Silicon-Based Negative Electrode Polymer Network Coating
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Solution Overview
Problem
Silicon-based negative electrode active materials in secondary batteries experience significant volume expansion during lithium intercalation, leading to pulverization and reduced cycle performance, which existing carbon coating methods attempt to mitigate but with complex processes and high costs.
Innovation Solution
A core-shell structured negative electrode active material with a silicon-based core coated by a polymer network layer, specifically derived from polymers with functional groups like cyano, amide, and sulfonyl groups, combined with an electrolyte solution containing sulfonimide lithium salt to enhance conductivity and inhibit expansion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If silicon-based material is used as negative electrode active material to achieve high capacity, then the theoretical capacity increases to 4200 mAh/g, but the material experiences significant volume expansion during lithium intercalation leading to pulverization and reduced cycle performance
Solution Approach 1:
The patent uses a composite structure consisting of silicon-based core material coated with a polymer network layer. The polymer network layer is formed by crosslinking polymers with functional groups (cyano, amide, imide, sulfonyl, or carboxyl groups) that create a flexible protective shell around the silicon core, allowing volume expansion while preventing pulverization and maintaining structural integrity during cycling.
Solution Approach 2:
The patent employs a flexible polymer network coating layer that can accommodate the volume expansion of silicon during lithium intercalation. The crosslinked polymer structure provides mechanical flexibility and elasticity, forming a protective shell that prevents direct contact between the expanding silicon and the electrolyte, thereby preventing pulverization and maintaining cycle performance.
2Reliability
If silicon-based material is coated with polymer network layer to inhibit expansion, then cycle performance is improved, but electrochemical performance such as rate performance deteriorates
Solution Approach 1:
The patent optimizes the parameters of the polymer network layer including the type of functional groups, crosslinking density, and coating thickness to achieve a balance between expansion inhibition and ion transport. The crosslinked network structure provides mechanical stability while maintaining sufficient porosity and ion conductivity for fast lithium ion diffusion, thus improving both cycle performance and rate performance simultaneously.
Solution Approach 2:
The patent creates a polymer network layer with non-uniform crosslinking density and local porosity distribution. The coating has regions of different mechanical properties that allow selective functions: denser regions provide expansion inhibition while more porous regions facilitate ion transport, achieving both improved cycle performance and maintained rate performance through spatially varying local quality.
3Reliability
If conventional carbon coating methods are used to mitigate expansion, then pulverization is reduced, but the process becomes complex and costs increase
Solution Approach 1:
The patent uses polymer molecules with specific functional groups as intermediary materials that can chemically crosslink to form a protective network layer. These polymer intermediaries (such as polyacrylonitrile, polyacrylamide, polyimide, polyacrylic acid, or alginate) serve as precursors that transform into a robust protective shell through crosslinking, providing an alternative to complex physical vapor deposition or chemical vapor deposition processes used for carbon coating.
Solution Approach 2:
The patent changes the chemical state and structural parameters of the coating material from traditional carbon to crosslinked polymer networks. This parameter change allows the use of simpler solution-based coating methods followed by crosslinking treatment, replacing complex multi-step physical vapor deposition processes while achieving comparable or superior protection against silicon pulverization.
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 achieves high energy density and improved dynamic cycle performance by inhibiting silicon-based material expansion and maintaining conductivity, resulting in a battery with enhanced rate and cycle performance.
Implementation Method 1
the surface of the silicon-based core material is coated with a polymer network coating layer, which can significantly inhibit the expansion of the silicon-based material
Implementation Method 2
a secondary battery with both good capacity and good dynamic cycle performance can be obtained by combining an electrolyte solution containing lithium sulfonimide with the negative electrode active material
Data Source
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AI summary
The present application relates to a secondary battery, comprising: a positive electrode plate, a negative electrode plate, a separator disposed between the positive electrode plate and the negative electrode plate, and an electrolyte solution, the negative electrode plate including a negative electrode current collector and a negative electrode active material layer provided on at least one side of the negative electrode current collector, and the electrolyte solution including an organic solvent and a lithium salt, wherein the negative electrode active material comprises a core structure and a polymer network coating layer coated on at least a part of the surface of the core structure, the core structure comprises SiOx (0 < x < 2), the polymer network coating layer accounts for at least 0.5 mass% and at most 10 mass% of the total mass of the negative electrode active material, and the network coating layer is derived from a polymer having one or more functional groups selected from a group consisting of cyano group, amide group, imide group, sulfonyl group, carboxyl group and sulfonyl group; and the lithium salt comprises a primary lithium salt represented by Formula I: in which Formula I, R1 and R2 each independently represent a fluorine atom, a fluoroalkyl group having 1-20 carbon atoms, or a fluoroalkoxy group having 1-20 carbon atoms, and n is an integer of 1, 2 or 3.