Here, we demonstrate stabilization of a newly reported tunnel manganese oxide phase, 2xn-MnO2, with the crystal structure consisting of 2x2, 2x3, and 2x4 octahedra tunnels containing Na+ stabilizing cations and water molecules. Building off of previous work by C.S. Johnson et al. [3], where the smaller tunnel structured α-MnO2 was stabilized with Li2O, we modified the structure and chemical composition of 2xn-MnO2 via mixing in methanol and lithium hydroxide, resulting in insertion of Li2O into the structural tunnels of 2xn-MnO2. In LIBs, the Li2O-stabilized 2xn-MnO2 demonstrates both higher initial capacity and superior capacity retention after 100 cycles. The initial capacity is improved from 93 mAh g-1 for the pristine material to 168 mAh g-1 for the stabilized 2xn-MnO2. Moreover, the galvanostatic discharge-charge profile for the stabilized 2xn-MnO2 exhibits a better pronounced plateau-shaped region compared to the original 2xn-MnO2 phase, indicating that the stabilized material contains more well-defined insertion sites. Similarly, in SIBs, the capacity of the stabilized 2xn-MnO2 was improved by 35% to 81 mAh g-1, and capacity retention increased from 43% to 75% after 100 cycles, demonstrating the effectiveness of this stabilization approach in both Li-ion and Na-ion battery systems. Thus, we show that stabilization with Li2O can be applied to various tunnel manganese oxide phase to improve their electrochemical performance as intercalation-based battery electrodes.
References
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- S. Johnson et al., J. of Power Sources (1997) 68, 570