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The Na3V2(PO4)2F3 (NVPF) cathode material is usually nano‐sized particles exhibiting low tap density, high specific surface area, correspondingly low volume energy density, and cycle stability of the sodium‐ion batteries (SIBs). Herein, a high‐temperature shock (HTS) strategy is proposed to synthesize NVPF (HTS‐NVPF) with uniform conducting network and high tap density. During a typical HTS process (heating rate of 1100 °C s−1 for 10 s), the precursors rapidly crystallize and form large‐sized and dense particles. The tight connection between particles not only enhances their contact with carbon layers, but also reduces the specific surface area that inhibits side reactions between the interfaces and the electrolyte. Besides, ultrafast synthesis of NVPF reduces the F loss and amount of Na3V2(PO4)3 impurities, which improve cycling capability. The HTS‐NVPF demonstrates a high energy density of 413.4 Wh kg−1 and an ultra‐high specific capacity of 103.4 mAh g−1 at 10 C as well as 84.2% capacity retention after 1000 cycles. In addition, the excellent temperature adaptability of HTS‐NVPF (−45–55 °C) and remarkable electrochemical properties of NVPF||HC full cell demonstrate extreme competitiveness in commercial SIBs. Therefore, the HTS technique is considered to be a high‐efficiency strategy to synthetize NVPF and is expected to prepare other cathode materials. [ABSTRACT FROM AUTHOR]

Defect engineering is demonstrated to be an important factor in enhancing the electrochemical performance of lithium‐ion batteries by improving structural stability and ion diffusion. However, conventional synthetic methods have long and complicated processes, making it challenging to effectively and easily introduce defects into electrode materials. In this work, a high‐temperature shock technique (HTS) with an ultrafast heating and cooling process that can quickly introduce twin boundaries (TBs) into phase‐pure spinel LiMn2O4 in seconds is reported. Various ex situ techniques reveal the crystallization mechanism of LiMn2O4 during ultrafast synthesis. LiMn2O4 with TBs exhibits a higher rate performance than that obtained from the traditional method. Additionally, alien elements can be evenly incorporated into LiMn2O4 in seconds, resulting in excellent cycling performance. For instance, 2% Ni‐doped LiMn2O4 shows an initial capacity of 121 mAh g−1 and retention of 86.5% after 500 cycles at 1 C. [ABSTRACT FROM AUTHOR]