Aqueous sodium‐ion batteries (SIBs) show promising applications in fields of sustainable energies such as wind and solar, owing to wide availability of sodium resources and incombustibility of aqueous electrolytes. However, they are still challenged by poor cycling performance of Na‐storage electrode materials. Herein, carbon‐coated Na_2.2V_1.2Ti_0.8(PO₄)₃ is reported as a novel cathode for high‐performance aqueous SIBs, which is obtained by studying the effect of Ti substitution on the charge/discharge properties of a Na_3‐xV_2‐xTi_x(PO₄)₃ (0≤x≤1) system in 6 M NaClO₄ aqueous electrolyte. Experimental results indicate that the material is composed of approximately 200 nm Na_2.2V_1.2Ti_0.8(PO₄)₃ crystals uniformly coated with a thin layer of carbon (ca. 4 nm). During Na extraction/insertion, it undergoes a one‐step, two‐phase reaction mechanism through the reversible electrochemistry of the V⁴⁺/V³⁺ redox couple, showing a reversible capacity of around 62 mAh g⁻¹ at the current rate of 1 C and a well‐defined potential plateau of 0.50 V (vs. Ag/AgCl). More importantly, it achieves outstanding high‐rate capability with a discharge capacity of approximately 40 mAh g⁻¹ at the current rate of 10 C, and excellent cycling performance with capacity retention of 93.4 % after 500 cycles. The good electrochemical performance is attributed to the unique Ti‐substituted composition, thin‐layered carbon coating and high‐concentration electrolytes.

中文翻译：

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具有出色循环性能的碳包覆Na2.2V1.2Ti0.8（PO4）3阴极，适用于钠离子电池

钠离子电池（SIB）由于钠资源的广泛可用性和水性电解质的不可燃性，在风能和太阳能等可持续能源领域中显示出广阔的应用前景。但是，它们仍然受到Na储存电极材料循环性能差的挑战。在此，碳涂层的Na _2.2 V _1.2 Ti _0.8（PO ₄）₃被报道为高性能水性SIB的新型阴极，这是通过研究Ti取代对Na _3-的充/放电性能的影响而获得的。_x V _{2‐ x} Ti _x（PO ₄）₃（0≤x≤1）体系中的6 M NaClO ₄水溶液。实验结果表明，该材料由大约200 nm的Na _2.2 V _1.2 Ti _0.8（PO ₄）₃晶体均匀覆盖着一层碳薄层（大约4 nm）组成。在Na提取/插入过程中，它通过V ⁴⁺ / V ³⁺氧化还原对的可逆电化学过程经历了一步，两阶段反应机制，显示出约62 mAh g ^-1的可逆容量。以1 C的电流速率和0.50 V（vs. Ag / AgCl）的明确定义的电位平稳段。更重要的是，在10 C的电流速率下，它的放电容量约为40 mAh g ^-1，可实现出色的高倍率性能；在500次循环后，其出色的循环性能和93.4％的容量保持率。良好的电化学性能归因于独特的Ti取代成分，薄层碳涂层和高浓度电解质。