REDOX

Electrons change hands

Every battery runs a redox reaction. One material is oxidized (loses electrons), another is reduced (gains them). Keeping the two apart forces the electrons through the wire.

OIL RIG: Oxidation Is Loss, Reduction Is Gain.

HALF REACTIONS

What happens at each side

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Anode (discharge) LiC₆ → C₆ + Li⁺ + e⁻

Cathode (discharge) Li_1−xCoO₂ + x Li⁺ + x e⁻ → LiCoO₂

Charge Both reactions run backwards

The lithium ion is the shuttle; the electron is the current.

THE LADDER

Voltage is a difference in potential

Each electrode material has its own potential. Cell voltage is the cathode's potential minus the anode's: pick a low anode and a high cathode for a big gap.

Voltage = E_cathode − E_anode.

WHY LITHIUM?

The lightest metal, and the most eager

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Low potential

Lithium sits about 3 V below the hydrogen reference, the lowest of any metal

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Light

The lightest metal: about 0.53 g/cm³, so lots of charge per gram

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Small ion

Li⁺ is tiny and slips in and out of crystal layers easily

High voltage plus low weight is why lithium powers almost everything portable.

THE NERNST EQUATION

Voltage depends on how full the cell is

E = E° − (RT / nF) ln Q
E° is the standard potential, R the gas constant, T temperature, n the electrons per reaction, F Faraday's constant and Q the ratio of products to reactants. As a cell empties, Q changes and the voltage slides.

Cell voltage is not fixed: it drifts with state of charge and temperature.

UNIT 2 STUDY COMPLETE

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Ready for the Fab Challenge?

You've seen how oxidation and reduction split across two electrodes, and how the gap between them sets the voltage.