Two-Layer Battery Anode Structure for Silicon Expansion Control
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Solution Overview
Problem
Existing nonaqueous electrolyte secondary batteries face challenges in achieving a balance between high energy density and excellent output characteristics due to the difficulty in managing the volume change of silicon-based active materials, which can lead to conduction path disruptions.
Innovation Solution
A negative electrode with a two-layer structure is employed, where the first layer contains a soft carbon-based active material with low compressive strength and a silicon-based active material, and the second layer contains a hard carbon-based active material with higher compressive strength, reducing the impact of volume changes and maintaining conduction paths.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If silicon-based active material is used to increase energy density, then the energy density of the battery is improved, but the volume change of the silicon-based active material causes conduction paths to be cut off, increasing resistance
Solution Approach 1:
The patent uses soft graphite particles with low 10% compressive strength (2 MPa or less) as a flexible matrix to accommodate the volume expansion of silicon-based active material during charging. The soft graphite acts as a flexible shell that can deform elastically to follow the volume change of silicon, preventing conduction path disruption while maintaining electrical connectivity throughout the electrode structure.
Solution Approach 2:
The patent creates a composite negative electrode active material consisting of silicon-based active material dispersed within a carbon-based active material matrix (soft graphite). This composite structure combines the high capacity of silicon with the flexibility and electrical conductivity of soft graphite, allowing the silicon to expand and contract during cycling without compromising the overall structural integrity or conduction paths.
2Power
If hard graphite particles with large amorphous component are used to improve output characteristics, then the output characteristics are improved, but the graphite particles cannot follow the volume change of silicon-based active material, cutting off conduction paths
Solution Approach 1:
The patent employs soft graphite particles with low 10% compressive strength (2 MPa or less) as a flexible matrix that can elastically deform to accommodate the volume expansion of silicon-based active material. This flexible shell-like structure maintains continuous conduction paths even during significant volume changes, preventing the cutoff of electrical pathways that would occur with rigid hard graphite particles.
Solution Approach 2:
The patent changes the mechanical parameter (10% compressive strength) of the graphite particles from hard (high strength) to soft (low strength ≤2 MPa). This parameter change enables the graphite matrix to undergo elastic deformation following silicon volume changes, maintaining conduction path connectivity while still providing sufficient structural support for good output characteristics.
3Quantity of substance
If silicon-based active material is used to increase energy density, then the energy density is improved, but the conduction paths are cut off due to volume change, increasing resistance value
Solution Approach 1:
The patent uses soft graphite particles with low 10% compressive strength (2 MPa or less) as a flexible matrix that can elastically deform to accommodate silicon volume expansion. This flexible structure prevents conduction path disruption, thereby avoiding the increase in resistance that would otherwise occur during charging and discharging cycles.
Solution Approach 2:
The patent creates a composite structure where silicon-based active material is dispersed within a soft graphite matrix. This composite design combines the high capacity of silicon with the flexibility and electrical conductivity of soft graphite, maintaining continuous conduction paths and preventing resistance increase during volume changes.
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 design achieves a nonaqueous electrolyte secondary battery with enhanced energy density and output characteristics by mitigating conduction path disruptions, ensuring favorable performance over time.
Implementation Method 1
a first carbon-based active material having a 10% compressive strength of 3 MPa or less and a silicon-based active material containing Si
Implementation Method 2
a second carbon-based active material having a 10% compressive strength of 5 MPa or more and has a lower content (mass ratio) of the silicon-based active material than the first layer
Data Source
Figure 1
AI summary
In this nonaqueous electrolyte secondary battery, a negative electrode mixture layer has a first layer and a second layer formed in that order from the side of a negative electrode current collector. The first layer includes a first carbon-base active material with a 10% proof stress of less than or equal to 3 MPa, and a silicon-base active material containing Si. The second layer contains a second carbon-base active material with a 10% proof stress of greater than or equal to 5 MPa, and has a lower content ratio (mass ratio) of the silicon-base active material than the first layer.