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Batteries & Rechargeables

World B — Acids, Bases & Solutions

23.A — PRIMARY & SECONDARY CELLS

VS
R23.01 Primary vs Secondary
  • Primary: Non-rechargeable. Reaction is irreversible. Dies when reactants consumed.
  • Secondary: Rechargeable. Reaction reversed by passing external current.
R23.02 Leclanché (Dry Cell)
  • Primary Cell. 1.5 Volts.
  • Anode: Zinc container.
  • Cathode: Graphite rod surrounded by MnO₂.
  • Electrolyte: Paste of NH₄Cl and ZnCl₂.
R23.03 Button Cells
  • Mercury or Silver Oxide cells.
  • Compact, steady voltage (~1.35V - 1.5V).
  • Used in watches, hearing aids.
  • Zinc anode, HgO/Ag₂O cathode.

23.B — THE LEAD-ACID ACCUMULATOR

R23.04 Lead-Acid Structure
  • Secondary cell used in automobiles (12V = 6 cells).
  • Anode: Spongy Lead (Pb).
  • Cathode: Lead Dioxide (PbO₂) grid.
  • Electrolyte: ~38% Sulfuric Acid (H₂SO₄).
R23.05 Discharging Phase
  • Acts as a Galvanic cell.
  • Both plates become coated with insoluble Lead Sulfate (PbSO₄).
  • Sulfuric acid is consumed; density drops.
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R23.06 Recharging Phase
  • Acts as an Electrolytic cell.
  • External voltage forces electrons backward.
  • PbSO₄ uncoats, restoring Pb, PbO₂, and H₂SO₄.

23.C — LITHIUM-ION & ADVANCED TECH

R23.07 Li-Ion Architecture
  • High energy density, lightweight.
  • Anode: Graphite (Carbon).
  • Cathode: Lithium Metal Oxide (e.g., LiCoO₂).
  • Electrolyte: Li salt in organic solvent.
R23.08 Intercalation Mechanism
  • The "Rocking Chair" battery.
  • Li⁺ ions do not react; they slip between the atomic layers (intercalate).
  • Move to graphite when charging, back to cathode when discharging.
R23.09 Solid-State Batteries
  • Replaces flammable liquid electrolyte with a solid conductive ceramic/polymer.
  • Higher energy density, much safer (no leaks/fires).
  • The frontier of EV technology.
H₂
O₂
H₂O
R23.10 Fuel Cells
  • Converts chemical energy of a continuous fuel supply directly to electricity.
  • H₂-O₂ cell: Reacts Hydrogen and Oxygen.
  • Byproduct is pure water. Highly efficient.

23.D — PERFORMANCE & DEGRADATION

5000 mAh
R23.11 Battery Capacity
  • Measured in Ampere-hours (Ah) or mAh.
  • Indicates total charge stored.
  • Higher mAh = longer runtime before needing a recharge.
R23.12 Degradation & Dendrites
  • Capacity fades over cycles due to side reactions.
  • Dendrites: Microscopic metal spikes that grow across the separator.
  • Causes internal short circuits and thermal runaway (fires).