5 Coin Cell Assembly Mistakes That Ruin Test Results

A coin cell can look perfectly normal and still give misleading data. One slightly off-center electrode, a separator that did not wet evenly, or an inconsistent crimp can change impedance and cycle behavior enough to make a good material look bad.

If four cells agree and the fifth one fails, the fifth cell is not automatically evidence of poor chemistry. It may be evidence of an uncontrolled assembly step.

This is why reliable CR2032 testing depends less on one “perfect” recipe than on controlling the same small details from cell to cell. The five mistakes below are common because they are easy to miss and because their effects often appear only after the cell reaches the tester.

1. Treating component drying as a fixed recipe

Moisture control matters, but “dry everything at one temperature for one amount of time” is not a sound rule. Active powders, coated electrodes, separators, salts, and polymer-containing components do not all tolerate the same conditions. An overly aggressive drying step can alter a binder or separator, while an insufficient one can leave enough moisture to disturb the electrolyte and interface chemistry.

Use a drying procedure that is appropriate for each material and consistent with its supplier documentation, safety data sheet, and your laboratory protocol. Just as important, record the procedure. A note such as “electrodes dried” is not enough to reproduce a batch. Record the temperature, duration, vacuum or atmosphere, transfer method, and time between drying and assembly.

After drying, keep components in a controlled dry environment. Repeatedly opening containers, leaving electrodes exposed during setup, or transferring them through ambient air can undo careful preparation before the first cell is assembled.

2. Allowing the stack to drift off-center

Small alignment errors are especially costly in coin cells because the working area is small. If the anode and cathode overlap poorly, the cell no longer represents the intended electrode area. If an electrode edge extends beyond the separator, the risk of an internal short rises sharply. A wrinkled or damaged separator creates a similar problem.

Check the stack from directly above as each layer is placed. The separator should fully isolate the two electrodes, with enough margin to accommodate normal placement variation. Many laboratories use an anode that is slightly larger than the cathode in half-cell work, but the appropriate diameters still depend on the chemistry and cell design. What matters is that the geometry is deliberate and repeated, not improvised during assembly.

A simple centering guide, consistent tweezers, and an unhurried placement sequence can do more for repeatability than assembling faster. Inspect the exposed edges before adding the spacer and spring. If the stack moves while the upper components are placed, reopen and correct it rather than assuming crimping will straighten the layers.

3. Using one electrolyte volume for every cell design

There is no universal microliter value that works for every CR2032 experiment. The required amount changes with separator thickness and porosity, electrode loading and porosity, disc diameter, electrolyte properties, and the intended test conditions.

Too little electrolyte can leave part of the porous structure unwetted, producing high resistance, delayed stabilization, or rapid apparent capacity loss. Too much can create another set of problems: excess liquid may be displaced during crimping, increase leakage risk, or make the assembly less consistent.

The practical goal is to establish an appropriate volume for a defined cell design, then deliver that exact amount in the same sequence and location for every cell in the batch. Use a calibrated pipette, avoid touching the tip to active material, and allow the same wetting time before closing each cell. If the separator or electrode format changes, re-evaluate the volume instead of carrying the old value forward automatically.

4. Ignoring stack height and the spring-spacer combination

The spring and spacer are not filler hardware. Together with the case geometry, they determine how pressure is maintained on the electrode stack after sealing. A stack that is too low may have poor or intermittent contact. A stack that is too high can deform components, damage the separator, or make sealing inconsistent.

Do not compensate for uncertain stack height by adding hardware casually. Define the case format, electrode and separator thicknesses, spacer thickness, spring type, and assembly orientation as one controlled configuration. If any of those elements changes, confirm that the closed cell still provides stable contact without excessive compression.

Hardware condition matters too. Burrs, warped spacers, flattened springs, contaminated surfaces, and mixed component lots can introduce variation that looks electrochemical. Clean inspection under good lighting is a small step, but it prevents many confusing failures.

5. Crimping by feel

A hand movement is not a process setting. Two operators can produce visibly similar cells with different sealing quality, and the same operator may vary over a long assembly session. Crimping should therefore be treated as a controlled machine step.

Use the die and operating procedure specified for the crimper and case type. Establish a validated setting with your own equipment rather than relying on a pressure number copied from an unrelated setup; machine readouts, die geometries, and force transmission are not necessarily equivalent. Keep the cell centered, use the same hold sequence, and inspect the result.

Useful checks include final cell height, edge symmetry, visible gasket damage, case distortion, and signs of electrolyte leakage. If sealing quality changes, inspect the die for wear or contamination before adjusting the process. A higher setting is not automatically a better seal.

Researchers who need a consistent component platform can compare our coin cell case sets and hydraulic coin cell crimper. The equipment still needs to be qualified for the laboratory's exact stack and protocol.

A failed cell usually leaves clues

Before discarding an outlier, look at how it failed. The pattern can narrow the investigation:

• Zero or unstable open-circuit voltage: check for reversed components, electrode contact, misalignment, separator damage, or conductive contamination.
• Unexpectedly high resistance: examine stack pressure, spacer and spring placement, current-collector contact, electrolyte delivery, and wetting time.
• Leakage or residue around the seal: review electrolyte volume, gasket condition, component orientation, die selection, and the crimped dimensions.
• Wide scatter across an otherwise identical batch: compare operator technique, elapsed time between steps, material exposure, pipetting sequence, and crimper settings.

Open-circuit voltage alone cannot prove that a cell is well assembled. A plausible voltage only shows that the intended electrochemical couple is present and not obviously shorted at that moment. Impedance, formation behavior, leakage inspection, and agreement among replicate cells provide a more useful picture.

The ten-minute batch record

A short assembly record often saves hours of speculation later. Before the cells leave the glovebox or dry room, capture:

• electrode, separator, electrolyte, case, spring, and spacer lot identifiers;
• electrode and separator diameters, plus any measured thickness or loading data;
• component drying and transfer conditions;
• electrolyte identity, delivered volume, dosing sequence, and wetting time;
• the exact stack order and spring-spacer configuration;
• crimper, die, setting, hold sequence, and operator;
• assembly time, initial voltage, rest time, and planned test start.

The record does not need to become a paperwork exercise. Its purpose is to reveal which variable changed when one batch behaves differently from another. Photographing one representative stack and one finished cell can also help identify orientation or hardware mistakes later.

Consistency is the real assembly target

Good coin-cell work is not about finding a single impressive-looking cell. It is about producing a group of cells whose differences are dominated by the material or condition being studied. That requires appropriate dryness, deliberate alignment, controlled electrolyte delivery, a defined internal stack, and repeatable crimping.

When those steps are documented and held constant, failed cells become easier to diagnose and successful results become far more credible.

References

• Best practices in lithium battery cell preparation and evaluation, Communications Materials (2022).
• Automated coin cell assembly for reproducible battery research, Nature Reviews Clean Technology (2026).
• Assembling coin cells in half cell format, National Physical Laboratory (2026).
• Reproducible Production of Lithium-Ion Coin Cells, Energies (2022).

Safety note: Lithium metal and battery electrolytes can be reactive, flammable, and moisture-sensitive. Work in the specified controlled atmosphere, follow current safety data sheets and laboratory procedures, and use appropriate personal protective equipment.