Polyimide Binder Silicon Anode Fracture Prevention
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Solution Overview
Problem
Lithium secondary batteries using silicon or silicon alloy as negative electrode active material face issues with binder resin fractures and peeling, leading to poor electron conductivity and cycle performance due to insufficient adhesion and strength.
Innovation Solution
A lithium secondary battery design incorporating a polyimide resin binder with silicon particles or alloy particles of 5 μm or greater average size, along with a negative electrode current collector and separator, enhances adhesion and prevents fractures, maintaining electron conductivity and improving cycle performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If silicon particles or silicon alloy particles are used as negative electrode active material to increase discharge capacity, then the energy density is improved, but the binder resin fractures and peeling occurs due to expansion and shrinkage during charge-discharge operations
Solution Approach 1:
The patent changes the particle size parameter of silicon particles to 5 μm or greater, which reduces the surface area to volume ratio and minimizes expansion-shrinkage stress during lithiation-delithiation cycles. This parameter modification prevents binder resin fractures while maintaining high discharge capacity, resolving the contradiction between energy density and cycle performance.
2Strength
If conventional polyimide resin is used as binder to improve adhesion, then the strength is partially improved, but the adhesion and strength are still insufficient to prevent fractures during repeated charge-discharge operations
Solution Approach 1:
The patent employs a composite binder system comprising polyimide resin combined with specific additives and uses a multi-component negative electrode active material layer including silicon particles, carbon particles, and conductive agents. This composite structure provides both mechanical strength and electrical conductivity, preventing binder fractures during cycling while maintaining adhesion to the current collector.
3Productivity
If smaller silicon particles are used to increase surface area for lithium ion insertion, then the reaction efficiency is improved, but the expansion and shrinkage causes more severe binder resin fractures
Solution Approach 1:
The patent optimizes the particle size parameter to 5 μm or greater, finding the optimal balance between surface area for lithium ion insertion and mechanical stability during expansion-shrinkage cycles. This parameter selection maintains adequate reaction efficiency while preventing binder resin fractures, resolving the contradiction between productivity and structural integrity.
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 resin with larger silicon particles improves the adhesion and strength of the binder, preventing fractures and maintaining electron conductivity, thus enhancing the battery's cycle performance and energy density.
Implementation Method 1
the binder contains a polyimide resin... the adhesion and the strength of the resin have still been insufficient... improves the adhesion and the strength of the binder
Implementation Method 2
silicon particles and silicon alloy particles, which can absorb a large amount of lithium per unit volume
Implementation Method 3
a non-aqueous electrolyte impregnated in the electrode assembly... lithium-ion batteries that perform charge and discharge by transferring lithium ions
Data Source
AI summary
A lithium secondary battery includes an electrode assembly having a positive electrode (1), a negative electrode (2) having a negative electrode current collector and a negative electrode active material layer formed on a surface of the negative electrode current collector and composed of a binder and negative electrode active material particles containing silicon and/or a silicon alloy, and a separator (3) interposed between the electrodes. The electrode assembly is impregnated with a non-aqueous electrolyte. The binder contains a polyimide resin represented by the following chemical formula (1):where R contains at least a benzene ring, and n is within the range of from 10 to 100,000, and the negative electrode active material particles have an average particle size of 5 μm or greater.