Polyimide Binder Molecular Weight Distribution for Silicon Anode Adhesion
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Solution Overview
Problem
Lithium secondary batteries with silicon or silicon alloy negative electrodes face degradation in current collection performance due to volumetric changes during lithium occlusion and release, leading to poor electron conductivity and cycle performance.
Innovation Solution
A lithium secondary battery design featuring a negative electrode with a polyimide resin binder having a specific molecular weight distribution (50:50 to 90:10 ratio of low to high molecular weight polyimide resins) and a copper or copper alloy current collector with controlled surface roughness, enhancing adhesion and conductivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If silicon or silicon alloy is used as negative electrode active material to increase capacity, then the discharge capacity increases, but the negative electrode active material pulverizes or peels off due to volumetric change during lithium occlusion and release
Solution Approach 1:
The patent employs a polyimide binder that forms a flexible binding network around silicon particles, accommodating volumetric changes during lithium occlusion and release. This flexible binding structure prevents pulverization and peeling of the active material, maintaining electrode integrity over multiple charge-discharge cycles while preserving high capacity.
2Strength
If conventional polyimide resin is used as binder to improve adhesion, then some adhesion is achieved, but the adhesive strength and strength of the resin are still insufficient, causing degradation of current collection performance
Solution Approach 1:
The patent optimizes the molecular weight distribution of the polyimide binder, specifically controlling the weight ratio of low molecular weight (less than 100,000) to high molecular weight (100,000 to less than 200,000) polyimide resin to be between 50:50 and 90:10. This parameter optimization enhances both the adhesive strength and the mechanical strength of the binder, preventing degradation of current collection performance during battery cycling.
Solution Approach 2:
The patent creates a composite binder system by combining polyimide resin with specific molecular weight distribution characteristics. This composite approach, where the binder comprises a controlled mixture of different molecular weight polyimide fractions, provides superior adhesive and mechanical properties compared to conventional single-species polyimide binders, thereby maintaining current collection performance.
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 solution inhibits degradation of current collection performance, improves initial charge-discharge efficiency, discharge rate performance, and cycle life by maintaining strong adhesion and conductivity within the negative electrode.
Implementation Method 1
the negative electrode binder contains a polyimide resin having a structure represented by the following chemical formula (1), and the polyimide resin has a molecular weight distribution such that the weight ratio of a polyimide resin having a molecular weight of less than 100,000 and a polyimide resin having a molecular weight from 100,000 to less than 200,000 is from 50:50 to 90:10
Implementation Method 2
a non-aqueous electrolyte impregnated in the electrode assembly
Implementation Method 3
lithium-ion batteries, which perform charge and discharge by transferring lithium ions between the positive and negative electrodes
Data Source
AI summary
A lithium secondary battery contains a negative electrode binder containing a polyimide resin having a structure represented by the following chemical formula (1), and the polyimide resin having a molecular weight distribution such that the weight ratio of a polyimide resin having a molecular weight of less than 100,000 and a polyimide resin having a molecular weight from 100,000 to less than 200,000 is from 50:50 to 90:10:where n is an integer equal to or greater than 1, and R is a functional group represented by the following chemical formula (2) or (3):