NCM622 cathode materials are gaining significant attention in lithium-ion batteries (LIBs) due to their high energy density and cycling stability. However, single-crystal NCM622 offers even greater performance, but its formation remains suboptimal due to the lack of an ideal sintering process. This study investigates three sintering systems: 950 °C for 7 h, 5 h, and 3 h, followed by a reduction to 820 °C for 3 h, 5 h, and 7 h. The optimal condition, 950 °C for 3 h and 820 °C for 7 h, resulted in improved crystallinity with an I(003)/I(104) ratio of 1.368. The particle morphology was uniform, closely resembling a single-crystal structure, with minimal residual lithium. Electrochemical performance showed an initial discharge capacity of 165.82 mAh g−1, which decreased by 17% to 137.48 mAh g−1 after 100 cycles. The Coulombic efficiency reached 99.77%, with a capacity retention of 88.87%. These findings underscore the potential of optimized sintering processes in advancing single-crystal NCM622 and enhancing the performance of lithium-ion battery cathodes.