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Potassium‐ion batteries (PIBs) are considered as competitive candidates for energy storage applications due to their abundant resources and low cost. K2Mn[Fe(CN)6] (KMnF) is an ideal cathode for PIBs because of its high theoretical specific energy (≈600 Wh kg−1). However, it suffers from severe Mn dissolution and complex phase transitions caused by Jahn–Teller distortion, resulting in rapid capacity decay. Here, a simple, controllable and universal "transition metal (TM2+) ion exchange" strategy is proposed to modulate the surface lattice of KMnF, not only stabilizing the structure but also maintaining its inherent high capacity. The surface Mn2+ is substituted by TM2+, including Fe2+, Ni2+, Cu2+, or Co2+, forming heterogeneous protection layer. Especially when the surface Mn2+ is modified by redox‐active Fe2+, it exhibits a capacity as high as 144 mAh g−1 and considerable energy density of 560 Wh kg−1 and a remarkable capacity retention (86% after 1,000 cycles at 50 mA g−1, and 71% after 5,000 cycles at 1,000 mA g−1, respectively). The surface‐modified KMnF cathode proved to be effective in stabilizing the structure by preventing the Mn dissolution and formation of tetragonal phase caused by Jahn–Teller distortion. This work provides a simple and universal strategy for stabilizing high‐energy Mn‐based cathode. [ABSTRACT FROM AUTHOR]

As a promising candidate for the flame‐retardant electrolyte, triethyl phosphate (TEP)/potassium bis(fluorosulfonyl)amide (KFSI)‐based electrolyte has drawn much attention in the K‐ion battery community. Although the TEP/KFSI formula at a moderate main salt concentration (normally, <3 m) enables the compatibility of the reactive K metal anode, the long‐standing oxidative instability of KFSI salt remains unsolved. Here, an additive strategy is reported to address the high‐voltage issue in the TEP/KFSI electrolyte, and generalize it to the other KFSI‐based electrolytes. The addition of potassium nitrate changes the surface charge distribution and effectively suppresses the decomposition of KFSI toward the high‐voltage cathode. The nitrate‐containing electrolyte enables superior stability of a 4.3 V‐class K‐ion battery, as evidenced by its 80% capacity retention over 2000 cycles (≈6 months) at the 1 C rate. Moreover, the long‐cycling stability of the graphite‐based full cell with Prussian Blue cathode is demonstrated. [ABSTRACT FROM AUTHOR]

Various electrolyte additives are developed to construct a cathode electrolyte interphase (CEI) layer for high‐voltage LiCoO2 since the cathode suffers severe interfacial degradation when increasing the cut‐off voltage over 4.55 V. However, the CEI derived from the additive sacrificial reaction faces the risk of rupture due to the corrosion reaction and the volumetric variation of the cathode. Herein, a non‐passivating cathode interface is realized for 4.6 V LiCoO2 with a non‐sacrificial electrolyte additive (TBAClO4) by regulating the solvent environment at the interface rather than the preferential decomposition for CEI formation. Owing to the novel protection mechanism, the cell performance shows little dependence on the CEI‐formation process. Therefore, an ultra‐high initial coulombic efficiency (96.63%) and excellent cycling stability (81% capacity retention after 300 cycles) are achieved in Li||LiCoO2 batteries. Moreover, even with the electrolyte containing 1000 ppm H2O, the remarkable water capture ability of the additive together with its interfacial regulation enables the 4.6 V Li||LiCoO2 battery to retain 80% capacity after 200 cycles. This non‐sacrificial strategy provides new insights into high‐voltage electrolyte additive design for high‐energy‐density lithium metal batteries. [ABSTRACT FROM AUTHOR]

Potassium ion batteries using graphite anode and high‐voltage cathodes are considered to be optimizing candidates for large‐scale energy storage. However, the lack of suitable electrolytes significantly hinders the development of high‐voltage potassium ion batteries. Herein, a dilute (0.8 m) fluorinated phosphate electrolyte is proposed, which exhibits extraordinary compatibility with both graphite anode and high‐voltage cathodes. The phosphate solvent, tris(2,2,2‐trifluoroethyl) phosphate (TFP), has weak solvating ability, which not only allows the formation of robust anion‐derived solid electrolyte interphase on graphite anode but also effectively suppresses the corrosion of Al current collector at high voltage. Meanwhile, the high oxidative stability of fluorinated TFP solvent enables stable ultrahigh‐voltage (4.95 V) cycling of a potassium vanadium fluorophosphate (KVPO4F) cathode. Using TFP‐based electrolyte, the 4.9 V‐class potassium ion full cell based on graphite anode and KVPO4F cathode shows rather remarkable cycling performance with a high capacity retention of 87.2% after 200 cycles. This study provides a route to develop dilute electrolytes for high‐voltage potassium ion batteries, by utilizing solvents with both weak solvating ability and high oxidative stability. [ABSTRACT FROM AUTHOR]

Batteries based on sodium superoxide and on potassium superoxide have recently been reported (1-3). However, there have been no reports of a battery based on lithium superoxide (Li[O.sub.2]), despite much research (4-8) into the lithium-oxygen (Li-[O.sub.2]) battery because of its potential high energy density. Several studies (9-16) of Li-[O.sub.2] batteries have found evidence of Li[O.sub.2] being formed as one component of the discharge product along with lithium peroxide ([Li.sub.2][O.sub.2]). In addition, theoretical calculations have indicated that some forms of Li[O.sub.2] may have a long lifetime (17). These studies also suggest that it might be possible to form Li[O.sub.2] alone for use in a battery. However, solid Li[O.sub.2] has been difficult to synthesize in pure form (18) because it is thermodynamically unstable with respect to disproportionation, giving [Li.sub.2][O.sub.2] (refs 19, 20). Here we show that crystalline Li[O.sub.2] can be stabilized in a Li-[O.sub.2] battery by using a suitable graphene-based cathode. Various characterization techniques reveal no evidence for the presence of [Li.sub.2][O.sub.2]. A novel templating growth mechanism involving the use of iridium nanoparticles on the cathode surface may be responsible for the growth of crystalline Li[O.sub.2]. Our results demonstrate that the Li[O.sub.2] formed in the Li-[O.sub.2] battery is stable enough for the battery to be repeatedly charged and discharged with a very low charge potential (about 3.2 volts). We anticipate that this discovery will lead to methods of synthesizing and stabilizing Li[O.sub.2], which could open the way to high-energy-density batteries based on Li[O.sub.2] as well as to other possible uses of this compound, such as oxygen storage., The crystalline Li[O.sub.2] reported here was made electrochemically using a cathode based on reduced graphene oxide (rGO) with added iridium (Ir) nanoparticles. Initially graphene oxide (GO) was prepared by a [...]