Sulphate-Based Cathode Materials for Potassium-Ion Battery

Abstract

The dominance of the lithium-ion battery in energy storage systems has been met with concerns over dwindling lithium resources and rising cost. A pragmatic alternative can be found in potassium-ion batteries owing to the abundance, lower cost and sustainable production and use of potassium-based cathode materials for largescale energy applications. Therefore, similar to the lithium chemistry, various potassium-based oxides ( e.g ., K x CoO 2 [1], K 0.7 Fe 0.5 Mn 0.5 O 2 [2] and K 0.27 MnO 2 [3]) have recently been reported. Parallel to the oxides, a number of polyanion insertion cathode materials have been discovered with credible electrochemical performance (e.g., K 3 V 2 (PO 4 ) 3 [4]). However, unlike the oxides, these polyanionic cathodes inherently suffer from lower theoretical capacity stemming from their high molecular weight, thus decreasing the net energy density. Whilst their capacity is moderate, polyanionic systems offer rich mineral and structural diversity to design potassium-based materials with tunable redox potentials. In this work, we explored the vast materials database of sulphate-based insertion materials for potassium-ion batteries. Apart from containing economic and Earth-abundant elements, sulphate-based minerals can, in principle, exhibit high theoretical capacities owing to their low molecular weight. In our exploration of the sulphate chemistry for potassium-ion batteries, we are able to take advantage of an extensive database of known minerals, particularly the bimetallic and hydrated sulphate derivatives such as karpovite, alunite, fedotovite K 2 Cu 3 O(SO 4 ) 2 , langbeinite (K 2 M 2 (SO 4 ) 3 ; M=Fe, Mn, Cu, Co, Ni), picromerite, mereiterite, etc . One such mineral is goldichite, with the general chemical formula K 2 M(SO 4 ) 2 ・nH 2 O. Noting that its structure contained possible K-ion diffusion channels, we attempted to design a yavapaiite insertion compound for potassium batteries. We will highlight the syntheses and electrochemical performance in K-ion cells of such sulphate-based minerals. Reference s : [1] Y. Hironaka, K. Kubota and S. Komaba, Chem. Commun. , 53 (2017) 3693. [2] X. Wang, X. Xu, C. Niu, J. Meng, M. Huang, X. Liu, Z. Liu and L. Mai, Nano Lett. , 17 (2017) 544-550. [3] C. Vaalma, G. A. Giffin, D. Buchholz and S. Passerini, J. Electrochem. Soc ., 163 (2016) A1295-A1299. [4] J. Han, G. –N. Li, F. Liu, M. Wang, Y. Zhang, L. Hu, C. Dai and M. Xu, Chem. Commun. , 53 (2017) 1805-1808. Figure 1