Model for charge/discharge-rate-dependent plastic flow in amorphous battery materials
Model for charge/discharge-rate-dependent plastic flow in amorphous battery materials
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DOI：
10.1016/j.jmps.2016.03.004
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发表时间：
2016-09
影响因子：
5.3
通讯作者：
S. M. Khosrownejad;W. Curtin
中科院分区：
文献类型：
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作者：
S. M. Khosrownejad;W. Curtin
塑性流动是松弛因电池材料充电/放电过程中膨胀/收缩而产生的应力的重要机制。非晶高存储容量Li-Si的流动应力比结晶材料低，但有证据表明塑性流动应力取决于充电和放电条件，这表明流动行为存在重要的非平衡方面。这里，基于两个物理概念开发了非晶材料（例如 LixSi 合金）在充电和放电过程中速率相关塑性流动的基于力学的本构模型：（i）由于非晶材料在充电/放电过程中无法完全松弛，因此在电化学充电和放电过程中，多余的能量存储在材料中；（ii）这种多余的能量减少了塑性流动过程的障碍，从而减少了引起塑性流动所需的施加应力。因此，塑性流动应力是充电/放电的时间尺度和玻璃态弛豫的时间尺度之间的竞争。这两个概念以及模型的其他方面均通过模型 Li-Si 系统上的分子模拟进行了验证。该模型用于检查由于组合充电/放电和应力历史而引起的典型样本几何形状的塑性流动行为，结果通常使实验观察结果合理化。
Plastic flow is an important mechanism for relaxing stresses that develop due to swelling/shrinkage during charging/discharging of battery materials. Amorphous high-storage-capacity Li–Si has lower flow stresses than crystalline materials but there is evidence that the plastic flow stress depends on the conditions of charging and discharging, indicating important non-equilibrium aspects to the flow behavior. Here, a mechanistically-based constitutive model for rate-dependent plastic flow in amorphous materials, such as LixSi alloys, during charging and discharging is developed based on two physical concepts: (i) excess energy is stored in the material during electrochemical charging and discharging due to the inability of the amorphous material to fully relax during the charging/discharging process and (ii) this excess energy reduces the barriers for plastic flow processes and thus reduces the applied stresses necessary to cause plastic flow. The plastic flow stress is thus a competition between the time scales of charging/discharging and the time scales of glassy relaxation. The two concepts, as well as other aspects of the model, are validated using molecular simulations on a model Li–Si system. The model is applied to examine the plastic flow behavior of typical specimen geometries due to combined charging/discharging and stress history, and the results generally rationalize experimental observations.