Experimental and Modeling Analysis of Graphite Electrodes with Various Thicknesses and Porosities for High-Energy-Density Li-Ion Batteries

Abstract

The influence of the negative electrode design on its electrochemical performance with regard to Li insertion/de-insertion is analyzed in this work. A combined experimental/modeling approach is undertaken relying on Newman continuum model. Various designs of industry-grade graphite electrodes (2-6 mAh cm −2 ) were previously characterized by measuring geometric and physical parameters that are used as input parameters in the present model analysis. The half-cell model is successfully validated against rate-capability experiments without any further parameter fitting. The various polarization contributions are then identified based on the model analysis of rate-capability tests on the various electrodes. It emerges that low-loading electrodes suffer from larger particle-scale limitations (mainly solid-diffusion limitation) than high-loading electrodes because of a lower active surface area per geometric area. However, high-loading electrodes undergo large liquid-phase limitations at medium to high current densities: a large overpotential develops because of the formation of a large salt concentration gradient across the cell. Finally, the graphite electrode model is used into a full-cell model vs. As of today, electric vehicles (EV) are being promoted as a substitute to internal-combustion-engine (ICE) vehicles in an effort to mitigate CO 2 , NO x and particulate matter (PM) emissions from the road transportation sector. Although the effectiveness of EV market penetration toward mitigating air pollution strongly depends upon the source of electricity production (e.g., fossil vs. nuclear or renewable), it may still improve air quality in cities and thereby citizens' health. In fact, the annual cost of air pollution was evaluated to over US$ 1.431 trillion in Europe by the World Health Organization in 2010.1 Nonetheless, the effectiveness of EV market penetration relies on whether consumers are willing to shift from ICE to electric vehicles. Among factors refraining citizens from shifting to EVs are the high price, the vehicle charging time and the driving range. The most straightforward way to tackle both the high price and limited driving range, with state-of-the-art Lithium-ion technology, is to increase electrode loading. Packing more active material in the electrode increases the cell energy density and decreases the amount of inactive material in a Lithium-ion battery pack. Fewer electrodes per stack are needed in a single cell, hence less current collector is used. However, high-loading electrodes suffer large power limitations, which might preclude fast charging of the EV battery pack. Power limitations mostly arise from lithium-ion transport limitations across the electrode porosity filled with the electrolyte and are known to increase with the electrode thickness and/or with a decrease in porosity.2-4 Accordingly, an optimization of the porous electrode design is necessary to achieve a high energy density while retaining enough power for the targeted application.Yet, electrode design optimization is not s...

Demystifying Charge Transport Limitations in the Porous Electrodes of Lithium‐Ion Batteries

“…the current literature provides invaluable information about the methods for measuring the effective ionic [3,[6][7][8][9] and electronic [9][10][11] conductivity in the lithium ion battery electrodes, but there are very limited comprehensive reports on the interplay between the electrode recipe, transport limitations, and the battery performance. [12][13][14][15] A variety of experimental and theoretical techniques have been proposed for the (in)direct measurement of the effective conductivities in the porous electrodes of LIBs. Several studies have investigated the ionic and electronic conduction in LIBs by reconstructing the 3D structure of the porous electrodes based on the cross sectional images obtained via X-ray tomography [6,[16][17][18][19] or focused ion beam-scanning electron microscopy (FIB-SEM).…”

Precise synthesis of N-doped graphitic carbon via chemical vapor deposition to unravel the dopant functions on potassium storage toward practical K-ion batteries

“…In contrast, the rate performance of HGNC is mediocre, with corresponding capacity retentions of 91%, 81%, 58%, 41%, 28% and 16%. Note that there is no obvious relationship between the rate performance and the Rct value, implying that the mass transfer (i.e., ion solid diffusion) procedure is the controlling step of this electrochemical reaction rather than the charge transfer process [41]. The surface-driven pseudocapacitive behavior mediated by high edge-N doping has faster reaction kinetics, contributing to better rate performance of HENC.…”

A review of thermal physics and management inside lithium-ion batteries for high energy density and fast charging

“…While these novel designs showed good promise in reducing the tortuosity, this review focuses on commercial electrodes which have a relatively high tortuosity. The thicker electrodes have higher tortuosity and larger liquid-phase polarization due to the porous structure and the increased thickness [79,80]. Lithium plating has a higher tendency to occur in thicker electrodes due to the higher tortuosity and larger polarization.…”

“…Lithium plating has a higher tendency to occur in thicker electrodes due to the higher tortuosity and larger polarization. Malifarge et al performed rate capability experiments of graphite electrodes with various areal loadings (2 -6 mAh/cm 2 ) and porosities (0.1 -0.45) [80]. Their analysis revealed different lithium plating mechanisms in electrodes with various areal loadings.…”