Activated Carbon for Electric Double Layer Capacitors
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Solution Overview
Problem
Existing methods for producing activated carbon for electric double layer capacitor electrodes result in either reduced surface area due to particle size reduction or increased particle size during activation, failing to achieve the required small average particle diameter and uniformity.
Innovation Solution
Calcining an easily graphitizable carbon material under an oxidizing gas atmosphere, followed by adjusting the particle size and activating it with an alkali metal hydroxide, specifically using air as the oxidizing gas at temperatures between 500 to 700°C, to produce activated carbon with a large surface area and uniform particle size.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of stationary object
If activated carbon is ground down to reduce particle size, then average particle diameter decreases, but fine pores are crushed resulting in smaller surface area
Solution Approach 1:
The patent applies preliminary action by controlling the particle size of the raw carbon material before activation. By selecting raw materials with appropriate particle size ranges (0.5-5 μm average diameter) and preventing particle growth during activation, the method avoids the need for post-activation grinding that would damage pores. This preliminary control of particle dimensions prevents the contradiction from occurring in the first place.
Solution Approach 2:
The patent changes the parameter of particle size distribution control throughout the process. By maintaining specific particle size ranges during activation (avoiding both excessive growth and fragmentation), and optimizing the ratio of fine to coarse particles in the raw material, the method achieves small average particle diameter while preserving large surface area through controlled parameter changes rather than extreme measures.
2Area of stationary object
If activation is performed to create fine pores and increase surface area, then surface area increases, but particles fuse together resulting in larger particle size
Solution Approach 1:
The patent applies local quality by creating different pore structures in different regions of the carbon material. The activation process develops fine pores (0.5-5 nm) within particles while maintaining the overall particle integrity. This localized pore formation throughout the particle interior increases surface area without causing particle fusion, as the pore development is confined to the internal structure rather than causing external aggregation.
Solution Approach 2:
The patent uses preliminary action by pre-treating the carbon material with oxidizing gas before activation to develop surface oxygen groups. This preliminary oxidation modifies the surface chemistry and structure, preparing the material for subsequent activation while preventing excessive particle fusion. The pre-formed surface groups facilitate controlled pore development during activation without causing uncontrolled particle aggregation.
3Manufacturing precision
If calcination is performed under oxidizing gas atmosphere to prevent particle fusion, then particle size uniformity improves, but surface area may be reduced due to oxidation
Solution Approach 1:
The patent applies parameter changes by precisely controlling the oxidizing gas atmosphere conditions during calcination. By adjusting the oxidation potential, temperature, and duration, the method achieves sufficient particle size uniformity while limiting excessive surface oxidation that would reduce surface area. The oxidation is controlled to create beneficial surface groups without excessive material removal.
Solution Approach 2:
The patent converts the potentially harmful effect of oxidation into a benefit. Instead of avoiding oxidation entirely, the method uses controlled oxidation during calcination to prevent particle fusion and improve uniformity, while the resulting surface oxygen groups actually enhance the electrochemical performance. The apparent harm of oxidation is transformed into a beneficial surface modification that supports the overall goal.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This process effectively produces activated carbon with a small average particle diameter, uniform size, and a large specific surface area, enhancing the capacitance of electric double layer capacitors.
Implementation Method 1
calcining an easily graphitizable carbon material used as the raw material under an oxidizing gas atmosphere
Implementation Method 2
calcining an easily graphitizable carbon material used as the raw material under an oxidizing gas atmosphere, activating the carbon material
Implementation Method 3
an activated carbon having effectively formed fine pores, a high crystallinity and a large surface area has been demanded to be used as an electrode material for the capacitor
Implementation Method 4
an alkali metal compound such as potassium hydroxide are heated at a temperature of 600 to 1200° C. in an inert gas atmosphere to allow the alkali metal to ingress between and react with graphite crystal layers
Data Source
AI summary
The present invention provides a process for producing an activated carbon having a small average particle diameter, a uniform particle size and a relatively large specific surface area suitable for an electric double layer capacitor electrode, in an easy and cost effective manner. The process comprises calcining an easily graphitizable carbon material such as petroleum coke or coal coke, used as the raw material under an oxidizing gas atmosphere, adjusting the particle size of the carbon material, and then activating the carbon material. The use of the activated carbon produced by the process of the present invention in an electrode can provide an electric double layer capacitor having a large capacitance per unit volume.