Jobst Nicola M, Paul Neelima, Beran Premysl, Mancini Marilena, Gilles Ralph, Wohlfahrt-Mehrens Margret, Axmann Peter
Accumulators Materials Research (ECM), ZSW Centre for Solar Energy and Hydrogen Research Baden-Württemberg, DE-89081 Ulm, Germany.
Heinz Maier-Leibnitz Zentrum (MLZ), Technische Universität München, DE-85747 Garching, Germany.
J Am Chem Soc. 2023 Mar 1;145(8):4450-4461. doi: 10.1021/jacs.2c09621. Epub 2023 Feb 17.
High voltage spinel is one of the most promising next-generation cobalt-free cathode materials for lithium ion battery applications. Besides the typically utilized compositional range of LiNiMnO4 0 < < 1 in the voltage window of 4.90-3.00 V, additional 1.5 mol of Li per formula unit can be introduced into the structure, in an extended voltage range to 1.50 V. Theoretically, this leads to significant increase of the specific energy from 690 to 1190 Wh/kg. However, utilization of the extended potential window leads to rapid capacity fading and voltage polarization that lack a comprehensive explanation. In this work, we conducted potentiostatic entropymetry, operando XRD and neutron diffraction on the ordered stoichiometric spinel LiNiMnO within 0 < < 2.5 in order to understand the dynamic structure evolution and correlate it with the voltage profile. During the two-phase reaction from cubic ( < 1) to tetragonal ( > 1) phase at ∼2.8 V, we identified the evolution of a second tetragonal phase with > 2. The structural evaluation during the delithiation indicates the formation of an intermediate phase with cubic symmetry at a lithium content of = 1.5. Evaluation of neutron diffraction data, with maximum entropy method, of the highly lithiated phase LiNiMnO with 2 < < 2.5 strongly suggests that lithium ions are located on octahedral 8a and tetrahedral 4a positions of the distorted tetragonal phase 4. Consequently, we were able to provide a conclusive explanation for the additional voltage step at 2.10 V, the sloping voltage profile below 1.80 V, and the additional voltage step at ∼3.80 V.
高压尖晶石是最有前途的下一代锂离子电池无钴正极材料之一。除了在4.90 - 3.00 V电压窗口中通常使用的LiNiMnO₄（0 < < 1）组成范围外，每个化学式单元还可额外引入1.5摩尔锂，使电压范围扩展至1.50 V。理论上，这会使比能量从690大幅提高到1190 Wh/kg。然而，扩展电位窗口的使用会导致快速的容量衰减和电压极化，对此缺乏全面的解释。在这项工作中，我们对有序化学计量尖晶石LiNiMnO（0 < < 2.5）进行了恒电位熵测定、原位XRD和中子衍射，以了解动态结构演变并将其与电压曲线相关联。在约2.8 V从立方相（ < 1）到四方相（ > 1）的两相反应过程中，我们确定了 > 2时第二个四方相的演变。脱锂过程中的结构评估表明，在锂含量 = 1.5时形成了具有立方对称性的中间相。用最大熵方法对高锂化相LiNiMnO（2 < < 2.5）的中子衍射数据进行评估，强烈表明锂离子位于畸变四方相4的八面体8a和四面体4a位置。因此，我们能够对2.10 V处的额外电压步长、1.80 V以下的倾斜电压曲线以及约3.80 V处的额外电压步长提供确凿的解释。
