Interfacial stability between the cathode and the electrolyte in Li-ion batteries directly determines durability upon cycling. Core-shell nanoscale heterostructures offer high precision when replacing redox-active ions on the surface with inactive species such as Al ions to suppress these deleterious reactions. However, the level of compositional complexity of leading cathodes for high-energy devices, while showing increased stability, remains to be demonstrated for these heterostructures. A combination of colloidal synthesis and subsequent post-annealing process was used to produce cores of LiCo_0.5Ni_0.25Mn_0.25O₂, a layered oxide with a high theoretical capacity, with epitaxial and conformal shells with increasing concentration of Al from the interior to surface. Thorough insight at high chemical and spatial resolution was obtained by a combination of characterization techniques. The gradient of Al was controlled by the initial content and the temperature of synthesis. The passivation layers play a critical role in notably increasing the retention of capacity, which was particularly considerable under harsh conditions such as wide potential window and, especially, elevated temperature, which accelerate side reactions. Spectroscopic analysis revealed that the tailored surface layers mainly stabilized the electronic environment at the surface, suggesting a possible explanation to the improved battery performance.

中文翻译：

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富钴阴极核-壳纳米晶体的合成与表征

锂离子电池中阴极与电解质之间的界面稳定性直接决定了循环时的耐久性。当用非活性物质（例如Al离子）代替表面上的氧化还原活性离子以抑制这些有害反应时，核-壳纳米级异质结构可提供高精度。但是，用于高能器件的前导阴极的组成复杂性水平虽然显示出增加的稳定性，但对于这些异质结构仍有待证明。结合胶体合成和随后的后退火工艺来生产LiCo _0.5 Ni _0.25 Mn _0.25 O _2的核，是一种具有高理论容量的层状氧化物，具有外延和共形的壳，从内部到表面的Al浓度都在增加。通过结合表征技术，可以在高化学和空间分辨率下获得透彻的见解。Al的梯度由初始含量和合成温度控制。钝化层在显着提高容量保持率方面起着至关重要的作用，在苛刻的条件下，例如宽电位窗口，尤其是高温，这会加速副反应，这特别重要。光谱分析表明，定制的表面层主要稳定了表面的电子环境，这为改进电池性能提供了可能的解释。