Lithium ion batteries
1. Basic Principle
A lithium-ion battery works on the movement of lithium ions (Li⁺) between two electrodes —
anode and cathode — through an electrolyte, with electrons moving through an external circuit
to provide electrical power.
2. Main Components
Cathode (Positive electrode) – Lithium metal oxide (e.g., LiCoO₂, NMC, LFP)
Anode (Negative electrode) – Graphite (carbon) or silicon-carbon
Electrolyte – Lithium salt (LiPF₆) dissolved in an organic solvent
Separator – Microporous polymer film preventing direct contact between electrodes
Current Collectors – Thin aluminum (cathode side) and copper (anode side) foils to
carry electrons
3. Working Operation
A. During Charging
1. External energy source (charger) applies voltage across the battery.
2. Lithium ions (Li⁺) move from cathode → through the electrolyte → to the anode.
3. At the anode, lithium ions are intercalated (inserted) between graphite layers.
4. Electrons flow through the external circuit to the anode (because they cannot pass
through the electrolyte).
5. Energy is stored in chemical form.
B. During Discharging
1. The battery is connected to a load (motor, electronics, etc.).
2. Lithium ions (Li⁺) move from anode → through the electrolyte → to the cathode.
3. Electrons flow through the external circuit from anode to cathode, powering the load.
4. At the cathode, lithium ions re-enter the crystal structure, restoring its original state.
4. EV Operation
Battery Management System (BMS) controls voltage, current, and temperature for
safety and longevity.
The process is reversible — hundreds to thousands of charge/discharge cycles.
Performance depends on temperature, current load, and battery chemistry.
Lead Acid Batteries
1. Introduction
Invented: 1859 by Gaston Planté
Type: Rechargeable electrochemical battery
Voltage per cell: ~2 V (A 12 V battery has 6 cells in series)
Common Uses: Automobiles (starting, lighting, ignition – SLI), UPS systems, forklifts,
solar storage.
2. Construction
A typical lead–acid battery consists of:
1. Positive plate – Lead dioxide (PbO₂)
2. Negative plate – Sponge lead (Pb)
3. Electrolyte – Dilute sulfuric acid (H₂SO₄, ~37% concentration)
4. Separators – Insulating materials to prevent short circuits between plates
5. Container – Acid-resistant plastic housing with vent caps
3. Working Principle
It operates on the reversible chemical reaction between lead, lead dioxide, and sulfuric acid.
A. Discharging
When the battery supplies power:
At positive plate (PbO₂):
PbO₂ + SO₄²⁻ + 4H⁺ + 2e⁻ → PbSO₄ + 2H₂O
At negative plate (Pb):
Pb + SO₄²⁻ → PbSO₄ + 2e⁻
Result: Both plates become lead sulfate (PbSO₄), sulfuric acid concentration decreases,
water content increases → voltage drops.
B. Charging
When an external charger applies voltage:
The chemical reactions reverse.
Lead sulfate on the positive plate converts back to lead dioxide (PbO₂),
Lead sulfate on the negative plate converts back to sponge lead (Pb),
Sulfuric acid concentration increases again.
4. Advantages
Low cost compared to other rechargeable batteries
Reliable & simple technology with decades of use
Can supply high surge currents (good for engine starting)
Recyclable (up to 95% of materials can be reused)
5. Disadvantages
Heavy and low energy density (~30–50 Wh/kg)
Shorter lifespan (300–500 cycles)
Slow charging compared to lithium-ion
Sulfation risk if left discharged for long periods
Requires maintenance in flooded types (checking electrolyte level)
