Sodium-ion batteries store electrical energy by moving sodium ions between two electrodes during charging and discharging. They matter for renewable energy because solar panels and wind turbines produce power at variable times, while homes and grids need steady supply. Sodium is much more abundant than lithium, so this battery chemistry could help lower the cost of large energy-storage systems.
A sodium-ion battery can be built as a cell, a module, and then a battery pack for renewable-energy storage.
Key Facts
- During discharge, Na+ ions move from the anode to the cathode through the electrolyte while electrons flow through the outside circuit.
- Battery energy is approximately E = VQ, where E is energy, V is voltage, and Q is charge capacity.
- Charge is related to current by Q = It, where I is current and t is time.
- Electrical power is P = IV, where P is power, I is current, and V is voltage.
- Energy in watt-hours is E = Pt, so a 500 W load running for 4 h uses 2000 Wh.
- Sodium-ion batteries often have lower energy density than lithium-ion batteries, but they can use cheaper and more abundant raw materials.
Vocabulary
- Sodium ion
- A positively charged sodium atom, written Na+, that moves through the electrolyte during battery operation.
- Anode
- The electrode where sodium ions are stored during charging and from which they leave during discharge.
- Cathode
- The electrode that receives sodium ions during discharge and helps set the battery voltage.
- Electrolyte
- A material that allows ions to move between electrodes while blocking most electron flow inside the cell.
- Energy density
- The amount of energy a battery can store per unit mass or volume, often measured in Wh/kg or Wh/L.
Common Mistakes to Avoid
- Thinking electrons flow through the electrolyte is wrong because electrons mainly travel through the external circuit, while Na+ ions move through the electrolyte.
- Assuming sodium-ion batteries are always better than lithium-ion batteries is wrong because sodium-ion cells may be cheaper but often store less energy per kilogram.
- Confusing power with energy is wrong because power measures how fast energy is delivered, while energy measures the total amount stored or used.
- Ignoring round-trip efficiency is wrong because some energy is lost as heat during charging and discharging, so the energy recovered is less than the energy put in.
Practice Questions
- 1 A sodium-ion battery pack has a voltage of 48 V and a capacity of 100 Ah. Calculate its stored energy in Wh using E = VQ.
- 2 A wind turbine charges a battery at 600 W for 5 hours. If the charging efficiency is 90%, how much energy is stored in the battery in Wh?
- 3 Explain why a sodium-ion battery could be useful for storing solar energy on a neighborhood grid even if it has lower energy density than a lithium-ion battery.