Part 1: In-depth analysis of the technical level of dry electrode 1, process introduction and material comparison between dry and wet process The traditional wet process is to mix the active substance, conductive agent and adhesive in proportion in the solvent, and coat the current collector surface and roll it through the slit coating die. The dry process is to add the adhesive after the active particles, conductive agent and dry mixing are homogeneous, and a self-supporting film is formed under the action of the adhesive fibrillation, and finally rolled to cover the surface of the current collector. 
2.2. Principle of fibrillation dry process technology Temperature and shear are important factors affecting PTFE fibrillation. When the temperature is above 19 degrees, PTFE changes from triclinic to hexagonal, and the molecular chain becomes softer, which is the main reason for the formation of fibrils. Fibrillated film making is the front stage of electrode sheet rolling, and the mainstream fibrillated film making machines are: 1) jet mill; 2) Screw extruder; 3) Open mill. After the PTFE is well mixed with the active substance, the mixture is fed into the fibrillated film making machine, where the mixture forms a self-supporting film under the roller pressure of the machine. Maxwell experimental data shows that the smaller the feed velocity, the greater the impedance of the fibrillated electrode membrane; At the same time, the impedance of the electrode film decreases as the rolling force increases. 
1. The dry process cost is lower, and the manufacturing cost is reduced by 18%.
The dry process is more environmentally friendly and more suitable for large-scale production. NMP (N-methylpyrrolidone) solvents are toxic, environmentally unfriendly, and need to be applied in traditional wet processes, which consumes a lot of energy. The dry process does not require solvents, reduces baking and solvent in the electrode coating process, the process flow is simpler, the equipment covers a smaller area, and is more suitable for the large-scale production of pole pieces. 
Dry electrodes are subject to PTFE fibrillation and can achieve a flatter topography than wet electrodes. Since the wet process requires a solvent, after the solvent evaporates, more voids are left between the active material and the conductive agent, resulting in a low compacted density of the material. The dry method does not have a drying process, so there are no voids left after solvent evaporation, and the contact between the particles is tighter. 
Dry electrodes can achieve greater compaction densities. After compaction under dry conditions, there are fewer problems such as cracks and micropores. Lithium iron phosphate compaction density can be from 230 g cm3 to 305 g cm3, an increase of 3261%；The compaction density of ternary materials can be from 334 g cm3 to 362 g cm3, an increase of 838%。The compacted density of the graphite anode can be reduced from 163 g cm3 to 181 g com3, an increase of 1104%。Due to the higher active material per unit volume, dry electrodes also have a technical path to achieve greater energy density. Under the same conditions, the energy density of dry process batteries can be increased by up to 20%. According to Maxwell's experimental data, dry electrodes can have energy densities of more than 300 Wh kg, with the possibility of achieving 500 Wh kg. The thickness limit of the dry electrode is larger, which can increase the surface capacity. The thickness limit of the conventional wet electrode coating is 160 m, while the thickness range of the dry process is 30 m to 5 mm. A wider range of thicknesses also allows for a wider variety of active substances. 
3. The electrical performance of the dry process battery is better, and the cycle performance, durability and impedance of the dry process battery are better under laboratory conditions. Since there is no actual industrial production data yet, this article cites the first public data of "Preparation and Performance of Solvent-free Dry Electrode for Lithium-ion Batteries". 
The fiber mesh improves the material stability of the dry electrode, which in turn enhances the electrical properties. In the wet process, after 500 cycles of the battery, the internal stresses of the active particles accumulate and cause cracks in the profile, ultimately reducing the performance of the battery. In the dry process, the fiber mesh is coated on the surface of the active material, and after 500 cycles of charging and discharging, the mesh structure remains intact and there are fewer cracks on the surface of the particles, while the fibrillated mesh structure can inhibit the volume expansion of the active material, prevent the particles from falling off the current collector, enhance the stability and improve the electrical properties. 
3. Application of dry electrode in the next generation of batteries 1. Solid-state battery & dry electrode: abandon traditional liquid raw materials, but all face the problem of solid-solid interfaceSolid-state battery is the next generation of lithium battery, abandoning traditional liquid electrolyte. Dry electrodes do away with traditional liquid solvents and are similar to solid-state batteries. With the empowerment of dry technology, the electrode piece manufacturing process of solid-state batteries can be completely dried, eliminating the problem of residual solvent molecules after wet process drying. In addition, the use of the fibrillation effect of the adhesive to make a solid electrolyte film can improve the performance of solid-state batteries: The film-forming is solvent-free, which improves the ionic conductivity The solid electrolyte and the adhesive are dry-blended to form a film, which does not require drying and the manufacturing cost is lower The process is simple and more suitable for large-scale mass production.
2. Pre-lithiation & dry electrode: Regardless of the compatibility of pre-lithiation materials and solvents, the pre-lithiation strategy is used to alleviate the lithium-ion loss in the first cycle of the battery. Lithium ions react with the negative electrode to form a SEI film, resulting in an irreversible loss of 6%-15% of lithium ions. The pre-lithium strategy prefers a dry electrode production environment. Under the wet process, the solvent will have a side reaction with the pre-lithium additive, which consumes the active lithium, increases the battery impedance and weakens the pre-lithium effect, and the dry process does not require solvent, and the dry production environment is more suitable for the needs of the pre-lithiation strategy.
Fourth, the technical difficulties and comprehensive comparison of dry electrodes.
The dry electrode process is a comprehensive upgrade compared to the traditional wet process. In terms of manufacturing process, there are fewer dry electrode steps, lower manufacturing cost and energy consumption, and the raw materials are environmentally friendly, which is more suitable for large-scale production. In terms of battery performance, dry batteries can achieve higher energy density, and the electrical and mechanical properties of the battery are better. On the application side, dry-process batteries are more suitable for the manufacturing needs of new generation batteries such as solid-state batteries and 4680.
Part II: Dry electrode binders.
PTFE reacts with lithium ions on the surface of the anode to form lithium fluoride, weakening the adhesion and reducing the capacity. A single gram of PTFE consumes about 1070mAh of lithium, and the higher the PTFE content in the battery, the more lithium is consumed. In the experiment, after excluding the influence of the formation of SEI film by charging and discharging in the first week, the higher the PTFE content in the second discharge curve, the smaller the discharge current, so it was confirmed that PTFE would react with lithium ions and affect the performance of the battery. Passivation of the adhesive is achieved by coating the surface of PTFE with conductive carbon. According to Tesla's patent, the coating material consists of electrical conductors (conductive carbon, carbon black, etc.) and granular materials (powdered carbon materials). The coating covers more than 90% of the surface of the PTFE particles, with a thickness of 01-100μm。The coating has the following functions: as a conductor to strengthen the electrical conductivity of the active substance, to modify the PTFE surface to improve the stability of the adhesive, and as a passivation material to inhibit the decomposition of materials such as electrolytes. After fibrillation of PTFE, the coating remains attached to the particle surface due to intermolecular interactions.
2. The self-supporting film formed after fibrillation of mixed non-fibrillated materials will still have the problem of reduced adhesion of active substances and adhesives, and the shedding of active materials will lead to an increase in the internal resistance of the battery and affect the performance of the battery. Mixing PTFE with non-fibrillated materials improves electrode membrane performance. Traditional non-fibrillated materials (e.g., PVDF, CMC) can be ground into smaller particle size materials and mixed with PTFE to form new adhesives. Tesla's patent has a 1:1:2 mass ratio of the blend of PVDF, CMC, and PTFE. Smaller particle sizes allow for a more uniform distribution of the electrode membrane actives, while smaller particle sizes allow for stronger adhesion.
3. The demand for PTFE for dry electrodes.
Part 3: Dry electrode processing equipmentThe mainstream self-supporting membrane manufacturing equipment is divided into jet mill, screw extruder and open mill. Jet mill has the highest efficiency, screw extruder has the highest yield Jet mill: After compressed air is injected into the pulverizer chamber at high speed through the nozzle, the active substance and binder mixture reach the pulverizer through the feed port. The mixture collides with each other under the action of high-pressure air flow to achieve fibrillation, and finally, the mixture rises with the air flow to the grading cavity to form a self-supporting film under the action of roller pressing equipment. Jet mills work the most efficiently. Screw extruder: After the mixture enters the screw filling groove from the material opening, it will be continuously compacted, stirred and mixed on the inner wall of the barrel and the surface of the screw under the action of the rotating screw. At the end of the compression section, the screw will extrude the evenly mixed material out of the head as required, where the mixture will be molded into an electrode film and sent away from the extruder, and the screw extruder has the highest yield.
Large-scale and integrated equipment is the future development trend. The functions of feeding, mixing, fibrosis, film making, rolling, slitting, and winding are integrated together to reduce turnover time, improve efficiency and consistency, etc., and increase the value of equipment. Tesla's calendering and trimming machine has a rolling part similar to an open mill. After unloading at the head of the machine, the mixture enters the rollers in the direction of the belt, and because the rollers downstream rotate faster than upstream, the high shear forces between the roll seams squeeze and mix the active material, conductive agents and adhesives. The self-supporting film formed by fibrillation adheres to the faster rollers downstream and is repeatedly calendered. The metering roller on the side of the machine can control the speed and temperature of the roller, and a slitting system will be set up at the rear of the machine to cut the formed wide electrode film into a narrow electrode film according to the requirements. Double-sided coating and current collector composite lamination machine is a collection of positive and negative electrode film production, electrode film and current collector lamination and pole piece winding, the essence of which is a calendering and trimming composite machine. The advantages of the calendering and trimming machine are: improving the efficiency of electrode production, reducing the circulation time of electrode pieces between equipment, reducing powder loss, better control of product yield, improving consistency, better detection of the thickness of electrode pieces, rolling uniformity and other indicators, double-sided coating and current collector composite lamination machine is a collection, positive and negative electrode film production, electrode film and current collector lamination and pole piece winding, the essence is a calendering and trimming composite machine.
Dry electrode is a comprehensive upgrade compared with traditional wet electrode PTFE, a new adhesive required for dry electrode, has a huge market space Equipment integration: large-scale equipment integrates functions such as feeding, mixing, fibrosis, film making, rolling, slitting, and winding, reducing circulation time, improving efficiency and consistency, and the equipment value is higher.