Comprehensive Guide to Lithium Battery Pack Production Process Standards
Lithium battery packs are critical components in electric vehicles, energy storage systems, and consumer electronics, where their performance and safety directly impact operational reliability. This guide provides a detailed overview of the production process standards for lithium battery packs, covering key stages from material preparation to final assembly and testing.
Material Preparation and Mixing Standards
Cathode Material Preparation
The cathode material consists of active substances, conductive agents, and binders. The production process begins with material inspection and pre-treatment:
Conductive Agent Baking: Typically, conductive agents require baking at approximately 120°C for 8 hours to remove moisture.
Binder Baking: Polyvinylidene fluoride (PVDF), a common binder, needs baking at around 80°C for 8 hours.
Active Material Inspection: Depending on the raw material state, active substances like lithium iron phosphate (LFP) or nickel-cobalt-manganese (NCM) may require drying to eliminate moisture.
During the mixing process:
Temperature Control: The mixing tank should be maintained at ≤30°C, with a vacuum level of ≤-0.085 MPa.
Stirring Parameters: The dispersion line speed should be ≥17 m/s, with strict control over the addition sequence and ratio of materials.
Quality Inspection: Regular checks on particle size and viscosity are essential, as these parameters significantly impact battery performance.
Anode Material Preparation
The anode material preparation process is similar to that of the cathode but involves additional dispersants due to the water-based mixing system:
Water Quality Control: The conductivity of deionized water used in the mixing process should be ≤1 μS/cm.
Mixing Process: The process includes dry mixing of graphite and conductive agents, followed by the addition of a binder solution. The final step involves adding styrene-butadiene rubber (SBR) under specific stirring conditions to maintain the polymer chain integrity.
Quality Parameters: The viscosity of the anode slurry should range from 2000 to 4000 mPa·s, with a particle size of ≤35 μm and a solid content of 40-70%.
Coating and Drying Standards
Cathode Coating
The cathode slurry is coated onto aluminum foil using an extrusion or spray coating method:
Coating Density: The single-sided coating density ranges from 20 to 40 mg/cm² for NCM power-type batteries.
Drying Temperature: The drying oven is divided into multiple sections, with temperatures ranging from 95°C to 120°C, adjusted according to the material and process requirements.
Quality Control: The coating thickness should be uniform, with a moisture content of ≤2000-3000 ppm after drying.
Anode Coating
The anode slurry is coated onto copper foil using a similar method:
Coating Density: The single-sided coating density is approximately 10-15 mg/cm².
Drying Temperature: The drying oven sections are set between 80°C and 105°C, depending on the process needs.
Quality Control: The coating should be free from cracks and solvent droplets, with a moisture content of ≤3000 ppm.
Calendaring and Slitting Standards
Calendaring Process
After drying, the coated electrodes undergo calendaring to improve particle contact and reduce thickness:
Calendaring Method: Both hot and cold pressing methods are used, with hot pressing offering higher compaction density and lower rebound rates.
Quality Parameters: The compaction density, rebound rate, and elongation should be controlled within specified limits to ensure uniform electrode thickness and surface quality.
Slitting Process
The calendared electrodes are then slit into strips of the required width:
Edge Quality Control: The slitting process must minimize burrs, with regular inspection using secondary element measurement devices to ensure burr lengths are within acceptable limits.
Environmental Control: The workshop environment should be maintained at ≤23°C with a dew point of ≤-30°C to prevent moisture absorption and contamination.
Electrode Preparation and Assembly Standards
Electrode Preparation
After slitting, the electrodes undergo further processing, including drying, welding of tabs, and tab insulation:
Drying Temperature: The drying temperature for cathode electrodes is typically 120°C, while for anode electrodes, it ranges from 105°C to 110°C.
Tab Welding: The length and shape of the tabs should be carefully controlled to ensure proper alignment and secure welding.
Tab Insulation: High-temperature adhesive tape is used to insulate the tabs, preventing short circuits caused by metal burrs or debris.
Cell Assembly
The prepared electrodes are then assembled into cells through a series of steps:
Winding or Stacking: Depending on the battery type, the electrodes and separator are wound or stacked to form the cell core.
Tension Control: Proper tension control during winding is crucial to prevent short circuits or breakage due to excessive or insufficient tension.
Alignment Control: The relative positions of the anode, cathode, and separator must be accurately aligned to ensure proper lithium-ion transport and prevent short circuits.
Final Assembly and Testing Standards
Cell Insertion and Sealing
The assembled cell cores are inserted into metal casings and sealed:
High-Potential Test: Before insertion, the cells undergo a high-potential test (200-500V) to detect any high-voltage shorts.
Dust Control: The cells are cleaned to remove dust and debris, minimizing the risk of internal short circuits.
Sealing Process: The cells are sealed using welding or crimping methods, ensuring a tight and secure fit.
Electrolyte Injection and Formation
After sealing, the cells are injected with electrolyte and undergo a formation process:
Electrolyte Injection: The electrolyte is injected under controlled conditions to ensure uniform distribution and minimize air bubbles.
Formation Process: The cells are charged and discharged under specific conditions to activate the electrodes and form a stable solid electrolyte interface (SEI) layer.
Final Testing and Quality Control
The final step involves comprehensive testing and quality control measures:
Electrical Performance Testing: The cells undergo tests for voltage, internal resistance, and capacity to ensure they meet specified performance criteria.
Safety Testing: The cells are subjected to safety tests, including overcharge, short-circuit, and over-discharge tests, to verify their compliance with safety standards.
Traceability and Documentation: Each cell is assigned a unique identification code, and detailed production records are maintained for traceability and quality control purposes.
By adhering to these production process standards, manufacturers can ensure the consistent quality, performance, and safety of lithium battery packs, meeting the demands of various applications in the electric vehicle, energy storage, and consumer electronics sectors.
