Battery electrode calendering process

What is calendering：

Calendering of battery electrodes is an important step in the production process of lithium-ion batteries, and its purpose is to obtain electrodes that meet design requirements. Calendering is a necessary process. After the electrode coating and drying, the peeling strength between the active material and the current collector foil is low. At this time, it needs to be calendering to enhance the bonding strength between the active material and the foil to prevent it from peeling off during electrolyte immersion and battery use.

The purpose of calendering:

The calendering process keeps the surface of the electrode smooth and flat. It can prevent battery short circuit caused by burrs on the electrode surface piercing the separator and improves the energy density of the battery. The calendering process can compact the electrode material coated on the electrode current collector, thereby reducing the volume of the electrode, increasing the energy density of the battery, and improving the cycle life and safety performance of the lithium battery.

Once calendering and secondary calendering:

Once calendering means rolling only once to make the electrode reach the designed thickness and density.

Secondary calendering is to first roll the electrode to a certain thickness, and then achieve the designed thickness and density through the second rolling.

Difference:

Once calendering can easily lead to cracking and pulverization of active particles, and the pore diameter above the electrode (away from the copper foil) will be larger than the pore diameter below the pole piece (close to the copper foil).

Secondary calendering not only reduce the breakage of active particles as much as possible, but also make the pore size distribution in the pole pieces uniform, thus promoting the infiltration of electrolyte and ultimately improving the performance of the battery.

Hot calendering and cold calendering：

Cold calendering technology: There is no heating measure during the rolling press process, and the temperature change is not controlled manually.

Hot calendering technology: Calendering technology that preheats the processed materials and uses a heating roller with high-precision temperature control to roll the processed materials.

Advantages of hot rolling technology:

As the temperature of the rolled electrode rises, the binder in the electrode coating softens, the deformation resistance is reduced, and compaction is easy, making the surface thickness of the pole piece more uniform.

Therefore, through precise temperature control, heated roller technology has the following advantages:

(1) Reduce the processing pressure and the rolling force can be reduced by up to 62%.

(2) Reduce electrode rebound by about 50%, effectively increasing the volume density of the battery.

(3) Enhance the bonding force between the coating material and the current collector, reduce damage to the binder in the battery electrode, and effectively improve the cycle life.

(4) Absorb the heat during the rolling process and improve the consistency of the battery.

(5) Reduces the internal resistance of the battery and many other advantages.

At present, flat plate pressing technology has been eliminated by the market, and cold calendering technology has been developed for a long time, and the technology is mature and has been mass-produced in the market. Compared with cold calendering technology, high-precision hot calendering technology has many advantages such as reducing pressure, reducing battery material loss, extending cycle life, and improving battery consistency. Therefore, heated calendering technology may be the main development direction of calendering technology in the future.