Active Material Ball Composite Layer for Silicon Electrode 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, decreased electronic and ion conductivity, and electrode brittleness, which are difficult to control with existing rigid binders.
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 control 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 constrained, but the electrode layer becomes brittle and cracks easily
Solution Approach 1:
The patent applies different binder types in different locations: rigid binder inside active material balls for volume constraint, elastic binder outside balls for flexibility maintenance. This local differentiation resolves the contradiction between volume control and flexibility.
Solution Approach 2:
The patent uses a composite binder system combining rigid and elastic binders in specific proportions. This composite approach allows simultaneous achievement of volume constraint (from rigid binder) and flexibility (from elastic binder), resolving the contradiction.
2Quantity of substance
If the proportion of active material is increased to improve capacity, then energy density improves, but the electrode layer becomes more prone to cracking
Solution Approach 1:
The patent segments the electrode structure into active material balls (high active material concentration) and binder matrix. This segmentation allows high active material proportion within balls while the binder matrix provides structural integrity, resolving the contradiction.
Solution Approach 2:
The elastic binder forms a flexible matrix surrounding rigid active material balls. This flexible shell structure accommodates volume changes and prevents cracking, enabling high active material proportion without compromising electrode integrity.
3Quantity of substance
If the thickness of the electrode layer is increased to improve capacity, then energy density improves, but the electrode layer becomes more difficult to coat and more prone to cracking
Solution Approach 1:
The patent uses pre-formed active material balls as discrete units that can be easily coated and handled. This segmentation simplifies the coating process for thick layers compared to conventional slurries, resolving the manufacturing difficulty.
Solution Approach 2:
The composite structure of rigid balls in elastic binder creates a self-supporting framework that maintains integrity in thick layers. This composite architecture reduces coating difficulty and cracking susceptibility, enabling thicker electrode fabrication.
4Quantity of substance
If silicon material ratio is increased to improve volumetric capacity, then energy density improves, but void formation increases due to volume change
Solution Approach 1:
The elastic binder is placed beforehand to surround and accommodate silicon particles. This cushioning effect prevents void formation by maintaining continuous contact during volume changes, resolving the contradiction between high silicon ratio and void prevention.
Solution Approach 2:
The patent creates different local environments: rigid inner binder for volume constraint inside balls, elastic outer binder for void prevention outside balls. This local quality differentiation simultaneously achieves high silicon ratio and prevents void formation.
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 manages volume expansion, maintains flexibility, and improves specific capacity, electrical conductivity, and ion conductivity, addressing the limitations of void formation and electrode brittleness in conventional silicon-based electrodes.
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
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.
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.