How lithium-ion batteries are manufactured - From cell to battery pack manufacturing

Introduction

MOTOMA Lithium-ion batteries are widely used in everything from smartphones and laptops to electric vehicles and solar energy storage systems. Despite their everyday appearance, the internal manufacturing process is incredibly complex, involving dozens of precise steps, cleanroom conditions, and advanced automation. This article offers a comprehensive walk-through of how lithium-ion batteries are made—based on actual industry process flowcharts and material formulations.

Part 1: Electrode Slurry Preparation

Electrode slurry is the “foundation” of any lithium-ion battery. Both the cathode and anode start as pastes made from a blend of active materials, conductive agents, binders, and solvents.

Cathode Slurry Composition:

• Active material: Lithium cobalt oxide (LiCoO₂), NMC, LFP
• Binder: PVDF (Polyvinylidene fluoride) — gives mechanical strength
• Conductive agent: Acetylene black (ensures electronic conductivity)
• Solvent: NMP (N-Methyl-2-pyrrolidone) — dissolves PVDF for uniform mixing

Anode Slurry Composition:

• Active material: MCMB (Mesocarbon microbeads graphite)
• Binder: PVDF
• Conductive agent: Acetylene black
• Solvent: NMP

Equipment & Steps:

1. Vacuum planetary mixer: Mixes the slurry in a vacuum environment to avoid moisture and oxidation.
2. Filtration: Removes agglomerates or foreign particles.
3. Viscosity control: Final slurry viscosity is fine-tuned for optimal coating thickness.

Part 2: Electrode Sheet Fabrication

Once the slurries are ready, they are used to create the actual cathode and anode sheets.

Key Steps:

1. Coating 

   

   • Slurry is coated uniformly on both sides of aluminum foil (for cathode) or copper foil (for anode) using precision coating machines.
   • Drying ovens immediately follow to remove the solvent (NMP).
2. Calendering 

   

   • Coated foils are compressed through heated rollers.
   • This increases density, improves adhesion, and enhances battery energy density.
3. Slitting 

   

   • Wide rolls are cut into narrow electrode strips of desired width using slitting machines.
4. Tab Welding & Notching 

   

   • Laser equipment is used to:
     • Cut the electrodes to cell dimensions.
     • Weld metal tabs onto electrode ends (current collectors).
     • Punch slots or shapes as needed for stacking or winding.

Part 3: Cell Assembly

This stage transforms prepared electrode sheets into functional battery cells. The method of assembly depends on the cell format—which plays a crucial role in energy density, mechanical stability, and application suitability.

Cell Format Differences

For Pouch Cells:

• Assembly Method: Electrode sheets are stacked layer by layer in the order of cathode → separator → anode.
• Structure: Flat and flexible, enclosed in a laminated aluminum pouch.
• Advantages: Lightweight, thin, ideal for tablets, smartphones, and drones.

For Cylindrical Cells:

• Assembly Method: Long electrode sheets are rolled into a jelly-roll spiral, like a Swiss roll, with separator sheets in between.
• Structure: Rigid metal casing (e.g., 18650, 21700).
• Advantages: High mechanical strength, automated production, commonly used in power tools and electric vehicles.

Assembly Process Steps:

1. Stacking / Winding 

   

   • Stacking machines are used for pouch and prismatic cells.
   • Winding machines create cylindrical jelly-rolls under tight control.
2. Tab Welding & Terminal Connection 
   • Tabs are welded to current collectors via laser welding.
   • Weld quality is critical for minimizing internal resistance.
3. Enclosure 
   • The electrode assembly is placed inside a casing:
     • Pouch cell: Aluminum laminated film
     • Cylindrical cell: Stainless steel or aluminum tube
4. Electrolyte Injection 

   

   • Liquid electrolyte (typically LiPF₆ in EC/DEC) is injected into the cell inside a vacuum glove box to eliminate moisture contamination.
5. Vacuum Sealing 
   • After electrolyte soaking, pouch cells are sealed under vacuum; cylindrical cells are crimped with metal caps.
   • Any air residue could reduce performance or cause swelling.
6. Drying 

   

   • Cells are placed into a vacuum oven at elevated temperatures (e.g., 60–85°C) to evaporate trace solvents and stabilize the internal structure.

Visual Recap

Expert Note

• Cylindrical cells excel in production speed and mechanical durability.
• Pouch cells offer better space utilization and energy density in compact electronics.

Part 4: Electrochemical Formation & Aging

Key Steps:

1. Formation 

   

   • The battery is charged and discharged under controlled currents.
   • This forms the Solid Electrolyte Interphase (SEI) on the anode, protecting it from degradation.
2. Aging
   • Cells are stored for several days at elevated temperatures.
   • This helps stabilize internal chemistry and voltage.
3. Grading and Testing
   • Capacity, voltage, IR (internal resistance), and leakage current are measured.
   • Defective cells are rejected.

Part 5: Battery Pack Assembly 

Qualified cells are grouped and turned into battery packs for various applications.

Key Components:

• PCM/BMS board: Prevents overcharge, over-discharge, short circuits.
• Thermal sensors and fuses: For safety monitoring
• Plastic shell, heat sinks, or aluminum case

Final Tests:

• Charge/discharge cycling
• High-temp and low-temp performance
• Drop tests, overcurrent simulation

Only certified packs are released to the market.

Simplified Flowchart of Lithium-ion Battery Manufacturing

The process of making lithium-ion batteries involves high-precision equipment, strict environmental control, and careful attention to chemical and mechanical details. From slurry mixing to battery pack testing, every step is engineered to ensure safety, consistency, and performance.

With ongoing innovation—MOTOMA technology, such as solid-state electrolytes, dry electrode processes, and AI-based quality control—the future of lithium battery manufacturing is becoming even more efficient, safe, and sustainable.