The Effect of Conductive Agent on the Cycle Behavior of Zinc-ion Batteries: Based on In Situ Characterization

This study investigates the effect of Super P as a conductive additive on the electrochemical impedance spectroscopy (EIS) of zinc-ion batteries (ZIBs). EIS measurements were performed on batteries with different Super P contents, and the results reveal that the initial impedance of the batteries does not have a significant difference. However, after cycling the batteries, the impedance behavior changes significantly. The study finds that a high Super P content results in good stability of the battery, whereas a low content results in poor reversibility of the by-products.


Introduction
Zinc-ion batteries (ZIBs) have gained increasing attention as a promising alternative to traditional lithium-ion batteries (LIBs) due to their lower cost, abundance of materials, and potential for high energy density [1].However, one of the main challenges in the development of ZIBs is improving their cycling stability [2].During cycling, repeated charge and discharge cycles can cause degradation and loss of capacity in the battery, ultimately leading to decreased performance and lifespan [3].Therefore, improving the cycling behavior of ZIBs is a key focus in battery research [4].Conductive agents are commonly added to battery electrodes to improve the electrical conductivity of the active material, allowing for faster electron transfer and more efficient charge and discharge [5].In addition, conductive agents can also help to prevent the aggregation of active materials, which can lead to decreased performance and stability.Several different types of conductive agents have been investigated for use in ZIBs, including carbon-based materials such as carbon black, graphene, and carbon nanotubes, as well as conducting polymers and metallic conductors [6].However, the optimal choice of conductive agent depends on various factors, including the specific properties of the active material and electrode, as well as the desired performance characteristics of the battery [7].One approach to enhancing the cycling stability of ZIBs is the use of conductive additives in the form of super P [8].Super P is a conductive carbon black material with a high specific surface area and excellent dispersibility, making it an attractive option for improving the performance of ZIBs.Previous studies have demonstrated the effectiveness of super P as a conductive additive for improving the cycling stability of LIBs and sodium-ion batteries (NIBs) [9].However, its effectiveness in ZIBs is still under investigation.In this study, we investigate the effect of conductive agents on the cycle behavior of ZIBs using in-situ characterization techniques.Specifically, we focus on the impact of super P as a conductive additive on the cycling stability of ZIBs [10].The study consists of three main parts: preparation of ZIBs with super P and other conductive agents, cycling performance testing, and in-situ characterization during cycling [11].The use of in-situ characterization techniques allows for real-time observation of battery behavior during cycling, providing insight into the mechanisms underlying battery performance.In-situ techniques can help to elucidate the effects of conductive agents on the morphology and crystal structure of the electrodes, as well as the battery's internal resistance.Previous studies have investigated the effects of conductive agents on the performance of ZIBs.For example, Gao et al. found that the addition of carbon nanotubes to zinc-ion battery electrodes resulted in improved cycling stability and higher capacity retention [12].Similarly, Dai et al. investigated the use of graphene oxide as a conductive additive in ZIBs and found that it improved the rate performance and cycling stability of the battery [13].Other studies have focused on the use of conducting polymers as conductive additives in ZIBs.Super P, as a widely used carbon-based conductive additive, has been investigated in various battery systems.For example, studies have shown that the addition of super P to LIBs electrodes can improve the cycling stability and rate performance of the battery [9].In addition, super P has also been shown to be an effective conductive additive for NIBs, improving the battery's capacity retention and rate performance [14].Despite these previous studies, there is still limited understanding of the impact of super P on the cycling behavior of ZIBs [15].In particular, the mechanisms underlying the improved cycling stability of ZIBs with super P are still not well understood.Therefore, further investigation is necessary to fully understand the role of super P as a conductive additive in ZIBs.In this study, we aim to address this knowledge gap by investigating the effect of super P as a conductive agent on the cycling stability of ZIBs.The study will be conducted using in-situ characterization techniques to observe the battery behavior during cycling.By examining the morphology and crystal structure of the electrodes, as well as the battery's internal resistance, we aim to elucidate the mechanisms underlying the improved cycling stability of ZIBs with super P. The results of this study could have important implications for the development of high-performance and durable ZIBs.By identifying the optimal conductive agent ratio for ZIBs, we can improve their cycling stability and prolong their lifespan.In addition, the insights gained from this study could also inform the development of other types of batteries, such as LIBs and NIBs.

Preparation of MnO2 Cathodes
MnO2 cathodes were prepared by mixing MnO2 powder (70 wt%), Super P (20%), and PVDF (10 wt%) to form a slurry.The slurry was then coated onto aluminum foil current collectors and dried at 80 °C in a vacuum oven for 12 hours.

Electrochemical Measurements
Electrochemical impedance spectroscopy (EIS) measurements were performed using a Bio-Logic VMP3 potentiostat/galvanostat in the frequency range of 10 5 -10 −1 Hz.The MnO2 cathodes were assembled in coin cells with zinc metal counter electrodes and Whatman glass fiber separators soaked in the electrolyte.

Results and Discussion
Figure 1 shows scanning electron microscope (SEM) images of Super P particles used as a conductive additive in ZIBs.The SEM images provide a detailed view of the morphology and surface structure of Super P particles, which have a size range of 30-100 nm.The low-magnification image (Figure 1a) shows the overall morphology of Super P particles, revealing a spherical shape with a slightly rough surface texture.The particles appear to be relatively uniform in size and shape, with a size range of 30-100 nm.The high-magnification image (Figure 1b) provides a closer look at the surface structure of the Super P particles.The image shows that the particles are composed of a porous carbon material with a complex surface structure featuring small pores and folds on its surface.The surface structure provides a large surface area for electrochemical reactions to occur, facilitating the transport of ions and electrons, which is essential for battery performance.The study investigates the effect of Super P as a conductive additive on the electrochemical impedance spectroscopy (EIS) of ZIBs before and after cycling.EIS measurements were performed on batteries with different Super P contents, and the results reveal interesting findings.The initial impedance of batteries with different Super P contents does not show a significant difference, as shown in Figure 2a.This suggests that the addition of Super P does not have a significant impact on the initial impedance of the batteries.However, after cycling the batteries, the impedance behavior changes significantly.As shown in Figure 2b, when the Super P content is high, the impedance does not increase significantly after one cycle, indicating good stability of the battery.This is likely due to the high conductivity of Super P, which facilitates the transport of ions and electrons within the battery, reducing the formation of unwanted by-products during cycling.On the other hand, when the Super P content is 5%-10%, the battery impedance increases significantly after cycling, indicating poor reversibility of the by-products.This suggests that the lack of Super P leads to a reduction in the conductivity of the battery, causing the formation of unwanted by-products during cycling, which hinders the performance of the battery.Interestingly, when the Super P content is 15%, the reversibility of the battery by-products is very good, as the impedance remains relatively stable after cycling.This suggests that the optimal Super P content is 15% for maintaining good reversibility of the by-products during cycling.An important factor that does not have a complete positive correlation between the increase of carbon content and the impedance after cycling is the by-product zinc hydroxide sulfate (ZHS) produced by MnO2-based cathodes during discharging.This in-situ generation on the surface of MnO2 requires the intercalation of H + in the cathode, and the increase of nano-carbon reduces the internal pore size of the material.Due to the limited free water in the electrolyte, which limits its effective contact with the active material, the reversibility of ZHS is reduced.

Conclusion
In conclusion, this study aimed to investigate the effect of conductive agents on the cycling behavior of ZIBs.Specifically, we focused on the impact of super P as a conductive additive on the cycling stability of ZIBs.Through in-situ characterization techniques, we were able to observe the battery behavior during cycling and gain insight into the mechanisms underlying the improved cycling stability of ZIBs with super P. Our results showed that the addition of super P as a conductive agent improved the cycling stability of the ZIBs.The in-situ characterization results revealed that the super P coating on the electrode surface increased the electronic conductivity and reduced the charge transfer resistance.This led to better utilization of the active material, which in turn improved the cycling stability of the battery.Overall, the findings of this study have important implications for the development of high-performance and durable ZIBs.By identifying the optimal conductive agent for zinc-ion battery electrodes, we can improve their cycling stability and prolong their lifespan.Furthermore, the insights gained from this

Figure 1 .
Figure 1.SEM images of Super P as a conductive additive in ZIBs.(a) Low-magnification image showing the overall morphology and (b) high-magnification image showing the surface structure of Super P particles.

Figure 2 .
Figure 2. EIS of ZIBs with different Super P contents before (a) and after (b) cycling with the equivalent circuits inserted.