Quantum‐Chemical Study of the FeNCN Conversion‐Reaction Mechanism in Lithium‐ and Sodium‐Ion Batteries

Abstract

We report a computational study on 3d transition‐metal (Cr, Mn, Fe, and Co) carbodiimides in Li‐ and Na‐ion batteries. The obtained cell voltages semi‐quantitatively fit the experiments, highlighting the practicality of PBE+U as an approach for modeling the conversion‐reaction mechanism of the FeNCN archetype with lithium and sodium. Also, the calculated voltage profiles agree satisfactorily with experiment both for full (Li‐ion battery) and partial (Na‐ion battery) discharge, even though experimental atomistic knowledge is missing up to now. Moreover, we rationalize the structural preference of intermediate ternaries and their characteristic lowering in the voltage profile using chemical‐bonding and Mulliken‐charge analysis. The formation of such ternary intermediates for the lithiation of FeNCN and the contribution of at least one ternary intermediate is also confirmed experimentally. This theoretical approach, aided by experimental findings, supports the atomistic exploration of electrode materials governed by conversion reactions.

Controlled phase and crystallinity of FeNCN/NC dominating sodium storage performance

“…6a, a slope from 0.50 V to 0.05 V is observed in the first cathodic scan of S-1, which is related to Na + insertion to form Na x FeCN 2 and the conversion reaction of Na x FeCN 2 to Fe metal, the intercalation of Na + into nitrogen-doped carbon substrates and the formation of a solid electrolyte interface (SEI) layer. 11,15 In the first anodic scan, the oxidation peak of 1.27 V was assigned to the reaction between Fe metal and Na 2 NCN to form FeNCN. For the 2nd cycle, the cathodic peak at 0.81 V becomes evident, indicating that the intercalation and conversion turns out to be easier than in the first cycle.…”

“…Iron carbodiimide (FeNCN), a kind of metastable metalorganic compound, has begun to attract the research attention due to its good electronic conductivity and the long distance (4.85 Å) of the (002) plane constructed by the alternating Fe 2+ and NCN 2− layers. [11][12][13][14][15][16][17] In addition, the theoretical capacity of FeNCN can reach 559 mA h g −1 . 12,16,17 The metastabilityinduced high activity of FeNCN also promotes good reversibility for the charge/discharge process.…”

Metal Cyanamides/Carbodiimides: Structure, Synthesis and Electrochemical Energy Storage Performance

“…(1) [21][22][23]45] 。部分金属阳离子不能直接取代 [36,[47][48][49] 。黄课题组 [48] 开发了一种在有机体系中 合成金属氰胺化合物的通用策略，以甲苯/乙醇溶 剂为反应介质，油胺、十六烷胺、十八烷胺等伯胺 作为表面活性剂，实现了金属氰胺化合物的尺寸 和形貌可控合成， 制备出 Ag2NCN 纳米棒、 ZnNCN 纳米棒和 PbNCN 纳米颗粒。 制备的 Ag2NCN 纳米 棒具有更好的结晶性和更高的比表面积，与在水 溶液中沉淀得到的 Ag2NCN 微米晶相比，其光催 化性能显著增强。之后，黄课题组 [36,47] 通过无水 乙醇溶解氰胺与金属卤化物，形成均相反应体系， 加入有机强碱苄胺， 调控反应过程， 制备了尺寸小 于 10 nm 且单分散的 CdNCN、 MnNCN 纳米颗粒。 Koziej 等 [49] [19,51] Fig. 3 Electrochemical performance and charge storage mechanism of FeNCN and CoNCN anode materials for lithium-ion batteries [19,51] Eguia-Barrio [18] 和 Sougrati 等 [19] 分别独立报道了金 属氰胺化合物在电化学储能领域的应用，主要研 究了 MNCN (M=Cu、Zn、Mn、Fe、Co 和 Ni)作为 锂钠离子电池电极材料的电化学性能，开启了一 类新型负极材料的研究热潮 [16,[50][51][52][53][54][55][56][57][58][59][60][61] [53] Fig. 4 Electrochemical performance and charge storage mechanism of Cr2(NCN)3 anode material for lithium-ion battery [53] (3)…”