Sodium superionic conductors (NASICONs) show significant promise for application in the development of cathodes for sodium-ion batteries (SIBs). However, it remains a major challenge to develop the desired multi-electron reaction cathode with a high specific capacity and energy density. Herein, we report a novel NASICON-type Na_3.5MnCr_0.5Ti_0.5(PO₄)₃ cathode obtained by combining electrospinning and stepwise sintering processes. This cathode exhibits a high discharge capacity of 160.4 mAh g⁻¹ and operates at a considerable medium voltage of 3.2 V. The Na_3.5MnCr_0.5Ti_0.5(PO₄)₃ cathode undergoes a multi-electron redox reaction involving the Cr^3+/4+ (4.40/4.31 V vs. Na/Na⁺), Mn^3+/4+ (4.18/4.03 V), Mn^2+/3+ (3.74/3.41 V), and Ti^3+/4+ (2.04/2.14 V) redox couples. This redox reaction enables a three-electron transfer during the Na⁺ intercalation/de-intercalation processes. As a result, the Na_3.5MnCr_0.5Ti_0.5(PO₄)₃ demonstrates a significant enhancement in energy density, surpassing other recently reported SIB cathodes. The highly reversible structure evolution and small volume changes during cycling were demonstrated with in-situ X-ray diffraction, ensuring outstanding cyclability with 77% capacity retention after 500 cycles. Furthermore, a NMCTP@C//Sb@C full battery was fabricated, which delivered a high energy density of 421 Wh kg⁻¹ and exhibited good cyclability with 75.7% capacity retention after 100 cycles. The rational design of composition regulation with multi-metal ion substitution holds the potential to unlock new possibilities in achieving high-performance SIBs.

Graphical Abstract

A novel NASICON-structured Na_3.5MnCr_0.5Ti_0.5(PO₄)₃ nanofiber was successfully designed and prepared. This nanofiber was employed to research the multi-electron reaction and the resulting structural evolution in SIBs. The optimal Na-migration pathway has also been investigated by DFT computations. A full SIB battery was fabricated and delivered a high energy density (421 Wh kg⁻¹) and cyclability (75.7% after 100 cycles at 100 mA g⁻¹).

中文翻译：

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用于高性能钠离子电池的新型NASICON型多电子反应Na3.5MnCr0.5Ti0.5(PO4)3纳米纤维

钠超离子导体（NASICON）在钠离子电池（SIB）阴极开发中显示出巨大的应用前景。然而，开发具有高比容量和能量密度的多电子反应阴极仍然是一个重大挑战。在此，我们报道了一种通过静电纺丝和逐步烧结工艺相结合获得的新型NASICON型Na _3.5 MnCr _0.5 Ti _0.5 (PO ₄ ) _{3阴极。该正极表现出160.4 mAh g} ^-1的高放电容量，并在3.2 V的相当大的中压下工作。Na _3.5 MnCr _0.5 Ti _0.5 (PO ₄ ) ₃正极经历涉及Cr ^{3+/的多电子氧化还原反应。 4+} (4.40/4.31 V vs. Na/Na ⁺ )、Mn ^3+/4+ (4.18/4.03 V)、Mn ^2+/3+ (3.74/3.41 V) 和 Ti ^3+/4+ (2.04 /2.14 V) 氧化还原对。这种氧化还原反应能够在Na ⁺嵌入/脱嵌过程中实现三电子转移。结果，Na _3.5 MnCr _0.5 Ti _0.5 (PO ₄ ) ₃表现出能量密度的显着提高，超过了最近报道的其他SIB阴极。原位X 射线衍射证明了其高度可逆的结构演变和循环过程中较小的体积变化，确保了出色的循环性能，500 次循环后容量保持率为 77%。此外，制备的NMCTP@C//Sb@C全电池具有421 Wh kg ^-1的高能量密度，并表现出良好的循环性能，100次循环后容量保持率为75.7%。通过多金属离子取代进行成分调节的合理设计有可能为实现高性能SIB带来新的可能性。

图形概要

成功设计并制备了新型NASICON结构的Na _3.5 MnCr _0.5 Ti _0.5 (PO ₄ ) ₃纳米纤维。这种纳米纤维用于研究多电子反应以及由此产生的 SIB 结构演化。最佳钠迁移路径也通过 DFT 计算进行了研究。制造了完整的SIB电池，并具有高能量密度（421 Wh kg ^{-1 ）和可循环性（100 mA g -1}下100次循环后为75.7% ）。