The pursuit of higher energy density and lower cost in lithium ion batteries continues to stretch the limits of manufacturing technology. The slurry based electrode process has supported the industry for decades yet its limitations—energy intensive drying, solvent recovery, electrode cracking at greater thickness and high capital cost—are increasingly apparent. Dry process electrode technology offers a compelling alternative by removing solvents and the challenges they bring.

In this new paradigm calendering takes on a central role. No longer a routine finishing stage, it becomes the decisive step where the dry electrode’s microstructure, strength and electrochemical performance are defined. Companies such as ULTPRE, also known as Shanghai Ultra Press Hydraulic Equipment Co., Ltd., are developing the precision hydraulic systems that make this transformation possible.

The dry electrode process

To see why calendering matters one must look at the process itself, which differs fundamentally from the traditional sequence of mixing, coating, drying then calendaring.

1. Dry mixing: Active material, conductive carbon and PTFE binder powder are blended into a uniform mixture.

2. Fibrillation: The mixture is exposed to shear in mills or extruders which causes PTFE particles to fibrillate into a fine web binding the components together.

3. Lamination: The fibrillated dry film is hot pressed onto a current collector foil.

Often it is the calendering rolls that perform both the final fibrillation and the lamination. They are therefore the true centre of the dry process line.

Calendering as transformation

In dry processing calendering achieves far more than compaction. It delivers:

• Densification to increase volumetric energy density

• Porosity control to maintain a connected network for ion transport

• Adhesion enhancement to ensure strong bonding with the current collector

• Surface finish to provide smoothness and uniform thickness for cell assembly

Unlike wet calendering which compresses a coated layer, dry calendering must simultaneously compress powder, complete fibrillation and laminate film to foil. That multi objective challenge is what makes it so critical.

ULTPRE’s Precision Hydraulic Systems

Founded in 2024 by Bob and Edward, ULTPRE draws on decades of hydraulic expertise with the aim of building a globally respected Chinese brand. The company focuses on delivering systems that combine efficiency, safety and reliability for industries where precision is paramount.

In dry electrode calendering ULTPRE’s advanced hydraulics are designed to provide control at microscopic scales. Its servo motor driven planetary gear systems actuate precision plunger pumps feeding hydraulic cylinders. By integrating non leak solenoid valves to prevent pressure drift and enabling oil output volumes as low as 8 ml, ULTPRE’s designs can deliver roll position accuracy to within tenths of a micrometre. That level of stability is essential to control electrode density and porosity without damaging fragile fibrillated structures or active particles.

Critical Parameters

1. Linear PressureThis is the key driver for density. Too little pressure yields poor adhesion and high resistance. Too much pressure risks pore collapse and particle fracture which restricts ion transport. ULTPRE’s stable hydraulics enable precise control within this narrow window.

2. Roller SpeedSpeed dictates dwell time under pressure. Lower speeds allow fibrils to align and binder to stretch, creating stronger networks. Excessive speed risks uneven density and poor contact. Synchronisation of roll speed and pressure is essential.

3. TemperatureHeating rolls softens PTFE making it viscoelastic. This lowers required pressure, reduces risk to fragile materials such as high nickel NMC or silicon, improves binder distribution and strengthens lamination. Precision at lower force ranges is particularly important here.

4. Number of PassesMulti pass calendering at gradually higher pressures or temperatures is often superior to a single heavy pass. It avoids closing surface pores and promotes uniform density throughout the electrode. The repeatability of ULTPRE’s systems allows identical performance across each pass.

Optimisation and challenges

The ultimate challenge is balancing electronic conductivity through particle contact with ionic conductivity through preserved pores. This balance often resembles a “Goldilocks curve” where performance peaks at an optimal porosity.

Material type also matters. Brittle chemistries such as LNMO or expanding ones such as silicon require softer, hotter protocols. More robust materials like LFP tolerate stronger compaction.

Optimisation must be systematic. A design of experiments approach that maps input settings—pressure, speed, temperature—against outputs such as density, porosity and adhesion, then against battery metrics such as cycle life and impedance, is essential. Inline monitoring using lasers or ultrasonics ensures closed loop quality control at scale.

Looking Ahead

The success of dry electrode technology will depend on mastery of calendering. ULTPRE’s innovations in hydraulic control point to the direction of travel. The future will likely include:

• Protocols tailored for solid state batteries where solid solid contact is critical
• Smart calendering systems that apply AI and machine learning for adaptive control
• Specialised strategies for lithium metal anodes, sulphur cathodes and other emerging chemistries

Calendering in dry electrode production has evolved into a sophisticated engineering process where control of force, heat and time determines performance. With its expertise in hydraulic precision ULTPRE is positioning itself at the heart of this transition. By enabling ultra fine stability and repeatability ULTPRE’s systems promise to unlock the full potential of dry electrode technology, paving the way for the next generation of high performance batteries.

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