Lithium Battery Dry Process vs. Wet Process: Analysis of Core Differences in the Entire Process

Electrode sheet preparation is the core link in lithium battery production, directly determining the battery's energy density, cycle life, production cost, and environmental friendliness. As the two mainstream technical routes for electrode sheet preparation, the dry process and wet process have essential differences from core logic to specific operation processes. Relying on its mature and stable characteristics, the wet process has long dominated the industry; the dry process, with the advantages of solvent-free, high efficiency, and low energy consumption, has become an important direction for the upgrading of the new energy industry. The differences between the two are not limited to a single link, but run through the entire process of "raw material processing - molding processing - finished product finishing". Only by accurately disassembling these process differences can we understand the applicable scenarios and development potential of the two processes.

I. Differences in Core Process Logic: Solvent Dependence vs. Solvent-Free Breakthrough

The fundamental difference between the dry and wet processes starts with the core logic of process design, which directly determines the operation mode of all subsequent links. The core logic of the wet process is "solvent carrier-mediated dispersion", which requires the use of organic solvents to uniformly mix active materials, conductive agents, and binders into a slurry, then remove the solvent through coating, drying and other links, and finally form the electrode sheet. Essentially, it is a multi-step process of "first dissolution and dispersion, then drying and shaping". The dry process completely breaks the dependence on solvents, with the core logic of "dry mixing + physical molding". It directly achieves uniform dispersion of various dry powder raw materials through mechanical shearing and high-speed mixing, and then composites them onto the current collector through physical methods such as calendering and spraying, without solvent participation. The process is simpler and more efficient, making it a typical "green process" route.

This difference in core logic not only leads to huge differences in equipment configuration and energy consumption between the two processes, but also affects the microstructure of the electrode sheet and the final performance of the battery — the wet process is prone to collapse of the electrode sheet's micropores due to solvent volatilization, while the dry process can retain a more complete pore structure of the active material, providing a smoother channel for ion transport.

II. Detailed Disassembly of the Entire Process: Differences in Each Step, Simplicity vs. Complexity

From raw material input to finished electrode sheet output, the dry and wet processes are divided into different core links. The operation details, technical requirements, and equipment needs of each link have significant differences, which are disassembled and compared one by one in the order of the process below.

(1) Raw Material Pretreatment Link: Simple Mixing vs. Fine Dispersion

The core goal of raw material pretreatment is to achieve uniform integration of active materials, conductive agents, and binders, laying the foundation for subsequent molding. The difference in operation complexity between the two processes initially appears here.

The raw material pretreatment of the dry process is extremely simple, requiring only two steps: "dry powder mixing + fibrillation". First, active materials (such as high-nickel ternary, silicon-based materials), conductive agents (such as carbon nanotubes), and dry binders (mainly PTFE, polytetrafluoroethylene) are put into high-speed mixing equipment in proportion, and initial uniform dispersion is achieved through mechanical shear force; then, the PTFE is stretched into fibers through continuous shearing, forming a three-dimensional fiber network that tightly wraps the active material and conductive agent particles to form a stable powder composite. No solvent is added during the entire process, and only the mixing speed, shear force, and mixing time need to be controlled to avoid agglomeration of raw material particles. The pretreatment equipment mainly includes high-speed mixers and shearing machines, which have a simple structure and small floor space.

The raw material pretreatment of the wet process is much more complex, with the core link being "slurry making", which is a key control point of the wet process. The first step is to dissolve the binder (such as PVDF) in a specific organic solvent (NMP is commonly used for the positive electrode, which is toxic and volatile), and stir until completely dissolved to form a uniform binder solution; the second step is to gradually put the active material and conductive agent into the solution, and through multiple processes such as low-speed stirring, high-speed dispersion, and vacuum defoaming, the dry powder raw materials are uniformly dispersed in the solvent, and finally a slurry with qualified solid content, viscosity, and dispersibility is formed — the solid content is usually controlled at 40%-70%, the viscosity needs to adapt to the subsequent coating requirements, and there should be no bubbles or agglomerates in the slurry, otherwise the electrode sheet quality will be seriously affected. The pretreatment equipment needs to be equipped with dissolution kettles, high-speed dispersers, vacuum defoamers, etc., with a long equipment chain. In addition, the temperature and humidity of the workshop need to be strictly controlled to prevent excessive solvent volatilization or slurry moisture absorption and deterioration.

(2) Core Molding Link: Physical Calendering vs. Coating and Drying

The molding link is the core step of converting the pretreated raw materials into the initial electrode sheet, and also the link with the most significant difference in the process flow of the two processes, directly determining the thickness, density, and bonding strength of the electrode sheet.

The molding link of the dry process is simple and efficient, with the core being "deposition/calendering + hot pressing composite", without the need for a drying step. There are two mainstream processes: one is electrostatic spray deposition, in which the pretreated powder composite is uniformly attached to the surface of the current collector (aluminum foil, copper foil) through electrostatic spray technology, using electrostatic adsorption to reduce powder loss, and then transported to hot rolls for hot pressing. The temperature of the hot rolls can activate the binder, enabling the dry powder particles to form sufficient bonding strength with the current collector; the other is roller calendering, in which the dry powder composite is directly put between a pair of oppositely rotating rolls, and a self-supporting film with a certain thickness and density is formed through high-pressure calendering of 100-200MPa, then hot-pressed and composited with the current collector to form a continuous dry-coated electrode film. The entire molding process only needs to control the calendering pressure, hot roll temperature, and conveying speed to obtain the initial electrode sheet, which is time-saving and low-energy-consuming, and can achieve a higher active material loading rate — usually more than 95%, far higher than that of the wet process.

The molding link of the wet process is divided into three steps: "coating - drying - solvent recovery", with a cumbersome process and high energy consumption. The first step is coating, in which the pretreated slurry is uniformly coated on the surface of the current collector through doctor blade coating, transfer coating and other methods. The coating thickness needs to be precisely controlled (the deviation is usually at the micrometer level) to ensure uniform thickness of the electrode sheet; the second step is drying, in which the coated current collector is sent to a drying tunnel dozens of meters long, and the solvent in the slurry is gradually evaporated through high-temperature heating at 120-150℃, so that the dry powder raw materials and binders are solidified on the surface of the current collector to form a dry initial electrode sheet — the drying speed needs to match the coating speed, which not only ensures sufficient solvent volatilization, but also avoids electrode material performance degradation caused by excessive temperature; the third step is solvent recovery, the volatile organic solvents (such as NMP) during the drying process need to be collected, purified and recycled through recovery devices, otherwise it will not only increase costs, but also emit VOCs (Volatile Organic Compounds), causing environmental pollution. This link needs to be equipped with large-scale equipment such as coating machines, long-distance drying tunnels, and solvent recovery systems, with a large floor space, and the energy consumption of the drying link accounts for more than 30% of the total energy consumption of electrode sheet preparation.

(3) Post-Processing Link: Simple Cutting vs. Calendering and Cutting

The core goal of the post-processing link is to process the initial electrode sheet into a finished electrode sheet that meets the requirements of battery assembly. The operation difference between the two processes is relatively small, but it is still affected by the previous links.

The post-processing of the dry process is extremely simple, requiring only two steps: "cutting + dust removal". Since the thickness and density of the dry electrode sheet have basically reached the standard after calendering and molding, no additional calendering process is needed. The electrode sheet is directly cut into the required size and shape through cutting equipment, and then the floating powder on the surface of the electrode sheet is removed through dust removal equipment to avoid short-circuit hidden dangers during subsequent assembly, and the finished electrode sheet can be obtained — only slight edge polishing is needed subsequently, no other processing is required, the process is simple, and the loss is low.

The post-processing of the wet process requires three steps: "calendering - cutting - dust removal". The initial electrode sheet after drying has low density and high porosity, so it needs to be calendered first through calendering equipment, and a certain pressure is applied to thin and compact the electrode sheet, improve the volume energy density of the electrode, and enhance the bonding firmness between the active material, conductive agent and current collector — the calendering density is usually controlled at 3.5-4.0g/cm³, which is adjusted according to the battery performance requirements; the calendered electrode sheet is then cut and dedusted to obtain the finished electrode sheet. It should be noted that the calendering force of the wet electrode sheet cannot be too large, otherwise it will damage the micropore structure of the electrode sheet, affect the ion transport efficiency, and lead to the decrease of battery cycle life.

III. Chain Reactions Caused by Process Differences: Performance, Cost, and Environmental Protection

The differences in the entire process between the dry and wet processes are not simply "complexity vs. simplicity", but also directly lead to chain differences in battery performance, production cost, and environmental friendliness, which in turn determine their respective applicable scenarios.

In terms of performance, relying on the solvent-free advantage, the dry process has higher electrode sheet calendering density and higher active material loading rate, and the corresponding battery energy density can be increased by 10%-20%. In addition, the three-dimensional fiber network formed by the binder can better buffer the volume expansion of the silicon-based negative electrode, resulting in better cycle stability — the capacity retention rate of the silicon-based negative electrode after 1000 cycles can reach 85%, far exceeding 70% of the wet electrode sheet; however, the consistency of the dry electrode sheet is poor, it is prone to powder loss, and has extremely high requirements on equipment accuracy. The wet process, relying on mature dispersion and coating technology, has good electrode sheet consistency and flat surface, and the battery rate performance is more stable. However, solvent residue may lead to an increase in electrode interface impedance, and the drying link is prone to damage the micropore structure, so the energy density and cycle stability are slightly inferior to those of the dry process.

In terms of cost, the dry process eliminates the links of solvent purchase, drying, and recovery, reducing the production cost of single GWh electrode sheets by 15%-20%, with less equipment investment, smaller plant floor space, and 40% lower energy consumption; however, the dry process is difficult to mass-produce, and currently only a few enterprises can achieve large-scale production, and the mass production cost still has room for optimization. The wet process has high hidden costs. Each 1GWh lithium battery electrode sheet production requires more than 500 tons of NMP solvent, and the investment in solvent recovery equipment accounts for 15%-20% of the total cost of the production line. In addition, the drying link has high energy consumption, so the comprehensive production cost is higher than that of the dry process. However, it has high mass production maturity, with a yield rate stably above 95%, and significant scale advantages.

In terms of environmental protection, the dry process does not involve solvents throughout the entire process, has no VOCs emissions, and does not require investment in solvent treatment costs, making it a typical green process that conforms to the "dual carbon" goal; the wet process uses toxic organic solvents, which will cause environmental pollution if not properly treated. It requires a lot of funds to build solvent recovery and waste gas treatment systems, with great environmental pressure. In addition, there will still be a small amount of loss during the solvent recovery process, which has potential environmental hazards.

IV.Process Differences Determine Adaptation Directions, and Collaborative Development Promotes Industrial Upgrading

The differences in the entire process between the lithium battery dry process and wet process are essentially the differences between the "traditional mature route" and the "innovative green route" — the wet process is characterized by "multi-links, high energy consumption, and high maturity", achieving precise dispersion through solvent mediation, adapting to the mass production needs of large-scale, high-consistency power batteries and energy storage batteries, and is still the mainstream of the industry; the dry process, with the advantages of "simple process, low energy consumption, and high performance", breaks through the bottleneck of the wet process through solvent-free physical molding, and is more suitable for high-end scenarios such as high-energy density power batteries and high-end energy storage batteries, making it the core direction of future process upgrading.

With the continuous iteration of technology, the mass production problems of the dry process have gradually been solved, and the solvent recovery efficiency and energy consumption level of the wet process have been continuously optimized. The two processes are not substitutes for each other, but develop collaboratively — the wet process consolidates the mid-to-low-end mass production market, and the dry process seizes the high-end upgrading market. The process optimization and technological integration of the two will jointly promote the lithium battery industry to develop in the direction of "higher energy, lower cost, and better environmental protection", providing core support for the upgrading of the new energy storage and new energy vehicle industries.