Amino Group-Aided Efficient Regeneration Targeting Structural Defects and Inactive FePO₄ Phase for Degraded LiFePO₄...

It is urgent to develop efficient recycling methods for spent LiFePO₄ cathodes to cope with the upcoming peak of power battery retirement. Compared with the traditional metallurgical recovery methods that lack satisfactory economic and environmental benefits, the direct regeneration seems to be a promising option at present. However, a simple direct lithium replenishment cannot effectively repair and regenerate the cathodes due to the serious structural damage of the spent LiFePO₄. Herein, the spent LiFePO₄ cathodes are directly regenerated by a thiourea-assisted solid-phase sintering process. The density functional theory calculation indicates that thiourea has a targeted repair effect on the antisite defects and inactive FePO₄ phase in the spent cathode due to the associative priority of amino group (─NH₂) in thiourea with Fe ions: Fe³⁺─N > Fe²⁺─N. Meanwhile, the pyrolysis products of thiourea can also create an optimal reducing atmosphere and inhibit the agglomeration of particles in the high temperature restoration process. The regenerated LiFePO₄ exhibits an excellent electrochemical performance, which is comparable to that of commercial LiFePO₄. This targeted restoration has improved the efficiency of direct regeneration, which is expected to achieve large-scale recycling of spent LiFePO₄.