Rolled Supercapacitor Electrode Structure for High Volumetric Energy
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Solution Overview
Problem
Current supercapacitors face challenges with graphene-based electrodes due to re-stacking of graphene sheets, low tap density, difficulty in producing thick layers, and low volumetric and gravimetric energy densities, which restrict their application in high-performance energy storage devices.
Innovation Solution
A rolled supercapacitor design featuring an electrolyte-impregnated laminar graphene structure with isolated graphene sheets alternately spaced by thin electrolyte layers, allowing for high tap density and specific surface area, and a process for producing these electrodes that prevents re-stacking and enhances porosity and thickness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If conventional slurry coating procedure is used to produce thick electrodes, then electrode thickness can be increased, but the electrodes become extremely brittle and of poor structural integrity
Solution Approach 1:
The patent uses a flexible binder polymer matrix to hold conductive particles together, creating a flexible electrode structure that maintains structural integrity at thick dimensions. The binder polymer forms a continuous phase that provides mechanical strength while allowing electrode thickness to exceed 200 micrometers without becoming brittle.
Solution Approach 2:
The electrode is formulated as a composite material containing conductive particles (5-50 weight percent), binder polymer (40-80 weight percent), and plasticizer (10-40 weight percent). This composite structure combines the electrical conductivity of particles with the mechanical strength and flexibility of the polymer matrix, enabling thick electrodes with good structural integrity.
2Quantity of substance
If high surface area activated carbon is used to increase volumetric capacitance, then specific surface area increases, but only 20-40 percent of the theoretical capacitance is observed due to micro-pore accessibility issues
Solution Approach 1:
The patent uses particles with mixed pore size distributions including meso-pores (2-50 nm) and macro-pores (>50 nm) in addition to micro-pores. The larger pores provide excellent electrolyte accessibility and ion transport channels, while the micro-pores contribute to surface area. This local variation in pore quality ensures both high volumetric capacitance and good electrolyte penetration.
Solution Approach 2:
The patent employs porous particles with controlled pore size distributions, emphasizing meso-pores and macro-pores that are easily accessible to electrolyte. The porous structure is optimized to balance surface area (for capacitance) with pore accessibility (for electrolyte penetration), achieving over 80% of theoretical capacitance.
3Quantity of substance
If active material mass loading is increased to improve energy density, then gravimetric capacitance improves, but the electrodes become harder to process and maintain porosity
Solution Approach 1:
The binder polymer acts as an intermediary material that facilitates processing of high loading electrodes. It provides a workable slurry consistency during coating, enables proper adhesion to current collectors, and maintains electrode structure during assembly. This intermediary allows active material loading to exceed 10 mg/cm² while remaining processable.
Solution Approach 2:
The patent optimizes the ratio of conductive particles to binder polymer, using 5-50 weight percent particles in the electrode composition. This parameter adjustment ensures sufficient active material loading for high energy density while maintaining enough binder to keep the electrode flexible and processable during manufacturing.
4Quantity of substance
If tap density of active material is increased to improve volumetric energy density, then volume efficiency improves, but porosity and electrolyte accessibility may be reduced
Solution Approach 1:
The electrode structure features local variations in density and porosity. Regions with higher tap density provide volumetric efficiency, while interconnected meso-pore and macro-pore channels maintain electrolyte accessibility and ion transport pathways. This local quality differentiation allows high volumetric energy density without sacrificing ion transport speed.
Solution Approach 2:
The patent uses particles with meso-pores and macro-pores that maintain porosity even at high tap densities. The larger pore sizes ensure electrolyte can penetrate and access the active material throughout the thick electrode, maintaining fast ion transport while achieving high volumetric energy density.
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 solution enables high volumetric capacitance, high active material mass loading, and high energy densities, overcoming the limitations of conventional graphene-based electrodes, and allows for flexible design and control of porosity and thickness.
Implementation Method 1
A polarized double layer is formed at electrode-electrolyte interfaces providing high capacitance. This double layer, created naturally at a solid-electrolyte interface when voltage is imposed, has a thickness of only about 1 nm
Implementation Method 2
Physical rather than chemical energy storage is the key reason for their safe operation and extraordinarily high cycle-life
Implementation Method 3
The high volumetric capacitance density of an EC relative to conventional capacitors (10 to 100 times greater than conventional capacitors) derives from using porous electrodes to create a large effective 'plate area'
Implementation Method 4
The specific capacitance of a supercapacitor is directly proportional to the specific surface area of the electrode material. This surface area must be accessible by electrolyte
Implementation Method 5
The multiple graphene sheets are alternately spaced by thin electrolyte layers, from 0.3 nm to 10 nm in thickness
Implementation Method 6
The resulting interfacial zones must be sufficiently large to accommodate the so-called electric double-layer charges
Data Source
AI summary
Provided is rolled supercapacitor comprising an anode, a cathode, a porous separator, and an electrolyte, wherein the anode contains a wound anode roll of an anode active material having an anode roll length, an anode roll width, and an anode roll thickness, wherein the anode active material contains isolated graphene sheets that are oriented substantially parallel to the plane defined by the anode roll length and the anode roll width; and/or the cathode contains a wound cathode roll of a cathode active material having a cathode roll length, a cathode roll width, and a cathode roll thickness, wherein the cathode active material contains isolated graphene sheets that are oriented substantially parallel to the plane defined by the cathode roll length and the cathode roll width; and wherein the anode roll width and/or the cathode roll width is substantially perpendicular to the separator.