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首页> 外文会议>Charging amp; infrastructure symposium 2018 >Correlation of Degradation and Thermal Stability of Different Positive Active Materials in Lithium Ion Batteries
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Correlation of Degradation and Thermal Stability of Different Positive Active Materials in Lithium Ion Batteries

机译：锂离子电池中不同正极活性物质降解与热稳定性的相关性

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摘要

Three aspects are considered key for active materials in future lithium ion battery applications: High energy density, long cycle life, and enhanced safety properties. Beyond that, a detailed knowledge of the interactions between electrochemical performance, degradation effects and the influence on the safety properties is of fundamental importance. In this regard, the thermal decomposition of state-of-the-art positive electrode active materials is known to be strongly exothermic in presence of electrolyte, thus, triggering numerous reactions that can eventually lead to a thermal runaway. Therefore, investigations on the thermal stability of different positive electrode active materials are essential in order to develop safer lithium ion batteries that also exhibit an enhanced energy density and a prolonged cycle life. Even though different active materials have been investigated with regard to their thermal stability in the charged and discharged state, [1-2] the influence of degradation effects on the thermal stability of active materials is widely unknown. Therefore, this study correlates degradation effects and their influence on the thermal decomposition of different layered, spinel-type, and olivine-type based positive electrodes at elevated temperatures. Specific positive electrode active materials suffer from different degradation effects during charge/discharge cycling that can influence the thermal stability. Thus, in a first step, it is crucial to identify and understand degradation effects for each specific active material in order to eventually reduce the degradation or the interference with the electrochemical performance and the cell safety properties. For this purpose, different layered, spinel-type, and olivine-type active materials were investigated in the charged and discharged state after charge/discharge cycling. Therein, thermogravimetric analysis (TGA) was used to investigate changes in the thermal stability of the electrodes. Amongst others, post-mortem analysis included structural investigations after heat treatment at different temperatures by X-ray diffraction analysis (XRD) to gain insights into the progression of the thermal decomposition of the active materials. Overall, the high thermal stability of spinel-type LiMn204 (LMO) is strongly affected by the presence of other transition metals like e.g. nickel in the high-voltage active material LiNi0.5Mnl.5O4 (LNMO). However, the negligible degradation of the spinel-type active materials during charge/discharge cycling results in consistent safety properties in terms of thermal stability. In contrast, the degradation effects on the surface of layered transition metal oxides like LiNixCoyMnz02 (NCM, x+y+z=l) can strongly reduce the thermal stability. [3] In addition, the thermal stability of NCM is strongly affected by the state of charge due to the reduced structural stability of layered transition metal oxides in the delithiated state. [1] Moreover, the increase of the nickel content in NCM in order to achieve higher specific capacities intrinsically leads to a reduction of the thermal stability of the active material. [2] In summary, by combining comprehensive post-mortem analysis and thermal analysis, the degradation effects of different positive active materials could be correlated with the thermal stability, hence the safety properties of different positive electrode active materials.
机译：对于未来锂离子电池应用中的活性材料，三个方面被认为是关键：高能量密度，长循环寿命和增强的安全性。除此之外，对电化学性能，降解效果以及对安全性能的影响之间相互作用的详细了解至关重要。在这方面，已知现有技术的正极活性材料在电解质存在下的热分解强烈放热，因此，引发许多反应，最终可能导致热失控。因此，对不同正极活性物质的热稳定性进行研究对于开发更安全的锂离子电池至关重要，该锂离子电池还具有增强的能量密度和延长的循环寿命。尽管已经研究了不同的活性材料在充电和放电状态下的热稳定性，[1-2]降解效应对活性材料的热稳定性的影响还是广为人知的。因此，本研究将降解效应及其对不同层状，尖晶石型和橄榄石型正极在高温下热分解的影响相关。特定的正极活性物质在充电/放电循环期间遭受不同的降解效应，这会影响热稳定性。因此，在第一步中，至关重要的是识别和理解每种特定活性材料的降解作用，以最终减少降解或对电化学性能和电池安全性的干扰。为此，研究了在充电/放电循环之后在充电和放电状态下不同的层状，尖晶石型和橄榄石型活性材料。其中，热重分析（TGA）用于研究电极热稳定性的变化。除其他外，验尸分析包括通过X射线衍射分析（XRD）在不同温度下进行热处理后进行的结构研究，以深入了解活性材料的热分解进程。总体而言，尖晶石型LiMn204（LMO）的高热稳定性会受到其他过渡金属（例如高锰酸盐）的强烈影响。高压活性材料LiNi0.5Mn1.5O4（LNMO）中的镍。然而，尖晶石型活性材料在充电/放电循环期间的可忽略的降解导致在热稳定性方面一致的安全性能。相反，层状过渡金属氧化物如LiNixCoyMnz02（NCM，x + y + z = 1）的表面降解效果会大大降低热稳定性。 [3]另外，由于在脱锂状态下层状过渡金属氧化物的结构稳定性降低，因此NCM的热稳定性受到电荷状态的强烈影响。 [1]此外，为了获得更高的比容量，NCM中镍含量的增加本质上导致活性材料的热稳定性降低。 [2]总之，通过综合的事后分析和热分析，可以将不同正极活性物质的降解效果与热稳定性相关，因此可以得出不同正极活性物质的安全性。

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  • 会议地点 Mainz(DE)
  • 作者

    Markus Boerner; M. Eilers-Rethwisch; Y.P. Stenzel; J. Henschel; F.M. Schappacher; M. Winter;

  • 作者单位

    University of Muenster, MEET Battery Research Center, Corrensstrasse 46, Munster, D-48149 Germany;

    University of Muenster, MEET Battery Research Center, Corrensstrasse 46, Munster, D-48149 Germany;

    University of Muenster, MEET Battery Research Center, Corrensstrasse 46, Munster, D-48149 Germany;

    University of Muenster, MEET Battery Research Center, Corrensstrasse 46, Munster, D-48149 Germany;

    University of Muenster, MEET Battery Research Center, Corrensstrasse 46, Munster, D-48149 Germany;

    University of Muenster, MEET Battery Research Center, Corrensstrasse 46, Munster, D-48149 Germany;

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