Abstract
The electrification of the powertrain requires enhanced performance of lithium-ion batteries, mainly in terms of energy and power density. They can be improved by optimising the positive electrode, i.e., by changing their size, composition or morphology. Thick electrodes increase the gravimetric energy density but generally have an inefficient performance. This work presents a 2D modelling approach for better understanding the design parameters of a thick LiFePO4 electrode based on the P2D model and discusses it with common literature values. With a superior macrostructure providing a vertical transport channel for lithium ions, a simple approach could be developed to find the best electrode structure in terms of macro- and microstructure for currents up to 4C. The thicker the electrode, the more important are the direct and valid transport paths within the entire porous electrode structure. On a smaller scale, particle size, binder content, porosity and tortuosity were identified as very impactful parameters, and they can all be attributed to the microstructure. Both in modelling and electrode optimisation of lithium-ion batteries, knowledge of the real microstructure is essential as the cross-validation of a cellular and lamellar freeze-casted electrode has shown. A procedure was presented that uses the parametric study when few model parameters are known.
Highlights
Rechargeable batteries are ubiquitous in everyday life
2D modelling approach for better understanding the design parameters of a thick LiFePO4 electrode based on the P2D model and discusses it with common literature values
Particle size, binder content, porosity and tortuosity were identified as very impactful parameters, and they can all be attributed to the microstructure
Summary
Rechargeable batteries are ubiquitous in everyday life. Especially lithium-ion batteries are nowadays some of the most used energy storage solutions, e.g., in mobile phones, laptops, household aids and consumer electronics, making them an essential player for the digitalisation of our society. The P2D model, which has proven to be very accurate [13], combines the porous electrode theory consisting of spherical particles [17], the concentrated solution theory and the kinetics equations This approach enables the simulation of several material properties and the prediction of battery performance under various design parameters. All studies have in common that they are very specialised on one or two parameters, which leads to a large uncertainty with the number of free parameters within the modelling approach presented here, when only a few model parameters are known This uncertainty was first discussed theoretically using the example of a thick porous LFP electrode and using the example of a cellular and lamellar freeze-casted electrode [39]. The lithiation along the LFP electrode after reaching particle radius, filler volume fraction, electrode height and, in broad terms, the tortuosity
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