Silicon-Polymer Anode Coating for Stable SEI Under Volume Expansion
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Solution Overview
Problem
Silicon-based anode active materials in secondary batteries face issues with volume expansion and contraction during charge and discharge, leading to mechanical instability and degradation of battery performance due to excessive formation of an unstable solid electrolyte interphase (SEI) layer.
Innovation Solution
A silicon-polymer composite is prepared by forming a polymer thin film on silicon particles using initiator-based chemical vapor deposition (iCVD), followed by optionally forming a carbon thin film, to maintain the original shape of silicon particles and act as a stable solid electrolyte interphase layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If silicon particles are used as anode active materials to improve capacity, then energy density is improved, but mechanical stability deteriorates due to volume expansion of up to 300% during charge and discharge
Solution Approach 1:
A polymer thin film is formed on the surface of silicon particles through initiator-based chemical vapor deposition (iCVD) to create a flexible protective shell. This shell accommodates the volume expansion and contraction during lithium insertion and extraction, preventing mechanical fracturing while maintaining structural integrity. The thin film acts as a buffer that flexes with the silicon particle volume changes.
Solution Approach 2:
The invention creates a composite structure by coating silicon particles with polymer material. This composite approach combines the high capacity of silicon with the mechanical stability and flexibility of the polymer matrix, resulting in an anode material that maintains structural integrity during charge-discharge cycles while preserving high energy density.
2Ease of manufacture
If silicon particles are pulverized to improve manufacturing, then ease of manufacture is improved, but excessive formation of unstable solid electrolyte interphase (SEI) layer occurs, leading to deterioration in battery stability
Solution Approach 1:
The polymer thin film is formed on the silicon particle surface before battery assembly and initial charging cycles. This preliminary coating prevents direct exposure of pulverized silicon surfaces to the electrolyte, thereby preventing excessive SEI formation. The polymer layer acts as a barrier that controls and stabilizes the interface between silicon and electrolyte from the outset.
Solution Approach 2:
The polymer thin film serves as an intermediary layer between the silicon particles and the liquid electrolyte. This intermediate layer prevents direct contact between the unstable silicon surface (especially after pulverization) and the electrolyte, thereby preventing excessive and unstable SEI formation while still allowing lithium ion transport.
3Stability of the object's composition
If carbon coating is applied using CVD method to protect silicon surface, then mechanical stability is improved, but volume expansion and contraction are not sufficiently suppressed
Solution Approach 1:
The invention changes the material parameter of the coating from traditional carbon (via CVD) to polymer material deposited through iCVD. This parameter change allows the coating to exhibit greater flexibility and elasticity, enabling it to accommodate volume expansion and contraction more effectively while maintaining mechanical stability. The polymer's viscoelastic properties allow it to deform with volume changes without cracking.
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 silicon-polymer composite preserves the shape of silicon particles, enhances electrical conductivity, and suppresses degradation in battery performance and lifespan by acting as a stable SEI layer, maintaining high specific power and Coulombic efficiency.
Implementation Method 1
forming a polymer thin film on surfaces of silicon particles by initiator-based chemical vapor deposition (iCVD)
Implementation Method 2
forming the polymer thin film on surfaces of the silicon particles by polymerizing the monomer through activation of the initiator
Implementation Method 3
the initiator may be activated through predetermined heat treatment, and the heat treatment may be performed at a temperature in the range of 135°C to 350°C
Data Source
Figure 1~2
Figure 3(a)~4(b)
Figure 5A~5B
AI summary
The present invention relates to a silicon-polymer composite, a preparation method therefor, and an anode active material comprising same. In the silicon-polymer composite according to an embodiment of the present invention, the original shape of silicon particles is preserved because a polymer thin film has excellent thickness uniformity, and the polymer thin film has little impact on electrical conductivity and lithium-ion conductivity, and thus, when the silicon-polymer composite is used as an anode active material, the silicon-polymer composite acts as a stable solid electrolyte interphase layer between silicon and an electrolyte, while still maintaining the high specific power and high Coulombic efficiency of silicon which is the main anode active material. Accordingly, degradation in battery performance and battery lifespan may be suppressed.