Structure Flexibility Enabled by Surface High-Concentration Titanium Doping for Durable Lithium-Ion Battery Cathodes

Ni-rich layered oxides have emerged as the most promising cathode materials for next-generation lithium-ion batteries due to their high energy densities. However, their strain-related instabilities, for example, microcracks and rock-salt phase formation, present a significant threat to battery performance. In this study, we successfully stabilize the structure of LiNi_0.8Co_0.1Mn_0.1O₂ using flexible TiO₆ octahedron units through high-concentration surface Ti doping. The TiO₆ octahedron can tolerate Jahn-Teller distortions of other neighboring structural units due to the absence of <i>d</i> electrons in Ti⁴⁺, allowing them to accommodate undesirable lattice distortions within the local domain and mitigate the lattice strain/changes. Compared with the conventional approach of increasing the rigidity of the layered structure, our strategy of using flexible TiO₆ structural units can fundamentally address the strain-related issues, contributing to significantly reduced lattice changes, especially along the <i>c</i>-direction (by 95.2%). This approach enables a high battery capacity (211.5 mAh g^-1 at 0.1 C) and long battery durability of Ni-rich cathodes, surpassing most commercial products on the market. The strategy of surface optimization using flexible structural units to stabilize Ni-rich layered oxides can be broadly applied to other battery materials to address performance issues due to the similarities among layered-structured cathode materials.