Flexible Polymer Binder for Lithium Battery Electrodes
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Solution Overview
Problem
The existing negative active material compositions for lithium rechargeable batteries face issues with electrode shrinkage due to dehydration reactions of polyimide precursors, leading to bending and reduced capacity, as well as surface cracking when attempting to straighten the electrodes.
Innovation Solution
Incorporating a highly flexible polymer with a glass transition temperature of about -60°C to 50°C and a weight average molecular weight ranging from 10,000 to 500,000 into the negative active material composition to mitigate the volume contraction of polyimide precursors, thereby preventing bending and ensuring flexibility.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If polyimide precursor compound is used as binder in negative active material composition, then adhesion characteristics and shape stability at high temperatures are improved, but volume contraction during dehydration reaction causes electrode bending and reduced capacity
Solution Approach 1:
The patent uses a composite binder system combining polyimide precursor compound with a flexible polymer (such as polyvinylidene fluoride or carboxymethyl cellulose). This composite approach allows the polyimide precursor to provide high-temperature stability while the flexible polymer compensates for volume contraction during dehydration, preventing electrode bending and maintaining structural integrity.
Solution Approach 2:
The patent modifies the binder composition by introducing a flexible polymer component with specific glass transition temperature characteristics. This parameter change in the binder system allows it to maintain flexibility during the dehydration reaction of polyimide precursor, counteracting the volume contraction and preventing electrode deformation while preserving adhesion and thermal stability.
2Strength
If polyimide precursor compound undergoes dehydration reaction to form polyimide, then adhesion and thermal stability are improved, but the rigid structure causes surface cracking when electrode is straightened
Solution Approach 1:
The flexible polymer component in the composite binder system acts as a crack-arresting phase. When the polyimide precursor undergoes dehydration and forms rigid polyimide structure, the flexible polymer maintains elasticity and prevents stress concentration, thereby avoiding surface cracking during electrode straightening while preserving adhesion strength.
Solution Approach 2:
The flexible polymer is incorporated into the binder composition before the dehydration reaction occurs. This beforehand cushioning effect allows the binder to absorb and distribute the stresses generated during volume contraction and subsequent electrode straightening, preventing surface cracking before they can occur.
3Shape
If electrode is straightened after bending to restore shape, then shape is improved, but surface cracking occurs reducing capacity and cycle-life
Solution Approach 1:
The flexible polymer provides beforehand cushioning by maintaining binder flexibility during and after the dehydration reaction. This prevents surface cracking from occurring in the first place, thereby preserving electrode integrity and maintaining high capacity and cycle-life without requiring post-processing straightening operations.
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 use of a flexible polymer binder suppresses electrode bending, maintains high capacity, and improves cycle-life characteristics by controlling volume changes during charge and discharge cycles.
Implementation Method 1
The conversion reaction, which is a dehydration reaction, causes shrinkage of the polyimide, resulting in bending of the negative electrode
Implementation Method 2
Polyamic acid (which is a precursor of polyimide) is converted into polyimide during drying of the negative electrode preparation. The conversion reaction, which is a dehydration reaction
Implementation Method 3
improves cycle-life characteristics by controlling volume changes during charge and discharge cycles
Data Source
AI summary
Negative active material compositions for rechargeable lithium batteries, negative electrodes for rechargeable lithium batteries, and rechargeable lithium batteries using the negative active material compositions are provided. The negative active material composition includes a negative active material, a polyimide precursor compound, and a highly flexible polymer. The negative active material composition prevents the electrode substrate from bending, thereby improving the capacity and cycle-life characteristics of the battery.