Tracking Sodium-Antimonide Phase Transformations in Sodium-Ion Anodes: Insights from Operando Pair Distribution Function Analysis and Solid-State NMR Spectroscopy.
Tracking Sodium-Antimonide Phase Transformations in Sodium-Ion Anodes: Insights from Operando Pair Distribution Function Analysis and Solid-State NMR Spectroscopy.
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DOI：
10.1021/jacs.5b13273
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发表时间：
2016-02-24
影响因子：
15
通讯作者：
Grey CP
中科院分区：
文献类型：
--
作者：
Allan PK;Griffin JM;Darwiche A;Borkiewicz OJ;Wiaderek KM;Chapman KW;Morris AJ;Chupas PJ;Monconduit L;Grey CP
采用操作对分布函数（PDF）分析和非原位23 Na魔角自旋固体核磁共振（MAS ssNMR）谱研究了钠离子电池高容量锑阳极的合金化机理。从总PDF中减去结晶NaxSb相的PDF，这是一种受参考相关模型化合物从23 Na ssNMR获得的化学相信息约束的方法，确定了两种先前未表征的电化学形成的中间物质; a-Na 3-xSb（x ≤ 0.4 - 0.5），局部类似于结晶Na 3 Sb（c-Na 3 Sb）的结构，但具有大量的钠空位和有限的相关长度，以及a-Na 1. 7Sb，具有一些Sb-Sb键合的高度非晶结构。第一次钠化分解结晶锑以首先形成a-Na 3-xSb，最后形成结晶Na 3Sb。去辐射导致形成由结晶和非晶锑网络的复合物形成的电极。我们将这些网络的不同反应性与一系列连续钠化反应联系起来，这些反应表现为在后续循环的电化学曲线中观察到的级联过程。无定形网络在较高电压下反应，形成a-Na 1. 7Sb，然后形成a-Na 3-xSb，而结晶锑的钠化需要较低的电位，其反应形成a-Na 3-xSb而不形成a-Na 1. 7Sb。a-Na 3-xSb在第二次放电结束时转化为结晶Na 3 Sb。没有发现NaSb形成的证据。变温23 Na NMR实验揭示了c-Na3Sb内显著的钠迁移率;这可能是Sb阳极优异倍率性能的一个促成因素。
Operando pair distribution function (PDF) analysis and ex situ 23Na magic-angle spinning solid-state nuclear magnetic resonance (MAS ssNMR) spectroscopy are used to gain insight into the alloying mechanism of high-capacity antimony anodes for sodium-ion batteries. Subtraction of the PDF of crystalline NaxSb phases from the total PDF, an approach constrained by chemical phase information gained from 23Na ssNMR in reference to relevant model compounds, identifies two previously uncharacterized intermediate species formed electrochemically; a-Na3–xSb (x ≈ 0.4–0.5), a structure locally similar to crystalline Na3Sb (c-Na3Sb) but with significant numbers of sodium vacancies and a limited correlation length, and a-Na1.7Sb, a highly amorphous structure featuring some Sb–Sb bonding. The first sodiation breaks down the crystalline antimony to form first a-Na3–xSb and, finally, crystalline Na3Sb. Desodiation results in the formation of an electrode formed of a composite of crystalline and amorphous antimony networks. We link the different reactivity of these networks to a series of sequential sodiation reactions manifesting as a cascade of processes observed in the electrochemical profile of subsequent cycles. The amorphous network reacts at higher voltages reforming a-Na1.7Sb, then a-Na3–xSb, whereas lower potentials are required for the sodiation of crystalline antimony, which reacts to form a-Na3–xSb without the formation of a-Na1.7Sb. a-Na3–xSb is converted to crystalline Na3Sb at the end of the second discharge. We find no evidence of formation of NaSb. Variable temperature 23Na NMR experiments reveal significant sodium mobility within c-Na3Sb; this is a possible contributing factor to the excellent rate performance of Sb anodes.