How do low ambient temperatures affect polarization voltage and lithium plating risks during lithium-ion battery testing?

Low ambient temperatures increase polarization voltage and make lithium plating more likely during charging. Cooling raises ohmic, charge-transfer, and diffusion resistance, so the cell experiences larger voltage losses under the same current. During charging, the required terminal voltage rises while the graphite anode potential can fall toward the lithium-plating threshold, reducing charge acceptance and increasing safety risk.

Low temperature does not create lithium plating simply because the cell is cold; it makes plating more likely by slowing transport and reaction kinetics. The combination of high polarization, limited diffusion, and sufficiently aggressive charging can cause metallic lithium to deposit on the graphite anode.

Why Polarization Voltage Rises in the Cold

Reduced Electrochemical Activity

Low temperature slows the electrochemical reactions at both electrodes. The resulting increase in charge-transfer resistance means that a larger voltage is required to drive the same current through the cell.

This additional voltage is part of the cell’s polarization voltage, or overpotential. As temperature falls, the voltage response becomes more sensitive to current, particularly during high-rate charge and discharge pulses.

Increased Ohmic Resistance

Cold conditions reduce electrolyte ionic conductivity and increase the cell’s DC resistance. Current therefore produces a larger instantaneous voltage drop through the electrolyte, electrodes, current collectors, and interfacial regions.

During discharge, this appears as a larger downward voltage drop. During charging, it appears as a higher terminal voltage requirement for the same applied current.

Slower Lithium-Ion Diffusion

Lithium ions move more slowly through the electrolyte and electrode particles at low temperature. Transport limitations become especially important at high current, when ions must move rapidly to sustain the imposed reaction rate.

The cell can therefore exhibit both ohmic polarization and concentration polarization. The total voltage deviation is the combined result of immediate resistive losses and slower concentration-related limitations.

How Cold Conditions Increase Lithium-Plating Risk

Limited Charge Acceptance

Graphite normally stores lithium by intercalating it into the electrode structure. At low temperature, the intercalation reaction becomes slower and lithium-ion transport into the graphite is restricted.

If the charging current remains unchanged, lithium arrives at the anode faster than the graphite can safely absorb it. The cell consequently accepts less charge efficiently, even though the charger continues supplying current.

Anode Potential Approaches the Plating Threshold

Lithium plating is governed primarily by the anode potential, not only by the measured cell voltage. Increased polarization can drive the graphite surface potential toward, or below, the potential at which metallic lithium deposition becomes favorable relative to intercalation.

This is why a cell may show an apparently reasonable terminal voltage while plating is already occurring locally at the graphite surface. Terminal voltage is a useful diagnostic, but it does not directly reveal the most critical local electrode potential.

Surface Concentration Gradients

Slow diffusion creates nonuniform lithium concentration within the electrode. The graphite surface can become heavily lithiated while lithium transport deeper into the particles remains limited.

This concentration gradient increases overpotential and makes localized deposition more likely. Plated lithium may later strip back into the cell, but some can become electrically isolated or react with the electrolyte, contributing to irreversible capacity loss.

What Testing Should Measure

Temperature-Dependent Voltage Response

Tests should record voltage behavior across controlled temperatures and current rates. Comparing charge and discharge curves reveals how much of the voltage response comes from temperature-dependent resistance and polarization rather than from changes in the cell’s fundamental open-circuit behavior.

Useful measurements include pulse resistance, charge overvoltage, discharge voltage drop, hysteresis, and recovery after current interruption. These parameters help distinguish fast ohmic losses from slower diffusion and relaxation effects.

Charge Acceptance and Capacity

A cold cell may reach its upper voltage limit before it has stored the expected amount of charge. Stopping the test based only on voltage can therefore make the measured usable capacity appear lower than the cell’s room-temperature capacity.

Capacity measurements should be interpreted together with temperature, current, rest periods, and cutoff conditions. Otherwise, temperature-induced polarization can be mistaken for permanent material degradation.

Evidence of Plating

Plating risk should be evaluated using more than a single voltage threshold. Researchers commonly examine unusual voltage relaxation, abnormal charge curves, coulombic-efficiency changes, differential-voltage features, and post-test capacity behavior.

These indicators are indirect unless supported by a suitable electrode-potential measurement or post-test physical analysis. A controlled test plan should therefore identify the measurement limits and avoid treating any one signal as definitive proof of plating.

Why Current Rate Matters

The Same Temperature Can Produce Different Risks

A modest current may be acceptable at room temperature but excessive at a low temperature. Increasing current amplifies ohmic losses, concentration gradients, and interfacial overpotential at the same time.

The relevant variable is therefore the combined operating condition: temperature, current rate, state of charge, cell design, and charge cutoff voltage. Plating risk is generally highest when cold charging is combined with high state of charge and high current.

Discharge and Charge Behave Differently

Cold temperatures strongly reduce discharge power by increasing voltage drop and limiting access to active material. However, cold charging presents the more serious lithium-plating concern because the anode must insert lithium while its reaction and transport processes are slowed.

A cell can remain usable for low-rate discharge while still being unsuitable for aggressive charging at the same temperature. Test protocols should evaluate the two directions separately.

Understanding the Trade-offs

Lower Current Reduces Risk but Extends Test Time

Reducing the charge rate lowers polarization and gives lithium more time to intercalate into graphite. The trade-off is a longer test duration and reduced relevance to applications that require fast charging.

A lower current is therefore a mitigation strategy, not evidence that the cell is intrinsically safe under the original fast-charge condition.

Higher Temperature Improves Kinetics but Accelerates Aging

Warming the cell generally improves ionic conductivity, reaction rates, charge acceptance, and dynamic voltage performance. Excessive temperature, however, accelerates parasitic reactions and can reduce cycle life and thermal safety margins.

Temperature should be controlled within the cell manufacturer’s and test program’s defined limits. Raising temperature to suppress cold polarization can exchange an immediate plating risk for longer-term degradation.

Terminal Voltage Alone Can Mislead

A high charging voltage at low temperature indicates increased polarization, but it does not uniquely identify the cause. Resistance growth, diffusion limitation, charge-transfer kinetics, and lithium plating can all influence the observed profile.

Likewise, a voltage profile that does not look abnormal does not guarantee that local plating is absent. Interpretation should combine voltage, current, temperature, state of charge, and, where possible, electrode-level diagnostics.

Common Testing Pitfalls

Comparing Temperatures Without Matching Conditions

Temperature comparisons are only meaningful when current rate, SOC window, rest time, cutoff limits, and thermal history are controlled. Otherwise, differences may reflect protocol changes rather than temperature itself.

Cells should also be allowed to reach a defined and verified thermal condition before testing. The ambient chamber setpoint alone may not represent the actual core temperature of the cell.

Ignoring Self-Heating

A cell tested at high current can warm internally even when the chamber temperature is stable. This creates a changing thermal boundary condition and can reduce the apparent severity of polarization during the test.

Temperature sensors, fixture design, and test duration should account for both ambient temperature and internal heat generation.

Treating Capacity Loss as Immediately Permanent

Low-temperature polarization can temporarily reduce accessible capacity because the cell reaches a voltage limit early. That result should not automatically be interpreted as irreversible degradation.

Repeated testing, recovery at a moderate temperature, coulombic-efficiency tracking, and appropriate post-test analysis help separate reversible underutilization from permanent damage caused by plating or other degradation mechanisms.

How to Apply This to Your Testing Program

Temperature-controlled testing should map the interaction between thermal condition, charge rate, SOC, polarization voltage, and post-test degradation.

• If your primary focus is polarization characterization: Measure pulse resistance, charge overvoltage, discharge voltage drop, and voltage recovery across a broad, controlled temperature range.
• If your primary focus is lithium-plating prevention: Restrict charge current and upper-SOC operation at low temperature, and monitor for electrode-potential or voltage-relaxation indicators of plating.
• If your primary focus is fast-charge performance: Establish a temperature-dependent charging map rather than applying one current limit across all temperatures.
• If your primary focus is accurate capacity measurement: Control the cell temperature, thermal equilibration time, cutoff conditions, and rest periods so cold-induced polarization is not confused with permanent capacity loss.
• If your primary focus is battery-model accuracy: Include temperature-dependent resistance, charge-transfer, diffusion, and dynamic-voltage parameters in the model.

Reliable low-temperature battery testing requires treating polarization as both a performance limitation and an early warning signal for lithium plating.

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