What are the criteria for a compound to be identified as an intercalation/conversion type?

peikai · March 12, 2021, 8:50am

Hi, I found the Battery Explorer Manual says that there are more than 4,000 intercalation compounds and 16,000 conversion compounds in Materials Project database. I am wondering how those compounds were identified as intercalation/conversion compounds. What were the criteria? And are there still some other potential intercalation/conversion compounds in the database that have not been identified.

Besides, why is it to say calculated properies of coversion materials are less accurate?

Thank you!
Kai

jshen · April 7, 2021, 5:47pm

Hi @peikai So the interaction materials are defined by matching similar structures after removing all the working ions. For conversion electrode, the voltage profile is essentially defined by traversing along the facets of the phase diagram for a given set of atoms, so you can generate a conversion electrode for any composition using this function with allow_unstable=True.

github.com

materialsproject/pymatgen/blob/04beca9af8e575005a40117f1779f1d464c0a697/pymatgen/apps/battery/conversion_battery.py#L113


    ]

    return cls(
        voltage_pairs=vpairs,
        working_ion_entry=working_ion_entry,
        _initial_comp_formula=comp.reduced_formula,
        _framework_formula=framework.reduced_formula,
    )

@classmethod
def from_composition_and_entries(cls, comp, entries_in_chemsys, working_ion_symbol="Li", allow_unstable=False):
    """
    Convenience constructor to make a ConversionElectrode from a
    composition and all entries in a chemical system.

    Args:
        comp: Starting composition for ConversionElectrode, e.g.,
            Composition("FeF3")
        entries_in_chemsys: Sequence containing all entries in a
           chemical system. E.g., all Li-Fe-F containing entries.
        working_ion_symbol: Element symbol of working ion. Defaults to Li.

The coversion data is less accurate for two main reasons:

The phase diagram might be incomplete so the chemical potentials (aka the voltage) might be wrong.
Some of the properties like volume change is calculated simply by linearly interpolating on a given facet of the phase diagram. While this is essentially the only thing we can do with the data that is given, we cannot comment on the accuracy.