KVPO₄F with excellent structural stability and high operating voltage has been identified as a promising cathode for potassium-ion batteries (PIBs), but limits in sluggish ion transport and severe volume change cause insufficient potassium storage capability. Here, a high-energy and low-strain KVPO₄F composite cathode assisted by multifunctional K₂C₄O₄ electrode stabilizer is exquisitely designed. Systematical electrochemical investigations demonstrate that this composite cathode can deliver a remarkable energy density up to 530 Wh kg⁻¹ with 142.7 mAh g⁻¹ of reversible capacity at 25 mA g⁻¹, outstanding rate capability of 70.6 mAh g⁻¹ at 1000 mA g⁻¹, and decent cycling stability. Furthermore, slight volume change (~5%) and increased interfacial stability with thin and even cathode–electrolyte interphase can be observed through in situ and ex situ characterizations, which are attributed to the synergistic effect from in situ potassium compensation and carbon deposition through self-sacrificing K₂C₄O₄ additive. Moreover, potassium-ion full cells manifest significant improvement in energy density and cycling stability. This work demonstrates a positive impact of K₂C₄O₄ additive on the comprehensive electrochemical enhancement, especially the activation of high-voltage plateau capacity and provides an efficient strategy to enlighten the design of other high-voltage cathodes for advanced high-energy batteries.

In the field of materials science and engineering, controlling over shape and crystal orientation remains a tremendous challenge. Herein, we realize a nano self-assembly morphology adjustment of Na₃V₂(PO₄)₂F₃ (NVPF) material, based on surface energy evolution by partially replacing V³⁺ with aliovalent Mn²⁺. Crystal growth direction and surface energy evolution, main factors in inducing the nano self-assembly of NVPF with different shapes and sizes, are revealed by high-resolution transmission electron microscope combined with density functional theory. Furthermore, NVPF with a two-dimensional nanosheet structure (NVPF-NS) exhibits the best rate capability with 68 mAh·g⁻¹ of specific capacity at an ultrahigh rate of 20 C and cycle stability with 80.7% of capacity retention over 1,000 cycles at 1 C. More significantly, when matched with Se@reduced graphene oxide (rGO) anode, NVPF-NS//Se@rGO sodium-ion full cells display a remarkable long-term stability with a high capacity retention of 93.8% after 500 cycles at 0.5 C and −25 °C. Consequently, experimental and theoretical calculation results manifest that NVPF-NS demonstrates such superior performances, which can be mainly due to its inherent crystal structure and preferential orientation growth of {001} facets. This work will promise insights into developing novel architectural design strategies for high-performance cathode materials in advanced sodium-ion batteries.

Flexible power sources featuring high-performance, prominent flexibility and raised safety have received mounting attention in the area of wearable electronic devices. However, many great challenges remain to be overcome, notably the design and fabrication of flexible electrodes with excellent electrochemical performance and matching them with safe and reliable electrolytes. Herein, a facile approach for preparing flexible electrodes, which employs carbon cloth derived from commercial cotton cloth as the substrate of cathode and a flexible anode, is proposed and investigated. The promising cathode (NVPOF@FCC) with high conductivity and outstanding flexibility is prepared by efficiently coating Na₃V₂(PO₄)₂O₂F (NVPOF) on flexible carbon cloth (FCC), which exhibits remarkable electrochemical performance and the significantly improved reaction kinetics. More importantly, a novel flexible quasi-solid-state sodium-ion full battery (QSFB) is feasibly assembled by sandwiching a P(VDF-HFP)-NaClO₄ gel-polymer electrolyte film between the advanced NVPOF@FCC cathode and FCC anode. And the QSFBs are further evaluated in flexible pouch cells, which not only demonstrates excellent energy-storage performance in aspect of great cycling stability and high-rate capability, but also impressive flexibility and safety. This work offers a feasible and effective strategy for the design of flexible electrodes, paving the way for the progression of practical and sustainable flexible batteries.