Solvent‐Free Mechano‐Thermal Synthesis of a Li‐Zn Phosphonate Cathode Framework

A solvent-free mechano-thermal method synthesizes the phosphono-phenolate-based positive electrode material Li₄-Zn-p-DOBDP_mt (LZP³) via solid-state grinding and thermal annealing. This approach enhances crystallinity and enables lithium incorporation during the formation of the anionic MOF. The resulting LZP³ exhibits reversible electrochemical capacity and quasi-solid-state ionic conductivity, offering a sustainable route to alkali-ion-containing organic electrode materials.

A key challenge in synthesizing alkali-ion metal–organic frameworks (MOFs) lies in the multistep procedures typically required, often involving solvothermal crystallization, desolvation, post-synthetic alkali-metalation, and controlled drying. To address this, a solvent-free mechano-thermal method is reported that combines solid-state grinding of precursors with thermal annealing under vacuum. This direct, scalable route offers a more sustainable alternative while enabling stoichiometric precision. We demonstrate this approach for the synthesis of Li₄-Zn-p-DOBDP_mt (LZP³; p-DOBDP⁶⁻ = 2,5-dioxido-1,4-benzenediphosphate), in which lithium is incorporated during MOF formation. The resulting material exhibits better crystallinity compared to its conventionally synthesized counterpart and retains its key functional properties, including a reversible capacity of 130 mAhg^{− 1} at 3.2 V versus Li⁺/Li and a quasi-solid-state ionic conductivity of 10⁻⁶ S cm^{− 1} at 303 K. These results underscore the viability of solid-state synthesis for constructing alkali-ion-containing organic electrode materials with reduced processing complexity.

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