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Na3V2(PO4)2O2xF3-2x (0≤x≤1) (NVPOF) is a promising cathode material for sodium-ion batteries, but conventional synthesis methods often require prolonged processing to obtain phase-pure material. Here, we report a 10-min microwave-assisted solution method that directly produces phase-pure, microscale NVPOF particles with well-defined tetragonal/cuboid morphologies using either NH4VO3 or V2O5 as the vanadium precursor. By systematically varying precursor chemistry, reaction temperature, and precursor concentration, we show that particle size (0.2–5 µm), crystallinity, morphology, and product yield can be tuned. The limited solubility of the V2O5 precursor leads to delayed and heterogeneous vanadium release, resulting in a bimodal particle-size distribution and possibly subtle differences in local vanadium redox environments, reflected in slightly different electrochemical behaviors. The as-synthesized micro-sized materials exhibit moderate rate capability and stable cycling. In situ XRD heating reveals a limited thermal stability window of the NVPOF sample. Guided by this result, a quick one-hour low-temperature heat treatment combined with carbon coating increases the discharge capacity to 118 mAh g-1 at C/10 and delivers 90.4% capacity retention after 300 cycles at 1C. These findings identify precursor selection and microwave reaction conditions as effective parameters for tailoring NVPOF structure and performance and provide a rapid route to NVPOF cathodes for sodium-ion batteries. 

Abstract Composite electrodes combine cathode active materials with solid electrolytes and are essential for all-solid-state batteries. Nevertheless, co-sintering these components introduces mechanical stresses that can lead to microstructural degradation. Understanding how defects evolve at the grain level during thermal processing is critical for designing mechanically robust composite electrodes. Here, we use in situ Bragg coherent diffractive imaging (BCDI) to investigate the microstructural stability of two key materials: the cathode LiNi0.8Mn0.1Co0.1O2 (NMC811) and the solid electrolyte Al-doped cubic Li7La3Zr2O12 (c-LLZO). We track individual crystalline grains during heating and image three-dimensional displacement fields to visualize embedded dislocations. NMC811 exhibits remarkable stability, with stationary dislocation networks and minimal changes in diffraction patterns up to 400 °C. In contrast, c-LLZO undergoes significant microstructural changes beginning at 200 °C, including strain relaxation and dislocation migration. These findings reveal that c-LLZO exhibits dislocation mobility at moderate temperatures that may enable it to accommodate thermal stresses when co-sintered with more rigid oxide cathodes, while the stability of NMC811 ensures structural integrity of the active material. This work demonstrates the value of single-grain characterization for understanding mechanical compatibility in composite electrode design. 

Sodium-ion batteries (SIBs) with Earth-abundant elements are promising for global electrification, but electrolyte stability impacts electrochemical performance and safety. This study compares non-fluorinated 1,2-diethoxyethane (DEE) and fluorinated 1,2-bis(2,2-difluoroethoxy)ethane (F4DEE) as electrolyte solvents in Na_0.97Ca_0.03[Mn_0.39Fe_0.31Ni_0.22Zn_0.08]O₂(NCMFNZO)/hard carbon (HC) pouch cells up to 4.0 V. Fluorination slightly reduces ionic conductivity and increases viscosity but significantly enhances electrochemical stability and safety. Cells with F4DEE exhibit lower impedance, reduced gas evolution, and less voltage decay during high-voltage storage at 40 °C. Long-term cycling shows ∼85% capacity retention after 500 cycles at 25 °C and ∼80% at 40 °C with less transition metal dissolution, outperforming DEE-based cells. Isothermal microcalorimetry reveals lower parasitic heat generation with F4DEE, while soft X-ray absorption spectroscopy confirms stabilized Ni and Mn oxidation states, indicating suppressed electrolyte oxidation. Accelerating rate calorimetry reveals improved thermal stability with F4DEE. These findings highlight fluorinated ether solvents as a promising approach to enhance SIB lifespan and safety, with ongoing challenges requiring further solvent and additive optimization. 

Despite extensive research efforts to develop non-aqueous sodium-ion batteries (SIBs) as alternatives to lithium-based energy storage battery systems, their performance is still hindered by electrode-electrolyte side reactions. As a feasible strategy, the engineering of electrolyte additives has been regarded as one of the effective ways to address these critical problems. In this review, we provide a comprehensive overview of recent progress in electrolyte additives for non-aqueous SIBs. We classify the additives based on their effects on specific electrode materials and discuss the functions and mechanisms of each additive category. Finally, we propose future directions for electrolyte additive research, including studies on additives for improving cell performance under extreme conditions, optimizing electrolyte additive combinations, understanding the effect of additives on cathode-anode interactions, and understanding the characteristics of electrolyte additives.