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Smart wearable electronic devices are becoming more prevalent in our daily life, exceedingly arousing the increasing demand for flexible energy storage devices. Herein, a sodium superionic conductor (NASICON)-structured Na3V2(PO4)2F3 (NVPF) self-standing cathode is fabricated via an electrospinning technique. NVPF particles at the nanoscale are encapsulated in or attached to the surface of carbon nanofibers to form an NVPF self-standing cathode, which exhibits a high-voltage platform of ∼4.07 V with a reversible capacity of 101.8 mAh g–1 at 0.2C and 98.3% capacity retention after 400 cycles. Moreover, the soft package full battery, assembled with an NVPF self-standing cathode and a Na3V2(PO4)3 (NVP) anode, can light up a light-emitting diode in the folded/unfolded states. The superior sodium storage performance was enabled by the stable structure of the NVPF self-standing cathode. Moreover, the nitrogen-doped carbon nanofiber network of the NVPF self-standing cathode not only ensures the flexibility but also facilitates electron and Na+ transportation. This work provides an NVPF self-standing cathode with excellent mechanical and electrochemical performance for high-voltage flexible sodium-ion batteries, which is beneficial for promoting the practical application of high-voltage flexible sodium-ion batteries. [ABSTRACT FROM AUTHOR]

Mn-based layered oxides, as potential cathodes for potassium-ion batteries (PIBs), face major challenges such as consecutive phase transition, serious capacity loss, and sluggish K+ transport kinetics. Herein, Co–Mg co-substituted K0.45Co1/12Mg1/12Mn5/6O2 is designed as a promising cathode material for PIBs to conquer the above issues in this work. Co3+–Mg2+ ions occupying the Mn3+ sites are confirmed to effectively alleviate the Jahn–Teller distortion induced by Mn3+ ions. P3-K0.45Co1/12Mg1/12Mn5/6O2 exhibits highly reversible single-phase structural evolution during the K+ deintercalation/intercalation. In contrast, the pristine K0.45MnO2 electrode experiences incompletely reversible structural variation from a P′3 to P3 phase. The increase of structural stability in the Co–Mg co-substituted sample is the main reason leading to improved cycling stability. Moreover, K0.45Co1/12Mg1/12Mn5/6O2 delivers better rate capability resulting from faster K+ diffusion compared to K0.45MnO2. Therefore, Co–Mg co-substitution is an effective strategy to enhance the structural stability and electrochemical properties of Mn-based layered oxides in PIBs. [ABSTRACT FROM AUTHOR]

O3-type NaCrO 2 is attracting increasing attention as potential cathode material for sodium-ion batteries (SIBs). Bare NaCrO 2 is usually synthesized by a solid-state reaction and suffers from serious capacity decay and poor power capability. Modification by coating is an effective method to improve the electrochemical properties, but it inevitably reduces the energy density. To avoid the decrease of energy density and optimize the electrochemical performance, a specific route, i.e., a freeze-drying-assisted sol-gel method, has been adopted to synthesize bare NaCrO 2 in this work. Three-phase coexistence during charging is confirmed for the first time, which contributes to delaying the disappearance of the O3 phase and then improving the structural reversibility, resulting in superior cycle stability (∼50% capacity retention after 3000 cycles at 5C). Meanwhile, as-synthesized NaCrO 2 delivers an outstanding rate capability (82.1 mAh g -1 at 50C), which is attributed to the fast Na + diffusivity and high electronic conductivity proved by density functional theory (DFT) calculations. It is worth mentioning that NaCrO 2 also exhibits excellent electrochemical properties when used as a cathode for potassium-ion batteries (PIBs). This work provides new perspectives on the structural evolution of NaCrO 2 , and the results are expected to contribute to the development of SIBs and PIBs.