Coin Cell Assembly Guide Step-by-Step for CR2032 and CR2025 in Lab Settings

Coin cell assembly is a fundamental process in electrochemical and battery research, especially for testing new electrode materials. Among the most commonly used formats are CR2032 and CR2025 coin cells, widely used in lithium-ion battery research due to their reliability, compact size, and standardized design.

This guide provides a step-by-step laboratory procedure for assembling coin cells while maintaining accuracy, safety, and reproducibility.

Understanding CR2032 vs CR2025 Coin Cells

Before assembly, it is important to understand the difference:

• CR2032
• Diameter: 20 mm
• Thickness: 3.2 mm
• Higher electrolyte volume
• More commonly used for long-cycle testing
• CR2025
• Diameter: 20 mm
• Thickness: 2.5 mm
• Smaller internal volume
• Used for compact or limited-material experiments

Both cells follow the same assembly principles but differ in internal spacing and electrolyte capacity.

Required Materials and Equipment

For proper coin cell assembly, you will need:

• CR2032 / CR2025 cell casing (cathode & anode parts)
• Lithium metal foil (anode)
• Cathode material (coated electrode disc)
• Separator (polypropylene or Whatman glass fiber)
• Electrolyte solution (commonly LiPF₆ in organic solvents)
• Stainless steel spacers and springs
• Hydraulic crimping machine
• Tweezers (non-metallic preferred)
• Gloves, safety goggles
• Argon-filled glove box (moisture < 1 ppm, oxygen < 1 ppm)

Step-by-Step Coin Cell Assembly Process

Step 1: Prepare the Glove Box Environment

The most critical part of coin cell assembly is maintaining a controlled inert atmosphere.

• Purge the glove box thoroughly to remove oxygen and moisture.
• Maintain ideal conditions:
• Oxygen level: < 1 ppm
• Moisture level: < 1 ppm
• Check gloves for any leakage, pinholes, or damage before starting.
• Transfer all required materials into the glove box using the airlock/pass-through system in advance.

Why this matters:
Lithium metal and most electrolytes are extremely sensitive to air and moisture. Even trace exposure can cause side reactions, poor SEI formation, or complete cell failure.

Step 2: Arrange All Cell Components in Proper Order

Before starting assembly, organize all components in a clean and logical layout:

• Bottom casing (stainless steel coin cell case)
• Spacer (stainless steel disc)
• Spring
• Cathode electrode disc
• Separator (glass fiber or polypropylene)
• Lithium metal foil (anode)
• Top casing

Pro tip:
A well-organized setup reduces handling time inside the glove box and minimizes contamination risk.

Step 3: Cathode Electrode Placement

• Place the bottom casing on a stable surface inside the glove box.
• Carefully pick the cathode disc using non-metallic tweezers.
• Ensure:
• The electrode surface is clean and dust-free
• It is properly centered inside the casing

Important note:
Misalignment can increase contact resistance and lead to inconsistent electrochemical performance.

Step 4: Separator Placement and Electrolyte Addition

• Gently place the separator over the cathode surface.
• Ensure it:
• Fully covers the electrode area
• Has no folds, wrinkles, or air gaps
• Add electrolyte using a micropipette or dropper:
• Add controlled volume (do not over-saturate)
• Ensure uniform wetting of the separator

Key insight:
Electrolyte distribution directly affects ionic conductivity, internal resistance, and cycle stability.

Step 5: Lithium Metal (Anode) Placement

• Cut lithium foil carefully inside the glove box.
• If necessary, remove any oxidized surface layer gently.
• Place lithium foil on top of the separator.

Handling notes:

• Lithium is soft and reactive — avoid pressure or deformation
• Ensure full and uniform contact with the separator surface

Step 6: Insert Spacer and Spring

• Place the stainless steel spacer on top of the lithium layer.
• Add the spring above the spacer.

Function of components:

• Spacer ensures structural alignment
• Spring maintains constant pressure throughout cycling
• Helps reduce interfacial resistance fluctuations

Step 7: Final Layer Alignment Check

Before sealing, carefully verify:

• All layers are properly centered
• No separator edges are exposed
• Electrolyte is not overflowing
• Spring is correctly seated

Why important:
Even minor misalignment can cause internal short circuits or unstable voltage behavior.

Step 8: Crimping (Sealing the Coin Cell)

• Transfer the assembled cell to a hydraulic crimping machine.
• Apply uniform pressure according to cell specifications.
• Ensure proper sealing of the casing.

Critical balance:

• Under-crimping → electrolyte leakage and poor contact
• Over-crimping → risk of internal short circuit or structural damage

Step 9: Post-Assembly Inspection

After sealing, perform final quality checks:

• Check for any leakage or deformation
• Verify uniform sealing edges
• Confirm proper labeling (sample ID, date, material details)

Best practice: Allow the assembled cells to rest for 6–12 hours before electrochemical testing to ensure proper electrolyte soaking and stabilization.

Important Safety Considerations

• Always handle lithium inside a glove box
• Avoid moisture exposure at all stages
• Do not overfill electrolyte
• Use proper PPE (Personal Protective Equipment)
• Dispose of lithium waste according to lab safety protocols

Common Mistakes to Avoid

• Incorrect stacking order of layers
• Uneven electrolyte distribution
• Poor sealing pressure during crimping
• Using contaminated separator or electrodes

Applications of Coin Cells

Coin cells are widely used in:

• Lithium-ion battery research
• Energy storage material testing
• Electrode performance evaluation
• Cycle life analysis
• Electrochemical impedance studies

FAQs

What is the main difference between CR2032 and CR2025 coin cells?

The main difference is thickness and internal capacity. CR2032 (3.2 mm thick) holds more electrolyte and is used for longer cycle testing, while CR2025 (2.5 mm thick) has a smaller internal volume and is used for compact or limited-material experiments.

Why is a glove box necessary for coin cell assembly?

A glove box provides an inert argon atmosphere with extremely low moisture and oxygen levels. This is essential because lithium metal reacts quickly with air and water, which can damage the cell and create safety risks.

What electrolyte is commonly used in CR2032 and CR2025 coin cells?

Most laboratory coin cells use a lithium salt electrolyte such as LiPF₆ dissolved in organic carbonate solvents (like EC, DMC, or DEC). The exact composition depends on the experimental design.

What are the common mistakes during coin cell assembly?

Common errors include:

• Incorrect layer stacking order
• Over or under-electrolyte filling
• Poor sealing during crimping
• Using contaminated electrodes or separators

Can CR2032 and CR2025 coin cells be assembled without a crimping machine?

No, a hydraulic crimping machine is essential to properly seal the coin cell. Manual sealing cannot provide the uniform pressure required, which may lead to leakage or unstable cell performance.

Conclusion

Coin cell assembly for CR2032 and CR2025 is a precise but highly standardized laboratory process. With careful handling, proper materials, and controlled environment, researchers can achieve highly reproducible results for battery testing and electrochemical analysis.