In this work, a two-dimensional heterogeneous model of lithium-ion battery electrode is developed. The electrode is reconstructed using a non-volume-averaging approach, generating a heterogeneous structure in which solid and liquid phase are characterized separately with respective real spatial occupation and boundaries between them. The heterogeneous model is parameterized using voltage and temperature curves at multiple C-rates. Mass and charge transport in the generated electrodes, coupled with interfacial reactions, are numerically solved. Three cases with different porosity profiles are compared. Without changing the amount of active materials and its particle size distribution, an improvement of rate performance up to 50% is achieved in the case with larger electrode porosity near the electrode-separator interface. Using the heterogeneous model as the benchmark, the precision of the pseudo-two-dimension model of lithium-ion battery electrode, which has been widely adopted in literatures and commercial computational softwares, can be improved by proper parameterization, including using the volume-averaged rather than number-averaged diameter as the negative electrode particle size; using the generated electrode structure, rather than the Bruggeman relationship, to calculate the tortuosity of porous electrodes; and using the size of primary particle, rather than that of the agglomerate, as the particle size at the positive electrode.

No abstract

An impedance model considering the electrochemo-mechanics of a single particle in lithium-ion batteries is proposed in the work. In this model, the interaction between the Li+ diffusion and the surface reaction and mechanics is considered. The characteristic semicircle in low frequency range, which is due to the stress effect, is found. The visualizability of the stress-induced semicircle in the experiments is found to be related to the characteristic frequency of the Li+ diffusion. Through simplifying the model expression under three different limiting cases, two dimensionless number α=-θRT/F/∂U/(∂c_s ) and β=1+θc ̅_s are defined to evaluate the stress effect. The proposed mechanic-modified model is verified through the results of thin-film electrode considering the difficulty in performing single particle experiments for nano-sized particle and similarity of the single particle and thin film electrode. This work can be supplemented with the theory of porous electrode to analyze the impedance response of a porous electrode, which will be discussed in the next part of this series of papers.

No abstract

No abstract