You must follow all requirements and instructions in this manual to properly set up, configure, and use the Battery Cell Quality Toolkit for battery tests.

Ensure the fixture design meets the following guidelines.

Probing Point Design

The probing mechanism must be mechanically stable to ensure a repeatable contact position. The probing mechanism must also be mechanically stable to prevent movement throughout the measurement process.

Movement of the probes during the measurement process introduces unwanted artifacts in the data.

Contact Quality and Consistency

Ensure that the probe tips and contact points on the battery are clean. Oxidation or contaminants on the surface of the cell introduce additional resistance and skew impedance measurements.

Spring-loaded probes must apply consistent pressure to ensure that contact is stable and repeatable. Variability in probe force leads to inconsistent measurements.

Probe Penetration of Surface Layers

Design spring-loaded probes to reliably and repeatably penetrate surface oxide layers commonly formed on aluminum terminals.

The material and design of the probe tip should minimize the risk of the following:

  • Puncturing the cell
  • Disrupting the solid electrolyte interface (SEI) layer

Consider using crown-style spring-loaded probes if you are using spring-loaded probes. Crown-style spring-loaded probes help with layer penetration.

Probing Points

For accurate impedance measurements, select probing points that are representative of the overall cell performance. Avoid probing points that might be affected by local defects or irregularities.

If possible, use multiple probing points to average out localized impedance variations. Multiple probing points allow for a more representative measurement of the cell impedance.

Probe Material and Tip Design

Material Compatibility

Choose probe materials that are compatible with the chemistry of the battery to avoid chemical reactions or degradation. Bronze tips, sometimes with silver plating or nickel plating, are commonly used because bronze tips resist corrosion. Bronze tips also provide stable electrical contact.

Corrosion Resistance

Choose probe materials that are resistant to corrosion. Choose probe materials that do not react with the electrolyte of the battery. Gold and platinum are commonly used for their inertness and resistance to corrosion.

Non-Reactive Materials

Materials like stainless steel or copper might react with battery components. Stainless steel or copper might suffer from corrosion, especially in the presence of the electrolyte. Using non-reactive materials helps prevent contamination of the cell or degradation of the probe.

Tip Shape and Size

Ensure that the probe tip design is appropriate for the cell contact point and curvature. Tips should be small enough to make good contact, but robust enough to avoid damage or excessive wear.

Environmental Factors

Battery impedance can be temperature-dependent. Perform measurements at a controlled temperature to ensure consistent and reliable measurements.

Self-Calibration

The Battery Cell Quality Toolkit support self-calibration for the SMUs and the DMMs. Self-calibration helps ensure accurate, repeatable, and precise measurements.

Refer to the SMU or the DMM user documentation to learn when to self-calibrate.

Accuracy Assurance

Self-calibration ensures that the measurements taken by the instrument are accurate. Self-calibration corrects for any drifts or errors in the instrument by adjusting the internal calibration constants.

Compensation for Drift

Electronic components drift from their nominal values over time due to factors like temperature changes, aging, and component wear. Self-calibration compensates for these drifts, maintaining the accuracy of the instrument.

Consistency

A consistent self-calibration schedule maintains consistent measurements. A consistent self-calibration schedule also ensures that the instrument performance remains within specified tolerances.

Consider the following factors when determining the frequency of self-calibration:

  • Application requirements. Applications that require high precision, are highly sensitive, or are in a regulated environment might require self-calibration more frequently.
  • Environmental conditions. Using an instrument in an environment with significant temperature fluctuations or other conditions that might affect performance might require self-calibration more frequently.
    Note

    The Battery Cell Quality Toolkit incorporates an API that you can configure to run self-calibration when the internal temperature measurement of the instrument changes by more than 1 °C.

  • Routine self-calibration. Perform self-calibration before each use or daily to ensure high-precision measurements.
  • Periodic self-calibration. Perform a weekly or monthly self-calibration for less demanding applications. Adjust the how frequently self-calibration is performed based on specific needs and performance.

Cabling

Ensuring accurate, repeatable, and precise measurements involves careful consideration of cabling and setup factors.

The following cabling considerations help ensure high-quality test results.

Minimize Electrical Noise

Shielded Cables

Use shielded cables for all connections, including connections to the cell terminals. Shielded cables minimize electromagnetic interference (EMI) and radio-frequency interference (RFI).

  • For SMUs, shielding source wires is necessary because source wires emit an electromagnetic field that can create noise on the sense cables.
  • For SMUs, shielding the sense cables is necessary so that do not absorb any noise coming from nearby noise sources.
  • For DMMs, shield one pair of wires so that the wires do not absorb noise from nearby noise sources.

Proper Grounding

  • Properly ground all equipment and connections to avoid ground loops and reduce noise.
  • Properly tie all connections to ground. Where applicable, ensure cable shields tied to ground follow the same proper grounding advice.
  • Provide a low resistance path to ground using appropriately sized grounding conductors.

Cable Connections

Secure all cable connections. Loose connections introduce noise and affect measurement accuracy.

Ensure cabling from the DMM and the SMU are fixed. Do not attach cables to automated fixtures that move.

Note Changes in the position of the cables require new compensation values.

Keep the length of the measurement cables as short as possible. Short cables help reduce the potential for noise pickup and inductive effects.

Four-Terminal (Kelvin) Measurement

Use a four-terminal (Kelvin) connection for impedance measurements.

A four-terminal measurement includes separate pairs of leads for applying the test signal and measuring the response. A four-terminal measurement helps eliminate errors due to lead resistance.

Mitigate Parasitic Elements

Minimize parasitic elements in your setup that could affect measurement accuracy. Parasitic elements include inductance and capacitance.