Standard production process flow for polymer lithium-ion batteries (LiPo batteries).
2026-07-20
Production Process Flow for Polymer Lithium-Ion Batteries
Stage 1: Electrode Preparation
- Material Mixing (Slurry Mixing)
- Positive electrode: Active material (LiCoO₂, NMC, LFP, etc.), conductive agent (carbon black), binder (PVDF), and solvent (NMP) are mixed into a homogeneous slurry.
- Negative electrode: Active material (graphite, silicon-carbon), conductive agent, binder (SBR, CMC), and solvent (deionized water) are mixed.
- Coating
- The positive slurry is coated onto aluminum foil; the negative slurry onto copper foil. This is done using a slot-die or transfer coating machine to achieve uniform thickness.
- Drying
- Coated electrodes pass through a long oven to evaporate the solvent completely.
- Calendering (Roll Pressing)
- Dried electrodes are compressed between high-pressure rollers to achieve the target density and porosity, ensuring good adhesion.
-
Slitting & Notching
- The large electrode sheets are slit into narrower strips of the required width. The positive and negative tabs are then cut (notched) to allow later tab welding.
Stage 2: Cell Assembly (Pouch Cell)6. Tab Welding
- Metal tabs (aluminum for positive, nickel or nickel-plated copper for negative) are ultrasonically welded onto the respective electrode current collectors.
- Separator Preparation
- A porous polymer separator (e.g., PP, PE, or coated separator) is cut to size, slightly larger than the electrodes.
- Stacking (Z-fold or Laminating)
- Electrodes and separators are alternately stacked in a precise sequence: Negative electrode → Separator → Positive electrode → Separator → Negative electrode... (for a bipolar design). Alternatively, a Z-fold winding method may be used.
-
Pouch Forming
- The aluminum laminated pouch film is formed (deep-drawn) into a pocket to hold the stacked electrode core.
- Core Insertion & Tab Sealing
- The stacked electrode core is inserted into the formed pouch. The top and side seals (except the electrolyte filling side) are heat-sealed, leaving the tab area sealed and one side open.
Stage 3: Formation & Finishing
- Vacuum Baking
- The sealed semi-finished cells are baked at a high temperature under vacuum to remove residual moisture (critical for preventing HF formation).
- Electrolyte Filling
- In a dry room (dew point < -40°C to -60°C), electrolyte (lithium salt LiPF₆ in organic solvents) is injected into the cell through the remaining opening.
- Final Sealing (Vacuum Sealing)
- The cell is placed in a vacuum chamber to remove gases and ensure electrolyte penetration, then the final side is heat-sealed.
- Wetting (Soaking)
- The filled cells are allowed to rest for several hours to days at elevated temperature to ensure complete electrolyte absorption into all electrode pores.
-
Pre-charge & Formation
- The cells undergo a low-current (C/20 to C/10) initial charge on a formation cycler. This creates the solid electrolyte interface (SEI) layer on the negative electrode, which is crucial for stability and safety.
- During formation, gases (ethylene, etc.) are produced. The pouch may bulge.
- Degassing & Secondary Sealing
- The gas-filled cell is pierced in a vacuum chamber, the internal gas is evacuated, and the area is immediately heat-sealed (forming the final "degas seal").
- Aging
- Cells are stored at room or elevated temperature (e.g., 45°C) for several days to stabilize the SEI and detect self-discharge or micro-shorts.
- Trimming & Visual Inspection
- Excess pouch film and tabs are trimmed to final dimensions. Visual inspection checks for pinholes, corrosion, or poor seals.
Stage 4: Testing & Packaging
- Capacity Grading (Sorting)
- Cells undergo one or more full charge-discharge cycles (e.g., 1C/1C) on automated test equipment. Actual capacity, internal resistance (ACIR), and voltage are recorded.
- Self-Discharge Measurement
- Cells are fully charged and stored for a defined period (e.g., 7 days), then voltage drop is measured to identify defective cells.
- OCV & Insulation Test
- Open-circuit voltage and insulation resistance (between tabs and pouch foil) are checked.
- Dimension & Appearance Check
- Automated vision systems or manual gauges verify thickness, width, length, and tab alignment.
-
Packaging
- Cells are packed into trays with anti-static material, vacuum-sealed with desiccant, or placed into final consumer packaging.
Key Supporting Processes (Not shown in main flow but critical)
- Electrolyte Preparation (Mixing solvents and LiPF₆ in a dry/glovebox environment)
- Separator Coating (e.g., ceramic coating for thermal stability)
- Battery Management System (BMS) attachment (for multi-cell packs)