The Na₃V₂(PO₄)₃ (NVP) cathode is deemed to be a promising candidate for sodium ion batteries due to its strong structural stability and high theoretical capacity. Nevertheless, its poor intrinsic conductivity restricts further development. To overcome these shortcomings, a dual modification strategy of Mn²⁺/Ti⁴⁺ co-substitution is proposed for the first time. Significantly, Mn doping can efficiently accelerate the transmission speed of electrons by introducing beneficial holes derived from the low valence state of +2, presenting the classical p-type doping modification. Moreover, the presence of Mn²⁺ with a larger ionic radius can support the crystal to stabilize the Na superionic conductor (NASICON) framework of the NVP system. Ti⁴⁺ is introduced for perfect charge compensation. Accordingly, the addition of Ti⁴⁺ can generate excess electrons due to the n-type substitution, which contributes to the favorable electronic conductivity. In addition, conductive carbon nanotubes (CNTs) are utilized to construct an efficient network to improve the rate capability of the NVP composite. Meanwhile, CNTs can inhibit particle growth and thus reduce particle size, shortening the transport path of Na⁺ and promoting the diffusion of Na⁺. Comprehensively, the optimized Na₃V_2−xMn_xTi_x(PO₄)₃/C@CNTs (x = 0.15) deliver high capacities of 70.3 and 68.2 mA h g⁻¹ at 90C and 180C, maintaining 58 and 53.8 mA h g⁻¹ after 1000 cycles with high capacity retention of 82.5% and 78.9%.

中文翻译：

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通过 p-n 型共取代在 Na3V2(PO4)3/C 正极中同时调控高性能钠离子电池的缺陷

Na ₃ V ₂ (PO ₄ ) ₃ (NVP)正极因其结构稳定性强和理论容量高而被认为是钠离子电池的有希望的候选材料。然而，其较差的本征导电性限制了进一步的发展。为了克服这些缺点，首次提出了Mn ²⁺ /Ti ⁴⁺共取代的双重改性策略。值得注意的是，Mn掺杂可以通过引入源自+2低价态的有益空穴来有效地加速电子的传输速度，呈现出经典的p型掺杂改性。此外，Mn ^2+的存在具有较大离子半径的晶体可以支撑晶体稳定NVP系统的Na超离子导体（NASICON）框架。引入Ti ⁴⁺以实现完美的电荷补偿。因此，添加Ti ⁴⁺可以由于n型取代而产生多余的电子，这有助于有利的电子导电性。此外，导电碳纳米管（CNTs）被用来构建一个有效的网络，以提高NVP复合材料的倍率性能。同时，碳纳米管可以抑制颗粒生长，从而减小颗粒尺寸，缩短Na + 的传输路径，促进Na ⁺的^扩散。综合来看，优化后的 Na ₃ V _{2− x} Mn_x Ti _x (PO ₄ ) ₃ /C@CNTs (x= 0.15) 在 90C 和 180C 下提供 70.3 和 68.2 mA hg ^-1的高容量，在 1000 次循环后保持 58 和 53.8 mA hg ^-1并具有 82.5 的高容量保持率% 和 78.9%。