In the lithium battery production line, the roll pressing process of Cathode and Anode is like an “ice and fire” — Cathode material is rolled under the hot roller at 80~120℃, while Anode material is “cooled and shaped” in the cold pressure at room temperature “. This difference in temperature is not a coincidence, but a combination of material properties and process requirements.
I. Cathode Hot Roller Press
1. Activation of binder
Cathode materials (e.g. ternary material NCM, lithium iron phosphate LFP) have high hardness and low surface energy of active substance particles, which have weak bonding force with binder (e.g. PVDF). The high temperature of the hot roller (80~120℃) is like “magic”, awakening the fluidity of the binder, making it wrap the active material like melted honey, and significantly improving the bonding strength of the electrode. Experimental data shows that the peeling strength of Cathode cathode can be increased by more than 30% after hot roll, effectively avoiding powder fall or delamination problems.
2. Leap in compaction density
The energy density of Cathode directly determines the battery’s range. During the hot roll process, the high temperature reduces the elastic modulus of the material, making the particles more prone to plastic deformation. Taking a power battery as an example, the compacted density of Cathode after hot rolling is raised from 2.5g/cm³ to 3.0g/cm³, and the energy density is increased by 20% synchronously, which is equivalent to “injecting more energy” into the battery.
3. “Highway” for Ion Transportation
The high temperature also optimizes the pore structure inside the electrode. SEM images show that the Cathode particles are tightly aligned after the hot roll, the number of micropores is reduced by more than 50%, the lithium-ion transmission path is shortened, and the battery’s fast-charging performance is improved by 30%. It’s like widening a country road into a highway.
II. Anode Cold Pressing
1.Stabilize graphite laminated structure
The lamellar structure of Anode materials (e.g. natural graphite) is extremely sensitive to temperature. Cold pressing (at room temperature or low temperature) can avoid the expansion of interlayer spacing or structural collapse caused by high temperature. Experiments show that the capacity decay rate of graphite Anode after high-temperature roll pressing is 15% higher than that of cold pressing, and the cold pressing process provides a stable channel for lithium ion embedding/de-embedding between graphite layers.
2. “Precise control” of binder
SBR+CMC binder commonly used in Anode can optimize the bonding effect at room temperature. Cold pressing avoids excessive softening of the binder, so that the precision of electrode thickness is controlled within ±1μm. Data from a factory shows that the thickness consistency of cold-pressed Anodes is 40% higher than that of hot rollers, providing “millimeter-level” precision for subsequent battery cell assembly.
3. Anode “firewall”
Anode is prone to generate SEI film during the charging process, and high temperature will accelerate the decomposition of electrolyte, leading to the instability of SEI film. Cold pressing controls the temperature below 30°C, the uniformity of SEI film thickness is increased by 50%, and the battery cycle life is extended to more than 1500 times. This is like putting a “bulletproof vest” on the battery to resist the “attack” of side reactions.
III. The “precision calculation” behind the process
1. “Balance” of equipment and cost
Hot rollers need to be equipped with a heating system, which increases energy consumption by 30%, but the total cost can be reduced by reducing the subsequent baking process. Cold pressing equipment is simple and suitable for mass production. After a GWh-class plant adopted cold pressing process, Anode production capacity increased by 50%.
2. Thickness difference
Cathode is usually 30% thicker than Anode, which requires higher pressure and temperature to assist compaction. The hot roller pressure can reach 10MPa, while the cold pressing pressure is only 3MPa. The combination of the two realizes the effect of “thick but not scattered, thin but not cracked”.
3. Industry-proven “Golden Rule”
Head enterprises such as Ningde Times and BYD have verified through millions of cycle tests that Cathode hot-negative-cooling process can increase battery energy density by 25% and prolong cycle life by 40%, which has become the industry’s default “standard formula”.
IV. Exceptions and the Future: Breaking the Mold
1. “Special treatment” for silicon-based Anodes
Silicon-based Anode requires hot rollers (100~150℃) to assist in stress relief due to volume expansion rate as high as 300%. Data from a laboratory shows that the cycle life of hot roller silicon-based Anode is 200% higher than that of cold pressing, but the cost increases by 15%, which is currently mainly used in high-end power batteries.
2. Intelligent “temperature revolution”
The new roller press is equipped with AI temperature control system, which can dynamically adjust the heating power according to the battery electrode real-time temperature. After the introduction of this technology in a factory, the energy consumption of hot rollers was reduced by 20%, and the thickness deviation was narrowed to ±0.5μm, realizing the process control “accurate to every degree”.
3 The “New Challenge” of Solid State Batteries
Solid state batteries use sulfide electrolytes, which need to be cold-pressed (<50°C) to avoid electrolyte decomposition. An enterprise developed all-solid-state batteries through the cold pressing process, interface impedance reduced by 50%, energy density exceeded 400Wh/kg, for the next generation of batteries to show the way.
From 18650 to 4680 large cylindrical batteries, from liquid to solid systems, the roll pressing process is always the “gatekeeper” of battery performance. The temperature difference between Cathode and Negative Cold is not only a compromise of material properties, but also the ultimate pursuit of energy efficiency by human beings.
In the future, with the integration of AI, new materials and intelligent equipment, battery manufacturing will enter the era of “nanoscale precision”, and this “ice and fire” will still be the protagonist in the center stage.
