Amorphous Carbon-Coated Graphite Anode for Stable SEI Formation
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Solution Overview
Problem
Conventional negative electrode active materials for lithium secondary batteries suffer from poor initial efficiency and reversible capacity due to the formation of an unstable Solid Electrolyte Interphase (SEI) layer and irreversible lithium ion consumption, especially when using soft carbon, which leads to increased irreversible capacity and degraded output characteristics.
Innovation Solution
A negative electrode active material is developed comprising low crystalline artificial graphite with an amorphous carbon coating layer, where the interplanar spacing d002 of the (002) plane is within a specific range of 0.338 nm to 0.3396 nm, as measured by XRD, facilitating the formation of a stable SEI layer and improving initial efficiency and reversible capacity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If soft carbon is used as negative electrode active material, then power and charging speed are improved, but irreversible capacity increases and initial efficiency deteriorates
Solution Approach 1:
The invention uses a composite structure consisting of low crystalline artificial graphite particles coated with amorphous carbon. This composite material combines the advantages of both materials: the graphite provides stable lithium ion insertion/extraction with high capacity, while the amorphous carbon coating improves power characteristics and charging speed. The composite structure resolves the contradiction by integrating two materials with complementary properties rather than using a single material that must compromise between power and efficiency.
Solution Approach 2:
The invention controls the interplanar spacing d002 of the (002) plane of low crystalline artificial graphite within a specific range of greater than 0.338 nm and less than 0.3396 nm. By precisely controlling this structural parameter, the material achieves optimal balance between lithium ion diffusion (affecting power) and SEI layer stability (affecting initial efficiency). This parameter optimization allows the material to simultaneously achieve good power characteristics and high initial efficiency.
2Speed
If soft carbon is used as negative electrode active material, then charging speed is improved, but irreversible capacity increases
Solution Approach 1:
The amorphous carbon coating on low crystalline artificial graphite creates a composite structure where the coating layer facilitates rapid lithium ion transport (improving charging speed) while the underlying graphite structure provides stable, reversible lithium ion storage. This composite approach allows the material to achieve fast charging without the excessive irreversible capacity loss that occurs with pure soft carbon materials.
Solution Approach 2:
By controlling the interplanar spacing d002 within the specific range of 0.338-0.3396 nm, the invention optimizes the balance between lithium ion diffusion rate (affecting charging speed) and lithium ion retention (affecting irreversible capacity). This precise parameter control enables fast charging while minimizing irreversible lithium ion consumption.
3Reliability
If SEI layer is formed during charging, then electrolyte decomposition occurs, but this causes increased irreversible capacity
Solution Approach 1:
The invention optimizes the interplanar spacing d002 to be greater than 0.338 nm and less than 0.3396 nm, which creates optimal conditions for forming a stable SEI layer. This specific parameter range allows the SEI layer to form with appropriate stability and composition, reducing electrolyte decomposition and minimizing irreversible lithium ion consumption during the initial charging cycles.
Solution Approach 2:
The amorphous carbon coating acts as an intermediary layer between the electrolyte and the low crystalline artificial graphite. This coating facilitates the formation of a stable SEI layer by providing a controlled interface for electrolyte decomposition, while preventing excessive or unstable SEI formation that would lead to high irreversible capacity loss. The coating mediates the interaction between electrolyte and graphite to achieve optimal SEI properties.
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 proposed negative electrode active material enhances the stability of the SEI layer, reducing side reactions with the electrolyte and improving the initial efficiency and reversible capacity of lithium secondary batteries, while maintaining optimal energy density and electronic conductivity.
Implementation Method 1
an amorphous carbon coating layer formed on low crystalline artificial graphite
Implementation Method 2
an interplanar spacing d002 of (002) plane is in a range of greater than 0.338 nm and less than 0.3396 nm, as measured by X-ray diffraction (XRD)
Data Source
Figure 1A~1B
Figure 2
Figure 3
AI summary
The present invention relates to a negative electrode active material and a method for preparing the same, the negative electrode active material comprising: low-crystalline artificial graphite; and an amorphous carbon coating layer formed on the low-crystalline artificial graphite, wherein the spacing d002 of (002) plane at the XRD measurement is 0.338 nm to 0.3396 nm. The use of the negative electrode active material of the present invention in a lithium secondary battery can form a more stable SEI layer at the time of reaction with an electrolyte, and thus can improve the initial efficiency and reversible capacity of the lithium secondary battery.