why can't electric cars use capacitors

[LucasRose]

Electric cars can't use capacitors as their primary energy source because capacitors, specifically supercapacitors, have an energy density that is far too low compared to lithium-ion batteries. While a modern EV battery can store enough energy to drive over 300 miles, a capacitor of the same weight might only power the car for a few miles. The fundamental trade-off is between energy density (how much total energy you can store) and power density (how quickly you can release that energy). Capacitors excel at the latter but fail at the former.

Think of it like a water storage system. A battery is a large reservoir that can release a steady flow of water for a long time. A capacitor is a powerful pressure washer that unleashes a massive burst of water very quickly but empties its small tank in seconds. For an EV, you need the reservoir, not just the pressure washer.

However, capacitors are incredibly useful in electric vehicles as a complementary technology. Their ability to charge and discharge in seconds makes them ideal for specific applications:

• Regenerative Braking: They can capture the large burst of energy from braking more efficiently than batteries, which can be stressed by rapid charging.
• Power Boosting: They can provide extra power for quick acceleration, reducing the strain on the main battery.
• Buffer for Battery Life: By handling peak power demands, capacitors can help smooth out the load on the battery, potentially extending its overall lifespan.

The following comparison highlights the core differences:

Feature	Lithium-Ion Battery (e.g., in a Tesla)	Supercapacitor
Energy Density (Wh/kg)	250 - 300	5 - 10
Power Density (W/kg)	250 - 350	10,000 - 15,000
Charge/Discharge Time	30 mins - 10 hours	Seconds to minutes
Cycle Life (Charges)	1,000 - 2,000	100,000 - 1,000,000
Cost per kWh	~$150	~$10,000

The future may involve hybrid systems where a small, high-power capacitor bank works alongside a high-energy battery, combining the strengths of both to create a more efficient and durable powertrain.

[KennedyLee]

It boils down to range. A capacitor can't hold enough juice for a practical trip. You'd be recharging every couple of miles. They're fantastic for quick bursts of power—like giving a car a real jolt off the line—but they drain almost instantly. It's like trying to run a marathon by taking one giant leap; you cover a short distance incredibly fast, but then you're done. Batteries are the steady runners that get you to the finish line.

[VanEverett]

The science is in the energy storage mechanism. Batteries store energy through slow, chemical reactions, which allows for high energy density. Capacitors store energy electrostatically, physically separating positive and negative charges. This physical method allows for incredibly fast charge/discharge cycles but severely limits how much total energy can be stored per unit of weight or volume. For the core requirement of an EV—storing massive amounts of energy—the chemical process in batteries is fundamentally superior.