138 research outputs found
On the Balance of Intercalation and Conversion Reactions in Battery Cathodes
We present a thermodynamic analysis of the driving forces for intercalation
and conversion reactions in battery cathodes across a range of possible working
ion, transition metal, and anion chemistries. Using this body of results, we
analyze the importance of polymorph selection as well as chemical composition
on the ability of a host cathode to support intercalation reactions. We find
that the accessibility of high energy charged polymorphs in oxides generally
leads to larger intercalation voltages favoring intercalation reactions,
whereas sulfides and selenides tend to favor conversion reactions. Furthermore,
we observe that Cr-containing cathodes favor intercalation more strongly than
those with other transition metals. Finally, we conclude that two-electron
reduction of transition metals (as is possible with the intercalation of a
ion) will favor conversion reactions in the compositions we studied
On the Active Components in Crystalline Li-Nb-O and Li-Ta-O Coatings from First Principles
Layered-oxide (NMC) positive electrodes
with high Nickel content, deliver high voltages and energy densities. However,
a high nickel content, e.g., = 0.8 (NMC 811), can lead to high surface
reactivity, which can trigger thermal runaway and gas generation. While claimed
safer, all-solid-state batteries still suffer from high interfacial resistance.
Here, we investigate niobate and tantalate coating materials, which can
mitigate the interfacial reactivities in Li-ion and all-solid-state batteries.
First-principles calculations reveal the multiphasic nature of Li-Nb-O and
Li-Ta-O coatings, containing mixtures of and
, or of and . The
concurrence of several phases in Li-Nb-O or Li-Ta-O modulates the type of
stable native defects in these coatings. Li-Nb-O and Li-Ta-O coating materials
can form favorably lithium vacancies and antisite
defects
() combined into
charge-neutral defect complexes. Even in defective crystalline
(or ), we reveal poor Li-ion conduction
properties. In contrast, and that are
introduced by high-temperature calcinations can provide adequate Li-ion
transport in these coatings. Our in-depth investigation of the
structure-property relationships in the important Li-Nb-O and Li-Ta-O coating
materials helps to develop more suitable calcination protocols to maximize the
functional properties of these niobates and tantalates
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