The principle, classification and formula of Farad capacitor!

Farad Capacitor: Also Known as Supercapacitor or Electric Double-Layer Capacitor

A Farad capacitor, also known as a supercapacitor or electric double-layer capacitor, is an electrochemical energy storage device based on the principle of electrostatic energy storage. Compared with traditional capacitors, Farad capacitors have higher energy density and power density, while maintaining the fast charging and discharging characteristics of the AD8183ARU capacitor. This article will elaborate on the basic principle, classification, and related formulas of Farad capacitors.

Principle

The basic working principle of a Farad capacitor is based on the electrochemical double-layer effect and pseudocapacitance effect. When an external voltage is applied to the interface between the electrode and the electrolyte, positive and negative charges accumulate on the surfaces of the two electrodes, while the ions in the electrolyte migrate toward the electrode with the opposite charge under the action of the electric field, forming a tightly arranged double-layer structure at the electrode/electrolyte interface. Since this process does not involve chemical reactions, charging and discharging speeds are fast, and cycle life is long.

1. Electric Double-Layer Capacitance

This type of capacitance is mainly formed by the pure separation of charges, and its energy storage capacity depends on the surface area of the electrode, the type and concentration of the electrolyte, and the distance between the two electrodes.

2. Pseudocapacitance

This occurs on special electrode materials, where charge storage is enhanced through rapid surface redox reactions or adsorption/desorption processes, thereby improving capacitance performance.

Classification

Farad capacitors can be classified in multiple ways based on different standards:

1. Classification by Electrode Material

• Carbon-Based Capacitors: The most commonly used electrode materials, such as activated carbon, carbon nanotubes, and graphene, feature low cost and good stability.

• Metal Oxide Capacitors: Such as ruthenium oxide (RuO₂) and manganese dioxide (MnO₂), which improve capacitance by increasing the roughness of the electrode surface.

• Conductive Polymer Capacitors: Such as polypyrrole and polythiophene, which utilize the redox reaction of polymers to increase capacitance.

2. Classification by Electrolyte

• Liquid Electrolyte Capacitors: Use organic solutions or aqueous solutions as the electrolyte, providing higher energy density but requiring specific sealing and temperature control.

• Solid Electrolyte Capacitors: Use gel-like or solid electrolytes, improving safety and reducing leakage current, making them suitable for high-temperature or extreme environments.

• Hybrid Electrolyte Capacitors: Combine liquid and solid electrolytes, aiming to balance performance and safety.

3. Classification by Structure

• Electric Double-Layer Capacitors (EDLCs): The most fundamental type, directly utilizing the electrochemical double-layer for energy storage.

• Pseudocapacitors: Store additional energy through surface redox reactions of electrode materials, offering higher energy density.

• Hybrid Supercapacitors: Combine electric double-layer capacitors and pseudocapacitors, aiming to achieve the optimal balance between energy density and power density.

Formulas

The key parameters and calculation formulas for Farad capacitors include:

1. Capacitance (C)

Capacitance, measured in Farads (F), represents the ability to store one coulomb of charge under one volt of voltage. The capacitance of Farad capacitors is significantly greater than that of ordinary capacitors, typically ranging from farads to thousands of farads.

C=I×tΔVC = \frac{I \times t}{\Delta V}C=ΔVI×t​

Where:

• $I$ = Charging current

• $t$ = Charging time

• $\Delta V$ = Voltage change

2. Energy Density (E)

Energy density, measured in watt-hours per kilogram (Wh/kg), represents the amount of energy stored per unit mass of the capacitor.

E=12×C×V2E = \frac{1}{2} \times C \times V^2E=21​×C×V2

Where:

• $C$ = Capacitance

• $V$ = Operating voltage

3. Power Density (P)

Power density, measured in watts per kilogram (W/kg), represents the maximum power output per unit mass of the capacitor.

P=EtP = \frac{E}{t}P=tE​

Or, expressed directly in terms of current and voltage:

$$P=I\times V$$

4. Equivalent Series Resistance (ESR)

ESR affects charging/discharging efficiency and thermal management, measured in ohms (Ω).

ESR=ΔVIESR = \frac{\Delta V}{I}ESR=IΔV​

Where:

• $\Delta V$ = Voltage drop measured during constant-current discharge

• $I$ = Current during discharge