Porous Silicon-Carbon Composite with Dual Carbon Shells for Cycle Life
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Solution Overview
Problem
Existing silicon-based negative electrode active materials for lithium secondary batteries face challenges such as significant volume expansion during lithium intercalation, leading to electrode destruction, reduced cycle characteristics, and capacity retention issues.
Innovation Solution
A porous silicon-carbon composite with a core-shell structure is developed, where the core comprises silicon particles and the shell consists of two or more carbon layers. This composite is prepared through a method involving etching of silicon-based raw material powder, filtering, drying, forming a first carbon layer, and subsequently a second carbon layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If silicon-based negative electrode active materials are used to enhance battery capacity, then the theoretical capacity increases significantly (4,199 mAh/g vs 372 mAh/g for graphite), but volume expansion of up to 300% occurs during lithium intercalation, destroying the negative electrode and reducing cycle characteristics
Solution Approach 1:
The patent applies the nested doll principle by creating a core-shell structure where silicon particles are embedded within a carbon matrix. The carbon shell encapsulates the silicon core, allowing the silicon to expand and contract during lithium intercalation without destroying the overall electrode structure. This nested configuration enables the high-capacity silicon to function while being protected by the stable carbon outer layer, thus resolving the contradiction between achieving high battery capacity and maintaining cycle characteristics.
Solution Approach 2:
The patent utilizes composite materials by combining silicon and carbon to form a silicon-carbon composite negative electrode active material. The composite structure leverages the high capacity of silicon while incorporating the structural stability and volume tolerance of carbon. This composite approach allows the material to withstand the 300% volume expansion during lithium intercalation without electrode destruction, thereby achieving both high battery capacity and reliable cycle characteristics.
2Quantity of substance
If silicon particles undergo volume expansion during lithium intercalation, then high capacity is achieved, but cracks form on the surface of the negative electrode active material, causing electrical detachment from the current collector and reducing capacity retention rate
Solution Approach 1:
The patent applies the flexible shells principle by forming a carbon matrix and carbon coating layers around the silicon particles. These carbon shells are designed to be flexible enough to accommodate the volume expansion of silicon during lithium intercalation without cracking. The carbon matrix provides a compliant framework that moves with the silicon expansion, preventing crack formation and maintaining electrical contact with the current collector, thus preserving both capacity and structural integrity.
Solution Approach 2:
The patent uses the carbon matrix as an intermediary material between the silicon particles and the current collector. This carbon intermediary absorbs and distributes the mechanical stress generated by silicon volume expansion, preventing direct transmission of cracking forces to the current collector. The carbon coating layers on silicon particles further mediate the interface, ensuring electrical connectivity is maintained even during significant volume changes, thereby protecting structural integrity while enabling high capacity.
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 porous silicon-carbon composite enhances the initial charge and discharge efficiency, charge and discharge capacity, and capacity retention rate of lithium secondary batteries, while also facilitating mass production through a continuous process with minimized steps.
Implementation Method 1
a first step of etching a silicon-based raw material powder using an etching solution containing a fluorine (F) atom-containing compound
Implementation Method 2
a third step of forming a first carbon layer on the surface of the porous silicon structure
Implementation Method 3
a fourth step of forming a second carbon layer on the surface of the first carbon layer
Data Source
AI summary
The present invention relates to a porous silicon-carbon composite having a core-shell structure, a preparing method therefor, and an anode active material comprising same, wherein the core comprises silicon particles and the shell comprises two or more carbon layers including a first carbon layer and a second carbon layer, so that the application of the composite as an anode active material for a secondary battery can enhance the discharge capacity, initial efficiency, and capacity retention rate of the secondary battery. In addition, the preparing method for the porous silicon-carbon composite having the core-shell structure enables the mass production through a continuous process with minimized steps.