Lithium Battery Electrode Binder to Prevent Slurry Phase Separation
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Solution Overview
Problem
Lithium-sulfur secondary batteries face issues with high solubility of lithium polysulfide, low life and output characteristics, and low electrical conductivity due to the use of lithium metal, leading to degradation and phase separation problems in existing binders like polyacrylic acid and polyethylene oxide.
Innovation Solution
A random copolymer binder composed of polyacrylic acid and polyethylene oxide is used, with functional groups substitutable with lithium ions, preventing phase separation and improving adhesive force and charging/discharging characteristics by forming a stable electrode layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If polyacrylic acid (PAA) is used as a water-based binder to improve charging/discharging life characteristics, then adhesive force is improved, but the electrode becomes rigid and flexibility deteriorates due to glass transition temperature and hydrogen bonding
Solution Approach 1:
The patent combines PAA and PEO into a copolymer structure where PAA segments provide adhesive force and charging/discharging life characteristics, while PEO segments provide flexibility. This merging allows both functionalities to coexist within a single binder material, resolving the contradiction between reliability and ease of operation.
Solution Approach 2:
The invention creates a composite binder system by forming a copolymer of PAA and PEO. The composite structure integrates the strengths of both polymers: PAA's carboxylic acid groups for strong adhesion and PEO's flexible ether chains for electrode flexibility, thereby simultaneously achieving improved reliability and ease of operation.
2Ease of operation
If polyethylene oxide (PEO) is used together with PAA to improve flexibility and adhesive force, then flexibility is improved, but phase separation occurs between PAA and PEO resulting in weak processability
Solution Approach 1:
Instead of physically mixing PAA and PEO which causes phase separation, the patent merges them at the molecular level by forming a copolymer. This ensures homogeneous distribution of both polymer segments throughout the binder, eliminating phase separation and improving processability while maintaining the desired flexibility and adhesive force.
Solution Approach 2:
The copolymer structure ensures homogeneous mixing of PAA and PEO segments at the molecular level. The random or block copolymer architecture prevents macroscopic phase separation that occurs in physical blends, thereby improving processability and electrode formation while maintaining the flexibility and adhesive benefits of both components.
3Reliability
If sulfur is impregnated into porous bodies to inhibit solubility of lithium polysulfide, then solubility is reduced, but the electrode structure becomes complex and manufacturing difficulty increases
Solution Approach 1:
The patent extracts the solubility resistance function from the complex porous body structure and transfers it to the binder molecule itself. The PAA segments with carboxylic acid groups can coordinate with lithium polysulfide, providing solubility resistance directly at the molecular level without requiring complex porous architectures, thereby simplifying the overall electrode structure.
Solution Approach 2:
The copolymer binder performs multiple functions simultaneously: it provides adhesive force, flexibility, and solubility resistance against lithium polysulfide. This multi-functionality eliminates the need for separate porous body structures designed solely for solubility resistance, reducing device complexity while maintaining reliability.
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 random copolymer binder enhances the solid content of the electrode slurry, reduces surface roughness and cracks, and improves the adhesive force, leading to better charging/discharging and life characteristics of lithium-sulfur batteries.
Implementation Method 1
it has been found that when a random copolymer is prepared from polyacrylic acid (PAA) and polyethylene oxide (PEO) instead of simply blending them
Implementation Method 2
the first block comprises a polymer containing functional groups substitutable with lithium ions
Implementation Method 3
improving the adhesive force of the electrode
Data Source
Figure 1~2
AI summary
The present invention relates to a binder, and an electrode and a lithium secondary battery comprising the same. More particularly, the binder includes a first block including a polymer having a functional group substitutable with a lithium ion, and a second block including a polymer containing oxygen atoms at a main chain thereof. Therefore, the binder can prevent agglomeration of a slurry for an electrode preparation, and thus can prevent cracks from occurring on a surface of an electrode and improve lifespan characteristics of a lithium secondary battery.