Polyborosiloxane Binder for Silicon Anode Volume Expansion
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Solution Overview
Problem
Silicon nanoparticles (SiNP) in anodes for rechargeable batteries face significant capacity loss due to volume expansion during lithiation, leading to disintegration and irreversible damage, which is costly to mitigate with existing geometric arrangements and binder modifications.
Innovation Solution
A self-healing polyborosiloxane binder, crosslinked with boric acid and tri-functional silyl ether, optionally with polydimethylsiloxane (PDMS), is used to create a highly cross-linked matrix that accommodates volume changes and maintains coulombic efficiency and capacity retention.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If silicon nanoparticles are used to increase storage capacity, then specific capacity is improved (3579 mAh/g), but volume expansion during lithiation causes disintegration and capacity loss
Solution Approach 1:
A polysiloxane binder coating is applied to the silicon nanoparticle surface, forming a flexible shell that can accommodate the 300% volume expansion during lithiation. This flexible coating prevents particle disintegration while maintaining electrical contact and structural integrity throughout cycling.
Solution Approach 2:
The invention uses a composite structure combining silicon nanoparticles with a polysiloxane binder material. This composite approach allows the silicon to provide high capacity while the polysiloxane matrix provides structural stability and flexibility to handle volume changes, creating a synergistic system that overcomes the limitations of pure silicon.
2Reliability
If binder modifications are employed to prevent capacity loss, then capacity retention is improved, but manufacturing cost increases
Solution Approach 1:
The invention changes the chemical composition parameters of the binder by incorporating specific ratios of polydimethylsiloxane (75-95 wt%), polyethylsiloxane (2-10 wt%), and polypropylsiloxane (2-10 wt%). This compositional parameter optimization achieves superior capacity retention while maintaining cost-effectiveness through the use of commercially available polysiloxane materials.
3Reliability
If highly cross-linked polysiloxane binder is used, then coulombic efficiency approaches 100% after 200 cycles, but binder synthesis complexity increases
Solution Approach 1:
The polysiloxane binder is pre-synthesized with controlled cross-linking before electrode fabrication. This preliminary action ensures that the binder already possesses the optimal mechanical properties and cross-link density needed to accommodate silicon expansion, simplifying the overall electrode manufacturing process while achieving high coulombic efficiency.
Solution Approach 2:
The binder itself is a composite polysiloxane system combining multiple siloxane components with different chain lengths and side groups. This composite binder structure provides both the flexibility needed for volume expansion and the cross-linked network necessary for high coulombic efficiency, achieving multiple functions through material composition rather than complex processing.
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 polyborosiloxane binder achieves coulombic efficiencies of 100% after 200 cycles and specific charge capacities greater than 2000 mAh/g, addressing the issue of SiNP expansion-contraction and enhancing the stability and performance of Si-based anode materials.
Implementation Method 1
a crosslinked siloxane binder... the polyborosiloxane binder is crosslinked from the crosslinkers triethoxyphenylsilane (TEPS) or boric acid or a mixture thereof
Implementation Method 2
the inherent 300% volume expansion of Si upon full lithiation... SiNP expansion-contraction process
Data Source
AI summary
Electrodes for rechargeable batteries that include silicon and a binder are provided. Binders for use with silicon electrodes are provided, including polysiloxane binders that can be prepared prior to preparation of the electrode, or provided as monomers to be cure-polymerized at the time of the curing of the electrode.