The VSe ₂ –ZrO ₂ /C/MXene composite derived from a MXene-MOF hybrid with excellent cycling stability and high reversible capacity exhibited satisfying lithium-ion storage performancedde.

Na metal batteries (NMBs) have received extensive attention due to their high theoretical capacity and low electrochemical redox potential. However, dendrite growth and an unstable solid electrolyte interphase (SEI) layer in Na anodes limit the development of NMBs. In this work, we attempt to introduce potassium bis(fluorosulfonyl)imide (KFSI) as an NMB salt additive in electrolyte and find that this KFSI-containing electrolyte can enable highly reversible and nondendritic plating–stripping of Na metal anodes. Excellent cycling stability for 400 h at 0.5 mA cm⁻² in a Na‖Na symmetric cell and a high coulombic efficiency of 97.7% after 200 cycles in a Na‖carbon cloth (CC) asymmetric cell can be achieved in KFSI containing electrolyte. From our results, we find that K-ions from KFSI can show electrostatic shielding on the tip of the dendrite and then guide the uniform deposition of Na ions due to the lower potential of the K/K⁺ couple (−2.93 V vs. the standard hydrogen electrode (SHE)) compared with that of the Na/Na⁺ couple (−2.71 V vs. SHE). In addition, the S–F bond cleavage from the FSI anion presents low dissociation energy of S–F from density functional theory calculation, contributing to the formation of a stable fluoride (NaF and KF) rich solid electrolyte interfacial layer on the Na anode surface, which is also in favor of a tough Na plating–stripping process. We believe our findings will guide salt engineering to enhance the electrochemical performance of the Na metal anode.

As a promising energy storage system, potassium (K) ion batteries (KIBs) have received extensive attention due to the abundance of potassium resource in the Earth’s crust and the similar properties of K to Li. However, the electrode always presents poor stability for K-ion storage due to the large radius of K-ions. In our work, we develop a nitrogen-doped carbon nanofiber (N-CNF) derived from bacterial cellulose by a simple pyrolysis process, which allows ultra-stable K-ion storage. Even at a large current density of 1 A g⁻¹, our electrode exhibits a reversible specific capacity of 81 mAh g⁻¹ after 3000 cycles for KIBs, with a capacity retention ratio of 71%. To investigate the electrochemical enhancement performance of our N-CNF, we provide the calculation results according to density functional theory, demonstrating that nitrogen doping in carbon is in favor of the K-ion adsorption during the potassiation process. This behavior will contribute to the enhancement of electrochemical performance for KIBs. In addition, our electrode exhibits a low voltage plateau during the potassiation–depotassiation process. To further evaluate this performance, we calculate the “relative energy density” for comparison. The results illustrate that our electrode presents a high “relative energy density”, indicating that our N-CNF is a promising anode material for KIBs.

The performance of potassium (K)-ion batteries (KIBs) is not only dependent on electrode materials but also highly related to the electrolyte. In this work, we obtained a cobalt sulfide (CoS)-containing hybrid by the hydrothermal method and subsequent thermal treatment for K-ion storage. After ether-based electrolyte matching, the CoS-containing hybrid achieves a specific capacity of 229 mA h g⁻¹ at 1 A g⁻¹ after 300 cycles, and presents enhanced performance in the ether-based electrolyte. According to our measurement and calculation, the CoS-containing hybrid in the ether-based electrolyte promotes the formation of a highly anionic coordination solvated structure, which contributes to the enhancement of the stability of the electrolyte for K-ion storage. In addition, the strong coordination of anions also facilitates the rapid separation of the solvent during the potassiation process, which is also in favor of the decrease of the side reaction of the CoS@RGO hybrid for KIBs. We believe that our work will provide a new perspective on electrolyte engineering to boost the electrode material performance for K-ion storage.