Epitaxially Grown Lattice-Coherent Surface Enabling Superior Mechanical Integrity for High-Voltage LiCoO Cathode.

The growing demand for high-energy-density cathode is pushing LiCoO towards 4.6 V operation. However, the structural and interfacial instability of high-voltage LiCoO is exacerbated when the charging cut-off voltage exceeds 4.55 V, resulting in severe mechanical failure and subsequent dramatic capacity decay. Herein, through thermally driven element interdiffusion, a highly durable Co-containing Li-rich phase with the lattice coherence has been epitaxially grown along LiCoO surface, which enhances the intrinsic mechanical integrity of high-voltage LiCoO. Through establishing the lattice-coherent Li-rich surface, adverse side reactions, irreversible phase transition and lattice oxygen loss are significantly inhibited in high-voltage LiCoO, thereby alleviating cracks formation and maintaining the structural integrity. The presence of the Li-rich phase endows LiCoO with the additional capacity and the excellent cycling stability at 4.6 V and even at 4.7 V. This work taps into a new avenue of surface engineering on high-voltage LiCoO.