Carbon-Sulfur Cathode Electrolyte for Higher Sulfur Utilization
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Solution Overview
Problem
Conventional nonaqueous electrolyte energy storage devices with carbon-sulfur composites have a low sulfur utilization factor, resulting in insufficient discharge capacity due to high electric resistivity of sulfur.
Innovation Solution
A nonaqueous electrolyte energy storage device is developed with a positive electrode containing a composite of porous carbon and sulfur, and a nonaqueous electrolyte comprising an unsaturated cyclic carbonate and a lithium salt, where the cumulative 70% pore size of the porous carbon is between 2.0 nm and 7.0 nm, and the unsaturated cyclic carbonate content is 10 vol % or more, allowing for a positive electrode potential at end-of-discharge voltage of 1.0 V vs. Li/Li+, enhancing sulfur utilization and ion conductivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If sulfur is used as a positive active material to increase theoretical capacity, then energy density is improved, but electric resistivity increases causing low sulfur utilization factor
Solution Approach 1:
The patent employs porous carbon materials with specific pore size distributions (cumulative 70% pore size of 2.0 nm or more and 7.0 nm or less) to encapsulate sulfur. The porous structure provides a large surface area and confined spaces that reduce sulfur's electric resistivity by facilitating electron and ion transport pathways, thereby maintaining high theoretical capacity while significantly improving sulfur utilization factor.
Solution Approach 2:
The patent creates composite structures combining porous carbon with sulfur, forming carbon-sulfur composites where the carbon matrix provides conductive pathways and structural support. This composite approach allows sulfur to maintain its high capacity advantage while the carbon component addresses the resistivity issue, achieving both high energy density and reliable sulfur utilization.
2Reliability
If conventional carbon-sulfur composites are used to reduce electric resistivity, then conductivity is improved, but discharge capacity remains insufficient due to low sulfur utilization
Solution Approach 1:
The patent optimizes specific parameters of the porous carbon material, particularly the cumulative 70% pore size controlled within 2.0-7.0 nm range, and the content of unsaturated cyclic carbonate in the electrolyte (10 vol% or more). These parameter changes create optimal conditions for sulfur utilization, enabling the system to achieve both low electric resistivity and high discharge capacity through precise control of material properties.
3Productivity
If deep discharge is performed to increase sulfur utilization, then discharge capacity is improved, but positive electrode potential drops to 1.0 V vs. Li/Li+ requiring special electrolyte composition
Solution Approach 1:
The patent modifies the electrolyte composition by incorporating unsaturated cyclic carbonate at 10 vol% or more, which enables the positive electrode to maintain stable operation at lower potentials (1.0 V vs. Li/Li+). This parameter change in electrolyte composition allows deep discharge to proceed without causing detrimental effects, thereby achieving high discharge capacity while managing the electrode potential effectively.
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 significantly increases the discharge capacity per mass of sulfur, improving sulfur utilization and energy density by forming a high-ion conductivity film within the composite, thereby enhancing the device's performance.
Implementation Method 1
a positive electrode containing a composite of porous carbon and sulfur, in which a cumulative 70% pore size of the porous carbon is 2.0 nm or more and 7.0 nm or less
Implementation Method 2
a nonaqueous electrolyte containing a nonaqueous solvent containing an unsaturated cyclic carbonate and a lithium salt, in which a content of the unsaturated cyclic carbonate in the nonaqueous solvent is 10 vol % or more
Implementation Method 3
a nonaqueous electrolyte interposed between the electrodes, and is configured to allow charge transport ions to be transferred between both the electrodes for charge-discharge
Data Source
AI summary
A nonaqueous electrolyte energy storage device according to one aspect of the present invention includes: a positive electrode containing a composite of porous carbon and sulfur; and a nonaqueous electrolyte containing a nonaqueous solvent containing an unsaturated cyclic carbonate and a lithium salt, in which a cumulative 70% pore size of the porous carbon is 2.0 nm or more and 7.0 nm or less, a content of the unsaturated cyclic carbonate in the nonaqueous solvent is 10 vol % or more, and a positive electrode potential at an end-of-discharge voltage in normal use is 1.0 V vs. Li/Li+ or less.