Carbon-Coated Hard Carbon Anodes With Uniform Coating for Initial Efficiency
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Solution Overview
Problem
Existing carbon-coated non-graphitizable carbon materials for lithium-ion secondary batteries suffer from low initial efficiency due to insufficient orientation and uniformity of the carbon coating layer, which affects discharge capacity and cycle characteristics.
Innovation Solution
A carbon-coated non-graphitizable carbon material with a carbon coating layer of predetermined average thickness (4 nm to 30 nm) and uniform thickness distribution, where the minimum thickness is 70% or more of the maximum thickness, is developed. This structure ensures high discharge capacity and initial efficiency by reducing surface reactivity and maintaining conductivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If non-graphitizable carbon material is used as negative electrode, then discharge capacity is improved (higher than 372 mAh/g), but initial efficiency deteriorates (low percentage of discharge capacity to initial charge capacity)
Solution Approach 1:
The patent applies composite materials by combining non-graphitizable carbon particles with a graphite coating layer. The core non-graphitizable carbon provides high discharge capacity through pore occlusion and non-oriented graphene layer units, while the outer graphite coating layer improves initial efficiency by providing stable Li insertion/extraction sites and reducing surface reactivity. This composite structure resolves the contradiction between high discharge capacity and low initial efficiency.
Solution Approach 2:
The patent changes the surface parameters of the non-graphitizable carbon by coating it with graphite. The coating thickness is controlled at 1-10 nm, and the graphite layer's crystal orientation is optimized with the (002) plane parallel to the substrate surface with 70% or more orientation. This parameter change transforms the surface properties to reduce harmful reactions while maintaining the bulk material's high capacity characteristics.
2Reliability
If carbon coating layer is applied to improve initial efficiency, then initial efficiency is improved, but discharge capacity deteriorates (insufficient discharge capacity and initial efficiency depending on charge/discharge conditions)
Solution Approach 1:
The patent optimizes the coating thickness parameter to 1-10 nm, which is thin enough to maintain electron conductivity and Li ion transport while providing sufficient surface protection. The graphite crystal orientation is controlled with the (002) plane parallel to the substrate surface with 70% or more orientation, ensuring stable Li insertion/extraction. These precise parameter controls prevent the discharge capacity deterioration that occurs with thicker or poorly oriented coatings.
Solution Approach 2:
The patent applies local quality by creating a graphite coating layer with specific local properties (thickness, orientation, crystallinity) on the surface of the non-graphitizable carbon particles. The coating is not uniform in all aspects: it is thin (1-10 nm) to maintain conductivity, highly oriented (70% or more with (002) plane parallel to surface) to provide stable Li sites, and crystalline to reduce surface reactivity. This localized optimization resolves the contradiction between improving initial efficiency and maintaining discharge capacity.
3Reliability
If coating carbon material with high orientation (70% or more) is used, then initial efficiency is improved, but thickness distribution uniformity deteriorates (did not take account of the distribution of orientation in the thickness direction)
Solution Approach 1:
The patent specifies precise parameters for the graphite coating: thickness of 1-10 nm, orientation of 70% or more with the (002) plane parallel to the substrate surface. By controlling these parameters during the coating process, the patent achieves both high initial efficiency and uniform thickness distribution. The narrow thickness range (1-10 nm) ensures uniformity while the orientation control (70% or more) ensures high initial efficiency.
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 carbon-coated non-graphitizable carbon material achieves both high discharge capacity and initial efficiency, enhancing the performance and durability of lithium-ion secondary batteries by improving the stability and conductivity of the negative electrode.
Implementation Method 1
a technique of coating a surface of a carbon material is known
Implementation Method 2
reacts with the electrolytic solution to form an SEI (solid electrolyte interphase) coating
Implementation Method 3
the non-graphitizable carbon material can occlude Li not only between layers but also in pores
Implementation Method 4
graphite-based materials generally have high capacity... can occlude Li between layers
Implementation Method 5
maintaining conductivity... improving the stability and conductivity of the negative electrode
Data Source
AI summary
Carbon-coated non-graphitizable carbon used for a negative electrode for a lithium-ion secondary battery, a negative electrode for a lithium-ion secondary battery using the carbon-coated non-graphitizable carbon, and a lithium-ion secondary battery including the negative electrode for a lithium-ion secondary battery are disclosed. The carbon-coated non-graphitizable carbon is carbon-coated non-graphitizable carbon comprising: non-graphitizable carbon; and a carbon coating layer provided on a surface of the non-graphitizable carbon, wherein an average thickness of the carbon coating layer is 4 nm or more and 30 nm or less, and a minimum value of a thickness of the carbon coating layer is 70% or more of a maximum value of the carbon coating layer.