Contents lists available at ScienceDirect Solid State Ionics journal homepage: www.elsevier.com/locate/ssi Effect of microstructure morphology on Li-ion battery graphite anode performance: Electrochemical impedance spectroscopy modeling and analysis 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: Microstructure Simulated annealing method Equivalent circuit Electrochemical impedance spectroscopy ABSTRACT Carbon graphite has received much attention over the last decades as the best candidate for negative Li-ion battery electrodes due to its thermal stability and optimal cycling capability. This paper aims to give a com- prehensive account of the effect of microstructure morphology such as porosity, tortuosity, solid-electrolyte interface area and active material particle geometry on the overall performance of an electrode. Simulated annealing method (SAM) was used to reconstruct a virtual microstructure of a graphite anode based on different active material particle configuration. The underlying species transport and reaction kinetics of an electro- chemical cell were modeled through an electrical circuit composed of different components. Simulated results show that active material particle geometry directly influences the tortuosity and specific surface area of the microstructure, thus affects the solid and electrolyte phase electronic/ionic mobility. Nyquist plot provided an overall impedance of ionic and electronic diffusion over a frequency range of 0.1 mHz to 20 kHz. The semi-circle in the high-frequency region is associated with charge transfer resistance and dielectric behavior of the solid- electrolyte interface (SEI) while the 45° slope at the low-frequency region is a result of lithium diffusion into the solid electrode. 1. Introduction Li-ion batteries are widely used for consumer electronics due to their high energy to weight ratio, minimal self-discharge, and optimal cycling capability [1,2]. Recent developments in battery chemistry and distributed grid management system extended Li-ion battery applica- tion for power storage devices in stand-alone photovoltaic systems and as a power source for electric and hybrid vehicles, thus reducing greenhouse gas emissions from motor vehicles [3,4]. However, there are still some critical issues that have to be addressed to realize mass electrification of road transport vehicles such as cost, safety, limited mileage and extended charging time. Generally, the performance of a Li-ion battery (cell potential and energy density) depend on cell chemistry and electrode microstructure morphology while its safety is mainly determined by the stability of the underlying chemical reactions and uncontrolled dendritic growth at SEI that could damage the se- parator and leads to the internal short circuit. From microscale point of view, performance optimization of Li-ion battery electrodes includes a systematic design of microstructure morphology parameters such as particle size and shape, porosity, tortuosity and effective solid-electro- lyte contact area. Although many researchers put a huge effort in the search and de- velopment of new and existing Li-ion battery anode materials, artificial graphite has been one of the main choices of negative electrodes, due to its high cycling performance, high reversibility and lower cost [5–8]. However, graphite electrodes have some limitations for high-power application due to limited intercalation capacity, a higher rate of li- thium plating at the end of charging [9] and evolution of SEI in the graphite surface [10] which is always associated with safety issues. The number of Li-ions inserted into the negative electrode during a single charging that determines the cell/battery potential is greatly influenced by microstructure morphology (particle size, porosity and tortuosity etc.) of the electrode, the electrolyte chemistry and the percentage of Li- ions delithiated from the positive electrode. Comprehensive under- standing of the underlying reaction kinetics at SEI and Li-ion diffusion in the electrolyte and solid-state electrode helps in a systematic design https://doi.org/10.1016/j.ssi.2017.11.024 Received 9 May 2017; Received in revised form 1 October 2017; Accepted 27 November 2017 ⁎ Corresponding author at: 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: jiangfm@ms.giec.ac.cn (F. Jiang). Solid State Ionics 314 (2018) 81–91 Available online 29 November 2017 0167-2738/ © 2017 Elsevier B.V. All rights reserved. T