Analysis of Performance Differences Between Dry Process and Wet Process for Supercapacitors

Electrode preparation process is the key link determining the core performance of supercapacitors, directly affecting their power density, cycle life, internal resistance, environmental protection and other core indicators. At present, the mainstream electrode preparation processes for supercapacitors are divided into dry process and wet process. There are essential differences between the two in preparation logic and core processes, which in turn lead to significant differences in product performance and adaptation to different application scenarios.

Among them, as a new type of green preparation technology, the dry process, relying on its core advantage of high compaction density, shows irreplaceable value in high-end application scenarios. It forms a distinct contrast with the traditional wet process and jointly supports the application of supercapacitors in different fields.

The core difference between the dry process and the wet process lies in whether organic solvents are used in the electrode preparation process: as a traditional mainstream process, the wet process relies on organic solvents to mix the slurry and then dry it at high temperature. Its core process revolves around "slurry mixing - coating - drying". Active materials, conductive agents, binders and organic solvents such as N-methylpyrrolidone (NMP) are mixed, stirred into a uniform slurry, which is then coated on the surface of the aluminum foil current collector, and then dried at 120-150℃ to remove the solvent and bond the electrode to the current collector. This process has been in operation for a considerable period of time.

The dry process, on the other hand, is a new preparation technology that has developed rapidly in recent years. Its core characteristics are "solvent-free and fewer processes". Without adding any organic solvents, it directly mixes active materials, conductive agents and binders into dry powder through high-speed shearing, and then directly presses it onto the current collector through precision calendering to form electrodes. According to different preparation methods, the dry process can also be divided into dry pressing method, powder spraying method, binder fiber film forming method, etc. Among them, dry pressing method and electrostatic spinning dry method are the most widely used in the field of supercapacitors. Its core advantage is high compaction density. The precision calendering process makes the dry powder closely adhere to the current collector, and the compaction density is 15%-25% higher than that of wet electrodes. This core characteristic also directly endows the dry process with excellent performance.

In terms of electrode structure and ion transport efficiency, due to the volatilization of solvents during high-temperature drying in the wet process, although the overall porosity is relatively high, the ion transport channels are relatively smooth, and the liquid injection process is relatively convenient, the binding force between active material particles and the current collector is weak, and there is still a small amount of solvent residue, which affects the charge transport efficiency to a certain extent.

With high compaction density, the dry process achieves a dense and integrated design of the electrode structure. Active material particles are closely stacked, forming a continuous and smooth conductive network with conductive agents and current collectors, without any interface impedance caused by solvent residue. At the same time, through precise control of powder particle size ratio and calendering parameters, a "dense and ordered" microporous structure is formed inside the dry electrode, which not only ensures the rapid migration of ions, but also greatly increases the load of active materials per unit volume, laying a solid foundation for the improvement of power density.

As the core performance indicators of supercapacitors, power density and response speed directly determine their adaptability in instantaneous power compensation scenarios, which is also the core advantage of the dry process. Affected by the loose electrode structure and high interface impedance, the supercapacitors prepared by the wet process can meet the basic scenario requirements in terms of response speed, but there is an obvious performance upper limit in high-frequency and high-power instantaneous output scenarios. With high compaction density, the dry process has achieved a qualitative breakthrough in power performance: on the one hand, the dense electrode structure greatly reduces the electron transport impedance and significantly improves the charge migration efficiency; on the other hand, the higher load of active materials per unit volume enhances the instantaneous power output capacity. Finally, the power density of supercapacitors prepared by the dry process is 20%-50% higher than that of the wet process. At the same time, relying on the advantages of no interface impedance and smooth conductive network, the response speed is further optimized, which can complete instantaneous power compensation within 20ms, perfectly adapting to the harsh requirements of high-end scenarios such as power grid frequency regulation and ultra-fast charging.

Cycle life and structural stability directly determine the full-life cycle cost and application reliability of supercapacitors, and in this dimension, the advantages of the dry process are also particularly prominent. In wet electrodes, solvent residue is likely to cause binder aging, and electrode shedding and active material loss are prone to occur after long-term high-frequency charge and discharge, and the stability will decrease significantly in extreme environments. With the extreme structural stability brought by high compaction density, the peel strength between active materials and current collectors of dry electrodes is more than 50% higher than that of wet electrodes, and there is no active material shedding, electrode delamination and other phenomena during charge and discharge. At the same time, the solvent-free characteristic avoids binder aging, interface reactions and other problems, making the cycle life reach 2-3 million times. Calculated at 50 cycles per day in industrial scenarios, the service life can exceed 100 years, almost matching the service life of the equipment itself, which greatly reduces the operation and maintenance replacement cost of end users and highlights extremely strong full-life cycle value.

In terms of wide temperature adaptability, the dry process achieves stable operation in extreme environments through the dual advantages of structure and materials, fully adapting to various complex industrial and outdoor application scenarios. Although there is a small amount of solvent residue in wet electrodes, the high porosity allows the electrolyte to fully penetrate, and it has a certain adaptability in extreme temperatures, but there is still a hidden danger of performance degradation. With the pure electrode system without solvent residue and the structural stability brought by high compaction density, the dry process can work stably in a wide temperature range of -40℃~85℃: in low-temperature environments, the dense electrode structure can reduce the impact of electrolyte viscosity changes on ion transport, and the capacity retention rate is still above 90% at -40℃; in high-temperature environments, the absence of solvent residue avoids the risk of high-temperature decomposition, and the thermal conductivity advantage of the dense structure can quickly export working heat, and it can still maintain stable charge and discharge performance above 70℃ without additional supporting temperature control facilities, showing more excellent environmental adaptability.

In terms of environmental protection and industrialization value, the dry process is more in line with the development direction of green manufacturing under the background of the "dual carbon" strategy. The wet process needs to consume a large amount of organic solvents. The solvent drying and recovery process not only accounts for more than 30% of the total production energy consumption, but also has the environmental risk of organic solvent volatilization, requiring high investment in the construction of environmental protection treatment facilities, resulting in great environmental pressure. The dry process achieves green manufacturing from the source, without any organic solvents, eliminating the processes of drying and solvent recovery. The production energy consumption is more than 40% lower than that of the wet process, and there is no pollutant emission throughout the process. At the same time, with the large-scale application of technology, the equipment investment cost is gradually decreasing. Its full-life cycle cost advantage brought by high life and high reliability has made it the core direction of high-end supercapacitor industrialization.

From the perspective of scenario adaptation, supercapacitors with wet process are more suitable for general industrial energy storage, consumer electronics, ordinary industrial equipment and other scenarios with low requirements for power density and wide temperature adaptability. Their core advantages are controllable cost and stable mass production, which can meet the basic needs of instantaneous power buffering and short-term power supply, and are suitable for large-scale popularization and application. Supercapacitors with dry process focus on high-end and high-power scenarios, such as power grid frequency regulation, rail transit braking energy recovery, aerospace, ultra-fast charging equipment, etc. Their core advantage is high compaction density, which in turn brings the advantages of high power density, long cycle life, stable structure and more environmental protection without solvent residue, and can meet the stable operation needs in high-frequency and high-power scenarios. Its full-life cycle operation and maintenance cost is lower, and it is more cost-effective for long-term application. With the continuous iteration of technology, its application scope is constantly expanding.

The dry process and the wet process are not opposites, but focus on different aspects and complement each other, jointly supporting the application of supercapacitors in different scenarios. Relying on the advantages of maturity, stability and controllable cost, the wet process is still the mainstream process for supercapacitor mass production, meeting the basic needs of general scenarios. As a new type of green technology, the core competitiveness of the dry process lies in its high compaction density, which derives a series of advantages such as high power density, long service life and environmental protection, breaking the performance bottleneck of traditional processes and becoming the preferred choice for high-end and high-power scenarios.

With the continuous expansion of supercapacitor application scenarios, the requirements for performance will continue to improve. Both processes will iterate towards the direction of "performance optimization, cost reduction and environmental protection upgrading". Among them, the dry process will further break through core technologies such as powder mixing, binder fiberization and liquid injection process. On the basis of retaining the core advantage of high compaction density, it will continuously optimize product performance, promote large-scale mass production, expand application scenarios, help supercapacitors achieve wider application in new energy storage, industrial anti-voltage sag, power grid regulation and other fields, and inject new momentum into the high-quality development of the energy storage industry.