In this work, we will use density functional theory (DFT) to explore the role of magnetism and disorder of the discharge product (KO2) in K-air batteries. We have calculated the formation energy of three different structures of potassium superoxide using the BEEF-vdW functional, in order to determine the most stable phase for both the antiferromagnetic and ferromagnetic configurations. The results of the calculations can be seen in Table I, and agree with previous work that using a metal-chloride reference for calculating the formation energy significantly reduces the mean absolute error (MAE), as well as the variation in calculated energy across various functionals . The BEEF ensemble results as shown in Table II illustrates how the scheme using the metal chloride reference gives the least standard deviation across the various functionals. Table III reveals that the ferromagnetic state is the more stable structure, which disagrees with experimental results that KO2 is paramagnetic at room temperature, and antiferromagnetic at temperatures below 7K . Thus, we will explore the more disordered phases of KO2 under various temperatures, including the tetragonal, monoclinic, and triclinic structures with different orientations of the oxygen dimers . We will report on energetics of these phases within the random phase approximation (RPA). We will discuss the band structures and the band gaps for these various phases and its implications for K-O2 batteries. Lastly, we will explore the possibility of magnetic substrates preferentially nucleating and growing KO2 phases with high electronic conductivity to maximize the battery capacity.
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