Amorphizing Iron Molybdate as a High-Capacity Cathode for Lithium Metal Batteries Enabled by Multiple Insertion Reactions in the Metastable Structure.

Abstract

The rising energy demand for electric vehicles and energy storage has revived interest in lithium-metal batteries (LMBs). However, present LMBs still mainly rely on conventional lithium-ion batteries (LIBs) cathodes (e.g., LiFePO₄ and LiNi_1/3Mn_1/3Co_1/3O₂) with limited reversible capacity (≈150 to ≈190 mAh g^-1 _cathode), necessitating the paradigm to achieve a new host with abundant Li⁺ accommodation sites. Herein, it is proposed a high-capacity amorphizing iron molybdate cathode a-Fe₂(MoO₄)₃ (a-FMO), which can reversibly unlock Fe³⁺/Fe²⁺ and Mo⁶⁺/Mo⁴⁺ redox insertion reactions in the metastable structure. Different from its parent crystal and stoichiometric oxides mixtures, a-FMO, with its inherent metastable structure, can not only augment the lithium storage capacities with fully activated redox centers, but also attenuate the lattice confinements for Li⁺ ion migration. Consequently, the in-situ generated a-FMO electrode exhibited a notable reversible capacity of 254 mAh g^-1 with stable cycling over 500 cycles. It endowed a specific energy density of 597 Wh kg^-1 and all-climate adaptability over 60 to -40 °C benefited from the amorphizing nature, as well as negligible capacity degradation when cycling at -30 °C. The identification of local structure evolutions and multiple-redox activations in amorphizing materials broadens the scope for designing high-energy-density cathodes.