I. Preparation of materials and equipment
Core materials
Battery cells: must be from the same batch, capacity difference ≤3%, internal resistance difference ≤5mΩ (ternary/lithium iron phosphate is recommended)
Protection board (BMS): supports quadruple protection of overcharge/overdischarge/overcurrent/short circuit (threshold accuracy ±0.5%)
Structural parts: nickel strip (thickness ≥0.2mm), high temperature resistant wire (silicone insulation layer), flame retardant PVC heat shrink tube
Auxiliary materials
Epoxy resin thermal conductive glue (filling the gap between battery cells)
Highland barley paper (ear insulation isolation)
Double-sided tape (3M VHB series)
Tool list
Spot welding machine (power ≥ 5kW)
Constant temperature soldering station (temperature range 200-400℃)
Antistatic bracelet (impedance 1MΩ)
Multimeter (accuracy ±0.5%)
Second, seven-step precision assembly process
Cell sorting and pairing
Measure the open circuit voltage of each cell (deviation ≤ 0.01V)
Internal resistance test (DC internal resistance meter, difference ≤ 3%)
Capacity pairing (0.5C discharge to cut-off voltage, capacity difference ≤ 2%)
Ear tab pretreatment
Scrape off the oxide layer of the ear (laser cleaning or sandpaper polishing)
Tin plating (tin layer thickness 0.05-0.1 mm)
Series/parallel welding
Series: nickel strip spot welding (pressure 200N, time 3ms)
Parallel: copper bar laser welding (melting depth ≥0.3mm)
Key quality inspection: solder joint pull-out force ≥50N
BMS system integration
Voltage sampling line welding (line sequence error ≤1mm)
MOSFET heat dissipation (apply thermal conductive silicone grease)
Function test: simulated overcharge (4.25V cut-off), over-discharge (2.8V cut-off)
Structural packaging
Filling thermal conductive glue between cells (thickness 1.0±0.2mm)
Barley paper wrapped pole ear (prevent short circuit)
Bracket fixation (anti-vibration design) =Measurement, amplitude ≤0.5G)
Insulation protection
Double-layer heat shrink tube packaging (inner layer 125℃ temperature resistance, outer layer flame retardant)
Hot air gun process: 120℃ uniform heating, shrinkage ≥30%
Port sealing: injection molding epoxy resin (waterproof IP67)
Aging test
Charge and discharge cycle 3 times (0.5C charge/1C discharge)
Temperature rise monitoring (surface temperature ≤55℃)
Internal resistance change rate detection (ΔR＜5%)
Five major safety operation prohibitions
Electrical safety
Reverse connection of positive and negative poles is strictly prohibited (reverse voltage＞1V triggers protection fuse)
Disconnect BMS connection during welding (to prevent static electricity from breaking down IC ）
Thermal management
When the spot welding temperature is greater than 250℃, the single point duration is less than 10ms
Forced air cooling is required for ambient temperature greater than 30℃
Mechanical protection
The threshold for cell extrusion deformation is 5% of the thickness (if exceeded, it will be scrapped)
Drop test height limit: ≤1m (hard ground)
Storage specification
Semi-finished product storage voltage: 3.8V±0.05V
Humidity control: RH45-65% (to prevent electrolyte from hygroscopicity)
Scrap treatment
Discharge to 0V (salt water immersion method: 5% NaCl solution for 24h)
Physical destruction: puncture and release pressure first, then disassemble and recycle
Material selection technical indicators
Components Preferred solution Key parameters
Cathode material NCM811 (power type) Specific capacity ≥ 200mAh/g
Anode material Artificial graphite + 5% silicon carbon First efficiency > 92%
Electrolyte LiPF6 + FEC additive Conductivity > 10mS/cm (25℃)
Separator Ceramic coating PE base film Closed cell temperature 135℃
Casing PC-ABS alloy Flame retardant grade V0
Fault prevention and maintenance
Cycle life optimization
Charge upper limit: 4.15V (extends life by 40% compared to 4.2V)
Discharge lower limit: 3.2V (avoids deep lithium precipitation)
Storage maintenance
Long-term storage: recharge to 3.8V every 3 months
Environmental requirements: temperature 15-25℃, humidity <60%
Abnormal diagnosis
Bulging threshold: immediately stop using if thickness increases by >3%
Voltage difference abnormality: single cell voltage difference >0.1V requires equalization
Technology outlook: The use of intelligent BMS can realize real-time monitoring of SOH (health), with a prediction error of <5%. Modular design increases the efficiency of battery cell replacement by 300%, and the electrolyte injection link will be eliminated in the future solid-state battery assembly, greatly reducing environmental requirements.
