The second is that the use of an aluminum current collector is available on the anode of NIBs. On the cathode materials, compared to cathode materials for LIB, the cathode materials for NIBs have lower operating voltage and lower specific capacity. Among them, the anode materials for NIBs should have lower operating voltage and higher specific capacity to increase the energy density of NIBs.
In this situation, an amorphous red phosphorus/carbon composite was introduced as a promising anode material for NIBs. And the composite can be one of the promising anode materials for NIBs by having high reversible capacity and low operating voltage. Dual-beam FIB image and EDS line profile plot (inset) of the phosphor/graphite composite.
Cycle performance comparison between GP55 FEC free and GP55 FEC for NIBs: a) specific capacitance, b) coulombic efficiency.
Introduction
Currently, our group has demonstrated the electrochemical performance of the amorphous red phosphorus/carbon composite as a promising anode material for NIBs. These amorphous red phosphorus/carbon composite powders were obtained by means of an easy and simple ball milling process using commercially available amorphous red phosphorus and Super P carbon with a weight ratio of 7:3. In this study, we try to introduce the phosphorus/graphite composite that shows a unique structure different from previous amorphous red phosphorus/carbon composite.
Difference of two composites is that the amorphous red phosphorus/Super P carbon composite has one dimensional connection between phosphorus and carbon which can be called dot contact. On the other hand, the phosphorus/graphite composite has two-dimensional links between exfoliated graphite and phosphorus that can be called planar contact. We also investigate different weight ratio effects for the phosphorus/graphite composite and failure mechanisms of the phosphorus/graphite composite.
Finally, we investigate the effects of the electrolyte additive fluoroethylene carbonate (FEC) for the phosphorus/graphite composite.
Literature Research
Introduction and Operation principle of Li-ion batteries (LIBs) and Na-ion batteries (NIBs)-3
- Anode materials
- Cathode materials
In the state of discharge, lithium ions go from the anode to the cathode and the discharge reaction occurs spontaneously. The degree of ionic radius difference between sodium ion and transition metals is greater than that between lithium ion and transition metals. Also, the heavier sodium ion and the sodium ion with a higher reduction potential affect a lower energy density than the lithium ion.
And due to the different thermodynamically stable phases between sodium and lithium, the NIBs cannot be perfectly applied in the LIB technologies. Like LIBs, NIBs are operated by reversible shuttling of Na ions between the anode and the cathode. Due to the working principle, the anode and the cathode should be used as materials that can be sodiated/desoditized, and the cathode materials can generally remove the Na ions during the charging process.
So to design new cathode materials for NIBs, we need to know differences between the Na cases and the Li cases.
Experimental
- Active material preparation
- Electrode preparation
- Electrochemical characterization
- Material characterization
The shape and structure of the composite material were examined by a scanning electron microscope (SEM; S-4800, Hitachi), and the elemental distribution of the energy dispersive spectroscopy (EDS) map was examined by a high-resolution transmission electron microscope (HR -I HAVE; I AM). -2100F, JEOL).
Results and Discussion
Analysis for the phosphorus/graphite composite as an anode for NIBs
- The phosphorus/graphite composite
- The ratio effects for the phosphorus/graphite composites
15 . patterns, and the phosphorus/graphite mixture has broad peak patterns of the red phosphorus and a strong sharp peak of 26.5˚ demonstrating [002] directions and corresponding to a d-spacing of 0.34 nm for graphite. But the GP55 composite and the GP37 composite show that they generally have broad peak patterns, and the peak for [002] directions at 26.5˚ is not shown. These XRD patterns of two composites indicate the clear exfoliation of the well-crystallized graphite and the amorphized red phosphorus.
When the conventional ball milling technique is used, the result of ball milling shows that the red phosphorus and graphite are converted into the exfoliated graphite/amorphous red phosphorus composite. Therefore, the Raman peaks and XRD patterns of the two GP composites indicate that the graphite has undergone a clear edge distortion caused by the reduction of the grain size by the conventional ball milling technique. The technique brings about the mechanochemical breaking of C-C bonds in the graphite.42 Thus, the well-crystallized graphite and the red phosphorus are amorphized, and the amorphized graphite encloses the amorphized red phosphorus that forms the composite, after which the composite is derived, which reduces the phosphorus intensity. and graphite peaks and patterns for Raman and XRD, respectively.10,42.
To define the ratio effects for the two phosphorus/graphite composites (GP55, GP37), the electrochemical performances of the two composites are tested, this is a type of half cell with a sodium metal as a counter and reference electrode at the same time. Consequently, the initial capacity of the GP37 composite is higher than that of the GP55 composite. But the cycling ability of the GP55 composite is better than that of the GP37 composite.
In addition, ex-situ electrode thickness measurements are performed to confirm the different structural effects between the GP55 composite and the GP37 composite. The cells are disassembled and each of the electrode thicknesses is manually measured at the various points indicated in the corresponding voltage profile. The change in electrode thickness between sodium and desodiation is reversible, and the initial electrode thickness is almost recovered after complete desodiation with an expansion ratio of only 5.3% until the redox potential of the working electrode reaches 2.0 V vs .
Therefore, combining the above results, the initial performance of the GP37 composite is higher than that of the GP55 composite, and the cycle performance of the GP55 composite is better than that of the GP37 composite. And the GP55 composite has a larger buffer matrix structure than the GP37 composite, so the cyclic ability of the GP55 composite is better. These phenomena are related to the fact that the expansion ratio of the GP55 composite electrode is lower than that of the GP37 composite and that the pore volume of the GP55 composite is larger than that of the GP37 composite.
Voltage profiles of GP55 (red line) and GP37 (black line) and the corresponding electrode thickness changes during sodiation and desodiation (red circle: GP55, black circle: .. Physisorption analysis of GP55 and GP37: a) pore diameter, b) nitrogen adsorption/desorption isotherms.
Effect of electrolyte additive FEC and failure mechanism for the composite
- Electrochemical performances for the composite
- Surface analysis for the composite and the Na metal
More polarization of the FEC case derives from the formation of different SEI layers which are based on the FEC additive. But, after the first cycle, the FEC case has less polarization than the free FEC case in the activation processes (Figures 14a, 15a), and the decreasing amount of feedback and the increasing amount of polarization of the FEC case are less than those of Free case FEC (Figure 14b, 15b). Also, the redox potential of the FEC case is smaller than that of the case without FEC.
Therefore, the addition of FEC not only has a positive effect on the cycle performance and coulombic efficiency, but also a better performance rate of the GP55 composite. In this research, this application allows identifying the effect of non-FEC case and FEC case on the charge transfer resistance (Rct) of the working electrode and Rct of the counter electrode. Therefore, the effect of the non-FEC case and the FEC case on the working electrode and the counter electrode can be determined by comparing the Rct of each electrode.44,45 In this study, the working electrode is a GP55 composite, and the counter electrode (as well as the reference electrode) is sodium (Na) metal.
This phenomenon implies that the FEC case makes the surface composition different from the FEC-free case. Likewise, in figure 18, in the symmetrical cells in the counter electrodes, they show that the FEC free housing and the FEC housing have different effects on. The FEC additive housing leads to higher Rct on the sodium metal electrode than the FEC additive housing.
But, in the half-cell (unsymmetrical cell, counter-working electrode), the additive FEC case causes lower Rct. In Figure 21, comparing between the free FEC case (Figure 21a) and the FEC case (Figure 21b), the free FEC case has the highest value (ratio of P-O to red P) than the FEC case. This point indicates that the amount of oxidized active material in the FEC case is more than that in the case without FEC.
In addition, the O 1s spectra are shown for electrodes (Figure 23a, 23c) and Na metals (Figure 23b, 23d), both in the case without FEC and in the case of FEC. In Figures 23a and 23c, there are many C=O bond compounds and C-O-C bond compounds in the case without FEC. While for sodium metals, the Rct in the case of FEC is greater than that of the case without FEC.
LiF compound is known to have poor ionic and electronic conductivity.50-52 Therefore, the Rct of the FEC case is larger.
Conclusion
Electrochemical performance of porous carbon/tin composite anodes for sodium and lithium-ion batteries. Better cycling performance of bulk Sb in Na-Ion batteries compared to Li-Ion systems: an unexpected electrochemical mechanism. Intrinsic thermodynamic and kinetic properties of Sb electrodes for Li-ion and Na-ion batteries: experiment and theory.
High-capacity post-storage and superior recyclability of nanocomposite Sb/C anode for Na-ion batteries. Facile synthesis and long service life of SnSb as negative electrode material for Na-ion batteries. Beyond intercalation-based Li-ion batteries: the state of the art and the challenges of electrode materials that respond via conversion reactions.
Electrochemical sodium uptake and solid electrolyte interphase for solid carbon electrodes and application in Na-ion batteries. Cyclic carbonate-based electrolytes that improve the electrochemical performance of Na4Fe3(PO4)2(P2O7) cathodes for sodium ion batteries.
