Active Material Ball Composite Layer with Dual-Binder Expansion Control
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Solution Overview
Problem
Conventional lithium ion battery negative electrodes with silicon materials face significant volume change during charging and discharging, leading to void formation and decreased electronic and ion conductivity, which is difficult to control with existing rigid binders that also increase brittleness and reduce coating flexibility.
Innovation Solution
A composite layer of active material balls with a high proportion of inner cross-linked binder for expansion control and an outer binder with higher elasticity to maintain flexibility, along with a higher volume content of electrically conductive material within the balls, addresses the volume change and conductivity issues.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If a rigid binder such as a cross-linked type is used to generate strong adhesion, then the volume change of the silicon materials during charging and discharging processes is controlled, but the electrode layer becomes brittle and easy to crack
Solution Approach 1:
The electrode layer is divided into multiple layers with different binder types: a first electrode layer containing cross-linked binder for volume control, and a second electrode layer containing non-cross-linked binder for flexibility. This segmentation allows each layer to perform its specific function without compromising the overall electrode integrity.
Solution Approach 2:
The invention uses a composite structure combining two types of binders with different properties. The cross-linked binder provides rigid support for volume control, while the non-cross-linked binder provides flexibility to prevent cracking. This composite approach resolves the contradiction between stability and strength.
2Stability of the object's composition
If the proportion of the rigid binder is increased to control volume expansion, then the volume change is reduced, but the thickness of the electrode layer is increased and it becomes more difficult to perform thick coating
Solution Approach 1:
The electrode is segmented into multiple layers with different binder proportions. The first layer uses high比例的 cross-linked binder for effective volume control, while the second layer uses non-cross-linked binder that is easier to coat. This allows thick coating to be performed without requiring excessive rigid binder throughout the entire electrode.
Solution Approach 2:
Different regions of the electrode have different binder compositions tailored to their specific functions. The region requiring volume control (first electrode layer) has high cross-linked binder content, while the region requiring ease of coating (second electrode layer) has non-cross-linked binder. This local optimization resolves the contradiction between volume control and coating ease.
3Quantity of substance
If the amount of electrically conductive material and binder is reduced to increase capacity, then the proportion of active material is increased, but the electrode layer becomes more prone to cracking and short circuit
Solution Approach 1:
The electrode is divided into layers where the second electrode layer contains non-cross-linked binder that provides flexibility and crack resistance. This allows the first electrode layer to have high active material proportion for capacity while the second layer provides the necessary mechanical reliability to prevent cracking and short circuits.
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
Effectively controls volume expansion, maintains flexibility, and enhances specific capacity, electrical conductivity, and ion conductivity while preventing void-related problems.
Implementation Method 1
the inner binder includes a cross-linked polymer
Implementation Method 2
an outer binder, adhering the active material balls and the second electrically conductive material
Implementation Method 3
an outer binder with higher elasticity outside the active material balls
Implementation Method 4
a first electrically conductive material and an inner binder, wherein the first active material particles and the first electrically conductive material are adhered by the inner binder
Implementation Method 5
the first active material particles are the active material particles with huge volume change during extraction and insertion reactions
Data Source
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AI summary
The invention discloses an active material ball composite layer. The active material ball composite layer includes a plurality of active material balls and an outer binder. The active material ball include a plurality of active material particles and a first conductive material. An inner binder is used to adhere the active material particles and the first conductive material to form the active material balls. Then, the outer binder is used to adhere the active material balls to form the composite layer. The elasticity of the inner binder is smaller than the elasticity of the outer binder. Therefore, the scale of expansion of the active material particles is efficiently controlled during charging and discharging. The unrecoverable voids would be reduced or avoided.