![]() ![]() In this study, we investigate how K dendrites in K-metal batteries respond to self-heat. ![]() In particular, we demonstrated a distinct regime in which the opposite was true, where at very high current densities (∼15 mA cm −2), the internal self-heating of the battery triggers extensive surface diffusion of Li, which smoothens (heals) the dendrites. In previous work ( 19, 20) on Li-metal systems, we demonstrated that this is not always the case. It is generally accepted that a higher current density (i.e., faster charge/discharge) would promote dendritic growth, since the diffusion-limited aggregation of dendrites should be favored under such conditions. Kinetically, the nucleation and growth of metal dendrites is highly favorable during electrochemical plating and stripping processes. Most importantly, these dendritic projections can pierce through the separating membrane and electrically short the battery, leading to a severe thermal runaway, which could result in a catastrophic fire hazard. The growth of dendrites is associated with irreversible capacity loss, a reduced Coulombic efficiency, as well as drying and degradation of the electrolyte ( 18). However, similar to Li, the K-metal anode is observed to develop dendritic projections during the electrochemical plating–stripping processes, which occur when the battery is being charged and discharged. In contrast to this, the direct use of K metal as the anode would allow for superior specific capacity than carbonaceous, alloying, or intercalation compounds as the packing density of K atoms is the highest in its metallic form. On the anode side, a variety of materials such as graphite ( 14), hard carbons ( 15), soft carbons ( 16) as well as phosphorous-based alloys ( 17) have been explored in secondary K batteries. synthesized a hierarchically structured P2-type layered K 0.6CoO 2 cathode which not only delivered a high specific capacity, but was also capable of cycling K + ions at reasonably high rates ( 13). Among these, Prussian Blue and its analogs have been reported to reversibly store K ions in nonaqueous electrolytes, but poor volumetric capacity due to the low density of hexacyanoferrates limits their practical applications ( 8, 11, 12). Owing to the larger ionic size and mass of K +, only a few cathode materials have been reported for KIBs. This allows for higher ionic conductivity and faster transport of solvated K ions, with prospects of improved high-power performance for KIBs.Ī variety of anode and cathode materials for K secondary batteries have been explored. Compared to LIBs and NIBs, another important benefit of KIBs is that the K ion exhibits much weaker Lewis acidity ( 9, 10) and forms smaller solvated ions than those of Li and Na. It should also be noted that K unlike Li, does not alloy with aluminum at low potentials ( 8), enabling the utilization of low-cost aluminum foils as the current collector for the anode. This low potential provides KIBs a superior position among possible alternatives to replace Li-based batteries. In the commonly used ethylene carbonate/diethyl carbonate (EC/DEC) electrolyte, it was determined that K +/K is −0.15 V versus the Li +/Li (ref. Also, K theoretically offers a higher operating voltage than Na, since the standard redox potential for Na +/Na is −2.71 V versus SHE. The standard potential for K +/K is −2.93 V versus the standard hydrogen electrode (SHE), which is comparable to −3.04 V for Li +/Li. We demonstrate that the K-metal anode can be coupled with a potassium cobalt oxide cathode to achieve dendrite healing in a practical full-cell device. ![]() We show that the reason for this is the far greater mobility of surface atoms in K relative to Li metal, which enables dendrite healing to take place at an order-of-magnitude lower current density. We discover that this process is strikingly more efficient for K as compared to Li metal. The healing is triggered by current-controlled, self-heating at the electrolyte/dendrite interface, which causes migration of surface atoms away from the dendrite tips, thereby smoothening the dendritic surface. Here, we report that K dendrites can be healed in situ in a K-metal battery. However, formation of dendrites on such K-metal surfaces is inevitable, which prevents their utilization. The use of potassium (K) metal anodes could result in high-performance K-ion batteries that offer a sustainable and low-cost alternative to lithium (Li)-ion technology. ![]()
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