Battery knowledge · Testing methods
Voltage relaxation analysis
Extracting diagnostic information from the way a cell’s voltage settles during a rest. After fast charging, a plateau in the relaxing voltage — a peak in dV/dt — reveals plated lithium re-entering the graphite; features of the relaxation curve also track capacity fade, and a rest voltage that keeps drifting down points to self-discharge.
- Also called
- rest-voltage analysis, relaxation voltage, rest voltage diagnostics
Example
Voltage response and relaxation
At τ = 20 s, 63.2% of the step response is complete; a relaxation retains 36.8%.
Two separate analytical experiments; normalized voltage, not measured data.
Explore the graph
One time constant completes about 63% of a first-order voltage change.
At τ = 20 s, 63.2% of the step response is complete; a relaxation retains 36.8%.
τ = RC; step response = 1 − e^(−t/τ)
Illustrative model. Two separate analytical experiments; normalized voltage, not measured data.
Use in Lemonergy
Design protocol or analysis tool
Inspect pulse characterization
HPPC alternates pulses, moves SOC and includes long rests.
Equation or tool to use
- Rest
Allows relaxation
Inputs & settings
- s
- Pulse
Excites charge/discharge
Inputs & settings
- a
- pulseS / restS
- Repeat
Repeats SOC points
Inputs & settings
- count
This overview identifies the components to use. Follow the example in Lemonergy for their connections and settings.
Example. 0.2 V change after a 10 A step gives 20 mΩ by ΔV/ΔI on the same cell/pack basis.
Observe. Long rests differ from the immediate resistive jump.
The estimate depends on timing, temperature and state; this is not AC impedance spectroscopy.
Open Design → Protocol bench →References & further reading
Further reading on this topic
These sources provide broader context; they are not presented as citations for every statement in this entry.
- Battery Test Manual For Electric Vehicles, Revision 3
Jon P. Christopherson · Idaho National Laboratory · 2015
Topic background · Performance characterization, pulse resistance/power, life testing and reference performance tests; historical 2015 edition.