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

5 years ago

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

Ke Sun, Paul V. Braun, Junjie Wang, Jinyun Liu, Sanghyeon Kim, Shen J. Dillon

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. Ni-supported 3D FeF2 electrodes are prepared by electrodeposition followed by fluorination. Atomic layer deposition coating of the FeF2 coated with Al2O3 improves its electrochemical properties. The electrode shows good cyclability under high current density and good rate performance, demonstrating that a 3D conductive scaffold, coupled with a thin oxide coating, significantly improves the performance of fluoride-based conversion cathodes.

Publisher URL: http://onlinelibrary.wiley.com/resolve/doi

DOI: 10.1002/adfm.201702783