Optimizing Vanadium Redox Reaction in Na₃V₂(PO₄)₃ Cathodes for Sodium-Ion Batteries by the Synergistic Effect of Additional Electrons from Heteroatoms

Abstract

Na 3 V 2 (PO 4 ) 3 (NVP) is one of the most potential cathode materials for sodium-ion batteries (SIBs), but its actual electrochemical performance is limited by the defects of large electron and ion transfer resistance. Multicomponent design is considered an effective method to optimize the conductivity of NVP electrodes. Therefore, Cr and Si are added in NVP to form a multielement component of Na 3 V 1.9 Cr 0.1 (PO 4 ) 2.9 (SiO 4 ) 0.1 (NVP-CS). It is confirmed that 3d electrons of Cr are beneficial for improving the conductivity and increasing the average potential by activating V 4+ /V 5+ . Theoretical calculations show that the introduction of Si changes the electronic structure of V and O, thus promoting the electrochemical reaction of V 3+ /V 4+ to exert higher capacity. Due to the coordination of the two elements, a lower migration barrier is obtained in NVP-CS. Specifically, NVP-CS retains the advantages of single-doped electrodes very well (capacity retention of 90% after 300 cycles at 1 C and a high capacity of 94.1 mA h g −1 at 5 C, compared to NVP with only 82.6% capacity retention at 1 C and 59.4 mA h g −1 at 5 C). The excellent electrochemical performance results show that NVP can be successfully optimized by the introduction of Cr and Si. This work can provide some inspiration for multicomponent material research of cathode materials. KEYWORDS: multielement system, Na 3 V 2 (PO 4 ) 3 cathode, vanadium redox reaction, electron energy level, sodium-ion battery

Boosted Redox Kinetics Enabling Na3V2(PO4)3 with Excellent Performance at Low Temperature through Cation Substitution and Multiwalled Carbon Nanotube Cross-Linking

“…In general, the decreased I D /I G value after K-substitution indicates the higher degree of graphitization and improved electronic conductivity, possibly resulting from catalytic graphitization of K source introduced in the precursor. 19,52,54 For the K-NVP@C/MWCNT, the introduction with MWCNT induces the increased disordered species in the composite, leading to the higher of I D /I G value. 22,47,55 S2 (Supporting Information) exhibits the TGA curves of NVP@C, K-NVP@C, and K-NVP@C/MWCNT, and the weight loss of 3.7, 4.2, and 7.6%, respectively, corresponds to the carbon contents in the three samples.…”

“…For the Raman spectra, the D band at around 1360 cm –1 and the G band at 1590 cm –1 , corresponding to the disordered structure and ordered domain, can be clearly observed (Figure c). In general, the decreased I D / I G value after K-substitution indicates the higher degree of graphitization and improved electronic conductivity, possibly resulting from catalytic graphitization of K source introduced in the precursor. ,, For the K-NVP@C/MWCNT, the introduction with MWCNT induces the increased disordered species in the composite, leading to the higher of I D / I G value. ,, Figure S2 (Supporting Information) exhibits the TGA curves of NVP@C, K-NVP@C, and K-NVP@C/MWCNT, and the weight loss of 3.7, 4.2, and 7.6%, respectively, corresponds to the carbon contents in the three samples. In principle, the in situ generated carbon coating layer from the pyrolysis of citric acid and introduction of MWCNT can not only accelerate the migration of electrons but also contribute to maintaining the integrity of electrode, resulting in improved electrochemical performance .…”

“…As a representative example of polyanion compounds, the NASICON cathode, featuring the superion conductor structure, demonstrates a 3D open framework with large channels. − Among all the NASICON materials, the sodium vanadium phosphate (Na 3 V 2 (PO 4 ) 3 , NVP) is deemed as a promising cathode candidate for high energy SIBs owing to the energy density of near 400 W h kg –1 based on the theoretical capacity of 117.6 mA h g –1 and voltage plateau of 3.4 V. − Nevertheless, such arresting features of NVP are not easy to receive even at low rate. In principle, structure collapse upon repeated insertion/extraction of Na + hinders the ionic diffusion channels, combined with the relatively poor intrinsic electronic conductivity, thus causing electrochemical polarization, especially at high rates, which in turn results in degraded specific capacity and unstable cyclic stability. − Moreover, such polarization, originating from the discrepancy of ionic and electronic transportation kinetics, will aggravate at low temperatures, thus restricting the application of NVP cathode in high altitude and high latitude areas. ,, …”

Understanding the Relationship Between Stress Change and Electrochemical Performance of a Heated SiO Anode Through In Situ Raman Spectrum

“…The demand for higher specific capacity and energy density of lithium-ion batteries (LIBs) has risen urgently due to its wide use in electric vehicles, electronic devices, energy storage power stations, and many other fields. − Compared with commercial graphite anode material (372 mAh g –1 ), Si-based anode materials stand out for their high capacity (4200 mAh g –1 for Li 22 Si 5 and 3579 mAh g –1 for Li 15 Si 4 ) and low Li-uptake voltage (≈0.4V), and are considered promising candidates for the next-generation LIBs. − However, the Si anode has some tough problems, which hinder its further development and commercial application. On the one hand, the severe volume expansion (∼400%) during the lithiation process leads to the pulverization of the active particles, causing loss of electrical contact and decrease in capacity. − On the other hand, the semiconductivity of Si makes it unsatisfying for transmission of electrons and ions, resulting in poor rate capability.…”

Influence of Process Parameters on the Electrochemical Properties of Hierarchically Structured Na3V2(PO4)3/C Composites

“…Xu et al demonstrated, that doping low amounts of cost-efficient Fe 2 + ions activates the V 4 + /V 5 + redox, which leads to a large reversible capacity of 133 mAh g À 1 . [9] Multicomponent doping of Cr and Si [10] or the combined approach of carbon coating together with Nb 5 + substitution into the crystal structure [11] recently proved the enhancement of the electronic conductivity of NVP composites. Beside this crystal-chemical modification of the NASICON structures, a different viable approach is microstructure engineering.…”