Chemical extraction of Zn from ZnMn sub(2)O sub(4)-based spinels

• Published in: Journal of materials chemistry. A, Materials for energy and sustainability Materials for energy and sustainability, 2015-10, Vol.3 (42), p.21077-21082
• Main Authors: Knight, James C, Therese, Soosairaj, Manthiram, Arumugam
• Format: Article
• Language: English
• Subjects: Cathodes; Diffusion; Electrostatics; Extraction; Lithium batteries; Rechargeable batteries; Spinel; Zinc
• ISSN: 2050-7488; 2050-7496
• DOI: 10.1039/c5ta06482a

With an aim to increase the energy density compared to current Li-ion batteries, there is immense interest in rechargeable batteries with multivalent cations, such as Mg super(2+) and Zn super(2+), as they could provide higher charge storage capacity. alpha -MnO sub(2) has been investigated as a cathode for Zn-ion batteries, but other structures could be explored. Accordingly, this study investigates the chemical extraction of Zn from the spinel compositions ZnMn sub(2-x)Ni sub(x)O sub(4) (x= 0, 0.5, and 1) using H sub(2)SO sub(4) and NO sub(2)BF sub(4). Acid treatment is able to extract Zn from the structure through a Mn super(3+) disproportionation reaction that is dependent on the Mn super(3+) content. Zn extraction decreases with increasing Ni content due to the decrease in Mn super(3+) content; in fact, ZnMnNiO sub(4) does not lose any Zn upon acid treatment because all of the Mn ions are in the 4+ state. Treatment with NO sub(2)BF sub(4), however, is unable to extract any Zn from the samples, unlike in the analogous LiMn sub(2)O sub(4) spinel. This is believed to be due to the high electrostatic repulsion that Zn super(2+) ions would feel from other Zn super(2+) ions in neighboring tetrahedral sites as they have to diffuse through the unoccupied octahedral sites in the spinel lattice, and Zn super(2+) does not prefer octahedral sites. Because NO sub(2)BF sub(4) more closely approximates the extraction mechanism experienced in a Zn-ion cell, it appears that the ideal spinel structure is not suitable as a Zn-ion battery cathode unless synthesis conditions or additional treatments were used to create vacancies in the structure that allows for easier Zn-ion diffusion without much electrostatic repulsion.