Hard-Carbon-Coated Graphite Anode for Fast-Charging Li-Ion Batteries
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Solution Overview
Problem
Lithium secondary batteries face challenges with rapid charging characteristics and high-temperature storage performance due to issues with graphite-based active materials, including difficulty in achieving desired electrode density and impregnability of electrolytic solution, as well as risks of short circuits and explosions associated with lithium metal use.
Innovation Solution
A negative electrode active material comprising first artificial graphite particles with a carbon coating layer of hard carbon and second artificial graphite particles, where the average particle diameter difference is 5 μm or less, and the carbon coating layer's exothermic peak temperature is between 580° C. and 690° C., enhancing hardness and lithium ion diffusion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If graphite-based active material is made hard to maintain structural stability, then structural stability is improved, but rolling difficulty increases and electrode density decreases
Solution Approach 1:
The patent applies local quality by creating a bi-modal particle size distribution where small particles (0.5-5 μm) fill the voids between large particles (5-20 μm). This local arrangement allows the electrode to achieve high density and good rolling characteristics without requiring the entire graphite structure to be soft, thus maintaining structural stability while improving manufacturability.
2Ease of manufacture
If graphite-based active material is made soft to facilitate rolling, then electrode density is improved, but voids between particles are blocked and electrolytic solution impregnability deteriorates
Solution Approach 1:
The patent utilizes porous material principles by intentionally creating a hierarchical pore structure through the bi-modal particle distribution. The small particles fill voids between large particles, creating a porous network that maintains electrolyte access while achieving high packing density. This resolves the contradiction by making the electrode structure inherently porous rather than relying on soft material properties.
3Quantity of substance
If lithium metal is used as negative electrode to achieve high capacity, then energy density is improved, but dendrite formation occurs causing short circuit and explosion risks
Solution Approach 1:
The patent introduces an intermediary layer - a carbon coating on the graphite particles - that mediates between the high capacity requirement and safety concerns. This carbon coating enables reversible lithium ion intercalation while preventing direct lithium metal deposition and dendrite formation, thus achieving high energy density without compromising safety.
4Speed
If particle size is reduced to improve lithium ion diffusion, then rapid charging characteristics are improved, but specific surface area increases causing damage during rolling
Solution Approach 1:
The patent applies segmentation by dividing the particle size distribution into two distinct segments: small particles (0.5-5 μm) for rapid lithium ion diffusion and large particles (5-20 μm) for mechanical strength and rolling resistance. This segmented approach allows each particle size to fulfill its specific function, resolving the contradiction between diffusion rate and mechanical durability.
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 improves high-temperature storage performance, rapid charging characteristics, and capacity efficiency by maintaining structural stability and reducing lithium ion diffusion resistance, while minimizing damage during rolling and maintaining specific surface area.
Implementation Method 1
reducing lithium ion diffusion resistance
Implementation Method 2
a temperature at an exothermic peak in differential thermogravimetric analysis of the carbon coating layer is in a range of 580° C. to 690° C.
Data Source
AI summary
A negative electrode active material for a lithium secondary battery, including: first negative electrode active material particles including first artificial graphite particles and a carbon coating layer on a surface of the first artificial graphite particles, wherein the carbon coating layer comprises hard carbon; and second negative electrode active material particles including second artificial graphite particles, wherein a difference between an average particle diameter D50 of the first negative electrode active material particles and an average particle diameter D50 of the second negative electrode active material particles is 5 μm or less, and a temperature at an exothermic peak in differential thermogravimetric analysis of the carbon coating layer is in a range of 580° C. to 690° C.