Dual-Binder Active Material Ball Layer for Silicon Anodes
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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 make the electrodes brittle.
Innovation Solution
A composite layer of active material balls with a high proportion of rigid inner binder and elastic outer binder is used, where the inner binder provides expansion constraint and the outer binder maintains flexibility, along with a higher volume content of conductive materials within the balls to manage volume change and enhance conductivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If a rigid binder is used to control volume change of silicon materials, then volume expansion is controlled, but the electrode layer becomes brittle and easy to crack
Solution Approach 1:
The electrode layer is segmented into multiple layers with different binder compositions. The first layer (closer to active material) uses rigid binder for strong adhesion and volume control, while the second layer (outer layer) uses flexible binder to maintain flexibility and prevent cracking. This segmentation allows each layer to perform its specialized function without the drawbacks of using a single binder type throughout.
Solution Approach 2:
Different regions of the electrode layer are assigned different binder properties tailored to their specific functional requirements. The inner region near active material particles requires rigid binder for strong bonding and volume constraint, while the outer region requires flexible binder for crack prevention and flexibility. This local differentiation of material properties optimizes overall performance.
2Quantity of substance
If the proportion of active material is increased to increase capacity, then specific capacity is improved, but the electrode layer becomes more prone to cracking and short circuits
Solution Approach 1:
The electrode is segmented into active material particles and a multi-layer binder system. This segmentation allows high proportion of active material (up to 98.5% by weight) while the layered binder structure provides distributed support and flexibility to prevent cracking, enabling both high capacity and reliability.
3Stability of the object's composition
If the amount of rigid binder is increased to control void formation, then volume change is constrained, but the electrode layer thickness increases and cracking becomes more likely
Solution Approach 1:
The binder system is segmented into two functional layers with different thicknesses and compositions. The first layer (thinner, 2-10 micrometers) uses rigid binder for void prevention, while the second layer (thicker, 10-20 micrometers) uses flexible binder for crack prevention. This segmentation allows effective void control without excessive overall thickness.
Solution Approach 2:
The binder system transitions from a single uniform composition to a gradient composition with different rigidity parameters in different layers. The rigid binder layer provides void control with minimal thickness, while the flexible binder layer provides crack resistance, optimizing the thickness-to-function ratio.
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
This configuration effectively controls volume expansion, maintains flexibility, and improves specific capacity, electrical conductivity, and ion conductivity while reducing the risk of void formation and electrode cracking.
Implementation Method 1
The elasticity of the inner binder is smaller than the elasticity of the outer binder, and the volume content of the first electrically conductive material within the active material balls is greater than the volume content of the second electrically conductive material of the total volume other than the active material balls. The huge volume change of the active material particles during charging and discharging processes is effectively controlled by the different elasticity of the inner binder and the outer binder of this invention.
Implementation Method 2
an outer binder with higher elasticity outside the active material balls. Therefore, in the case of controlling the volume expansion of the active material particles, the flexibility of the composite layer is retained
Implementation Method 3
The elasticity of the inner binder is smaller than the elasticity of the outer binder
Implementation Method 4
a higher volume content of conductive materials within the balls to manage volume change and enhance conductivity
Data Source
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.