Surface engineering based on element interdiffusion and interfacial reactions to boost the performance of LiCoO2 cathode material

Surface coating has been extensively demonstrated as an effective modification strategy for cathode materials, often involving a heat-treatment step to achieve desirable coatings. However, high-temperature annealing can induce element interdiffusion and interfacial reactions between the active material and the coating material, complicating the composition coating. Herein, we attempt to uncover the element interdiffusion and interfacial reactions between LiCoO2 and the Ti(SO4)2 coating precursor. Our findings show that Li, present on the surface of LiCoO2, preferentially diffuses into the coating precursor phase and combines with SO42- to form Li2SO4. Co diffuses into the coating precursor and reacts with the Ti-containing species, resulting in the formation of Li2CoTi3O8 coating. The surface structure of LiCoO2 tends to undergo reconstruction, partially transforming into Co3O4. The stable Li2SO4 coating acts as a physical barrier, preventing direct contact between the cathode and electrolyte, while the Li2CoTi3O8 coating not only stabilizes the cathode/electrolyte interface but also promotes efficient lithium-ion transport due to its high lithium-ion conductivity. The small Co3O4 spinel phase serves as a bridge between the Li2CoTi3O8 coating and the LiCoO2 host. Understanding the element interdiffusion and interfacial reactions occurring at the interface is essential for developing effective surface engineering techniques.