Rational Design of Layered Oxide Materials for Batteries

ConspectusLayered transition metal (TM) compounds are pivotal in the development of rechargeable battery technologies for efficient energy storage. The history of these materials dates back to the 1970s, when the concept of intercalation chemistry was introduced into the battery. This process involves the insertion of alkali-metal ions between the layers of a host material (e.g., TiS₂) without causing significant structural disruption. This breakthrough laid the foundation for Li-ion batteries, with materials like LiCoO₂ becoming key to their commercial success, thanks to their high energy density and good stability. However, despite these advantages, challenges remain in the broader application of these materials in batteries. Issues such as lattice strain, cation migration, and structural collapse result in rapid capacity degradation and a reduction in battery lifespan. Moreover, the performance of batteries is often constrained by the properties of the available materials, particularly in layered oxide materials. This has driven the exploration of materials with diverse compositions. The relationship between composition and structural chemistry is crucial for determining reversible capacity, redox activity, and phase transitions, yet predicting this remains a significant challenge, especially for complex compositions.In this Account, we outline our efforts to explore rational principles for optimal battery materials that offer a higher performance. The core of this is the concept of ionic potential, a parameter that measures the strength of the electrostatic interaction between ions. It is defined as the ratio of an ion's charge to its ionic radius, offering a quantitative way to evaluate interactions between cations and anions in crystal structures. By building on this concept, we introduce the cationic potential, which is emerging as a crystallographic tool that captures critical interactions within layered oxide materials. This approach provides insights into structural organization, enabling the prediction of P2- and O3-type stacking arrangements in layered oxides. A key advantage of using the cationic potential is its ability to guide the rational design of electrode materials with improved performance. For example, introducing P-type structural motifs into the material framework can significantly enhance ion mobility, mitigating detrimental phase transitions that often compromise battery efficiency and longevity. Furthermore, ionic potential serves as a representative parameter to quantitatively describe the properties of various TM compositions, providing a straightforward calculation method for designing multielement systems. We anticipate that this Account will provide fundamental insights and contribute to significant advancements in the design of layered materials, not only for battery applications but also for broader fields that require control of the material properties.