Reaction Mechanism of Na-Ion Deintercalation in Na₂CoSiO₄

Abstract

Sodium transition metal silicates are potential candidate electrode materials to enable two-electron redox per transition metal ion center. Yet, the electrochemical reaction mechanism remains elusive despite the widely reported electrochemical activity for this class of materials as intercalation cathodes for Na-ion batteries. Adopting monoclinic Na 2 CoSiO 4 as a model compound, we used high-resolution synchrotron X-ray diffraction (XRD) and X-ray pair distribution function (PDF) analysis to elucidate the structure of the partially desodiated Na 2-x CoSiO 4 phases for the Co 3+ /Co 2+ redox couple. The appearance of satellite reflections in the intermediate Na 1.5 CoSiO 4 and NaCoSiO 4 phases manifests the formation of modulated structures, which are induced by Na + /vacancy and Co 2+ /Co 3+ charge orderings. Accounting for these structural orderings is important to understand the function and performance of sodium transition metal silicate electrodes.

Mn‐doping ensuring cobalt silicate hollow spheres with boosted electrochemical property for hybrid supercapacitors

“…The redox peak in these CV curves appears, but it is not obvious, indicating the storage mechanism with battery-type behavior and capacitive behavior. 54 In CoMnSi-2, two pairs of redox peaks appeared, corresponding to the two reactions of Co 2+ /Co 3+ and Mn 2+ /Mn 4+ , respectively. However, the redox peaks corresponding to MnSiO 3 were not obvious due to the smaller capacity of MnSiO 3 itself compared with Co 2 SiO 4 , and the polarization phenomenon shifted the oxidation peaks to the right and reduction peaks to the left due to the increase in the sweep speed, so only one oxidation peak and two reduction peaks were shown in the CV of CoMnSi-2.…”

“…Figure 5A and Supporting Information: Figure S10 shows CV curves of CoSi, MnSi, and CoMnSi‐1~3 at different scan rates, and Figure 5B compares their CV curves at 20 mV s −1 . The redox peak in these CV curves appears, but it is not obvious, indicating the storage mechanism with battery‐type behavior and capacitive behavior 54 . In CoMnSi‐2, two pairs of redox peaks appeared, corresponding to the two reactions of Co 2+ /Co 3+ and Mn 2+ /Mn 4+ , respectively.…”

Recent Advances in Sodium-Ion Batteries: Cathode Materials

“…Silicate compounds, such as lithium orthosilicate Li 2 FeSiO 4 with a theoretical capacity of approximately 300 mAh g −1 , generally have a higher theoretical capacity than other polyanions owing to their low molecular weight [146]. Similar to Li 2 FeSiO 4 , the sodium silicate Na 2 MSiO 4 compound consists of MO 4 (M = Fe, Ni, Mn, Co) and SiO 4 sites, forming a framework that allows the diffusion of Na ions [147][148][149]. Silicates were previously popular in the glass industry owing to their high thermal and physical stabilities [150].…”

“…However, the material's capacity quickly degrades owing to the collapse of the crystal into an amorphous structure. Meanwhile, Na 2 CoSiO 4 demonstrated a better stability; however, its capacity was approximately 100-120 mAh g −1 [148,149,155]. Guan et al resolved the stability issue of Na 2 FeSiO 4 by introducing a fluorine dopant, which delivered a high capacity of approximately 270 mAh g −1 as a SIB cathode [156].…”

Mineral-like Synthetic Compounds Stabilized under Hydrothermal Conditions: X-ray Diffraction Study and Comparative Crystal Chemistry

“…These difficulties were apparently connected to the Na 2 CoSiO 4 pseudo-orthorhombic symmetry of actually monoclinic crystals with β close to 90 • , which exhibited a pseudo-merohedral twinning. Recently, by means of high-resolution X-ray powder diffraction using a synchrotron radiation source, a group of researchers [19] demonstrated the splitting of ( 101) and (101) reflections. Additionally, the absence of a small-angle (010) reflection undoubtedly confirmed the true monoclinic symmetry and the real value of the b parameter of the unit cell.…”