On the microscopic origin of reversible and irreversible reactions of LiNixCoyMnx cathode materials: Ni-O hybrid bond formation vs. cationic and anionic redox
Karin Kleiner, Claire A. Murray, Cristina Grosu, Sarah J. Day, Martin Winter, Peter Nagel, Stefan Schuppler, Michael Merz
Energy density limitations of layered oxides with different Ni contents, i.e., of the conventional cathode materials in Li-ion batteries, are investigated across the first discharge cycle using advanced spectroscopy and state-of-the-art diffraction. For the first time unambiguous experimental evidence is provided, that redox reactions in NCMs proceed via a reversible oxidation of Ni and a hybridization with O, and not, as widely assumed, via pure cationic or more recently discussed, pure anionic redox processes. Once Ni-O hybrid states are formed, the sites cannot be further oxidized. Instead, irreversible reactions set in which lead to a structural collapse and thus, the lack of ionic Ni limits the reversible capacity. Moreover, the degree of hybridization, which varies with the Ni content, triggers the electronic structure and the operation potential of the cathodes. With an increasing amount of Ni, the covalent character of the materials increases and the potential decreases.
High Reversibility of Lattice Oxygen Redox in Na-ion and Li-ion Batteries Quantified by Direct Bulk Probes of both Anionic and Cationic Redox Reactions
Suppressing initial capacity fade in Li-rich Li$_5$FeO$_4$ with anionic redox by partial Co substitution
随着储能技术的日益发展，锂离子电池需要高容量的正极材料。最近，富Li缺陷抗萤石Li $_5$ FeO $_4$已经作为高容量阴极材料出现，其表现出同时的阴离子和阳离子氧化还原而没有显著的氧释放。但是在循环过程中遭受不可逆的结构变化和容量衰减。在这里，我们调查的抑制容量衰减报告在Co取代Li $_5$ FeO $_4$和建立最佳性能，通过调整的浓度和氧化态的Co。我们取代了Co在Fe网站，并进行了详细的分析，结构，磁性，电子和电化学性能，使用第一性原理密度泛函理论计算。扩展的稳定性和抑制容量衰减被发现只有在特定的组合物中取决于Co/Li浓度和氧化态的Co。背后的原因抑制容量衰减在Co取代的系统已被揭露的基础上的键合分析，并提出了作为一种策略，以抑制电压衰减在富锂材料由于过渡金属迁移。从热力学稳定性和电子结构的评价，发现Li $_{5.5}$ Fe $_{0.5}$ Co $_{0.5}$ O $_4$、Li $_5$ Fe $_{0.25}$ Co $_{0.75}$ O $_4$和Li $_{4.5}$ Fe $_{0.5}$ Co $_{0.5}$ O $_4$表现出比Li $_5$ FeO $_4$更好的导电性。所有这些系统具有在3至5V范围内的电压，并且表现出具有约0.3eV的扩散势垒高度的三维Li扩散路径。从Li $_5$ Fe $_{0.25}$ Co $_{0.75}$…
Mechanism-Dependent Descriptors Enable Predictive Design of Oxygen Capacity in Perovskite Oxides
Shanghai Jiao Tong University（上海交通大学）；Northwestern University（西北大学）；University of Science and Technology Beijing（北京科技大学）；University at Buffalo, The State University of New York（纽约州立大学布法罗分校）；Acceleration Consortium（加速联盟）
