Progress and Prospects of Emerging Potassium–Sulfur Batteries

Abstract

The potassium–sulfur battery (K–S battery) as an innovative battery technology is a promising candidate for large‐scale applications, due to its high energy density and the low cost of both K and S. The development of the K–S technology is, however, inhibited by its low reversible capacity and the safety issues related to the K metal anode. Here, the review starts by discussing the mechanism of the redox reactions for the K–S batteries and emphasizes the challenges for this battery system based on its current research status. Furthermore, the current improvement strategies for the K–S system in terms of the sulfur cathode, electrolyte, separator, and K metal anode are summarized. Finally, future perspectives on the development of the K–S system are proposed.

Rechargeable Metal-Sulfur Batteries: Key Materials to Mechanisms

“…On the other hand, the formation energy of K 2 S 2 is higher than those of K 2 S 3 and K 2 S, resulting in its worse thermodynamic stability. 47 Consequently, the K 2 S 2 phase tends to be less prevalent than the more stable K 2 S 3 and K 2 S phases, indicating a tendency for disproportionation. Since the final discharge product determines the number of electrons involved in the reaction, it is closely linked to the achievable theoretical capacities, as shown in Table 3.…”

“…Although this value seems to be lower than those of Li-S and Na-S batteries, it still surpasses the theoretical energy density of commercially available LIBs, such as LiCoO 2 -graphite, LiFePO 4 -graphite, LiNiCoMn-Si/C, and others. 47 Moreover, the abundance of potassium in the Earth's crust contributes to reducing the cost associated with the production and transportation of raw materials. Additionally, the standard reduction potential of K-metal (−2.93 vs SHE) is lower than that of most other metallic elements, excluding Li.…”

“…In comparison to Li-S and Na-S systems, a range of stable K 2 S n intermediate phases (n = 1, 2, 3, 4, 5, 6) have been identified at RT, providing an opportunity to study the mechanisms with pure solid polysulfide phases. 47 This unique characteristic enables the examination of electrochemical pathways involving key potassium polysulfide intermediates (K 2 S 3 and K 2 S) in K-S configurations. During the discharge process, K 2 S 2 and K 2 S 3 can be further reduced to K 2 S through solid-state conversion.…”

Reducing Overpotential of Solid‐State Sulfide Conversion in Potassium‐Sulfur Batteries

“…Sulfur electrodes can be conjugated with a range of metal anodes in rechargeable metal-sulfur (M-S) batteries and have demonstrated promising potential for practical energy-storage applications. [1][2][3][4][5][6][7] However, sulfur reduction reaction (SRR) and sulfur oxidation reaction (SOR) in M-S batteries involve conversions between various solid-state insulating elemental sulfur, metal disulfides and metal sulfides. [8,9] The high kinetical bottleneck of these solid-state sulfide conversions causes large overpotentials and incomplete conversion even under low rates, leading to low discharged capacity and fast capacity decay.…”

Advances in Selenium Sulfides Cathodes for Lithium/Selenium–Sulfur Batteries

“…Recent strategies to develop Se x S y -based cathode materials have included optimizing the electrochemical performance by adjusting the selenium and sulfur proportions at the atomic scale. Se x S y compounds can be broadly divided into sulfur-rich (e.g., Se 2 S 6 , Se 2 S 5 , Se 0.06 S 0.94 ) and selenium-rich (e.g., SeS 2 , Se 6 S 2 ) systems. − More sulfur offers higher capacity but can hinder electrode kinetics due to its insulating property. Thus, careful addition of selenium to sulfur can act as a eutectic accelerator to improve Li–S batteries, enhancing ionic and electronic conductivity, reaction kinetics, and overall electrochemical performance. − However, an optimal balance must be struck; higher selenium content, while increasing ionic conductivity, may lower both theoretical and practical specific capacity .…”