6.1 Principles of supercapacitor operation

Supercapacitors store energy through electrostatic charge separation and fast, reversible reactions. They form an electrochemical double layer at the electrode-electrolyte interface, with some materials exhibiting additional pseudocapacitive effects for increased storage capacity.

Key performance metrics include specific capacitance, energy density, power density, and cycle life. Supercapacitors excel in power delivery and longevity, making them ideal for applications requiring rapid charge-discharge cycles and long-term stability.

Charge Storage Mechanisms

Electrochemical Double Layer Formation

Top images from around the web for Electrochemical Double Layer Formation

• 

  Frontiers | Three-Dimensional Architectures in Electrochemical Capacitor Applications – Insights ... View original

  Is this image relevant?

• 

  EDLC Series Electric Double Layer Capacitors/Supercapacitors rated at 500mF - Electronics-Lab.com View original

  Is this image relevant?

• 

  Frontiers | Three-Dimensional Architectures in Electrochemical Capacitor Applications – Insights ... View original

  Is this image relevant?

• 

  Frontiers | Three-Dimensional Architectures in Electrochemical Capacitor Applications – Insights ... View original

  Is this image relevant?

• 

  EDLC Series Electric Double Layer Capacitors/Supercapacitors rated at 500mF - Electronics-Lab.com View original

  Is this image relevant?

1 of 3

Top images from around the web for Electrochemical Double Layer Formation

• 

  Frontiers | Three-Dimensional Architectures in Electrochemical Capacitor Applications – Insights ... View original

  Is this image relevant?

• 

  EDLC Series Electric Double Layer Capacitors/Supercapacitors rated at 500mF - Electronics-Lab.com View original

  Is this image relevant?

• 

  Frontiers | Three-Dimensional Architectures in Electrochemical Capacitor Applications – Insights ... View original

  Is this image relevant?

• 

  Frontiers | Three-Dimensional Architectures in Electrochemical Capacitor Applications – Insights ... View original

  Is this image relevant?

• 

  EDLC Series Electric Double Layer Capacitors/Supercapacitors rated at 500mF - Electronics-Lab.com View original

  Is this image relevant?

1 of 3

• Occurs at the electrode-electrolyte interface when a voltage is applied
• Consists of two layers of charge: the electronic charge on the electrode surface and the solvated ions in the electrolyte
• Ions in the electrolyte diffuse across the separator and accumulate at the electrode of opposite charge
• Forms a double layer of charge, similar to a parallel plate capacitor, with an extremely small charge separation distance (Angstroms)

Electrostatic Charge Storage

• No transfer of charge between electrode and electrolyte
• Purely electrostatic storage of electrical energy achieved by charge separation at the interface
• Charges are distributed on two surfaces, similar to a traditional capacitor
• Highly reversible process that allows for high power and long cycle life

Faradaic Reactions in Pseudocapacitors

• Some electrode materials exhibit faradaic reactions in addition to double layer formation
• Involves transfer of charge between electrode and electrolyte through fast, reversible redox reactions, intercalation, or electrosorption
• Pseudocapacitance can increase the specific capacitance and energy density beyond double layer capacitance alone
• Examples of pseudocapacitive materials include transition metal oxides (RuO2, MnO2) and conducting polymers (polyaniline, polypyrrole)

Performance Metrics

Specific Capacitance

• Capacitance per unit mass or volume of the electrode material (F/g or F/cm³)
• Depends on the surface area accessible to electrolyte ions, pore size distribution, and conductivity of the electrode
• Higher specific capacitance indicates greater charge storage capability for a given electrode mass or volume
• Can be increased through high surface area materials (activated carbon, graphene, CNTs) and pseudocapacitive contributions

Energy and Power Density

• Energy density is the amount of energy stored per unit mass (Wh/kg) or volume (Wh/L)
• Power density is the rate of energy delivery per unit mass (W/kg) or volume (W/L)
• Supercapacitors typically have higher power density but lower energy density compared to batteries
• Energy density is proportional to capacitance and the square of the operating voltage (E = 1/2 CV²)
• Power density depends on the equivalent series resistance (P = V²/4R) and can be improved by reducing internal resistance

Cycle Life and Stability

• Supercapacitors can undergo hundreds of thousands to millions of charge-discharge cycles with minimal degradation
• Electrostatic charge storage mechanism is highly reversible, allowing for long cycle life
• Cycle life depends on factors such as electrode and electrolyte stability, operating voltage, and temperature
• Pseudocapacitive materials may have shorter cycle life due to irreversible redox reactions or structural changes during cycling
• Proper cell design and material selection are crucial for maximizing cycle life and overall performance