Cross-linked Polymer Binder for Lithium Battery Anodes
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Solution Overview
Problem
Lithium batteries with metallic active materials face challenges due to volume changes during charging/discharging, requiring a binder that enhances mechanical properties, binding strength, and stability while maintaining initial efficiency and lifespan.
Innovation Solution
A cross-linked polymer binder is developed by combining polyamic acid and polyvinyl alcohol through an ester bond, providing improved mechanical stability and suppressing volume expansion, achieved by heat-treating the polymer mixture at 160°C or greater.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a water-soluble binder (SBR-CMC) is used in electrodes with metallic active materials, then mechanical properties and binding strength are improved, but volume change during charging/discharging is not suppressed
Solution Approach 1:
The patent uses a composite binder system combining polyvinyl alcohol (PVA) and polyamic acid (PAA) in a weight ratio of 9:1 to 1:9. This composite approach leverages the water solubility and initial efficiency of PVA while incorporating the volume stability and mechanical strength of PAA, resolving the contradiction between binding strength and volume stability that cannot be achieved with single-component binders.
Solution Approach 2:
The patent changes the chemical composition parameters of the binder by introducing polyamic acid into the polyvinyl alcohol matrix. This parameter change transforms the binder's properties to simultaneously achieve water solubility (for good initial efficiency), adequate binding strength, and volume stability during charging/discharging cycles, overcoming the limitations of conventional SBR-CMC binders.
2Strength
If polyimide binder is used, then mechanical properties and heat resistance are improved, but initial charging/discharging efficiency decreases due to water insolubility
Solution Approach 1:
The patent changes the chemical composition by using polyamic acid instead of fully imidized polyimide. Polyamic acid retains carboxyl groups that provide water solubility, enabling good initial charging/discharging efficiency, while still maintaining the mechanical strength and heat resistance characteristics of the polyimide backbone structure.
Solution Approach 2:
The patent introduces functional groups (carboxyl groups from polyamic acid) at specific locations within the binder molecule to provide water solubility, while the main polymer backbone maintains the mechanical and thermal properties. This local functional differentiation allows simultaneous achievement of water solubility and mechanical strength.
3Productivity
If polyvinyl alcohol binder is used, then initial charging/discharging efficiency and lifespan are improved, but slurry stability and electrode plate uniformity deteriorate
Solution Approach 1:
The patent creates a composite binder system where polyvinyl alcohol (90-10 wt%) provides water solubility and initial efficiency, while polyamic acid (10-90 wt%) contributes to slurry stability and electrode uniformity through its unique molecular structure and bonding characteristics. The synergistic combination resolves the contradiction between initial efficiency and slurry stability.
4Productivity
If polyvinyl alcohol binder is used, then initial efficiency is improved, but electrode stability decreases due to cracking and separation
Solution Approach 1:
The patent combines polyvinyl alcohol with polyamic acid to create a composite binder that maintains the water solubility and initial efficiency of PVA while incorporating the crack-resistant properties and strong adhesion of PAA. This composite structure prevents electrode cracking and separation during cycling, resolving the contradiction between initial efficiency and long-term stability.
Solution Approach 2:
The polyamic acid component in the composite binder provides preemptive structural support and crack prevention mechanisms that cushion against the stresses that would otherwise cause electrode failure. This beforehand cushioning effect ensures electrode stability is maintained throughout the battery's operational life.
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 cross-linked polymer binder enhances the lithium battery's initial capacity, lifespan, and electrode stability, reducing volume changes and maintaining binding strength during charging/discharging cycles.
Implementation Method 1
combining polyamic acid and polyvinyl alcohol through an ester bond
Implementation Method 2
achieved by heat-treating the polymer mixture at 160°C or greater
Data Source
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AI summary
A binder includes a third polymer including a cross-linked product of a first polymer and a second polymer, wherein the first polymer includes a first functional group and is at least one selected from a polyamic acid and a polyimide, wherein the second polymer includes a second functional group and is water-soluble, and wherein the first polymer and the second polymer are cross-linked by an ester bond formed by a reaction of the first functional group and the second functional.