Re-entrant Lithium Local Environments and Defect Driven Electrochemistry of Li- and Mn-Rich Li-Ion Battery Cathodes,Journal of the American Chemical Society

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Re-entrant Lithium Local Environments and Defect Driven Electrochemistry of Li- and Mn-Rich Li-Ion Battery Cathodes
Journal of the American Chemical Society ( IF 14.4 ) Pub Date : 2015-02-09 , DOI: 10.1021/ja511299y
Fulya Dogan ₁ , Brandon R. Long ₁ , Jason R. Croy ₁ , Kevin G. Gallagher ₁ , Hakim Iddir ₁ , John T. Russell ₁ , Mahalingam Balasubramanian ₁ , Baris Key ₁

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Direct observations of structure-electrochemical activity relationships continue to be a key challenge in secondary battery research. (6)Li magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy is the only structural probe currently available that can quantitatively characterize local lithium environments on the subnanometer scale that dominates the free energy for site occupation in lithium-ion (Li-ion) intercalation materials. In the present study, we use this local probe to gain new insights into the complex electrochemical behavior of activated 0.5(6)Li2MnO3·0.5(6)LiMn(0.5)Ni(0.5)O2, lithium- and manganese-rich transition-metal (TM) oxide intercalation electrodes. We show direct evidence of path-dependent lithium site occupation, correlated to structural reorganization of the metal oxide and the electrochemical hysteresis, during lithium insertion and extraction. We report new (6)Li resonances centered at ∼1600 ppm that are assigned to LiMn6-TM(tet) sites, specifically, a hyperfine shift related to a small fraction of re-entrant tetrahedral TMs (Mn(tet)), located above or below lithium layers, coordinated to LiMn6 units. The intensity of the TM layer lithium sites correlated with tetrahedral TMs loses intensity after cycling, indicating limited reversibility of TM migrations upon cycling. These findings reveal that defect sites, even in dilute concentrations, can have a profound effect on the overall electrochemical behavior.

中文翻译：

重入锂局部环境和富锂和富锰锂离子电池阴极的缺陷驱动电化学

结构-电化学活性关系的直接观察仍然是二次电池研究中的一个关键挑战。（6）Li魔角旋转（MAS）核磁共振（NMR）光谱是目前唯一可以在亚纳米尺度上定量表征局部锂环境的结构探针，该环境支配着锂离子（Li-离子）嵌入材料。在本研究中，我们使用这种局部探针对活化的 0.5(6)Li2MnO3·0.5(6)LiMn(0.5)Ni(0.5)O2、富含锂和锰的过渡金属的复杂电化学行为有了新的认识(TM) 氧化物插层电极。我们展示了路径依赖的锂位点占据的直接证据，与金属氧化物的结构重组和电化学滞后相关，在锂的嵌入和脱嵌过程中。我们报告了以~1600 ppm 为中心的新 (6) Li 共振，这些共振分配给 LiMn6-TM(tet) 位点，特别是与位于上方的一小部分重入四面体 TM (Mn(tet)) 相关的超精细位移或低于锂层，与 LiMn6 单元协调。与四面体 TM 相关的 TM 层锂位点的强度在循环后失去强度，表明循环后 TM 迁移的可逆性有限。这些发现表明，缺陷位点，即使浓度很低，也会对整体电化学行为产生深远的影响。位于锂层上方或下方，与 LiMn6 单元协调。与四面体 TM 相关的 TM 层锂位点的强度在循环后失去强度，表明循环后 TM 迁移的可逆性有限。这些发现表明，缺陷位点，即使浓度很低，也会对整体电化学行为产生深远的影响。位于锂层上方或下方，与 LiMn6 单元协调。与四面体 TM 相关的 TM 层锂位点的强度在循环后失去强度，表明循环后 TM 迁移的可逆性有限。这些发现表明，缺陷位点，即使浓度很低，也会对整体电化学行为产生深远的影响。

更新日期：2015-02-09

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