Seong Shik Kim, David N. Agyeman-Budu, Joshua J. Zak, Jessica L. Andrews, Jonathan Li, Brent C. Melot, Johanna Nelson Weker and Kimberly A. See*,
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引用次数: 0
Abstract
New energy storage methods are emerging to increase the energy density of state-of-the-art battery systems beyond conventional intercalation electrode materials. For instance, employing anion redox can yield higher capacities compared with transition metal redox alone. Anion redox in sulfides has been recognized since the early days of rechargeable battery research. Here, we study the effect of d–p overlap in controlling anion redox by shifting the metal d band position relative to the S p band. We aim to determine the effect of shifting the d band position on the electronic structure and, ultimately, on charge compensation. Two isostructural sulfides LiNaFeS2 and LiNaCoS2 are directly compared to the hypothesis that the Co material should yield more covalent metal–anion bonds. LiNaCoS2 exhibits a multielectron capacity of ≥1.7 electrons per formula unit, but despite the lowered Co d band, the voltage of anion redox is close to that of LiNaFeS2. Interestingly, the material suffers from rapid capacity fade. Through a combination of solid-state nuclear magnetic resonance spectroscopy, Co and S X-ray absorption spectroscopy, X-ray diffraction, and partial density of states calculations, we demonstrate that oxidation of S nonbonding p states to S22– occurs in early states of charge, which leads to an irreversible phase transition. We conclude that the lower energy of Co d bands increases their overlap with S p bands while maintaining S nonbonding p states at the same higher energy level, thus causing no alteration in the oxidation potential. Further, the higher crystal field stabilization energy for octahedral coordination over tetrahedral coordination is proposed to cause the irreversible phase transition in LiNaCoS2.
除了传统的插层电极材料外,新的能量存储方法也在不断涌现,以提高最先进电池系统的能量密度。例如,与单独使用过渡金属氧化还原法相比,使用阴离子氧化还原法可以产生更高的容量。硫化物中的阴离子氧化还原早在充电电池研究初期就已得到认可。在此,我们研究了通过移动金属 d 波段与 S p 波段的相对位置来控制阴离子氧化还原的 d-p 重叠效果。我们旨在确定 d 带位置移动对电子结构的影响,并最终确定对电荷补偿的影响。我们直接比较了两种同结构硫化物 LiNaFeS2 和 LiNaCoS2,并假设钴材料应产生更多的共价金属阴离子键。LiNaCoS2 每式单位的多电子容量≥1.7 个电子,但尽管 Co d 带降低,阴离子氧化还原电压却接近 LiNaFeS2。有趣的是,这种材料的容量衰减很快。通过结合固态核磁共振光谱、Co 和 S X 射线吸收光谱、X 射线衍射和部分态密度计算,我们证明了 S 非键 p 态氧化为 S22- 发生在电荷的早期状态,这导致了不可逆的相变。我们的结论是,Co d 带的能量较低,增加了它们与 S p 带的重叠,同时将 S 非键 p 态保持在相同的较高能量水平,因此不会改变氧化势。此外,八面体配位比四面体配位具有更高的晶场稳定能,这也是导致钴酸锂发生不可逆相变的原因。
期刊介绍:
The journal Chemistry of Materials focuses on publishing original research at the intersection of materials science and chemistry. The studies published in the journal involve chemistry as a prominent component and explore topics such as the design, synthesis, characterization, processing, understanding, and application of functional or potentially functional materials. The journal covers various areas of interest, including inorganic and organic solid-state chemistry, nanomaterials, biomaterials, thin films and polymers, and composite/hybrid materials. The journal particularly seeks papers that highlight the creation or development of innovative materials with novel optical, electrical, magnetic, catalytic, or mechanical properties. It is essential that manuscripts on these topics have a primary focus on the chemistry of materials and represent a significant advancement compared to prior research. Before external reviews are sought, submitted manuscripts undergo a review process by a minimum of two editors to ensure their appropriateness for the journal and the presence of sufficient evidence of a significant advance that will be of broad interest to the materials chemistry community.