycling for more than 10 000 h without short-circuiting at 0.2 mA cm⁻², with a low overpotential of only ∼10 mV and ultrahigh cumulative capacity close to 2.5 A h cm⁻². The all-solid-state conversion reaction batteries, with a high mass loading of FeF₃ cathode up to 6 mg cm⁻², achieve a high specific capacity of 300 mA h g⁻¹ after 300 cycles at 0.3C. The reversible capacity still exceeds 250 mA h g⁻¹ even under an ultrahigh current density of 712 mA g⁻¹. This study demonstrates a dual fluorination effect on both anode and cathode sides to develop high-capacity AS-LMBs based on the conversion cathode systems.