Electric Double Layer Capacitor Low-Temperature Reliability

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Solution Overview

Problem

Conventional electric double layer capacitors experience capacitance reduction and increased resistance due to electrochemical reactions between the driving electrolyte and acidic surface functional groups on the polarizable electrodes, particularly at low temperatures, leading to reliability issues.

Innovation Solution

The use of activated carbon made from phenol resin with surface roughness not exceeding 0.6 μm and electrode density between 0.5 g/cm3 to 0.7 g/cm3, combined with a driving electrolyte containing an aprotic polar solvent and amidine salt, minimizes electrochemical reactions and maintains capacitance and reliability even at low temperatures.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Quantity of substance

If activated carbon with abundant acidic surface functional groups is used to increase pseudocapacitance, then capacitance is improved, but electrochemical reactions with the driving electrolyte produce reactants that block capacitance sites and increase resistance, particularly at low temperatures

Engineering Contradiction:

ImprovecapacitanceVSAvoidlow-temperature performance

Core Design Contradiction:

Quantity of substanceVSReliability

Solution Approach 1:

The patent changes the chemical composition parameters of the driving electrolyte by selecting specific aprotic polar solvents (cyclic carbonates, chain carbonates, cyclic carboxylic acid esters) and combining them with amidine salts in specific concentration ratios. This parameter optimization reduces the electrochemical reactivity with acidic surface functional groups while maintaining adequate ionic conductivity, thereby suppressing reactant formation and capacitance site blocking at low temperatures

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent uses a composite electrolyte system combining multiple solvent components (cyclic carbonate + chain carbonate + cyclic carboxylic acid ester) with amidine salts. This composite formulation creates a synergistic effect where the different solvent components work together to minimize electrochemical reactions while maintaining electrolyte performance, effectively reducing the harmful interactions between the electrolyte and acidic surface groups on activated carbon

Inventive Principle:

Principle #40Composite materials

2Quantity of substance

If conventional electrolytes are used to achieve large capacitance, then capacitance is improved, but the electrolyte electrochemically reacts with acidic surface functional groups during charge-discharge cycles, producing reactants that block capacitance sites and deteriorate characteristics

Engineering Contradiction:

ImprovecapacitanceVSAvoidreactant formation

Core Design Contradiction:

Quantity of substanceVSObject-generated harmful factors

Solution Approach 1:

The patent optimizes the chemical parameters of the electrolyte by selecting specific solvent types (cyclic carbonates, chain carbonates, cyclic carboxylic acid esters) and controlling the concentration of amidine salts. These parameter changes reduce the electrochemical reactivity with acidic surface functional groups, thereby minimizing reactant formation that would otherwise block capacitance sites and deteriorate capacitor characteristics

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent converts the potential harm of electrochemical reactions into a benefit by using amidine salts in the electrolyte formulation. The amidine salts interact with the acidic surface functional groups in a controlled manner that prevents harmful reactant formation while maintaining or even enhancing the pseudocapacitance effect, thus turning a potentially harmful interaction into a beneficial one

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

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 configuration results in an electric double layer capacitor with stable capacitance and low resistance at both room and low temperatures, ensuring high long-term reliability and performance.

Implementation Method 1

An electric double layer capacitor including polarized electrode layers containing activated carbon with abundant acidic surface functional groups (carboxyl group, carbonyl group, phenolic hydroxyl group, lactone group) has a large site contributing to the capacitance of the capacitor, accordingly having a large pseudocapacitance

Methodology Applied

Scientific EffectPseudocapacitance: Capacitance

Implementation Method 2

a driving electrolyte impregnated in the first polarizable electrode layer and the second polarizable electrode layer

Methodology Applied

Scientific EffectCapillary action: Capillary Action

Data Source

PatentUS8351182B2Electric double layer capacitor

Publication Date: 2013.01.08 PANASONIC HOLDINGS CORP

AI summary

An electric double layer capacitor includes a first collector, a first polarizable electrode layer provided on the first collector, a second collector, a second polarizable electrode layer provided on the second collector and facing the first polarizable electrode layer, a separator having an insulating property and provided between the first polarizable electrode layer and the second polarizable electrode layer, and a driving electrolyte impregnated in the first polarizable electrode layer and the second polarizable electrode layer. The polarizable electrode layers mainly contain activated carbon made from phenol resin, have a surface roughness not larger than 0.6 μm, and have an electrode density ranging from 0.5 g/cm3 to 0.7 g/cm3. This electric double layer capacitor has characteristics deteriorating little even at low temperatures, thus having a reliability for a long time.