Hwang Taesoon, Lee Jung-Hyun, Choi Seung Hyun, Oh Rye-Gyeong, Kim Duho, Cho Maenghyo, Cho Woosuk, Park Min-Sik
Department of Mechanical and Aerospace Engineering , Seoul National University , Gwanak-ro 1 , Gwanak-gu, Seoul 08826 , Republic of Korea.
Advanced Batteries Research Center , Korea Electronics Technology Institute , 25 Saenari-ro , Bundang-gu, Seongnam 13509 , Republic of Korea.
ACS Appl Mater Interfaces. 2019 Aug 28;11(34):30894-30901. doi: 10.1021/acsami.9b08987. Epub 2019 Aug 19.
Recently, the substitution of inactive elements has been reported as a promising strategy for improving the structural stability and electrochemical performance of layered cathode materials for sodium-ion batteries (SIBs). In this regard, we investigated the positive effects of inactive Ti substitution into O3-type NaFeNiMnO based on first-principles calculations and electrochemical experiments. After Ti substitution, Na[Ti(FeNiMn)]O exhibits improved capacity retention and rate capability compared with Ti-free NaFeNiMnO. Such an improvement is primarily attributed to the enhanced structural stability and lowered activation energy for Na migration, which is induced by Ti substitution in the host structure. Based on first-principles calculations of the average net charges and partial densities of states, we suggest that Ti substitution effectively enhances the binding between transition metals and oxygen by increasing the oxygen electron density, which in turn lowers the energy barrier of Na migration, leading to a notable enhancement in the rate capability of Na[Ti(FeNiMn)]O. Compared with other inactive elements (e.g., Al and Mg), Ti is a more suitable substituent for improving the electrochemical properties of layered cathode materials because of its large total charge variation contributing to capacity. The results of this study provide practical guidelines for developing highly reliable layered cathode materials for SIBs.
最近，据报道，用非活性元素进行替代是一种很有前景的策略，可用于提高钠离子电池（SIBs）层状正极材料的结构稳定性和电化学性能。在这方面，我们基于第一性原理计算和电化学实验，研究了将非活性Ti替代物引入O3型NaFeNiMnO中的积极效果。Ti替代后，与不含Ti的NaFeNiMnO相比，Na[Ti(FeNiMn)]O表现出更好的容量保持率和倍率性能。这种改善主要归因于结构稳定性的增强以及Na迁移活化能的降低，这是由主体结构中的Ti替代所引起的。基于对平均净电荷和态密度的第一性原理计算，我们认为Ti替代通过增加氧电子密度有效地增强了过渡金属与氧之间的结合，这反过来又降低了Na迁移的能垒，从而导致Na[Ti(FeNiMn)]O的倍率性能显著提高。与其他非活性元素（如Al和Mg）相比，Ti是一种更适合的替代物，因为其较大的总电荷变化有助于提高容量，从而改善层状正极材料的电化学性能。本研究结果为开发用于SIBs的高度可靠的层状正极材料提供了实用指导。
