Model Parameterization of Li-Ion Cell with Blended Cathodes
Authors: Rashid Muhammad , Pathan Tanveerkahn S. , Malcolmson Ryan , Somerville Limhi , McGordon Andrew , Kendrick Emma , Widanage Widanalage Dhammika 
Published: February 2020

The high power and high energy density of the Li-ion batteries (LIBs) are highly desirable for automotive applications which can be achieved by using cathodes with higher specific energy and rate capability. The existing cathode materials have various merits and demerits such as LiMn2O4 (LMO) has good rate capability, high power and low cost but lower energy and higher capacity fade due to manganese dissolution; LiNixMnyCo1-x-yO2 (NMC) has higher energy with issues of lower power and operating voltage; LiFePO4 (LFP) has higher energy, lower voltage and better thermal stability but very low electronic conductivity and lithium diffusivity; LiCoO2 (LCO) has higher energy but poor thermal stability and Co toxicity [1-2]. The blending of two cathode materials has been used in an attempt to overcome these shortcomings, to enhance the energy and power densities, as well as life cycle of the batteries [1]. In this regard, the blend of NMC and LMO has been used in commercial cells which has better performance with lower price than LCO [1]. The optimization of the blend’s percentage is a critical aspect to enhancing the electrochemical performance that requires several experimental iterations and is quite expensive and time consuming. Very few studies on mathematical modelling of the blended electrodes to optimize the composition of the blends have been performed [2-3]. This technique can minimize the number of experiments required to design the electrodes which can lead to improved cycle life and electrochemical performance of the batteries.
In this study, different blends of LMO and NMC will be used as a cathode to fabricate Li-ion coin cells against the graphite anode. The electrochemical performance of these cells will be analysed using galvanostatic charge-discharge, electrochemical impedance spectroscopy, and cyclic voltammetry. In addition 3-electrode cells will be utilised to determine the open circuit potential (OCP) and lithium diffusivity in the solid matrix of the different blended cathodes and anodes through galvanostatic intermittent titration technique (GITT). Electrode thickness, porosity, particle size will also be measured in these cases, and a correlation for the OCPs will be fitted based on the blend compositions which will be used as an input for the numerical modelling of these cells. The pseudo 2-D electrochemical model [4] will be used to imitate the charge-discharge behaviour of the graphite-LMO:NMC cells. This study will pave the way to numerically analyse the cycling performance of the LIBs using the blended systems and would assist the development of the battery management systems for these battery chemistries.

References:

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Jung, Mathematical model of lithium-ion batteries with blended-electrode system, J. Power Sources. 264 (2014) 184–194.

A. Appiah et al., Comparative study on experiments and simulation of blended cathode active materials for lithium ion batteries, Electrochim. Acta. 187 (2015) 422–432.

Rashid et al., Effect of relaxation periods over cycling performance of a Li-ion battery, J. Electrochem. Soc. 162 (2015) A3145–A3153.