Alternating Edge- and Face-Sharing Octahedra with Partial Super-Exchange Enabling High-Voltage Layered Cathodes.

Traditional O3-type layered oxides with edge-sharing (ES) octahedra suffer from structural instability under high-voltage operation. To address this, we propose a stable edge-sharing coplanar (ESC) O2-type layered structure. In this structure, Li-O octahedra share edges on one side and faces on the other with Co-O octahedra. This ESC-configuration effectively suppresses Co migration and enhances intrinsic structural stability. Furthermore, the 180°Ni-O-TM (TM = paramagnetic transition metal) super-exchange interactions along the edge-sharing directions are introduced to improve high-voltage cycling stability. With an optimal amount of Ni, the unit-cell volume expands, reducing the activation energy for Li-ion diffusion. As a result, the modified ESC-cathode delivers a high discharge capacity of 247 mAh g-1 and a capacity retention of 79% at 1 C after 100 cycles between 3.0 and 4.65 V, far exceeding that of conventional edge-sharing LiCoO2 (210 mAh g-1, 26%). Interestingly, unlike in conventional edge-sharing layered cathodes, where Ni contributes directly to capacity, increasing Ni content in ESC cathodes leads to a decrease in capacity because additional Ni ions enter the Li layer and obstruct Li-ion diffusion pathways. Overall, this work presents an effective strategy for regulating the local coordination environment of layered oxide cathodes to achieve high performance.