Sodium vanadium phosphate cathodes for Na-ion batteries: Carbon modification strategies and electrolyte compatibility

Sodium-ion batteries (SIBs) are promising for large-scale energy storage, owing to their resource abundance and low cost. However, long-term stability is constrained by complex interfacial interactions and microstructural degradation. This study investigates the mechanistic coupling between anode composition, electrolyte chemistry, and solid electrolyte interphase (SEI) evolution in full-cell SIBs employing sodium vanadium phosphate (NVP) cathodes. Pure tin (Sn), hard carbon (HC), and Sn-HC composite anodes were systematically evaluated with carbonate ester- and ether-based electrolytes. Microscopic and spectroscopic analyses reveal that Sn-rich electrodes undergo significant pulverization and unstable SEI formation, whereas HC maintains structural integrity and forms kinetically stable SEI. On the other hand, the Sn-HC composite mitigates Sn's mechanical degradation while enhancing capacity retention. Electrochemical analysis highlights the critical role of electrolyte choice in modulating redox reversibility and interfacial integrity. Accelerating rate calorimetry (ARC) links interphase behavior to distinct thermal decomposition pathways and self-heating rate. These findings provide mechanistic insights into the electro-chemo-mechanical degradation processes dictating the long-term stability and thermal safety of SIBs.

Pre-curing treatment optimises the grain growth of high-performance Na super ionic conductor-type Na3V2(PO4)3 thin films for sodium-ion batteries.

Aqueous zinc-ion batteries (ZIBs) exhibit severe performance degradation at low temperatures primarily due to the freezing of water. To mitigate this issue, we engineered a dual-salt super-chaotropic eutectic electrolyte that exploits the strong Hofmeister effect of zinc salts to disrupt the ordered hydrogen-bonding network of the electrolyte, significantly lowering its freezing point. The electrolyte, formulated with Zn(ClO4)2·6H2O, NaClO4·H2O, and acetamide, leverages the strong chaotropic properties of ClO4 - ions to dismantle the hydrogen bonding network of water molecules, realizing an ultra-low freezing point of -75.9 °C. Additionally, the electrolyte minimizes water activity, suppresses the hydrogen evolution reaction, and mitigates corrosion through the robust coordination among ClO4 -, acetamide, and Zn2+ ions, enabling uniform and compact Zn deposition. The Zn||sodium vanadium phosphate (NVP) battery demonstrates higher redox potential, exceptional low-temperature cycling performance, achieving over 5500 cycles at -20 °C with 81.2% capacity retention and nearly 100% Coulombic efficiency. Furthermore, the pouch cell retains 94.8% of its capacity after 250 cycles at -20 °C. This innovative chaotropic eutectic electrolyte provides a promising pathway for advancing low-temperature ZIBs with extended operational lifespans.

Abstract Aqueous zinc‐ion batteries (ZIBs) exhibit severe performance degradation at low temperatures primarily due to the freezing of water. To mitigate this issue, we engineered a dual‐salt super‐chaotropic eutectic electrolyte that exploits the strong Hofmeister effect of zinc salts to disrupt the ordered hydrogen‐bonding network of the electrolyte, significantly lowering its freezing point. The electrolyte, formulated with Zn(ClO 4 ) 2 ·6H 2 O, NaClO 4 ·H 2 O, and acetamide, leverages the strong chaotropic properties of ClO 4 − ions to dismantle the hydrogen bonding network of water molecules, realizing an ultra‐low freezing point of −75.9 °C. Additionally, the electrolyte minimizes water activity, suppresses the hydrogen evolution reaction, and mitigates corrosion through the robust coordination among ClO 4 − , acetamide, and Zn 2+ ions, enabling uniform and compact Zn deposition. The Zn||sodium vanadium phosphate (NVP) battery demonstrates higher redox potential, exceptional low‐temperature cycling performance, achieving over 5500 cycles at −20 °C with 81.2% capacity retention and nearly 100% Coulombic efficiency. Furthermore, the pouch cell retains 94.8% of its capacity after 250 cycles at −20 °C. This innovative chaotropic eutectic electrolyte provides a promising pathway for advancing low‐temperature ZIBs with extended operational lifespans.

For sodium-ion batteries, addressing the issue of limited cycle life is crucial for their widespread industrial application, and the electrolyte plays a pivotal role in this context. In this study, a practically viable electrolyte with industrial potential is proposed, introducing sulfone and borate as cooperative electrolyte additives to improve cycling stability. The optimized electrolyte formulation is composed of NaPF6 (sodium hexafluorophosphate) dissolved in a mixed solvent of PC (propylene carbonate)/EMC (ethyl methyl carbonate), supplemented with PES (prop-1-ene-1,3-sultone) and NaODFB (sodium difluoro(oxalato)borate). In this system, the decomposition of PES generates S-Ox species, which modify the interfacial chemical environment and promote a more complete decomposition of ODFB-. As a result, B- and S-containing organic intermediates are further transformed into oxygen-coordinated inorganic species (e.g., B-Ox and S-Ox), which subsequently reconstruct into a crosslinked inorganic interphase. This cooperative interfacial evolution leads to the formation of more uniform, compact, and chemically stable CEI/SEI layers, thereby enabling superior cycling stability. As a demonstration, the Na||NVP (sodium vanadium phosphate) half-cell retains a specific capacity of 109.8 mAh·g-1 after 5000 cycles, corresponding to a capacity retention of 96.7%. This work offers valuable insights and experimental support for the large-scale industrialization of long-life sodium-ion battery electrolytes.

Conventional methods for recycling metals from the leachate of spent sodium-ion batteries (SIBs) cathodes encounter several challenges, such as high energy consumption, complicated process and environmental pollution. Herein, a capric acid-driven three-phase antisolvent precipitation (CTAP) strategy is used for the low-energy and sustainable recovery of metal and lixiviant from the leachate associated with SIBs cathode vanadium phosphate sodium (NVP) and low-melting mixture solvents (LoMMSs). The CTAP strategy results in a three-phase precipitation, with the upper layer representing the capric acid phase, the middle layer consisting of the lixiviant phase, and the bottom layer comprising the solid phase. Through the CTAP strategy, capric acid achieves the antisolvent precipitation efficiencies of 86.8% for Na and 50.5% for V when applied to leachate from NVP and LoMMS polyethylene glycol 200:phytic acid; nevertheless, capric acid is ineffective in precipitating metals from leachate derived from LoMMSs that combine polyethylene glycol 200 with citric acid, benzoic acid, urea, or acetamide. Additionally, the LoMMSs using polyethylene glycol 200:phytic acid as the lixiviant achieve maximum leaching efficiencies of 99.1% for Na and 94.4% for V from NVP at a mild temperature of 80 °C over 24 hours, with a liquid-to-solid ratio of 200 after optimizing factors, such as hydrogen bond donors, molar ratios, temperature, time, liquid-to-solid ratio and scalability. This work provides an energy-saving, process-simplified and eco-friendly strategy for the separation of metals from SIBs leachate.

Ultrathin Layered Vanadyl Phosphate Nanosheets as an Ultrasensitive Electrochemical Sensor for Dihydroxybenzene Isomers in Biological and Environmental Matrices

Sodium vanadium phosphate (Na3V2(PO4)3) has emerged as a promising cathode candidate for advanced sodium-ion batteries due to its advantageous characteristics, including elevated operating voltage, rapid ionic transport, and exceptional structural stability. However, its practical application is hindered by its low electronic conductivity. To address this limitation, we prepared a Na3V1.95Tm0.05(PO4)3@C sample (Tm0.05-NVP@C) using a Thulium3+ (Tm3+) doping strategy to improve both high-rate performance and long-term cyclability. Electrochemical kinetic analyses combined with theoretical calculations confirm that the incorporation of Tm3+ into Tm0.05-NVP@C effectively narrows the electronic bandgap and reduces Na+ migration energy barriers, thereby accelerating charge transfer processes. Furthermore, the more negative integrated crystal orbital Hamilton population values of V-O and Tm-O bonds manifest improved lattice stability. Accordingly, the prepared Tm0.05-NVP@C exhibits significant electrochemical performances: it achieves a high reversible capacity of 88.65 mAh g-1 at 40 C while maintaining exceptional capacity retention of 79.64% after 2500 cycles at 10 C. In situ X-ray diffraction analysis further elucidates the reversible biphasic transformation between Na3V1.95Tm0.05(PO4)3 and NaV1.95Tm0.05(PO4)3. This comprehensive investigation not only demonstrates the efficacy of Tm3+ doping in optimizing NASICON-typed cathodes but also provides valuable insights for developing next-generation Na3V2(PO4)3-based cathodes with improved rate capability and cycle life.

Abstract High‐safety sodium energy storage across a broad‐temperature range is essential for large‐scale energy storage systems. Effective ion transport in the electrolyte and stable interface phase on the electrode are essential prerequisites for the secure operation of sodium ion batteries under challenging environmental conditions. Herein, a non‐flammable electrolyte with high ionic conductivity is designed by incorporating low‐melting‐point, weak solvation methyl propionate (MP) and a flame‐retardant triethyl phosphate (TEP). The dipole‐dipole interaction between MP and TEP weakens the coordination of TEP, thereby increasing the proportion of anions involved in the solvation structure. This electrolyte configuration promotes the formation of a resilient inorganic‐enriched interface and enhances the electrode compatibility of the TEP‐based electrolyte, enabling the sodium vanadyl phosphate (NVP)||Na half cell and NVP||hard carbon (HC) full cell to deliver excellent electrochemical performance from −40 to 50 °C. Undoubtedly, this work proposes a new electrolyte design strategy based on synergistic dipole–dipole interaction, paving the way for high‐safety sodium‐ion batteries operating in extreme environments.

Crystal chemistry engineering via Sn4+ and Cr3+ Co-doping in sodium vanadium phosphate: Enabling reversible V4+/V5+ redox and boosting sodium storages

Emerging intertwined nanofibers stabilized two-dimensional sodium vanadium pyrophosphate network for high-potential electrode in sodium-ion storage

Advances in lithium-ion battery (LIB) technology have taken center stage over the past decade due to their high energy densities compared to other battery chemistries. However, resource limitations are expected to increase production costs, prompting interest in alternative technologies. Sodium-ion batteries (SIBs), which share similar chemistry with LIBs but rely on more abundant elements, have emerged as promising next-generation energy storage solutions. In this context, solid electrolyte materials are crucial for enabling safe and efficient sodium batteries by mitigating the risks associated with flammable liquid electrolytes. Sodium-Super-Ionic-Conductor (NASICON) structures like Na₃Zr₂Si₂PO₁₂ (NZSP) have attracted considerable attention for their excellent ionic conductivity and thermal stability. However, their practical use is often hindered by inherent porosity and low density, which degrade ionic conductivity and electrochemical stability, ultimately limiting battery performance.In this study, we significantly enhance the performance of NZSP solid electrolyte materials tailored for All-Solid-State batteries (ASSBs) through a successful densification process. By introducing a densification agent that interacts effectively with the sodium-ion conducting matrix, we achieved notable improvements in both material compactness and ionic transport properties. The densified sample exhibited an impressive room-temperature ionic conductivity of 8.4 × 10⁻⁴ S/cm and attained ~98% of the theoretical density, resulting in a robust and mechanically stable electrolyte structure. This process also reduced porosity and grain boundary resistance, enabling faster and more efficient sodium-ion conduction. Comprehensive electrochemical evaluations were conducted to assess the performance of the optimized solid electrolyte. The densified sample exhibited a high critical current density (CCD) of 6 mA cm⁻², which is three times greater than that of the pristine counterpart. This high CCD signifies the ability of the electrolyte to support high rates of sodium-ion transport without significant polarization, a crucial parameter for high-power applications.To further validate the effectiveness of our densification approach, full cells were assembled using the densified NZSP electrolyte paired with a sodium vanadium phosphate (NVP) cathode. These cells exhibited a marked increase in capacity, reflecting the improved ionic conductivity and reduced interfacial resistance achieved through densification. The results demonstrate the practical viability of the optimized electrolyte in real battery systems. Such advancements are crucial for the commercialization of high-energy-density sodium batteries, paving the way for safer and more sustainable energy storage technologies. Figure 1

Numerous electroactive materials for the negative and positive electrode have been studied since the Na-ion batteries were proposed in the 1980s.[1] Carbonaceous materials have been extensively used in battery research, however sodium ions do not readily insert into graphite, therefore various hard carbons have been investigated as the negative electrode.[2] One example of a positive electrode active material, that is of interest for commercialisation, is the polyanionic structure sodium vanadium phosphate (Na3V2(PO4)3), which delivers a theoretical capacity of 118 Ah/kg with reasonable cycle stability. Both hard carbons and Na3V2(PO4)3 have been studied extensively for use in sodium ion cells, mainly separately within half cells vs. sodium metal. However, limited studies have been undertaken on full cell configurations to understanding degradation processes and the stability and evolution of the solid-electrolyte interphase (SEI) and cathode-electrolyte interphase (CEI).Shell Isolated Nanoparticles for Enhanced Raman Spectroscopy (SHINERS) is a powerful characterisation tool for the investigation of battery electrode interfaces at the molecular scale (Figure 1). Shell isolated nanoparticles (SHINs) consist of a core metal nanoparticle, that can produce a localised surface plasmon resonance (LSPR) when light is shone on them, e.g. gold, and a thin (2 - 4 nm), optically inert, continuous shell, e.g. SiO2.[4, 5] The LSPR enhances the electromagnetic field around the particles, which in turn enhances the Raman signal being detected. SHINERS is a surface specific technique that can detect surface species allowing for more insight into degradation mechanisms, chemical interactions, and changes on the surface of electrodes. SHINERS has been previously used to study the effect that electrolyte additives have on the SEI formation and stability on Li-ion full cell electrodes before and after cycling the electrodes to formation of the SEI and cycling to end of life.[3]Herein, ex situ SHINERS has been employed to investigate sodium ion battery electrodes (hard carbon and Na3V2(PO4)3) before and after cycling at 3.8 V, 4.4 V, and 4.8 V to ascertain the effects of this change in voltage, degradation of the materials, and changes in surface species. By increasing the cycling voltage, the degradation of these materials is accelerated, notably on the cracking of the conductive carbon coating upon Na3V2(PO4)3 and observation of the appearance of Na2CO3 upon cycling.[1] C. Delmas, Adv. Energy Mater., 2018, 8, 1703137.[2] D. A. Stevens, J. R. Dahn, J. Electrochem. Soc., 2000 147 1271.[3] C. Wölke et al., Adv. Energy Mater., 2024, 14, 2402152.[4] T.A. Galloway, L.J. Hardwick, J. Phys. Chem. Lett., 2016, 7, 2119.[5] Y.J. Zhang et al., Nat. Rev. Metho ds Primers,2023, 3, 36. Figure 1: An array of battery electrode processes that can be investigated via SHINERS [5]. Figure 1

Achieving reversible multi-redox activity in NASICON-type sodium vanadium phosphate towards ultrafast and high-energy sodium storage

Exploring the genuine effect of fluoroethylene carbonate on cathode in virtue of sodium vanadium phosphate

Antimony lithium vanadium phosphate for sorption and chromatographic separation of cesium and europium ions from an aqueous solution

Structural Water-Induced Proton Storage in Two-Dimensional Vanadyl Phosphate for Energy Storage: Experimental and Theoretical Studies

Polyanion-substituted sodium vanadium phosphate (Na3V2(PO4)3, NVP) derivatives, including SO4, BO3, WO4, and SiO4 substitutions, were systematically synthesized and impregnated with a nanocarbon network via ultracentrifugation. Among them, nanosized (5-30 nm), highly crystalline, and well-dispersed sulfate-substituted NVP (NVPS) nanodots were directly nucleated onto multiwalled carbon nanotubes, enabling ultrafast electrochemical kinetics. This nanoscale architecture delivered exceptional rate capability, achieving 97 mAh g-1 at 1000C (3.6 s discharge), corresponding to 83% of the theoretical capacity, outperforming conventional NVP. The electrochemical kinetics analysis using a cavity microelectrode revealed reduced polarization, enhanced capacitive charge storage, and rapid sodium ion diffusion during intercalation/deintercalation, facilitated by the conformal interface between NVPS and MWCNT, possibly by sulfate-induced surface modifications. These findings establish polyanion substitution and ultracentrifugation-assisted materials processing as a transformative strategy for overcoming intrinsic transport limitations in NASICON-type phosphates, positioning NVPS as a benchmark material for next-generation high-power sodium-ion batteries and hybrid capacitors.

Biphasic vanadyl phosphate promoted phenol electro-oxidation for efficient hydrogen evolution and effective management of water pollution