Porous Carbon Anode Material With SiCx Coating for Cycle Stability
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Solution Overview
Problem
Silicon-based negative electrode materials for lithium secondary batteries face challenges such as significant volume change during charging and discharging, leading to pulverization, electrical disconnection, and low cycle life due to the formation of a thick solid electrolyte interface (SEI) layer and oxide films, which hinder the commercialization of high-capacity batteries.
Innovation Solution
A negative electrode active material is developed with a carbon-based particle having pores and a silicon-based coating layer containing silicon carbon compounds, where the silicon carbon compound satisfies SiCx (0<x≤2), and the silicon-based coating layer includes Si nano-particles with controlled crystallinity and thickness, formed using chemical vapor deposition to alleviate volume expansion and suppress oxide film formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If silicon-based negative electrode material is used to increase capacity, then charge capacity is improved, but volume change during charging and discharging causes pulverization and low cycle life
Solution Approach 1:
The patent embeds silicon particles inside hollow carbon spheres, creating a nested structure where the inner silicon particles are protected by the outer carbon shell. This nesting approach allows the silicon to undergo volume expansion during lithiation while the carbon shell maintains structural integrity, preventing pulverization and maintaining cycle life while preserving high capacity.
Solution Approach 2:
The patent employs a carbon shell surrounding the silicon particles that acts as a flexible protective layer. This shell can accommodate the volume changes of silicon during charging and discharging cycles without breaking, thereby preventing pulverization and maintaining electrical connectivity over many cycles while enabling high capacity performance.
2Quantity of substance
If thick silicon-based coating layer is applied to increase capacity, then charge capacity is improved, but thick SEI layer formation causes electrolyte depletion and increased resistance
Solution Approach 1:
The patent creates a localized high-capacity region by placing silicon particles only in the interior of hollow carbon spheres, while the outer carbon shell provides a stable interface with the electrolyte. This local quality differentiation allows the silicon to contribute high capacity without exposing a large silicon surface area to the electrolyte, thereby minimizing SEI layer formation and electrolyte depletion.
Solution Approach 2:
The carbon shell acts as an intermediary layer between the silicon particles and the electrolyte. It allows lithium ions to reach the silicon particles for high capacity while preventing direct contact between the silicon surface and the electrolyte, thus minimizing unwanted side reactions and SEI layer formation that would deplete the electrolyte.
3Ease of manufacture
If silicon is exposed to air during manufacturing, then material preparation is simplified, but oxide film formation decreases capacity
Solution Approach 1:
The patent forms the carbon shell around the silicon particles during the manufacturing process itself, creating a protective enclosure before the material is exposed to air. This preliminary protective action prevents oxidation of the silicon surface during subsequent handling and storage, maintaining high active capacity while allowing straightforward manufacturing procedures.
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 solution enhances the capacity and cycle life of lithium secondary batteries by reducing stress from volume expansion, preventing electrical isolation, and maintaining high-capacity retention, while minimizing the formation of oxide films and side reactions with the electrolyte.
Implementation Method 1
the silicon-based negative electrode material causes a significant volume change at the time of intercalation/deintercalation of lithium
Implementation Method 2
when silicon is exposed to the air at the time of pulverizing the negative electrode active material or manufacturing the negative electrode, the silicon reacts with oxygen, such that an oxide film is formed on a surface of the silicon
Implementation Method 3
the more the amount of silicon, the more severe the volume expansion occurring at the time of charging and discharging of the secondary battery. Therefore, as a new surface of silicon in the composite negative electrode material is continuously exposed to an electrolyte to continuously form a solid electrolyte interface (SEI) layer
Data Source
AI summary
Provided is a negative electrode active material for a lithium secondary battery according to the present invention, including a carbon-based particle including pores in an inner portion and/or a surface thereof; and a silicon-based coating layer positioned on a pore surface and/or a pore-free surface of the carbon-based particle and containing silicon carbon compound.