How to Adequately Describe Full Range Intercalation - a Two-Sided Approach.

One of the key-challenges in battery research is to quantitatively describe the intercalation storage capacity as a function of the reversible cell voltage. The reason that such endeavors have not yet been very successful, lies in the lack of an adequate charge carrier treatment. Using the most challenging example of nano-crystalline lithium iron phosphate where the full range from FePO 4 to LiFePO 4 is accessible without miscibility gap, we show how a quantitative description of literature results can be achieved even for such a huge window. For this purpose we apply point-defect thermodynamics and tackle the problem from the two end-member sides including saturation effects. In a first, rather heuristic treatment we interpolate in-between using the safe thermodynamic criterion of local phase stability. Already this straightforward approach works very satisfactorily. In order to also gain mechanistic insight, interactions among and between ions and electrons have to be taken account of. We show how to implement them into the analysis. This article is protected by copyright. All rights reserved.