基于蒙特卡罗模拟的离子导体热力学与动力学特性

刘金平, 蒲博伟, 邹喆乂, 李铭清, 丁昱清, 任元, 罗亚桥, 李杰, 李亚捷, 王达, 何冰, 施思齐

Investigating thermodynamic and kinetic properties of ionic conductors via Monte Carlo simulation

Jinping LIU, Bowei PU, Zheyi ZOU, Mingqing LI, Yuqing DING, Yuan REN, Yaqiao LUO, Jie LI, Yajie LI, Da WANG, Bing HE, Siqi SHI

图7 MC模拟对正极材料相变与开路电压的分析：(a)MC模拟模型，上图为Li x FePO4 中Li的分布；下图为对应的能量图。绿色的球代表了锂离子[59]；(b) 在不考虑电荷间作用能的情况下，Li离子沿着 a 轴的排布。如图所示，LiFePO4(LFP)和FePO4(FP)相之间形成了清晰的相边界，Li0.5FePO4 相收缩到一个有限的区域[59]；(c) Li x FePO4 橄榄石纳米晶体在室温下恒电流放电过程的MC模拟。灰点代表活性颗粒中的锂原子，表面电流密度为0.5 A/m2。四组图分别为0 s：初始固溶体，0.0001 s：形成两个富锂相并结合在一起，0.00056 s：富锂相生长，10.81 s：贫锂相几乎完全被消耗；(d) 电池电压与活性材料中Li浓度(mol)的关系[64]；(e) MC模拟计算出的Li/LiNi x Mn2-x O4 电池电压分布，分别为 x = 0.1、 x = 0.2、 x = 0.3、 x = 0.5[65]；(f) 全电池(LiMn2O4 正极和碳负极)开路电位与放电期间正极材料中Ni占据率的关系[19]

Fig. 7 MC simulation for phase transition and open circuit voltage of positive material: (a) MC simulation model (The above figure shows the distribution of Li ions in Li x FePO4, the corresponding energy diagram is shown below, the green balls represent Li ions); (b) the arrangement of Li ions along axis a without considering the interaction energy between charges. As shown in the figure, a clear phase boundary is formed between the LiFePO4 and FePO4 phases, and the Li0.5FePO4 phase shrinks to a limited region; (c) MC simulation of constant current discharge process of Li x FePO4 olivine nanocrystals at room temperature. The gray dots represent lithium atoms in the active particles with a surface current density of 0.5 A·m-2. The four groups are 0 s: initial solid solution, 0.0001 s: forming two Li-rich phases and combining together, 0.00056 s:Li-rich phase growth, 10.81 s: the Li-poor phase was almost completely consumed; (d) the relationship between the battery voltage and the concentration of Li ions in the active material; (e) the voltage distribution of Li/LiNi x Mn2-x O4 battery calculated by MC, x = 0.1, x = 0.2, x = 0.3, x = 0.5, respectively; (f) the relationship between the open circuit potential of a full battery (LiMn2O4 anode and carbon cathode) and the Ni occupation of the cathode during discharge