High-Rate-Capacity Cathode Based on Zn-Doped and Carbonized Polyacrylonitrile-Coated Na4MnV(PO4)3 for Sodium-Ion Batteries

Clozapine boosting N/Cl co-doped carbon skeleton synergistically optimizing Na3V2(PO4)3 with superior performance and excellent thermal stability

Nowadays, the limited electronic conductivity and structural deterioration during battery cycling have hindered the widespread application of Na3V2(PO4)3 (NVP). In response to these challenges, we advocate for a technique involving the application of carbon modifications to NVP to enhance its suitability as cathode material. This work involves the synthesis of N/Cl co-modified in situ carbon coatings derived from clozapine (CZP) through a facile hydrothermal route. By incorporating N elements into the carbon layer, we promote the generation of defects, which increases the exposure of active sites and facilitates greater involvement of Na+ in the electrochemical reaction. Additionally, the integration of chloride ions into the carbon layer enhances the electronic conductivity of NVP. Ex-situ X-ray diffraction (XRD) analysis reveals that the modified carbon layer acts as a buffer against the Na+-induced volume expansion of the single cell during the de-embedding process. Furthermore, ex-situ X-ray photoelectron spectroscopy (XPS) results show a reversible transformation between pyrrolidone N, pyridine N, and graphite N, resulting in improved electron transfer rate and maintenance of the carbon skeleton's stability, thereby providing robust support for NVP. Accordingly, the CZP-5 % displays a remarkable reversible capacity of 115.6 mAh g-1 at 0.1C, suggesting full activation of Na+. It can deliver 85 and 84.6 mAh g-1 at 20 and 40C, even after 1500 cycles, the residual capacity remain at 72.7 and 67.6 mAh g-1, respectively, with high retention values of 85.5 % and 79.9 %. The optimized CZP-5 % sample is subjected to thermal stability testing using an adiabatic accelerating calorimeter, systematically evaluating the battery's thermal stability and providing valuable insights for the design of the battery management system.

Sodium-Ion Storage in Na4VMn(PO4)3/C Porous Nanorods Electrode

Na4VMn(PO4)3 (NVMP) is a prospective cathode for sodium-ion batteries (SIBs) due to its low cost and extraordinary structural stability. However, poor conductivity restricts the electrochemical performance of NVMP, which limits its development and application. Herein, carbon-encapsulated NVMP porous nanorods are prepared via a convenient electrospinning method. The prepared one-dimensional (1D) structure can effectively accelerate the transmission rate of electrons, and the porous structure of NVMP/C nanorods can increase the contact area between the electrolyte and electrode material, which can enhance the diffusion rate of sodium ions. Owing to this advantageous nanoarchitecture, the obtained NVMP/C porous nanorods delivered an initial reversible capacity of 90.9 mA h·g-1 at 0.2 C and a discharge capacity of 68.0 mA h g-1 at 5.0 C. NVMP/C can also achieve a good cycling stability with ideal capacity retentions of 90.4% and 89.8% after 800 cycles at 1 and 3 C, respectively. Moreover, even at a temperature of -30 °C at 0.3 C, the discharge capability was up to 40.1% of that at 20 °C, suggesting an impressive low-temperature tolerance. In situ X-ray diffraction demonstrated that there was no crystal distortion of the NVMP/C electrode during charge and discharge. This work can provide a high-performance strategy on modification of polyanion-positive electrode materials for SIBs.

Cation/Anion Doping Strategy for Na4MnV(PO4)3 with High Energy Density and Long Cycling Life through Construction by Aspergillus niger

Na4MnV(PO4)3 (NMVP) has gained attention for its high redox potential, good cycling stability, and competitive price but suffers from poor intrinsic electronic conductivity and Jahn-Teller effect from Mn3+. In this work, cation/anion doping strategy was used for Aspergillus niger-bioderived carbon-coated NMVP (NMVP/AN) to improve the structural stability and electrochemical performance, where Al3+ doping inhibited the dissolution of Mn and enhanced the Mn3+/Mn2+ redox pair activity; besides, F- doping not only weakens the Na2-O bond but also endows the hierarchical and porous structure of NMVP/AN, which led to a more rapid and fluid transfer of Na+. The elaborately designed Na3.9Mn0.9Al0.1V(PO4)3/AN (NMAVP/AN) exhibits 105.9 mA h g-1 at 0.5 C, and the as-prepared Na3.1MnV(PO3.7F0.3)3/AN (NMVPF/AN) delivers 104.1 mA h g-1 at 5 C. Further demonstration of the hard carbon//NMAVP/AN full cell manifests the good potential of Al3+-doped NMVP/AN for practical applications (100.6 mA h g-1 at 1 C). These findings open up the possibility of unlocking the high-performance Na superionic conductor (NASICON).

Sc3+ substituted Na3V2(PO4)3 on N-doped porous carbon skeleton boosting high structural stability and superior electrochemical performance for full sodium ion batteries

The poor structural stability and conductivity of Na3V2(PO4)3 (NVP) have been serious limitations to its development. In this paper, Sc3+ is selected to replace partial site of V3+ which can enhance its ability to bond with oxygen, forming the ScO6 octahedral unit, resulting in improved structural stability and better kinetic properties for the NVP system. Moreover, due to the larger ionic radius of Sc3+ compared to V3+, moderate Sc3+ substitution can support the crystal framework as pillar ions and expand the migration channels for de-intercalation of Na+, thus efficiently promoting ionic conductivity. The introduction of polyacrylonitrile (PAN) to provide an N-doped porous carbon substrate is another key aspect. The low-cost carbon resource of PAN can induce a beneficial nitrogen-doped carbon skeleton with defects, enhancing electronic conductivity at the interface to reduce the polarization phenomenon. The established pore structure can serve as a buffer for unit cell deformation caused by Na+ migration. Furthermore, the enlarged specific surface area provides more active sites for electrolyte infiltration, improving the material utilization rate. The after cycling X-ray Diffraction/scanning electron microscope (XRD/SEM) further confirms the stabilized porous carbon skeleton and improved crystal stability of Sc-3 material. Ex-situ XRD analysis shows that the crystal volume change in the Sc-3 cathode is relatively slight but reversible during the charge/discharge process, indicating that Sc3+ doping plays a crucial role in stabilizing the unit cell structure. The hybrid Sc/VO6 and PO4 units jointly build a strong bone structure to resist stress and weaken deformation. Accordingly, the optimized Sc-3 sample reveals an initial capacity of 115.9 mAh/g at 0.1C, with a capacity retention of 78.6 % after 2000 cycles at 30C. The Sc-3//CHC full battery can release a capacity of 191.3 mAh/g at 0.05C, accompanied by successful illumination, showcasing its promising practical applications.

Synergistic Strain Suppressing and Interface Engineering in Na4MnV(PO4)3/C for Wide-Temperature and Long-Calendar-Life Sodium-Ion Storage

A Na4MnV(PO4)3 (NMVP) cathode is regarded as a promising cathode candidate for sodium-ion batteries (SIBs). However, issues such as low electronic conductivity and partial cation dissolution contribute to high polarization and structure distortion. Herein, we engineered the local electron density and reaction kinetic properties of NMVP cathodes with varying oxygen vacancies by introducing varying amounts of Zr doping and carbon coating. The optimized sample exhibited a high-rate capacity of 71.8 mAh g-1 at 30 C (83.1% capacity retention after 1000 cycles) and excellent performance over a wide temperature range (84.1 mAh g-1 at 60 °C and 61.4 mAh g-1 at -30 °C). In situ X-ray diffraction technology confirmed a redox solid solution and a two-phase reaction mechanism, revealing minor changes in cell volume and slight strain variations after Zr doping, effectively suppressing the structural distortion. Theoretical calculations illustrated that Zr doping largely shrinks the band gap of NMVP, enriches local electron density, and slightly alters the local element distribution and bond lengths. Moreover, full-cells have shown high energy density (259.9 Wh kg-1) and outstanding cycling stability (200 cycles). The work provides fresh insights into the synergistic effect of strain suppressing and interface engineering in promoting the development of wide temperature range and long-calendar-life SIBs.

NASICON-Type Na3V1.5Cr0.4Fe0.1(PO4)3: High-Voltage and High-Rate Cathode Materials for Sodium-Ion Batteries

Cationic alteration related to a sodium super ion conductor (NASICON)-structured Na3V2(PO4)3 (NVP) is an effective strategy for formulating high-energy and stable cathodes for sodium-ion batteries (SIBs). In this study, we altered the structure of NVP with dual cations, namely, Cr and Fe, to develop Na3V1.5Cr0.4Fe0.1(PO4)3 cathodes for SIBs with high-rate capability (∼71 mAh g-1 at 100 C) and an extreme cycle life output (∼75 mAh g-1 with 95% capacity retention for 10,000 cycles). These excellent electrochemical properties can be ascribed to the synergistic effects of Cr and Fe in the NVP structure, as verified experimentally and theoretically. Therefore, the proposed cosubstitution method can enhance the performance of SIBs by improving their structural stability, electronic conductivity, and phase-change behavior.