Carbon-Coated Graphite Anode for Rolling Density and Fast Charging
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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 electrolyte solutions, as well as risks of dendrite formation and explosion with lithium metal.
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, enhancing hardness and lithium ion diffusion, and a method involving heat treatments and polymers to form the carbon coating layer, improving structural stability and charging performance.
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 becomes difficult and electrode density decreases
Solution Approach 1:
The invention applies different mechanical properties to different components: hard graphite particles provide structural stability while soft rubber particles provide flexibility and rolling processability. This local differentiation of material properties resolves the contradiction between structural stability and manufacturability.
Solution Approach 2:
The invention creates a composite material system combining hard graphite particles with soft rubber particles. The composite structure allows the hard component to provide structural stability while the soft component enables easy rolling and high electrode density, simultaneously satisfying both requirements.
2Ease of manufacture
If graphite-based active material is made soft to facilitate rolling and achieve high electrode density, then rolling processability is improved, but voids between particles are blocked and electrolyte impregnability deteriorates
Solution Approach 1:
The soft rubber particles are distributed among hard graphite particles, creating localized soft regions that facilitate rolling while maintaining overall particle rigidity. This ensures good rolling processability while preventing complete void blockage, thereby maintaining electrolyte impregnability.
Solution Approach 2:
The composite of hard graphite and soft rubber particles creates a balanced structure where the soft component aids rolling without completely filling voids, and the hard component maintains structural integrity for electrolyte penetration. This composite approach resolves the contradiction between manufacturability and reliability.
3Use of energy by moving object
If lithium metal is used as negative electrode to achieve high energy density, then energy density is improved, but dendrite formation occurs causing short circuit and explosion risk
Solution Approach 1:
The invention uses carbon-coated graphite particles as an intermediary material between lithium metal and the electrolyte. This intermediate layer provides high energy density like lithium metal while preventing dendrite formation, thus maintaining safety. The carbon coating acts as a protective mediator that enables safe high-energy operation.
Solution Approach 2:
The invention converts the potential harm of dendrite formation into a benefit by using carbon-coated particles that prevent dendrites while maintaining high capacity. The carbon coating transforms the unsafe lithium metal interface into a safe, reversible lithium-ion insertion/extraction interface, turning a safety hazard into a reliable energy storage mechanism.
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 minimizing particle damage during rolling and optimizing lithium ion diffusion, while maintaining structural stability and reducing charge transfer resistance.
Implementation Method 1
a method involving heat treatments and polymers to form the carbon coating layer, improving structural stability and charging performance
Implementation Method 2
first artificial graphite particles with a carbon coating layer of hard carbon
Implementation Method 3
optimizing lithium ion diffusion, while maintaining structural stability and reducing charge transfer resistance
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.