Crosslinked Silicon Anode Binder for Cycle-Stable Li-Ion Batteries
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Solution Overview
Problem
Lithium ion secondary batteries using silicon as a negative electrode active material face significant challenges due to volume expansion during charging, leading to deterioration of cycle characteristics, such as cracking and peeling at the interface between the negative electrode and current collector, and decomposition of the solid electrolyte interphase coating.
Innovation Solution
A cured product for lithium ion secondary batteries is developed, comprising water-soluble polymers, a crosslinking agent, and cellulose nanofibers, with specific X-ray scattering characteristics, to improve the adhesion and flexibility of the negative electrode, thereby enhancing cycle characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If silicon is used as a negative electrode active material to increase capacity, then the theoretical capacity increases significantly, but the volume expansion during charging causes deterioration of cycle characteristics
Solution Approach 1:
The patent uses a composite binder system comprising water-soluble polymer, crosslinking agent, and cellulose nanofibers. This composite material provides both adhesion strength and flexibility to accommodate silicon's volume expansion while maintaining electrode integrity over multiple charge-discharge cycles.
Solution Approach 2:
The patent modifies the binder's physical and chemical parameters by controlling the molecular weight of water-soluble polymer (9,000-200,000), the degree of crosslinking, and the crystallinity (half-value width ≤5.5°). These parameter changes enable the binder to simultaneously provide strong adhesion and sufficient flexibility for silicon electrode applications.
2Quantity of substance
If the negative electrode active material undergoes volume expansion, then the capacity increases, but cracks occur in the negative electrode active material and peeling occurs at the interface
Solution Approach 1:
The patent creates a flexible binder film through crosslinking of water-soluble polymer with cellulose nanofibers. This flexible film can accommodate the volume expansion of silicon during charging without cracking, while maintaining strong interfacial adhesion between the active material and current collector.
Solution Approach 2:
The crosslinked binder structure provides beforehand cushioning by creating a resilient matrix that absorbs the mechanical stress of silicon expansion before damage can occur to the active material or interface. The binder acts as a cushioning layer that prevents crack propagation and peeling.
3Quantity of substance
If the negative electrode active material undergoes volume expansion, then the capacity increases, but the solid electrolyte interphase coating cracks
Solution Approach 1:
The flexible binder film maintains continuous contact with the solid electrolyte interphase coating during silicon expansion, preventing coating cracks. The binder's ability to deform elastically ensures the coating remains intact and functional throughout charge-discharge cycles.
4Reliability
If a binder is used to maintain electrode integrity, then cycle characteristics improve, but the binder must simultaneously provide adhesion and flexibility
Solution Approach 1:
The patent employs a composite binder system where each component serves a specific function: water-soluble polymer provides adhesion, crosslinking agent creates a resilient network, and cellulose nanofibers enhance flexibility and mechanical strength. This composite approach allows simultaneous achievement of adhesion and flexibility while maintaining manageable complexity through clear functional分工.
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 proposed solution significantly improves the cycle characteristics of lithium ion secondary batteries by maintaining the integrity of the electrode structure and preventing degradation, thus extending the battery's lifespan.
Implementation Method 1
The crosslinking agent crosslinks different water-soluble polymers or the water-soluble polymer and the cellulose nanofibers
Implementation Method 2
when wide-angle X-ray scattering (WAXS) measurement is performed using CuKα rays, the diffraction angle 2θ has a peak in a range of 16° or more and 21° or less
Data Source
AI summary
A cured product for lithium ion secondary batteries includes water-soluble polymers, a crosslinking agent and cellulose nanofibers. The crosslinking agent crosslinks different water-soluble polymers or the water-soluble polymer and the cellulose nanofibers. When wide-angle X-ray scattering (WAXS) measurement is performed using CuKα rays, the diffraction angle 2θ has a peak in a range of 16° or more and 21° or less. The half-value width of the peak is 5.5° or less.