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 Li₂M_IO₃-Li₂M_IIO₃ cathodes, in which M_I and M_II 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 Li₂M_IO₃-Li₂M_IIO₃ 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.

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