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 PC (compared with CC) 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 , ...