Preparation and Electrochemical Properties of LiNi _0.89 Co _0.09 Al _0.02 O ₂ Submicron‐Sized Single‐Crystal and Superflexible High‐Strength Buckypaper Cathode Composites for Lithium‐Ion Battery

ABSTRACT Single‐crystalline ultra‐fine sized LiNi _x Co _y Al _1‐x‐y O ₂ (NCA) features stable Al─O bonds and crack‐resistantance due to no grain boundaries, exhibiting excellent long charge–discharge cycle stability as a lithium‐ion battery cathode. With flexible electronics growing, flexible energy storage materials are urgently needed. However, preparing single‐crystalline ultra‐fine NCA particles and assembling them into a self‐supported superflexible cathode is still a tough challenge. Here, submicron‐sized Ni‐rich LiNi _0.89 Co _0.09 Al _0.02 O ₂ single‐crystals were made via a molten‐salt‐assisted high‐temperature solid‐phase method with lithium added during annealing. Then, they were combined with carbon nanotubes by directional pressure filtration to form a superflexible porous hybrid buckypaper (BP). Under O ₂ , sintering at 750°C for 15 h with 1.03 Li addition and annealing with a Li source at 750°C for 5 h gave the optimal submicron‐sized NCA single crystals. The BP could curl around a 2 mm‐radius rod, bend 180°, knot without damage, and had 9.59 MPa tensile strength. In a lithium‐ion battery, at 1C, its initial and 200‐cycle capacities were respectively 192.27 and 179.3 mAh/g (93.2% retention); at 5C, respectively 135.4 and 132.9 mAh/g (98% retention). This work offers a new idea for self‐supported flexible cathode construction.