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the best candidate for prospective application on account of their low cost, easy synthesis, and renewability. Although already commercialized in LIBs, graphite cannot be formed binary intercalation compounds with sodium unless appropriate electrolyte, like diglyme-based [10] or etherbased [11] electrolyte, is employed.Therefore, hard carbon as a typical nongraphitic carbon has become a research hotspot. Normally, the capacities of hard carbon in SIBs originate from two parts: slope capacity above 0.1 V and plateau capacity below 0.1 V. As first proposed by Stevens and Dahn, the sodium storage behaviors of hard carbons were defined as "house of cards" model. [12] Namely, the slope and plateau capacities correspond to Na intercalation between graphene layers and nanopore filling/nanoplating, respectively. However, Cao et al. [13] indicated that the slope capacity is due to adsorption of Na at vacancies and the plateau capacity is attributed to Na + deintercalation behavior between graphite layers, which was further verified by other researchers. [14] In a word, the Na + storage mechanism can be summarized as (1) intercalation between the graphene layers, (2) storage in the defective turbostratic structure, (3) adsorption on the surface, and (4) filling in nanopores. Based on these mechanisms, tremendous efforts, including optimizing calcination temperature, [5,15] expanding interlayer lattice distance, [16] increasing specific surface area, [17] have been used to improve the electrochemical performance of hard carbon. In addition, doping covalent heteroatom (e.g., N, [18] S, [16,19] and F [20] ) is another efficient way to elevate sodium storage capacity by enhancing Na adsorption capability and electronic conductivity. However, these carbon anodes generally have two characteristics, namely the large specific surface area and high voltage plateau, which lead to the formation of excess and undesirable solid electrolyte interface (SEI) and thus limiting the practical utilization.To avoid these issues, we adopt electrospinning technology to fabricate phosphorous-functionalized hard carbon with low specific surface area and low operation potential, aiming at maximizing the desodiation capacity and further improving the energy density. Phosphorous as a nonmetallic chemical element has already been used in SIBs reported by Yang and co-workers [9a] due to its high theoretical specific capacity of 2596 mA h g −1 . Similar to N or S atoms, P can also serve as electron donors doped into carbon to induce a shift of the Fermi level to the conducting band. Nevertheless, it is very difficult Hard carbon as a typical anode material for sodium ion batteries has received much attention in terms of its low cost and renewability. Herein, phosphorusfunctionalized hard carbon with a specific "honeycomb briquette" shaped morphology is synthesized via electrospinning technology. When applied as an anode material for Na + storage, it exhibits an impressively high reversible capacity of 393.4 mA h g −1 with the capacity retention up to 9...

The renewable energy sources with intermittent nature call for fast development of electrical energy storage (EES) devices for practical applications. [1] Over the past decades, lithium-ion batteries (LIBs) have pervaded our daily lives, ranging from portable electronics to large-scale EES systems. [2] However, the cost of rare lithium resources involving electrical grid and large-scale storage purposes have raised widespread concerns. In this regard, sodium-ion batteries (SIBs) are highly promising to meet these demands due to that sodium is practically inexhaustible and easily accessible around the globe. [3] However, the higher standard electrochemical potential of Na + /Na (−2.71 V versus SHE) than that of Li + / Li (−3.04 versus SHE) and the larger ion radius of Na + compared with Li + (1.02 Å versus 0.76 Å) mean that SIBs possess a lower energy density, and most conventional electrode materials of LIBs are not suitable for SIBs. Hence, it is of great significance to explore advanced electrode materials that could provide satisfactory specific capacities and rapid ion diffusion kinetics. So far, the development of the cathode materials for SIBs has progressed rapidly, including layered oxides [4] and polyanionic compounds. [5] As for the anodes, although hard carbon as a hotspot has been widely studied due to its high capacity and lower voltage platform, [6] the random adsorption sites and irregular channels for Na + migration lead to a relatively poor sodium-ion diffusion. 2D transition metal chalcogenides (TMCs) have been broadly reported as a kind of promising electrode materials for both LIBs and SIBs due to their open framework and unique electrochemical properties. [7,8] Among them, WS 2 as a typical 2D TMCs has a much larger interlayer spacing of 0.62 nm and weaker van der Waals interaction, which enables fast reversible Na + diffusion and avoids terrible volume expansion during Na + intercalation/deintercalation processes. [9] However, the terrible issue of pure WS 2 anode applied in SIBs is its low intrinsic electronic conductivity, significantly limiting the specific capacity, and rate performance. [10] Generally, the electrochemical properties of materials are strongly dependent on the conductivity of electrode materials as well as the diffusion rate of Na +. Thus, the scrupulous design and rational controllable synthesis of Engineering novel electrode materials with unique architectures has a significant impact on tuning the structural/electrochemical properties for boosting the performance of secondary battery systems. Herein, starting from well-organized WS 2 nanorods, an ingenious design of a one-step method is proposed to prepare a bimetallic sulfide composite with a coaxial carbon coating layer, simply enabled by ZIF-8 introduction. Rich sulfur vacancies and WS 2 /ZnS heterojunctions can be simultaneously developed, that significantly improve ionic and electronic diffusion kinetics. In addition, a homogeneous carbon protective layer around the surface of the composite guarantees an outstandi...