锂离子电池石墨负极微结构数值重建及特征化分析

doi:10.15541/jim20150051

摘要/Abstract

摘要：

实际锂离子电池石墨负极由鳞片状石墨层叠而成, 具有明显的各向异性。本文基于椭球颗粒的模拟退火法对其进行三维微结构数值重建。重建微结构乃三相(孔或电解液、石墨和固体添加物)复合结构, 很好地再现了实际电极各向异性特征。对重构电极进行特征化分析, 得到了电极内固/孔相的连通率、比表面积以及孔径分布等信息; 发现石墨颗粒尺寸对电极特性有重要的影响: 椭球形石墨颗粒尺寸越大, 则重建微结构的平均孔径越大, 比表面积越小; 相对于赤道半径, 椭球颗粒的极半径对重建电极特性的影响更为明显。

关键词: 锂离子电池, 石墨负极, 微结构重建, 模拟退火法, 椭球颗粒

Abstract:

The real graphite anode of lithium-ion battery is of evident non-isotropic characteristic due to its cascading graphite flakes. An ellipsoid particle-based simulated annealing method is developed to numerically reconstruct the three-dimensional microstructure of graphite anode. The reconstructed anode is a composite of three clearly distinguished phases: pore (or electrolyte), graphite and solid additive, well representing the non-isotropic characteristic of real graphite anode. Characterization analysis of reconstructed electrodes gives information such as the connectivity, the specific surface area of solid or pore phase, and the pore size distribution. The results show that the size of graphite ellipsoids has important effects on the characteristics of electrode: 1) larger size graphite ellipsoids result in larger mean pore size and smaller specific surface area in the reconstructed electrode; 2) changing the polar radius of graphite ellipsoid particles has more pronounced influence on the characteristics of electrode than has changing its equatorial radius.

Key words: lithium-ion battery, graphite anode, microstructure reconstruction, simulated annealing method, ellipsoid particles

中图分类号:

TQ174

何绍阳, 曾建邦, 蒋方明. 锂离子电池石墨负极微结构数值重建及特征化分析[J]. 无机材料学报, 2015, 30(9): 906-912.

HE Shao-Yang, ZENG Jian-Bang, JIANG Fang-Ming. Numerical Reconstruction and Characterization Analysis of Microstructure of Lithium-ion Battery Graphite Anode[J]. Journal of Inorganic Materials, 2015, 30(9): 906-912.

图/表 7

图1 锂离子电池电极的FIB/SEM照片

Fig. 1 FIB/SEM images of lithium-ion battery electrodes (a) LiCoO2 cathode; (b) Graphite anode

图2 椭球颗粒

Fig. 2 Ellipsoid particle The a, b and c are the three semi axial lengths of ellipsoid. The α, β and γ are the three rotation angles for the X’-Y’-Z’ coordinates relative to the X-Y-Z coordinates

图3 重建的石墨负极三维微结构

Fig. 3 3D microstructure of reconstructed graphite anode (a) Spatial distribution of graphite; (b) Spatial distribution of solid additive; (c) Spatial distribution and topological relation of graphite anode microstructureconsisting of 3 components. Yellow denotes graphite, blue solid additive and transparent pore or electrolyte

图4 各相体积分数在沿X轴方向(电极厚度方向)的分布

Fig. 4 Distribution of volume fraction of each component along X direction (i.e. the electrode thickness direction)

图5 重建石墨负极内微结构孔径分布

Fig. 5 Pore size distribution inside the reconstructed graphite anode

表1 颗粒尺寸变化对重建微结构特性的影响

Table 1 Effects of particle size on microstructural characteristics of the reconstructed anode

Particle size (2a/ 2b/ 2c) /μm	Average pore diameter /μm	Specific surface area /m^-1	Connectivity /%
Particle size (2a/ 2b/ 2c) /μm	Average pore diameter /μm	Specific surface area /m^-1	Solid	Pore
4/8/16	3.88	539430	99.62	98.68
4/8/24	3.98	479619	99.73	98.42
4/16/24	4.45	456897	99.60	98.00
4/16/32	4.80	437198	99.04	98.35
4/24/32	4.87	418739	99.62	97.66
2/16/24	3.26	563154	99.86	95.86

图6 颗粒尺寸对重构微结构内孔径分布的影响

Fig. 6 Pore size distribution for microstructures reconstructed with particles of different sizes

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