Electrostatic Interactions versus Second Order Jahn–Teller Distortion as the Source of Structural Diversity in Li₃MO₄ Compounds (M = Ru, Nb, Sb and Ta)

With the advent of layered rocksalt oxides showing anionic redox activity toward Li, there has been an increased focus on designing new rocksalt structures and, more particularly, compounds pertaining to the Li₃MO₄ family. The structural richness of this family is nested in its ability to host many different cations, leading to the formation of superstructure patterns whose predictability is still limited. Thus, there is a need to understand the formation of such superstructures, as cationic arrangements have a crucial effect on their physical properties. Herein we propose a combined experimental and theoretical approach to understand the interactions governing cation ordering in binary systems of general composition given by Li₃M_<i>y</i>M′_1–<i>y</i>O₄ (M and M′ being Ru, Nb, Sb, and Ta). Through complementary X-ray diffraction and X-ray absorption spectroscopy techniques, we reveal a solid-solution behavior for the Li₃Ru_<i>y</i>Sb_1–<i>y</i>O₄ system, as opposed to Li₃Sb_<i>y</i>Nb_1–<i>y</i>O₄ that enlists four rocksalt structures with different cation orderings. We use DFT calculations to rationalize such a structural diversity and find that it is controlled by a delicate balance between electrostatic interactions and charge transfer due to a second order Jahn–Teller distortion. This insight provides a new viewpoint for understanding cationic arrangements in rocksalt structures and guidelines to design novel phases for applications such as Li-ion batteries or ionic conductors

The Li₃Ru_<i>y</i>Nb_1–<i>y</i>O₄ (0 ≤ <i>y</i> ≤ 1) System: Structural Diversity and Li Insertion and Extraction Capabilities

Searching for novel high-capacity electrode materials combining cationic and anionic redox processes is an ever-growing activity within the field of Li-ion batteries. In this respect, we report on the exploration of the Li₃Ru_<i>y</i>Nb_1–<i>y</i>O₄ (0 ≤ <i>y</i> ≤ 1) system with an O/M ratio of 4 to maximize the number of oxygen lone pairs, responsible for the anionic redox. We show that this system presents a very rich crystal chemistry with the existence of four structural types, which derive from the rocksalt structure but differ in their cationic arrangement, creating either zigzag, helical, jagged chains or clusters. From an electrochemical standpoint, these compounds are active on reduction via a classical cationic insertion process. The oxidation process is more complex, because of the instability of the delithiated phase. Our results promote the use of the rich Li₃MO₄ family as a viable platform for a better understanding of the relationships between structure and anionic redox activity

Electrostatic Interactions versus Second Order Jahn–Teller Distortion as the Source of Structural Diversity in Li₃MO₄ Compounds (M = Ru, Nb, Sb and Ta)

With the advent of layered rocksalt oxides showing anionic redox activity toward Li, there has been an increased focus on designing new rocksalt structures and, more particularly, compounds pertaining to the Li₃MO₄ family. The structural richness of this family is nested in its ability to host many different cations, leading to the formation of superstructure patterns whose predictability is still limited. Thus, there is a need to understand the formation of such superstructures, as cationic arrangements have a crucial effect on their physical properties. Herein we propose a combined experimental and theoretical approach to understand the interactions governing cation ordering in binary systems of general composition given by Li₃M_<i>y</i>M′_1–<i>y</i>O₄ (M and M′ being Ru, Nb, Sb, and Ta). Through complementary X-ray diffraction and X-ray absorption spectroscopy techniques, we reveal a solid-solution behavior for the Li₃Ru_<i>y</i>Sb_1–<i>y</i>O₄ system, as opposed to Li₃Sb_<i>y</i>Nb_1–<i>y</i>O₄ that enlists four rocksalt structures with different cation orderings. We use DFT calculations to rationalize such a structural diversity and find that it is controlled by a delicate balance between electrostatic interactions and charge transfer due to a second order Jahn–Teller distortion. This insight provides a new viewpoint for understanding cationic arrangements in rocksalt structures and guidelines to design novel phases for applications such as Li-ion batteries or ionic conductors