Abstract
An analytical model is proposed to investigate properties of composite electrodes that utilize more than one active material. We demonstrate how the equations can be applied to aid in the design of electrodes by comparing silicon-graphite and tin-graphite composite negative electrodes as examples with practical relevance. Based on simple assumptions, the results show how volume expansion tolerance and initial porosity are important factors for the achievable gravimetric and volumetric capacities as well as volumetric energy density. A Si-alloy/graphite composite electrode is used as an experimental system to corroborate the formulated analysis. Kinetic limitations are also addressed based on a novel heuristic approach.
Highlights
In the present work, we derive analytical model equations that can be utilized using simple spread-sheet software, and describe the relevant material and electrode parameters needed for making the calculations
In automotive applications, in many cases restrictions in space are more severe than weight restrictions, which makes the volumetric capacity increasingly relevant compared to the gravimetric capacity
We have developed a set of analytical equations suited to undertake design considerations for combined active materials in practical lithium ion-battery electrodes
Summary
We derive analytical model equations that can be utilized using simple spread-sheet software, and describe the relevant material and electrode parameters needed for making the calculations These equations utilize a full-electrode expansion factor E, which has similarities to the swelling coefficient used in the model by Gomadam et al.[6]. For the first case-study, illustrated on the upper right of Fig. 1, the expansion factor will be set to zero, E = 0, which means that the battery stack is not allowed to increase in volume This case is similar to the calculation performed by Dash et al.[8], but our results lead to different conclusions using the equations given below. To the best of our knowledge, we find for the first time a very general behavior that can be used heuristically to study the influence of kinetics properties on the capacity of the material
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