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Stabilizing zinc anode is a systematic project for aqueous zinc ion batteries (ZIBs), which needs to solve many problems such as dendrite growth, corrosion, hydrogen evolution, and other side reactions. It is urgent to develop a protective layer for zinc anode to solve these problems at one time. Based on the results of calculation, a hydrophobic multifunctional fluorinated carbon dots (F-CDs) protective layer with three kinds of zincophilic groups (-CO, -CHO and -F) was constructed on the Zn anode surface. As expected, these zincophilic groups on the F-CDs layer functioned as zincophilic sites to achieve uniform Zn deposition. Especially, the -F group could in-situ promote the formation of ZnF2under the F-CDs layer and the ZnF2layer is usually considered as a solid Zn2+conductor layer to further even Zn deposition. Additionally, the experimental results also demonstrated that the F-CDs layer coupled with in-situ generated ZnF2interlayer can not only tackle above issues in an integrated way, but also induce the deposition of Zn on the preferred (002) plane. Therefore, the Zn@F-CDs anode exhibits an ultra-long cycling life over 3500 h at 1 mA cm–2, together with an excellent average coulombic efficiency (99.32% for over 1100 h) in half cells.

Sodium-ion batteries (SIBs) are regarded as a promising candidate for large-scale energy storage applications, however, its sluggish sodiation kinetics limit high power capabilities. First-principles density functional theory (DFT) calculations demonstrates that the replacement of large anions, within a Co3X4(X = O, S, Se) complex, can facilitate electron transfer through the reduction of the energy band gap (Eg) and the regulation of structural, electronic and bonding properties of Co-X, suggesting that the substituted Co3X4in the following order O < S < Se can provide enhanced Na-storage capability. Accordingly, Co3X4have been successfully designed, in which the selection of anions induces the evolution of microstructure, creating an enhancement of specific surface area with the effective introduction of defects. Note that the similar phys/chemical properties of anions within the Co3X4possess analogous conversion mechanisms, further confirmed by in-situ XRD. Quantitative kinetics analysis reveals that the levels of the surface-dominated redox behaviors are greatly promoted by the decreased binding energy of Na2X (Na2O > Na2S > Na2Se) with the increased active sites, which are paramount for electrochemical properties. The work in this article sheds light on the in-depth understanding of the improved sodium-storage behavior with the advancing VI group anions and provides an effective strategy for the design of high-rate electrode materials for SIBs.

Designing highly active electrocatalysts that are inexpensive, highly efficient, and durable for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) in rechargeable zinc–air batteries (ZABs) is vital. A peapod-like CoSe2@NC bifunctional electrocatalyst is successfully fabricated herein by confining CoSe2nanoparticles (NPs) to one-dimensional (1D) N-doped carbon (NC) nanorods based on a polyaniline encapsulation strategy. The electronic coupling role between NC and CoSe2is revealed via X-ray photoelectron spectroscopy and synchrotron radiation X-ray absorption spectroscopy. In situ Raman spectroscopy is conducted to examine the structure of CoSe2@NC under the OER in an alkaline electrolyte. The peapod-like CoSe2@NC nanorods exhibit superior activity towards the ORR (E1/2= 0.83 V) and OER (η = 340 mV @10 mA cm−2) in a 0.1 mol L−1KOH solution. The as-assembled rechargeable ZAB achieves a large peak power density of 137.1 mW cm−2and outstanding stability for 500 cycles at 10 mA cm−2. The encapsulation of CoSe2NPs in the NC shells impedes their aggregation and corrosion during the ORR and OER processes. Experimental and DFT-based computational analyses assist in ascribing the outstanding bifunctional catalytic performance to the formation of N-CoSe2active sites. These results provide a facile pathway for the development of efficient bifunctional electrocatalysts for high-performance rechargeable metal–air batteries.

The practical application of aqueous Zn-ion batteries has been largely plagued by the poor reversibility of Zn anode, mainly associated with the dendritic growth and interfacial parasitic reaction. Hereby, electrochemically stable Zn anode is successfully designed by manipulating nucleation process through the introduction of hydrophilic graphene quantum dots (GQDs). Notably, the enhanced binding effect of GQDs with Zn2+is aroused from the lower electronegativity of GQDs, which is conducive to accelerating uniform Zn deposition, resulting in the robust Zn anode without dendrites. Concomitantly, interfacial hydrogen bonds are excited by the GQDs with oxygen-containing groups, which is beneficial for mitigating water-induced side reaction and improving Zn ion reaction kinetics. Greatly, polarization voltage of symmetric cells is decreased from 80 to 50mV at 0.8mAcm-2, presenting a prolonged lifespan of 2200h. As a result, the assembled ZIBs with vanadium cathode exhibit superior performance with capacity of 164.3 mAh g-1after 600 cycles at 1Ag-1. Given this, this elaborate work might inaugurate a potential avenue for rationally tuning the electrode/electrolyte interface evolution towards advanced aqueous batteries.

Molybdenum (Mo)-based transition metal oxides normally delivery superior energy density in lithium ion batteries through electrochemical conversion reactions. The main challenge for this kind of electrode material is to promote reversible transformation of Li2O and alleviate the volume expansion during lithiation/delithiation processes. Here, electrochemical reaction mechanism of CoMoO4investigated by in-situ X-ray diffraction and ex-situ Transmission electron microscopy reveals the irreversible transformation from CoMoO4to CoO and MoO3in the first cycle. During subsequent charge/discharge process, high valence state cobalt ions originated from Co2+provide additional capacity and promote the electrochemical reversible reaction between MoO3and Li2O, thus facilitating the release of irreversible capacity. Benefited by the contributor of high valence state cobalt ion, when CoMoO4was utilized as Li-storage anode, high reversible capacity (1585.5 mAh g−1at 200 mA h−1after 150 cycles) and excellent cyclic stability (~100% retention after 400 cycles at 1000 mA g−1) are delivered. Such an optimized anode material expands the potential to develop lithium-ion batteries with significantly higher energy density.