Tetramethyl ammonium cation intercalated layered birnessite manganese dioxide for high-performance intercalation pseudocapacitor

We develop an effective strategy to prepare intercalation pseudocapacitor by enlarging interlayer spacing of layered birnessite MnO2 through a controllable intercalation of K+, H+, TMA+/H+, TMA+ cations. The interlayer spacing of K-birnessite is swollen from ∼0.52 nm to 0.77 nm of TMA-birnessite. TMA+/H+ = 1000 sample exhibits an impressively high specific capacitance of 580.05 F g−1, much larger than that of K-birnessite, H-birnessite, TMA+/H+ = 800 (352.8, 414.9, 497.25 F g−1) at current density of 2 A g−1, showing excellent cycling performance with 112% capacitance retention after 10000 cycles. Even upon 20 A g−1, the capacity of TMA+/H+ = 1000 still remains a high level of 503 F g−1, while K-birnessite, H-birnessite, TMA+/H+ = 800 undergo a severe degradation to 180, 216, 433 F g−1. The expanded interlayer spacing enlarges the ion diffusion tunnels, weakens the layer interaction and decreases the resistance of charge diffusion, which easily enables the sufficient utilization of the active material through rapid ion intercalation. More importantly, the molecular-level thickness of host MnO2 layers that expose almost all the active sites on both sides of diffusion tunnels, thus greatly enhances the electrochemical storage capacitance. The results prove the feasibility of this method to prepare new intercalation pseudocapacitor and provide hints for other layered materials.