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Manufacturing Process of Prismatic Lithium-Ion Batteries

2025-09-29

Manufacturing Process of Prismatic Lithium-Ion Batteries



Lithium-ion batteries are composed of multiple components, including positive and negative electrodes, separators, electrolytes, current collectors, binders, and conductive additives. Their operation involves electrochemical reactions at the electrodes, ionic and electronic conduction, and heat transfer within the cell.

The general manufacturing process of lithium-ion batteries consists of the following major steps:

  1. Slurry Preparation: Mixing active materials, binders, and conductive agents into a uniform slurry.

  2. Coating & Drying: Applying the slurry onto aluminum or copper foil current collectors, followed by drying to remove solvents.

  3. Calendering & Cutting: Densifying the electrode coating via calendering, then slitting or cutting it to size.

  4. Cell Assembly: Stacking or winding electrodes and separators into a cell structure, injecting electrolyte, and sealing.

  5. Formation & Testing: Charging and discharging to activate the cell, followed by inspection and grading to produce finished batteries.

Based on cell format, lithium-ion batteries can be categorized as prismatic, cylindrical, or pouch cells. The manufacturing workflow can be divided into three main stages:

  • Front-end: Electrode preparation

  • Middle: Cell assembly

  • Back-end: Formation and testing



🧪 1. Front-End Process – Electrode Manufacturing

The front-end stage focuses on producing the positive and negative electrode sheets. Main processes include slurry mixing, coating, calendering, slitting, and die cutting. 

Key equipment: mixers, coating machines, calendering rollers, slitters, and die cutters.


① Slurry Mixing

This step involves dispersing active material powders, conductive carbon, binders, additives, and solvents into a homogeneous suspension under controlled conditions. 

The slurry’s formulation, viscosity, dispersion uniformity, stability, and adhesion directly impact battery performance.

  • Mixing elements: Wetting, dispersing, and stabilizing.

  • Blade types: Serpentine, butterfly, paddle, spherical, and gear.

    • Serpentine, butterfly, and paddle blades are used for difficult dispersions or initial mixing.

    • Spherical and gear types are for easier dispersions with better uniformity.

  • Mixing speed: Higher speed improves dispersion but may damage materials or equipment.

  • Viscosity: Lower viscosity improves dispersion but excessive thinning causes sedimentation.

  • Vacuum: Helps remove trapped air, improving dispersion.

  • Temperature: Proper temperature improves fluidity; too hot causes skinning, too cold increases resistance.

High-quality mixing is the foundation for precise coating, calendering, and ultimately for battery safety and electrochemical performance.


② Coating

The slurry is evenly applied on aluminum (cathode) or copper (anode) foils and dried to form electrode sheets.

  • Pump speed and die gap thickness control coating thickness.

  • Drying removes solvents and ensures firm adhesion of the active layer.
    The coating process strongly affects cell consistency, safety, and lifespan, making the coating machine one of the most critical pieces of equipment.


③ Calendering

Electrodes are compressed to:

  • Improve contact between active material and current collector

  • Reduce internal resistance

  • Increase energy density and volumetric utilization


④ Slitting

Electrode rolls are slit into uniform widths according to cell design.


⑤ Die Cutting

Anode and cathode sheets are cut into specific shapes with precise tab spacing using mechanical or laser die-cutting methods.

 2. Middle Process – Cell Assembly

The assembly stage transforms electrodes and separators into functional cells.
Prismatic and cylindrical cells typically use a winding process, while pouch cells use stacking.

Main steps:
Winding → Hot pressing → X-ray inspection → Cell pairing → Tab welding → Ultrasonic welding → Insulation placement → Cell insertion → Lid welding → Leak testing → Vacuum baking → Electrolyte filling → Soaking.


① Winding

Positive and negative electrodes and separators are wound into a jelly roll.

  • Prismatic winding demands precise tension control to avoid misalignment, burrs, or tab folding.

  • Automated tension control and edge correction systems ensure dimensional accuracy.


② Hot Pressing

Hot pressing shapes the jelly roll, removes internal air, eliminates separator wrinkles, and improves contact between electrodes and separators, thereby lowering internal resistance and improving uniformity.
Key parameters: pressure, temperature, pressing time.


③ X-ray Inspection

Ensures dimensional accuracy and detects internal defects before sealing.


④ Cell Pairing

For multi-roll (multi-JR) prismatic cells, multiple jelly rolls are stacked to achieve higher capacity and reduce scrap rates.


⑤–⑦ Welding & Shell Insertion

  • Soft tab welding: Connects electrode tabs to current collectors.

  • Ultrasonic welding: Ensures good electrical contact with minimal heat damage.

  • Shell insertion: Cells are inserted into aluminum cases with insulation pads to prevent short circuits.


⑧–⑫ Final Assembly Steps

  • Lid welding seals the case.

  • Leak testing (often helium-based) ensures airtightness.

  • Vacuum baking removes residual moisture.

  • Electrolyte injection introduces electrolyte for ionic conduction.

  • Soaking/Standing allows electrolyte to fully penetrate electrodes, typically under controlled temperature conditions.


 3. Back-End Process – Formation and Testing

At this stage, the cell structure is complete. The purpose is to activate, test, and grade the cells to ensure safety and performance.

Main steps:
Formation & capacity grading → Laser cleaning → Sealing pin welding → Cleaning → Dimensional inspection.


① Formation & Capacity Grading

  • Cells undergo the first charge, during which the SEI (Solid Electrolyte Interphase) layer forms on the anode.

  • This is a crucial step for ensuring safety, capacity, and cycle life.

  • Cells are aged for 2–3 weeks, then defective cells are rejected, and remaining cells are capacity graded and packaged.


②–⑤ Final Finishing

  • Laser cleaning: Cleans injection ports to ensure weld quality.

  • Pin welding: Seals the cell under inert gas.

  • Surface cleaning & measurement: Ensures appearance and dimensional consistency.



Conclusion


The above outlines the standard manufacturing process of prismatic lithium-ion batteries. Each stage — electrode preparation, cell assembly, and formation/testing — plays a critical role in determining final battery quality, performance, and safety. High-precision equipment, process control, and material consistency are key to producing reliable, high-performance lithium-ion batteries.

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