Contents lists available at ScienceDirect Microporous and Mesoporous Materials journal homepage: www.elsevier.com/locate/micromeso Microstructure reconstruction and impedance spectroscopy study of LiCoO 2 , LiMn 2 O 4 and LiFePO 4 Li-ion battery cathodes Bereket Tsegai Habte a,b , Fangming Jiang a,∗ a Laboratory of Advanced Energy Systems, CAS Key Laboratory of Renewable Energy, Guangdong Key Laboratory of New and Renewable Energy Research and Development, Guangzhou Institute of Energy Conversion, Chinese Academy of Sciences (CAS), China b University of Chinese Academy of Sciences, China ARTICLE INFO Keywords: Cathode materials Microstructure Impedance spectroscopy Equivalent circuit ABSTRACT Cathode materials have been the focal point of research in the quest for high-performance secondary battery technology in consumer electronics and electric vehicles. The present work investigates the effect of the mi- crostructural morphology of major cathode materials (LiCoO 2 , LiMn 2 O 4 , and LiFePO 4 ) on the performance of the Li-ion battery related to the charge and species transport. Simulated annealing method (SAM) was implemented to generate a virtual 3D domain of the electrode microstructure using a spherical particles, average radius of 3 and 6 μm. An equivalent circuit composed of resistance, capacitance and Warburg impedance was used to model the impedance response of the overall electrochemical reaction occur inside a typical battery system. Electrochemical impedance spectroscopy (EIS) results show that the ionic and electronic mobility in the solid electrode and bulk electrolyte were significantly determined by the morphology of the electrode microstructure. Higher porosity microstructures usually tend to have larger solid-electrolyte interface (SEI) area and lower pore tortuosity which improves the ionic diffusivity in solid and electrolyte phase. Furthermore, the Bruggeman's exponent for effective conductivity and diffusivity was derived from geometrical parameters of the reconstructed microstructure. The real and imaginary parts of the impedance were then presented in Nyquist plot on a fre- quency range of 20 kHz to 10 mHz. 1. Introduction Since the first commercialization in 1991, Li-ion batteries become the main power source for many portable devices such as cellular tel- ephones and other electronics. When compared with the more con- ventional power storage devices such as lead-acid and Ni-Cd, Li-ion batteries provide high working voltage and high specific capacity up to 280 mAh/g [1,2]. The fact that Li-ion battery is regarded as ‘green battery’ is due to minimized capacity fade over several cycling, lower self-discharge rate (less than 5% monthly) and non-toxicity to the en- vironment [3–5]. Recent hybrid and pure electric vehicles require en- ergy storage system designed to meet prolonged mileage per single charging (high energy density), proper acceleration and torque (high power density), safety operation and lower cost [6–8]. The quest for next-generation Li-ion batteries attract the attention of many researchers and generates a significant number of publications. Despite several efforts, the storage capacity of Li-ion battery improves slowly over the past several years. Limited intercalation dynamics of Li- ions in the active material and slow diffusion process through porous electrode are major capacity restraining factors. The former can be im- proved through nanosynthesis such as chemical doping while the later can be addressed experimentally via microstructure engineering and numeri- cally through mesoscale modeling of porous electrodes. Essential input parameters for numerical microstructure reconstruction are particle mor- phology, volume fraction of porosity and two-point autocorrelation func- tion. Specific surface area (electrode-electrolyte interface area) and tor- tuosity are distinctive parameters derived from the 3D reconstruction. Tortuosity can be expressed geometrically as the ratio of the average pore capillary length between two random points to the geometrical shortest path between the points. Li-ion cathodes have been evolved through various material combinations such as lithium cobalt oxide (LCO), lithium manganese oxide (LMO), lithium iron phosphate (LFP), nickel cobalt aluminum (NCA) and nickel cobalt manganese (NCM) proving a wide range of cell voltage capacity, energy density, and cost. Generally, Li-ion battery cathodes are composed of active particles (LCO, LMO, LFP etc.), cathode binders such as polytetrafluoroethylene (PTFE) and poly- vinylindene fluoride (PVDF) immersed in an electrolyte solution of lithium hexafluorophosphate (LiPF 6 ). https://doi.org/10.1016/j.micromeso.2018.04.001 Received 13 January 2018; Received in revised form 21 March 2018; Accepted 1 April 2018 ∗ Corresponding author. Laboratory of Advanced Energy Systems, Guangzhou Institute of Energy Conversion, Chinese Academy of Sciences (CAS), 2 Nengyuan Rd, Wushan, Tianhe District, Guangzhou 510640, China. E-mail address: fm_jiang2000@yahoo.com (F. Jiang). Microporous and Mesoporous Materials 268 (2018) 69–76 Available online 04 April 2018 1387-1811/ © 2018 Elsevier Inc. All rights reserved. T