High Throughput Screening of Na-Fe-Mn-O Sodium-Ion Cathode Materials

Abstract

With the rapid development of sodium-ion batteries in recent years, the prospect of replacing lithium-ion batteries for some applications like personal electronics is more and more promising. The abundant reserve of sodium element and the cheap transition metals for layered oxides are the decisive advantages to solve the cost of electricity storage and environmental pollution, which may make massive energy storage accessible. During the past ten years, layered oxides of the form NaxFeyMnzO2 have received a lot of attention with high specific capacities and eco-friendly transition metal selection. Since the radius of sodium ion is significantly larger than that of lithium ion, the configurations of the sodium layered oxides are more complex, which allows sodium ions to be located in either octahedral (O-type) or prismatic (P-type) sites. Meanwhile, the electrochemical properties of sodium layered oxides vary dramatically with the composition. Despite this, a relatively small number of compositions have been studied to date in the Na-Fe-Mn-O system. Herein, we apply high-throughput methods to systematically analyze both structures and battery performance across the entire NaxFeyMnzO2 system.The high-throughput methods established elsewhereare used here to make and characterize 64 different materials simultaneously. In total, materials at 304 different compositions were made for this study, all of which were examined by X-ray diffraction (XRD) and 184 compositions were also studied by high-throughput electrochemistry as they are particularly interesting as potential battery materials. Qualitative phase identification based on the XRD is performed as well as quantitative fitting of the data to extract phase compositions and lattice parameters. Each of P2-, P3- and O3-type sodium layered oxides are identified in the phase diagram and their solid solution regions were determined and will be discussed in detail. High-throughput cyclic voltammetry (CV) is used to obtain the charge/discharge voltages and specific capacities for 15 cycles thereby allowing some discrimination of the quality of extended cycling. These methods enable a rapid and highly precise screening across very wide compositions. Figure 1 shows both the experimental setup used for key steps in the synthesis and also a map of specific capacity across the phase diagram. Such maps will be correlated to the structural phase diagram obtained by XRD in order to extract meaningful structure-property relationships. Moreover, high-throughput XPS is used to study the surface stability after over 6 months of storage in air. Interestingly, some compositions show a greater tendency to form carbonates and have consequences on the electrochemical performance. Figure 1. Steps in the high-throughput electrochemical methods used to study 64 samples at once: a) a well plate containing sol-gel precursors in various ratios to map out a region of the phase diagram, (b) the samples after sintering at 850 °C, (c) combinatorial cell used to collect the CVs shown in (d), and (e) specific capacities extracted from the CVs plotted on the Na-Fe-Mn-O pseudo-ternary Gibbs triangle. Compositions P2-Na2/3Fe1/2Mn1/2O2 and O3-Na2/3Fe1/2Mn1/2O2 are labeled on the ternary plot.References Liu, Q.; Hu, Z.; Chen, M.; Zou, C.; Jin, H.; Wang, S.; Chou, S. L.; Dou, S. X., Recent progress of layered transition metal oxide cathodes for sodium‐ion batteries. Small 2019, 15 (32), 1805381.Yabuuchi, N.; Kajiyama, M.; Iwatate, J.; Nishikawa, H.; Hitomi, S.; Okuyama, R.; Usui, R.; Yamada, Y.; Komaba, S., P2-type Na x [Fe 1/2 Mn 1/2] O 2 made from earth-abundant elements for rechargeable Na batteries. Nature materials 2012, 11 (6), 512.Adhikari, T.; Hebert, A.; Adamic, M.; Yao, J.; Potts, K.; McCalla, E., Development of High-Throughput Methods for Sodium-Ion Battery Cathodes. ACS combinatorial science 2020, 22 (6), 311. Figure 1