Expanded Graphite Sheet for Air Battery Electrode
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Solution Overview
Problem
Ordinary expanded graphite sheets used as positive electrodes in air batteries may swell when exposed to water-based electrolyte solutions, leading to potential electrode breakage and reduced battery performance.
Innovation Solution
Incorporating a polyolefin resin, such as polypropylene, into the expanded graphite sheet to enhance water repellency and maintain electrical conductivity, with a surface water contact angle of ≥90° and surface resistivity ≤70 mΩ/sq, preventing swelling and optimizing gas permeability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If an ordinary expanded graphite sheet is used as the positive electrode for an air battery, then the battery can achieve high discharge capacity and size reduction, but the expanded graphite sheet may swell when exposed to water-based electrolyte solutions, leading to electrode breakage and reduced reliability
Solution Approach 1:
The patent creates a composite material by combining expanded graphite with a hydrophobic substance (having a water contact angle of 90° or more). This composite structure allows the expanded graphite to maintain its high discharge capacity while the hydrophobic substance prevents water penetration and swelling, thereby resolving the contradiction between productivity and reliability
Solution Approach 2:
The hydrophobic substance acts as an intermediary layer that mediates between the expanded graphite and the water-based electrolyte solution. It allows the electrolyte to contact the graphite for electrochemical reactions while preventing excessive water penetration that would cause swelling, thus maintaining both high capacity and electrode stability
2Reliability
If the expanded graphite sheet is made more hydrophobic to prevent swelling, then electrode stability improves, but electrical conductivity may deteriorate
Solution Approach 1:
The hydrophobic substance is applied in a controlled manner to specific regions or surfaces of the expanded graphite sheet, creating local hydrophobicity where needed for water resistance while preserving the bulk electrical conductivity of the graphite structure. This selective application maintains both stability and conductivity
Solution Approach 2:
The patent carefully controls the parameters of the hydrophobic substance application, including the amount, distribution, and type of hydrophobic material, to achieve the optimal balance between water repellency (contact angle ≥90°) and electrical conductivity (surface resistivity ≤70 mΩ/sq). By adjusting these parameters, both reliability and manufacturing precision are maintained
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 expanded graphite sheet effectively inhibits swelling, improves reliability, and prolongs the service life of air batteries while maintaining high electrical conductivity and gas permeability, enhancing battery capacity and performance.
Implementation Method 1
Incorporating a polyolefin resin, such as polypropylene, into the expanded graphite sheet to enhance water repellency
Implementation Method 2
the capability of supplying oxygen-originating hydroxide ions... a carbon material that permeates gas but does not permeate liquid
Implementation Method 3
the positive electrode for the air battery have electrical conductivity
Data Source
Figure 5~6
Figure 7
AI summary
An expanded graphite sheet and a battery using the expanded graphite sheet are provided, that can inhibit the expanded graphite sheet from swelling even when the expanded graphite sheet is used for, for example, a positive electrode for an air battery. An expanded graphite sheet includes an expanded graphite and has a surface water contact angle of greater than or equal to 90 degrees and a surface resistivity of less than or equal to 70 mΩ/sq. It is desirable that a polyolefin resin be contained in the expanded graphite sheet in a dispersed state. It is desirable that the polyolefin resin be polypropylene.