Min Dong,Qingya Sun,Zhihua Wang,Zixin Rui,Zhe Zhang,He Zhu,Si Lan
Layered LiNi x Co y Mn z O 2 (NCM) cathode materials have emerged as the best choice for high-energy-density lithium-ion batteries for powering electric vehicles. Despite significant research efforts, the understanding of complex structural dynamics during lithium (de-) intercalation still remains a subject of debate, especially in scenarios where morphology and composition vary. In this study, we carried out in situ high-energy synchrotron X-ray diffraction experiments on commercial NCM523 cathode materials in both single crystal and polycrystalline forms to probe the structural changes during charging and discharging in detail. Our findings reveal that both single crystal and polycrystalline materials exhibit typical H1–H2–H3 phase transitions. However, in polycrystalline NCM532, a monoclinic intermediate phase emerges between the H1 and H2 phases. During this process, symmetry reduces from R -3 m to C 2/ m , which is attributed to a shear distortion along the ab plane. In contrast, for single crystal materials, the H1 phase directly transforms into the H2 phase without the monoclinic phase. The observed monoclinic distortion significantly impacts structural stability and material cycling performance. This study provides new insight into the structural dynamics in NCM532 cathode materials, particularly concerning morphology-dependent behaviors, which could deepen our understanding of the relationship between NCM material structures and their performance.
Surface coating of lithium layered oxide cathode (e.g., LiNi 0.5 Co 0.3 Mn 0.2 O 2 , NCM532) has become an important modified method in lithium-ion batteries for pursuing higher capacity and rate performance and safety. However, the design and synthesis of polymetallic oxide (PMO) coatings on lithium layered oxide is still a challenge. Herein, polymetallic alloys (PMA) such as NiCoMn alloys (NCM), LaZrHfMo alloys (LZHM) and LaZrHfZn alloys (LZHZ) are introduced to synthesize PMO coatings on NCM532 by a surface topological conversion strategy. The advantage of this method is that numerous kinds of elements could be converted into PMO coating layer with high reaction efficiency, element universality and uniform arrangement at atomic scale. The PMO coatings modified cathodes show excellent rate performance. All of these are attributed to the fact that the PMO coating layers can effectively reduce the side reaction with electrolyte, increase the conductivity of Li + and effectively reduce the mixing of Li + /Ni 2+ , maintain the stability of structure, and greatly increase the reversible capacity of NCM532. Our PMO coating strategy is also applicable to other cathode materials , such as Ni-rich and Li-rich cathode materials.
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