Polyimide Binder for Silicon Anodes Reducing Swelling
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Solution Overview
Problem
Silicon-based negative electrode active materials in lithium-based batteries experience significant volume expansion and contraction during charging/discharging, leading to mechanical degradation, reduced adhesion with conductive fillers, and poor cycling performance due to the presence of ether and carbonyl groups in polyimide binders, which react with electrolytes and cause swelling.
Innovation Solution
Incorporating a polyimide binder with no ether groups and no more than one carbonyl group in its backbone structure, combined with graphite particles to reduce volume changes and enhance adhesion, thereby improving the cycling performance and capacity retention of silicon-based negative electrodes in lithium-ion and lithium-sulfur batteries.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If silicon-based negative electrode active materials are used to achieve high capacity, then the battery capacity increases, but the material experiences significant volume expansion and contraction during charging/discharging, leading to mechanical degradation and poor cycling performance
Solution Approach 1:
The patent modifies the chemical structure parameters of the polyimide binder by controlling the number of carbonyl groups (0-2 groups) and specific functional groups in the repeating unit. This parameter change optimizes the binder's interaction with silicon active material, reducing mechanical degradation during volume changes while maintaining high capacity
Solution Approach 2:
The patent creates a composite negative electrode material consisting of silicon-based active material combined with specifically structured polyimide binder. This composite structure allows the binder to effectively accommodate silicon's volume expansion and contraction, improving cycling performance while maintaining high capacity
2Strength
If conventional polyimide binders containing ether and carbonyl groups are used, then the binder provides adhesion, but the carbonyl groups react with electrolytes causing binder swelling and reduced adhesion
Solution Approach 1:
The patent precisely controls the number of carbonyl groups in the polyimide repeating unit (no more than 2 groups) and specifies the absence of ether groups. This parameter optimization reduces the binder's reactivity with electrolytes, preventing swelling and maintaining compositional stability while preserving adhesion strength
Solution Approach 2:
The patent introduces specific local structural features in the polyimide backbone, including particular substituent groups (such as fluorinated groups or aromatic groups) at specific positions. These local structural modifications create regions of low reactivity with electrolytes while maintaining overall binder adhesion
3Stability of the object's composition
If the polyimide binder structure is modified to reduce electrolyte reaction, then binder stability improves, but adhesion strength may be compromised
Solution Approach 1:
The patent optimizes multiple parameters simultaneously: the number of carbonyl groups (0-2), the type of substituent groups (fluorinated, aromatic), and their positions in the repeating unit. This multi-parameter optimization achieves both reduced electrolyte reactivity and maintained adhesion strength
Solution Approach 2:
The patent creates a composite binder system where the specifically structured polyimide provides both stability and adhesion. The unique molecular structure combines low-reactivity features with high-adhesion features, achieving both objectives simultaneously
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 polyimide binders with specific structural constraints and graphite reduces electrolyte absorption, minimizing swelling and mechanical stress, resulting in improved capacity retention and reduced capacity fade, enhancing the overall performance and lifespan of lithium-based batteries.
Implementation Method 1
The use of polyimide binders with specific structural constraints and graphite reduces electrolyte absorption, minimizing swelling and mechanical stress
Data Source
AI summary
A negative electrode material includes an active material, which is present in an amount ranging from about 60 wt % to about 95 wt % of a total wt % of the negative electrode material. The negative electrode material further includes a polyimide binder, which is present in an amount ranging from about 1 wt % to about 20 wt % of the total wt % of the negative electrode material. The polyimide binder contains a repeating unit, where a backbone structure of each repeating unit has no ether group present and no more than one carbonyl group present. The negative electrode material also includes a conductive filler, which is present in an amount ranging from about 3 wt % to about 20 wt % of the total wt % of the negative electrode material.