development of anode materials because graphite as the most successful commercial anode for LIBs has a poor Nastorage performance due to the mismatch between the large ion radius of Na + and the relatively narrow interlayer distance (<0.37 nm). [7][8][9] Hard carbon, composed of rich graphitic microcrystallites, pores, and defects, has been considered as a potential anode candidate for commercialization because it can deliver a considerable capacity of ≈300 mAh g -1 with a low discharge voltage and has abundant resources and low cost. [10][11][12][13] However, hard carbon still suffers from challenges of poor rate capability and cyclability. Great efforts have been made to overcome these obstacles. One strategy is to optimize precursors and reaction conditions. Based on this, a series of hard carbons derived from cellulose, [14] sugar, [15] polymers, [16,17] and biomass-based materials [18][19][20] have been reported with long cycle performance but limited storage capacity (<350 mAh g −1 ). Another strategy is to tune intrinsic carbon structures by heteroatom doping, such as boron, nitrogen, phosphorus, and sulfur. [21] Among them, N doping and S doping are the most widely investigated, since they can promote the adsorption of Na + and introduce abundant active sites for sodium storage, leading to an enhanced capacity. But they also bring an issue of relative high discharge voltage related to the high average oxidation voltage of N-related functional groups or reactive S dopant. [22][23][24][25][26] Compared with N and S doping, P doping can exhibit a stronger adsorption ability and display a great superiority of low discharge voltage (<1.0 V). [27][28][29][30][31][32][33] Unfortunately, the doping content of P is relatively low (<10 wt%), resulting in insufficient active sites for limited Na-storage capacity of hard carbon (<400 mAh g −1 ). The low doping levels can be attributed to following aspects: 1) The high binding energy and long bond length of PC (compared with CC) lead to severe lattice distortion when P is incorporated into the carbon skeleton, thus requiring a higher reaction energy. 2) The doped phosphorus is mostly in the form of PO x rather than elemental phosphorus. The electron-donating properties of P make it oxygen-sensitive and easy to oxidize to PO x groups, which can only be suspended outside the carbon plane, further hindering more P doping. 3) Most of the synthesis systems reported currently are unable to construct an oxygen-free Phosphorus doped carbons are of particular interest as anode materials because of their large interlayer spacing and strong adsorption of Na + ions. However, it remains challenging to achieve high phosphorus doping due to the limited choices of phosphorus sources and the difficulty in constructing oxygen-free synthesis system. Herein, a new synthesis strategy is proposed to prepare ultrahigh phosphorus-doped carbon (UPC) anodes for high performance sodium ion batteries (SIBs). By using two commonly available, miscible, evaporable liquids in PCl 3 and C 6 H 12 , ...

A covalent sulfur−carbon (covalent-SC) composite is successfully prepared in situ by a wet-chemical solvothermal method based on the strong interaction between carbon disulfide (CS 2 ) and red phosphorus. It is demonstrated that sulfur uniformly distributes among the boundary and interior of the carbon skeleton with the formation of S−C bonds. Moreover, the interior sulfur can be electrochemically activated under 0.5 V and then functions as a capacity sponsor, because Na + can freely transfer into the carbon interlayer (with a stable enlarged distance of ∼0.4 nm after the first cycle) via adsorption-like behavior to be combined with the interior sulfur in the following cycles. Thus, the activated covalent-SC composite delivers ultrahigh reversible capacities of 888.9 and 811.4 mAh g −1 after 600 and 950 deep cycles at 0.8C and 1.6C, respectively. Furthermore, it exhibits outstanding rate performance with the capacity of 700 mAh g −1 at a high rate of 8.1C.

Prussian blue analogues (PBAs) are considered one of the promising cathodes for sodium-ion batteries because of their low cost and tunable structure. As an intrinsic characteristic, the influence of structured water in PBAs on the electrochemical properties is still controversial. Herein, low-vacancy iron hexacyanoferrate with different interstitial water contents is synthesized through the citric acid-assisted single iron source method. Ex situ Fourier transform infrared and X-ray diffraction characterization reveals that the interstitial water can stably exist in the Prussian blue framework during repeated cycling. The longstanding interstitial water can reduce the volume change during the Na + insertion/extraction process, resulting in improved cycling stability. Thanks to the low Fe(CN) 6 4− vacancies and pillar role of interstitial water in the crystal framework, the HW-PB exhibits a high reversible capacity of 117 mAh g −1 and excellent long cycle performance with a capacity retention of 91% after 1380 cycles. This work broadens the understanding of the relationship between the interstitial water in PBAs and Na-storage performances, providing guidance for the precise synthesis of high-quality PBAs.

Lithium metal anodes have long been considered as "holy grail" in the field of energy storage batteries, but dendrite growth and large volume changes hinder their practical applications. Herein, a facile and eco-friendly CF 4 plasma treatment is employed for the surface modification of Li anodes, and an artificial layer consisting of LiF and Li 2 C 2 is fabricated for the first time. Experimental results and theoretical calculations reveal that the high adsorption energy of LiF and low Li + diffusion barriers in Li 2 C 2 induce uniform nucleation and planar growth of Li, guaranteeing a stable and dendrite-free Li structure during the repeated plating/stripping process of cycling. Symmetric cells using CF 4 plasma-treated Li operate stably for more than 6500 h (at 2 mA cm −2 and 1 mAh cm −2 ) or 950 h (at 1 mA cm −2 and 10 mAh cm −2 ). When paired with a LiFePO 4 cathode, full batteries deliver a high reversible capacity of 136 mAh g −1 (at 1 C) with considerable cycling stability (97.2% capacity retention over 200 cycles) and rate performance (116 mAh g −1 up to 5 C). This powerful application of plasma technology toward novel LiF-Li 2 C 2 artificial layers provide new routes for constructing environment-friendly and high-performance energy storage devices.

Enhanced phosphorus (7.2 wt%) and sulfur (15.7 wt%) co-doped carbon (PSC) is synthesized via a one-step sintering of carbon disulfide and red phosphorus in a vacuum.