锂离子电池(lithium ion batteries,LIBs)具有高比容量和良好的循环稳定性等优点,广泛应用于动力电池和储能领域.然而正极材料理论比容量不高,传统的制备过程会带来电极电化学性能不均匀等问题,制约了LIBs的进一步发展.电极多孔结构优化设计是突破此瓶颈的一种有效方法.本文将以磷酸铁锂(LiFePO4,LFP)为正极电极,锂金属为负极的LIBs作为研究对象,建立了基于粒子Packing的活性材料球形颗粒填充模型和基于三周期极小曲面(triply periodic minimal surface,TPMS)的电极微结构三维模型;研究了电极的比表面积等特征参数对不同类型多孔结构的影响以确定代表性体积单元;建立了LFP正极的LIBs放电过程多尺度数学模型,并对恒电流密度放电过程进行数值模拟.研究表明:粒径为3200nm的球形颗粒填充电极以5C放电倍率放电时容量减小量为47％,以1C放电倍率放电时电极表面浓度差异为66％;而4种新型TPMS电极以5C放电倍率放电时容量减小量均在1％以内,以1C放电倍率放电时电极表面浓度差异也均在1％以内,极大提升了电池的性能,且Gyroid型结构表现最优.本文对后期LIBs的优化设计具有指导意义,并提供数据和理论基础支持.
Multi-scale model-based optimal design of electrode microstructures for lithium ion batteries
Lithium-ion batteries(LIBs)are known tor their high specific capacity and good cycle stability.However,their further development is limited due to the low energy density of LiFePO4(LFP)electrodes.Optimization design for porous electrode structure is expected to break through this bottleneck.Furthermore,the electrochemical inhomogeneity of LIBs is closely related to the structure of the electrode.Currently there are mainly four methods to describe electrode structure:Models composed of homogeneous spherical particles,models composed of multi-size spherical particles,models simulated by complex mathematical methods and models reconstructed by focused ion beam-scanning electron microscopy(FIB-SEM)and X-ray computed tomography(XCT).Triply periodic minimal surfaces(TPMS)are described as surfaces with zero mean curvature.Compared with other porous structures,TPMS have the potential advantages of high specific surface area and enhanced pore connectivity.As interconnecting structures,TPMS are expected to be used as electrode structures to avoid battery degradation,because they are continuous and interconnected throughout three dimensions.In this paper,two methods were used to describe electrode structure:A filling model based on spherical particles and a model based on TPMS.Specific surface area and porosity were chosen as characteristic parameters to determine the appropriate size of the representative volume element(RVE).Furthermore,a multi-scale mathematical model of the LIBs discharge process was established and used to simulate the galvanostatic discharge process.The effects of TPMS structures and porosities on rate performance and solid diffusion performance were tested at varying discharge rates.The results show that the capacity loss of particles filling electrodes with particle sizes of 3200 nm is 47％when the discharge rate is 5C,while those of the four TPMS-based electrodes are all within 1％.The concentration difference on the electrode surface is 66％when the discharge rate is 1C,while that of the four TPMS-based electrodes are all within 1％.Therefore,TPMS-based electrodes perform much better than particles filling electrodes with particle sizes of 3200 nm,and the Gyroid structure has the best performance.Furthermore,low porosity electrode has higher discharge capacity but will restrict the transport of lithium ions which results in the loss of voltage at high discharge rates.This paper has guiding significance for the optimization design of LIBs and provides the theoretical basis and data support.
lithium ion batteriesmulti-scale mathematical modelinggenetic algorithmtriply periodic minimal surfacesnumerical simulation
NETL
NSTL
万方数据
维普
