Amorphous Carbon-Coated Graphite for Lithium Deposition Tolerance
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Solution Overview
Problem
Lithium ion secondary batteries with graphite as a negative electrode active material face issues with insufficient lithium ion acceptability, leading to lithium deposition, increased reaction resistance, and deteriorated life performance, which are not effectively addressed by increasing the BET specific surface area.
Innovation Solution
A negative electrode active material is produced by coating graphite particles with amorphous carbon, adjusting the BET specific surface area to a specific range, which enhances lithium ion acceptability and suppresses electrolyte solution decomposition, thereby improving tolerance against lithium deposition and extending battery life.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the BET specific surface area of graphite is increased to improve lithium ion acceptability, then lithium ion acceptability is improved, but life performance deteriorates
Solution Approach 1:
The patent applies composite materials by coating graphite particles with amorphous carbon to create a dual-function surface structure. The graphite core provides high lithium ion acceptability through its layered structure, while the amorphous carbon coating suppresses electrolyte solution decomposition and improves life performance. This composite structure resolves the contradiction by combining materials with complementary properties.
Solution Approach 2:
The patent applies local quality by creating a differentiated surface structure where only the outer layer of graphite particles is modified with amorphous carbon coating. The inner graphite core maintains its original high lithium ion acceptability properties, while the outer coating layer provides protection against electrolyte decomposition. This localized modification resolves the contradiction without compromising the bulk properties of the graphite.
2Reliability
If the BET specific surface area of graphite is increased to improve lithium ion acceptability, then lithium ion acceptability is improved, but reaction resistance increases
Solution Approach 1:
The amorphous carbon coating forms a protective interface between the graphite and electrolyte solution, reducing unwanted side reactions while maintaining lithium ion insertion/extraction pathways. This composite structure simultaneously achieves high lithium ion acceptability and low reaction resistance.
Solution Approach 2:
The amorphous carbon coating acts as an intermediary layer between the graphite particles and the electrolyte solution. It mediates the interaction by preventing direct contact between the electrolyte and graphite surface, thereby suppressing decomposition reactions and reducing reaction resistance while still allowing lithium ion transport.
3Duration of action of stationary object
If graphite surface is coated to suppress electrolyte solution decomposition, then life performance is improved, but lithium ion acceptability decreases
Solution Approach 1:
The coating is applied locally and selectively on the graphite particle surfaces with controlled thickness, ensuring that the protective function is achieved without excessively blocking lithium ion access. The local modification maintains the underlying graphite's high lithium ion acceptability while providing surface-level protection.
Solution Approach 2:
The patent optimizes the coating parameters including coating thickness, amorphous carbon content, and coating uniformity to achieve the right balance. By controlling these parameters, the coating provides sufficient protection against electrolyte decomposition while maintaining adequate lithium ion acceptability.
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 amorphous carbon-coated graphite particles achieve improved lithium ion acceptability and reduced reaction resistance, enhancing the battery's performance and lifespan by maintaining a balance between surface area and coating thickness.
Implementation Method 1
a surface of the graphite having a large BET specific surface area and a high lithium ion acceptability is appropriately coated with the amorphous carbon, which does not easily cause the decomposition reaction of the electrolyte solution
Implementation Method 2
Graphite has a graphite structure and occludes many lithium ions
Data Source
AI summary
A method for producing a negative electrode active material realizing both of improvement in tolerance against the deposition of lithium and improvement in life performance is provided. A method for producing a negative electrode active material includes the steps of preparing graphite particles having a BET specific surface area of 10.3 m2/g or larger and 12.2 m2/g or smaller; and coating at least a part of a surface of the graphite particles with amorphous carbon. In the step of coating, at least the part of the surface of the graphite particles is coated with the amorphous carbon such that a value obtained by subtracting a BET specific surface area of the negative electrode active material from a BET specific surface area of the graphite particles is 6.9 m2/g or larger and 8.3 m2/g or smaller.