Affiliation:
1. Max Planck Institute for Solid State Research Heisenbergstraße 1 70569 Stuttgart Germany
Abstract
AbstractOne 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 are not yet very successful, lies in the lack of an adequate charge carrier treatment. Using the most challenging example of nanocrystalline lithium iron phosphate, where the full range from FePO4 to LiFePO4 is accessible without miscibility gap, this study shows how a quantitative description of literature results can be achieved even for such a huge window. For this purpose, point‐defect thermodynamics is applied and the problem is tackled from the two end‐member sides including saturation effects. A first, rather heuristic treatment interpolates 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. This study shows how to implement them into the analysis.
Subject
Mechanical Engineering,Mechanics of Materials,General Materials Science
Reference22 articles.
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2. Within this paper we definexand [defect] as molar ratios e.g. relative to the number of moles of FePO4in lithium iron phosphate. (Thexshould not be confused with the superscript inLiix${\mathrm{Li}}_{\mathrm{i}}^{\mathrm{x}}$ which denotes the relative charge of zero.) If Li is only present in neutral form i.e. asLiix${\mathrm{Li}}_{\mathrm{i}}^{\mathrm{x}}$ aLi=xLifollows from the mass action law forLi+Vi⇌Liix${\mathrm{Li + }}{{\mathrm{V}}}_{\mathrm{i}} \rightleftharpoons {\mathrm{Li}}_{\mathrm{i}}^{\mathrm{x}}$. If Li is only present in dissociated form i.e.xLi=[Lii·]=[e′] aLi=xLi2${x}_{\mathrm{Li}}=[{\mathrm{Li}}_{\mathrm{i}}^{\cdot}]=[{\mathrm{e}}^{\prime}] \ {a}_{\mathrm{Li}}={x}_{\mathrm{Li}}^{2}$follows from the mass action law for Equation (1).
3. Thermodynamics of Electrochemical Lithium Storage
4. Lithium intercalated compounds
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