Researchers from MIT and the Lawrence Berkeley National Laboratory have now completed a relatively thorough and systematic evaluation (one of the first) of the performance of spinel-structure compounds as multivalent intercalation cathode materials, according to a recent press release.
The evaluation — which was performed utilizing high-throughput, first-principles calculations — spanned a “matrix of five different intercalating ions and seven transition metal redox active cations.”
Batteries that utilize multivalent ions — think Mg2+ and Ca2+ — have for a while now been considered to be promising candidates for use in the creation of batteries with higher energy-densities than is available with current conventional lithium-ion technologies. (For example, Mg is theoretically considered to be a lot more capable of delivering a higher volumetric energy density, at 3833 mAh cm-3, than Lithium, at 2061 mAh cm-3.)
But identifying electrode materials that are capable of reversibly storing and releasing these multi-valent cations has remained something of an important challenge, one that would/does need to be addressed before multi-valent battery technology can move forward.
That’s where this new work comes in — the researchers at the Berkeley Lab and MIT were able to estimate the “insertion voltage; capacity; thermodynamic stability of charged and discharged states; and the intercalating ion mobility and then used these properties to evaluate promising directions.”
Here’s some of the details in the researchers’ own words:
Our calculations indicate that the Mn2O4 spinel phase based on Mg and Ca are feasible cathode materials. In general, we find that multivalent cathodes exhibit lower voltages compared to Li cathodes; the voltages of Ca spinels are ~ 0.2V higher than those of Mg compounds (versus their corresponding metals), and the voltages of Mg compounds are ~1.4 V higher than Zn compounds; consequently, Ca and Mg spinels exhibit the highest energy densities amongst all the multivalent cation species.
The activation barrier for the Al3+ ion migration in the Mn2O4 spinel is very high (~1400 meV for Al3+ in the dilute limit); thus, the use of an Al based Mn spinel intercalation cathode is unlikely. Amongst the choice of transition metals, Mn-based spinel structures rank highest when balancing all the considered properties.
Here’s the abstract.
The new work and findings have been detailed in a paper published in the journal Energy & Environmental Science.
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