Silicon-Graphite Negative Electrode Alignment for Stable Li-Ion Cycling
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Solution Overview
Problem
Lithium secondary batteries face challenges in achieving high energy density and long-term charge and discharge stability due to the combination of carbon and silicon materials as negative electrode active materials, which suffer from significant volume changes and reduced adhesion, leading to degraded charging and life characteristics.
Innovation Solution
A negative electrode for lithium secondary batteries is designed with a carbon-based and silicon-based active material layer, where the carbon material's alignment after activation is controlled to maintain a specific ratio relative to its initial alignment, ensuring a high slope with the current collector, and the materials are combined in a specific weight and particle size ratio to stabilize the structure during charge and discharge.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If silicon materials are used as negative electrode active material to increase capacity, then energy density is improved, but adhesion between negative electrode active layer and current collector deteriorates due to large volume change
Solution Approach 1:
The patent controls the alignment parameter of graphite crystal faces by managing the change in alignment from before to after activation. By maintaining the alignment (O.Ia) at 3.0 or less and controlling the ratio O.Ia/O.Ir to be 0.05 or more and less than 1, the patent optimizes the structural parameters to accommodate silicon's volume expansion while preserving adhesion and charging characteristics.
Solution Approach 2:
The patent uses a composite negative electrode active layer containing both carbon-based material (graphite) and silicon-based material. This composite structure allows the graphite to provide structural stability and maintain adhesion to the current collector, while the silicon contributes high capacity, thereby resolving the contradiction between energy density and adhesion reliability.
2Productivity
If graphite crystal faces are oriented to improve charging performance, then electronic conductivity is improved, but charging characteristics and life characteristics are degraded due to damage from silicon volume change
Solution Approach 1:
The patent precisely controls the alignment parameter of graphite crystal faces by managing the change from before to after activation. By setting O.Ia ≤ 3.0 and 0.05 ≤ O.Ia/O.Ir < 1, the patent maintains optimal orientation for electron conduction while ensuring the structure can withstand silicon's volume expansion during cycling, thus preserving both charging performance and life characteristics.
3Quantity of substance
If carbon and silicon materials are combined to achieve high capacity, then energy density is improved, but structural stability deteriorates due to significant volume change
Solution Approach 1:
The patent controls the alignment parameter of graphite to maintain structural stability. By limiting O.Ia to 3.0 or less and controlling the ratio O.Ia/O.Ir to be 0.05 or more and less than 1, the patent ensures the graphite structure remains stable enough to accommodate silicon's volume expansion while maintaining high energy density through the silicon component.
Solution Approach 2:
The composite structure of carbon-based and silicon-based materials allows the graphite to provide structural stability and the silicon to contribute high capacity. The controlled alignment parameters ensure the composite maintains its integrity during volume changes, resolving the contradiction between energy density and structural stability.
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 solution enhances the charge and discharge capacity, energy density, and maintains high charging characteristics and life characteristics of the battery by minimizing damage to the carbon-based material alignment and stabilizing the structure despite silicon's volume changes.
Implementation Method 1
graphite has a layered structure in which layers of carbon atoms formed in a reticulated structure are stacked. Accordingly, the graphite is capable of allowing lithium ions to enter the edge face (the surface where the layers are overlapped) of the carbon layer during charging and diffuse between the layers
Implementation Method 2
release the diffused lithium ions from the edge face of the carbon layer during discharge by deintercalation
Implementation Method 3
a technique for orienting the graphite contained in the negative electrode in a magnetic field to improve the charging performance of the negative electrode of a lithium secondary battery utilizing carbon materials such as graphite has been proposed in the art
Implementation Method 4
silicon materials exhibit a large volume change (∼300%) during charge and discharge
Data Source
AI summary
A negative electrode for a lithium secondary battery includes a carbon-based negative electrode active material and a silicon-based negative electrode active material together as a negative electrode active material. The negative electrode exhibits excellent characteristics of charge and discharge capacity and energy density. Furthermore, the negative electrode has the advantage of exhibiting high charge characteristics and life characteristics during long-term charge and discharge by realizing the alignment (O.Ia) of the carbon-based negative electrode active material after activation in a predetermined range that is lower than the alignment (O.Ir) of the carbon-based negative electrode active material before activation. A lithium secondary battery including the negative electrode is also provided. Further, methods of manufacturing the negative electrode and the lithium secondary battery are also provided.