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Northwestern, Argonne team IDs promising Li-rich layered oxide electrode pairs for high-energy-density Li-ion batteries

30 August 2017

A team from Northwestern University and Argonne National Laboratory have used multi-faceted high-throughput density functional theory (HT-DFT) screening to identify a number of new Li2MIO3-Li2MIIO3 active/inactive electrode pairs—MI and MII being transition- or post-transition metal ions—that can be tested experimentally for high-energy-density LIBs.

In a paper published in the RSC journal Energy & Environmental Science, they presented their top 30 active/inactive pair cathode composite systems, ranked by gravimetric energy density, with a focus on the material properties with respect to operating voltage; stability against oxygen loss and metal-migration; and the formation of solid-solution and/or coherent nanocomposites. In particular, they proposed that Li4CrTiO6 and Li4CrMnO6, in which Cr6+ oxidation is accessible during lithium extraction, are worthy candidates. (Cr6+ is a health hazard and such experiments would have to be conducted with caution, they noted.)

The concept of incorporating a Li2MnO3 component into a conventional layered LiM′O2 structure has received substantial attention to date. More recently, there has also been a greatly increasing interest in using high-capacity Li2MO3-type structures, apart from Li2MnO3, alone as a cathode.

… The current understanding of Li2MO3-based cathodes is that, while reversible oxygen redox reactions can contribute to additional capacity, they may also be responsible for metal-migration within the anionic oxide array and oxygen loss, both of which are detrimental to the electrochemical performance of a Li/Li2MO3 cell. Composite Li2MIO3-Li2MIIO3 cathodes, in which MI and MII are transition- or post-transition metal ions, and where redox activities can be tuned by the relative amounts and voltages of the active/inactive components, provide a potential pathway to mitigate such problems. The judicious design of such composite electrode pairs requires a knowledge, not only of their thermodynamic stability at various states of charge, i.e., the cell voltage, but also structural instabilities, such as metal migration, phase transitions, and the tendency of the delithiated electrodes to lose oxygen during charge.

Clearly, a systematic survey of these parameters that control the electrochemical performance of Li2MO3 electrodes is essential for identifying new materials with inherently superior structural and electrochemical properties.

—Kim et al.

The team we performed a multi-faceted HT-DFT screening study of single- and mixed- metal Li2MO3 and Li2MIO3-Li2MIIO3 compounds, identifying promising new candidate cathodes. They started by identifying all of the thermodynamically-stable Li2MO3 (M = Ti, V, Cr, Mn, Fe, Co, Ni, Ge, Zr, Mo, Ru, Rh, Pd, Sn, Hf, Os, Ir, Pt, and Pb) Li-rich, layered oxides. They then calculated the delithiation voltage windows and determined the tendencies for oxygen evolution and structural transformation for each material.

Using this data, they developed a classification scheme that differentiates end-member Li2MO3 compounds as active cathodes and/or inactive stabilizers within integrated cathode structures.

Kim
Voltage vs. capacity chart of the top 30 cathode pair candidates, ranked by gravimetric energy density. The researchers used the average voltage and composite capacity to calculate the gravimetric energy density of all active/inactive Li2MIO3-Li2MIIO3 cathode pairs. An element M inside a box indicates the active component Li2MIO3, and the inactive stabilizers are shown in the legends (i.e., Li2MIIO3, MII = Ge, Mn, Ti, Ni, Sn, Zr, Co, and Cr). The researchers expect the active/inactive cathode pairs to either form a solid-solution (Li4MIMIIO6) or a nanocomposite (Li2MIO3-Li2MIIO3) based on the corresponding mixing energetics. “NCM”, “LFP”, and “LCO” denote LiNixCoyMnzO2, LiFePO4, and LiCoO2, respectively. Kim et al. Click to enlarge.

Resources

  • Soo Kim, Muratahan Aykol, Vinay I Hegde, Zhi Lu, Scott Kirklin, Jason Croy, Michael M. Thackeray and Chris M Wolverton (2017) “Materials Design of High-Capacity Li-rich Layered-Oxide Electrodes: Li2MnO3 and Beyond” Energy Environ. Sci. doi: 10.1039/C7EE01782K

August 30, 2017 in Batteries | Permalink | Comments (0)

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