Unfortunately, the volume changes of such metals and metal oxides during sodiation/desodiation processes are more severe than those during lithiation/delithiation processes, resulting in a large loss of electric contact and eventually rapid capacity decay. [7d,10a] To circumvent above volume change issues of metals and metal oxides during sodiation/desodiation processes, various metal (oxide)-carbon nanocomposites such as Sb/carbon fibers, [7d,11] Sb/ porous carbons, [12] and Sb 2 O 3 /Sb@graphene architectures [13] have been recently designed and fabricated via various chemical approaches and demonstrated improved gravimetric capacities, cycle performances, and high-rate capabilities. Although it has been a great achievement, these metal (oxide)/carbon nanocomposites commonly show very low volumetric capacities (100-350 mAh cm −3 ), [14] largely hampering the development, and practical applications of sodium ion batteries.Different from other metals, metallic Sb with gray allotrope (R3m space group) has rarely been considered from the viewpoint of 2D layered system is actually a graphite-like layered material, in which Sb layers consist of fused, ruffled, six-membered rings; [15] the nearest and next-nearest Sb atoms form an irregular octahedral complex, with three atoms in each double layer slightly closer than the three atoms in the next. Such close packing generates a high density of 6.7 g cm −3 for gray Sb, [15b] and the weak bonding between the layers enable to be a potential candidate for the top-down fabrication of Sb nanosheets. Given that metallic Sb nanosheets can be played like graphene, it would be anticipated to obtain a new anode material with superior electrochemical performances for sodium storage.In this work, we propose an efficient strategy to fabricate free-standing metallic Sb nanosheets via liquid-phase exfoliation of gray Sb powder in an isopropyle alcohol (IPA) solution with a constant concentration of sodium hydroxide. Remarkably, the resultant metallic Sb nanosheets have ultrathin (≈4 nm), foldable features and large aspect ratios. Such unique features render metallic Sb nanosheets behaving like graphene and enable to construct uniform and compacted films with other nanosheets. As a proof of the concept, several hybrid films composed of metallic Sb nanosheets and graphene with tunable densities are achieved, in which the notorious volume change of metallic Sb can be efficiently alleviated with the aid of Metallic antimony (Sb) with gray allotrope has rarely been considered from the viewpoint of two-dimension layered system is actually a graphite-like material, in which Sb layers consist of fused, ruffled, and six-membered rings. Given that metallic Sb nanosheets can be played like graphene, it would be anticipated to obtain a new anode material with superior electrochemical performances for sodium storage. In this work, we propose an efficient strategy to fabricate free-standing metallic Sb nanosheets via liquid-phase exfoliation of gray Sb powder in an ios-propyle alcohol (IPA) so...

Although lithium–sulfur (Li–S) batteries are one of the most promising energy storage devices owing to their high energy densities, the sluggish reaction kinetics and severe shuttle effect of the sulfur cathodes hinder their practical applications. Here, single atom zinc implanted MXene is introduced into a sulfur cathode, which can not only catalyze the conversion reactions of polysulfides by decreasing the energy barriers from Li2S4 to Li2S2/Li2S but also achieve strong interaction with polysulfides due to the high electronegativity of atomic zinc on MXene. Moreover, it is found that the homogenously dispersed zinc atoms can also accelerate the nucleation of Li2S2/Li2S on MXene layers during the redox reactions. As a result, the sulfur cathode with single atom zinc implanted MXene exhibits a high reversible capacity of 1136 mAh g−1. After electrode optimization, a high areal capacity of 5.3 mAh cm−2, high rate capability of 640 mAh g−1 at 6 C, and good cycle stability (80% capacity retention after 200 cycles at 4 C) can be achieved.

Lithium (Li) metal has been considered as one of the most prospective anodes for Li-based batteries owing to its high theoretical gravimetric capacity (3860 mAh g–1) and low potential (−3.04 V vs standard hydrogen electrode (SHE)). Unfortunately, there commonly exist uncontrollable dendrites in lithium anodes during the repeated plating–stripping processes, causing short cycle life and even short circuiting of lithium batteries. Here, single zinc atoms immobilized on MXene (Ti3C2Cl x ) layers (Zn-MXene) were produced to efficiently induce Li nucleation and growth. At the initial plating stage, lithium tended to nucleate homogeneously on the surface of Zn-MXene layers due to the large presence of Zn atoms and then grow vertically along the nucleated sites owing to a strong lightning rod effect at the edges, affording bowl-like lithium without lithium dendrites. Thus, a low overpotential of 11.3 ± 0.1 mV, long cyclic life (1200 h), and deep stripping–plating levels up to 40 mAh cm–2 are obtained by using Zn-MXene films as lithium anodes.

Single atom catalysts possess attractive electrocatalytic activities for various chemical reactions owing to their favorable geometric and electronic structures compared to the bulk counterparts. Herein, we demonstrate an efficient approach to producing single atom copper immobilized MXene for electrocatalytic CO 2 reduction to methanol via selective etching of hybrid A layers (Al and Cu) in quaternary MAX phases (Ti 3 (Al 1−x Cu x )C 2 ) due to the different saturated vapor pressures of Al-and Cu-containing products. After selective etching of Al in the hybrid A layers, Cu atoms are wellpreserved and simultaneously immobilized onto the resultant MXene with dominant surface functional group (Cl x ) on the outmost Ti layers (denoted as Ti 3 C 2 Cl x ) via Cu−O bonds. Consequently, the as-prepared single atom Cu catalyst exhibits a high Faradaic efficiency value of 59.1% to produce CH 3 OH and shows good electrocatalytic stability. On the basis of synchrotron-based X-ray absorption spectroscopy analysis and density functional theory calculations, the single atom Cu with unsaturated electronic structure (Cu δ+ , 0 < δ < 2) delivers a low energy barrier for the rate-determining step (conversion of HCOOH* to absorbed CHO* intermediate), which is responsible for the efficient electrocatalytic CO 2 reduction to CH 3 OH.

High‐entropy materials (HEMs) have great potential for energy storage and conversion due to their diverse compositions, and unexpected physical and chemical features. However, high‐entropy atomic layers with fully exposed active sites are difficult to synthesize since their phases are easily segregated. Here, it is demonstrated that high‐entropy atomic layers of transition‐metal carbide (HE‐MXene) can be produced via the selective etching of novel high‐entropy MAX (also termed Mn+1AXn (n = 1, 2, 3), where M represents an early transition‐metal element, A is an element mainly from groups 13–16, and X stands for C and/or N) phase (HE‐MAX) (Ti1/5V1/5Zr1/5Nb1/5Ta1/5)2AlC, in which the five transition‐metal species are homogeneously dispersed into one MX slab due to their solid‐solution feature, giving rise to a stable transition‐metal carbide in the atomic layers owing to the high molar configurational entropy and correspondingly low Gibbs free energy. Additionally, the resultant high‐entropy MXene with distinct lattice distortions leads to high mechanical strain into the atomic layers. Moreover, the mechanical strain can efficiently guide the nucleation and uniform growth of dendrite‐free lithium on HE‐MXene, achieving a long cycling stability of up to 1200 h and good deep stripping–plating levels of up to 20 mAh cm−2.

Pyridinic nitrogen‐enriched carbon nanogears (PNCG) are achieved via controllable synthesis of a well‐defined polyimide and subsequent pyrolysis at tunable temperatures. The resultant PNCG possesses unique structural and compositional characteristics, which significantly promote the fast transports of both lithium and electron. Consequently, the optimal pyridinic nitrogen‐enriched carbon nanogears exhibit a very high reversible capacity and long cycle life for lithium storage.

the formation of Zn dendrites, but also suppress the side reactions by shielding the Zn anode from contact with the electrolyte. In this regard, various functional materials have been reported as artificial interfaces on Zn anodes and efficiently improve the cycle performances. [24][25][26] For example, the introduction of highly latticematched materials on Zn anode enables to reduce the energy barrier of zinc crystal growing in (002) direction and induce horizontal growth of Zn. [27][28][29] By designing ion-selective or nanoporous artificial interface, the migration pathway of Zn 2+ can be well controlled. [30][31][32] However, during the charging-discharging processes, especially at high current densities, there are a large ionic concentration gradient around Zn anodes, facilely causing the formation of dendrites.Herein, a charge-enriched strategy through spraying MXenebased polypyrrole (MXene-mPPy) layers with high charge capabilities on zinc foil is developed for dendrite-free Zn metal anode (denoted as MXene-mPPy/Zn). The MXene-mPPy layers are not only favorable for accumulating the charge concentration, but also facilitating to homogenize the dispersions of electric field and ion flux as used as an artificial interface on Zn anode. Thus, the MXene-mPPy/Zn symmetric battery delivers an extremely long cycle life over 2500 h and superior rate capability with a dendrite-free morphology. When the MXene-mPPy/Zn is further applied as an anode for aqueous zinc ion battery, a stable cycling performance up to 3000 cycles at 10 A g −1 is achieved.

Metallic aluminum (Al) have been explored as potential anode materials for lithium storage because of its high theoretical capacity (993 mAh g–1) and low voltage plateaus. Al possesses high electric conductivity, low cost and environmental friendliness. Unfortunately, Al suffers from huge volume change (>100%) during the lithiation/delithiation process, which inevitably results in the pulverization of electrode and rapid capacity decay during cycling processes. To circumvent above issues, a simple but efficient strategy is demonstrated to fabricate free‐standing multi‐atomic layers of metallic Al by harnessing the good ductility of Al under pressure. The resultant multi‐atomic Al layers are ultrathin, ≈3 nm, and have a large aspect ratio. Such unique features enable multi‐atomic Al nanosheets to construct uniform and compact films with graphene. Thus, the hybrid films with different ratios are achieved, in which the notorious volume change of metallic Al can be efficiently circumvented via the good flexibility of graphene, and the density of whole electrode can be significantly enhanced. As a consequence, the optimized multi‐atomic Al layers‐graphene (AlL‐G) film exhibits a very high volumetric capacity of 1089 mAh cm–3, high‐rate capability and ultralong cycle life up to 20 000 cycles for lithium storage.