Cross-Linked Multilayer Anode for Silicon Expansion Control
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Solution Overview
Problem
Lithium secondary batteries face issues with mechanical stability and cycle life due to volume expansion of silicon-based anode active materials, despite improvements in binder types and content.
Innovation Solution
An anode with a multi-layer structure is designed, comprising a first layer without or with minimal cross-linker and a second layer with a cross-linker, using specific binders and cross-linkers to enhance adhesion and flexibility, thereby stabilizing the anode.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If silicon-based anode active material is used to increase capacity, then energy density is improved, but volume expansion occurs leading to deterioration of mechanical stability and cycle life
Solution Approach 1:
The anode active material layer is divided into multiple sub-layers with different compositions and functions. The first sub-layer contains silicon-based material for high capacity, while subsequent layers contain carbon-based materials and binders to provide structural stability, effectively segmenting the functional requirements of energy storage and mechanical support
Solution Approach 2:
The patent uses composite material structure combining silicon-based anode active material with carbon-based materials and specific binders. This composite approach allows the silicon layer to provide high energy density while the carbon and binder components provide mechanical stability and accommodate volume expansion, resolving the contradiction between capacity and stability
2Strength
If binder content is increased to improve adhesion, then adhesive strength is improved, but flexibility and mechanical stability are still insufficient
Solution Approach 1:
The patent optimizes the parameters of the binder including its chemical composition, molecular weight, and cross-linking degree. By changing these parameters, the binder achieves optimal balance between adhesion strength and flexibility, allowing it to maintain strong bonding while accommodating the volume changes of silicon during cycling
Solution Approach 2:
Different regions of the anode active material layer have different binder contents and types. The binder concentration is optimized locally in different sub-layers to provide appropriate adhesion and flexibility characteristics for each functional region, rather than using a uniform composition throughout
3Stability of the object's composition
If cross-linker is added to enhance mechanical stability, then adhesion is improved, but electrode resistance increases
Solution Approach 1:
The patent uses a controlled, partial amount of cross-linker rather than excessive cross-linking. This partial action approach provides sufficient mechanical stability and adhesion improvement while minimizing the formation of overly rigid cross-linked structures that would impede lithium ion transport and increase electrode resistance
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 anode exhibits improved mechanical stability and cycle life characteristics, with enhanced adhesion and reduced electrode resistance, leading to more efficient lithium secondary batteries.
Implementation Method 1
a second anode active material layer formed on at least one surface of the first anode active material layer and including a second anode active material, a second binder and a cross-linker
Data Source
Figure 1~2
Figure 3
AI summary
An anode for a lithium secondary battery according to exemplary embodiments includes: an anode current collector; a first anode active material layer formed on at least one surface of the anode current collector and including a first anode active material and a first binder; and a second anode active material layer formed on at least one surface of the first anode active material layer and including a second anode active material, a second binder and a cross-linker, wherein the first anode active material layer does not include a cross-linker or includes the cross-linker in a content smaller than that in the second anode active material layer based on weight. Accordingly, the adhesive strength, flexibility, brittleness, and rigidity of the anode are enhanced, and the cycle life characteristics of the lithium secondary battery are improved.