THE TOOLKIT

Which test tells you that?

Every question about a cell, from how long it lasts to whether it burns, has a test designed to answer it.

Life, power, resistance and safety each get their own test.

CYCLING

Charge, discharge, repeat

Constant current, constant voltage (CC-CV) Charge at a set current to the top voltage, then hold the voltage while the current tapers

Constant current discharge Down to the lower cutoff

Logged each cycle Capacity, energy, coulombic efficiency and resistance

Time 1,000 cycles at 1C takes about three months

Cycling is slow, so labs run hundreds of channels at once.

IMPEDANCE

Electrochemical impedance spectroscopy

EIS applies a tiny AC signal across many frequencies. The Nyquist plot separates the ohmic resistance, the SEI and charge-transfer semicircles, and the diffusion tail.

EIS shows which part of the cell is slowing it down.

IN THE LAB

Three electrodes, one material

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Half cells

Test one electrode against lithium metal in a coin cell

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Reference electrode

A third electrode shows which side is causing a problem

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Rate test

Step the current up from 0.1C to 5C to see how capacity holds

New materials start as coin cells, long before they reach a factory.

ABUSE TESTS

Breaking cells on purpose

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Nail penetration A steel nail forces an internal short

Crush Simulates a car crash

Overcharge Pushes past the upper cutoff

Thermal Heats the cell in an oven until something happens

Standards Shipping cells needs UN 38.3 testing; cars have their own standards

Safety tests are about what happens on the worst day.

UNIT 15 STUDY COMPLETE

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Ready for the Fab Challenge?

You've seen the main tests a cell goes through, from gentle cycling to nails and fire.