Strategies towards Low‐Cost Dual‐Ion Batteries with High Performance

Reversible Alloying of Phosphorene with Potassium and Its Stabilization Using Reduced Graphene Oxide Buffer Layers

High specific capacity materials that can store potassium (K) are essential for next-generation K-ion batteries. One such candidate material is phosphorene (the 2D allotrope of phosphorus (P)), but the potassiation capability of phosphorene has not yet been established. Here we systematically investigate the alloying of few-layer phosphorene (FLP) with K. Unlike lithium (Li) and sodium (Na), which form Li₃P and Na₃P, FLP alloys with K to form K₄P₃, which was confirmed by ex situ X-ray characterization as well as density functional theory calculations. The formation of K₄P₃ results in high specific capacity (∼1200 mAh g^-1) but poor cyclic stability (only ∼9% capacity retention in subsequent cycles). We show that this capacity fade can be successfully mitigated by the use of reduced graphene oxide (rGO) as buffer layers to suppress the pulverization of FLP. We studied the performance of rGO and single-walled carbon nanotubes (sCNTs) as buffer materials and found that rGO being a 2D material can better encapsulate and protect FLP relative to 1D sCNTs. The half-cell performance of FLP/rGO could also be successfully reproduced in a full-cell configuration, indicating the possibility of high-performance K-ion batteries that could offer a sustainable and low-cost alternative to Li-ion technology.

Fibrous Network of C@MoS2 Nanocapsule-Decorated Cotton Linters Interconnected by Bacterial Cellulose for Lithium- and Sodium-Ion Batteries

To protect the structure of MoS₂ from collapse, a strong skeleton is expected to help maintain the integrity. In this study, cotton linters burdened with hollow C@MoS₂ nanocapsules are added into nutrient medium for the growth of a bacterial cellulose membrane. Benefitting from good conductivity and structural integrity, the resultant fibrous membrane anode gives reversible capacities of 559 and 155 mAh g^-1 for Li-ion batteries and Na-ion batteries after 100 cycles, respectively. The structural transformation and component evolution in lithiation-delithiation and sodiation-desodiation was elucidated by in situ Raman spectroscopy. After sodiation, the Na₂ S did not transform back into MoS₂ but was more likely converted into elemental sulfur during the conversion reaction. Layered semiconducting transition metal chalcogenides, such as molybdenum disulfide (MoS₂ ), feature open 2 D ion-transport channels amenable to receive various guest ions with high theoretical capacities.^[2] One serious challenge curtailing the applicability of such materials is their volume changes during discharge-charge processes.^{[3, 4]} However, particular morphologies of MoS₂ are proposed to improve the specific capacity.^[5,6,7] Many works have focused on core-shell and hollow MoS₂ micro- and nanostructures, and the results validate the advantages of shortening the lithium-ion diffusion distance and enhancing specific capacity.^[8,9] Unfortunately, the issue of inferior capacity stability is not resolved, because the structure is not effectively protected and is prone to collapse.

Rechargeable Zinc-Air Battery with Ultrahigh Power Density Based on Uniform N, Co Codoped Carbon Nanospheres

Highly efficient catalysts for both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are key to the commercialization of rechargeable zinc-air batteries (ZABs). In this work, a catalyst with uniform nanospherical morphology was prepared from cobalt nitrate, acetylacetone, and hydrazine hydrate. The final catalyst possesses high ORR and OER performances, with a half-wave potential of 0.911 V [vs reversible hydrogen electrode (RHE)] for ORR and a low potential of 1.57 V (vs RHE) at 10 mA cm^-2 for OER in 0.1 M KOH solution. Specially, a ZAB based on the catalyst demonstrates an ultrahigh power density of 479.1 mW cm^-2, as well as excellent stability, and potential in practical applications.

Anatase TiO2 as a Na+-Storage Anode Active Material for Dual-Ion Batteries

Anatase TiO₂ used as the sodium-storage anode is coupled with a graphite cathode to construct dual-ion batteries. The batteries display wide voltage window (1.0-4.7 V), long cycling stability (98 mAh g^-1 after 1400 cycles at 500 mA g^-1), and considerable rate performance (102 mAh g^-1 at 1500 mA g^-1). Furthermore, the kinetic behaviors of Na⁺ and PF₆^- ions are investigated through electrochemical impedance spectroscopy, the galvanostatic intermittent titration technique, and the potentiostatic intermittent titration technique. The corresponding apparent ion diffusion coefficient is calculated, and the results indicate that the transport of PF₆^- anions in the graphite cathode is swift.