Читать книгу First virtual Bilateral Conference on Functional Materials (BiC-FM) - Сборник статей, Андрей Владимрович Быстров, Анна Владимировна Климович - Страница 19

Trussov I. A.¹, Nazarov E. E.¹, Aksyonov D. A.¹, Fedotov S. S.¹

1 – Skolkovo Institute of Science and Technology, Moscow, Russia

s.fedotov@skoltech.ru

LiFePO₄ is a commercialized cathode material ensuring wide applications of Li-ion battery technology for stationary energy storage and renewable energy sources. Regardless of the obvious simplicity of its crystal structure and chemical composition, LiFePO₄ holds astonishing defects chemistry arising from the rearrangement of cations and vacancies within tetrahedral and octahedral sites, variations in their occupancies and iron oxidation state. It was demonstrated that so-called “Li-rich” phases might form with the Li excess being located at the Fe sites reaching up to 10 %. At the same time the polyanion sublattice was rarely considered defective. It was taken for granted that the PO₄ group is highly durable, with no defects being possible at the P site.

In this talk, we will concentrate upon various old and new defect peculiarities in LiFePO₄ and its Li-rich counterpart studied by combined X-ray and neutron diffraction methods coupled with high-throughput DFT and MD calculations. The recently discovered cations arrangements and off-stoichiometry in LiFePO₄ due to a partial replacement of Fe with Li atoms or PO₄ with hydroxyl groups for hydrothermally prepared samples at different synthesis conditions will be discussed. Such off-stoichiometries can reach over 10 % yielding Li_1+xFe_1-xPO₄ (x ≤ 0.1) and Li_1-xFe_1+x(PO₄)_1-y(OH)_4y (x ≤ 0.05, y ≤ 0.1) solid solutions respectively. Both Li and OH-substitutions trigger essential changes in the crystal structure and properties, increasing the migration barriers for Li ions and affect the electrochemical performance. We demonstrated that the off-stoichiometry significantly depends on the precursors and reducing agent concentrations and the order of mixing thereof, rendering them critical parameters that control the defects formation of the hydrothermally synthesized LiFePO₄-based cathode materials.

More data on the crystal structure and properties of Li-rich LiFePO₄ and OH-substituted LiFePO₄ as well as the interrelation between “new” and “old” defects in synthetic phosphates and natural olivine-type minerals will be presented and analyzed.

Acknowledgement.This work was supported by the Russian Foundation for Basic Research, grant 18-29-12097.