ABSTRACT
Coating and single crystal are two common strategies for cobalt-free nickel-rich layered oxides to solve its poor rate performance and cycle stability. However, the action mechanism of different modification protocols to suppress the attenuation are unclear yet. Herein, the Li2MoO4 layer-coated polycrystalline LiNi0.9Mn0.1O2 (1.0 %-Mo + NM91) and single crystal LiNi0.9Mn0.1O2 (SC-NM91) are prepared to investigate this difference, respectively. By focusing on the interior of particles, the relationship between structure evolution and electrochemical behavior is systematically studied, and the intrinsic mechanism of coating/single-crystallization modifications on suppressing the attenuation is clarified. The results show that microcracks in LiNi0.9Mn0.1O2 (NM91) are the main culprit leading to the rate capability decay, and the coating can effectively prevent the radial diffusion of microcracks from the center to surface, inhibiting the generation of surface side reactions. Therefore, the coating has a more advantage in improving the rate performance at 5.0C, the discharge capacity of 1.0 %-Mo + NM91 (130.6 mAh/g) is 7.9 % higher than that of SC-NM91 (121.0 mAh/g). In contrast, the single-crystallization can effectively prevent the formation of intergranular cracks arising from the anisotropic stress in NM91, which causes the severe cycle degradation. Correspondingly, the grain boundary-free SC-NM91 shows superior cyclability. The capacity retention rate of SC-NM91 (80.8 %) at 0.2C after 100cycles is 6.3 % higher than that of 1.0 %-Mo + NM91 (74.5 %). This work concludes the effect difference of different modification methods on enhancing the electrochemical performance, which provides theoretical and technical guidance for the optimized and targeted modification design in the cobalt-free high nickel cathode materials.
