Exploring Lithium-Ion Batteries: How they Work, Recharge, and Degrade

Introduction

• Inside smartphones, a chemical reaction occurs continuously, essential for the device's operation.
• The lecture explores how lithium-ion batteries power smartphones, the recharging process, and reasons for battery degradation.

How Lithium-Ion Batteries Power Smartphones

• Battery Terminals:
  • Positive terminal and negative terminal supply electricity.
  • Electricity = flow of electrons.
• Electron Flow:
  • Electrons flow from the negative terminal (anode) to the positive terminal (cathode).
  • Electron flow powers components like speakers and displays.
• Anode (Negative Terminal):
  • Lithium stored in layers of carbon graphite (intercalation).
  • Lithium dislikes its outer electron and gives it up, becoming a lithium ion.
• Cathode (Positive Terminal):
  • Contains cobalt, which is positive due to electron loss to oxygen.
  • Electrons flow to cobalt which wants to regain electrons.

Role of Electrolyte

• Provides a path for positively charged lithium ions to move to the cathode.
• Prevents electron flow through it, balancing charge buildup.
• Lithium ions intercalate with cobalt and oxygen at the cathode.

Recap of Battery Discharge

• Lithium atoms leave graphite, electrons flow through circuits.
• Lithium ions travel through the electrolyte to neutralize charge build-up.
• End of day: lithium forms lithium cobalt oxide at the cathode.

Recharging Process

• USB charger applies higher force on electrons in the opposite direction.
• Electrons are pulled out of cobalt, returning cobalt to +4 state.
• Electrons forced onto graphite, pulling lithium ions back to anode.
• Reversible reaction, making the battery rechargeable.

Additional Details

1. Separation of Anode and Cathode:
   • A non-conductive semipermeable separator prevents contact.
2. Conductive Layers:
   • Copper next to graphite and aluminum next to cobalt.
   • These layers are called collectors.
3. Partial Lithium Movement:
   • Not all lithium moves during charge/discharge.
4. Design:
   • Layers folded into a rectangular prism package.
5. Circuitry:
   • Prevents overcharging and battery damage.

Battery Degradation

• Solid Electrolyte Interphase (SEI):
  • Formation of SEI consumes lithium and electrolyte irreversibly.
• Irreversible Compounds:
  • Fully discharging can create Lithium oxide and Cobalt (II) Oxide.
• Tip:
  • Recharge battery at 30-40% rather than letting it run until empty.

Conclusion

• Variety of battery chemistries work on similar principles.
• Key materials: electron donor, electron acceptor, and neutralizing path.
• Encouragement to ask questions, discuss, and explore related topics.