Abstract: This paper summarizes the operational and inspection standards for key processes throughout the entire production workflow of lithium battery PACKs. Covering every stage from incoming cell inspection to finished product shipment, the guidelines aim to ensure the safety, consistency, and reliability of the battery packs.
I. Incoming Inspection and Pre-processi
1. Full Visual Inspection Standards for Battery Cells
Cylindrical Cells: Inspect for the absence of short circuits, oxidation or rust, missing or misaligned face pads, ruptured films, film wrinkles, and similar defects.
Prismatic (Square) Cells: Inspect the surface for the absence of electrolyte residue, burrs, or other contaminants; check for no leakage, bulging, deformation, or short circuits. Face pads must be free of misalignment or lifting; composite nickel strips must show no signs of oxidation, contamination, or detachment (cold solder joints).
Polymer Cells: Inspect the surface for the absence of electrolyte residue or other contaminants; check for no leakage, gas expansion (swelling), or deformation. Ensure the electrode tabs are intact (not broken), corners are undamaged, and folded edges show no signs of delamination.
2. Standards for Applying Face Pads to Battery Cells
Requirements: The face pads must be adhered firmly, without misalignment or lifting, and must not extend beyond the edges of the cell's end face. Furthermore, they must not cover the negative terminal rivet on aluminum-cased cells, nor the positive terminal cap on steel-cased cells.
3. Standards for Electrical Performance Testing of Battery Cells
Test Method: Utilize equipment such as multimeters/multifunctional test fixtures, battery internal resistance testers, etc. Conduct the test by bringing the positive and negative terminals of the battery cell into contact with the corresponding polarity pins on the test fixture.
Polarity Identification: For steel-cased cells, the cap serves as the positive terminal, while the casing serves as the negative terminal. For aluminum-cased cells, the rivet serves as the negative terminal, while the casing serves as the positive terminal.
II. Battery Cell Assembly and Connection Processes
1. Standards for Cell Bonding and Assembly
Scope of Application: Applicable to cylindrical battery cells configured in multi-parallel and series arrangements, utilizing adhesive or double-sided tape for bonding.
Process Requirements: The end faces of adjacent cells being bonded together must be flush (aligned). Prior to applying adhesive, an insulating material-such as high-temperature-resistant tape-must be applied to the bonding surface of at least one of the cells (covering a height no lower than the end face) to prevent short circuits during subsequent spot welding. The adhesive must be dispensed evenly into the gaps between cells and must not overflow onto the end faces of the cells.
2. Welding Process Standards
Soldering Standards:
The soldering time for protection board leads/plugs must be ≤ 3 seconds.
Requirements: The solder joint must completely encapsulate the wire tip, with no defects such as cold joints, desoldering, bridging, solder dross, solder spikes, component detachment, or wire insulation burns.
Spot Welding Standards:
Welding of Battery Cells to Nickel Strips:
Prismatic Cells: Spot weld 2 points on the negative terminal rivet; spot weld 4 points on the positive terminal composite nickel strip (avoiding the laser-welded points located at both ends).
Cylindrical Cells: Spot weld 4 square-shaped points on both the positive and negative terminals; on the negative terminal, avoid the central circular area with a diameter of approximately 4mm.
Polymer Cell Tabs: For nickel strips with a width of 3mm or less, spot weld 2 points; for widths greater than 4mm, spot weld 4 points.
Welding of Protection Board to Nickel Strips:
Prerequisite: A nickel-plated steel sheet must be affixed to the solder pads on the protection board.
The weld joints must be secure, with no arcing/sparking or desoldering. The number of weld points is determined by the pad size: 2 points for pads measuring 4mm x 4mm or smaller; 4 points for pads larger than 4mm x 4mm.
III. Insulation and Safety Protection
Insulation Tape Application Standards：
This is a critical process for preventing short circuits; insulation protection must be applied at the following locations:
Between the contact surface of the protection board and the battery cell.
At locations on the protection board where conductors of different polarities (nickel sheets, solder pads, circuit traces) may overlap with plugs or leads.
At specific structural points on steel-cased or aluminum-cased cells (e.g., bent nickel strips, exposed rivet terminals) where short circuits could potentially occur.
When connecting cells in parallel or series, insulating materials-such as integrated insulation pads, barley paper, or high-temperature tape-must be applied between adjacent cells and between series-connected terminal faces.
For longer leads of differing polarities within the battery pack, the exposed wire cores must be covered with heat-shrink tubing or wrapped with insulation tape to prevent accidental contact and short circuits.
IV. External Packaging and Final Assembly
1. PVC Heat-Shrink Film Application Standards
Film Application: Adjust the length of the heat-shrink film according to the shape of the battery pack; the overhang length at the flat ends may differ from that at the curved ends by 1–3mm to ensure complete encapsulation. Heat Shrinking: The finished product must be flat and smooth after heat shrinking, free from wrinkles, film ruptures, or skewed edges, and must not expose the internal battery cell, protection board, or wire cores.
2. Battery Housing/Frame Assembly and Ultrasonic Bonding Standards
Housing Assembly: The protection board must be accurately snapped into the designated positioning structure within the plastic housing or frame, followed by the insertion of the battery body. The assembly must be fully seated and properly aligned, free from any shifting, tilting, or misalignment.
Ultrasonic Bonding: Used for fusing the upper and lower housing shells. The weld seam must be uniform, free from excess material overflow or misalignment, and must not cause compression damage or thermal burns to the housing surface or internal metal components.
V. Identification, Testing, and Final Inspection
1. Coding and Labeling Standards
Coding: Content typically includes the company logo, battery cell model, capacity, voltage, and production date. The content must be accurate, the text clear and legible, and free from broken characters or misalignment.
Labeling: Categorized into three types: full-wrap labeling, plastic housing labeling, and PVC film labeling. The label placement must be accurate and free from tilting, air bubbles, impurities, creases, peeling edges, or similar defects.
2. Performance Testing Standards
Basic Parameters: Testing covers voltage, internal resistance, overcurrent protection, short-circuit protection, NTC/ID functions, etc. All parameters must comply with process specifications (e.g., voltage range of (3.75~4.15) * N, internal resistance increase not exceeding 20%).
Aging Test: For multi-series/parallel battery packs, a specific charge-discharge regimen (e.g., 0.5C charging, 0.2C discharging) is used to verify functionality, capacity, and stability. Particular attention must be paid to ensuring correct polarity during connection.
Special Functions: For "smart" batteries, specific functions such as communication protocols, program writing, and code locking must be tested.
ACEY-BA3020-18 Battery Aging Machine is designed for evaluating the aging characteristics of various battery types, including ternary, lithium iron phosphate, lead-acid, and nickel-metal hydride/nickel-cadmium.
3. Finished Product Appearance Inspection Standards
Plastic Housing Type: Inspect the housing for any damage or deformation; verify that the weld seams are uniform and that all metal components and labels are intact.
PVC Film-Wrapped Type: Verify that the PVC heat-shrink wrapping is intact and properly applied, and that the labels and coding meet all requirements.
Full-Wrap Labeling Type: Inspect the overall appearance quality of both the label and the plastic housing.
VI. Packaging and Warehousing
Packaging Standards
Batteries without external housings are to be packed flat in blister trays and stacked.
Standard batteries must first be placed in a plastic bag and inserted into an inner box, which is then placed into an outer carton; alternatively, cardboard dividers (knife cards) may be used to secure the batteries in place. The batteries must be placed flat and securely, ensuring they do not shift within the carton; the correct shipping marks must be affixed to the exterior of the carton.
