Although it is known that a supercapacitor suspension cathode using activated carbon powder (ACP) with a large surface area can significantly improve the OER/ORR kinetics, commercial binders (e.g., using a synthesized polymer binder, we fabricated a liquid cathode made of hydrophilic powder with activated carbon (ACP). In order to improve the performance of SWB, we synthesized a bio-inspired hydrophilic binder and developed a slurry cathode to increase the specific electrode surface area.
The results showed that the slurry cathode using the hydrophilic binder reduced the voltage gap (~64 %) and improved the energy efficiency (~46 %) compared to the activated carbon fabric cathode and the slurry cathode using PvdF as the hydrophobic binder. To find out why the hydrophilic sludge cathode showed better performance, we measured the specific surface area of each electrode and the specific capacitance of each SWB through cyclic voltammetry and galvanostatic charge-discharge test. Supercapacitor formation on high surface area carbon electrodes and sodium ion permeation through the cathode current collector.
9 Figure 2.5 The schematic diagram of interaction mechanisms for DPA642 binder 9 Figure 2.6 1H-NMR spectrum of dopamine methacrylamide (DMA) in DMSO 10.
Introduction
Usually, the metal-based current collector cannot be used in SWBs due to seawater because the presence of threatening chloride ions in seawater can weaken the metal oxide films on the surface of other metals, leading to the degradation of metals in seawater19,20. In the previous study, the SWBs using hydrophilic activated carbon cloth (ACC) showed high performance in the overall electrochemical test due to the high specific surface area26. However, intrinsic slow kinetics cannot be improved due to the absence of Pt/C catalyst which can increase the kinetics of ORR31,32.
The slurry form is an attractive method due to not only catalyst loading but also to expand the surface area of activated materials. DOPA is also used as an antioxidant to prevent metal oxidation and DNA oxidation due to its redox-active properties35,38–40. We also fabricated a suspension cathode using hydrophilic (DPA642) and hydrophobic binder (PvdF) with ball milled activated carbon powder (ACP) and Pt/C ORR catalyst and loaded it onto the NASICON solid electrolyte.
The overall results demonstrated the feasibility of slurry cathode using DOPA-based binder and it can remarkably improve the energy efficiency and cycle stability.
Development of DOPA-based hydrophilic binder and its slurry cathodes
Experimental sections
- Dopamine methacrylamide(DMA) synthesis
- Synthesis of poly(Dopamine methaacrylamide-co-poly(ethylene glycol)-
- Characterization of DMA and DPA642 and current collector
- Water contact angle measurement of binders
- Preparation of the coin cell component for SWBs
- Fabrication of various cathode current collectors
- Assembly of the various cathode current collector SWBs
- Electrochemical characterization
- Secondary battery test using metal-free SWBs
We confirmed the structure of the synthesized DMA monomer and DPA642 binder via nuclear magnetic resonance (NMR; 400 MHz FT-NMR, Bruker). To measure the hydrophilicity of the DPA642 binder and PvdF, commercial hydrophobic binder, the measurement of the water contact angle was performed using a drop shape analyzer (DSA100S, Krüss Gmbh). The Na/C composite was prepared by the following procedure for stable cycling performance to prevent the formation of sodium metal dendrite42.
1 M NaCF3SO3 in tetraethylene glycol dimethyl ether (TEGDME) was prepared by stirring for 4 hours with molecular sieves. All procedures were performed in a glovebox under a high-purity Ar atmosphere. Composites of ACP bound to DPA642 and PvdF were prepared using the following procedure: 9 mg of DPA642 or PvdF were dissolved in 1 mL of ethanol or NMP by sonication.
The DPA642 slurry was placed on top of the assembled button cell and dried at room temperature for 24 hours. The paste placed on top of the coin was dried in a drying oven at 90 ⁰C for 3 days and assembled according to the previous procedure. A 14 mm perforated black titanium grid, which was the cathode current collector, was placed on each coin cell or
The machined button cell was fabricated with a flow cell test zig-cell (4TOONE co. Ltd., Republic of Korea) following the previous work to test the operation of each pantograph32. The charge-discharge cycle test of each sodium metal anode SWB was performed by a WonATech battery testing system (WBSC3000L32 battery cycler). A hard carbon anode and a SWB anode with a nickel mesh were prepared by attaching them to a spacer by spot welding.
The Na metal precipitation test was performed using Ni mesh anode at 0.2 mA (0.13 mA cm-2) for 30 hours of charging and disassembled in the Ar-filled glove box. Before the secondary battery test, the hard carbon electrode was produced using commercialized artificial carbon (Aekyung Petrochemical, Korea) (90 wt%) coated with Cu foil.
Results and discussions
- Synthesis of the DMA monomer and DPA642 hydrophilic binder
- Water contact angle measurement and water dissolve resistance of hydrophilic
- Characterization of ACC and ACP active materials
- Development and characterization of slurry cathodes and characterization
- Characterization of slurry electrodes
- Electrochemical test
- Secondary battery test using metal-free SWBs
- Utilization of DPA642 slurry cathode at pouch-type cells for energy storage
A schematic diagram of the interaction mechanism between the carbon material and the Pt/C catalyst is shown in Figure 2.5. A low-magnification SEM image shows bundles of carbon fibers (Figure 2.9a) and ACC fibers forming well-connected network structures (Figure 2.9b). In addition, microporous structures on ACC surfaces can be observed using high-magnification SEM images (Figure 2.9c)26.
In the case of ACP, Figure 2.10 shows the morphology of the ACP powder at different times of ball milling. Typically, as the particle size decreased, the stability of the slurry electrode decreased. In addition, the 1.5-min slurry did not form and the carbon powder was aggregated after mixing (Figure 2.11c).
We can observe the network structures in figure 2.12a and c. Furthermore, Figure 2.12b and d show that the polymer matrix was covered with ACP surfaces. Low-magnification SEM images and (c, d) high-magnification SEM images of ACP-DPA642 and ACP-PvdF, respectively. We can observe that the spherical structure (Figure 2.13a) was Pt/C catalyst and the DOPA-based binder was well distributed along Pt/C and ACP, using EDX data.
However, in the case of ACP-PvdF (Figure 2.13b), we can see from the SEM and EDX images that the carbon material was covered with PvdF. However, the PvdF slurry cannot absorb seawater and floated on the seawater surface due to its hydrophobic nature (Figure 2.14 c, d). The soaking test of the slurry electrodes. a, c) pouring seawater and (b, d) after soaking DPA642 and PvdF slurry, respectively.
Also, the load-discharge profiles in the first cycle and the 100th cycle are shown in figure 2.15b. However, that of ACP-DPA642 SWBs increased slightly over the first cycle, possibly. The results of galvanostatic charge-discharge profiles using metal-free SWBs were shown in Figure 2.18.
So we can confirm that ACP-DPA642 can be used in mass production bags.
Conclusion
Investigation of supercapacitor effect of SWBs
Experimental sections
- Measurement of surface properties of the current collectors
- Electrochemical characterization
Results and discussion
- Investigation of the surface morphologies of each carbon current collector
- Measurement of specific capacitance of each SWB
In previous studies, it has been revealed that the cathode current collector having a high surface area can stabilize the voltage and improve the overall efficiency of batteries. This phenomenon is called EDL capacitance and it occurred through these steps. i) The anions in the electrolyte are accumulated on the charged cathode current collector. When the surface was larger, the anions are easily stacked, and the amount of charge is increased.
When the voltage drops due to unexpected problems, EDL stabilizes the power supply by degrading the charge layer. On the other hand, the voltage suddenly increases, the cathode current collector charge becomes more positive and the common ions in the electrolyte stack. These steps can stabilize the voltage profile of liquid electrolyte batteries that use a large surface area22.
We can note that the voltage ranges of EDL formation occurred from 0 to 0.3 V, which was used in previous work. We also measured the CV curves from 0 to 0.3 V at a scan rate of 0.5 mA s-1 and the specific area of SWBs was calculated using the equation (1). The measured CV curves are shown in Figure 3.4 and specific surfaces are included in Table 3.1.
We also investigated the specific capacitance using the GCD test in the range from 0 to 0.3 V. The voltage-time profile and the results of the calculated specific capacitance are shown in Figure 3.5 and Table 3.2. d) The line graph of specific capacitance according to carbon electrodes. When the EDL formation was complete, the voltage plateau occurred at voltage profiles and a large voltage gap was observed due to sluggish kinetics of the OER/ORR process. However, the ACP-DPA642 voltage profiles (Figure 3.6a) did not show the voltage plateau despite the high current of 2 mA.
On the other hand, the other SWBs showed a voltage plateau at 2 mA current in Figure 3.6b and c. Therefore, it can be observed that even if the specific surface area of ACC was larger than ACP-DPA642, the electrochemical performance and cycle retention of ACP-DPA642 SWB were better than ACC.
Conclusion
Accordingly, the development of efficient and highly efficient energy storage systems (ESS) is being considered due to its unstable energy generation and replenishment. Because it can use huge and reasonable ESSs, seawater batteries (SWBs) using naturally abundant and environmentally friendly material are promising ESSs. However, the slow kinetics of OER/ORR may degrade the energy efficiency due to the induced overvoltage.
To solve this problem, we proposed the slurry cathode which has a large surface area to improve the reaction kinetics using activated carbon powder (ACP) produced by ball milling of activated carbon cloth (ACC) and platinum on carbon as ORR catalyst. The large-area electrode can stabilize the voltage profiles and improve the energy efficiency due to the capacitance effect related to EDL formation. To investigate the performance of secondary batteries, we operated the metal-free SWBs using a 0.2 mA (0.13 mA cm-2) hard carbon anode with a capacity control of 200 mAh g-1 and a discharge voltage limitation of 0. 5 V.
Overview of energy storage systems for storing electricity from renewable energy sources in Saudi Arabia. A metal-organic framework-derived porous cobalt-manganese oxide bifunctional electrocatalyst for hybrid Na-air/seawater batteries. A metal-free ORR/OER bifunctional electrocatalyst derived from metal-organic frameworks for rechargeable Zn-air batteries.
3D amorphous carbon with controlled porous and disordered structures as a high-rate anode material for sodium-ion batteries. Graphene oxide-encapsulated amorphous copper-vanadium oxide with improved capacitive behavior for high- and long-life lithium-ion battery anodes. Moving to Aqueous Binder: A Valid Approach to Achieving High-Rate Capability and Long-Term Durability for Sodium-Ion Battery.
Electrochemical sodium uptake and solid electrolyte interphase for solid carbon electrodes and application in Na-ion batteries. Physiosorption of gases with special reference to the estimation of surface area and pore size distribution (IUPAC Technical Report).
Summary
