纳米粒子嵌入过程中的尺寸依赖性调幅能隙和可伸缩能隙
Size-dependent spinodal and miscibility gaps for intercalation in nano-particles
摘要：
使用最近提出的相分离材料中插层动力学的数学模型[Singh、Ceder、Bazant、Electrochimica Acta 53，7599（2008）]，我们表明，随着宿主颗粒尺寸减小到纳米级，旋节线和混溶性间隙通常会缩小。我们的工作受到最近对高倍率锂离子电池材料LiFePO 4的实验的启发;这是我们例子的基础，但我们的分析和结论适用于任何插层材料。我们描述了两种抑制纳米颗粒相分离的一般机制：（i）经典的体效应，由Cahn-Hilliard方程预测，其中扩散相边界受到颗粒几何形状的限制;和（ii）一种新的表面效应，由化学势依赖的反应动力学预测，其中插入/提取反应稳定了与局部环境平衡的表面附近的组成梯度。成分依赖的表面能和（特别是）弹性应变可以有助于这些效果，但不需要预测减少的调幅和可伸缩性间隙在纳米尺度。
英文摘要：
Using a recently-proposed mathematical model for intercalation dynamics in phase-separating materials [Singh, Ceder, Bazant, Electrochimica Acta 53, 7599 (2008)], we show that the spinodal and miscibility gaps generally shrink as the host particle size decreases to the nano-scale. Our work is motivated by recent experiments on the high-rate Li-ion battery material LiFePO4; this serves as the basis for our examples, but our analysis and conclusions apply to any intercalation material. We describe two general mechanisms for the suppression of phase separation in nano-particles: (i) a classical bulk effect, predicted by the Cahn-Hilliard equation, in which the diffuse phase boundary becomes confined by the particle geometry; and (ii) a novel surface effect, predicted by chemical-potential-dependent reaction kinetics, in which insertion/extraction reactions stabilize composition gradients near surfaces in equilibrium with the local environment. Composition-dependent surface energy and (especially) elastic strain can contribute to these effects but are not required to predict decreased spinodal and miscibility gaps at the nano-scale.
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