The relationship between the volume available within the crystal structure of a material and the size of charge-carrying ions is investigated by evaluating the performance of two manganese oxides with controlled variations in crystal tunnels, α-MnO2 (K0.11MnO2) and todorokite MnO2 (Mg0.20MnO2), in Li-ion and Na-ion batteries. These materials consist of MnO6 octahedra building blocks arranged into square tunnel configurations around different stabilizing cations, with α-MnO2 possessing structural tunnels of 4.6 Å by 4.6 Å and todorokite MnO2 possessing tunnels of 6.9 Å by 6.9 Å. Electrochemical testing of these materials revealed that despite its smaller crystal tunnel size, α-MnO2 exhibits higher capacities in both battery systems. However, at higher current rates it was found that todorokite MnO2 maintained a greater amount of its initial capacity. These findings provide valuable insight into the relationship between crystal structure composition and charge-carrying ion size to develop more efficient intercalation cathodes for Li-ion and Na-ion batteries.
Bryan W. Byles and Ekaterina Pomerantseva, "Effect of manganese oxide crystal tunnel size on Li-ion and Na-ion battery performance," Proc. SPIE 9924, Low-Dimensional Materials and Devices 2016, 992406 (Presented at SPIE Nanoscience + Engineering: August 30, 2016; Published: 16 September 2016); https://doi.org/10.1117/12.2238638.
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