A Complete Guide to the 18650 Cylindrical Cell Manufacturing Process

The 18650 cylindrical lithium‑ion cell remains one of the most widely used battery formats in industrial electronics, medical devices, IoT systems, power tools, and energy‑storage applications. Its popularity comes from its stable structure, high energy density, and mature manufacturing technology. Behind every high‑performance 18650 cell is a rigorous production process that ensures safety, consistency, and long cycle life.

This article provides a comprehensive, engineering‑level overview of the entire 18650 cell manufacturing process, based on PKCELL’s production standards and quality‑control system.

Slurry Preparation: The Foundation of Cell Performance

Cathode Slurry (NCM System)

Cathode materials such as NCM, conductive additives, binders, and solvents are mixed in a controlled sequence. Key parameters include:

• Mixing speed and duration
• Cooling‑water temperature
• Iron‑removal efficiency (Cu/Ni < 100 ppm)
• Cleanliness of the mixing tank

A uniform slurry ensures stable capacity, low internal resistance, and long cycle life.

Anode Slurry (Graphite System)

Graphite, conductive agents, CMC, SBR, and solvents are blended under strict moisture control to maintain consistency and adhesion.

 Coating: Precision Determines Capacity Consistency

The prepared slurry is coated onto copper (anode) or aluminum (cathode) foil using a high‑precision coating machine.

Critical specifications:

• Copper foil thickness: 10 ± 2 μm
• Aluminum foil thickness: 16 ± 2 μm
• Surface uniformity without streaks, dents, wrinkles, or powder drops
• Coating speed: 10 m/min

Uniform coating directly affects energy density and safety.

Calendering: Increasing Density and Structural Stability

Calendering compresses the coated electrode to achieve the required density and thickness.

Key parameters:

• Cathode pressure: 130–170 t
• Anode pressure: 100 t
• Thickness control:
  • Cathode: 135–140 μm
  • Anode: 180 ± 3 μm (1st pass), 158 ± 3 μm (2nd pass)

Proper calendering improves conductivity, reduces internal resistance, and enhances cycle performance.

Slitting and Electrode Drying

After calendaring, electrodes are slit into precise widths and then baked to remove moisture.

Drying conditions:

• Cathode: 75°C for 8 hours
• Anode: 65°C for 10 hours

Moisture control is essential to prevent gas generation and performance degradation.

Winding: Forming the Core of the 18650 Cell

The cathode, anode, and separator are wound into a cylindrical jelly‑roll structure.

Quality requirements:

• Anode overlaps cathode by 1 ± 0.7 mm
• Separator fully covers the anode by 1 ± 0.5 mm
• Tab welding strength ≥ 15 N
• Winding must be tight and uniform

Winding accuracy directly affects safety and internal resistance.

Cell Assembly: Insertion, Grooving, and Pre‑Bake

The wound cell core is inserted into the steel can, grooved for structural stability, and baked under vacuum.

Pre‑bake conditions:

• 85°C
• Vacuum: –0.085 to –0.1 MPa
• Duration: 4 hours

This step ensures the cell is completely dry before electrolyte filling.

 Electrolyte Filling: A Critical Step for Performance

Electrolyte moisture content must be extremely low:

• ≤ 20 ppm

Typical fill volume for a 2600 mAh 18650 cell:

• 5.3 ± 0.2 g

Electrolyte quality determines SEI formation, cycle life, and safety.

Sealing, Cleaning, and Traceability

After filling, the cell undergoes:

• Laser welding
• Multi‑stage sealing
• Two rounds of cleaning
• Shell coding and traceability marking

Each cell receives a unique code for full production tracking.

 Formation and Aging: Activating the Cell

Formation is the first controlled charge of the battery, creating a stable SEI layer.

Conditions:

• 0.2C CC/CV charge for 420 minutes
• Temperature monitoring to detect abnormal cells

After formation:

• Room‑temperature storage
• High‑temperature aging (42–48°C for 3 days)
• Voltage and internal‑resistance testing

This stage determines the long‑term stability of the cell.

 Capacity Grading and Final Inspection

Cells undergo:

• Capacity grading (sorting by performance)
• X‑ray alignment inspection
• Final appearance check
• Heat‑shrink labeling
• Packaging and warehousing

Only cells that pass all tests enter the final shipment stage.

Conclusion: High‑Precision Manufacturing Ensures High‑Performance 18650 Cells

The production of 18650 cylindrical cells involves dozens of tightly controlled processes. Every step—from slurry preparation to formation—directly affects the cell’s safety, consistency, and lifespan.

With advanced equipment, strict quality control, and full traceability, PKCELL delivers high‑reliability cylindrical cells for global industrial and OEM applications.