Thermodynamic Properties of Polymorphs of Fluorosulfate Based Cathode Materials with Exchangeable Potassium Ions |
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| Authors: | Dr. Radha Shivaramaiah Laura Lander Dr. G. P. Nagabhushana Prof. Gwenaëlle Rousse Prof. Jean‐Marie Tarascon Prof. Alexandra Navrotsky |
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| Affiliation: | 1. Peter A. Rock Thermochemistry Laboratory and NEAT ORU (Nanomaterials in the Environment, Agriculture and Technology Organized Research Unit), University of California Davis, Davis, CA, USA;2. UMR 8260“Chimie du Solide et Energie”, Collège de France, Paris Cedex 05, France;3. Réseau sur le Stockage Electrochimique de l'Energie (RS2E), FR CNRS 3459, France;4. Sorbonne Universités—UPMC Univ. Paris 06, Paris, France |
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| Abstract: | FeSO4F‐based frameworks have recently emerged as attractive candidates for alkali insertion electrodes. Mainly owing to their rich crystal chemistry, they offer a variety of new host structures with different electrochemical performances and physical properties. In this paper we report the thermodynamic stability of two such K‐based “FeSO4F” host structures based on direct solution calorimetric measurements. KFeSO4F has been reported to crystallize in two different polymorphic modifications—monoclinic and orthorhombic. The obtained enthalpies of formation from binary components (KF plus FeSO4) are negative for both polymorphs, indicating that they are thermodynamically stable at room temperature, which is very promising for the future exploration of sulfate based cathode materials. Our measurements show that the low‐temperature monoclinic polymorph is enthalpically more stable than the orthorhombic phase by ≈10 kJ mol?1, which is consistent with the preferential formation of monoclinic KFeSO4F at low temperature. Furthermore, observed phase transformations and difficulties in the synthesis process can be explained based on the obtained calorimetric results. The KMnSO4F orthorhombic phase is more stable than both polymorphs of KFeSO4F. |
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| Keywords: | calorimetry fluorosulfate cathode Li-ion batteries phase transition polymorphs |
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