Influence of MnO2-Birnessite Microstructure on the Electrochemical Performance of Aqueous Zinc Ion Batteries

Abstract

KxMnO2 materials with birnessite-type structure are synthetized by two different methods which make it possible to obtain manganese oxides with different degrees of crystallinity. The XPS results indicate that the sample obtained at high temperature (KMn8) exhibits a lower oxidation state for manganese ions as well as a denser morphology. Both characteristics could explain the lower capacity value obtained for this electrode. In contrast, the sample obtained at low temperature (KMn4) or by hydrothermal method presents a manganese oxidation state close to 4 and a more porous morphology. Indeed, in this case higher capacity values are obtained. At current density of 30 mA g−1, the KMn8, KMn4, and HKMn samples display a capacity retention of 88, 82, and 68%, respectively. The higher capacity loss obtained for the HKMn compound could be explained considering that the incorporation of Zn2+ in the structure gives rise to the stabilization of a ZnMn2O4 spinel-type phase. This compound is obtained in the discharge process but remains in the charge stage. Thus, when this spinel-type phase is obtained the capacity loss increases. Moreover, the stabilization of this phase is more favorable at low current rates where 100% of retention for all samples, before 50 cycles, was observed.

Electrochemical Performance of Tunnelled and Layered MnO2 Electrodes in Aluminium-Ion Batteries: A Matter of Dimensionality

“…These experiments confirm the presence of K + and H 2 O species within the structure of both samples, as previously reported. 21 Indeed, the quantity of these interlayer species is a critical factor for the emergence of one phase or the other. 30 It can be observed that T-KMn (δ-MnO 2 lamellar phase) shows higher content of K + and H 2 O than SG-KMn (α-MnO2 tunnelled phase), in agreement with previously reported results.…”

“…Thus, MnO 2 structures offer a wide variety of crystal structures and chemistries to be unravelled as promising efficient cathode materials for AIBs. 18 Within the vast manganese dioxide family, α-MnO 2 (cryptomelanelike) has been reported as an electrode in aqueous AIB, 19 aqueous zinc-ion, 20,21 and lithium batteries. 18,22 The extensive study of different hollandite-type electrode materials is largely due to the particular octahedra framework of this structure-type.…”

Mechanism of Chalcophanite Nucleation in Zinc Hydroxide Sulfate Cathodes in Aqueous Zinc Batteries

“…Mn oxides are a popular choice as the ZIB cathode, with numerous studies exploring the performance of different MnO 2 polymorphs in this application. ,,− Multiple reaction mechanisms have been reported in Zn–Mn batteries, including intercalation of Zn 2+ /H + into the MnO 2 lattice tunnels or layers, − direct conversion of MnO 2 to MnOOH, − and a dissolution-deposition reaction oscillating between MnO 2 (or another phase containing Mn 3+/4+ such as chalcophanite or vernadite) and Mn 2+ on charge and discharge, respectively. ,− These mechanisms are not necessarily exclusive of each other, as Huang et al reported a mixed insertion of Zn 2+ and H + that promoted a conversion reaction of MnO 2 into Zn x MnO 4 , MnOOH, and Mn 2 O 3 when using α-MnO 2 …”