Impact of Stabilizing Cations on Lithium Intercalation in Tunneled Manganese Oxide Cathodes

Stabilizing cations such as K+, Ba2+, and Ag+ are known to provide charge neutrality and enhance structural stability in low-cost tunneled manganese dioxide (MnO2) cathodes for Li ion batteries. However, a fundamental understanding of the role of these cations in the electrochemical performance of tunneled MnO2 cathodes remains unclear, especially at low stabilizing cation concentrations. Here, we employ density functional theory (DFT + U) calculations to reveal the impact of stabilizing potassium cation (K+) concentration on the structural stability, electronic properties, and kinetics of lithium transport in 2 x 2 tunneled manganese oxide (alpha-KyMn8O16, at y = 0, 1, and 2) battery cathodes during lithium intercalation. Specifically, we provide insights into the effect of K+ ions on several critical factors governing the electrochemical storage performance of tunneled MnO2 cathodes, including (a) energetically favorable Li+ host sites, (ii) Li+ and electron transport capabilities, (iii) optimal intercalation pathways, crystal distortion, microstructural stability, and tunneled-to-layer phase transformation as a function of lithium content, and (iv) cell output voltage profile. Interestingly, we find that low K+ concentrations (y < 1) yield partially cation-deficient tunnels in the MnO2 cathode. Such unique tunnel structures in the cathode enable (a) low kinetic barriers for Li transport, (b) excellent thermodynamic stability of the tunneled structure even at a high Li+ loading (up to similar to 0.625 Li/Mn), and (c) good electronic conductivity facilitated by Jahn-Teller distortions; all of which are critical for achieving high capacity batteries with enhanced rate capability. In addition, these results provide perspectives to design low-cost transition metal oxide cathodes for high-performance Li-ion batteries with excellent cycle life.

Automated summary

This study used density functional theory calculations to examine the impact of stabilizing potassium cation concentration on tunneled manganese dioxide cathodes in lithium intercalation. Low K+ concentrations were found to result in partially cation-deficient tunnel structures with excellent thermodynamic stability and electronic conductivity, critical for achieving high capacity batteries with enhanced rate capability. These findings offer perspectives for designing low-cost transition metal oxide cathodes for high-performance Li-ion batteries with excellent cycle life.