钴含量对NCA型正极材料电化学性能和结构稳定性的影响
Effect of Cobalt Content on the Electrochemical Properties and Structural Stability of NCA Type Cathode Materials
摘要：
目前，最常用的正极材料NCA [Li_（1-x）Ni_（0.80）Co_（0.15）Al_（0.05）O_2，x = 0 ~ 1]中钴含量很高。由于钴有毒且昂贵，现有的阴极材料设计既不具有成本效益，也不环保。我们已经进行了密度泛函理论（DFT）计算，以研究电化学，电子和结构性质的四种类型的NCA阴极材料的同时减少Co的含量随着Ni含量的增加。结果表明，即使钴浓度从16.70%（NCA_I）显著降低到4.20%（NCA_IV），插层电位和比容量的变化也不显著。例如，在50%Li浓度的情况下，电压降仅为~17%，而比容量的变化可以忽略不计。此外，我们还探讨了钠掺杂在插层位置上的电化学，电子和结构性能的影响。通过考虑国家竞争行动的两种极端情况（即，具有最高和最低Co含量：分别为NCA_I和NCA_IV），我们已经从结构和电子观点证明了Na掺杂的重要性。我们的研究结果为设计环境友好，低成本的阴极材料提供了深入的了解，降低了钴浓度。
英文摘要：
At present, the most common type of cathode materials, NCA [Li_(1-x)Ni_(0.80)Co_(0.15)Al_(0.05)O_(2), x = 0 to 1], have a very high concentration of cobalt. Since cobalt is toxic and expensive, the existing design of cathode materials is neither cost-effective nor environmentally benign. We have performed density functional theory (DFT) calculations to investigate electrochemical, electronic, and structural properties of four types of NCA cathode materials with the simultaneous decrease in Co content along with the increase in Ni content. Our results show that even if the cobalt concentration is significantly decreased from 16.70 % (NCA_I) to 4.20 % (NCA_IV), variation in intercalation potential and specific capacity is not significant. For example, in case of 50% Li concentration, the voltage drop is only ~17% while the change in specific capacity is negligible. Moreover, we have also explored the influence of sodium doping in the intercalation site on the electrochemical, electronic, and structural properties. By considering two extreme cases of NCAs (i.e., with highest and lowest Co content: NCA_I and NCA_IV respectively), we have demonstrated the importance of Na doping from the structural and electronic point of view. Our results provide insight into the design of environmentally benign, low-cost cathode materials with reduced cobalt concentration.
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