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Flexible Metal Organic Frameworks for new generation of Li-Air batteries

Yujie Zhang 1, 2 
Abstract : Li-O2 technology offers very promising energy densities (1700 Wh/kg vs 160 Wh/kg for current Li-ion batteries). However, their performance is often limited by the efficiency of the ORR/OER reactions, as well as by the formation of lithium peroxide Li2O2 that progressively clog the cathode’s pores. This explains the rapid loss of performance after only a few cycles. Porous MOF (Metal- Organic Framework) solids have high specific surface areas and high porosity. Their open framework structure provides not only a host network for Li+ ion and oxygen diffusion, but also sufficient space for the deposition of discharge products. Some MOFs exhibit structural flexibility properties that allow the pore size and thus the volume of the pores to be reversibly modified by adsorbed molecules and would be suitable for storing discharge products.The objective of this work is to study the electrochemical performance of flexible MIL-53(Al), MIL-53(Fe) materials. MIL-53(Al) solids were synthesized by two synthesis routes leading to different morphologies and particle sizes. The Al and Fe analogues exhibit different flexibility behaviors: MIL- 53(Al) solid pores contract in the presence of host molecules while the MIL-53(Fe) solid pores are open.The synthesized three solids in this thesis show interesting discharge capacities in the 1st cycle (~1000 mAh/g for MIL- 53(Al) and ~2000 mAh/g for MIL-53(Fe)). The synthesis route used for MIL-53(Al) solids does not seem to impact the 1st discharge capacities or the observed behavior. Indeed, in some cases (~33%), an activation step seems to be necessary in order to observe an effective ORR capacity. The volume expansion observed for MIL-53(Fe) (pore opening) seems to be in favor of a better distribution of the discharge products and would also favor their dissolution during the charging of the battery (effective OER).Ex-situ analyses (XRD, SEM, XPS) have identified Li2O2 as the main discharge product. Its morphology evolves according to the observed discharge capacities (platelets, toroids or spherical particles).
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Submitted on : Friday, May 13, 2022 - 6:36:27 PM
Last modification on : Saturday, November 5, 2022 - 4:41:05 AM

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  • HAL Id : tel-03667952, version 1

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Yujie Zhang. Flexible Metal Organic Frameworks for new generation of Li-Air batteries. Material chemistry. Université Paris-Saclay, 2022. English. ⟨NNT : 2022UPAST002⟩. ⟨tel-03667952⟩

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