Exploring Dry Electrodes: Ushering in a New Era of Battery Manufacturing

In the field of battery manufacturing, innovations in electrode preparation processes have always been a key driver of industry development. Traditional wet electrode processes have long dominated, but with technological advancements and evolving market demands, their drawbacks are becoming increasingly apparent. Against this backdrop, dry electrode processes have emerged, offering unique advantages and bringing new ideas and solutions to battery manufacturing.

I. The Dilemma of Traditional Wet Electrode Processes

Traditional lithium-ion batteries use wet slurry coating processes to manufacture electrodes, which involves a relatively complex procedure. First, active materials, conductive agents, and binders (such as PVDF) are mixed into solvents like N-methyl-2-pyrrolidone (NMP) to form a uniform slurry. This slurry is then coated onto current collectors, followed by a lengthy drying process to remove solvents, and finally, the toxic NMP solvent is recovered. This series of steps is not only cumbersome but also costly. Specifically, the coating, drying, and solvent recovery stages account for 22.76% of equipment, labor, and factory costs, and 53.99% of energy costs.

Moreover, wet processes present several issues that affect electrode performance. For example, residual solvents in electrodes can react with electrolytes over time, reducing capacity, generating gas, and shortening lifespan. During solvent evaporation, binders and conductive agents may float and accumulate near the surface, while active materials settle, causing electrode stratification. This impairs the formation of a 3D conductive network and weakens the bond between active materials and current collectors. Additionally, wet coatings are prone to cracking during drying, especially for thick electrodes, limiting their thickness due to process constraints.

II. Analysis of Dry Electrode Processes

(1) Process Principles

Dry electrode processes eliminate the need for solvents, relying entirely on dry-state operations. The core principle involves preparing electrode materials through physical processing: first, active materials, binders, and conductive agents are mixed as dry powders in high-speed mixers. Shear and friction forces break up particle agglomerations, creating a uniform mixture. Next, rolling equipment compresses the mixture into thin films, with precise control of roller pressure and speed to adjust film thickness and uniformity. Finally, the electrode film is laminated with current collectors via hot rolling, using the adhesive properties of PTFE (polytetrafluoroethylene) to form a strong interface bond, resulting in a complete electrode structure. Post-lamination, rolling and cutting processes ensure uniform electrode density and standard dimensions.

(2) Process Steps

Dry Powder Mixing: Active materials, binders (e.g., PTFE), and conductive additives are thoroughly mixed to form a final powder blend. Ensuring uniform distribution of components at this stage lays a critical foundation for subsequent processes.

Powder-to-Film Formation: The powder mixture is extruded and calendered using rolling equipment to form continuous, self-supporting dry electrode films, which can also be rolled into coils. By adjusting processing conditions (temperature, pressure, speed), material loading and film thickness are precisely controlled, enabling the production of various dry electrode structures.

Film-Current Collector Lamination: The thin electrode layer is pressed onto current collectors to form battery pole pieces. Parameters such as pressure and temperature during lamination significantly impact pole piece quality and performance.

(3) Key Equipment

Jet Mills: These use high-pressure airflow to crush and fibrillate materials. Compressed air is injected into the grinding chamber at high speed, causing particles to collide, fragment, and fibrillate. The processed material is then rolled into films in a classification chamber. Jet mills offer high efficiency, meeting large-scale production needs.

Screw Extruders: These integrate mixing, stirring, compaction, and blending functions. After being mixed, compacted, and blended by the screw, the material is extruded from the die to form electrode films. Screw extruders boast high yield rates, ensuring consistent film quality.

Open Mills: These use the speed difference between two rollers to generate shear forces, breaking molecular chains. Materials are repeatedly processed between rollers to form electrode films. Precise control of roller pressure, temperature, and material residence time is required to ensure film performance.

High-Speed Mixers: These blend dry powders (active materials, binders, conductive agents) using intense shear and friction forces to break agglomerations, ensuring uniformity and reliability for subsequent steps.

Rolling Equipment: Includes machines for pressing electrode materials into films and hot rollers for laminating films with current collectors. High precision is critical—for example, Shanghai Lianjing’s hot rollers use electromagnetic induction heating, with roller accuracy controlled to ±0.001mm (@RT) and ±0.005mm (@PT), and roller surface temperature variation within ±1℃—ensuring uniform film thickness and high strength.

III. Advantages of Dry Electrodes

(1) Cost Reduction

Equipment and Energy Costs: By eliminating wet process steps (coating, drying, solvent recovery), dry processes drastically reduce equipment footprint and energy consumption. Data shows dry processes lower production costs by ~20% and reduce equipment investment by 35% compared to wet processes.

Material Costs: Dry electrodes use lower-cost PTFE binders, often in smaller quantities. Additionally, eliminating solvent procurement, transportation, storage, and waste disposal further cuts expenses.

(2) Performance Improvements

Energy Density: Dry processes compact powders directly into films, achieving higher compaction density and reducing cracks and pores. For example, lithium iron phosphate compaction density increases from 2.30g/cm³ to 3.05g/cm³ (+32.61%); ternary materials and graphite anodes improve by 8.38% and 11.04%, respectively. This allows batteries to store more energy in the same volume: dry-process batteries achieve 20% higher energy density than wet-process counterparts, with potential to exceed 500 Wh/kg.

Cycle Performance and Stability: Lab tests show dry-process batteries outperform wet-process versions in cycle life, durability, and impedance. After 500 charge-discharge cycles, wet-process battery active particles develop cracks due to stress buildup, degrading performance. In dry electrodes, PTFE’s fibrous network acts as a robust "shield," tightly encapsulating active materials. This network remains intact through repeated cycles, inhibiting active material expansion and detachment, ensuring long-term stability.

Conductivity and Capacity: Without solvents, dry electrode binders exist as fibers, making only point contact with active particles and preserving interparticle connections. This enhances conductivity and facilitates Li⁺ intercalation/deintercalation, boosting capacity and high-rate discharge performance. Four-point probe tests show dry graphite anode sheet resistance is 4.66mΩ—26% lower than wet-process equivalents.

(3) Environmental Benefits

Dry processes eliminate toxic NMP solvents, preventing solvent evaporation and emission of hazardous gases/wastewater, significantly reducing environmental impact. In an era of stricter environmental regulations, this aligns closely with sustainable development goals.

(4) Process Compatibility

Adaptation to New Battery Technologies: Dry electrodes are highly compatible with next-gen technologies like solid-state batteries, prelithiation, and 4680 large cylindrical cells. For example, solid-state batteries (which avoid liquid electrolytes) benefit from dry processes’ elimination of solvent residues. For sulfide electrolytes (sensitive to solvents), dry electrodes’ PTFE 2D network inhibits active material expansion, preventing detachment and enhancing safety. Dry processes also support prelithiation, avoiding solvent-prelithium additive reactions, improving first-cycle efficiency and energy density, and stabilizing electrode structures by pre-forming SEI layers.

Material Versatility: Dry processes have demonstrated stability and versatility with commercial anode materials (e.g., silicon-based, LTO) and cathode materials (e.g., layered NMC, NCA, LFP, sulfur).

IV. Application Fields

(1) Lithium-Ion Battery Manufacturing

Dry electrodes produce high-performance positive and negative pole pieces, optimizing structure and performance to enhance energy density, cycle life, and charge-discharge capabilities. This meets demands for high-performance batteries in electric vehicles, energy storage systems, and portable electronics.

(2) Other High-Energy Battery Systems

Beyond lithium-ion batteries, dry processes show potential in sodium-ion, potassium-ion, and other emerging battery technologies. Their unique advantages could improve performance and reduce costs for these new systems.

(3) Fuel Cell Membrane Electrode Preparation

In fuel cells, dry processes enable precise control of electrode thickness and uniformity, enhancing catalyst layer performance and improving fuel cell efficiency and lifespan.

V. Challenges and Solutions

(1) Process Optimization Challenges

Despite advantages, dry processes face optimization hurdles, such as improving self-supporting film quality and stability to ensure strong particle bonding in 3D networks. Solutions include:

(2) Equipment Development Challenges

Dry processes demand high-performance equipment, some of which currently struggles to meet large-scale production needs (e.g., roller precision and stability for uniform film thickness/strength). Addressing this requires:

(3) Material Performance Enhancement

Key materials like PTFE binders require improved fibrillation and uniformity to boost electrode performance. Solutions include:

VI. Future Outlook

As new energy vehicles and energy storage industries boom, demands for battery performance continue to rise. Dry electrode processes—with their low cost, superior performance, strong compatibility, and environmental benefits—are emerging as a key driver of battery technology transformation. While challenges remain in large-scale application, advancements in materials science, equipment manufacturing, and process optimization are poised to resolve these issues.

In the near future, dry electrode processes are expected to see widespread adoption in battery manufacturing, gradually replacing traditional wet processes. This will deliver batteries with longer range, faster charging, lower environmental impact, and reduced costs—propelling the entire battery industry and related sectors into a new era of development.