Silicon Anode Granules With Carbon Coating for Cycle Stability
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Solution Overview
Problem
Silicon-based negative electrode materials in lithium-ion batteries suffer from surface electrolyte decomposition leading to increased resistance and decreased cycle characteristics due to volume changes during charging and discharging, despite efforts to improve with fine pulverization or compositing.
Innovation Solution
Forming a Si-based powder into a granulated body with a carbon film and incorporating a conductive material bound by a binder, ensuring a carbon film coverage of 30% or more, and maintaining a strength of 1.0 MPa or more to prevent electrolyte decomposition and volume-induced collapse.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If Si-based powder is used to achieve high capacity, then the capacity increases about 10 times that of graphite, but the volume change during charging and discharging causes particle collapse and poor cycle characteristics
Solution Approach 1:
The patent creates a composite granulated body comprising Si-based powder particles bound together by a binder material. This composite structure allows the Si particles to maintain their high capacity while the binder holds them together during volume changes, preventing collapse and improving cycle characteristics.
Solution Approach 2:
The patent forms a carbon film coating on the surface of the granulated body. This thin film shell protects the Si-based powder from direct contact with the electrolyte, preventing electrolyte decomposition and film formation that would otherwise increase resistance and degrade cycle performance.
2Quantity of substance
If Si-based powder is finely pulverized to improve capacity utilization, then the capacity increases, but the surface area increases leading to more electrolyte decomposition and thicker resistance-increasing films
Solution Approach 1:
The carbon film coating acts as a protective barrier that prevents the electrolyte from contacting the Si-based powder surface. This eliminates electrolyte decomposition and the formation of resistive films, even when the Si particles are finely pulverized to maximize capacity utilization.
Solution Approach 2:
The carbon film serves as an intermediary layer between the Si-based powder and the electrolyte. It allows Li ion transport while blocking direct contact between the electrolyte and Si surface, preventing harmful decomposition reactions.
3Stability of the object's composition
If a binder is used to form granulated bodies to prevent collapse, then the structural stability improves, but the conductivity of the granulated body decreases
Solution Approach 1:
The patent creates a composite granulated body that combines Si-based powder with conductive materials. This composite structure maintains the structural stability provided by the binder while the conductive material network preserves electrical conductivity throughout the granulated body.
Solution Approach 2:
The patent incorporates conductive material specifically at strategic locations within the granulated body structure. This localized addition of conductive material restores conductivity pathways without requiring excessive binder material that would compromise 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 maintains excellent cycle characteristics and initial discharge capacity by preventing electrolyte decomposition and collapse, while enhancing conductivity through the carbon film and binder, thus improving the electrode's performance.
Implementation Method 1
an electrolytic solution is decomposed during charging and discharging, and a film made of the decomposition product is formed on the surface
Implementation Method 2
by using a binder in forming the granulated body, it is possible to prevent collapse of the granulated body due to a volume change during charging and discharging
Implementation Method 3
the inventors have conceived that a decrease in conductivity can also be prevented by forming a granulated body using a conductive material together with the Si-based powder
Data Source
AI summary
The present invention relates to a lithium-ion battery negative electrode active material that is a Si-based granulated body in which a Si-based powder and an electroconductive material are bonded using a binder, the Si-based powder containing a Si phase, and the Si-based granulated body having a carbon coating on a surface thereof.