Modified Activated Carbon for Low-Gas EDLC Electrodes
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Solution Overview
Problem
Existing methods for improving the durability and reducing resistance in electric double layer capacitors are insufficient, particularly under severe conditions, as they focus only on reducing surface functional groups of activated carbon without addressing intra-skeletal oxygen, leading to gas generation and capacity retention issues.
Innovation Solution
A modified activated carbon with controlled BET specific surface area, hydrogen content/carbon content ratio, intra-skeletal oxygen, and particle size distribution is produced through acid washing, pulverization, classification, and heat treatment under inert gas atmospheres, reducing both surface and intra-skeletal oxygen content.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If surface functional groups of activated carbon are reduced by heat treatment, then durability is improved, but intra-skeletal oxygen remains high causing gas generation
Solution Approach 1:
The patent applies parameter changes by conducting heat treatment at a specific temperature range of 800-1200°C to simultaneously reduce both surface functional groups and intra-skeletal oxygen content. This temperature parameter optimization enables the activated carbon to achieve low surface oxygen (0.1-1.0 mmol/g) and low intra-skeletal oxygen (0.5-2.0 mmol/g), thereby resolving the contradiction between improving durability and suppressing gas generation
Solution Approach 2:
The patent replaces conventional surface-only treatment with a comprehensive thermal treatment mechanism that penetrates into the skeletal structure. By using high-temperature heat treatment (800-1200°C), the method substitutes superficial chemical modification with deep thermal decomposition, effectively removing intra-skeletal oxygen that conventional methods cannot address
2Quantity of substance
If activated carbon is used in electric double layer capacitors, then high energy density is achieved, but gas generation occurs during charge/discharge
Solution Approach 1:
The patent changes the oxygen content parameters of activated carbon through controlled heat treatment at 800-1200°C, reducing both surface and intra-skeletal oxygen to specific ranges. This parameter optimization maintains the high specific surface area (1000-2000 m²/g) necessary for high energy density while eliminating the gas generation problem that occurs during capacitor charge/discharge cycles
3Reliability
If heat treatment temperature is increased to reduce surface functional groups, then durability improves, but production energy consumption increases
Solution Approach 1:
The patent optimizes the heat treatment temperature parameter to a specific range of 800-1200°C, which is sufficient to reduce both surface functional groups and intra-skeletal oxygen to the desired levels. This optimized temperature range achieves effective oxygen removal (surface oxygen 0.1-1.0 mmol/g, intra-skeletal oxygen 0.5-2.0 mmol/g) while avoiding excessive energy consumption that would occur at higher temperatures
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
The modified activated carbon enhances durability, suppresses gas generation, and reduces resistance, maintaining high electrostatic capacity and capacity retention rates, especially under severe conditions.
Implementation Method 1
An electric double layer capacitor which is one of energy storage devices uses a capacity (electric double layer capacity) obtained only from physical ion adsorption/desorption without chemical reaction
Implementation Method 2
it is known that the durability of the capacitor is significantly affected by a reactivity between a surface functional group of activated carbon to be used and an electrolytic solution, and Patent Document 1 discloses a method for producing activated carbon in which surface functional groups are reduced by a heat treatment of a coconut shell-derived activated carbon at 900 to 1200 °C under an inert gas atmosphere
Data Source
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AI summary
The present invention relates to a coconut shell-derived modified activated carbon having a BET specific surface area of 1400 to 2000 m2/g, a value of hydrogen content/carbon content of 0.0015 to 0.0055, and intra-skeletal oxygen of 0.9 mass% or less.