Improved Performance in FeF₂ Conversion Cathodes through Use of a Conductive 3D Scaffold and Al₂O₃ ALD Coating

FeF₂ is considered a promising conversion compound for the positive electrode in lithium-ion batteries due to its high thermodynamic reduction potential (2.66 V vs Li/Li⁺) and high theoretical specific capacity (571 mA h g⁻¹). However, the sluggish reaction kinetics and rapid capacity decay caused by side reactions during cycling limit its practical application. Here, the fabrication of Ni-supported 3D Al₂O₃-coated FeF₂ electrodes is presented, and it is shown that these structured electrodes significantly overcome these limitations. The electrodes are prepared by iron electrodeposition on a Ni support, followed by a facile fluorination process and Al₂O₃ coating by atomic layer deposition. The 3D FeF₂ electrode delivers an initial discharge capacity of 380 mA h g⁻¹ at a current density of 200 mA g⁻¹ at room temperature. The 3D scaffold improves the reaction kinetics and enables a high specific capacity by providing an efficient electron pathway to the insulating FeF₂ and short Li diffusion lengths. The Al₂O₃ coating significantly improves the cycle life, probably by preventing side reactions through limiting direct electrode–electrolyte contact. The fabrication method presented here can also be applied for synthesis of other metal fluoride materials on different 3D conductive templates.